230522 memorandum laser inertial fusion energy

Summary

M EMORANDUM Laser Inertial Fusion Energy Expert Com ission m Prof. Dr. Constantin Leon Haefner (Head) Neil Alexander, PhD Prof. Riccardo Betti, PhD Omar Hurricane, PhD Tammy Ma, PhD Prof. Dr. Robert Stieglitz Prof. Dr. Hartmut Zohm 1 MEMORANDUM LASER INERTIAL FUSION ENERGY Table of Contents

1. Executive Summary …1
2. Conclusion and High-Level Recommendations …

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M EMORANDUM Laser Inertial Fusion Energy Expert Com ission m Prof. Dr. Constantin Leon Haefner (Head) Neil Alexander, PhD Prof. Riccardo Betti, PhD Omar Hurricane, PhD Tammy Ma, PhD Prof. Dr. Robert Stieglitz Prof. Dr. Hartmut Zohm 1

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MEMORANDUM LASER INERTIAL FUSION ENERGY Table of Contents

1. Executive Summary …1
2. Conclusion and High-Level Recommendations …13 2.1 Fusion Energy is in the National Interest: Pursuing Both an IFE and an MFE Program is Essential …14 2.2 Urgency to Move Now …15 2.3 Building Trust for Fusion Energy …16 2.4 Need for Establishing Competency-Based Fusion Hubs …17 2.5 Focus Needed for Establishing Successful Leadership in IFE …18 2.6 Evaluating and Prioritization of IFE concepts …19 2.7 Develop an Integrated System …20 2.8 Establish Public Private Partnerships …20 2.9 Establish International Collaborations …21 2.10 Strategize on IFE Implosion Facility…22 2.11 Maintain IFE Approaches until Assessment Studies are Done …22 2.12 Assess IFE Programs for Accountability …24 2.13 Build and Maintain German Competencies …24 2.14 Development of an IFE Curriculum is needed …25 2.15 Need for a High Brilliance, Pulsed Fusion Neutron Source …26 2.16 Support German Industry …27
3. Overview …28 3.1 Overarching Introduction …29 3.1.1 The enormous potential of fusion makes it Hard to Ignore …29 3.1.2 Fusion is Inherently Safe …31 3.1.3 Proliferation …32 3.1.4 Why Inertial Fusion Energy? …33 3.1.5 International Research of Inertial Fusion Energy …33 3.1.6 German Research in Laser Inertial Fusion …35 3.1.7 Approach by the Fusion Expert Panel to this Effort …36
4. Potential Role of Nuclear Fusion for Global Energy System …39
5. Science and Technology of Inertial Fusion Energy (IFE) …42 5.1 Scientific Introduction of IFE …43 5.2 Approaches to Laser Driven Nuclear Fusion …45
6. Expertise, competence, and capabilities organized by modular technologies/Research Areas …49

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TABLE OF CONTENTS 6.1 Fusion Plasma and Ignition …50 6.1.1 Role of Fusion Plasma and Ignition in IFE …50 6.1.2 R&D Status Worldwide …50 6.1.3 Capabilities and Competencies in Germany …52 6.1.4 Findings and Recommendations …53 6.2 Targets …56 6.2.1 Role of Targets in IFE …56 6.2.2 R&D Status Worldwide …58 6.2.3 Capabilities and Competencies in Germany …63 6.2.4 Industry Led R&D for IFE …64 6.2.5 Findings and Recommendations …65 6.3 Reaction Chamber …68 6.3.1 Role of Reaction Chamber in IFE …68 6.3.2 R&D Status Worldwide …69 6.3.3 Capabilities and Competencies in Germany …71 6.3.4 Industry Led R&D for IFE …71 6.3.5 Findings and Recommendations …71 6.4 First Wall and Blanket, Fuel Cycle …72 6.4.1 Role of First Wall, Blanket and Fuel Cycle in IFE …72 6.4.2 R&D Status Worldwide …82 6.4.3 Capabilities and Competencies in Germany, Europe and Worldwide …84 6.4.4 Industry Led R&D for IFE …86 6.4.5 Findings and Recommendations …87 6.4.6 Time Table and Investments …89 6.5 Laser Drive and Optics …91 6.5.1 Role of Drive Laser Technology in IFE …91 6.5.2 R&D and Capability Status Worldwide …94 6.5.3 The Development Path to High Repetition Rate, High Average Power IFE Drivers …97 6.5.4 Capabilities and Competencies in Germany …101 6.5.5 Industry Led R&D for IFE …102 6.5.6 Findings and Recommendations …103 6.5.7 Conclusion and Summary …111 6.6 Fusion Power Plant …112 6.6.1 Role of Fusion Power Plant in IFE …112 6.6.2 R&D Status Worldwide …112 6.6.3 Capabilities and Competencies in Germany and Europe …113 6.6.4 Industry Led R&D for IFE …113 6.6.5 Findings and Recommendations …113 6.7 Diagnostics, Data Acquisition and Interpretation …114 6.7.1 Role of Diagnostics in IFE …114 6.7.2 R&D and Capability Status Worldwide …116 6.7.3 Commonalities with Magnetic Fusion …116 6.7.4 Capabilities and Competencies in Germany …118 6.7.5 Industry Led R&D for IFE …118 6.7.6 Findings and Recommendations …118 6.8 Artificial Intelligence (AI) and High Performance Computing (HPC) …120 6.8.1 Role of AI and HPC in IFE …120 6.8.2 Capabilities and Competencies in Germany …120 6.8.3 Industry Led R&D for IFE …120 6.8.4 Findings and Recommendations …121

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MEMORANDUM LASER INERTIAL FUSION ENERGY 7. Education, Training, Outreach, Cooperation and Networking in Germany …122 7.1 Status & Needs for Education & Training …123 8. APPENDIX …127 8.1 References …128 8.2 Abbreviations …139 8.3 Terms of Reference …144 8.4 Expert Panel …146

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01 Executive Summary

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MEMORANDUM LASER INERTIAL FUSION ENERGY Deutsch Fusion ist der Prozess, bei dem zwei leichte das zunächst erzeugte Plasma durch die ein- Atome unter Freisetzung einer großen Menge setzenden Fusionsreaktionen ohne weitere Energie zu einem schwereren Atom verschmel- Energiezufuhr von außen selbst weiter auf- zen. Dieser Prozess ist die Hauptenergiequelle heizt und die dabei entstehende Energie nicht unserer Sonne. Wenn es uns gelingen würde, nur die zunächst eingesetzte Energie zur Er- diese Reaktionen auf der Erde kontrolliert zu zeugung des Fusionsplasmas einschließlich replizieren, könnte dies auch eine bedeuten- aller Leistungsverluste aufgewogen hat, son- de Quelle für erneuerbare Energie sein. In dern auch noch darüberhinausgehend Ener- den letzten Jahren haben Fusionsforscher:in- gie freigesetzt hat. Neben der Demonstration nen und Unternehmen auf der ganzen Welt der wissenschaftlichen Machbarkeit bietet die bedeutende Fortschritte bei der Entwicklung Trägheitsfusion auch andere technologische von Möglichkeiten zur Nutzung dieser Ener- Vorteile und Vielfalt in einem Bereich mit im- giequelle erzielt. Im Dezember 2022 gelang mensem kommerziellem Potenzial. ein bahnbrechender wissenschaftlichen Mei- lenstein an der National Ignition Facility (NIF) Ausgelöst durch die jüngsten Fortschritte am Lawrence Livermore National Laboratory hat das Bundesministerium für Bildung und in den USA: Erstmals wurde aus einer laser- Forschung (BMBF) seit 2022 eine Reihe von gesteuerten Fusionsreaktion mehr Energie ge- Aktivitäten initiiert, um den Bedarf und das wonnen, als durch die Laser zur Auslösung der Potenzial für IFE zu bewerten. Für die Erlan- Reaktion in die Brennstoffkapsel eingebracht gung eines umfassenden Verständnisses, be- wurde. Dass dies zum ersten Mal unter kont- auftragte es eine Gruppe von weltweit, in ver- rollierten Laborbedingungen erreicht werden schiedenen für die Fusionsenergie relevanten konnte, ist das Ergebnis von mehr als 60 Jahren Technologiebereichen führenden Experten, wissenschaftlicher Forschung und Entwick- die Möglichkeiten und Chancen für Deutsch- lung. Sie umfassen eine Reihe von Bereichen, land auf dem Gebiet der Trägheitsfusionsener- einschließlich der Fusion- und Plasmaphysik, gie zu evaluieren. Nach einer umfassenden Materialwissenschaften, Lasertechnologie Bewertung des aktuellen Standes der Technik und Technologie-Fortschritten. Für diesen Er- kam das Gremium zu dem Schluss, dass die folg waren Ausdauer, öffentliche Investitionen Fusion ein großes Potenzial für die zukünfti- und die Zusammenarbeit brillanter Köpfe aus ge Energieversorgung der Welt bietet und für der ganzen Welt ausschlaggebend. die deutsche Industrie und Gesellschaft eine hervorragende Chance darstellt, die notwen- In der Fusionsforschung werden mehrere digen Hightech-Entwicklungen zu einer saube- technische Ansätze verfolgt. Bei der Trägheits- ren, robusten und nachhaltigen Energiever- fusion (Inertial Confinement Fusion, IFE), auf sorgung voranzutreiben. Auch wenn es noch die sich dieses Memorandum konzentriert, einige wissenschaftliche Hürden zu überwin- werden gepulste Treiber wie etwa starke La- den gibt, wurde nun die Realisierbarkeit der ser oder elektrische Ströme verwendet, um Zündung durch Laser gezeigt. Deshalb sollte die Implosion einer brennstoffgefüllten Kapsel der Fokus jetzt darauf liegen, die Forschungs- auszulösen. Dabei entstehen für kurze Zeit Be- und Entwicklungsanstrengungen auf Konzept, dingungen, die sogar die im Zentrum der Son- Technologie, Konstruktion und Betrieb eines ne übertreffen. Der Brennstoff brennt dann Fusionskraftwerks, sowie die Entwicklung des für einige zig Billionstel Sekunden, wobei er Geschäftskonzepts, der Lieferketten und des währenddessen durch seine eigene Trägheit Produktionsingenieurwesens dafür auszuwei- an der Expansion gehindert wird. Der Ansatz, ten. der an der NIF gewählt wurde, ist derzeit der einzige, bei dem die Zündung eines Plasmas Die jüngsten Fortschritte in der Fusionstech- gelang. Von Zündung spricht man, wenn sich nologie haben auch den Wettlauf um die Kom- 2

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EXECUTIVE SUMMARY merzialisierung der Fusionsenergie weltweit Das Gremium ist der Ansicht, dass mit einem angeheizt: Mit einer Gesamtinvestition von zielgerichteten IFE-Programm und starken über 5 Milliarden US-Dollar verfolgen mehr internationalen Partnerschaften die Schlüs- als 38 Start-ups, darunter vier in Deutschland, seltechnologien für das Design eines ersten Forschung und Entwicklung für die Nutzung IFE-basierten Fusionskraftwerks innerhalb von Fusionsenergie. Doch trotz des schnellen von zehn bis zwanzig Jahre entwickelt wer- Fortschritts sind noch erhebliche Fortschritte den könnten. Mit einem ehrgeizigen und gut erforderlich, bevor Fusion zu einer wirtschaft- finanzierten Forschungs- und Entwicklungs- lich tragfähigen Energiequelle werden kann. plan ist es Stand heute unter Berücksichtigung Eine wesentliche Herausforderung besteht typischer Entwicklungs- und Bereitstellungs- darin, den technischen Break-Even nachzuwei- horizonte denkbar, dass eine betriebsfähige sen und den sogenannten “Balance of Plant” Demonstrationsanlage für die Trägheitsfusion zu realisieren, der die Gesamteffizienz eines bis etwa 2045 in Betrieb sein könnte. Folglich Kraftwerks beschreibt. Die Fusionsenergie geht das Gremium davon aus, dass die Fusi- muss also zeigen, dass sie mehr Energie erzeu- onsenergie voraussichtlich nicht zur laufenden gen kann, als das Fusions-Kraftwerk für seinen Energiewende beitragen wird, die bis 2045 ab- eigenen Betrieb verbraucht. geschlossen sein soll. Die Forschung im Bereich der Fusionsener- Dies unterstreicht die Dringlichkeit für gie ist ein kritisches und risikoreiches Unter- Deutschland, in die IFE zu investieren und ei- fangen, das die Verfolgung eines breiten nen Rahmen zu schaffen, der ein lebendiges Spektrums von Ansätzen und Technologien Fusionsenergie-Ökosystem aufbaut und för- erfordert, um die Erfolgsaussichten zu erhö- dert, welches auf vier Eckpunkten basiert: hen. Magnetische (Einschluss-)Fusionsenergie (MFE) und Inertiale (Einschluss-)Fusionsener- 1. einem starken wissenschaftlichen Pro- gie (IFE) sind zwei vielversprechende Techno- gramm, um die nächste Generation von logien, die dazu beitragen können, das Ziel Wissenschaftlern:innen auszubilden und einer nachhaltigen Energieversorgung zu er- zu trainieren, während gleichzeitig vor- reichen. Angesichts der Vielzahl und Größe wettbewerblich wissenschaftliche Frage- der Herausforderungen, die noch in beiden stellungen gelöst werden, Ansätzen zu bewältigen sind, wäre es ver- 2. einer offenen Forschungsinfrastruktur für früht, sich auf eine endgültige Siegertechno- sowohl Wissenschaft als auch Industrie, logie festzulegen. Indem wir in Forschung und 3. einer kompetenten Industrie, die sich an Entwicklung sowohl für MFE als auch für IFE Innovationen beteiligt und einen Techno- investieren, erhöhen wir die Wahrscheinlich- logietransfer befähigt, und keit, unsere Ziele für eine nachhaltige Energie- 4. der internationalen Zusammenarbeit zwi- versorgung zu erreichen. Unser Expertengre- schen Regierungen, um Ressourcen und mium hat sorgfältig Berichte der Nationalen Fördergelder zu bündeln und Überschnei- Akademie der Wissenschaften der USA und dungen dabei zu vermeiden. des US-Energieministeriums sowie die wissen- schaftliche Fachliteratur geprüft. In diesem Letztendlich erfordert die erfolgreiche Kom- Memorandum haben wir uns speziell auf die merzialisierung der Fusionsenergie eine star- Verwendung von Lasern als Treiber für IFE ke Zusammenarbeit und die Partnerschaft konzentriert, da klar wurde, dass nicht-laser- zwischen Industrie, Regierungen und Wissen- basierte Ansätze für IFE viele der Schlüssel- schaft. Nur mit umfangreichen, risikotoleran- vorteile von Lasern nicht aufweisen und nicht ten öffentlich-privaten Partnerschaften kann so weit in ihrem Technologiereifegrad fort- die Ausrichtung an Marktanforderungen er- geschritten sind. Zudem besitzt Deutschland zielt, Risiken und Kosten für Steuerzahler ge- weltweit führende Expertise im Bereich Laser- senkt, die Stärken sowohl des öffentlichen als technologie. auch des privaten Sektors genutzt, Arbeits- plätze in neuen Branchen geschaffen und 3

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MEMORANDUM LASER INERTIAL FUSION ENERGY Deutschlands Führung bei der kommerziellen verschiedenen Budget-Szenarien dar. Der im Nutzung der Fusionsenergie durch wissen- Jahr 2021 erschienene Bericht “Strategic Plan schaftliche und technische Innovationen ge- for U.S. Burning Plasma Research”, erstellt von sichert werden. der Nationalen Akademie der Wissenschaf- ten, Technik und Medizin (NASEM), war einer Eine entscheidende und maßgebliche Voraus- von mehreren Berichten, die eine vergleich- setzung für die Kommerzialisierung der Fu- bare Bewertung für die Fortschritte in der sionsenergie ist ein starkes Bekenntnis und Fusionswissenschaft und der Entwicklung der Engagement der politischen Führung. Um den Fusionsenergie in den USA boten. Der Bericht Aufbau eines erfolgreichen Innovationsöko- über grundlegende Forschungsanforderun- systems zu erleichtern, ist es entscheidend, gen (Basic Research Needs, BRN), erschienen einen technologieoffenen regulatorischen Anfang 2023, der von einem großen wissen- Rahmen zu schaffen, der Sicherheitsbeden- schaftlichen Gremium zusammengestellt ken berücksichtigt, Innovationen fördert, wurde, das auch einige Mitglieder der Fach- Technologieexportvorschriften harmonisiert, kommission dieses Memorandums umfasst, wirksame Exportkontrollen implementiert, enthält einen Leitfaden zur Forschungsförde- Lieferketten unterstützt und die Öffentlichkeit rung für die US-Regierung, die Wissenschaft einbezieht. Hierzu ist anzumerken, dass die und die Industrie. Er identifiziert die wissen- Dual-Use-Bedenken hinsichtlich IFE auf be- schaftlichen und technologischen Herausfor- stimmte Design-Technologien beschränkt sind derungen, die überwunden werden müssen, und nicht auf IFE-Anlagen im Allgemeinen zu- und bietet Empfehlungen zur Förderung von treffen. Die Schaffung eines präzisen, techno- Wissenschaft und Technologie hin zu einem logieoffenen Fusionsregulierungssystems wird Demonstrator für ein Fusionskraftwerk. Der Investoren anziehen, die fundamentale Ana- Bericht bietet eine aktuelle und umfassende lysen und Due Diligence priorisieren und sich Übersicht über IFE und ist eine wertvolle Res- langfristig engagieren möchten. source für dieses Memorandum. Um dies zu unterstreichen, hat die US-Regie- Auf dem Weg zu einer kommerziellen Anwen- rung unter Biden beispielsweise angekündigt, dung der lasergetriebenen IFE sind mehrere im Jahr 2024 für die Fusionsforschung 1,01 Herausforderungen zu bewältigen. Dazu gehö- Milliarden US-Dollar bereitstellen zu wollen, ren das Verständnis brennender Plasmen, die was den jüngsten bahnbrechenden Erfolg und Entwicklung von Laserquellen und geeigneter den parteiübergreifenden Konsens im Kon- Targets, die Herstellung von Materialien, die gress widerspiegelt. Hiervon sind 135 Millio- Fusionsbedingungen standhalten können, und nen US-Dollar für ein öffentlich-privates Part- die Lösung komplexer technischer Probleme. nerschaftsprogramm reserviert, das im Herbst Da das weltweite Programm nun stark in Rich- 2022 angelaufen ist. Auf dem White House Fu- tung Energiegewinnung aus Trägheitsfusion sion Summit 2022 wurde ein Programm ange- drängt, müssen IFE-spezifische Technologien kündigt, das das Ziel verfolgt, kommerzielle Fu- deutlich weiterentwickelt werden, da es in der sionsenergieinitiativen zu beschleunigen, um Vergangenheit nur sehr begrenzte Anstren- dem ganzen Land zu nutzen. Die im Rahmen gungen in diese Richtung gegeben hat. Und des Programms bereitgestellten Fördergelder obwohl sich die FuE in der Plasmaphysik und sollen die Entwicklung innovativer Technolo- dem Design der Reaktionskammer zwischen gien für saubere Energielösungen beschleu- MFE unterscheidet, gibt es wesentliche Syn- nigen und die Kommerzialisierung der Fusion ergien bei spezifischen Komponenten, speziell als eine vielversprechende Quelle sauberer jenen, die vom Fusionsplasma weiter weg ent- Energie fördern. Darüber hinaus legte im Jahr fernt sind. Insbesondere in diesen Bereichen 2020 das Fusion Energy Sciences Advisory sollte Deutschland seine vorhandenen Stärken Committee (FESAC), welches das US-Energie- aus der MFE-Fusionstechnologie zukunftswei- ministerium (Department of Energy, DOE) be- send nutzen. Um den Erfolg sicherzustellen, rät, Prioritäten für die Fusionsforschung unter müssen die IFE-Akteure in Deutschland eine 4

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EXECUTIVE SUMMARY technologische Führungsposition erreichen Deutschland verfügt bereits über umfangreiche und ihre Fähigkeiten weiterentwickeln. Expertise und Fähigkeiten bei den Fertigungs- technologien von Targets. Somit hat Deutsch- Die Forschungsarbeiten im Bereich der Fu- land aufgrund der bestehenden Kompetenzen sionstechnologie müssen Technologie- und bei der Herstellung von kugelförmigen Kap- Konstruktionsentwicklungen für ein Fusions- seln mit Schaumstoffauskleidung, bei der Me- kraftwerk einschließen, nicht nur Grundlagen- tallbearbeitung und bei den entsprechenden forschung zur Plasmaphysik. Der Schwerpunkt Prüftechniken die Chance, auf dem Gebiet der sollte zunächst auf Konstruktionsstudien für Targetentwicklung führend zu werden. Wenn ein IFE-Kraftwerk gelegt werden, um eine nicht in die Zielentwicklung investiert wird, umfassende FuE-Strategie zu entwickeln. könnte dies bedeuten, dass ein bedeutender Auf diese Weise werden die Ressourcen auf Energiemarkt verpasst wird und Deutschland relevante technologische Fortschritte kon- bzw. Europa für eine kritische Komponente zentriert und künftige Risiken im Zusammen- für IFE-Reaktoren auf ausländische Hersteller hang mit IFE-Konzepten vermindert. Um das angewiesen ist, wodurch wirtschaftliche Un- Wachstum entscheidender und renditestar- sicherheit und Energieversorgungsrisiken ge- ker Technologien für Deutschland zu fördern, schaffen werden. Das Expertengremium emp- wird empfohlen, die Entwicklung von Schlüs- fiehlt ein engagiertes Entwicklungsprogramm seltechnologien, Kompetenzen und Fähig- zur Massenproduktion von IFE-Targets und In- keiten in Innovationshubs zu organisieren. jektorsystemen anzulegen, dass auch die De- Prinzipien offener Innovation sollten ermutigt monstration genauer Zielerfassungssysteme werden, um rasche Fortschritte in der Fusi- einschließt. onsforschung und deren Kommerzialisierung zu ermöglichen. Die Hubs könnten in der Rei- Nach der Zündung des Plasmas und der Frei- henfolge ihrer Dringlichkeit auf die folgenden setzung seiner Energie sind die Werkstoffe Bereiche ausgerichtet sein: für Struktur, Funktion und Abschirmung die größten Herausforderungen für ein zukünfti- Deutschlands weltweit führendes Know-how ges Fusionskraftwerk und bestimmen die An- in der Lasertechnologie und forschung stellt forderungen an das technische Design der Re- einen entscheidenden Vorteil bei der Entwick- aktionskammer des Kraftwerks. Dies umfasst lung der Trägheitsfusionsenergie (IFE) dar. In- auch optische Materialien, die einem Bom- dem sich Deutschland auf die Entwicklung bardement von Neutronen, Röntgenstrahlen geeigneter Treiberkonzepte für einen IFE-De- und kleinen Trümmern ausgesetzt sind. Auf all monstrator konzentriert und die Fähigkeiten diesen Gebieten verfügt Deutschland über be- von Laser-Treibern und Multigigashot-Lasern trächtliche Erfahrungen und hat Forschungsla- verbessert, kann es seine Position als führen- bors für Materialcharakterisierung eingerich- der Akteur in der Laserindustrie nutzen, um tet, ergänzt durch beträchtliche Bemühungen eine solide Grundlage für die wettbewerbs- bei der Modellierung und Simulation von Mate- fähige Produktion von fortschrittlichen Hoch- rialien, ohne die kein Kraftwerk gebaut werden leistungslasern für IFE zu schaffen. Dies wird kann. Hier gibt es viele Überschneidungen mit Deutschlands Wettbewerbsvorteil auf dem dem deutschen MFE-Programm; eine Zusam- internationalen Markt stärken und zu neuen, menarbeit wäre ein Katalysator für einen be- einzigartigen Alleinstellungsmerkmalen füh- schleunigten Fortschritt. Sollten sich deutsche ren. Wenn es nicht gelingt, hier unverzüglich zu Institutionen hier nicht engagieren, würde eine handeln, könnte der Wettbewerbsvorteil auf einzigartige Gelegenheit für den öffentlichen dem Lasermarkt langfristig verloren gehen. und privaten Sektor Deutschlands verloren ge- hen, eine Schlüsselrolle in der zukünftigen Ent- Für IFE sind kostengünstige, massenproduzier- wicklung zu spielen. te Fusionstargets erforderlich. Derzeit gibt es jedoch weltweit keinen Lieferanten, der die er- Das Blanket ist für die Energiegewinnung und forderliche Menge und Qualität liefern könnte. den Brennstoffkreislauf notwendig und somit 5

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MEMORANDUM LASER INERTIAL FUSION ENERGY ein entscheidender Bestandteil eines Fusions- sind, und ohne Investitionen in IFE-spezifische kraftwerks. Ein konsistentes Blanketdesign ist Anwendungen wird Deutschland keine Spitzen- für ein wirtschaftlich rentables Kraftwerk mit position aufbauen können. langer Lebensdauer und einfacher Fernkontrol- le unerlässlich. Weltweit sind bisher nur wenig Obwohl die Reaktionskammer eine kritische Bemühungen zum Blanketdesign erfolgt, und Komponente jedes zukünftigen IFE-Kraftwerks der private Sektor erwartet vom öffentlichen ist, wurden bisher erstaunlich wenige Konzept- Sektor, dass dieser diese komplexe Komponen- studien dazu durchgeführt. Die Schnittstellen te entwickelt. Deutschlands Erfahrungen in der zwischen der Reaktionskammer und dem Rest Entwicklung von Fertigungs- und Fügeverfah- des Kraftwerks erfordern einen integrierten ren sowohl im öffentlichen als auch im privaten Entwurfsprozess, um Kompromisse abzuwä- Sektor sind weltweit führend. Mit einer erfolg- gen und Informationen über die Auslegungs- reichen Beteiligung an diesem noch nicht sehr bedingungen für den Rest des Kraftwerks zu weit entwickelten Element könnte Deutschland erhalten. Es ist daher wichtig, den technischen seine Führungsrolle ebenfalls in der Fusion si- Einsatzreifegrad zu steigern und mit den Län- chern. Zur Erzeugung von Energie in einem Fu- dern zusammen zu arbeiten, die bereits Stu- sionskraftwerk ist darüber hinaus die Trennung dien durchgeführt haben, insbesondere mit und Wiederaufbereitung der Wasserstoffisoto- den Vereinigten Staaten und dem Vereinigten pe (Tritium, Deuterium) aus dem Abgas oder Königreich. dem Blanket notwendig. Deutschland führt weltweit bei der Prozesssteuerung, Diagnos- Der deutsche Privatsektor entwickelt derzeit tik und der Entwicklung neuer Technologien ein Konzept und ein Betriebsmodell für ein IFE- für Tritium-Forschung und Einrichtungen wie Kraftwerk. Ein Instrument für integrierte Kon- Tritium-Labors. Mit zunehmender Bedeutung zeptstudien für IFE-Kraftwerke fehlt jedoch in der Wasserstofftechnologie ist der Ausbau der der IFE-Gemeinschaft. Ein solches Instrument deutschen Kompetenzen und Fähigkeiten in ist für Scoping-Studien unerlässlich, um die op- diesem Bereich sowohl für die Fusion als auch timale Kombination verschiedener Elemente in für Wasserstoffanwendungen von entschei- einem IFE-Kraftwerk zu ermitteln und die An- dender Bedeutung. forderungen an die Komponenten in integrier- ter Weise festzulegen. Wir schlagen vor, dass Im Bereich der Hochdichten und heißen Plas- Deutschland dringend mit der internationalen men (Fusionsplasmen) verfügt Deutschland Gemeinschaft zusammenarbeitet, um einen auf der einen Seite nur über wenig Kompeten- umfassenden Systemcode zu entwickeln und zen, auf der anderen Seite verfügt Deutschland dafür seine eigene Expertise auf diesem Gebiet aber über umfangreiche Kompetenzen in den zu nutzen. Bereichen künstliche Intelligenz (KI) und High- Performance-Computing (HPC). Diese können Hochspezialisierte Diagnostik ist erforderlich, genutzt werden, um IFE-Simulationscodes zu um die extremen Bedingungen von ICF-Plas- entwickeln, die verschiedene Bereiche wie Mul- men zu untersuchen, während sie komprimiert, tiphysik, Multi-Fidelity und Multisystemmodel- geheizt und gezündet werden. Darüber hinaus le integrieren. Auf diese Weise können Experi- muss die Diagnostik Informationen über die mente und Simulationen effektiv ausgewertet Lasertreiber und die das Plasma umgeben- werden und es können Experimente mit hohen den Systeme liefern. Die gewonnenen Daten Wiederholungsraten (>10 Hz) durchgeführt dienen der Validierung und Überprüfung von und analysiert werden. Diese sind notwendig Theorien, Modellen und Codes, die für die Aus- für die Entwicklung vollständiger Systemmo- legung und Vorhersage verwendet werden. delle und IFE-Kraftwerken. KI und HPC werden In einem voll funktionsfähigen kommerziellen in Zukunft voraussichtlich auch erforderlich Fusionskraftwerk wird die Diagnostik voraus- sein, um ein IFE-Kraftwerk automatisiert zu be- sichtlich minimal sein, aber in den zwischen- treiben. KI und HPC sind Querschnittsthemen, geschalteten Test- und Pilotanlagen, die zu die für die IFE-Forschung absolut notwendig diesem Punkt führen, wird die Diagnostik eine 6

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EXECUTIVE SUMMARY entscheidende Rolle bei der Förderung des Dennoch sind die Herausforderungen, die Gesamtverständnisses spielen. Zwar verfügt diese Technologie mit sich bringt, enorm und Deutschland derzeit nicht über besonders ein- Deutschland hat jetzt die einmalige Chance, zigartige oder fortschrittliche ICF-Diagnoseka- mit seinen vorhandenen Kompetenzen einen pazitäten, aber die Entwicklung von Diagnosen wesentlichen Beitrag zu leisten und sich als und die Fähigkeit, Behauptungen und experi- wichtiger Partner in diesem Bereich zu eta- mentelle Ergebnisse zu validieren und zu veri- blieren. Um dieses Ziel zu erreichen, muss fizieren, müssen für jede neue Fusionsanlage Deutschland internationale Partnerschaften (einschließlich Test- oder Zwischenanlagen) mit strategischen Verbündeten und führen- und für Fortschritte Deutschlands in allen an- den IFE-Technologien aufbauen und stärken. deren, in diesem Bericht erörterten Bereichen, geschaffen werden. Zur Ausschöpfung des Potenzials der Fusions- energie ist in Deutschland ein umfassendes Die Entwicklung eines soliden Fusionsenergie- und gut koordiniertes Programm mit lang- programms in Deutschland kann als attrak- fristigen Investitionen erforderlich. Durch die tiver Anziehungspunkt für Talente aus der Etablierung an der Spitze dieser vielverspre- ganzen Welt dienen. Dies unterstreicht die chenden Technologie könnte Deutschland Bedeutung und den Wert von Hightech-Ent- von den wirtschaftlichen, ökologischen und wicklungen, insbesondere inmitten des inter- strategischen Vorteilen der Fusionsenergie nationalen Wettlaufs um die Fusionsenergie. profitieren und gleichzeitig eine führende Rol- Eine echte Herausforderung für Deutschland le bei der Weiterentwicklung dieses Bereichs ist jedoch die begrenzte Verfügbarkeit erfah- auf europäischer und globaler Ebene spielen. rener Arbeitskräfte in den Bereichen Plasma- Es besteht dringender Investitionsbedarf. Es physik mit hoher Energiedichte bzw. der damit muss schnell gehandelt werden, um in diesem verbundenen Technologieentwicklung, Kern- Bereich eine Vorreiterrolle einzunehmen. Die technik und Energielaserentwicklung. Um den Nutzung der Fusionsenergie würde zweifels- wachsenden Personalbedarf des privaten Sek- ohne den Lauf der Menschheitsgeschichte tors zu decken und gleichzeitig die Exzellenz verändern. Sie hätte das Potenzial, die Art und der öffentlich finanzierten Forschung und Ent- Weise, wie wir diese lebenswichtige Ressour- wicklung aufrechtzuerhalten, ist es von ent- ce nutzen, zu verändern und Energieresilienz scheidender Bedeutung, in die Entwicklung und Energiesouveränität zu gewährleisten. einer umfassenden und modernen Ausbildung an Universitäten und Hochschulen schnell zu investieren. Spezialisierung und praxisorien- tierte Ausbildung sind wichtige Komponenten und erfordern experimentelle Einrichtungen und moderne Entwicklungsfinanzierung. Uni- versitäten und Hochschulen sollten in Zu- sammenarbeit mit Partnern aus der Industrie Programme entwickeln, die praktische Ausbil- dungsmöglichkeiten in Versuchsanlagen bie- ten. Im Vergleich zu den Vereinigten Staaten, Großbritannien, Japan, Italien oder Frankreich hat sich Deutschland noch nicht als ein we- sentlicher Akteur auf dem Gebiet der ICF oder IFE etabliert. China und Russland haben noch keine IFE-Ambitionen bekannt gegeben, aber sie haben bereits mit dem Bau von großer ICF- Anlagen begonnen, die der NIF ähnlich sind. 7

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MEMORANDUM LASER INERTIAL FUSION ENERGY English Fusion is the process by which two light at- ated a series of activities starting in 2022 to oms combine to form a heavier atom. This assess the need and potential for IFE. To gain creates a large amount of energy. This process a comprehensive understanding, it charged is the primary source of energy in the sun. If a group of world-leading experts in various we were able to replicate these reactions on technology fields relevant to fusion energy to Earth, it would serve as a significant source evaluate the opportunities for Germany to en- of renewable energy as well. In recent years, gage in the field of inertial fusion energy. After fusion researchers and companies around the a comprehensive assessment of the current world have made significant progress in de- state of the art, the panel concluded that fu- veloping ways to harness this energy source. sion holds great promise for the world‘s future In December 2022, the U.S.’s Lawrence Liver- energy supply and represents an outstanding more National Laboratory‘s National Ignition opportunity for German industry and society Facility achieved a groundbreaking scientific to pursue high-tech development towards milestone: generating more energy from a achieving a clean, resilient, and sustainable en- laser-driven fusion reaction than delivered by ergy source. Although there are still scientific the lasers to start it. This was the first time hurdles to overcome, the feasibility of ignition this has been achieved in a controlled labo- has already been demonstrated with lasers. ratory environment and is the result of over Therefore, the focus should now shift towards 60 years of scientific research and develop- expanding research and development (R&D) ment. It spans multiple fields, including fusion efforts on concept, technology, construction, and plasma physics, materials science, laser and operation of a fusion power plant, as well technology, and engineering advances. It has as the development of the business case for taken dedication, perseverance, public invest- it, including supply chains and production en- ment, and collaboration among brilliant minds gineering. from around the world. The recent advancements in fusion technolo- There are various technical approaches to gy have also fueled the race for commercial- fusion being pursued. Inertial confinement izing fusion energy worldwide: with a total fusion (IFE), on which this report is centered, private investment of over $5 billion, more uses a pulsed driver, such as massive lasers than 38 start-ups, including four in Germany, or electric currents, to induce an implosion are pursuing R&D for the use of fusion energy. of a fusion fuel capsule, creating conditions However, even with the rapid progress, signif- that surpass those at the center of the sun. icant advancements are still needed before The fuel then burns for tens of trillionths of fusion can become an economically viable en- seconds, confined by its own inertia. The ap- ergy source. One of the most critical challeng- proach demonstrated at the NIF is currently es is the balance of plant, or overall efficien- the only one to have achieved burning plas- cy of a fusion energy system and the need to ma, where fusion reactions are strong enough demonstrate engineering gain. Fusion energy to allow the plasma to self-heat, and then be- will need to show that it can create more pow- yond that to ignition, where the reaction pro- er than the power plant consumes for its own duces more energy than it consumes. Besides operation. the essential demonstration of scientific via- bility, inertial fusion also offers technological Fusion energy research is a critical and high- advantages and diversity in a field with im- stakes endeavor that requires the pursuit of a mense commercial potential. diverse range of approaches and technologies to increase the chances of success. Magnetic Inspired by recent progress, the Federal Min- (confinement) fusion energy (MFE) and iner- istry of Education and Research (BMBF) initi- tial (confinement) fusion energy (IFE) are two 8

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EXECUTIVE SUMMARY promising technologies that can help achieve ernments to leverage resources and fund- the goal of sustainable energy. Given the mag- ing while reducing duplication of efforts. nitude and large quantity of challenges still to be overcome in both approaches, it would Ultimately, the successful commercialization be premature to declare a definitive winning of fusion energy will require strong collab- technology at this stage. By investing in re- oration and partnership between industry, search and development (R&D) for both MFE government, and academia. Comprehensive, and IFE, we increase the likelihood of success risk-tolerant public-private partnerships are in achieving our sustainable energy goals. The needed to ensure alignment with market re- panel carefully reviewed reports from the U.S. quirements, reduce risks and costs for taxpay- National Academy of Sciences, the Depart- ers, leverage the strengths of both public and ment of Energy and peer-reviewed science private sectors and stakeholders, create jobs literature. In this memorandum we focused in new industries, and ensure that scientific specifically on using lasers as a driver for IFE and technical innovations lead to Germany‘s because it became clear that non-laser ap- leadership in commercial fusion energy and proaches to IFE lack a lot of the key advantag- enabling technologies. es of lasers and were not as advanced in their technology readiness level, and furthermore A strong backing and commitment from po- Germany possesses world leading expertise in litical leadership to fusion energy is an essen- lasers. tial and paramount prerequisite for facilitat- ing the commercialization of fusion energy. The panel believes that with an aggressive IFE To facilitate building a successful innovation program and strong international partner- ecosystem, it is crucial to establish a technol- ships, the enabling technologies for a first-of- ogy-open regulatory framework that address- a-kind IFE based fusion power plant design es safety and security concerns and fosters could be developed within the next decade innovations, harmonizes technology export or two. With an ambitious and well-funded regulations, implements effective export con- research and development roadmap, it is con- trols, supports supply chains, and engages the ceivable that an operational inertial fusion en- public. It should be noted that the dual-use ergy (IFE) demonstration power plant could be concerns regarding IFE are limited to certain achievable by approximately 2045, following design technologies and not applicable to IFE typical development and deployment sched- plants in general. Establishing a concise, tech- ules. Consequently, the panel believes that fu- nology-open fusion regulatory framework will sion energy is not anticipated to contribute to help attract investors who prioritize funda- the ongoing energy transition that is slated to mental analysis and due diligence, and who be completed by 2045. are committed to investing for the long term. This underscores the urgency for Germany to To put this into perspective, the U.S.’s Biden invest in IFE and establish a framework that Administration has issued its intent to fund builds and promotes a vibrant fusion energy fusion research with $1.01 billion in 2024, ecosystem based on four main pillars: reflecting the recent breakthrough poten- tial of fusion energy and bipartisan consen-

1. a strong science program to educate and sus in Congress. $135 million are reserved train the next generation while solving for the private-public partnership program precompetitive science questions, that launched in fall 2022. At the 2022 White
2. an open research infrastructure for both House fusion summit, a program was an- academia and industry, nounced with the objective of expediting
3. a competent industry that participates commercial fusion energy initiatives to bene- in innovation and facilitates technology fit the entire country. The funding provided by transfer, and the program seeks to hasten the development
4. international collaboration between gov- of innovative technologies for clean energy 9

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MEMORANDUM LASER INERTIAL FUSION ENERGY solutions and facilitate the commercialization for a fusion power plant, not just basic plasma of fusion as a promising source of clean ener- science. Initial emphasis should be placed on gy. Furthermore, the Fusion Energy Sciences design studies for an IFE power plant to inform Advisory Committee (FESAC), which advises a comprehensive R&D strategy. This will con- the U.S. Department of Energy (DOE), laid out centrate resources on pertinent technology research priorities under different budget sce- advancements and diminish future risks re- narios in 2020. The 2021 “Strategic Plan for lated to IFE concepts. To promote the growth U.S. Burning Plasma Research“ report by the of crucial and high-return-on-investment National Academies of Sciences, Engineering, technologies for Germany, it is recommend- and Medicine (NASEM) was one of several re- ed to organize the development of enabling ports that offered a comparable evaluation technologies, competencies, and capabilities for the progression of burning plasma science in hubs. Open innovation principles should and fusion energy development in the United be encouraged to facilitate rapid progress in States. The 2023 Basic Research Needs (BRN) fusion research and commercialization. The report, compiled by a large scientific panel hubs could be based on the following areas in that includes some members of this memo- order of urgency: randum‘s expert panel, provides guidance for research funding by the US government, aca- Germany‘s world-leading expertise in laser demia, and industry. It identifies the scientif- technology and research is a key advantage in ic and technological challenges that must be developing Inertial Fusion Energy (IFE). By fo- overcome and offers recommendations for cusing on developing capable driver concepts advancing science and technology towards a for an IFE demonstrator and improving laser fusion power plant demonstrator. The report driver and multi-gigashot laser capabilities, provides a recent and comprehensive over- Germany can leverage its position as a lead- view of IFE and forms a valuable resource for er in the laser industry to lay a solid founda- this memorandum. tion for competitive production of advanced high-power lasers for IFE. This will strengthen To achieve commercial laser driven IFE, sever- Germany‘s competitive edge in the interna- al challenges need to be addressed, including tional marketplace and lead to new distinc- understanding burning plasmas, developing tive unique selling points (USP). Failure to act efficient laser drivers and suitable targets, promptly could result in the long-term in losing creating materials that can withstand fusion the competitive advantage in the laser market. conditions, and solving complex engineering problems. As the worldwide program now IFE requires cost-effective, mass-produced fu- starts to strongly push towards inertial fusion sion targets, but there are currently no sup- energy, IFE-specific technology will have to be pliers in the world that can meet the required developed substantially, since there has only quantity and quality. Germany has already been very limited dedicated effort in the past. vast expertise and capability in target manu- Although the R&D involved in plasma phys- facturing technologies. Thus, the country has ics and reaction chamber is distinct for IFE an opportunity to lead the way in target de- and MFE, some significant synergies exist in velopment due to the expertise in fabricating specific elements, particularly those further spherical capsules lined with foam, metalwork- from the fusion-generating plasma. Germa- ing, and verification techniques. Failure to in- ny should leverage its strength in MFE fusion vest in target development could mean missing technology in these areas while planning the out on a significant energy market and relying way forward. To ensure success, IFE stake- on foreign nations for a critical component holders in Germany must attain technological for IFE reactors, creating economic uncertain- leadership and enhance their capabilities. ty and energy security risks. The expert panel recommends establishing strong program for The fusion energy research portfolio must mass-producing IFE targets and injectors, as include technology and engineering research well as demonstrating accurate targeting. 10

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EXECUTIVE SUMMARY Once the plasma has ignited and released its multi-fidelity, and multi-systems, to extract ex- energy, the structural, functional, and armor perimental and modeling insights, to execute materials present the greatest challenges for experiments at the high repetition rates (>10 a future fusion power plant and set the con- Hz) that will be required of IFE power plants straints for the engineering design of the pow- and develop full systems models. In the future, er plant‘s reaction chamber. This includes opti- AI and HPC will be required to run an IFE power cal materials exposed to neutrons, x-rays, and plant in an automated fashion. AI and HPC are debris. In all these areas, Germany has con- cross-cutting areas that will be required for IFE siderable experience and has established re- research across the board, and without invest- search labs for material characterization, com- ment in this area for IFE-specific applications, plemented by considerable material modelling Germany will not be able to establish a leader- and simulation efforts, without no power plant ship position. can be built. There is quite a bit of overlap with the German MFE program, and accession Although the reaction chamber is a critical would be a catalyst for accelerated progress. If component of any future IFE power plant, sur- German institutions do not participate in this prisingly few conceptual design studies have area, a unique opportunity for Germany’s pub- been conducted. Its interfaces require an in- lic & private sector to play a key role in future tegrated design process to balance trade-offs development will be lost. and inform design constraints for the rest of the power plant. It is important to increase the The blanket is necessary for energy recovery level of technical readiness and to collaborate and the fuel cycle, and as such a crucial com- with countries that have already conducted ponent of a fusion power plant. A consistent studies, principally the US and UK. blanket design is essential for an economically viable power plant, with long service life and Germany’s private sector is currently involved easy remote handling. Globally, efforts have in developing an understanding and operations been very limited in blanket design and the model for an IFE power plant. However, there private sector is looking to the public sector is a notable absence of a tool for integrated to develop this challenging component. Ger- conceptual studies of IFE fusion power plants many’s experience, both in the public and pri- in the community. Such a tool is essential for vate sector are leading the way in developing scoping studies to guide the optimal combina- its manufacturing and joining processes. Ger- tion of various elements in an IFE power plant many‘s successful participation in this under- and to set component requirements in an in- developed element could secure its leadership. tegrated fashion. We strongly suggest that Furthermore, to produce energy in a fusion Germany collaborates with the international power plant, hydrogen isotopes (tritium, deu- community to create a comprehensive system terium) must be separated and reprocessed code, leveraging its own expertise in the field. from the exhaust gas or the blanket. Germany leads the way globally in process control, diag- Highly specialized diagnostics are required to nostics, and developing new technologies for study the extreme conditions of ICF plasmas tritium research and facilities, such as tritium while being compressed, heated and ignite. laboratories. As hydrogen technology grows in Furthermore, diagnostics must provide infor- importance, expanding Germany‘s expertise mation on the drivers and systems surrounding and capabilities in this area is crucial for both the plasma. Data obtained are used to validate fusion and hydrogen. and verify theories, models, and codes used for design and prediction. In a fully operation- While Germany has no strong IFE physics ca- al commercial fusion power plant, diagnostics pability, it can leverage its existing substan- are expected to be minimal, but on the inter- tial expertise in Artificial Intelligence (AI) and mediate test facilities and pilot plants leading High-Performance Computing (HPC) to devel- up to that point, diagnostics will play a critical op IFE simulation codes bridging multi-physics, role in advancing overall understanding. While 11

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MEMORANDUM LASER INERTIAL FUSION ENERGY Germany does not currently have a particularly the climate crisis by utilizing existing technolo- unique or advanced ICF diagnostic capability, gies and establishing Germany and Europe as the development of diagnostics and the ability a clean energy innovation hub. Fusion holds to validate and verify claims and experimental promise as a long-term solution to the climate results must be established for any new fusion crisis while providing economic, sovereignty, facility (including test or intermediate facilities) and national security benefits. However, to be and for Germany to make progress in any of successful, IFE must compete with other clean the other areas discussed in this report. energy sources such as solar, wind, advanced nuclear reactors, and fossil fuels with carbon Establishing a robust fusion energy program capture and storage. To realize the potential in Germany can serve as a compelling draw of IFE, Germany must launch a significant, for global talent and reinforce the signifi- well-coordinated program with long-term in- cance and worth of high-tech advancements, vestments. By establishing itself at the fore- especially in the midst of the international front in this promising technology, Germany race to fusion energy. However, it is indeed could reap the economic, environmental, and a challenge for Germany to address the lim- strategic benefits of fusion energy while play- ited availability of experienced workforce in ing a leading role in advancing the field on a the areas of IFE plasma science and engineer- European and global scale. The need to invest ing, nuclear engineering, and energetic laser is urgent and swift action is required to lead development. To meet the growing demands rather than follow in this area. Harnessing fu- of the private sector while maintaining the sion energy would undoubtedly change the excellence of publicly funded research and course of human history, with the potential to development, it is crucial to invest in building transform how we use this vital resource and up a comprehensive and modern curriculum provide for energy resilience and energy sov- at universities and colleges. Specialization and ereignty. hands-on training are important components and require experimental facilities and cut- ting-edge development funding. Universities and colleges should work with industry part- ners to develop programs that offer practical training opportunities in experimental facili- ties. Germany has not yet established itself as a sig- nificant contributor to the field of ICF or IFE when compared to the United States, United Kingdom, Japan, Italy, or France. While China and Russia have yet to declare IFE ambitions, they have already embarked on building large- scale ICF lasers that resemble the NIF. Nev- ertheless, the challenges posed by this tech- nology are vast, and Germany has a unique opportunity to utilize its capabilities to make a significant impact and establish itself as a cru- cial partner in this area. To achieve this goal, Germany must establish and strengthen inter- national partnerships with strategic allies and IFE technology leaders. We are in a pivotal decade, and it‘s important to take ambitious action towards addressing 12

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MEMORANDUM LASER INERTIAL FUSION ENERGY Energy is at the heart of modern economies, ber of exciting emerging technologies making and recent global events point to the impor- progress, we are at a pivotal juncture in IFE tance of energy security and sovereignty for research. It is an opportune time for Germany Germany. While a diversified portfolio of en- to get involved in inertial fusion energy. ergy sources is likely needed to fulfill future needs, fusion offers a potential long-term en- The main findings and recommendations of ergy source that is not only clean, but virtual- the IFE Expert Panel are set out below and ly limitless, and does not produce long-lived are further explained and substantiated in the radioactive waste. main body of this report. IFE-specific science and IFE technology elements are each de- With the recent demonstration of fusion ig- scribed in separate chapters, along with their nition on the NIF; the growing scientific basis role in IFE, existing capabilities and competen- of fusion ignition, burn, and energy gain; sig- cies, challenges and technical gaps, and specif- nificant growth from the private sector and ic priority research opportunities. new public-private partnerships; and a num- 2.1 Fusion Energy is in the National Interest: Pursuing Both an IFE and an MFE Program is Essential Finding Fusion energy is of national interest. It can provide for energy sovereign- ty, resilience, and contribute to a diverse energy portfolio. While Germa- ny does not currently have an IFE program, it would be in its interest to pursue one. IFE represents a viable path towards achieving fusion energy, presenting distinct technical advantages, disadvantages, risks, and bene- fits when compared to MFE. Both fusion technologies need cutting-edge science and sophisticated engineering and as such will spur innovation, attract talent, strengthen international competitiveness, contribute to a modern society and foster economic growth. Recommendation Germany should pursue both a strong MFE and IFE program. Where ap- propriate, the two programs should work closely together to accelerate progress on their technological commonalities, build a brand such as Fu- sion Lighthouse Germany, and strengthen Germany’s position in interna- tional competition for resources and intellectual property. Fusion energy research is a critical and high- A society that is committed to finding sustain- stakes endeavor that requires the pursuit of a able and environmentally friendly solutions to diverse range of technologies to increase the meet its energy needs must invest in fusion chances of success. Both magnetic confine- energy R&D and demonstrate openness to ment fusion (MFE) and inertial confinement various technologies. By doing so, it can po- fusion (IFE) are promising technologies that sition itself as a leader in the transition to a can contribute to achieving this goal. While more sustainable future. a winning technology cannot be identified at this stage, pursuing both MFE and IFE research In Germany, building an IFE program along- and development can increase the chances of side the ongoing and strong MFE program success. could lead to advanced innovation and pro- 14

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS grammatic pace, ultimately moving the coun- neering design, there are some commonal- try forward. While the plasma physics and ities that could apply to both types of pow- reaction chamber of the two approaches are er plants, such as in developing a regulatory quite different, synergies exist in the elements framework for commissioning, operation and further away from the plasma and should be decommissioning, power plant balancing, fuel explored. leading to a collaborative effort to cycle, thermoelectric conversion and turbines, advance fusion energy research and develop- cooling mechanisms, blanket materials devel- ment, build a vital program with the ultimate opment and design, waste stream manage- goal of achieving sustainable, clean, and limit- ment, safety, etc. Government should incen- less energy. tivize the building of joint working groups to foster solutions to these problems and initiate While magnetic and inertial fusion use very collaboration. different physics approaches and there power plants are vastly different in their core engi- 2.2 Urgency to Move Now Finding IFE is a burgeoning field, has enormous potential, and is essential to a future diversified energy portfolio. It promotes high-tech innovations in areas in which Germany has unique competencies. Numerous countries worldwide are taking action to develop IFE technology and claim the in- tellectual property essential to serving the growing global energy market. Recommendation Germany needs a robust, aggressive IFE program with a sustained and critical mass of funding to enable the country to get a foothold in the field. The pursuit of both an applied research and technology program and a supporting basic science program is of the utmost importance as the race for fusion energy unfolds worldwide. Germany should strive to be a leader in laser fusion energy and enabling technologies and a strategic partner for its allies in these fields. The fusion experiment at Lawrence Livermore gether and pool their resources to advance fu- National Laboratory‘s National Ignition Facili- sion energy. IFE technologies are currently at ty on 12/5/2022 has provided evidence that different Technology Readiness Levels (TRLs), scientific inertial confinement fusion with la- ranging from 1 to 5, as indicated in this re- sers is feasible, demonstrating the viability of port and in [BRN2022], with Germany leading laser fusion. Among others, the 2013 report in some of the higher TRL IFE-enabling-tech- from the United States National Academy of nologies. This implies that a robust basic and Sciences, Engineering, and Medicine (NASEM) applied research program is necessary to de- recommended the establishment of a com- velop these technologies. Given the complex prehensive program to explore inertial fusion scientific and engineering challenges involved, energy once ignition had been demonstrated. substantial (initial >€150Million/yr), sustained As such, the time has come to take action, as long-term (horizon 10 yrs minimum) public the world has already begun to make progress funding is essential to attract talent and es- in this area. tablish the workforce, commitment, passion, capabilities, and competencies needed to ad- It is, however, such a large challenge to achieve vance the field. The facilities required to sup- this that no one country can do it alone. It is port IFE development in Germany may take therefore essential that countries work to- several years to construct and bring online, 15

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MEMORANDUM LASER INERTIAL FUSION ENERGY and are essential prerequisites for successful this opportunity and leverage its strengths to technology transfer. Additionally, sustained become a leader in IFE. Failure to do so may public funding is necessary to create a stable result in missed opportunities for the country environment that encourages private industry and will leave it lagging behind other countries to invest in long-term projects and enter into in the IFE space. public-private partnerships in Germany that may have significant payoffs in the future. The urgent prioritization of IFE R&D is crucial to make it technically and economically via- By developing a robust IFE ecosystem in Ger- ble within a reasonable timeframe that aligns many, the country can not only reap the ben- with the projected increase in global energy efits of IFE developments worldwide but also demand. It is therefore imperative that both bolster its economy in areas where it already an applied research and technology program excels while simultaneously creating new ar- and a supporting basic research program be eas of growth. The country may need to un- implemented simultaneously and on an expe- dertake concurrent efforts and take on more dited schedule to provide the technological risks, which could result in higher costs, to in- basis for planning a fusion power plant in the crease the chances of success and acceleate near future. the development timeline. It is imperative that Germany moves quickly to capitalize on 2.3 Building Trust for Fusion Energy Finding The success of fusion energy hinges on a supportive social and political environment that accelerates research, development, and deployment efforts. The timeline for achieving fusion energy depends on the level of investment, commitment, and determination. Recommendation The German government needs to foster an ecosystem that enables fu- sion, builds trust, and engages the public to build support for IFE develop- ment and deployment. As with many emerging technologies, the gov- facilitate knowledge sharing and collabora- ernment can spur the development and adop- tion, tion of fusion by setting up the conditions that » a welcoming regulatory environment, promote innovation and provide the incen- e.g. providing a planning base for investors tives to accelerate. This includes and private industry, as well as assuring the public that the technology is being devel- » public policy, e.g. promote trust by imple- oped responsibly, menting transparent and open communi- » vigorous funding opportunities, including cation with the public about the country’s cooperative programs with other coun- commitment, progress, benefits, and risks tries, and providing funding and support associated with IFE development, for education and outreach programs to » creating markets, e.g. Implementing poli- promote scientific literacy and public un- cies that encourage innovation, providing derstanding of IFE, financial support through grants and fund- » and investment in signature IFE technolo- ing programs, reducing regulatory barriers, gy testbed and training facilities. promoting entrepreneurship and a start-up culture, and creating networks and part- Throughout the expert panel hearings, repre- nerships with industry and academia to sentatives from startups and private industry 16

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS emphasized the crucial importance of govern- areas and become a leader in this field. These ment commitment and trust-building. may include energetic high-power lasers; ac- celerated testing of optical materials; target For example, the current “Atomgesetz“ pri- manufacturing; target injection, tracking and marily regulates nuclear fission and the han- laser engagement; blanket development; and dling of (fissile) radioactive materials, so it reaction chamber (first wall) materials devel- does not specifically address fusion energy. opment and testing. However, it does regulate the licensing and operation of nuclear facilities, and new reg- By establishing such facilities, Germany can ulations or amendments may be necessary become a strong partner to its strategic allies to address the safety and licensing of fusion in IFE, providing the necessary resources and facilities in Germany. This is because fusion is expertise to advance the development and fundamentally different from fission and car- implementation of this critical technology. ries no risk of runaway or long-lasting radio- The functional requirements and primary cri- active waste streams, nor is it associated with teria for these facilities should be developed nuclear weapon development or proliferation in an open dialogue with stakeholders, such as risks. Therefore, it is crucial that the German private fusion companies pursuing a distinct government assist and guide the develop- and credible approach to fusion energy, na- ment of a regulatory framework that supports tional laboratories, and relevant government fusion power (both IFE and MFE) and R&D, agencies. rather than obstructing it, and that clearly distinguishes fusion from fission. The United By fostering collaboration with stakeholders Kingdom has already done this, and the Unit- and investing in these facilities, Germany can ed States is poised to follow. Establishing an accelerate the transition to the practical ap- international agreement on this issue would plication of fusion energy, benefiting both its be beneficial. Without a suitable policy and own energy security and the global commu- regulatory framework, startup companies, in- nity. dustry, and investors may look to other coun- tries with more favorable opportunities. Finally, well-designed public-private partner- ships should be used to leverage the capabili- To accelerate the transition from fundamen- ties and resources of both sides while creating tal science to practical application in fusion competition through appropriate Request for energy, it is essential to establish specialized Proposals (RFP). Funding mechanisms that of- facilities that can enable accelerated learning fer greater predictability and accountability, and experimentation with new technologies. such as milestone-based programs, can be Given the limited required IFE technology used, while international partnerships can be capabilities, there is an opportunity for Ger- leveraged to increase access to facilities that many to establish signature facilities with cut- are unavailable in Germany. ting-edge technology in various IFE-relevant 2.4 Need for Establishing Competency-Based Fusion Hubs Finding Germany already harbors many areas of unique competence and expertise of relevance to IFE. Recommendation Organize “hubs” or “centers of excellence” around competencies and capabilities that can grow the most crucial and highest re- turn-on-investment science and technologies for Germany. Princi- 17

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MEMORANDUM LASER INERTIAL FUSION ENERGY ples of open innovation should be promoted so that fusion research and commercialization can move as fast as possible. Creating hubs or centers of excellence that to both help set the needs and requirements, combine expertise and resources from vari- but to also partner and provide joint funding. ous regions of Germany is a swift and impact- ful way to tackle shared challenges encoun- Several areas identified by this expert panel tered by different approaches to IFE, and thus with high potential include: also shared by multiple private and public ven- tures. These hubs should be established on 1. High power optics and laser systems existing German strengths and expand their 2. Target manufacturing areas of competence by pooling resources, 3. Fusion materials generating new skills, knowledge, techniques, 4. Nuclear process engineering and technologies. Such hubs must involve uni- 5. Nuclear/safety engineering versities, national labs, and private industry to 6. Simulations and modeling (as a crosscut ensure comprehensive and robust solutions to supporting the other hubs) complex problems. Applying open innovation principles enables By organizing around community needs, the access to a broader range of expertise and development and integration of technologies resources, tapping into a larger network of re- through the hubs can help demonstrate the searchers, entrepreneurs, and startups. This required performance is possible and provides can reduce costs and risks while accelerating a community technology development test- development, fostering a wider range of ideas bed. Advancements that can solve the highest and approaches, ultimately promoting great- number of common problems should be tar- er creativity and innovation, and spin-outs geted, with the efforts within the hubs aligned along the way. We also note that bullet points to ongoing overall systems efforts to further 3, 4 and 5 present excellent opportunities for inform requirements and ensure consistency. synergy with existing or to be developed MFE The private sector should be strongly engaged programs in this area. 2.5 Focus Needed for Establishing Successful Leadership in IFE Finding Several private fusion companies have recently been established in Ger- many. Each is pursuing a different fusion engine (fusion-driver) approach, and their R&D is solely focused on that one design. Recommendation A significant government-led effort in IFE is required to coordinate and focus the overall IFE effort in Germany, and to establish leadership for the country. Recently, several private fusion companies provide enabling technologies are driving the have been established in Germany. In addi- commercialization of fusion energy, and pub- tion to securing investment and developing lic-private partnerships could greatly acceler- innovative concepts for fusion energy, these ate the development of a healthy ecosystem private fusion companies also play a vivacious for fusion technology innovation and grow role in promoting the acceptance of IFE by in- new markets. dustry and the public. In addition, fusion com- panies and the established private sector that During our discussions with MFE and IFE start- 18

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS ups, we were impressed by their impressive Another large challenge is, that significant in- levels of motivation, despite facing highly frastructure is needed to test the approaches ambitious goals and resource limitations. Al- touted by these companies and to establish though many have made good progress in both scientific and commercial viability. This hiring skilled personnel to develop their con- infrastructure includes experimental facilities, cepts, it is clear that a fully-fledged develop- production capabilities, theory, computation, ment effort is necessary to bring IFE to frui- and modeling expertise, and workforce. De- tion and construct a functioning power plant. veloping the necessary infrastructure for IFE In the previous statement, we noted that the cannot be accomplished solely by single pri- scale of technological development required vate companies in the near or long term. It to achieve these goals is too great for any one necessitates the participation of public sector country to undertake, given the unavailability organizations that have expertise in construct- of manpower and the limited infrastructure ing and operating large-scale facilities and and test capabilities that are absolutely neces- user facilities, such as the Helmholtz-Associa- sary to develop a FOAK IFE demonstrator. tion, Fraunhofer Gesellschaft, Max-Planck-So- ciety and universities. These institutions have In the IFE sector specifically, German start- abundant knowledge and resources that can ups Marvel Fusion and Focused Energy are be utilized. focused on developing a First-Of-A-Kind pow- er plant. This involves research and develop- Consideration should be given to engaging in ment of enabling technologies as well as the collaborative efforts between private industry development of plasma physics and target and the research organizations for the devel- concepts. Each of these areas has tremen- opment of these facilities, as it can stimulate dous opportunity but must also be developed technology innovation and facilitate technol- in close collaboration and integration with ogy transfer. Therefore, the development of the larger project to develop an IFE demon- IFE will require collaboration and coordination strator. Addressing this challenging task may among diverse fields and public sector orga- be possible if either a national laboratory that nizations. In fact, growing a healthy IFE eco- provides integrity and confidence and has ex- system will require some assistance through tensive expertise in systems engineering, or partnerships with leading universities. a professional systems integration firm with comparable capabilities, assumes responsibil- To best steward public funds, and ensure that ity for managing and communicating perfor- Germany is on the best path, coordination mance and risk budgets on behalf of a wider should programmatically be managed and IFE program. occur at the central level. Periodic re-assess- ment is also recommended to assure agility as new knowledge is gained. 2.6 Evaluating and Prioritization of IFE concepts Finding There are many IFE concepts. It is difficult to make measurable progress if the efforts are too diffuse. Recommendation Maximize the return on investment (ROI) for public funding by targeting high-potential concepts and technologies via scoping studies with thor- ough physics review to inform a careful selection process that allocates resources to have the greatest impact and drive innovation in key areas of research. 19

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MEMORANDUM LASER INERTIAL FUSION ENERGY To ensure that public funding for research and start-ups or private industry rather than pro- development initiatives in Germany generates viding subsidies to fund their R&D), and oth- the highest possible return on investment, it is er methods are best suited to manage risk, important to prioritize concepts and technol- stimulate the economy and create demand, ogies with the greatest potential for success. incentivize short time-to-market, and ensure A careful selection process should be under- cost-effectiveness. Each IFE effort should also taken to identify the most promising concepts allow support for open technology, high risk, and allocate resources where they will have high reward approaches if their idea is scien- the greatest impact. Comprehensive scoping tifically feasible. studies, with input from stakeholders such as the power generation industry and experts in By adopting a targeted approach to public fusion science and technology, should be con- funding, Germany can effectively support ducted to pre-select and provide direction for innovative and high-impact initiatives, drive technology development. Independent peer progress in key areas of research, and position review, milestone-based programs, market itself as a global leader in science and tech- creation (buying products and services from nology. 2.7 Develop an Integrated System Finding Globally, there is a gap and need for integrated systems models for IFE, which are necessary for evaluating risk and tradeoffs. Recommendation Germany should build up a capability to model full integrated fusion pow- er plant systems. While there have been several notable full sys- ferent approaches and compare and contrast tem IFE studies in the past (HAPL, LIFE, HYLIFE, their advantages and disadvantages. This type SOMBREO, etc.), there currently does not exist of appraisal is necessary to guide the govern- a fully integrated systems modeling (systems ment and the field in making the best deci- engineering) capability anywhere globally. sions on how to invest their limited resources Such systems models are required to man- and workforce. age the complexity of a fusion plant concept, identify areas for development, understand The expert panel finds that this may be a par- challenges and risks, and determine perfor- ticularly good place for international collab- mance or engineering tradeoffs between sub- oration. While Germany has strong systems systems. Such an integrated systems model is engineering expertise to bring to the table, necessary to help define the roadmap of sci- the historical IFE system knowledge-base still ence and technology development. sits outside the country, and collaboration may bring both to bear. Furthermore, an integrated systems model that can evaluate design choices is crucial to Systems modeling is also a need in workforce help Germany determine the viability of dif- and training. 2.8 Establish Public Private Partnerships Finding As investments in both the private and public sector for fusion are ramping up, significant opportunity exists to create appropriate and well-thought- out public-private partnerships (PPP) that are mutually beneficial and can accelerate the development and commercialization of IFE. 20

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS Recommendation Germany should facilitate PPP structures and programs that enable an en- vironment where both public and private ventures can support each oth- er, and enable both to be competitive with the global ecosystem. Germany should help facilitate public-private edge and intellectual property could then be IFE partnerships that serve the needs of both shared. the public and private sector and can help ac- celerate the development of IFE. The public Such PPP’s could be used to address founda- sector possesses considerable expertise in a tional research and development, next-gen- range of R&D areas relevant to IFE, and these eration test and support facilities, licens- capabilities can and should be appropriately ing and regulatory issues, and workforce leveraged via PPP’s to help grow the fusion development. Appropriate joint planning and sector. By planning appropriate programs, road-mapping activities facilitated by PPP’s resources, facilities, and streamlined commu- would be useful to guide investments for both nity access, PPP’s can be thoughtfully devel- the public and private sectors. PPP’s may also oped to help advance both individual com- play an essential role in developing the nec- pany concepts while sustaining and growing essary workforce for the future. Initiatives foundational capabilities that serve the entire where the public and private sector are work- community. The hubs described in Recom- ing together can enlarge the available work- mendation 4 are one such mechanism that force and widen the training opportunities, would allow for joint development of com- while providing increased vitality and flexibil- mon technologies, where subsequent knowl- ity to the overall fusion ecosystem. 2.9 Establish International Collaborations Finding Challenges in fusion energy are significant and multifaceted, and Germany need not try to solve all of them on its own. Recommendation Use international collaborations to reduce the risk and cost of a German fusion program while protecting German intellectual property and com- petitive advantages. In IFE, there are numerous technical and sci- practical for any one country or organization entific challenges that must be addressed to to attempt to solve all of them on their own. develop a viable and sustainable fusion ener- Instead, it is important for countries like Ger- gy source. Some of these challenges include many to focus their resources and efforts on achieving high target gains, improving the specific areas of expertise and where they can efficiency of laser systems, developing target make the most meaningful contributions and fabrication methods capable of producing not replicate efforts other strategic allies are high quality fuel capsules in large quantities. already pursuing. While the challenges facing Moreover, solutions are still needed for first IFE are significant and multifaceted, it is im- wall materials and breeding blankets in fusion portant for Germany to focus its efforts and reaction chambers in general. expertise on specific areas where it can make the greatest impact and collaborate with oth- Given the breadth and complexity of the ers to collectively advance the field. challenges facing IFE, it is unrealistic and im- 21

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MEMORANDUM LASER INERTIAL FUSION ENERGY 2.10 Strategize on IFE Implosion Facility Finding There are limited experiments available on existing implosion facilities, worldwide, to rapidly advance IFE ignition and gain, and technology de- velopment. Recommendation Germany should develop a strategic plan for testing target concepts on IFE implosion facility, including considering building a next generation IFE implosion facility with international partners as appropriate, to accerate the pace of IFE research and development. Compression and fuel assembly are key re- op a strategic plan for the next ten years on quirements for achieving a self-sustaining where and how testing of target concepts on burning plasma that can ignite. Specifically an IFE implosion facility can be accomplished lower adiabat, high gain targets have proven and consider building the next generation IFE tricky when scaling from subscale experimen- implosion facility with international partners tal results, requiring full-scale testing and tun- as appropriate. Consideration should be given ing. Currently, only the NIF at LLNL in the US is to scale, phasing, access to testing, concept a full-scale fusion facility capable of conduct- variety, etc. and build on the Key Enabling ing implosion experiments and generating a Technology program (lasers, targets, first wall burning plasma. Three other facilities, LMJ in and reaction chamber etc.) that has been as- France, OMEGA at LLE, and SG-III in China can sembled prior. Such a facility could facilitate study sub-scale spherical implosions, but do research on implosion physics in direct or in- not have the drive energy to achieve fusion direct drive configuration, target injection, burn or burn propagation. and tracking, debris removal, materials and component testing. Strategy and scoping is To accelerate progress, it is imperative to needed within the next two years to inform conduct more experiments to test different Germany’s overall IFE program and prepare designs – this is true not only for Germany accordingly. but globally. Hence, Germany should devel- 2.11 Maintain IFE Approaches until Assessment Studies are Done Finding The optimal target-drive-configuration for high gain is still to be deter- mined. Both the direct and indirect drive approaches, have potential, but with risks and unknowns. Other alternate schemes such as fast ignition or shock ignition could potentially achieve higher gain; however, their physics and technologies are at even lower technical readiness levels (TRL). Recommendation It would be prudent to keep both potential pathways open, as well as ex- ploring alternate, viable concepts. There are pros and cons to both direct drive validated on a full-scale ignition target. While and indirect drive. Our analysis shows that current indirect drive concepts may be limit- there is not yet a winner for either concept ed in maximum gain, the advantages of direct due to unknowns or scaling that has not been drive may also be outweighed by increased 22

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS system and laser complexity, including less la- with the electron-conduction as opposed to ser efficiency. Therefore, it would be prudent the less steep profile in x-ray driven ablation. to keep both avenues open and explore alter- Direct-drive implosions have an additional native concepts that are viable at the same seed for high-mode (>30) hydrodynamic in- time. Here is why: stability, laser “imprinting,” that indirect-drive avoids by use of a hohlraum. Because of the For a fixed laser, direct drive has greater en- laser directly impinging upon a direct-drive ergy coupling to the capsule by avoiding the capsule and because of the relatively thin intermediate hohlraum laser-to-x-ray energy ablators used in the direct-drive, electron conversion step of indirect-drive. This can be preheating of direct-drive capsules is corre- an energy advantage of 7-10x. Some of this en- spondingly more difficult of an issue than for ergy advantage may be offset by cross-beam indirect-drive. energy transfer (CBET) which can redirect in- ward coming energy outward. While the ab- Indirect drive has demonstrated ignition. Di- lation pressures for direct and indirect-drive rect drive has not yet, and it is to be seen if the are similar, the mass ablation-rate for indi- issues described above are surmountable and rect-drive is larger, because of the deeper pen- whether direct drive can indeed provide the etration into the ablator of x-rays. This leads ~3x improvement in energy coupling. See Sec. to a higher hydrodynamic efficiency (ratio of 5.2 for more detail. implosion kinetic energy to energy absorbed) in the case of indirect-drive. Taken together On the engineering of the fusion reaction (the two bullets above) the overall laser ener- chamber and fuel injection, the indirect drive gy to implosion kinetic energy conversion of approach to convert laser energy to x-rays direct-drive is ~5% while for indirect-drive it’s through the hohlraum leads to a more com- ~1.5%. plex target, but also protects the fragile ID capsule and DT fuel within when entering the Due to the energy advantage of direct-drive, hot reaction chamber. The target could be rap- the stagnation pressure requirement for ig- idly spun around its cylindrical axis to provide nition of a direct-drive implosion is approxi- stability during its flight phase to the point of mately half that of indirect-drive. This leads engagement with the lasers. For direct drive to lower implosion convergence requirements (DD) capsules, a solution1 is required to pro- for ignition. This then leads to larger capsules tect them during injection into the chamber allowable for direct drive, which can provide environment and to prevent them from heat- larger fusion yields (~4x) for a given implosion ing2 or deforming during their transition to velocity. the point of engagement. Reducing the cham- ber buffer gas, as compared to indirect drive However, the direct-drive advantage in en- configurations, to protect the DD target will ergy coupling is offset by the higher adiabat increase the risk of damage to the first wall. (lower fuel compression) requirements of di- A sabot (a casing that protects the capsule in rect-drive that are needed for hydrodynamic flight phase and opens before laser engage- stability control. This increased sensitivity of ment) has been proposed to encase the DD direct-drive implosions is essentially due to capsule. the steeper ablation density profile associated 1 Two methods have been proposed and one demonstrated. Mechanical deflection of the sabot (after leaving barrel and befo- re entering chamber) into a collector. Sabots would then be recycled by regrinding and remolding. This method was demon- strated. The other method is electromagnetic deflection and recirculation of the sabot (after leaving the barrel and before entering the chamber). This is still in the concept stage. 2 Heating would cause increase in entropy and asymmetry. Protection could be by IR reflective layer, working with liquid fuel, injection at much higher speed, reduced chamber buffer gas work to protect target, however that would increase the heat load and damage effects on the chamber walls. 23

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MEMORANDUM LASER INERTIAL FUSION ENERGY 2.12 Assess IFE Programs for Accountability Finding Defined metrics and milestones are necessary in programmatic initiative to assess and measure progress. Recommendation Government-initiated IFE programs should include performance metrics and milestones. A fusion working group should be established loan. Metrics should be inclusive of different to establish meaningful metrics and mile- approaches and allow for risk-taking and inno- stones for the particular IFE program and its vation, while remaining technically rigorous. associated R&D that can measure progress Key performance indicators and project mile- and serve as markers of success. Entities re- stones with associated completion criteria are ceiving government funding must participate an example of how program progress can be in time-bound reporting and meet delivera- measured. bles to continue to have access to the grant or 2.13 Build and Maintain German Competencies Finding Inertial Fusion Energy is a multi-disciplinary field that requires a diverse range of expertise from various fields, including physics, engineering, ma- terials science, optics, and computer science. As a potential carbon-free, abundant energy source, IFE is a great motivating goal to attract new tal- ent and inspire the next generation. Recommendation IFE can and should be used to attract diverse talent to MINT: Conduct a study of the fields, skills, and career types that are required to develop IFE and operate a fusion plant in the future. Promote study results to MINT and STEM audiences through appropriate advertising material. Demon- strate commitment to fusion by providing programs for fusion develop- ment and education (see Sec. 2.14). IFE is an emerging field with the potential to ral Sciences, and Technology), it is important revolutionize the way we generate energy and to promote the exciting career opportunities solve the global energy crisis. This potential that exist in the development of IFE (Inertial for impact can attract a wide range of people Fusion Energy) and the operation of a fusion who are passionate about making a difference power plant in the future. A study of the fields, in the world. By highlighting the opportuni- skills, and career types required to develop IFE ties for innovation and collaboration in this and operate a fusion facility can be an effec- field, new talent can be encouraged to pursue tive way to showcase these opportunities and careers in STEM. However, there has always attract diverse talent. been a lack of diversity in STEM fields, partic- ularly in terms of gender and race. Using IFE The fields involved in IFE development and op- as a means to attract diverse talent can help eration include physics, engineering, materials close this gap and create more opportunities science, computer science, and mathematics. for underrepresented groups in STEM fields. Skills required include experimental and the- oretical physics, both in the area of materi- In order to attract diverse talent to the STEM als, lasers, nanoengineering, production en- fields (Mathematics, Computer Science, Natu- gineering and so on, engineering design and 24

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS analysis; high performance computing, mate- » Recruit and retain diverse faculty and staff rials science, data analysis and visualization, at universities, and project management. Career types in this » Support student organizations and initia- field include research scientists, engineers, tives technicians, project managers, and adminis- » Partner with organizations that promote trative personnel. diversity » Enable defined and simple routes for stu- To attract diverse talent to this field, it is im- dents to engage in hands-on experiences portant to and connect with potential employers. » demonstrate a commitment to fusion by Appropriate promotional materials, such as providing programs for related education. brochures, websites, social media campaigns, This may include international and domes- and outreach events, can be developed to tic scholarships, internships, financial aid promote the study results and career oppor- for underrepresented groups, and training tunities to STEM audiences. It is important programs for students and early career to highlight the potential impact of fusion on professionals from diverse backgrounds. It society and the environment, as well as the may also include partnerships with univer- exciting research and development opportu- sities and research institutions to advance nities in the field. fusion research and development, 2.14 Development of an IFE Curriculum is needed Finding Germany (and the world) is currently lacking and IFE curriculum at the universities and schools. Recommendation A concerted effort to develop an IFE curriculum is crucial to building up the necessary IFE workforce of the future. University level curricula are the most urgent can be used to guide the development of since IFE in a research and development phase. IFE-related programs and workshops. Then high school curricula as high schools are » Establish IFE-relevant programs: Universi- a pipeline of students to universities. When ties can establish or expand programs that IFE nears or reaches a deployment stage, focus on IFE-related topics such as plasma technical school curricula will be needed. physics, ICF/IFE, materials science, nuclear engineering, high-energy laser engineer- An IFE curriculum is needed to train and build ing, and power plant systems engineering. up the workforce of the future that will be These programs can be designed to meet capable of taking on the challenges of devel- the needs of students and industry profes- oping IFE. The curriculum can be designed for sionals. undergraduate and graduate students, as well » Organize workshops and conferences: as for professionals. Such a curriculum should: These events can bring together experts from academia, industry, and government » Develop a core competency framework: to discuss the latest developments in IFE This framework should outline the key com- research and technology. They can also petencies needed to work in IFE. It should provide opportunities for networking and include technical skills as well as non-tech- learning about career opportunities in the nical skills such as communication, team- field. work, and problem solving. This framework » Promote education in the MINT fields: 25

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MEMORANDUM LASER INERTIAL FUSION ENERGY MINT stands for mathematics, computing, tions that have expertise in IFE and work to- science, and technology. Universities can gether on joint research projects, exchange promote MINT education by offering schol- programs, and international conferences. arships, mentoring programs, and outreach » Build an IFE community: Universities can activities to encourage students to pursue create a community of IFE profession- careers in these fields. als and students by establishing student » Connect with IFE research centers: Univer- groups and organizing events such as sem- sities can connect with IFE centers of ex- inars, guest lectures, and social gatherings. cellence and research to provide students This community can help foster collabora- and professionals with first-hand, hands-on tion, knowledge sharing, and career devel- expertise. This can be done through intern- opment. ships, joint research projects, and collabo- » Attract new talent: Universities can attract ration on workshops and conferences. new talent by promoting the excellence » Develop international partnerships: Inter- and opportunities available in IFE. This can national collaborations can help expand be done through marketing campaigns, the scope of IFE research and develop- outreach activities, and partnerships with ment. Universities can partner with institu- industry and government organizations. 2.15 Need for a High Brilliance, Pulsed Fusion Neutron Source Finding A pulsed neutron source prototypical of an IFE reaction chamber does not exist and is needed to fully develop and qualify IFE reaction chamber first walls and blankets. Germany already possesses key competencies in blanket and first wall design and structural engineering, but this pulsed neutron source for testing materials is missing. Recommendation Germany must advance the research and development of the blanket and first wall by working with its partners to construct a pulsed fusion neutron source. This facility, which does not exist anywhere in the world, is ur- gently needed and will allow for the study of fusion materials damage and lifetime. By leveraging its competencies, Germany can play a significant role in advancing the IFE sector here. The blanket is a critical component of a fusion and capabilities of different classes of materi- power plant, performing multiple functions als. Scaled experiments under fusion-typical such as power extraction, fuel growth, and conditions are necessary, and experimental shielding the reaction chamber from the en- data obtained by IFMIF DONES should be used vironment. However, the current technology for structural materials. In addition, there are readiness level (TRL) of the blanket for IFE de- synergies between magnetic fusion R&D and vices is still rudimentary due to limitations and ICF/IFE in the areas of blanket breeding, heat constraints on the blanket material resulting extraction, shielding, and fuel cycle process- from the unique conditions and goals of the ing modes and sequences. fusion power plant. As a result, the fuel cycle boundary conditions are also at a low TRL lev- Germany has unique expertise in the fuel cy- el. cle, materials research on irradiated structural and functional materials, and integrated blan- To achieve optimal performance, it is essential ket design, and its involvement in fusion en- to conduct extensive studies on the limitations ergy research includes several industrial part- 26

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CONCLUSION AND HIGH-LEVEL RECOMMENDATIONS ners. However, activities and expertise have neutron source could build on the expertise focused primarily on magnetic fusion, and a developed with the high-energy, high-rep- comprehensive approach is needed to consid- rate laser beamline, and it is essential to maxi- er all fusion options. mize the synergistic expertise in both the U.S. and Germany. The near-term focus should be To test and validate material damage, degra- on those aspects that are unique to ICF/IFE, dation and survivability, a scaled pulsed neu- such as pulsed operation and different first tron source capable of generating relevant wall loads, which require investment in exper- fluxes with energy spectra as seen in a full- imental facilities. scale IFE power plant will be required. This 2.16 Support German Industry Finding Currently, several industries lack the capacity to support the construc- tion of multiple laser-driven IFE power plants. These industries include the production of large laser amplifier glass, manufacturing of pump la- ser diodes, and fabrication of large aperture precision optics. Additionally, certain industries such as IFE target manufacturing do not exist yet. Recommendation Establish a robust supply chain and skilled workforce to facilitate the deliv- ery of fusion technology and enable German industry to thrive in a future global fusion market. Create a fusion industry that sets global standards and can export fusion technology worldwide in the coming decades. 27

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03 Overview 28

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OVERVIEW 3.1 Overarching Introduction 3.1.1 The enormous potential of fusion makes it Hard to Ignore Energy has driven innovation and economic performance of a fusion device is determined growth, increased life expectancy and health, by three parameters: density, temperature, and enabled the accelerated growth of the and “confinement” time in which these con- world’s population by tenfold over the last ditions can be maintained in a plasma. There 300 years. Fossil fuels, which store the sun’s are mainly two credible approaches to gener- energy over millions of years, have powered ate these conditions: industrial revolutions and sustained our life- styles with mankind learning to convert heat » Inertial confinement fusion (ICF): The con- into mechanical power. Today, energy is not cept of laser-driven ICF was originally de- only used to sustain our lifestyles, but abun- scribed in the initially classified work of dant, reliable energy is also the key to raising John Nuckolls and Nikolay Basov. To achieve the standard of living for developing nations. the extreme temperatures (>100 Million However, as global temperatures rise and en- Degree Celsius) and densities (>1000 times ergy demands increase, transitioning to clean solid density) necessary, typically pulsed energy sources becomes imperative. high-power lasers are used for imploding a hollow spherical shell a few millimeters The pursuit of fusion energy, the process that in diameter containing the fusion fuel. To powers the sun, as an inexhaustible source achieve energy gain, a considerable portion of power has been an enduring aspiration for of the fuel must undergo burn before the humanity for over seven decades. If this en- internal pressure breaks apart the fusion ergy source could be tapped for controlled conditions. The fuel’s inertia confines it for power generation on Earth, humanity would a brief moment, which is why it is called have access to a weather-, and location-inde- Inertial Fusion. Using lasers as the driver is pendent, greenhouse gas-free, inexhaustible, the most extensively researched type of in- and ubiquitous energy source. Furthermore, ertial fusion, followed by magnetically driv- the energy density in fusion fuels is 100 mil- en inertial fusion concepts. Inertial Fusion lion times higher than in fossil fuels and the Energy (IFE) uses the principles of ICF in the highest overall in the universe. In a decentral- development of a practical power plant de- ized energy grid, there will always be a need sign. Typically, it will run ICF reactions at rep- for small-footprint, high energy density pow- etition rates around 15 times per second. er sources that can provide 24/7 baseload There are mainly two ways to drive the fuel energy located next to large consumers such capsule: as chemical plants, metropolitan regions, sea- • “Indirect drive” is a technique in water desalination plants, or carbon capture which the fuel capsule is not irradiat- and sequestration plants. Even though con- ed directly by the laser beams, but by structing a fusion power plant is a formidable X-rays generated by the interaction of undertaking, its vast potential makes it a nec- the laser with a high-Z material, such essary attempt, a moonshot, that can aid in as gold or lead, surrounding the cap- addressing both the energy and climate pre- sule (“hohlraum”). The X-rays heat and dicaments. compress the capsule, causing the fuel to ignite and undergo fusion reactions. The effort to achieve the extraordinary condi- Indirect drive has a crucial benefit of tions where fusion occurs with net energy gain smoothing the light used to drive the is technologically very challenging. In fact, the implosion. This technique also reliefs 29

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MEMORANDUM LASER INERTIAL FUSION ENERGY requirements on the drive laser. more fusion reactions, and thus releasing • The “direct drive approach” to laser more energy. This took roughly 80 trillionth fusion, where the laser beams impinge (10-12) of a second. directly on the implosion shell. Direct drive is expected to be more efficient The breakthrough at the NIF ended the than indirect drive. However, laser long-standing debate about whether fusion driver technology is more challenging ignition was possible in the laboratory. It pro- and complex. vided scientific proof of laser-driven inertial » Magnetic Confinement Fusion (MCF): A confinement fusion and now forms the basis large volume (~1000 cubic meters) of hot of a possible path toward inertial fusion ener- (>100 Million Degree Celsius), low densi- gy. This exciting result by NIF spurred signifi- ty (approximately 100 billion times less cant government, private industry, and inves- dense than in ICF) deuterium-tritium (DT) tor interest. plasma is confined in a stationary manner by strong magnetic fields. Heating up to An IFE plant would encompass a substan- burn temperature occurs through elec- tial number of components and subsystems, trical currents, radio wave, and particle where technologies will need to be researched beam injection. MCF has not yet demon- and developed, production engineered and strated self-sustaining fusion burn as there scaled to mass-production and transported is no full-scale facility existent till now (the to various construction sites across the globe. maximum ratio of fusion power divided One of the key subsystems of an IFE power by heating power deposited in the plasma plant is the laser driver system, comprising was 0.67 in D-T experiments in the JET to- hundreds of 100kW-class high energy laser kamak). The first facility capable of demon- system modules. Production of these and ser- strating fusion burn in an experimental vicing them and other components for plants setting (no net power generation) is the could bring significant economic benefits to International Thermonuclear Experimental communities and regions both in Germany Reactor (ITER) currently under construc- and internationally. tion in France, with a planned start of DT fusion gain experiments in 2035. The term To date, the main fusion approach pursued by “magnetic fusion energy,” or MFE, refers to Germany has been Magnetic Fusion Energy the application of magnetic confinement (MFE). The basic science mission is funded by fusion principles to energy production. the German Federal Ministry of Education and Research (BMBF) with €149 million per year On December 5th, 2022 the National Ignition (2023) and includes smaller efforts for mate- Facility (NIF), a large laser fusion facility at rials studies and development efforts for the Lawrence Livermore National Lab (LLNL) in the first wall in the reaction chamber, fuel cycle or United States, conducted a successful fusion blanket development. As such, Germany is a experiment, where the energy produced from world leader in plasma science and technolo- a fusion reaction of a mixture of Hydrogen gy for the Tokamak, and especially the Stellar- isotopes Deuterium and Tritium released 3.15 ator line. Germany is the largest contributor Megajoule in energy surpassing the laser ener- to the EUROfusion consortium that strongly gy of 2.05 Megajoule that was used to initiate supports ITER and aims to develop the phys- it. This is the first time in human history such a ics and technology basis for a European MFE feat has been achieved in the laboratory. The demonstration plant (DEMO). Germany con- experiment demonstrated a self-burning plas- tributes to ITER via the EU domestic agency ma with a target gain of 1.5, a capsule gain of F4E (for development of diagnostics and heat- ~12, and a fuel gain of ~120. This means that ing and current drive systems) and other in- after the laser ignited the DT-fuel, the ener- ternational programs in the US, UK or China. gy released from the first fusion contributed While reactor concepts and associated tech- to further heating the fusion fuel, triggering nological developments are more advanced in 30

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OVERVIEW MFE, the studies of burning plasma physics in Generating power from any type of fusion IFE have already progressed into the burning technology presents significant scientific and plasma regime. Investing in the R&D of both technological difficulties. There are many approaches hence increases our chances of ways to make fusion and today there are a achieving sustainable energy goals. plethora of concepts that have been tried. Each concept has its own pros and cons, there Triggered by the advancements in laser in- is no magic shortcut – in the fusion plasma, ertial fusion, the BMBF initiated a process in sufficient density and temperature must be September 2022 to explore the potential of la- achieved over a long enough timescale to ser inertial fusion and to outline the path to a generate enough burn and overcome the possible power plant, with the participation of numerous loss mechanisms, and the various recognized experts from German science and subsystems must be compatible and togeth- industry that led to organizing this expert pan- er form an integrated power plant solution el to take a deeper look at Germany’s compe- that is economically viable. Due to the many tencies and capabilities, and how to best align remaining unknowns, but also the significant them. potential benefits, it is crucial to maximize the chance of success, on as fast a timescale as Extensive research is still necessary in the field possible, by exploring multiple avenues in the of plasma science and fusion in order to real- pursuit of fusion energy. To achieve power ize a fusion power plant. However, even at this generation from fusion energy by the middle stage, such a power plant should be designed of the century, it is essential to commence with a focus on feasibility and economic viabil- the development of enabling technologies ity. As the technology readiness levels of the and underlying engineering for IFE without key technologies are matured, it is expected delay, even though there are still obstacles to that there will be many spin-out technologies overcome in ICF science. Although the plasma and opportunities. A few examples include: la- physics and reaction chamber of IFE and MFE ser-driven secondary sources for medical and differ significantly, there are commonalities in semiconductor technology, future analysis of the technological elements further away from defense components, nuclear radiation effects the plasma that can be leveraged. Therefore, testing, target production, sensor technology conducting a joint program to study these as- and diagnostics, simulation and modeling, and pects will lead to synergies, particularly in ar- material development, among others. eas such as the outer fuel cycle and material questions. 3.1.2 Fusion is Inherently Safe Understanding the distinction between nucle- ergetic x-rays and particles, but any activation ar fission and fusion is crucial. Fusion works of the reaction chamber walls is expected and by releasing energy by forcing together light well-understood, and can be safely accommo- atoms such as hydrogen, which requires a dated. By the choice of appropriate materials very precise balance of temperature, pressure in a fusion reaction chamber, the radioactive and fuel density. The reaction is self-limiting waste produced will decay on the order of ~80 because in any event of a malfunction, the years vs. 100,000’s of years for fission, hence reaction will automatically stop – defined by no long-lived radioactive waste is generated. the underlying physics. The fusion reaction that is easiest to initiate in conditions we can In contrast, the current conventional nucle- achieve on earth, is between the two hydro- ar power stations are based on nuclear fis- gen isotopes, Deuterium and Tritium, result- sion that rely on splitting heavy atomic nuclei ing in the production of one Helium nucleus through fission reactions. Nuclear fission en- (an alpha particle) and one energetic neutron. tails the division of a heavy atomic nucleus This process will also produce some very en- into two or more smaller nuclei, resulting in 31

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MEMORANDUM LASER INERTIAL FUSION ENERGY What is Fusion? Fusion, the power that drives the sun and stars, combines the release of energy. This process can be- light elements in the form come chain-reactive and lead to an uncon- of plasma - the hot, charged trolled release of energy, potentially causing state of matter composed of melt-down and catastrophic destruction. This free electrons and atomic nu- cannot happen with fusion. Additionally, the clei - that generates massive by-products of nuclear fission are highly ra- amounts of energy. Scientists dioactive and can remain hazardous for thou- are seeking to replicate fusion sands of years, posing significant risks to hu- of Earth for a virtually inex- man health and the environment. haustible supply of power to generate electricity. Another very significant concern with nuclear fission plants is the proliferation of fissile nu- clear material that may be used in a nuclear weapon. In contrast, Fusion enhances non- proliferation efforts. Fusion does not produce plutonium and would not involve enrichment, reprocessing, or other technologies with greater proliferation potential. This will allow for the confident sharing of fusion technolo- gy and construction of fusion power plants worldwide, even in countries that may be geo- politically less stable. 3.1.3 Proliferation Nuclear proliferation concerns for ICF typ- fusion power plant would likely be detect- ically center around the spread of nuclear able, and reprocessing facilities would also weapons technology, knowledge, and materi- need to be constructed – an activity that is als to countries or organizations that did not not easily hidden. previously have access to these capabilities. 2. Tritium is an essential fuel for a fusion pow- Furthermore, there is worry about the abili- er plant and can also be used to fuel mod- ty to enrich uranium or plutonium into fissile ern nuclear weapons. It is conceivable that materials which can then be used for nuclear tritium could be diverted from the power weapons, or tritium diversion. The prolifer- plant, however, tritium can be produced in ation risks associated with IFE and ICF R&D several ways in sufficient amount, and with have previously been assessed ([NASEM2013]: current technologies tritium alone is not Assessment of Inertial Confinement Fusion useful for building a nuclear weapon. Targets), with the high-level findings being: 3. Much of the information related to ICF tar- gets is already declassified. Only some as-

1. While it is technically possible to utilize the pects of computer codes and certain target large neutron fluxes generated in a fusion designs remain classified. The pursuit of ICF reaction chamber to enrich U or Pu, to do does not directly provide insight into that so covertly would be incredibly difficult classified information, and furthermore, and current IAEA monitoring would be suf- that information is primarily useful only in ficient to safeguard against this scenario as the presence of the large database of his- transfer of the material into and out of the torical underground tests. 32

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OVERVIEW 4. Fusion research facilities can provide in- It has been assessed that the risk of prolifer- sight into fusion physics; however, this is ation from nuclear fusion power plants is far not the same as information about weap- less than fission power plants and the authors ons design. Fusion power plants will likely of this Memorandum are in full support of the be engineered for economics and effi- above findings. ciency, with minimal diagnostics, so would provide only limited information about the physics itself. 3.1.4 Why Inertial Fusion Energy? When considering power generation from fu- » The modular technology of IFE is further- sion energy, laser driven IFE offers several ad- more expected to generate technology vantages [BRN2022] over other approaches: and science spin-offs that will provide early return on investment (EROI). » IFE is highly modular and uses separable components, providing flexibility in devel- Researching and developing fusion energy is oping subsystems and future commercial a major scientific and technical challenge that fusion reaction chamber. requires different approaches and paths to » IFE has multiple target concepts that can maximize the probability of success. Against be tested with the same driver, reducing the backdrop of significant progress in the risk and allowing for varied testing with the last two years, several countries are launching same facility. new initiatives and investments to accelerate » IFE targets typically require approximately technology development for energy produc- 0.3 milligrams of DT, which aligns with the tion from IFE and to build innovation ecosys- anticipated burn-up fraction for IFE with a tems with industry and position themselves gain of 100, estimated to be around 30%. in international competition. Known coun- » IFE offers a development path that enables tries include USA, the United Kingdom, Japan, methodical progress on systematically France and China. more complex facilities. 3.1.5 International Research of Inertial Fusion Energy There are several laser fusion schemes, in- which have a combined funding of around cluding indirectly or directly driven with hot USD 420 million and employ about a thou- spot ignition, and advanced schemes such sand individuals. NIF is the largest and most as shock ignition, electron fast ignition, and energetic laser system in the world, and it is proton fast ignition. The latter approaches used to study a range of scientific phenom- are less explored and vastly more complex, ena, including high-energy-density physics, but theoretically have the potential for higher astrophysics, and materials science. The Lab- fusion energy gains (>100) suitable for pow- oratory for Laser Energetics (LLE) in the USA er generation. The two main ICF programs in leads direct drive research using the OMEGA the US are carried out at the National Ignition laser facility (approximately 60x smaller than Facility (NIF) at Lawrence Livermore National the NIF), yet still the fourth largest laser sys- Laboratory (LLNL) in California and the OME- tem in the world. While ignition is not possible GA Laser Facility at the University of Roches- on OMEGA due to the insufficient laser ener- ter in New York. The ICF program within the gy, it is possible to study, on this downscaled Department of Energy’s (DOE) National Nucle- platform, hydrodynamics and material science ar Security Administration funds both entities, relevant to fusion ignition. 33

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MEMORANDUM LASER INERTIAL FUSION ENERGY At the time of this writing, there are no coor- Density HED science, attracting new talent. dinated IFE programs anywhere in the world that are publicly funded by governments. From 2000 to 2008, the US had an internal However, there are ongoing efforts to devel- program for high average power lasers (HAPL) op IFE programs in various regions such as the for IFE that also developed elements of an IFE United States, Asia, and Europe. power plant based on direct drive. From 2007 until 2013, LLNL carried out an extensive in- The confluence of steady progress in NNSA’s ternal program called Laser Inertial Fusion En- ICF program in the United States, the endorse- ergy (LIFE) which delivered a conceptual de- ment by the DOE’s Fusion Energy Sciences Ad- sign for a fusion power plant based on indirect visory Committee (FESAC) to create an IFE ini- drive ICF. It is one of the most comprehensive tiative, robust backing from U.S. Congress, and studies performed worldwide and is contribut- significant private investment in emerging fu- ing strongly to establishing confidence in the sion startups creates a distinct and stimulating transition from ICF to IFE while there are still moment for the advancement of Inertial Fu- unresolved physics challenges. An evaluation sion Energy research and development (R&D). of the potential of IFE was conducted by the This has grown significant political interest to US National Research Council and published launch an inertial fusion energy research pro- in 2014 [NASEM2014]. The recently published gram. The U.S. White House’s Office of Science Basic Research Needs report emphasizes and Technology Policy (OSTP) announced in strongly that a US IFE program should be rein- March 2022 a decadal push for commercial- stated due to recent advancements. ization of fusion. The INFUSE program, which provides public funding and seeks private in- Similar to NIF, the French Laser Megajoule vestment, was initiated by the DOE several (LMJ) near Bordeaux, France, is a facility with years ago to foster collaborative research and similar size and mission (although only 174 la- technology ventures among national labora- ser beams to NIF’s 192), and also configured tories, private industry, and universities. The for indirect drive approach. Research efforts ultimate objective was to facilitate technology for academic purposes in laser fusion in France transfer to the private sector by minimizing primarily concentrate on shock-ignition and obstacles to cooperation and leveraging the fast ignition. expertise and distinctive resources offered by DOE laboratories and universities. Similar- China is investing heavily in both indirect ly, ARPA-E has developed several programs to and direct drive inertial fusion, even though support high-risk, high-reward, innovative re- their current lasers are below ignition-scale. search in alternative fusion energy concepts, Its SG-III facility operates at 180 kJ in the UV and the CHIPS-Act passed in 2022 provides [Zhe2016]. A full-scale ignition laser facility funding to the private-public-partnership pro- SG-IV was proposed several years ago with an gram (PPP) of DOE, launched in fall of 2022, initial design goal of achieving 1.5 MJ or great- that aims for at least a 50/50 cost share in er energy. Specific information about the con- developing concepts for fusion power plants struction progress of this facility is limited. within ten years. Last but not least, the Fusion Energy Sciences Program within the Depart- Russia has a similar program to that of NIF or ment of Energy gathered the community to LMJ and operates already their first 64 beams develop an IFE Basic Research Needs report of its UFL-2M laser in Sarov that is designed published in January 2023 that developed a to deliver 2.8 MJ at 527 nm from 192 beams set of priority research opportunities for a U.S. [Sci2022] when complete. The longer wave- inertial fusion energy research program. Thus, length at the second harmonic of Nd:Glass build-up of a strong IFE program in the Unit- distinguishes it from NIF and LMJ, both of ed States is underway, including the estab- which operate at 351 nm. lishment of new Professorships at universities in the area of fusion energy and High Energy Japan‘s research is centered on electron 34

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OVERVIEW fast-ignition, which is conducted using the 12 for only ~€1 Million across all of Europe. kJ GEKKO XII/FIREX laser facility. From 2008 to 2011, the European ESFRI Road- In Europe (including in France, the UK, Germa- map program was used to prepare for explor- ny, and the Czech Republic) several high en- ing a European fusion facility (HiPER). Euro- ergy (kilojoule-class) facilities exist. These pro- pean scientists are now working on a plan to vide some capabilities of studying laser-plasma revive the HiPER project. Various academic interaction processes but are not suitable institutions in several European countries, for conducting implosion and integrated fu- including Germany, Italy, Spain, the Czech Re- sion experiments. Funding is very limited and public, Hungary, Greece, and France are still comes from various national programs and to conducting research on laser fusion. a small degree from EUROfusion, accounting 3.1.6 German Research in Laser Inertial Fusion The expert panel spoke to representatives ser matter interaction and shock physics. GSI from German research organizations and na- operates PHELIX, Germany’s highest energy tional labs to develop a better picture of the laser experimental facility with short pulse German ICF/IFE scientific research landscape. and nanosecond pulse capability approach- In addition, a whitepaper was initiated by ing 1kJ. HZDR has a short pulse laser program German attendees of the 43rd Workshop on and operates the ultrafast Petawatt laser DRA- High-Energy-Density Physics with laser and CO suitable for training students. PENELOPE, Ion beams in Hirschegg, coordinated by Prof. another more energetic diode pumped laser M. Zepf from University of Jena. (DPSSL) Petawatt laser is under construction and will address similar high intensity laser German research groups have a wide range of physics. Similar to PENELOPE, HIJ operates skills and expertise directly relevant to laser POLARIS, another multi-hundred-Terawatt fusion research. Currently they are conduct- laser system. There is also a dedicated HED ing experiments on national and European beamline on DESY’s XFEL (HIBEF) suited for laser facilities, in the United States, Japan and basic HED-plasma and shock physics experi- occasionally also in China. Several key groups ments using the ultrabright beam from X-FEL have expertise in plasma and HED science (in as a high resolution plasma probe. Within this both the experimental and theoretical realms) facility there are several modern medium-en- on laser matter injections, instrumentation, ergetic lasers, such as the DiPOLE laser from and target diagnostics. Indeed, the U.S. ICF the UK with ~100Joules energy per pulse. community has recruited repeatedly from this Plans exist to co-locate a multi-kJ laser, mak- pool of talent in Germany. Universities such ing it ideally suited for ICF/IFE related science as TU Darmstadt, TU Dresden, University of and code benchmarking. Access to HIBEF is Düsseldorf, University of Jena, LMU Munich, high in demand and thus very competitive. the University of Rostock are directly active CALA (TU Munich) is Germany’s highest peak in plasma science, high power laser research power facility, delivering 2 Petawatt with 60J. and/or computation and therefore already While not suited for compression or implosion have many of the relevant skill-sets required experiments, fast ignitor science can be ex- to contribute to an ICF/IFE program and train- plored. ing of young researchers. Although these facilities offer exceptional ex- GSI Darmstadt, Helmholtz Zentrum Dres- perimental capabilities for high-intensity laser den Rossendorf (HZDR), XFEL/DESY Ham- matter interaction, secondary-source science, burg, Helmholtz Institute Jena (HIJ), and For- and some ability to study shock physics or schungszentrum Jülich conduct experiments warm-dense-matter science, their capacities in the field of high energy density science, la- for ICF or IFE physics are significantly limited. 35

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MEMORANDUM LASER INERTIAL FUSION ENERGY Research efforts in current high-power laser of plasma and HED science, high-power laser and capability development are insufficiently physics, engineering, material science and en- coordinated, resulting in suboptimal national gineering is necessary to establish a compre- capability. Marvel Fusion and Focused Ener- hensive research and development program gy, the two IFE startups in Germany, plan to aimed at initiating and sustaining a robust IFE construct their own experimental capabilities program in Germany. to explore and validate their concepts. How- ever, their and any other private fusion com- The Laser Inertial Fusion Expert Panel agrees pany’s growth is constrained by the available with these overall recommendations We have workforce, and the projected need in S&T ca- discovered that Germany‘s ICF efforts are pability of the private sector cannot be met nascent but have enormous potential, and by talent from the national or European pro- are currently driven by a small, but motivat- fessional ICF or high power laser community ed group of individuals. The concept of clean, without negatively impacting other critical abundant energy from fusion science is very experimental programs. The Hirschegg group appealing to new talent, but the current num- recommends investing in expanding the cur- ber of competent individuals, funding and ca- riculum and constructing dedicated facilities pabilities cannot support it. We also learned in Germany that combine multiple ICF la- that the field suffers from the stigma that IFE ser driver beams with multi-kJ capability per is a type of nuclear energy or is associated beam. Additionally, establishing a robust sci- with nuclear weapons research. This has ac- ence and engineering program in the fields celerated brain drain from these areas. 3.1.7 Approach by the Fusion Expert Panel to this Effort Fusion energy research and development vened to explore the prospects of fusion en- is a major scientific and technical challenge ergy for Germany. In November 2022, a group that requires multiple approaches and path- of seven renowned international experts in ways to maximize the likelihood of success. the fields of laser-driven inertial confinement NIF demonstrated exceeding the Generalized fusion, power plant and reactor physics, and Lawson Criterion on August 8th, 2021. Given magnetic fusion energy were convened for the significant acceleration in inertial confine- the first time at BMBF. They were tasked by ment fusion including the creation of several Minister Bettina Stark-Watzinger to assess and startups worldwide with significant funding provide recommendations in various areas, in- in this field, several countries are currently cluding: launching new initiatives and investments to accelerate the development of fusion energy » Approaches to inertial fusion and their spe- technologies and to establish innovation eco- cific physics case systems with industry, thus positioning them- » International players and programs in ICF/ selves in the international competition. These IFE countries include China, France, the United » Status and gaps in competencies and capa- Kingdom and the United States. bilities, and enabling technologies, both in Germany and internationally Hence, the BMBF convened in May of 2022 a » Training and workforce development in round of stakeholders from private industry, Germany to support ICF/IFE specifically from the energy sector, heavy (en- » Role of industry ergy demanding) industry, high-tech technol- » Framing of an ICF/IFE program ogy firms and Germany’s fusion startups. The meeting concluded that the stakes are high, The panel conducted a thorough examina- and a scientific expert panel should be con- tion of the BRN report [BRN2022], as well as 36

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OVERVIEW other relevant technical literature and similar is generated by means of a Laser Driver. The reports, to gather information in these areas. target for ICF/IFE is injected through a target Over the course of three months, the panel injector into the center of the reaction cham- convened for multi-day in-person meetings at ber and then hit by lasers. The target injector BMBF and Lawrence Livermore National Lab, must launch a target with the pulse repetition in addition to holding seven online meetings. rate of the power plant, typically between 10 During these meetings, the panel explored, to 15 Hz. It must also collect the remains or reviewed, discussed and drew conclusions to shrapnel. The reaction chamber‘s innermost achieve their objectives. layer, facing the target, is known as the first wall and blanket, which collects the neutrons The panel interviewed German fusion start- and sees – dependent on the plant design- ups (incl. MFE), energy industry professionals, x-rays and fast ions emitted from the target. and other experts to form recommendations. Outside the reaction chambers are the drive lasers which deliver the energy to the target In assessing competencies and capabilities the in order to ignite it and the fuel cycle that re- panel followed a logical structure outward covers unspent fuel and delivers new fuel to from the heat generating plasma, similar like the targets. Finally, the outermost shell of the to peeling an onion. The group termed this Fusion power plant is responsible for convert- “plasma onion” and it is the approach that ing the high-grade heat generated by fusion was also followed in this memorandum. Go- processes into heat/steam to drive the ther- ing from inside to the outside: The core of moelectrical converters. the IFE system is the burning plasma, which Fig. 1: Fusion Power Plant concept. Courtesy of LLNL 37

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MEMORANDUM LASER INERTIAL FUSION ENERGY Fig. 2: Elements of the “Plasma Onion”. 38 ygrene morf ecnatsiD amsalp gnicudorp Technical Element Scientific fields Plasma Physics and modelling Target » Capsule » Cavity (LID) » Coupling, Ignition and gain » Production scaling » Insertion and removal Reaction chamber Radiation & Debris mitigation 1st Wall and Blanket » Radiation mitigation, materials » Fuel cycle » Cooling and heat removal Laser Driver » Final optics » Beam transport » Laser system » Laser support systems Fusion Power Plant Electrical conversion

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04 Potential Role of Nuclear Fusion for Global Energy System

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MEMORANDUM LASER INERTIAL FUSION ENERGY The fusion expert panel reviewed current lit- dustrial competitiveness of Germany’s indus- erature [Mas2018], [IEA2022] and spoke to try is directly linked to the affordability, stating Prof. Henning, Head of the Expert Council for that the cost of energy must not rise further, Climate Issues of the German Federal Gov- specifically in comparison to Germany’s neigh- ernment and to Siemens Energy about the boring countries. In this context and in view World Energy Outlook and the role of Fusion of the continuously growing demand for elec- in a global energy market. The following rep- trical energy, industry states, that fusion-gen- resents our takeaway: erated electricity is an attractive and highly interesting power source, even after 2045 but In 2019, Europe adopted the Fit for 55 Pact as not much later as industry might move out of an interim step in its commitment to become the country to more energy-economic loca- the world’s first climate neutral continent by tions. 2050. This pact requires the European Union to reduce greenhouse gas emissions by at However, given the amount of technology de- least 55% compared to 1990 levels. As a result velopment ahead of making IFE a viable power of burden-sharing agreements within the EU, source, fusion energy won’t contribute to Ger- Germany has also adjusted its climate targets, many’s energy transition to net-zero in 2045 committing to become climate neutral by but present a very attractive opportunity to 2045 and to reduce emissions by 65% by 2035 maintain net-zero in ever growing electrical compared to 1990. demand not only in Germany but globally. Due to its high technical complexity and required At present, 72% of the Germany’s primary investment into a power station, fusion ener- energy is imported, mainly from fossil fuels. gy will need to be source that runs 24/7, pro- Energy forecasting studies suggest that glob- viding base load capacity. However, electricity al energy demand is predicted to increase by generated by fusion -specifically in periods of up to 30 percent until 2050, with electricity low consumption- could be used for afford- becoming a dominant primary energy source able production of energy carriers (e.g. hy- globally. When compared to 2020, electricity drogen or ammoniac), which will be needed in demand is expected to grow by a factor of areas where direct electrification is either too two or three globally as well as in Germany. expensive or not feasible. Electrolytically pro- Thus, different energy sources (e.g. electricity, duced hydrogen will play a crucial role here, hydrogen, heat) are required for an integrat- either as a final energy carrier or as an inter- ed future energy system It is expected that mediate for producing larger molecules. Both at least one-third of Germany’s energy needs processes generate significant power demand will still have to be met by imports, although it that could be met by fusion power stations. is predicted that two-thirds of Germany’s en- Another increasingly important challenge in ergy needs could be met by domestic renew- many regions of the world is the lack of access ables by 2045 [Mas2018]. to potable water. Desalination is a very ener- gy-intensive process for the removal of salt Models of the future energy system indicate and other impurities from seawater. Demand higher dynamics of the energy market de- for such techniques is expected to increase manding increased flexibility. The daily de- sharply in the future - fusion energy could mand for electricity is expected to fluctuate provide a clean and efficient power source to considerably. Power plants will need to be drive the process, underscoring the need for quickly ramped to supplement power gener- energy equity. Furthermore, fusion power can ation; a function that is covered by storage be directly used to operate air capture sys- power plants and gas plants. However, rep- tems for negative emission technologies. resentatives of German heavy industry state, that future baseload requirements will be at There is more than net-zero goals and efficien- least 25 percent, requiring secure supply 365 cy, which is energy diversity and resilience. In 24/7. Furthermore, industry stresses, that in- its analysis of the current energy crisis in Eu- 40

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POTENTIAL ROLE OF NUCLEAR FUSION FOR GLOBAL ENERGY SYSTEM rope, the IEA stated in 2022 [IEA2022]: “Rus- tries with an unstable geopolitical setting. De- sia’s invasion of Ukraine triggered a global en- veloping a power source that is available 24/7 ergy crisis, impacting households, businesses, and independent of weather and energy im- and economies. Europe is the main stage for ports provides a strong incentive to move the the crisis and high energy prices are trans- Fusion technology development forward. ferring wealth from consumers to producers. Fuel prices are responsible for over 90% of the The panel drew the conclusion, that meeting increase in global electricity generation costs the likely increase in electricity demand after (data from 12/2022), with renewables and mid-century, especially to produce non-fossil carbon dioxide playing a minimal role. “The energy and raw materials, requires consider- costs of renewables and carbon dioxide have ing additional new technologies and advanc- played only a marginal role, underscoring that ing their development through dedicated re- this is a crisis where energy transitions are the search programs. In the post-energy transition solution, rather than the problem.” Energy re- period, fusion-generated electricity could be a silience can be gained by energy sovereignty, reliable and very attractive option for securing reducing dependencies specifically from coun- Germany’s energy sovereignty. Fig. 3: Final energy mix in the scenarios of the ARIADNE project for the overall energy system [Uec2021]. 41 )% ni(ygrene laniffonoitcarF )% ni(ygrene laniffonoitcarF Green hydrogen and fuels are no regret solutions for industry and transport sectors 100 Electrical applications today 75 Direct electrification in all scenarios Electricity mainly in cars and buildings Energy carrier Scenario 50 Competition between direct electricity Technology mix and indirect electrification, e.g. fossil fuels and feedstocks Electrification for heavy-duty transport and hydrogen + e-fuels Hydrogen process heat heat networks E-Fuels 25 biomass Green hydrogen and e- Hydrogen in industry, aviation fuels in all scenarios and shipping 0 2020 2025 2030 2035 2040 22004455

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05 Science and Technology of Inertial Fusion Energy (IFE) 42

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SCIENCE AND TECHNOLOGY OF INERTIAL FUSION ENERGY (IFE) 5.1 Scientific Introduction of IFE In the 1920‘s it was conjectured that all ele- rium (D) and tritium (T) into a fast “14 MeV” ments in the periodic table are constituted neutron (which carries 80% of the produced out of hydrogen atoms bound together and by energy) and a helium-4 nuclei, also termed an the 1930’s it was fully understood that stars, alpha-particle (which carries 20% of the pro- like our Sun, made their energy by fusing hy- duced energy). Very occasionally, a tiny 4x10-5 drogen nuclei together thus creating all ele- fraction of D+T fusion reactions generate a ments via a chain of fusion processes termed gamma ray and helium-5 nuclei. “stellar nucleosynthesis.” The advantages of D+T fusion, as compared to The potential usefulness of fusion for terres- other terrestrial fusion reactions, is that the trial energy production comes from noting reaction-rate peaks at the lowest tempera- that the mass of fusion products do not quite ture of any other fusion reaction (see Fig. 4) add up the mass of the reactants in a fusion the tipping-point where fusion power just bal- reaction; there is instead a small difference ances cooling by bremsstrahlung x-ray emis- called the “mass deficit” that, because of sion also occurs at the lowest temperature of Einstein’s energy (E) to mass (m) equivalency any other fusion reaction (see Table 1), the formula (E=mc2, where c is the speed of light), theoretical ratio of energy output over energy corresponds to a “binding energy” that is lib- input (Gain) is significantly higher than any erated during fusion. For example, the mass other reaction, and the D isotope is plentiful in difference between one helium-4 atom and seawater. The Gain advantage of D+T comes four hydrogen atoms is 4.87x10-29 kilograms about from its reaction-rate advantage and which is equivalent to 4.4x10-12 Joules. Thus 1 ignition temperature advantages, but also be- kilogram of hydrogen undergoing fusion could cause the heat capacity, which is a measure of yield 7x1014 Joules of energy – enough energy the energy required to bring a mass to a given to supply 20,000-30,000 German households temperature is significantly lower than that of for a year. non-hydrogen isotope fuels (for example, DT All hot fusion schemes involve a “plasma” (a highly ionized gas) because high inter-atom ki- netic energy is needed to overcome the elec- trical repulsion between positively charged nuclei thus forcing the reactants close enough to each other to have a nuclear fusion reaction. The probability of overcoming the inter-atom electric repulsion increases with temperature, but raising the temperature of any material, gas, or plasma, costs energy. The energy cost of electric repulsion is why practical fusion fa- vors isotopes of hydrogen, rather than atoms higher up on the periodic table (i.e. elements with higher atomic number, Z). Stellar fusion reactions are far too slow for Fig. 4: The reaction-rates of select reactions terrestrial energy use, so fusion scientists are plotted based versus thermal tempera- mainly concentrate on reactions that involve ture. The temperature region, 2 keV < T < 20 heavy isotopes of hydrogen which have high- keV of practical interest to D+T based ICF is er reactivity. The most reactive terrestrial highlighted. The top curve is the DT reaction fusion reaction involves the fusion of deute- rate, while the tangent line is the power-law. 43

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MEMORANDUM LASER INERTIAL FUSION ENERGY Fusion Reaction k T (keV) Q (MeV/reaction) B crit D + T → n + 4He 4.3 17.6 D + 3He → 4He + p 28 18.3 p + 11B → 3 × 4 He 300 8.7 Table 1: The “critical temperature” T [Pos1956], where fusion energy production just bal- crit ances x-ray energy losses, is shown for some commonly discussed fusion reactions assuming thermal equilibrium in energy units (kB being the Boltzmann constant). Temperatures greater than T are generally required for ignition. Q is the total fusion energy liberated per reaction. crit The T value for pB11 comes from a modern revaluation [Put2019]. crit heat capacity is 115 MJ/g/keV whereas pB11 the Lawson Criterion [Law1957], which is a nu- heat capacity is 555 MJ/g/keV). The disadvan- merical threshold involving the fusion plasma tages of D+T fusion is that the T isotope is ra- density (or pressure), thermal temperature, dioactive (a beta emitter) with a 12-year half- and confinement-time. The Lawson Criterion life, so T must be made to fuel the D+T for ignition in magnetic fusion energy (MFE) reaction, and the neutron product of the reac- systems is numerically different and generally tion (which is the primary mechanism for ex- less restrictive than the generalized Lawson tracting heat) damages materials of the reac- Criterion (GLC) appropriate for inertial con- tion chamber. Nevertheless, it is the consensus finement fusion (ICF) plasmas [Bet2010], the scientific view that D+T fusion is the most principal difference coming about from the practical fusion fuel in the short term. impulsive nature of ICF/IFE fusion systems. Since it takes energy to heat a fusion plasma to A low-density DT plasma of small spatial size the state where a significant number of reac- has a very low probability of stopping al- tions occur, fusion becomes a lot more attrac- pha-particles. To increase the chance of stop- tive if one can engineer a situation where the ping the alpha-particle fusion products one some of the energy produced by fusion can must either engineer the fusion volume to be be retained in the fusing region, thus heating large, add strong magnetic fields to force al- itself. The principal way to get the plasma to pha-particles into a helical trajectory that traps be self-heating is to create conditions where the alpha-particles inside the plasma volume, there are sufficient inter-atomic collisions be- or greatly increase the density of the plasma tween the fusion products and the fusion re- via a compression scheme (or a combination actants. For DT fusion, self-heating relies upon of these three tactics). Since compressing and alpha-particles generated by DT fusion collid- heating a large mass of fusion fuel is energet- ing with electrons in the DT plasma to “stop” ically costly, ICF/IFE systems focus upon heat- the alpha-particle, which then adds heat to ing small masses of fuel, on the order of 10’s the DT plasma (stopping the 14 MeV fusion to 100’s of micrograms, in their operation. neutrons in the fusion plasma is not practical for inertial confinement fusion [ICF] systems). At fusion relevant temperatures (> 10 keV, If the plasma self-heating heating is sufficient- where 1 eV = 11,600 Kelvin), DT plasmas have ly intense, such that the self-heating overtakes significant pressure, for example a DT plasma all the processes that cool the plasma, the of 0.001 g/cc density at 10 keV has 7.7 Mbar of plasma has “ignited” and a thermodynamic in- pressure (where atmospheric pressure at sea stability is generated resulting a rapid increase level is about one bar). Stainless steel yields in fusion energy production. The plasma con- at 2 kbar and in general no material can con- ditions needed for ignition are determined by tain Mbar’s of pressure. Thus, magnetic fusion 44

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SCIENCE AND TECHNOLOGY OF INERTIAL FUSION ENERGY (IFE) approaches that use confining pressure ves- ered into the hohlraum. For ICF schemes not sels work with large volume very low-density involving a hohlraum, capsule gain and target plasmas with pressures of a 3-7 bar in a quasi- gain are the same thing. G >1 was achieved target stead-state. Whereas ICF plasmas impulsively in the laboratory in 2022 [LLN2022], by gener- create microscopic scale high density plasmas ating 3.15 MJ of total fusion energy from 2.05 via an “implosion” that compresses the fusion MJ of laser energy input into the target (as a fuel to the conditions needed for ignition, practical reference point, note that 1 kWh = holding the fuel together inertially but for a 3.6 MJ and the average German household moment (about 100 picoseconds) as fusion energy use is 15-30 kWh per day). power is generated, then becoming a mi- cro-explosion due to the ultra-high pressures None of these gain definitions account for (100’s of Gbar) that are generated. the energy expended by the facility (usually orders of magnitude greater than the energy Fusion power integrated over sufficiently long than what is delivered to an ICF target). Thus, times can result in energy gain. Since ICF/IFE fuel gain, capsule gain, or target gain greater systems are energy density concentrators than unity do not imply net energy produc- that have elements of successively smaller tion. “Engineering gain” (G ) is usually engineering components of decreasing size nested inside defined to include the energy used by the fa- each other, an “energy gain” can be defined cility, thus G > 1, would imply net en- engineering for each layer of the system. The central el- ergy gain in the practical sense of interest for ement of physical interest in an IFE system is IFE. No manmade laboratory fusion system in the fusion fuel, thus one can define a “fuel existence has yet achieved G > 1. engineering gain” (G ), which is the ratio of fusion energy fuel produced over the net energy that was exter- In addition to the plasma condition differenc- nally delivered into the fusion fuel. G >1 was es between MFE and IFE, IFE systems require fuel achieved in the laboratory in 2014 [Hur2014]. expendable targets that contain the fusion The fusion fuel in an IFE system that involves fuel which are injected into a target chamber, an implosion is carried inside a shell of mate- “shot” with an intense source of concentrated rial, the capsule, thus “capsule gain” (G ) energy (e.g. lasers), and the target then oper- capsule defines the ratio of fusion energy produced ates as a power and energy-density amplifier over the net energy absorbed by the capsule. bringing the fusion fuel to ignition conditions G >1 was achieved in the laboratory in thus generating fusion energy impulsively. For capsule 2021 [Abu2021]. In the case of x-ray driven quasi-continuous power generation, IFE sys- ICF designs (see Section 2.2), a metallic outer tems require a continuous stream of targets structure, a “hohlraum”, surrounds the cap- entering the target chamber which are then sule, completing the ICF target, and thus one shot one-after-another at a rapid rate (many can define a “target gain” (G , or some- times per second), which is a significant engi- target times simply G) which is the ratio fusion ener- neering challenge. gy produced as compared to the energy deliv- 5.2 Approaches to Laser Driven Nuclear Fusion There are principally four experimental target based upon experimentally demonstrated lev- concepts in laser driven IFE that are at various els of performance, where indirect-drive has levels of development: Indirect-drive (TRL 3), demonstrated ignition on the U.S. National Ig- Direct-drive (TRL 2), Fast-ignition (TRL 1), and nition Facility (NIF), direct-drive is projected to Shock-ignition (TRL 1) [Shc1983]. The noted TRL ignite at NIF-scale levels of laser energy based levels reflect the maturity of each approach upon experimental work on the Omega laser 45

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MEMORANDUM LASER INERTIAL FUSION ENERGY [Gop2019], while fast-ignition and shock-igni- In all cases, as the capsule surface absorbs tion approaches are further behind in testing energy and ablates, ablation pressure accel- with conceptual and experimental work ongo- erates the shell of remaining ablator and DT ing [Bet2016]. fuel inwards; the implosion stage of opera- tion. By the time the shell is at approximate- In typical cases for these four target concepts, ly one-fifth of its initial radius it is imploding a (usually) spherical capsule is prepared with a at a speed of many hundreds of kilometers layer of DT fuel on its inside surface (see Fig. per second – generally slower for fast-igni- 5). In the case of the indirect-drive (IDD) ap- tion/shock-ignition schemes and faster for di- proach, the capsule is suspended inside a high rect-drive schemes. For the indirect-drive and atomic number (high-Z) volume that coverts direct-drive approaches by the time the im- laser energy into a nearly Planckian bath of plosion reaches minimum volume, a hotspot x-rays that ablate the capsule surface gener- of DT has formed in the center of the capsule, ating ablation pressures of 100-200 Mbar (de- surrounded by colder and denser DT fuel and pending upon ablator material). In the case of if the conditions satisfy the Lawson Criterion, direct-drive (DD) a hohlraum is not used, and ignition starts in the hotspot and then prop- instead the capsule surface is directly illumi- agates into the surrounding cold fuel over a nated by laser beams in as uniform a fashion short duration of time. In the case of fast-ig- as possible. Fast-ignition and shock-ignition nition and shock-ignition, a hotspot is not targets can be designed to either use IDD or generated by the implosion. For fast-ignition, DD illumination to compress their fusion fuel ignition is triggered by an auxiliary short-pulse payload. laser that is directed into a conical section of the target geometry (see Fig. 5). For shock-ig- Fig. 5: (Left) IDD target configurations use a hohlraum as a converter of laser energy into x-rays, where the x-rays surround and implode a smaller fuel carrying capsule. (Middle) DD targets are capsules of fusion fuel directly illuminated by laser beams. (Bottom) In both the IDD and DD cas- es, ablation of the capsule surface generates pressure that accelerates a layer of fusion fuel to high velocity. At peak compression, kinetic energy is transformed into internal energy heating a central hotspot. (Right) Fast ignition (FI) targets split the compression of fusion fuel and ignition into two steps.(Adapted from [Bet2016]). 46

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SCIENCE AND TECHNOLOGY OF INERTIAL FUSION ENERGY (IFE) nition the target configuration can appear tially due to the steeper ablation density similar to either IDD or DD, but generally with profile associated with the electron-con- a thicker capsule, and the operation emulates duction as opposed to the less steep pro- fast-ignition in the separation of the compres- file in x-ray driven ablation. sion and ignition stages. At the end of the » Direct-drive implosions have an additional compression stage of the shock-ignition im- seed for high-mode (>30) hydrodynam- plosion an “ignitor shock” is launched into the ic instability, laser “imprinting,” that indi- implosion by spike in laser-power. rect-drive avoids by use of a hohlraum. » Because of the laser directly impinging Key differences between indirect and direct upon a direct-drive capsule and because drive are listed below: of the relatively thin ablators used in the direct-drive, electron preheating of di- » For a fixed laser energy, direct drive has rect-drive capsules is correspondingly more greater energy coupling to the capsule by difficult of an issue than for indirect-drive. avoiding the intermediate hohlraum la- » Direct-drive would greatly benefit from ser-to-x-ray energy conversion step of in- broadband lasers, since high bandwidth direct-drive. This can be an input energy can suppress imprinting, CBET, and other advantage of 7-10x. Some of this energy LPI. advantage may be offset by cross-beam energy transfer (CBET) which can redirect While the U.S. Department of Energy (DOE) inward coming energy flux outward. ICF Program on the NIF has been a nucle- » While the ablation pressures for direct and ar weapons program with the objective of indirect-drive are similar, the mass abla- achieving thermonuclear ignition to support tion-rate for indirect-drive is larger, be- the stockpile stewardship program (SSP) and cause of the deeper penetration into the study high-energy-density (HED) regimes at ablator of x-rays. This leads to a higher the extreme temperature, pressure, and den- hydrodynamic efficiency (ratio of implosion sity, the indirect-drive advantages of higher kinetic energy to ablator energy absorbed) hydrodynamic efficiency and hydrodynam- in the case of indirect-drive. ic stability control, mention above, were the » Taken together (the two bullets above) the principal reasons for indirect-drive being cho- overall laser energy to implosion kinetic en- sen over direct-drive for the NIF. As a result, ergy conversion of direct-drive is ~5% while it is a mistake to discount IDD as a potential for indirect-drive it’s ~1.5%. path for IFE because of its choice for the DOE » Due to the energy advantage of direct-drive, SSP mission. Instead, the above physics com- the stagnation pressure requirement for ig- parison implies there is no clear winner for IFE nition of a direct-drive implosion is about ½ applications at this time. that of indirect-drive. This leads to lower implosion convergence requirements for Key differences between conventional ICF us- ignition. Higher degrees of convergence re- ing IDD or DD and more advanced, but less de- quire more physics and engineering control veloped concepts of FI and SI are: of the laser drive and targets. » The energy advantage of direct-drive leads » The two-step nature of FI and SI allows the to larger capsules, which can provide larger use of relatively slow implosions that are fusion yields (~4x) for a given implosion ve- less susceptible to the detrimental effects locity simply due to their increased volume. of hydrodynamic instabilities. » The direct-drive advantage in energy cou- » Lower laser intensities can be used for the pling is offset by the higher adiabat (low- compression stage of FI and SI schemes er fuel compression) requirements of making them less prone to exciting la- direct-drive that are needed for hydrody- ser-plasma instabilities. namic stability control. This increased sen- » Ignitor physics is less well developed than sitivity of direct-drive implosions is essen- hotspot ignition. Ignition using an ignitor 47

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MEMORANDUM LASER INERTIAL FUSION ENERGY pulse is yet unproven albeit the principals are sound, whereas hotspot ignition is proven. Uncertainties surround the very high laser intensity laser-plasma interac- tion needed for the ignitor. The FI and SI alternatives to the conventional DD and IDD approaches, that are at the core of the US national program, are being investi- gated at the university level in the US, Europe, Japan, and China. 48

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06 Expertise, competence, and capabilities organized by modular technologies/Research Areas

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.1 Fusion Plasma and Ignition 6.1.1 Role of Fusion Plasma and Ignition in IFE A high-energy-density igniting fusion plasma is the experience of people trained in physics or at the heart of any IFE system, yet the physics even magnetic fusion plas-mas, where most of of ICF/IFE is extremely specialized and outside Germany’s fusion plasma expertise resides. 6.1.2 R&D Status Worldwide The worldwide expertise in ICF/IFE is limited been limited to reaction chamber design stud- to a few thousand people worldwide. Most ies, laser technology development and more R&D has been focused upon fundamental recently an integrated study of an IFE power studies and getting to an ignited plasma in the plant called LIFE (Laser Inertial Fusion Energy) laboratory, with little consideration given to [Mos2009]. The LIFE project ended in 2013 IFE applications or practicality. The number of and LLNL has not been directly involved in IFE people worldwide who have investigated IFE research activities since then. While mostly concepts with any seriousness is less than a devoted to IDD, some polar-DD studies have hundred, at best. taken place on the NIF (see Sec. 2.4). The US has led research in DD and IDD, where Most DD R&D in the US has been concentrat- the ideas originated. IDD R&D has been the ed at the University of Rochester’s Laborato- focus of Lawrence Livermore National Lab- ry for Laser Energetics (LLE), which operates oratory (LLNL) home to the NIF, Los Alamos the OMEGA laser facility (a 60 beam 40 kJ National Laboratory (LANL), and to a less- long-pulse system plus EP, a two-beam short- er extent Sandia National Lab (SNL). Due to pulse system with two-additional long pulse their national security mission, these US labs beams), and at the Naval Research Laborato- house most of the US expertise in the physics ry (NRL).Though smaller in size, the NRL effort of IDD implosions, radiation-hydrodynamics, has been effective in developing the appli- nuclear and x-ray diagnostics, multi-physics cations of excimer lasers for IFE through the super-computer simulations, and research fa- NIKE laser, a 56-beam krypton fluoride laser cility operations such as the NIF at LLNL and producing 3-kJ deep-UV (248 nm) light. In ad- the Z-machine at SNL. The NIF is a 192-laser dition, the NRL Electra laser is capable of 5Hz beam long-pulse facility that can deliver a repetition rates and 90,000 shots of contin- maximum of 2.05 MJ of 351 nm laser light uous operation. Primary areas of study for at a maximum of 500 TW of power into the DD include the fundamentals of laser driven target chamber. Experiments on the NIF are fusion, DT-layered implosions, target design, divided into the three general areas of ICF, laser-matter interactions, laser development, HED, and national security. ICF work on the and target fabrication [LLE2021]. NIF has been focused on achieving robust and repeatable ignition and maximizing the fusion University or laboratories worldwide that Gain. Technically, no IFE specific work has tak- have programs that touch upon IFE relevant en place on the NIF. IFE research at LLNL has R&D programs are given in Table 2: Institution Location R&D Topic CALA/LMU Germany Laser-matter interactions, computational plasma physics Table 2: Universities and Research Institutions with IFE relevant R&D programs worldwide. 50

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS Institution Location R&D Topic CEA France Target fabrication, ICF, laser facilities Centre Lasers Intenses et Applications, U. France Laser-matter interactions Bordeaux ELI Czech Republic Laser-matter interactions ENEA Italy HED/Laser-matter interactions/ICF General Atomics US Target fabrication GSI/TU Darmstadt Germany Laser-matter interactions, target labora- tory HIJ/University of Jena Germany Laser-matter interjection HZDR/ TU Dresden Germany Laser-matter interactions Imperial College UK ICF/Radiation-hydrodynamics codes Institute of Laser Engineering, Osaka Univer- Japan Laser-matter interactions sity Institute of Physics, Chinese Academy of China Laser matter interactions Sciences Institution of Russian Academy of Sciences Russia IFE Reaction chamber LANL US ICF/Plasma Diagnostics/IDD LLNL US ICF/Plasma Diagnostics/Laser facilities/ IDD/laser-matter interactions LULI France Laser-matter interactions Massachusetts Institute of Technology US ICF/Plasma Diagnostics National Institute for Fusion Science Japan IFE Reaction Chamber Rutherford Appleton Laboratory, Oxford UK ICF/Laser-matter interactions SLAC-MEC US Laser-matter interactions SNL US ICF/Plasma Diagnostics U. of California US (Berkeley, Davis, Los Laser-matter interactions Angeles, San Diego) U. of Madrid Spain HED/Radiation-hydrodynamics codes U. of Michigan US HED/Laser-matter interactions U. of Nevada, Reno US HED U. of Rochester/LLE US ICF/Plasma Diagnostics/Laser facilities/DD/ laser-matter interactions University of Rostock Germany Laser-matter interaction Table 2: Universities and Research Institutions with IFE relevant R&D programs worldwide. 51

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.1.3 Capabilities and Competencies in Germany Radiation hydroydynamic codes are an essen- overdense plasma is computationally too ex- tial component of the simulation capability pensive. Hybrid-PIC codes can simulate both for studying implosion physics and predict- particle acceleration in underdense plasmas ing implosion performance of IFE targets. and energetic particle transport in overdense There are only few rad-hydro codes connect- plasmas. However, Hybrid-PIC codes are less ed to German developers. MULTI is a 1D and developed and only few versions are available. 2D rad-hydro code originally developed at Dr. Javier Honrubia, currently with Focused Max-Planck-Institute for Quantum Optics in Energy developed hybrid codes for fast igni- 1988 by Ramis, Schmalz and Meyertervehn as tion [Hon2009] Whereas, PIC codes are widely a 1D planar code [Ram1988]. It was extended available at Max-Plank-Institute and at Ger- to spherical geometry and 2D at the Universi- man universities. For example, VSPL by A. Puk- dad Politecnica de Madrid, Spain [Ram2009]. hov [Puk1999] at the University of Dusseldorf. A widely used open-access PIC code is ORISIS, To study fusion schemes based on electron or developed at UCLA (USA) and Instituto Superi- proton fast ignition, PIC and Hybrid-PIC codes or Tecnico in Lisbon (Portugal). are required. PIC codes can simulate the par- ticle acceleration from the interaction of a Below is a comprehensive list of radiation hy- preformed plasma with a high-intensity short drodynamic codes, PIC codes and other spe- picosecond laser pulse. Using PIC codes to cial-use codes of interest to IFE studies. simulate the transport of energetic particles in Code Maintainer/Company Description CHICAGO/LSP Voss Scientific Radiation/ Hydrodynamics/ Magneto- hydrodynamics/3D PIC EPOCH University of Warwick 3D PIC for LPI studies FLASH Flash Center Code Group/University 3D Radiation /Hydrodynamics/ Mag- of Rochester/Petros Tzaferacos netohydrodynamics FLYCHK NIST Atomic level populations and charge state distributions HELIOS Prism Comp Sci 1D Radiation/Hydrodynamics HYDRA Marty Marinak/LLNL 3D Radiation/Hydrodynamics/Magne- tohydrodynamics OSIRIS Warren Mori/UCLA 3D PIC code for LPI studies PICLS Yasuhiko Sentoku 3D PIC code for LPI studies PROPACEOS Prism Comp Sci Equation of State and Opacity SPECT3D/ PrismSPECT Prism Comp Sci Collisional-radiative spectral analysis codes VISRAD Prism Comp Sci Viewfact/Experimental Design Vorpal TechX 3D PIC code for LPI studies VPIC R. F. Bird/ LANL 3D PIC code for LPI studies WarpX Jean-Luc Vay/LBNL 3D PIC code for LPI studies MULTI Meyer-Ter-Vehn (Germany) Rad hydro/PIC on GPU DUED Atzeni 2D rad hydro HYADES Cascade Applied Science 1D and 2D rad hydro H2D Table 3: Overview of Open Codes. 52

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS 6.1.4 Findings and Recommendations To enhance its involvement in the IFE field, tists to have a more active role and contribute Germany should establish international part- to the IFE community. Furthermore, Germany nerships with prominent IFE facilities, given its should collaborate with European and global current lack of intense research in IFE plasmas. partners to improve its physics understanding This collaboration would enable German scien- through enhancement of open codes. 6.1.4.1 Research Opportunity in the 1-3 Year Timescale Finding Insufficient data is available concerning the performance of wetted foam targets for laser direct and indirect drive implosions. Recommendation Codes with adaptive mesh capabilities or ad-hoc turbulent models with appropriate closure and validated equation-of-state are required to sim- ulate wetted foam target implosions. Theory regarding physics models of equation of state and turbulent dynamics suitable for wetted foam targets as well as direct numerical simulations resolving relevant small scale flow should be impactful if validated against experiments. Since the implosion of a solid sphere of fusion cess [Zyl2018], but no relevant wetted foam fuel is energetically unfavorable as compared implosion data yet exists for DD. Questions to the implosion of a hollow shell of cryogenic remain about the non-uniformities seeded temperature fusion fuel (a “DT layer”), most by the foam structure than can contribute to present-day IFE concepts focus upon implo- seed hydrodynamic instability and about the sions involving a frozen fusion fuel layer sur- turbulence ensuing after the first shock pass- rounded by a spherical shell of ablator materi- es through foam. When compressed, turbu- al, as shown in Fig. 6. The preparation involved lence can channel energy away from internal in preparing a fuel layer inside an ICF target for energy into small scale kinetic energy. To di- present-day experiments is considerable and rectly simulate the effects on implosions of impractical for IFE applications. Wetted foam small scale turbulence, it requires codes with targets (where a foam wicks cryogenic liquid adaptive mesh capabilities or ad-hoc turbu- fusion fuel into a hollow shell form) offer a po- lent models with appropriate closure. Ques- tential solution to bypass the complications of tions also remain about the equation-of-state a cryogenic layering process. (EOS) of wetted foams, limiting the capability of simulations to correctly model wetted foam However, there is little data on the fusion per- implosions. Theory and computations work formance of wetted foam targets. Some IDD on wetted foams, validated against experi- implosion tests with wetted foams have been ments, could be impactful for all potential IFE performed on the NIF, with some mixed suc- schemes. Finding Few radiation-hydrodynamics codes suitable for laser driven implosions are available with open access. None of them include all the physics rele- vant to the different IFE concepts. Recommendation Develop a rad-hydro code with open access to the IFE community. Carry out an assessment of the currently available open-access radiation-hydro- dynamic codes and evaluate the best path forward to developing a com- prehensive community code. 53

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MEMORANDUM LASER INERTIAL FUSION ENERGY Few radiation-hydrodynamics codes suitable capable of simulating laser-driven implosions for laser driven implosions are available to but are widely used in the HEDP community the broader IFE community (e.g. MULTI1D/2D, to simulate HEDP experiments at laser facili- DEUD, and HYADES). None of these codes have ties. For instance, the code FLASH is a capable undergone extensive validation with implosion AMR rad-hydro code with laser ray-tracing, experiments or against the codes used at the SESAME tables and multi-fluid hydrodynam- American national laboratories. Additionally, ics, widely used around the world. none of the above accessible codes include all the relevant physics (e.g. cross-beam-en- The capabilities of FLASH can be extended ergy-transfer (CBET), and non-local energy to simulate laser-driven spherical implosions transport are not yet available in these codes). though some important physics (CBET and There is a need to develop a radiation-hydro- non-local transport) are absent in the cur- dynamics code that is open to the IFE com- rent version of that code. Possible collabora- munity, with all the relevant physics includ- tions with the FLASH team at the University of ed and with adequate experimental testing. Rochester can be established to further devel- There are other state-of-the-art open-access op FLASH and extend its capabilities. radiation hydrodynamic codes that are not yet Finding Despite advances in numerical simulations, even the state-of-the-art radi- ation hydrodynamics codes at the US national laboratories are not capable of accurately predicting experimental outcomes and guiding the design of implosion experiments. Recently, machine learning algorithms have been successfully applied to laser fusion implosions leading to improved exper- imental predictions. Recommendation Explore the latest advances in machine learning to develop algorithms to bridge the gap between experiments and simulations thereby improving the predictive capability of implosion experiments. Even the American national laboratory simu- [Hum2021], [Gaf2019]). Another approach lations have shown deficiencies in capability. developed at University of Rochester, uses Having limited laser-plasma instability (LPI) Bayesian inference and dimensional analysis predictive capability (important for energy to map experimental observables onto sim- coupling and laser safety) and poor hohlraum ulated observable [Gop2019], [Lee2021]. The predictive capability (need laser power energy Rochester approach provides a predictive ca- ad-hoc multipliers to match observed energet- pability for the fusion yield within a 10% error ics and symmetry). Questions remain about and it was used to improve the target design the accuracy of the material equation-of-state and laser pulse shape to increase the fusion (EOS) and opacity properties that ICF/IFE sim- yield by over 5-fold. ulations use. Reliable simulations reduce the empiricism needed for IFE development. Applications of Machine Learning to improve There are exciting recent opportunities for the predictive capability of the radiation hy- developing a machine learning framework to drodynamic codes used to simulate ICF implo- bridge the gap between simulations and ex- sions is a fertile new area of research. Further- periments. Recent efforts at LLNL have been more, many other applications of ML can be successful in improving the predictive capa- envisioned in all the disciplines relevant to IFE bility by first training Deep Neural Networks development. on large simulation databases and then re-re- training them (“transfer learning”) on the limited available experiments ([Spe2018], 54

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS 6.1.4.2 Research Opportunity on the 3-6 Year Timescale Finding High target gains in excess of 100x are required for an IFE power plant using laser drivers. For hot spot ignition, such high gains require highly convergent implosions with convergence ratio well above 20x. To date, implosion experiments designed with radiation hydrodynamic codes to produce high convergence and high target gains have underperformed expectations. Performance degradation at high convergence is common to both direct and indirect drive. Recommendation Collaborate with target design and experimental groups at the major im- plosion facilities to develop a robust physics understanding of the causes limiting implosion performance at high convergence and develop mitiga- tion strategies. Fusion fuel compression is essential for burn implosions. In DD, high convergence (CR>20) efficiency, but theory generally overpredicts has been out of reach thus far regardless of DT fuel compression. In 1D implosion theo- the fusion performance. DD implosions de- ry, high convergence leads to high compres- signed to achieve highest convergence led in- sion, high areal densities and high fusion yield. stead to the lowest measured convergence in However, when high convergence is achieved experiments. This fuel compression problem in experiments, the fusion yield and core pres- is a priority for the US ICF program since it is sure are much lower than predicted and even the key path to higher Gain. below those of equivalent lower-convergence Finding Hotspot ignition has been demonstrated at the NIF with indirect drive leading to a target gain of 1.5x. Laser direct drive experiments on the 30kJ OMEGA laser scale to about one megajoule of fusion yield at 2MJ of laser energy. Other ignition schemes require major R&D for proof of principle experiments demonstrating target gains above unity. Recommendation Other approaches using different ignition schemes, such as fast ignition, should be evaluated to assess their requirements for an ignition-scale proof-of-principle demonstration necessitating new large laser facilities. While hotspot ignition has been demonstrat- Both fast and shock ignition require a fuel as- ed on the NIF using a low compression design sembly that achieves high densities and areal [Kri2022], [Zyl2022], other ignition schemes densities. Shock ignition makes use of a single (e.g. fast-ignition, shock-ignition, or ignition us- laser type to assemble the fuel and to shock ing fuels other than DT) require major R&D for it right before peak convergence. The high proof-of-principle. New facilities are required intensities required to launch a strong shock to advance the physics of fast-ignition, since near the end of the implosion are of concern fast-ignition requires an integration of a com- due to the excitation of laser plasma instabil- pression laser plus ignitor laser. The NIF and ities. There is very little data on laser-plasma OMEGA facilities could provide some valuable instabilities at the UV intensities of ~1016 W/ data, but they are presently oversubscribed. cm2 relevant to shock ignition. 55

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.1.4.3 Research Opportunity on the 6-9 Year Timescale Finding ICF targets that are proven to ignite are complicated, expensive, fragile (see Fig. 6) thus making them inappropriate for direct application in IFE. Recommendation The community needs to leverage the physics understanding of what ig- nites into developing target concepts that are ignition/Gain capable, but that make much more sense from an engineering practicality perspective. Economically viable IFE is not possible without this step. Additional target engineering challenges are addressed in Sec. 6.2. Fig. 6: An example IDD target used in ig- nition experiments on the NIF facility at LLNL, key components are labeled, Cour- tesy of LLNL. 6.2 Targets 6.2.1 Role of Targets in IFE Targets form the central nexus of activity in Upon ignition and burn, the fused fuel and tar- an IFE power plant. The targets contain small get parts emit neutrons, gamma rays, and ions quantities of fusion fuel that are carefully (helium and target element ions), that are col- shaped to allow successful implosion and ig- lected by the reaction chamber first wall and nition when shot by the laser driver beams. blanket. The high energy and intensity of the A target injector shoots the target into the emissions from the target are a severe threat center of the reaction chamber, where the la- to the lifetime of the blanket and first wall. ser driver beam must precisely hit the target. 6.2.1.1 Target Design As discussed in Sec. 6.1, there are many types final energy output per capsule. This factor of target designs. Fig. 7 shows a number of often leads to the selection of polymer ma- typical laser-driven target types. Most target terials as the best choice. Currently, solid or designs contain a spherical capsule The selec- solid composite materials, such as diamond tion of material for ICF targets is determined and diamond film sequences, are used as ICF by various physical properties necessary for targets. The capsule is often lined inside with a fusion, but the ultimate and most crucial fac- uniform layer of low-density foam (<~50 mg/ tor is the total effort required to produce the cm3). Capsule diameters typically of interest 56

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS are in the range of 3 – 8 mm. Capsule wall and these defects larger than a micron or two are foam layer wall thicknesses typically of inter- allowed. Dimension and tolerances thereof est are in the range of a few microns to a few are still being determined and will ultimately hundred microns. The tolerance of capsule need experimental verification. IFE targets be- and foam layer diameter, thickness, spherici- ing larger than today’s targets (in the ignition ty is typically a few microns to a few 10’s of target at NIF the capsule diameter was 2 mm) microns. Capsule surface smoothness in to- may end up with somewhat relaxed toleranc- day’s science targets is less than a few 10’s of es. Some target designs have additional parts nm. Additionally, pit, voids, and high-density such as a hohlraum (an open ended can), a inclusions in the capsule wall must be kept to cone, and membranes. a minimum. In today’s targets only a few of Capsule with IR (a) (b) reflective coat (c) Hollow cone Sealed capsule with IR Hohlraum(High Z interior) reflective coat Fig. 7: Some abstracted typical target types, others exist [Set2010]. (a) a la- ser direct drive, HAPL like configuration [Ols2021]. (b) a laser direct drive liquid DT wetted foam configuration. (c) a cone-in- shell fast ignition configuration [Sha2012], P2 Shield (High Z ( ) d) T a h nd in s f u il p m p o w r i t n s dows (e) [Bet2016], [Norimatsu2017], [Dit2021]. (d) a laser indirect drive, LIFE like config- Distributed radiators uration [Mil2014]. (e) a heavy ion indirect (metal foams) drive distributed radiator configuration Solid pure DT layer Solid DT in foam Liquid DT in foam [Cal1999]. Courtesy of General Atomics. 6.2.1.2 Target Supply, Filling and Injection Typical IFE reaction chamber concepts are de- add to the challenge, fueled targets, delivered signed for shooting targets at rates between to reaction chamber center, will likely need to 1 and 15 targets per second (Hz). Thus, each cost less than between 20 cents and 1 euro reaction chamber requires a supply of tar- to allow the reaction chamber to function gets (unfueled) of between 86 thousand and economically. Studies of concepts to produce, 1,3 million targets per day. At each reaction fuel, and inject targets indicated this may be chamber there will be a cryogenic filling and feasible [Goo2004], [Mil2009]. layering station to fill the target with fuel (typ- ically DT) and create a uniform thickness fuel The fusion fuel typically used in targets is DT layer within the target. Also, at each reaction due to its high reactivity. Cryogenic tempera- chamber there will be a target injector. Both tures, approximately 20 K, are required to con- filling and layering station, and injector must dense DT gas; liquid or solid DT depending on operate at the reaction chamber shot rate. target design. The reaction chamber tempera- Developing mass production manufacturing ture will be high, which will lead to a high ther- methods for targets, especially given the ex- mal radiation heat load being placed on the pected tolerances, is a challenging endeavor. target during injection into the reaction cham- Similarly challenging are the cryogenic fill and ber. This can be compounded by methods to layering station, and the target injector. To protect the chamber first wall from the threat 57

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MEMORANDUM LASER INERTIAL FUSION ENERGY of the target emission, for instance adding gas around the chamber. Careful materials selec- into the chamber to slow and or spread out in tion must be done to insure that, once cooled, time the ions and photons. A balance must be these target materials can be removed from carefully struck between protecting the tar- the reaction chamber. The target elements get from thermal damage in the chamber and will recombine to form various chemical com- protecting the chamber first wall when imple- pounds or remain elemental in some cases. menting chamber protection schemes. Target The target’s materials will become activated injectors are typically designed to launch the and not all fuel will be burnt. Thus, the target targets at 50 – 200 m/s to limit exposure time materials should be selected to minimize nu- in the reaction chamber, and with the accel- clear activity in times scales appropriate for eration limited to less than 1000g to prevent reaction chamber maintenance, to minimize damage to the target or its DT fuel layer. waste disposal ratings at end-of-life decom- missioning time scales, and to minimize pro- After targets are shot, the target and its fuel duction of tritiated compounds (e.g. tritiated become the waste “ash” of the IFE reaction hydrocarbons) that complicate the tritium chamber. When shot, the target becomes processing and purification systems of the re- a plasma and its ionized elements blown all action chamber. 6.2.2 R&D Status Worldwide 6.2.2.1 Target production in general Currently no one can produce IFE targets in the quantities needed for an IFE reaction. Tar- gets are currently made individually for sci- ence experiments in small quantities and with substantial efforts in characterization. Most target fabrication methods utilized for science targets are chosen for flexibility of changing target dimensions, since scientists continually change the target design to be able to learn new information about the target physics and performance. Current targets are also exten- sively measured and characterized, so that simulations can be checked against as-built dimensions. Target injectors have been or are in development. Single shot, room tempera- ture prototypes have been built and tested for accuracy. Cryogenic injectors with automatic target loading are in the planning stages at most. Research and development efforts in mass production of targets for IFE and devel- Fig. 8: Parts of an IDD Target, Courtesy of opment of IFE target injectors has or is going LLNL. on at several locations. 6.2.2.2 Capsule IFE relevant, spherical capsule fabrication ing a spherical mandrel has been used to form methods include overcoating a spherical man- capsules of HDC (a nano-crystalline diamond drel followed mandrel removal; drop-tower material), DLC, beryllium, and an amorphic blowing; and micro-encapsulation. Overcoat- plastic referred to as GDP. It is notable that the 58

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS first laboratory fusion ignition with gain great- drop tower capsule production, granules con- er than 1, occurred at the NIF at LLNL on 5 taining a blowing agent (e.g. a polystyrene December 2022, using a capsule made of HDC granule saturated with an organic solvent) are (high density carbon). This coating was done dropped through a vertical oven/furnace. The by Diamond Materials GmbH in Germany on a oven heats the granule past the melting point, silicon sphere. The silicon sphere was removed and the blowing agent is vaporized. In the zero at General Atomics (GA) in USA by laser drilling g fall through the oven, the vapor blows the a small hole through the HDC coating and dis- melted granule into a spherical capsule. For solving the silicon with acid. Typically, PE-CVD thicker wall capsules, wall uniformity can be (for HDC, DLC, and GDP) and sputtering (for an issue since the blowing agent vapor bubble Be) are used for coatings. Capsules are fabri- may be first nucleated anywhere within gran- cated this way at GA (GDP, Be, DLC), LLNL (GDP, ule. Polystyrene capsules are/were fabricat- HDC), CEA-Val Duc (GDP), and Diamond Ma- ed this way at the Lebedev Physical Institute terials. The LIFE reaction chamber project of [Mer1994], [Coo1994] where they uniquely LLNL considered both GDP and HDC capsules shoot the granules up into the drop tower (foam lined). HDC coating equipment would and then let them fall out of the tower. Glass need to be modified for mass production. capsules were formerly made at LLNL and GA During the HAPL project GA built a prototype by dropping glass frit down drop tower ovens. mass production GDP coater based on a “rota- Micro-encapsulation can create solid wall cap- ry kiln” configuration [Ver2007], with solenoid sules or spherical foam shells. In micro-encap- coils extending over the length of a rotating sulation, compound droplets are formed and tube to inductively couple to the plasma. In suspended in solution to cure the layer of the compound droplet that has polymer dissolved in it. The solutions that form the compound droplet and the suspension fluid are immis- cible in each other. This is effectively blowing liquid bubbles in solution. Surface tension and energy minimization naturally want to make the droplet spherical and smooth. The ma- jor technical difficulties occur during curing: maintaining smoothness and homogeneity of the capsule wall and maintaining concentricity between the inner and outer wall since there is not a centering force for a static compound drop. Methods for making compound drops of IFE size (several mm in diameter) include concentric nozzles, T-junction, micro-fluidic droplet combination. Micro-encapsulation in an ICF or IFE context has/is done at GA, LLE, LLNL [Coo1994], ILE, CEA Val Duc, Hamamat- su, Cardiff University under aegis of CLF (Prof. David Barrow’s research group [Li2021]). LLE has studied using dielectrophoretic force (ap- plying AC electric fields) to deterministically force the inner and outer walls of capsules to be concentric during curing [Wan2011], Fig. 9: Spherical IFE capsules (top) and foam [Cho2016]. It should be noted that micro-en- shells (buttom) of IFE size (~4-5 mm diameter) capsulation at smaller scales and more relaxed made by General Atomics using micro-encap- tolerances is a highly used industrial process. sulation. Lower scale at left has minimum di- For instance, fertilizers, perfume, medicines, visions of mm. Courtesy of General Atomics. nutrients, and epoxies are just a few of the 59

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MEMORANDUM LASER INERTIAL FUSION ENERGY items that are micro-encapsulated into com- layer from the inner surface and studied ran- mercial products. dom rotation to uniformly coat the capsule interior with foam forming solutions. For the IFE target designs often call for a spherical third method, additive manufacturing could capsule lined with a uniform layer of foam. be used, although considerable development There are three generic ways to accomplish is needed to increase the production rate. this: coat a foam shell with a solid layer, coat The two photon polymerization (2PP) addi- the inside of a solid capsule with a foam layer, tive manufacture method has the submicron and create both solid wall and the foam layer resolution desired to form smooth capsules at the same time. For the first method, during and low density small pore foams. Currently, the HAPL program, GA utilized interfacial con- for ICF targets, 2PP is being pursued by LLNL, densation chemical reaction [Schr2007] to LANL, GA, LLE, and University of Nebraska coat foam shells, and the rotary GDP coater; [Coo2020],[Ols2021]. Many other institutions also see [Schro1995]. For the second meth- and companies develop 2PP additive manu- od, during the LIFE program, LLNL studied facturing in a general context. surface catalyzed ROMP to grow the foam 6.2.2.3 Hohlraum More complex targets include additional parts besides capsules, such as hohlraums or cones. Currently, these are typically made by electroforming on a precision machined mandrel (used at AWE, CEA Val Duc, CLF, GA, ILE, LANL, LLE, LLNL, TU Darmstadt, and Sci- tech Precision). Rapid production of precision mandrels to electro-plate onto would make this technique applicable to IFE. Stamping of cone mandrels, and injection molding of cone mandrels followed by sputtering for a con- ductive layer have been investigated at GA. Stamping and deep drawing were also looked at for cone mass production by GA. Potential hohlraum mass production methods include stamping, swaging (cold forging), deep draw- ing, die casting, injection molding. Applicabil- ity will depend on hohlraum material choice. Note that only the interior few tens of microns of needs to be of a high Z material. So, a plas- tic hohlraum lined with lead may be accept- able, although this much carbon and protium may prove expensive for a tritium processing system to handle. Swaging, deep drawing, and die casting were investigated for LIFE hohl- Fig. 10: top - Lead hohlraums produced by swaging at General Atomics. Coin in the mid- dle is a USA penny. Buttom – gold cones pro- duced by electro-forming using a stamped mandrel at General Atomics. Courtesy of General Atomics. 60

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS raum production using lead by LLNL and GA. have dimensional variance of less than 10 mi- Swaging for instance is used to produce air cron and hohlraum production investigated rifle pellets, where competition grade pellets [Alex2013]. 6.2.2.4 Nanostructured Targets Flat targets, especially with a laser facing to effect burning of the fuel. Processes for fab- surface with engineered micro or nano en- ricating micro and nanostructures on surfaces gineered structures have applicability to fast include lithography, MEMS, LIGA, 2PP print- ignition and non-thermal ion targets. In fast ing, laser patterning and etching, catalyzed ignition a surface in the cone when hit by a growth of nano fibers, and AAO templating. short pulse laser generates an electron or ion One or more of these techniques is employed beam which then impinges on a compressed by all the previously mentioned institutions, core to ignite the core. In a non-thermal ion and many more as well. This includes but is target, ions generated in nano structures in- not limited to ENEA, HZDR, LMU, and UPM. tersect inculcating fuel and the nanostructure 6.2.2.5 Assembly of Targets Complex targets required assembly. Today with more than one part. Robotic assembly for ICF targets this is most typically done on development for targets is being developed at optical coordinate measuring machines in LLNL and GA[Lee2011], [Car2016], [Boe2017] conjunction with custom fixtures and manual but is currently at assembly rates much lower or motorized precision stages. Automated ro- than required for IFE. botic assembly will be required for IFE targets Fig. 11: Robots set up and programmed to assemble cone-in-shell targets at General Atomics. Cone tips centered to capsule center to within +/- 10 microns. Courtesy of General Atomics. 61

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.2.2.6 Filling of Target with Fuel After the structure of the target is complete it ture tube as is done by the Lebedev Institute must be filled with fusion fuel. The typical fuel (referred to as FST layering) [Alek 2020]. FST is is DT which is a gas at room temperature. The a fast layering technique which is helpful for DT must be cooled to cryogenic temperature, IFE. However, FST cannot make uniform layers ~20K to condense to a liquid, and a bit cold- if the layer is too thick, placing some limits on er to solidify into ice. Additionally, the con- target design. Beta-layering uses the volumet- densed DT must be reshaped into a uniform ric heating of the DT ice (caused by the tritium layer on the inside of the capsule of the target. beta decay radiation) to sublimate and recon- Filling may be accomplished by permeation dense the solid DT until the entire DT ice inner (diffusion) through polymer capsules walls at surface is at a uniform temperature. Holding room temperature in a pressure cell capable the capsule in a spherical temperature field of holding high pressure. The pressure must will cause the DT to move to a uniform spher- be ramped up slowly, or the capsule will be ical layer. Many e-folding times, 26 minutes crushed, and 100’s of atmospheres of gas pres- each, are required to reach the uniformity of sure are required to get the necessary amount the layer required, so many hours are required of gas into the capsule to form a thick ice layer to layer a capsule. During the HAPL program, once the gas is condensed at cryogenic tem- GA developed a prototype of a cryogenic flu- perature. Permeation filling takes many hours idized bed [Boe2011] for beta-layering large to complete. An alternative is wicking liquid DT batches of capsules simultaneously. Here the into the capsule through a fill tube (ICF target) fast agitation and random rotation in the bed or hole in the capsule wall (IFE target). If the was expected to provide the needed spherical capsule has a foam layer, the capillary action isotherm at each capsule on a time averaged will wick the liquid to fill the foam and thus basis (rotation rates >> layering e-fold time). create a uniform layer as it is being filled. Only This long layering time is a drawback for IFE, sub-atmospheric pressures are required for since slow filling and layering lead to large wicking liquid DT into foam, so this is a safe- batches of capsules being required to be pro- ty advantage relative to permeation filling. cessed together, which leads to large tritium Over filling may be a challenge that requires inventory. A HAPL like target fill and layering precision dosing or draining to get the correct station was calculated to need, at bare mini- amount of liquid into the capsule to just fill mum, an inventory of 500 to 1000 g of tritium the foam. This so called “wetted foam target” in an IFE filling and layering station [Schw2003]. [Ols2021] is a design that the USA program is In contrast, wetted foam filling and layering just starting efforts to field on the OMEGA and times are expected to be about 10 seconds, NIF lasers. The filling and layering of a wetted which would only need less than about 10 g foam target is expected to be fast, on the or- of tritium for the filling and layering system. der of about 10 seconds. Layering of a solid DT The wetted foam target has the disadvantage layer can be done by beta-layering [Mar1988], of mixing foam into the fuel which makes the [Hof1988] as is done by the ICF programs in fuel harder to ignite. Other fuel layering sys- the USA (LLNL, LANL, LLE, and GA) and France tems may be possible, including dynamically (LMJ. CEA-Val Duc and CEA-SBT), or by rolling forming the fuel layer during the laser shot as the capsule down a spiral cryogenic tempera- was proposed by Goncharov [Gon2020]. 6.2.2.7 Target Injector Target injectors are also required to shoot gets. A full size and speed gas gun prototype the target into the chamber. Gas-guns, elec- was developed at GA for the HAPL program tro-static and various electro-magnetic pro- [Fre2005]; speeds up to 400 m/s. Direct drive pulsion methods can be used for injecting tar- targets were protected with a two-piece sab- 62

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS ot. During the LIFE program LLNL was working tems, Marvel Fusion, and Xcimer Energy) with on a gas gun for indirect drive targets. In Japan their partners likely are starting the develop- IFE, Gifu University, and Hiroshima University ment or are planning the development of tar- were working on a hybrid gas-gun with elec- get manufacture and target injectors. HB11 tro-magnetic speed trim and sabot removal has received a $20M (Australian) grant for tar- for cone-in-shell targets. This injector was ca- get/ hydrogen boron fuel development. Also pable of ~100 m/s. During the HAPL program, of note is that the ICF program in China, is ac- GA developed a low-speed prototype of an tively working to duplicate the target capabil- electro-static injector with target steering. ities of the USA program [Liu2016] [Du2018]. For the LIFE reaction chamber, GA developed a prototype of a linear induction accelerator [Pet2015] which could inject indirect drive tar- gets with electrically conductive hohlraums, Location of final or direct drive targets using a conductive sab- (verification) position sensors ot. This injector featured electro-magnetic steering post barrel to improve accuracy. It reached ~60 m/s with surrogate targets, and Location active steering coils target placement consistency of 0.14 mrad ra- Second position dially. the Lebedev Institute is developing an detector injector based on an HTSC sabot [Alek 2020], First position [Alek2022] that is electro-magnetically driven, detector and have demonstrated initial propulsion of Location passive the HTSC sabot. For HiPER, CEA-SBT proposed steering coils a laser ablation driven sabot followed by and Linear Induction Accelerator coil magnetic Halbach array for a non-contact barrel [Per2011]Ex-Fusion in Japan has devel- Fig. 12: Target injector room temperature prototype opment of IFE target injectors as part of their based linear induction accelerator built at General business plan. All of the above prototypes Atomics. The prototype shot surrogate targets at ~57 were only operated at room-temperature (or m/s with a placement repeatability of 0.14 mrad. Cour- liquid nitrogen temperature in the Lebedev tesy of General Atomics. Institute case) and single shots at a time. IFE injector development needs to continue to in- clude continuous auto-loading of targets, and full cryogenic operation. The IFE reaction chamber commercial compa- nies (Focused Energy, First Light Fusion, HB11, Innoven, Laser Fusion X, Longview Energy Sys- 6.2.3 Capabilities and Competencies in Germany Germany has expertise that can be applied about 2% of the world supply of deuterium. in this area targets. Germany has long been In the field of micro-encapsulation, several known for extensive expertise and capability members of the editorial board of the Journal in chemistry particularly organic, polymer, res- of Microencapsulation are from German Uni- in, photo-initiator, and dye chemistry, which versities. Microencapsulation is a specialty of can be applied to polymer capsule and foam Fraunhofer ICT (Fraunhofer Institute for Chem- shells fabrication via micro-encapsulation or ical Technology) and IAP (Fraunhofer Institute additive manufacturing. Deuteration of the for Applied Polymer Research). German com- precursor chemicals will be beneficial for tri- panies involved in microencapsulation include tium purification systems. Germany produced BRACE, Follmann, BASF SE, Symrise, Koehler 63

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MEMORANDUM LASER INERTIAL FUSION ENERGY Innovation Solutions, and Evonik. Germany Institute of Nuclear Physics of TU Darmstadt, has made major investments in additive man- Institute for Nano- and Microfluidics of TU ufacturing including the very high resolution Darmstadt, the Integrated Micro- and Nano- 2PP method. Capability and competence in systems Laboratory of TU Darmstadt, the 2PP exist at Fraunhofer IPT (Fraunhofer Insti- Technology Laboratory of LMU (Ludwig-Max- tute for Production Technology), Fraunhofer imilians-Universität Munich), and at HZDR ILT (Fraunhofer Institute for Laser Technolo- (Helmholtz-Zentrum Dresden Rossendorf). gy), Fraunhofer ISC/CESMA (Fraunhofer Insti- Focused Energy is hosting and expanding the tute for Silicate Research), Fraunhofer IPMS TU Darmstadt Target Laboratory and is devel- (Fraunhofer Institute for Photonic Microsys- oping fabrication for their cone-in-shell target. tems), KIT (Karlsruher Institute for Technolo- Marvel Fusion and its partners are developing gy)/EDMM2O, TU Darmstadt and others. The expertise and capability for nano-structured first commercial 2PP printer was introduced target fabrication. by NanoScribe, and others have followed (e.g. Multi-Photon Optics). The strong competence Micro and nano structuring of surfaces can and capability in Germany in the fields of op- be accomplished via lithography, MEMS (Mi- tics, optomechanics, and lasers are ideal to ap- cro-Electronic-Mechanical-Systems), and LIGA ply to faster 2PP printing. Spherical diamond (Lithographie). These techniques are available coating, layer sequencing, and processing for a numerous German universities, companies, HDC capsules was pioneered by Fraunhofer and research institutions. There is experience IAF and was successfully commercialized by applying nano structuring to laser targets at its spin-off Diamond Materials. Diamond Ma- Fraunhofer IOF (Fraunhofer Institute for Ap- terials spherical coatings were used in the first plied Optics and Precision Engineering) Jena. successful laboratory ignition of a laser target done at the NIF. The KIT Karlsruhe Tritium Laboratory (TLK) has expertise in tritium and cryogenics which High resolution/accuracy metrology, inspec- could be applied to filling wetted foam cap- tion, and characterization are essential for sules with liquid DT. Cryogenic and vacuum developing targets. Germany is renown for industries will likely be drawn from for build- expertise in optical and x-ray metrology and ing such a device. Initial development can be inspection. Commercial companies of equip- done with liquid deuterium, but ultimately ment in this area include Bruker, Leica Mi- liquid DT will be needed to verify such issues crosystems, and Zeiss. Research institutions as handling and movement of DT filled targets for x-ray inspection include Development Cen- which will self-charge due to tritium beta de- ter X-ray EZRT of Fraunhofer IIS (Fraunhofer cay. This will lead to electro-static charging of Institute for Integrated Circuits), Nuernberg. targets not present in liquid deuterium filled targets. Expertise and capability in laser target fabri- cation exist at the Target Laboratory of the 6.2.4 Industry Led R&D for IFE IFE targets will be a mass-produced product for IFE targets. Although some manufacturing that ultimately will likely be fabricated by in- techniques developed for IFE targets could dustry. Industry provides much of the exper- prove useful in other arenas (e.g. ultra fast, tise in mass production of components and high resolution additive manufacturing, and assemblies so it would be valuable to involve fast micro-assembly robotic automation). This industry in the development of fabrication leaves existing industry unlikely to develop methods for targets. However, the commer- IFE target mass-production techniques un- cial market for IFE targets is decades away less provided funding to do so from the public and there are no obvious alternative markets sector or from private IFE reaction chamber 64

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS companies. Further industry will be most effi- chemical resins, polymers, optics, optical me- ciently involved if clear target design specifica- chanics, and short pulse lasers. For hohlraum tions and tolerances are provided and iterated and cone type target parts industries could upon, from either or both of national labora- include machine tool makers, tool and die tories or IFE reaction chamber companies makers, press, stamping, deep drawing, and injection molding machines. Assembly could There are numerous industries that could be involve automation and robotics industries. drawn into the development of IFE targets. In fuel production, the deuterium and lithi- For capsules these include chemical, polymer um extraction industries. In fueling and layer- (deuterated polymers), micro-encapsulation, ing systems cryogenic and vacuum industries and instrumentation companies for character- could be drawn upon. Injectors could involve ization especially optical and x-ray techniques. electromagnetic systems providers. For fast additive manufacturing industries of 6.2.5 Findings and Recommendations The DOE BRN [Ma2022] identified the TRL for was also identified as TRL 2. This means that manufacturing and mass production of reac- a substantial technology development gap ex- tion compatible targets for laser driven IFE re- ists before these areas are ready for use in an action chamber concepts as TRL 2. The TRL for IFE reaction chamber, even a pilot plant scale target injection, tracking, and engagement at reaction chamber. reaction chamber -compatible specifications Finding Large quantities of low-cost targets, continually injected into the IFE reac- tion chamber, are essential for an IFE reactor’s operation and economic viability. Currently, the capability to mass manufacture IFE targets at the preci-sion and quantity required does not exist. Recommendation Germany should establish a program to develop economic mass manufac- turing methods for IFE precision targets. The program could be to, in particular, could be by modelling or experiment. An ex- demonstrate high-volume and eventually low- periment could consist of a low-speed injec- cost techniques for spherical capsule or wet- tion of a target through a short vacuum oven ted foam capsule fabrication (DOE BRN PRO such that the time in the oven was the same as 5-1). This includes both the structure of the the flight time of a high-speed injection into a target and methods to fill and layer the tar- large chamber. Pulsed x-ray or optical imaging get structure with fuel (e.g. DT). Additionally, could be employed upon exit from the oven to this should include demonstrating that the inspect the target and its fuel. Additional in- cryogenic target survives a thermal exposure formation on development approaches is pro- equivalent to that expected during injection vided later in this section. of a target into the reaction chamber. This Finding A key requirement in an IFE reaction chamber is to accurately hit the tar- get with the laser beams while the tar-get is flying through the center of the reaction chamber. Recommendation Germany should establish a project to demonstrate the accurate engage- ment of a target shot at full reaction chamber relevant velocity with a laser beam of reaction chamber relevant diameter. An actual IFE target or suitable surrogate may be used in the demonstration. 65

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MEMORANDUM LASER INERTIAL FUSION ENERGY Demonstrating accurate engagement on-the- ing at high speed, to ~<10 µm accuracy from fly of IFE targets by a driver beam was DOE large distances away (10 m) will be challeng- BRN Report PRO 5-2. This is a key risk or be- ing. Also, rapidly (a few msec) slewing a large lievability issue for IFE reaction chamber, ( 1 m diameter) laser beam several tenths of completion of which will provide higher con- mrad will be a challenging development for fidence for public and private decision makers beam steering optics. Surrogate targets and to invest in IFE. To date target engagement simplified target injectors may be used for this has only been demonstrated at low speed demonstration. The technologies must also (~5 m/s) and with small diameter laser beams be compatible with the laser and final optics (~25mm) [Car2010]. The gap here is that track- design. Finding An injector for shooting delicate cryogenic targets into an IFE reaction chamber is a key need of an operational IFE reactor. Full speed, contin- uously loaded (with targets), cryogenic target injectors have yet to be demonstrated. Recommendation Germany should establish a program to develop a full speed, continuously loaded, cryogenic target injector. Developing an IFE target injector for cryogenic of section 6.2.5, a critical gap for an IFE reactor IFE targets capable of reaching reaction cham- is mass production of wetted foam capsules at ber-relevant velocity without damaging the an economically viable cost. This includes not target or its fuel layer is DOE BRN report PRO only the wetted foam capsule structure, but 5-3. The gap in injector development is that also systems to fill and layer the capsule with while room temperature, single shot injectors liquid DT. The production rate needed is ~1-15 have been demonstrated, what is needed is a Hz/reactor, with reaction chambers requiring fully cryogenic injector, that is automatically fueled targets 24/7. The cost of targets includ- and continuously loaded with cryogenic tar- ing DT fueling and injecting will likely need to gets. For DT fueled targets, the injector will be ≤~20% of the electricity value produced also have to be designed with tritium contain- by the targets’ implosion. The cost of just the ment and safety in mind. Schemes to block target structure will likely need to be ≤~5% of neutrons, emanating from the ignited targets, the electricity value produced by the targets’ from damaging the injector (aka dynamic neu- implosion. tron shielding) are also likely to be required. Potential international partners that could be This is important because economic produc- considered for such a program include CEA- tion of the targets is one of the key needs for SBT, LLNL, and GA. IFE reactor to be economically viable. Without large numbers of low-cost targets, IFE reac- Additionally, target fabricability, survivabili- tion chambers are not viable. Germany should ty, compatibility with reduced activation al- pursue this because targets, along with lithi- lowing reaction chamber maintenance and um and deuterium are the fuel for IFE reaction waste disposal, tritium inventory implications chambers. Germany or German companies in- from filling and layering, and implications on volved in the ongoing production of fuel for the tritium recovery and purification systems future energy sources will provide Germany should be considered in system studies of IFE with long-term benefits. As a key enabling reaction chambers. Conducting such system technology for IFE, helping to bring IFE power studies is included in the High-Level Recom- reactors will be of great economic and securi- mendation 2.7. This was also included in the ty benefit (domestic supply of base load elec- DOE BRN report PRO’s (4-1). tricity and or high temperature process heat). As noted in the first Finding/Recommendation Partners in wetted foam capsule mass pro- 66

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS duction could include CLF/research group of between the inner and outer surfaces of the Prof. David Barrow, Cardiff University; DOE capsule is one of the key challenges. Surface laboratories LLNL, LANL, SRNL, and support tension of the encapsulated, liquid suspended, contractor General Atomics, and ILE/Osaka compound drop that when cured will form the University, Japan. An all-domestic program capsule will naturally want to form a smooth could also be considered. spherical shape. For (3) additive manufactur- ing using two photon polymerization (2PP) is Development of mass production of wetted method that could fabricate the inner and out- foam capsules should start now because it is a er layers of the capsule simultaneously. The difficult task. Roughly, for each reaction cham- key development in this case is to drastically ber, one million, high precision targets need to increase the speed of this production method, be made each day for a cost of a few tens of currently ~1 day to make one capsule. Options cents each. Tolerances of microns on dimen- include but are not limited to massive paral- sions, and tens of nanometers on surface fin- lelization of optics of the AM system, faster/ ish are typical for capsules of a few millimeters lower power setting print resins, holograph- in diameter. If taking on the liquid DT filling de- ic projection, and resin chemistries naturally velopment, tritium systems go through exten- forming foam so that individual foam cells or sive design, engineering, and review to ensure ligaments do not have to be traced, but rather safety, which lengthens development time. entire area cross-sections can be micro-pro- jected into the resin. For wetted foam targets, Three generic approaches to making the struc- it is assumed that liquid DT will be wicked into ture of the wetted foam capsule are: (1) create the foam of the capsule to simultaneously fill a solid wall spherical capsule, then coat the in- and layer the capsule with DT. Here the key terior of the capsule with a uniform foam lay- development points are compatibility of the er, (2) create a spherical foam shell, then coat foam with liquid DT (surface tension collaps- the exterior with a solid wall, and (3) create ing the foam and holding up to beta radiation both the solid exterior and foam interior lay- damage from the tritium), and precision fill- ers at the same time. For (1) micro-encapsula- ing to the correct DT layer thickness. Where tion can be used to form the solid capsule. The the issue for the latter is that capillary action inner foam layer could then be catalyzed of will cause an overfill of the capsule (meniscus the inner surface by ROMP (ring opening me- forming inside the capsule). Options here in- tathesis polymerization) from injected solu- clude precision dosing the wetted foam cap- tion, or injected foam forming solution can be sule with liquid DT, and heating the capsule to injected into the capsule followed by random drive would the extra liquid DT after the cap- rotation to evenly coat the inner surface. For sule has been removed from contact with the (2) micro-encapsulation can be used to form liquid DT filling reservoir. the foam shell. The outer solid layer can be formed with an interfacial condensation re- A coarse notional timeline for target systems action. If needed, this thin (few micron) coat- development could be as follows: ing can be thickened via PE-CVD (e.g. GDP) of polymer while agitating the targets in the coat- ing region. Note that for the micro-encapsu- lation in (1) and (2) maintaining concentricity 67

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MEMORANDUM LASER INERTIAL FUSION ENERGY 0 Yrs 3 Yrs 6 Yrs 9 Yrs 12 + Yrs Target design and System Code (DD) fabrication participation System Code (1D) in FPP system design CDR Engineering Design wetted foam capsule Investigate fab methods development including (includes fuellingstudy) lab scale demos of Lab production line for fuelling methods scalable to IFE. wetted foam capsules at Prototype Fill & rates suitable for short FPP Layering Station runs (e.g. 3hr) Fill & layering pilot plant for wetted station built foam capsules built suitable to supply one reactor 24/7 Hit target on-the-fly concept for, tracking accurately demo and steering compatible Demonstrate accurate Incorporate elements with laser and chamber target engagement into laser or final optics as needed target injector (cryo with automated target concept for, initial loading) design) Prototype built Update/upgrade for DT. Integrate with an MSB FPP Add toa FPP Fig. 13: National timeline for target system development. The funding level to take these areas from the be less costly to develop mass manufacturing current TRL 2 level to a TRL 6 level (ready for in- for than indirect drive targets. This funding stallation on IFE reaction chamber pilot plant) level is for developing one target concept in is expected to be at the 200M€ level to within these areas. If additional target concepts are a factor of a few depending on the complexity selected for development, then the funding of the target chosen for development. That is level would rise commensurately. to say direct drive or shock ignition targets will 6.3 Reaction Chamber 6.3.1 Role of Reaction Chamber in IFE In the ‘IFE onion model’ used in this memo- » Access for auxiliary systems (diagnostics, randum, the definition of the Reaction Cham- monitoring) ber reads ‘everything between the plasma » Removal of fuel and ash (He and unspent and the wall’. This implies that there are criti- D-T) cal interfaces to (at least) the target, the driv- » Removal of impurities/debris from both er, the first wall and the fuel cycle (including target and first wall (anything that is not He removal of non-fuel elements). The Reaction and unspent D-T) Chamber itself then has to fulfill the following (sometimes conflicting) functions: Most of these critical items arise from the high rep rate operation sustained over long time, » First wall protection by mitigating the flux and have not been a real issue so far (e.g. for of particles and radiation originating from NIF). It is important to note that the last two the imploding target points must allow to re-establish identical » Allow good coupling of the driver (access conditions after each implosion, which will ports, beam propagation and absorption in pose very strict limitations on the remaining the chamber) non-removed fraction that can lead to large » Protection of final optics from target debris build-up over time. 68

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS The possible solutions to fulfill these functions are listed in the table below, taken form the IFE BRN report [Ma2022]: Concept Wall/chamber Advantages Challenges Solid Wall/vacuum Simplest Chamber Material survival Easier Laser/Target Issues Magnetic Intervention/Vacuum Smallest Chamber Ion Dumps Mitigates first wall thermal Load Replaceable Solid Wall/Vacuum Easier Laser/Target Issues Operational Complexity Solid Wall/Gas in Chamber Smaller Chamber Laser/Target Issues (hot gas/ residu- al plasma Chamber Recovery Much Reduced Materials and Neu- Thick Liquid Walls Droplet Formation tronics Issues Difficult to modify Table 4: High level description of the advantages and challenges of IFE reaction chamber and wall concepts 6.3.2 R&D Status Worldwide The R&D status in this area is in general quite low, as indicated in the TRL self-assessment from the BRN report3: IFE concepts → Laser Laser Fast Heavy Magnet- Indirect Direct ignition Ion ically Critical aspects for Drive Drive Fusion Driven IFE development ↓ (Including Shock Fusion ignition) Demonstration of ignition and reactor- level 4 3 2 1 3 gain Manufacturing and mass production of reactor 2 2 2 2 1 compatible targets Driver technology at reactor-compatible ener- 4 4 3 2 3 gy, efficiency, and repetition rate Target injection, tracking, and engagement at 2 2 2 2 1 reactor-compatible specifications Chamber design and first wall materials 1 1 1 1 1 Table 5: TRL for five IFE concepts for the seven aspects critical for an IFE development path. 3 While there are ongoing discussions about the absolute values of the TRLs in Fusion in general, we take the table as an indi- cation of the relative TRL of the individual elements of the IFE onion. 69

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MEMORANDUM LASER INERTIAL FUSION ENERGY IFE concepts → Laser Laser Fast Heavy Magnet- Indirect Direct ignition Ion ically Critical aspects for Drive Drive Fusion Driven IFE development ↓ (Including Shock Fusion ignition) Maturity of Theory and Simulations 3 3 2 2 2 Availability of diagnostic capabilities for critical 3 3 2 2 2 measurements Table 5: TRL for five IFE concepts for the seven aspects critical for an IFE development path. Studies of an integrated concept have only terfaces and boundary conditions, a system- been conducted on a conceptual level on paper atic treatment in a ‘systems code’ approach is (for an overview see[Mei2010]. LIFE [Lat2010] recommended. This is in line with BRN PRO 6-3 proposed a Xe fill gas at about 1 mbar pres- ‘develop synergistic target/fuel cycle co-de- sure at normal conditions. This would have sign between the plasma physics community the effect of converting all kinetic energy in and the fuel cycle teams and chamber design charged particles into a flash of X-rays with teams. In such an activity, we recommend a first peak and a retarded wave profile. The that adequate weight is given to the chamber SOMBREO study [SOM1994] applied a similar clearing, noting that existing studies address principle (6 mbar at normal conditions). The in detail mostly the wall protection aspect. start-ups which whom we discussed in the course of this assessment did not present a Experimental verification of the individual definition of a concept for a reaction chamber elements of the technologies needed has so and hence did not give specific input to the far only been performed on some individual assessment for the reaction chamber. points (e.g. mock-up of the Flibe spray), but will need a serious coordinated effort in any The studies found that the buffer gas does not IFE development program. An important part affect laser beam propagation and absorption of the strategy will be to separate items that or the injection of indirectly driven targets. can be done in a non-nuclear environment, to However, studies focused on directly driven develop corresponding evaluation concepts targets revealed that the buffer gas can cause and to work towards an integrated test that surface modifications, which would negative- finally has to be transferred to the nuclear en- ly impact symmetric coupling. [Goo2001].. vironment. While isolated aspects such as the Clearly, more detailed assessments are need- interaction of the target with the fill gas, the ed here. formation of solid debris from first wall mate- rials or the hydrodynamics of liquid wall mate- For concepts that do not use a specific fill gas, rials can be studied individually, an integrated these problems are not of concern, but the demonstration will finally have to prove the problem is transferred to the protection of expected steady state conditions achievable the first wall, usually envisaged by liquids on in the chamber for long operation periods the first wall. (with millions of targets imploded). This will require a dedicated facility generating repre- Concerning the chamber clearing of debris sentative debris at realistic rep rate to demon- from target, ablation of the first wall, and un- strate the desired level of removal. Without spent fuel, studies are not very detailed and any detail, the Expert Group discussed a pos- must be taken to a more concrete level. Since sible timeline for such an approach which is this is an optimization problem with many in- given below. 70

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS year 1 2 3 4 5 6 7 8 9 10 11 12 >> integrated plant description System code (0-D) System Code (1-D) CDR FPP design Engineering design removal of material Conceptual study 3 options experiments on isolated aspects steady state demonstration integrated non-nuclear steady state demonstration including specif- integrated nuclear ic first wall damage 1st strawman Plant conceptual design Fig. 14: Timeline for reaction chamber design. A very rough estimate for the resources indi- ed nuclear test would need a larger dedicated cates that the experiments on isolated aspects facility. The integrated nuclear test requires a and the development of evaluation concepts dedicated IFE facility to which costing is large- might require several Mio € in total over the 3 ly determined by other elements and hence years time span proposed, while an integrat- not attempted here. 6.3.3 Capabilities and Competencies in Germany The present level of capabilities is clearly in- testing facilities. The problem is very specific sufficient and must be upgraded substantially to IFE and does not have significant common- for any serious IFE program. The existing capa- alities with R&D carried out in MFE. At pres- bilities (codes, simple mock-ups for individual ent, Germany does not hold special capabili- elements exist mainly in the US. As pointed ties or competencies in this field. out above there is a serious lack of integrated 6.3.4 Industry Led R&D for IFE This is at present a basic research activity that does not lend itself well to involving industry led R&D. 6.3.5 Findings and Recommendations The gaps pointed out in Sec. 6.3.2 are implosions). » Develop an integrated concept that takes Since the problem has to be solved for any IFE into account all of the constraints and FPP design (although with different solutions boundary conditions. For this, one or sev- for the individual elements depending on the eral ‘strawman’ IFE plant conceptual de- schemes chosen for the IFE FPP), it would be a signs need to be established at systems very good field for international collaboration, code level. especially if the systems code approach can » Demonstrate individual engineering solu- be developed jointly in such an environment. tions for all elements that can be separat- The integrated test will need a large installa- ed. Establish which ones can be tested in a tion with high rep rate, also pointing to a large non-nuclear environment. benefit of international collaboration since » Demonstrate integrated solution to val- not many of these facilities will exist (there is idate that the requirements can be met none at present). Prime partners for collab- over long periods of time (i.e. millions of orations are those who have conducted ICF/ 71

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MEMORANDUM LASER INERTIAL FUSION ENERGY IFE programs in the past, i.e. US, UK, France, political environment). Japan (China and Russia could in principle be partners as well, but that would need a stable Finding The reaction chamber concept has important interfaces to the concepts of target design and injection, coupling of the driver wall protection and removal of debris and unspent fuel. While so far, a lot of focus has been put on wall protection. The design choices in all these areas are interlinked and need to be optimized together. Recommendation Initiate an integrated study that takes into account the different interface aspects, at least on a systems code level. Finding There are only a few integrated studies on the reaction chamber concept, and especially no recent ones. Recommendation Initiate a thorough study on the reaction chamber concepts. Finding The concept studies on the reaction chamber are mostly theoretical and no clear path for an experimental validation exists. Recommendation Establish a path for experimental validation, first for individual aspects, then for an integrated non-nuclear test (if meaningful) and then in a nu- clear environment. 6.4 First Wall and Blanket, Fuel Cycle 6.4.1 Role of First Wall, Blanket and Fuel Cycle in IFE The first wall and the blanket are central ele- conversion to a thermodynamic power cycle, ments of a future fusion power plant. Like the must perform two other tasks that distinguish combustion chamber walls of a fossil fuel pow- a fusion power plant from other types of pow- er plant, they enclose the power plant core in er plants. First, the blankets shield the radia- which the fusion reaction takes place, as illus- tion generated during the fusion reaction so trated in Fig. 15 of a generic fusion power plant that no radiological hazard to the environment design. The interface between the blanket occurs outside the biological shield. More im- and the plasma is the so-called first wall. In ad- portantly, however, the blankets generate the dition to the high temperatures of the fusion fusion fuel, tritium, using an appropriate con- reaction and, above all, the high-energy parti- figuration of breeding and, if necessary, mul- cle stream (-particles) as well as the radiation tiplier materials, so that a fusion power plant from the reaction, the first wall is exposed to does not require an external fuel feed. The special stresses. In addition, it experiences tritium produced in the blanket by means of a time-dependent loading during inertial fusion, nuclear breeding reaction is extracted from it which places extreme demands on the mate- and fed to the fuel preparation of the internal rial. Immediately adjacent to the first wall is fuel cycle, which processes the unburned fuel the blanket, which, in addition to extracting (exhaust processing), in the so-called external the heat generated in the fusion reaction for fuel cycle. The bred fuel is reinserted for com- 72

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS bustion in the reaction chamber. a laser induced fusion process. Although the power level may differ between the fusion re- The first wall of a reaction chamber is exposed actor concepts (laser or magnetic fusion) the to extreme loads originating from the burning principal damage features are more or less the fusion targets. Extreme heat load includes same, but with a different emphasize of the x-rays and charged particles but also neutrons. individual damage types. In both confinement The charged particle spectrum consists of al- concepts the first wall is facing power densi- pha particles, carbon ions, protons, deuterons ties of the order of MW/m2, see e.g. [Lat2017], and tritons. Thermal reactions of materials [Tak2015] or [Lin2011] and numerous other leads to serious damage in a fusion reactor articles. independent of how the fusion is achieved ei- ther by magnetic confinement or by means of Fig. 15: Functional diagram of the reaction chamber of a fusion reactor, its interfaces and the associated power systems and process cycles. Laser fusion offers a higher degree of freedom indispensable in order to concretely formulate to design the in-vessel -components of the clear requirements for the first wall, the dam- core than magnetic confinement fusion, due age to the structural material, but also the to the absence of forming a magnetic cage requirements for the blanket (heat removal, for the fusion plasma. Thus, in principle to burn rate) and the fuel cycle, so that a target- in-vessel configurations are conceivable. But ed development of a fusion reaction chamber a closed fusion reactor concept has not yet and the components inside it can take place. been formulated. Such a concept is therefore 73

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MEMORANDUM LASER INERTIAL FUSION ENERGY There are in principle two options to design only in a concept form, the current power the reaction chamber as outlined below. plant studies mainly rely on a solid-state de- sign, in which the so-called in-vessel compo-

1. Integral In-vessel Design nents (first wall plus attached blanket) are Provide a sufficiently thick liquid film on the constructed in the form of an onion skin. The reaction chamber walls that will not cause interface between the reaction chamber and permanent damage to the armor material the blanket is formed by the first wall com- and will remove helium atoms and unburned posed of a so-called armor material, which fuel such as debris. This can be either liquid consists of a low-activation high-melting metal or a liquid salt compound. Such a de- temperature material. Behind this is then the sign option limits laser access to the reaction composite of structural and functional ma- chamber and also is challenging for required terial that forms the blanket. Both the first in-vessel remote handling operations. But it wall and the blanket must be replaced several substantially reduces the thermal and neu- times during the life of a fusion power plant tron wall load on the solid reactor boundar- due to high material degradation, typically in ies. cycles of 3-5 years. Due to the high activation during operation, the replacement must be
2. Solid State Design done remotely. At the same time, in order to Both the shield and the blanket are designed keep the radiological load outside the power as solid structural units, which facilitates re- plant low, they should be designed to ensure mote handling installation and removal oper- good recyclability of functional and structural ations while providing a high degree of wall materials. Integral designs (option 1) seem to coverage for successful tritium breeding, but be simple at first glance, however, they exhib- also, reduces the lifetime of this component it several challenges, such as film instabilities, due to material degradation of the solid ar- dissolution of fuel and debris in the liquid so mor. that they are currently considered to be very advanced concepts. While option 1 has been explored up to now 6.4.1.1 Armor Materials In case neutrons and charged particles irra- material candidates and potential failure and diate and heat the first wall material with a degradation aspects, because pre-mature fail- high intensity directly, a series of competing ure of the plasma facing components (in-ves- effects take place damaging the material al- sel-components) affects not only the safety tering is thermophysical properties and then performance of the plant but also comprises even more the material can be sputtered off maintenance and thereby availability. or ablated. Once the wall is ablated, expand- ing gas or plasma can disturb the propagation Irrespective of the fusion reaction principles of laser light irradiating the fuel target in case tungsten is the primary candidate as first wall of inertial confinement fusion or to prevent ig- material for several reasons. Tungsten reveals nition in case of magnetic confinement fusion not only a high thermal conductivity and a devices. high melting point which makes it ideal as heat sink material. Moreover, tungsten exhib- There are many studies on laser fusion such its a relatively high thermal shock resistance, as the LIFE-program (laser inertial fusion en- low physical and chemical sputtering and re- ergy) in the US, the HiPER (high-power laser veals a relatively low tritium retention, which energy research), the HAPL program (High is favorable to safety of a nuclear installation. Average Power Laser (HAPL) and for magnet- From the nuclear point tungsten creates some ic fusion Studies in the US (ARIES) or Europe transmutation products and shows a rather (EUROfusion) identifying potential first wall large activation, however, this is decaying fast 74

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS and only the transmutation products create » Spalling, sputtering of the wall. challenges to the material’s mechanical be- » First wall hydrogen embrittlement havior. Some studies related to He-particle damage The major challenges for the armor are and its effects have been executed both in the US and in Europe, indicating a high suscepti- » neutron damage (dpa and He/dpa trans- bility of the armor material to He-irradiation. mutation), and combined effect (see Sec. Also, the effect of pulsed irradiation on armor 6.4.1.2), due to permanent cycling and the associat- » damage to the first wall by the Helium ions, ed modifications in the grain structure have creating high close to surface heat fluxes been identified. Especially the high peak loads by stopping of the Helium-atoms near to released in the armor yield power releases in the surface (stopping in a boundary layer the lattice structure being of orders of about of only about 6µm depth). 103 higher than the mean value causing like- » Helium-ions displacement damage in the ly grain and lattice structure modification im- tungsten or iron lattice leading to aging ef- pacting the material properties. For fusion re- fects such as softening due to phase trans- actor applications however, there is a lack of formations. reliable data on limitations, in particular from » Helium implantation in the wall causing the combined exposure to neutrons and gam- continuous cracking and permanent swell- ma radiation. ing. 6.4.1.2 Structural Materials Helium-particles and gamma-irradiation chal- trons (>100 keV), still a high nuclear cross-sec- lenge the armor material mainly in form of tion, there is basically no alternative to the use heat release. However, neutron damage and of steel as structural material, neither in terms Helium transmutation pose a similarly high of activation nor in terms of manufacturing, challenge for the structural material, since bonding/welding techniques and versatility of neutrons with a kinetic energy of 14.1 MeV design. are penetrating deep into the blanket material structure and are creating dislocations, vacan- Fusion reactor concepts all focus to use low cies etc., expressed by the quantity displace- activation ferritic martensitic (RAFM) steels ments per atom (dpa). Typical damage rates such as EUROFER97 or F82H as structure ma- for fusion reactors are in the range of >10dpa terial, in which the conventional steel alloying per full power year. Moreover, their energy elements are replaced by lower activation el- is high enough to cause a neutron induced ements. Only ferritic martensitic (FM) steels transmutation reaction generating Helium at- provide sufficiently high heat conductivity at oms within the material. The mobility of the low swelling rates at high material damage generated Helium-atoms, measured in appm and thereby allow for the exchange of reac- in the structure material lattice is very low; tion chamber and first wall parts. There are limiting values for structure materials are of promising attempts to develop so-called ODS order of O(500-1000 appm). The uniqueness steels (oxide dispersed strengthened), see of simultaneous material damage by neutrons [Zin2017], allowing for higher high tempera- and transmutation expressed by the He/dpa tures (>600°C) and with potentially very high ratio (on the order of 10 appm/dpa) is specific resistance to fusion neutron-induced prop- to fusion, and differs significantly, for example, erty degradation. The currently available from knowledge in nuclear lattice or accelera- results show for the ODS steels higher tem- tor science. perature-dependent uniaxial yield strengths, higher tensile elongation, better high-tem- Although especially iron exhibits, for fast neu- perature thermal creep, and lower ductile 75

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MEMORANDUM LASER INERTIAL FUSION ENERGY to brittle transition temperature (DBTT) as challenges arise from the pulsed operation of well as a superior fracture toughness behav- some Hz repetition rate, which may cause seg- ior compared to conventional RAFM steels. regation processes that can further degrade However, they require a powder metallurgical the structural mechanical properties, espe- production route and a nuclear qualification cially aging effects such as creep and fatigue is similarly absent as well as qualified joining could lower the material limits. The funda- technologies in case of replacement. Thus, the mental challenges faced by laser fusion here focus in most research projects is directed to- correspond almost to those of the armor ma- wards RAFM steels and their qualification, see terial except for the Helium implantation. for laser fusion e.g. [Alv2011]. The challenges for structural materials inte- grally correspond in laser fusion to those also being present in magnetic fusion. Specific 6.4.1.3 Functional Materials One advantage of laser fusion is a potentially a affected by the pulsed operation of a laser higher wall coverage of the reaction chamber fusion plant, since the time averaged fluxes by blankets, since this fusion power plant con- are the same for laser fusion and magnet- cept does not require a large particle exhaust ic confinement. But, the structural behavior device and comparably smaller openings for and properties of solid breeder/multipliers, driver systems than magnetic devices, in which which in the prior studies were identified as several heating systems must be integrated. reference solutions for a laser fusion plant, Thus, neutron multipliers such as beryllium/ are strongly impacted by pulsed operation. beryllides or lead are virtually not required if For the breeder material in pulsed laser fusion a wall coverage by blankets of more than 85% plants this is associated to the exothermal re- of the reaction chamber by a credible blanket action of lithium with the neutrons generating design can be ensured using lithium or lithium tritium. By pulsed operation the peak flux den- salt mixtures simultaneously as breeder and sity and the temporal power release yields to coolant and keeping the steel fraction of the temperatures causing segregation within the coolant confining structures considerably be- material also altering grain structure, which is low 10% of the blanket volume, see [Saw2007] challenging especially to the long term integ- or [Mei2013]. rity of the breeder. Current assessment tools are not capable to depict these effects with Some principal computational studies on the sufficiently high local resolution in correlation suitability of breeder and neutron multiplier with impact on the materials (both breeder studies have been conducted in the context and multiplier). However, at least conservative of the HAPL program. The functionality of the validated tools are mandatory to establish a breeder and multiplier material itself is not closed substantiated blanket concept. 6.4.1.4 Blanket Development The blanket is the key component of any fu- » Heat removal of the energy released by the sion reaction and irrespective of the fusion neutrons in the bulk and heat sink for the power plant concept to be followed has three armor material. major functionalities. » Radiation shielding of the reaction cham- ber vessel towards the ambient. » Breeding of tritium to an extent to allow for self-sufficiency of the plant (potentially fur- The evaluation of the power released on ther other fusion power plants-FPP). the wall and within the structures as well as 76

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS on the interface by ion, photon, X-Ray and lars of the nuclear safety (operational safety, neutron radiation necessitates a coupling of plant safety, radiation waste handling) and fi- plasma burn physics with radiation transport nally logistics and maintenance in the view of modelling to interface the different physics the entire power plant. This holistic approach domains. The transport calculations of neu- is reflected by a balance of plant (BoP) anal- trons and photons is for fusion reactor types ysis, which interlinks the power production (inertial fusion and magnetic fusion) by now by the fusion reaction with the components mostly based on a steady state Monte-Carlo and the required operational units such as the simulations using fusion special IAEA certified tritium plant, the laser, the vacuum systems, nuclear fusion data libraries (JEFF – OECD, the diagnostics and potential electric/thermal ENDF/B-VIII-USA, JENDL-Japan, CENDL-China, buffer volumes. A simplified sketch is illustrat- TENDL-CERN) which allows to calculate ed in Fig. 16, from which it becomes obvious that the only power source driving the plant is » neutron wall load, the blanket, which has to feed all other power » material damage (through linear energy consuming units. transfer models -), » transmutation rate, The key elements of the blanket development » activation of material (and thus shut down are the structural materials confining the cool- dose rate, nuclide vector as function of ant, the coolant itself and the functional mate- time, decay heat development at operation rials, such as the armor and in case of magnet- and for extraction, ic confinement fusion neutron multiplier and » radiation release through ambient and breeder material. Closely reviewing the BRN most important, report [Ma2022], the formulated focused Pri- » tritium breeding ratio (TBR), which spec- ority Research Opportunities (PRO) for Power ifies the amount of tritium generated by Systems Science, Engineering, & Technology incident fusion born neutron as well as en- addresses that closed requirements sets for ergy amplification through exothermal re- a blanket design in the view of holistic power action of neutron with matter. plant concept is one of the most urgent steps to be mastered. By now the blanket require- Since the blanket constitutes the major heat ments are only indirect addressed via two pri- source in a future fusion reactor for electric ority formulations reading to energy production through a thermodynamic cycle process an efficient blanket design has » Undertake a series of system-design stud- not only to meet the component function- ies to establish a suite of self-consistent, alities but also must match superior power quantitative IFE plant models, and use plant objectives these to guide each aspect of the R&D pro- gram (PRO 6-5); » predictable sizeable electric power output, » Develop a test facility with a neutron » flexible integration in a variable electric source to evaluate blanket technologies grid architecture with, and to test fuel cycle components and sys- » potential plant black-out start-up capabil- tems at scale, including tritium extraction ity, and transport, and the potential for direct » at highest nuclear safety levels, internal recycle (DIR) (PRO 6-4). » with a high availability, Moreover, the reaction chamber (blanket, such as formulated in [Fed2017]. This re- vacuum systems) associated technologies are quirement set-exceeds by far the aspect of still in a state of concept proof on the level of functionality but intrinsically necessitates an feasibility identification. This additionally re- integrated approach of the blanket design quires a concept for the inner and outer fuel into the context of a closed balance of plant cycle layout (blanket, vacuum systems - un- architecture (BoP), considering all three pil- burned fuel) and the associated technologies. 77

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MEMORANDUM LASER INERTIAL FUSION ENERGY Fig. 16: Simplified sketch of the Balance of Plant (BoP) scheme for a Laser driven fusion power plant. Without this synergetic functionality, howev- and in-line coolant control systems. er, a functioning power plant is inconceivable. » The vacuum and shielding systems acting as static radiological barrier and life-time To summarize a closed blanket design requires installation but allow for power installation as input some cornerstones of the plant archi- lines (heating systems), safety monitors tecture (logistics & maintenance, power train, and diagnostics. fuel cycle, power requirements by auxiliaries) » Logistics systems providing access for re- and is tightly linked to the fuel cycle and the mote maintenance, recovery & repair ac- material development and qualification. This tions, …. has been identified stringently in magnetic confinement fusion about more than a de- Thus, the blanket design always represents a cade ago at several sites (US, China, Japan, compromise between the actual functional EuroFusion) and has been implemented in the requirements (breeding, power extraction, fusion power plant development projects but shielding) and the requirements from the still with a varying degree of stringency. The power plant context. Another important issue range of requirements management and the is the coolant selection for the blanket. The interaction between blanket development following points are particularly relevant in and the requirements for a power plant are the context of the power plant: described, for example, in [Cis2017]. The main systems impacted by the breeding blanket ar- » Tritium inventory and potential migration chitecture and technology are: through power train (mainly for safety). » Efficiency of the tritium extraction tech- » Primary heat transfer system not only de- nology and development of a tritium fuel livering the heat to the power conversion cycle. systems but also confining the tritium with- » Coolant compatibility with structural mate- in its barrier, a reliable tritium extraction, rials, in-line coolant purification (affinity to 78

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS H, C, O, alloying element of structures, etc.) traction limits, dimensioning of ducts, age- and coolant management through regular/ ing), accidental plant operations, » thermal conversion efficiency, » coolant limitations (temperature range, » capability to integrate thermal storage sys- Magneto-hydrodynamic effects, heat ex- tems Finding Principal studies on the functionality of the blanket and its ingredients have been conducted in prior laser fusion programs. However, they´ve been not integrated in an overall plant concept. In turn no blanket design team composed of several expert profiles has been established. Recommendation » For a closed blanket design first a consistent closed plant design is man- datory, in which the high-level requirements of a power plant are for- mulated. This allows to establish a raw functional plant concept, for which different technical solutions can be analyzed in terms of feasibil- ity and robustness on the plant level. Such a plant study should aim at identifying principal reference design options for different blanket con- cepts, armor and material options and elaborate potential fallback de- sign options. Therefore, a plant design team is required, which consists of target and material experts as well as reaction chamber component and power conversion system designers. » Set-up a blanket design team elaborating fundamental blanket con- cepts meeting the fundamental requirement such as breeding shielding matching to comply high level requirements. This team shall provide interfacing information to a plant design team. » In a second step a system study needs to executed scoping a sensitiv- ity and uncertainty study, which, on its part, enables the largest risk elements and systems to be registered and recorded in terms of their impact. Based on such an analysis research priority in terms of infra- structures and human capacity building to develop a roadmap contain- ing milestones to reach that high-level goal can be extracted for devel- opment. To speed the first two processes likely to be » liquid metal engineering and coolant chem- executed in parallel and potentially scoping istry a period of about 3 years, participants from » neutron – resistant material engineering prior studies such as HAPL or LIFE as well as » fuel cycle and process engineering. experts for blankets and materials should be » system integration into the plant. part of the studies. After the second step re- » Safety analyses. quiring approximately also 3 years a solidified basic and robust design should be existent al- With respect to blanket engineering, there is lowing for larger scaled investment decisions a broad synergy between magnetic and laser on priority facilities required to substantiate a fusion not only for fusion specific expertise closed reaction chamber design. but also in neighboring science fields such as accelerator sciences, nuclear engineering and Regarding purely the blanket functionality it- process engineering. self, the following competencies are required: » coupled neutronics, thermomechanics and thermal hydraulics to extract a basic con- cept underpinned by expert know how in 79

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.4.1.5 Fuel Cycle and Tritium Management The fuel cycle of any fusion power plant is in is not provided. Additionally, as input a high composed of an inner fuel cycle in which un- tritium breeding ratio (TBR>>1.2) and highly burned fuel is extracted from the exhaust efficient tritium extraction from lithium for stream, processed in fuel plant to achieve an the outer fuel cycle and a high burn-up frac- adequate 50:50 ratio of the fusion fuels deute- tion of the Deuterium-Tritium fuel by the re- rium and tritium and a fueling system to re-in- action (assumed ~30%) are considered as in- ject the matter into the reaction chamber. puts to achieve a viable architecture. To what While deuterium is provided from outside the extent this can be realized is not yet clear, but reaction chamber the tritium has to be bred the technologies of the inner fuel cycle allow in the blankets during plant operation and ex- for cross-fertilization of magnetic fusion and tracted from the blanket within the outer fuel laser fusion once a closed fuel cycle design cycle to be fed into the inner fuel cycle. Thus, for laser fusion is established. The synergetic the functionality of the inner fuel cycle covers: effect is given that most of the processes are gas/solid or fluid/solid interfacial process with » exhaust gas cleaning (removal of the He- allow a transfer and a modular arrangement lium ash- alpha particles, cleaning of the by up or downscaling. exhaust gas from all other species than hy- drogen and its isotopes), Outer Fuel Cycle » detritiation of the exhausts (steam, hydro- The outer fuel cycle cannot be treated in carbons), a similar manner to the inner fuel cycle and » isotope rebalancing (to attain a favorable strongly depends on the coolant breeder con- 50:50 mixture of fuel), and figuration of the blanket technology chosen. » fuel storage. Regarding the functionality of the blanket in- terfacing the fuel cycle several tasks has con- The principal functionalities here are the same tinuously to manage: in magnetic fusion and in laser fusion, howev- er, the inner fuel cycle design poses different » Tritium extraction from breeder (either sol- challenges. The tasks of the inner fuel cycle id or liquid), are to: » breeder fluid purification (only liquid breeder blankets), » ensure a continuous removal of the ash » corrosion control of structures and and, » permeation control of tritium. » removal of radiative gases injected to en- sure armor (puffing, detached operation), For laser fusion liquid breeders seem to be » diffusion losses of fuel evaporating from an attractive design option, since large wall the pellet, coverage of the reaction chamber by blankets » detritiation of the exhaust constituents. seems to be feasible; discussed are even liquid lithium and lithium-based salts. Both, options This requires dedicated vacuum systems such allow a high tritium breeding ratio, however, as diffusion and/or cryopumps and exhaust also exhibit challenges in extraction of triti- cleaning systems. Concerning the laser-based um and several technologies have been de- fusion, the fuel cycle design database is quite veloped, such as permeation against vacuum scarce. Most papers adopt a single cycle once (PAV), Gas Liquid Contactor (GLC) and Liquid through cycle as described e.g. in [Rey2013] Vacuum Contactor (LVC), however, the matu- and the literature cited therein. The fuel cycle rity level of all technologies still is insufficient itself and most of the components contain a for up-scaling. functional description, however, a quantifica- tion of throughputs, process efficiencies and Regarding laser fusion the extraction of hy- times as well as the inventories located there- drogen isotopes, mainly tritium from liquid 80

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS lithium requires high purity liquid lithium. Due neutrons for material irradiation and qualifica- to the high reactivity with nitrogen, oxygen tion studies. and carbon and their detrimental effect on material compatibility [Bor1987], [Cho1985] More promising for the extraction of triti- purification systems are necessarily needed. um are cold traps where protium is added to Cold traps (200°C) for oxygen, carbon and the lithium and by reducing the temperature corrosion products and hot traps (600°C) for (200°C). The dissolved hydrogen isotopes will, nitrogen with getter materials like titanium due to the large difference of the solubility, alloys or niobium are applied. The very high precipitate. These precipitations will be heat- solubility of tritium in liquid lithium combined ed for tritium recovery and separated by a with the low partial pressure over the lithi- cryogenic distillation. Here, an efficient cold um even at 500°C(3.41*10-9Pa) prevents the trap design and the extraction of the precip- recovery via the vapor phase as studied in itates formulate the major challenges. detail in [Mor1995]. Different techniques are elaborated like the Maroni process based on Electrochemical extraction using solid lith- molten salt extraction [PAT1976] and comple- ium-ion conductors as also discussed (Te- menting research of [Mor1991] by gettering by provich, et al., 2019, [Tep2019]) relies on the yttrium or a combination of both, permeation electrode development for lithium-ion bat- windows, fraction distillation, cold traps and teries. Besides high ion conductivity chem- recently electrochemical extraction using sol- ical stability in contact with liquid lithium at id lithium-ion conductors. Efficiency has also around 500°C is as well required. Selection been studied by [Tep2019]. But all of these of the most suitable ion conductors, includ- methods exhibit specific challenges associat- ing scale-up and process optimization are the ed with drawbacks which are mostly associat- most challenging issues. Thus, the process de- ed with insufficiently low efficiency of tritium sign of the outer fuel cycle is still an open is- recovery. The established Maroni process is sue, which is also addressed in the BRN report very complex and suffers from considerable in the context of Priority Research Opportuni- corrosion issues and potential impacts on the ties (PRO) PRO 6-4 reading to: neutronics. The gettering process using yttri- um suffers from the low dissociation pressure “Develop a test facility with a neutron source of the LiT, which results in low efficiency. Get- to evaluate blanket technologies and to test tering combined with the molten salt process fuel cycle components and systems at scale, improves the efficiency of LiT dissociation and including tritium extraction and transport, eliminates negative effects from the molten and the potential for direct internal recycle salts on the lithium but adversely increases (DIR).” complexity. Permeation windows like zirconi- um-palladium usually suffer from slow diffu- Whether it makes sense to develop a fuel sion rates and surface contamination. Frac- cycle in the context of a volumetric neutron tion distillation requires high temperatures source can be questioned, especially when (>900°C) with all associated material prob- the individual modules in the process chain lems. All these aspects have been extensively are not yet validated and up-scalable, but the studied in the context of the IFMIF-DONES fa- need for an infrastructure depicting the fuel cility since it produces the neutron fusion like cycle and the development of a verified and spectrum by bombarding a free surface liquid validated fuel cycle simulator are essential for lithium film with 40MeV deuterons (125 mA a future fusion power plant and thus not de- current) to produce a fusion like spectrum of batable. 81

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MEMORANDUM LASER INERTIAL FUSION ENERGY Finding A rudimentary sketch of a fuel cycle facility has been developed in the pri- or US programs aiming to identify potential process engineering elements mainly with respect to their principal viability. In the absence of a refer- ence target and blanket such an approach is justified. However, a closed concept has not been elaborated. Recommendation Once given a plant concept urgently all fuel process concepts developed in the past need to re-evaluated, the efficiency of the individual process elements need to be analyzed and interfaces have to be formulated tar- geting to develop fuel cycle simulator. This is mandatory not only to ensure the self-sufficiency of the power plant but also to develop an accountancy approach required for the licensing of a power plant. 6.4.2 R&D Status Worldwide 6.4.2.1 Materials Laser and magnetic fusion experience sim- Technology (KIT) the Fusion material laborato- ply bLaser and magnetic fusion experience ry (FML- www.iam.kit.edu/mmi/Fusion_Mate- simply by the fusion reaction itself the same rials_Laboratory.php). High heat flux simula- fundamental material damage mechanisms tion laboratories are available e.g. at IPP (Max for armor and structural materials. Laser fu- Planck Gesellschaft, Gladys) or at KIT (Helo- sion poses additional challenges for the reac- ka-High pressure). tion chamber wall by fast ion (mainly -parti- cles) and hard-X-ray radiation even capable of The main individual damage mechanisms such causing gamma-neutron reactions and thus as dpa damage, helium transmutation within induces additional material damage. This type the material and the associated mechanistic of damage mechanisms and its impact has and structure modifications have been iden- been studied mainly in the context of acceler- tified more than 20 years ago. In a fusion re- ator sciences within the context of spallation actor both damage types occur simultaneous- sources such as spallation neutron sources in ly and in the presence of hydrogen isotopes Europe e.g. the European Spallation Source having a non-linear impact on the material (ESS, see https://europeanspallationsource. properties, such as yield strength, increased se/) and in the US at Oak Ridge (https://neu- hardening, altered creep and fatigue behavior. trons.ornl.gov/sns). Fundamental fusion stud- By now this cannot be predicted by numerical ies devoted the Helium effect on armor mate- tools. Hence, a solid experimental data base rials such as tungsten are exploited in the US in and corresponding modelling and evaluation collaboration with Oak Ridge e.g. at University efforts for all types of materials exposed to of California San Diego [Wan2017], Universi- neutrons at fusion relevant kinetic energies is ty of Wisconsin (Fusion Technology Institute, indispensable if not even fundamental impor- e.g. [Zen2010]). The European counterparts tance for the viability of any type of deuteri- are Technical University Eindhoven, DIFFER um-tritium reactor based fusion power plant (https://www.differ.nl/research/plasma-mate- independent if it is laser based or relying on rial-interactions), Forschungszentrum Jülich magnetic confinement. Neutron and Helium (FZJ ) being also equipped with correspond- transmutation within the structural materi- ing facilities such as MAGNUM-PSI at DIFFER al is quite similar for laser and magnetic fu- or Jule-PSI at FZJ (https://www.fz-juelich.de/ sion requiring an irradiation facility providing en/iek/iek-4) and the corresponding mate- neutron energies in the range of 14.1 MeV rial analysis labs e.g. at Karlsruhe Institute of and a He/dpa ratio of the order of 10 appm/ 82

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS dpa, especially to qualify structural materials. of the same order of magnitude as those for Such a neutron source for structural material structural materials, but they must provide qualification is developed currently in Europe prototypical parameters in the energy spec- in the context of EUROfusion under the label trum, helium ions damage and neutron flux. IFMIF-DONES (International Fusion Material Irradiation Facility- Demo Oriented Neutron In addition to the determination of the dam- Source, https://ifmif-dones.es/ [IFM2022], for age to the different material classes and the technical details see [Iba2018] based on the verification and validation of correspond- preceding joint Japan-European project in the ing calculation tools for the establishment of context of the Broader approach IFMIF-EVE- corresponding design tools, other parame- DA demonstrating the viability of such a neu- ters central to the design of a fusion power tron source, for more information see https:// plant can thus be obtained. For example, for www.ifmif.org/). a future fusion power plant, technical quan- tities such as tritium breeding ratio (TBR), lo- Observation cal power release, etc., are of relevance as a With respect to dpa damage and He/dpa ef- function of neutronic and thermal boundary fects synergies between both magnetic fusion conditions. Such quantities can be determined and laser fusion are obvious although they´ve using high-performance computers within been not exploited visibly by now. Nonethe- multiphysics and multiscale computational less, a single facility for the qualification of tools. However, the computations reveal a structural materials and the verification of considerable sensitivity to boundary condi- low activation FM-based steels only without tions, which is considerably increased by the cross-referencing is a critical strategy in itself. propagation of uncertainties and therefore in- But, apart from a structure materials qualifi- volves large uncertainties. A significant reduc- cation facility, there is a lack of infrastructure tion can only be achieved by an experimental for armor materials, as well as for functional validation using a small-scale neutron source materials such as breeding materials and po- providing fusion-type neutron energies in a tential neutron multipliers. These need not be sufficient volume. Finding » For the structural materials of the in-vessel components there is practi- cally no alternative to low activation ferritic martensitic steels (RAFM). And both laser and magnetic fusion have to rely on the material type furthest developed by now. Here, also laser fusion should synergisti- cally make use of the data base being existent by now and incorporate all upcoming experimental findings to be obtained from IFMIF-DONES. » For the armor materials inertial/laser fusion is facing substantially larger challenges than magnetic fusion. This is related not only by the pulsed operation leading to considerably higher heat loads through the armor than in magnetic fusion, but also through the helium implantation into the armor material. » In order to achieve a sufficiently high tritium breeding ratio and simul- taneous gut neutronic shielding of the reaction chamber, adequate functional materials such as breeder and neutron multiplier materials are necessary. Their qualification also necessitates an experimental val- idation at prototypical neutron energies and boundary conditions to ensure power plant functionality by up-scaling. Moreover, after valida- tion fabrication qualification tests on scalable mock-up tests are in-dis- pensable for a fusion power plant at prototypical neutron energies, neutron flux and temperatures to enable a licensing procedure. 83

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MEMORANDUM LASER INERTIAL FUSION ENERGY Recommendation » Maximize use of experimental data for structural materials from IF- MIF-DONES to enable a closed consistent blanket program. » For the armor materials the specific impact of Helium and gamma-in- duced surface material degradation especially due to the pulsed opera- tion in laser fusion should be internationally strength-ened, since there is no counterpart in magnetic fusion. Existing facilities both in US and Europe should be updated or if possible reactivated to provide a solid design basis. » Rapid development of a small scaled neutron source to allow for ver- ification and validation of functional materials (breeder and neutron multiplier) scalable to a blanket program. 6.4.2.2 Blanket Engineering The blanket is the most essential part of a fu- design concepts based on partial validation sion reactor due to this multi-functionality of through single or some multi-effect studies. heat extraction, fuel breeding and shielding and thus requires a multi-disciplinary interac- Fuel Cycle tion of different expertise incorporated in a For the fuel cycle several technologies have design team. The bandwidth is from physics been developed already in the context of nu- (neutronics), engineering (system integration, clear engineering, such as detritiation of water coolant technologies, thermal-hydraulics, or extraction of hydrogen from gas streams thermal-mechanics), material sciences (fabri- also on a large scale. However, fusion systems cation & manufacturing, welding, corrosion) pose challenges currently not mastered on and process engineering (coolant chemistry, a larger scale and even not fully developed. purification, selective extraction). This wide Also, the modelling of some effects like dif- range of required expertise is available only fusion through structures, super-permeation, in a few research institutions and/or large ex- fast and efficient isotope rebalancing are still periments and hardly to be found in universi- in rudimentary state. The largest deficits arise ties. Major integrated expert groups in this fu- here mainly for the outer fuel cycle. Thus, the sion-specific field are to be found in the USA, depiction of a fully closed fuel inner and outer Japan, Korea, China, India, Europe and ITER, fuel cycle by all modules has not been realized which have elaborated more or less closed in practise but also on model scale. 6.4.3 Capabilities and Competencies in Germany, Europe and Worldwide 6.4.3.1 Material Research Most sites mentioned in the material con- United States text host single effect experiments, which are Oak Ridge National Laboratory (ORNL), UT complemented by extensive computational Battelle– radiation damage, (Spallation neu- efforts from atomistic (Molecular dynamics, tron source-SNS, HFIR reactor), Lawrence MC and rate theory) to scale bridging model- Livermore National Laboratory -neutron radi- ling. ation, Fusion Technology Institute University Wisconsin Madison- Helium effects, Universi- ty of California San Diego – pulsed irradiation (Laser) 84

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS Europe ment, material damage; Karlsruhe Institute DIFFER (Netherlands) - Plasma-wall interac- of Technology (KIT)- material development tion (Magnum-PSI, Ion Beam facility), CCFE (Fusion material laboratory-FML, Heloka- high (UKAEA- United Kingdom, Materials research pressure) -low activation steels, breeder & Facility (MRF)- National nuclear user facility, multiplier materials, damage characterization, hot cell- material characterization), CEA (West corrosion, high heat flux testing, Fraunhofer – Cadarache, France- structure materials- cor- ILT (Fraunhofer Institute for Laser Technolo- rosion, erosion, manufacturing); ENEA (Italy- gy), Fraunhofer IGCV (Fraunhofer Institute for material damage, ion implantation), CIEMAT Casting, Composite and Processing Technol- (Spain-electron accelerator, ion implanter, ogy), Fraunhofer IWM (Fraunhofer Institute source – radiation shielding, insulator, breed- for Mechanics of Materials) in additive man- ing materials). ufacturing, other production technologies, material characterizations methods, mate- Germany rials modelling, and hydrogen isotope isola- Institute for Plasma Physics (IPP-Garching- tion (Fraunhofer IFAM-Fraunhofer Institute High heat flux materials, Gladys), Forschungsz- for Manufacturing Technology and Advanced entrum Jülich (FZJ)- Plasma-wall interac- Materials). tion-High temperature material laboratory, JUDITH 1, JUDITH 2, PSI-2- Tungsten develop- 6.4.3.2 Blanket Design Regarding Blanket design and its multidis- But expert know how is present in different ciplinary nature only a few sites worldwide fields at: Fusion Technology Institute Univer- offer the capability and the resource to pro- sity Wisconsin Madison (neutronics, material), vide a closed design. Mainly the ITER contrib- Oak Ridge National Laboratory (ORNL), Law- utors for the ITER test blanket such as Japan rence Livermore National Laboratory (LLNL), (NIFS), China (Chinese Academy of Sciences, Argonne National Laboratory (ANL) & Idaho China National Nuclear Corporation), Korea National Laboratory (INL) for multi-physics (KAERI), India (Institute for Plasma Research), multiscale neutronics, thermomechanics, the United States and Europe have developed thermal-hydraulics. these capabilities aside from the ITER team it- self. The experimental infrastructures consist Europe mostly of thermal-hydraulic loop systems (gas, Integrated Blanket concepts: CCFE (UKAEA- water, liquid metal operated) connected high JET Culham, Unitewd Kingdom); ENEA (Ita- power heat flux simulators to mimic prototyp- ly-Frascati-Brasimone) ical power densities at reduced scale (mock- ups) fusion typical operation conditions out of Expert know-how: CEA (Saclay, France), CIE- pile. However, none of the facilities worldwide MAT (Spain), CERN (Switzerland) University has the scope of even a small-scale neutron Polytecnica de Madrid (UPM) source to simulate a fusion type load scenario. Germany United States Integrated Blanket concepts: Karlsruhe Insti- Integrated Blanket concepts: Princeton Plas- tute of Technology (KIT) ma Power Laboratory (PPPL), University of California (UCLA) 85

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.4.3.3 Competence Holders Liquid Metal Engineering, Coolant Chemistry, Safety United States Germany Argonne National Laboratory (ANL), Univer- Karlsruhe Institute of Technology (KIT), Hel- sity of California Los Angeles (UCLA), Idaho holtz-Zentrum Dresden Rossendorf (HZDR) National Laboratory (liquid metals, salts), Oak Ridge national laboratory (salts) Europe CEA (Saclay & Cadarache , France), ENEA (It- aly-Brasimone) with focus on also on Lithium 6.4.3.4 Fuel Cycle Similar as for the blanket engineering lots of study of a fusion fuel cycle experimental facil- worldwide research labs have special know ity with tritium is under erection in the United how in singular process technologies relevant Kingdom (Hydrogen-3Advanced Technology- for a fusion fuel cycle, since they are essen- H3AT). All elements of a fuel cycle and a civil tial for hydrogen process engineering or for tritium laboratory is also present at Karlsruhe nuclear safety (e.g. detritiation in CANDU re- Institute of Technology (KIT)- Tritium laborato- actors as in Darlington Canada). Currently, the ry Karlsruhe (TLK). world-wide first facility allowing for a full chain 6.4.3.5 Competence Holders Fuel Cycle and Process Engineering United States (PPPL), Argonne National Laboratory (ANL) Lawrence Livermore National Laboratory (LLNL- cryo engineering, tritium process- Europe ing), Savannah River Site National Laborato- CEA (Valduc, France) -Military (aspects on- ry (SRNL), Los Alamos National Laboratory ly-limited access), ENEA (Rome, Italy) – pro- (LANL), Princeton Plasma Physics laboratory cess technology 6.4.4 Industry Led R&D for IFE The role of industry with respect to materi- with the industry. In the absence of a business als, blanket engineering and fuel processing is model for fusion by now the development risk mainly governed by the economic market sit- for fusion specific products is considered high uations. For armor materials such as tungsten by industry so that most efforts are concen- there is a vital interest of defense technology trated on niche markets with use cases like and space industry in e.g. robust shielding or fusion. for high heat flux applications. However, for functional materials as well as for fusion spe- A similar observation holds for blanket engi- cific structure materials the development is neering. While for some multi-physics and focused on the national laboratories and only multi-scale code systems developed in the fabrication routes or dedicated material treat- context of fusion exist use cases such as for ment aspects are developed in collaboration accelerator applications (e.g. pharmaceutical 86

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS radioisotope production, neutron imaging, Regarding the fuel cycle technologies, some ion therapy) most of these applications are technologies have already gained interest by not in the core fusion applications and are of- process industry, such as selective separation ten at the border of their applicability. Here, of hydrogen from gas streams, or detritiation two measures would be helpful to stimulate of water in nuclear stations. However, some indispensable industry engagement: technologies such as isotope rebalancing, cryo-distillation and others are rather fusion » development of a fusion market to encour- specific nature. Nonetheless, promotion of fu- age industry to collaborate by investments sion to industry via private public partnership in experimental infrastructures. projects could stimulate the development and » active marketing of fusion on public basis validation of process simulators also to speed to profit from vast industry experiences in up fusion fuel cylce development. manufacturing processes, remote handling techniques, control diagnostics. 6.4.5 Findings and Recommendations 6.4.5.1 Materials Finding Experimental platforms for the verification and validation of material re- search needed. Recommendation » Provision of fusion neutron energy typical source(s) complementary to IFMIF-DONES also accessible through universities & industry to execute research on structural, functional and armor materials. » Maximize utilization of experimental data to be gathered by IFMIF-DO- NES for structural material damage through fusion typical neutron op- eration for laser fusion by cooperation of both communities (laser and magnetic fusion). » Strengthening/reactivation of material research facility allowing to study effect of Helium implantation, especially with respect to pulsed power exposure of structural, armor and functional materials. » Enhancement of collaboration with material research laboratories al- lowing for post-test analysis of irradiated materials (PIE) requiring for in-pile specimens requiring hot-cells. In particular, the worldwide lim- ited availability of material characterization equipment for irradiated samples (PIE) requires not only the joint use by laser and the magnetic fusion community, but also the development of international collabo- rations. » Establishment of research cooperation of national laboratories with universities on national and international level targeting at increased modelling as well as verification and validation of predictive numerical tool sets for all types of fusion typical materials. In materials development, a number of re- ically on the micro level using high resolution search options arise for both structural mate- ab-initio models but also corresponding micro rials and armor and functional materials. Sin- characterization experimentally, even if not gle effects of material damage by neutrons or always understood in full detail. The analysis even helium formation by transmutation are of coupled phenomena like the dpa/He appm- well studied experimentally as well as numer- ratio on the materials requires the synergetic 87

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MEMORANDUM LASER INERTIAL FUSION ENERGY interaction both on the model level not only ed components and diagnostic tools. on the micro-scale but also the transfer to the meso-scale and up to the macro-scale. This is To mimic all kinds of material damage aspects only possible with the help of the cooperation and allow for material characterization for of universities with research institutes in a na- a quite large bandwidth of materials an ac- tional as well as international context, since celerator type facility with a rather diverse both have the necessary expertise as well spectrum is required. Only accelerator-based as the computer capacities, which make the facilities allow for a high degree of flexibility solution of such questions possible. (source: protons, deuteron, Helium), by us- ing a dual beam facility set-up allow not only Nevertheless, experimental platforms for the short-term proof of principle tests but also verification and validation of numerical re- long-term performance testing can be execut- sults are indispensable. Even if IFMIF-DONES ed with a high timely availability at relatively is projected to be a facility in which the fusion low cost compared to fusion based neutron power plant-typical damage of structural ma- source. (Moreover, the high neutron flux also terials at different temperatures will be pos- allows the installation of an additional target sible for the first time, the spectrum of struc- station with a moderator to generate slow tural, functional and armor materials is so neutrons. The availability of cold neutrons en- large that one facility cannot do this alone. In ables material investigations e.g. by neutron addition, validation of materials for diagnos- reflectometry, small angle neutron scattering tics in a fusion reactor requires not only long- and neutron diffraction (e.g. for battery re- term experiments at a typical fusion neutron search or other diagnostics) and substantially spectrum, but also short-term experiments to increases the facility utilization). identify complementary damage mechanisms and to map them appropriately in models. IF- Further, even if the structure, armor and func- MIF-DONES offers only limited flexibility here, tional material are fully characterized at fu- focusing exclusively on structural materials at sion typical neutron energies and fluxes, still various boundary conditions. Here, at least fabrication technologies to towards a blanket one or better two/three flexible small-scale design need in-pile validation at least a down- neutron sources are required to substantially scaled level to allow for demonstration for a accelerate the development of fusion-adapt- licensing process. 6.4.5.2 Blanket Finding The same applies to blanket technology as to materials research, although the starting point is different. A credible blanket program first requires the definition of a reaction chamber concept and at least the cornerstones of a possible mode of operation in order to determine, for example, rudi- mentary dimensions of the reaction chamber and thus the power density on the first wall, the neutron flux and many other parameters. Recommendation » Therefore, first a fusion reactor study at the beginning of the program is mandatory to condense the solution space for a laser fusion power plant to a manageable number of options. This also requires at least a rudimentary description of the mode of operation. Such a study should include experts not only in fusion physics, but also in blankets, ma- terials, fuel cycle, driver systems, and diagnostics to avoid dead ends that assign physically infeasible tasks to a system. The goal of the study should be a simplified 1-1.5-dimensional power plant model from which cornerstones for the blanket can be extracted such that a closed-loop design activity can be incorporated. Ideally, national and international 88

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS experts should be part of this activity. » The second step is to build a design team for the blanket, with the goal of creating a feasible base design that would meet all functionalities. This should essentially be led by research laboratories, as only they have the sufficient range of expertise. However, industry participation is strongly advised, especially with respect to manufacturing, opera- tions and exchange, to ensure design consistency. » Verification and validation play a central role in the design consolida- tion phase. This requires two pillars • first, the use of the neutron source(s) already addressed in materi- als to optimize the design concept through scaled small mock-ups. • The second pillar is the use of industry expertise in highly scalable component manufacturing, coolant purity control, remotely man- ageable logistics concepts and interface management. 6.4.5.3 Fuel Cycle Finding Fuel cycle development needs a feasible power plant design. Recommendation Fuel cycle is modular, individual technologies can be built up, develped and analysed separately. Fuel cycle development also needs a feasible velopment of the modular process modules, power plant design (pulsed repetition rate, the corresponding models must be validated fuel burnup, …) as a basis to determine the by means of the individual modules. This can amount of fuel, the possible amount of ex- be done at universities, research institutes or haust gas, debris, etc., and to match the in- industry, so that at the end of the fuel cycle ner and outer fuel cycle. Since the fuel cycle development a simulation model for the en- is modular, the individual technologies can be tire process chain is available. developed, built up and analyzed at different locations with the available expert know-how. However, validation and verification of the entire process chain is required by a scaled- To verify and validate most modular systems, down experimental process simulator. Wheth- the availability of a tritium laboratory is not er this must necessarily be implemented in a necessarily mandatory, for some specific pro- tritium laboratory can only be demonstrated cesses and for the determination of materi- by a sensitivity study, where critical interac- al parameters small tritium test capabilities, tions between process modules occur. however, are mandatory. Parallel to the de- 6.4.6 Time Table and Investments A rough time table for blanket, materials and year to the design team during the conceptu- fuel cycle is depicted below. It requires a al design phase (CDP) and engineering design closed program reflected on the plant level by phase (EDP), while the blanket, material re- a design team. Here, only current similar proj- search and fuel cycle are covered by own R&D ects can be compared. The UK STEP program projects. assigns a yearly effort of more than 50M€/ 89

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MEMORANDUM LASER INERTIAL FUSION ENERGY The conceptual design of an IFE power plant Assuming a full utilization of IFMIF-DONES and needs to be advanced, which analyzes the the access for the blanket team to existing US requirements and limitations of each mod- or European R&D facilities for thermal-hy- ule required for a laser fusion power plant draulics mock-up/prototype verification and within the framework of a balance-of-plant qualification the major investments up to the model, taking into account sensitivities and blue print phase are associated with a com- uncertainties. To develop the tools and under- bined neutron, alpha-particle (Helium implan- standing concisely, a development program tation) and gamma radiation source providing is needed that we estimate to a few million at small scale numerical tool verification & val- euros per year and, since Germany does not idation and a downscaled fuel cycle demon- have sufficient expertise in all expertise areas, strator, each requiring an investment in the it must be carried out in the framework of in- range of about 40-100M€ depending on the ternational cooperation. requirements requested by a design team. year 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 plant level CDPplant layout CDPplant analysis EDPplant design + BoP PEP system ntegration, layout blanket CDPconcept screening CDPconcept analysis + selection EDPdesign verification

• validation Materials Structure materials DONES-erection data (50dpa) data (100dpa) ICF armour materials existing facilities functional materials neutron source neutron source utilization (neutrons) combined neu- eastblish dual beam facility utilize dual beam facility trons+ α+ γ-rad Fuel cycle CDPbasic concept EDPsingle system, cycle simulator PEP accountancy concept blueprint ready Fig. 17: Timetable for 1st Wall and Blanket design. Conceptional design phase = CDP, engineering design phase = EDP, project execution phase = PEP. 90

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS 6.5 Laser Drive and Optics 6.5.1 Role of Drive Laser Technology in IFE In the last six decades, lasers have evolved achieve efficient and reliable ignition. Achiev- from being a solution in search of a problem ing the optimal combination of these parame- to an integral part of our daily lives. Their im- ters is a critical area of research, as it is essen- pact has been felt in various fields such as tial to making fusion energy possible. Enabling fiber-based communication, medical proce- a viable clean energy source for the future. dures, materials processing, and fusion re- search. Laser fusion has played a crucial role Some fusion schemes (e.g. “electron fast ig- in pushing laser technology to the limits of nition”, “ion fast ignition”, “shock ignition”) extremely high energies, posing unique chal- require energetic ignition lasers in addition lenges. to the compression laser drivers. These can year 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 generate bursts of electrons or ions for fast plant level In inertial fusion energy (IFE), the driver is ignition schemes and typically require laser CDPplant layout used to initiate and control the fusion reac- pulse durations 1000 times shorter than the tion. The driver is responsible for delivering compression drivers, i.e., on the order of pi- CDPplant analysis the energy required to compress and heat the cosecond-duration. For IFE, where the times- EDPplant design + BoP fusion fuel to the necessary conditions for nu- cales on which fusion occurs and a burn wave PEP system ntegration, clear fusion to occur. High-power lasers are a propagates are on the order of several tens layout suitable and elegant technology for achieving of picoseconds, pulse durations less than 1 ps fusion plasma conditions. So far, most of the are less likely to be relevant – an important blanket inertial confinement fusion (ICF) experiments consideration when developing laser architec- CDPconcept screening have employed lasers as the primary energy tures that can serve both as compression or CDPconcept analysis + source to compress and heat the fusion tar- after appropriate changes as a fast ignition or selection gets. While there have been other proposed shock driver. “drivers” for ICF such as heavy ion particle EDPdesign verification accelerators, pulsed power, gas guns, or mag- To compress the fusion fuel capsule to ignition

• validation netic flux compression, lasers are currently conditions, target concepts with a target gain Materials the most advanced technology possessing the of >30 require a laser system capable of deliv- Structure materials DONES-erection data (50dpa) data (100dpa) necessary combination of characteristics. ering a high-energy pulse of at least a few MJ at UV wavelengths, with precise control of the ICF armour materials existing facilities The use of laser beams allows the concentra- pulse shape, lasting a few nanoseconds, and functional materials tion of abundant energy (several MJ) in the with a peak power of approximately 500 TW. neutron source neutron source utilization (neutrons) form of light onto a small capsule of fusion For a power plant with an electrical output of fuel from a considerable distance, allowing a one GW, these pulses must be delivered at a combined neu- eastblish dual beam facility utilize dual beam facility trons+ α+ γ-rad substantial distance between the walls of the repetition rate of 10-20 Hz. This corresponds fusion reactor and the ignited fusion plasma. to an average power of about 40 MW. As the Fuel cycle IFE lasers must be pulsed, delivering pulses energy is distributed across multiple beam- CDPbasic concept of concentrated energy in time and space to lines, at least several hundred beamlines must EDPsingle system, compress the fuel capsule. In addition to the be employed to ensure sufficiently symmetric cycle simulator pulsed laser operation, other factors such illumination of the target. For a larger number as laser energy, pulse duration, focusability, of lasers the energy could be distributed over PEP accountancy wavelength, bandwidth, and the often-over- more apertures, thus reducing optics sizes concept looked power balance and laser pulse fidelity and the cost per optic, respectively. However, blueprint ready (its temporal pulse shape and temporal pulse an increasing number of beamlines growths Fig. 17: Timetable for 1st Wall and Blanket design. Conceptional design phase = CDP, engineering structure) are critical parameters that must the complexity of the overall system and a design phase = EDP, project execution phase = PEP. be optimized to create a uniform, spherical- balance between cost and practicability must ly-symmetric implosion of the fuel target and be found. 91

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MEMORANDUM LASER INERTIAL FUSION ENERGY High wall-plug efficiency is a critical consider- cost modeling plays a crucial role in the design ation in the design of laser architectures for of laser systems for fusion power plants. fusion power plants. This metric measures the overall energy efficiency of a laser system by Besides the laser itself, a beam transport and comparing the output optical power to the to- delivery system are needed in a fusion pow- tal electrical power input required to operate er plant. It performs the critical task of trans- the laser, including cooling, power condition- porting laser beams from the laser system to ing systems and laser control systems. Achiev- the target chamber and consists of a series of ing high wall-plug efficiency simplifies heat re- mirrors, lenses, and other optical components moval from the laser and reduces the amount that are used to focus and steer the laser. The of recirculating power required in the power system must maintain the high quality and in- plant, Fig. 18. This results in more efficient tegrity of the laser beams, as any distortion and cost-effective operation, as well as higher or loss of beam quality can significantly re- overall power output. A general rule of thumb duce the effectiveness of the laser system and suggests that the product of laser wall-plug ef- its capability to ignite the fusion fuel. Target ficiency and target gain should be greater than tracking and fast beam steering are required 10, otherwise most of the power generated is to detect and hit the target in the reaction consumed by the driver [Mei2008]. Thus, the chamber with the precision of less than the recirculating power fraction must remain un- width of a human hair. While the function of der 20%. The desired goals for an IFE power- these systems may appear simple, the under- plant are therefore a laser wall-plug efficiency lying technology required to meet the specifi- of >10% and a target gain of 100. Considering cations for high performance, durability, and the cost of electricity (COE), it can be shown material compatibility with the target cham- that the cost of the laser driver is more heav- ber environment is extremely challenging to ily influenced by laser energy rather than its develop and manufacture, requiring signifi- repetition rate [Mei2009]. However, it’s worth cant research and testing efforts. noting that laser systems designed to maxi- mize efficiency may have added complexity, There are different types of laser concepts reduced flexibility, and higher construction considered for IFE, such as solid-state lasers costs, and a power plant’s cost model may dic- and excimer lasers, which operate in different tate a different laser concept and architecture configurations (laser-indirect-drive or laser-di- than what would be selected based solely on rect-drive). Both solid state and excimer lasers power and efficiency considerations. As such, are advanced and have their unique advantag- Fig. 18: Basic parameters of an IFE power plant (left). Illustration of a “1 ω beam box” provid- ing 8.1 kJ at 1.05 µm (converted to 5.7 kJ at 0.35 µm close to the target chamber) as a modular component of an IFE laser system (right) [Bay2011]. 92

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS es and limitations. Solid-state lasers and exci- or xenon) as their gain media. The halogen gas mer lasers are fundamentally different in their utilized depends on the desired output wave- construction, design, and operation. length and other factors pertinent to the laser design. An electrical discharge at a high voltage Solid-state lasers employ a gain medium that excites the gas mixture, causing the halogen is typically a crystal or glass containing rare and noble gas molecules to combine briefly earth or transition metal ions such as Neo- and form an excited dimer or trimer molecule dymium or Ytterbium. These ions are excit- called an excimer. The excimer rapidly de-ex- ed by light emitted from either flashlamps cites and emits a photon of laser light in the or semiconductor diode lasers to produce ultraviolet or deep-ultraviolet range. Excimer laser light. Solid-state lasers can operate in gain media have a lower energy storage ca- continuous wave or pulsed modes and emit pacity than typical solid-state laser materials. light mostly in the near-infrared wavelength Despite their limited wall plug efficiency due regions. They can access UV wavelengths to the intrinsic efficiency of the laser medium, through nonlinear optical processes: harmon- they offer some distinct advantages over typ- ic generation and sum frequency generation. ical solid-state lasers for IFE drivers. They can Harmonic generation involves the use of a deliver even shorter ultraviolet wavelengths crystal with nonlinear optical properties to without the need for frequency conversion which a highly intense beam of light passes, and can operate within a frequency bandwidth generating new wavelengths of light at integer of a few Terahertz, which reduces laser plas- times the original frequency, such as the third ma effects such as Stimulated Brillouin Scat- harmonic (ultraviolet) of a NIR laser. Harmonic tering (SBS) and Stimulated Raman Scattering generation is a special case of sum frequency (SRS) and improves therefore energy coupling generation, which works similar and where a to the fuel capsule in laser-direct-drive or to new wavelength is generated by sum frequen- the hohlraum in laser-indirect-drive. Even cy generation of a pump and signal wave in a though high-energy excimer lasers are not as nonlinear crystal. technically advanced as DPSSL, they are still a promising option for achieving large band- A subset of solid-state lasers are fiber lasers width in the deep UV with high rep rates, high that are widely used in industry. While fiber power, and wall-plug efficiencies ranging from lasers have become increasingly popular in 5-10%. Therefore, it is important to explore la- many applications due to their high efficiency ser-plasma-interaction physics at ignition-rel- and compact size, they have not yet demon- evant scale using existing facilities to derive strated to produce the high-energy pulses re- needs and requirements for broadband UV ar- quired for IFE. Despite this, some research has chitectures. Meanwhile, it is recommended to been conducted into the use of fiber lasers evaluate both excimer lasers and broadband for IFE, as noted in several studies [Lab2008], DPSSL to determine their potential broadband [Mor2013], [Kle2018]. These investigations performance and efficiencies. First estimates are still in the early stages, and it remains to can be found in [BRN2022]. be seen if they can be scaled up to the levels necessary for IFE. To explore this exciting ap- In comparison, solid-state lasers typically ex- proach, a full conceptual system design study hibit 2-3× higher wall plug efficiency, are eas- with an associated cost model is required. This ier to scale up to higher output energies than will help to determine the feasibility of using excimer lasers, which makes them more suit- fiber lasers for IFE and to assess the potential able for high-energy applications like inertial benefits and drawbacks of this technology. confinement fusion. Furthermore, solid-state lasers offer more precise control over pulse Excimer lasers, on the other hand, are a type shape, duration, and energy than excimer la- of laser that use a gas mixture consisting of sers. This is particularly important in inertial halogen gases (such as fluorine, chlorine, or confinement fusion, where precise timing and bromine) and a noble gas (like argon, krypton, energy control are critical. DPSSL exhibit the 93

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MEMORANDUM LASER INERTIAL FUSION ENERGY highest technical readiness level [BRN2022] quire optimization of wall-plug efficiencies, and are the most likely and common building scaling, materials, architecture, and technolo- block for IFE drive lasers. Therefore, we will gy to develop fusion power plant-ready devic- not elaborate on other approaches in this dis- es. In addition to designing effective laser driv- cussion, and readers can refer to [BRN2022] ers, it is important to consider ways to reduce for more information. However, it is important production costs and future maintenance and to conceptually explore various laser architec- operation expenses, as well as establish and tures that use different gain media to ensure secure reliable supply chains. Target tracking that any emerging requirements from techno- and beam steering are also necessary for la- logical advancements in fusion plasma and LPI ser drivers. Additionally, development of stan- research are considered. In general, it is im- dardized, integrated machine safety and per- portant to maintain technological openness to formance control systems is needed. identify the best suited design. It is noteworthy, that laser technologies have matured considerably, but all approaches re- 6.5.2 R&D and Capability Status Worldwide Laser-based ICF (implosion) facilities are de- the laser beam injection into the target cham- signed in a configuration that supports a spe- ber. The National Ignition Facility (NIF) where cific drive scheme, either the Laser-Driven Di- ignition was achieved in December 2022 is rect Drive (LDD) or Laser-Driven Indirect Drive configured for polar indirect drive, Fig. 19. (LID) target concept, defining the layout of It is a unique laser facility with the size of Opticsassembly Deformablemirror building mount assembly Main amplifier Cavityspatialfilters Pockelscellassembly Power amplifier Transport spatialfilters Control room Power conditioning Master oscillatorroom transmission Switchyard lines support structure Amplifier power conditioning modules Periscope polarizer mount assembly Beam control & laserdiagnostic systems Pre-amplifier modules Diagnostics Transport turning building mirrors Target chamber Final opticssystem Fig. 19: Setup of the National Ignition Facility (NIF) [MOS2002]. 94

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS three football fields located in Livermore, test bed for high energy density (HED) and fu- California, and operated by the Lawrence Liv- sion science, and therefore provide a critical ermore National Laboratory (LLNL). It is the foundation for IFE driver development. The largest and most powerful laser in the world NIF is the result of LLNL’s half-century-long de- and the only facility with the ability to ignite velopment of increasingly powerful Neodym- a deuterium-tritium (DT) plasma. Its focus is ium-doped Glass (Nd:Glass) laser systems. In the research of high energy density plasmas, the early 1990s, the conceptual design for NIF and specifically the scientific achievement of was created, followed by its construction in igniting a DT plasma on laboratory scale. 1997 and commissioning in 2009. The cost for the design and construction of NIF was $3.5B, While the United States achieved ignition first, with additional investments into diagnostics, other countries are following a similar path: targets and other facility improvements after. The laser system is configured with sixteen 3.4 » France has built the Laser MegaJoule (LMJ) cm thick Nd:Glass amplifier slabs in a single that currently operates at 350 kJ and will beamline. To reduce reflective losses in the reach 1.3 MJ when complete in 2026, a laser beam, the slabs are arranged vertical- facility very similar to the NIF with some ly on edge at Brewster’s angle. The slabs are jointly developed laser and diagnostics stacked four high and too wide to accommo- technologies; date a bundle of eight laser beams and pro- » Russia operates at 128 kJ from their first 64 vide an unprecedented high beam packaging beams of its UFL-2M laser in Sarov that is density. Beam transport between the amplifi- designed to deliver 2.8 MJ at 527 nm from er sections is accomplished by two transport 192 beams [Sci2022] when complete. The telescopes that are 82 meters long (Fig. 20 longer wavelength at the second harmon- left). The required image depth for the Brew- ic of Nd:Glass distinguishes it from NIF and ster-angled slabs and the intensity limitations LMJ, which operate at 351 nm; in the pinhole plane of the telescopes are the » China operates its SG-III facility at 180 kJ in main factors driving the length of the laser the UV [Zhe2016] and has reported some chain (105 m). However, with the transition years ago designing a full-scale ignition la- to diode face pumping of the amplifier slabs, ser facility SG-IV with an initial design goal the length of the laser chain can be reduced of achieving 1.5 MJ or greater energy. to a fraction of the length of the amplifier cassette. NIF was the first ICF laser configured Apart from the large-scale ICF implosion ca- as a 4-pass amplifier instead of a linear Mas- pable facilities discussed above, key research ter Oscillator Power Amplifier (MOPA) chain and development supporting fusion science is [Spa2016]. This required the development of a also being carried out at the OMEGA facility large aperture (40×40 cm2) active laser cavity at LLE in Rochester, US and at several small- electrooptical switch (plasma electrode Pock- er facilities (5 kJ or less) such as in the UK at els cell - PEPC). Other main key technologies VULCAN [Dan2004] and ORION [Hop2015], in developed for NIF were large aperture, high France at LULI 2000 [Zou2008], in the US the energy adaptive optics; the development of Excimer Facility NIKE [Obe2015], in Germany the preamplifier module (PAM) amplifying the at the Phelix Laser at GSI Darmstadt [Bag2010] laser by ×1010 from nJ to 10 Joule, smoothing and the POLARIS Laser at the Helmholtz Cen- and precision-shaping the beam dynamically ter Jena [Hor2016]. in time and space; a 320 MJ electrical Power Conditioning System (PCS), which consists of To fully appreciate the daunting challenges the highest energy array of electrical capaci- facing an inertial fusion energy (IFE) driver, it is tors ever assembled; high damage threshold critical to gain a comprehensive understanding lenses and optical coatings for ultraviolet in- of the complexity and scale of today’s inertial cluding a refurbishing and recycling loop; a confinement fusion lasers. These sophisticat- control system that automatically aligns and ed systems serve as the preeminent scientific controls the performance of the laser; and the 95

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MEMORANDUM LASER INERTIAL FUSION ENERGY Advanced Radiographic Capability, the world’s Laser System (HAPLS) [Hae2016], [Hae2017], most energetic short pulse laser for back- a Helium-gas-cooled Nd:Glass laser is an ap- lighting dense targets including the develop- erture-downscaled fusion laser derived from ment of many new optical elements to gen- LLNL’s Laser inertial fusion energy study (LIFE) erate high intensity laser beams [Bar2004], [Bay2011] developed until 2012, Fig. 20 left. [Hae2009], [DiN2015], [Ale2020]. The greatly increased repetition rate and ef ficiency over NIF required modifications to its NIF represents the largest optical system in architecture, including replacing flashlamps the world and an IFE driver will be of similar with laser diode arrays and pulsed power sup- scale though its footprint will/must be much plies to reduce heat load and increase overall smaller. Hence, the many optical components efficiency. In addition, optical components, required represent a significant challenge for especially laser gain media and frequency con- the supply chain. version crystals, required active cooling. This system tested several critical components to To name the most significant, NIF developed an IFE driver laser. In the future, the substi- with Schott and Hoya the continuous melt tution of Nd:Glass slabs with crystalline gain production of high-quality Nd:glass (Fig. 20 media, preferably with higher intrinsic effi- right) to provide the required amount of gain ciency [Erl2011], promises a path to high en- material for NIF (145 tons of laser slabs in- ergy IFE drive lasers that do not require the stalled at NIF) and its French sister, the Laser bandwidth of Nd:Glass. Another laser, aka “Di- MegaJoule; in-house (now outsourced) the POLE”, Fig. 20 right, developed by the Central rapid growth of potassium dihydrogen phos- Laser Facility in the United Kingdom also uses phate (KDP) for frequency conversion and Helium-gas-cooling to remove the heat from PEPC; and many optical finishing and coating its amplifier slabs made out of Yb:YAG. Due to techniques used by industry today. Till today, its low gain at room temperature and high en- NIF is sourcing critical optics from companies ergy storage, the gain medium must be cryo- in the U.S., Germany (e.g. Schott, Heraeus, La- cooled to ~100 K to overcome this limitation, seroptik, Schott Lithotec), Japan (Nikon, AGC, however reducing its spectral bandwidth sig- Ohara, Inhabata, Hoya), the U.K. and others. nificantly. Thus, it would not be suitable for Overall, the construction of NIF has signifi- a fast-ignition driver but may be suited for a cantly advanced the optics and laser industry DPSSL-fusion driver if the additional cooling in the United States, Germany and worldwide, effort is balanced by higher optical-optical ef- enabling many advances that would not have ficiency than a material at room temperature. been possible otherwise. DiPOLE100 laser systems have been built for HILASE in the Czech Republic [Pilar018] and The High Repetition Rate Advanced Petawatt Fig. 20: NIF laser facility (left), continuous strip of laser glass exciting the melter at NIF (right). 96

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS the HIBEF endstation on Germany’s X-ray la- ser at DESY. Fig. 21: High repetition rate, high energy lasers: HAPLS (left) comprising a Nd:Glass laser with 200 J at 10 Hz, and DiPOLE (right), a cryogenically cooled Yb:YAG laser with up to 150 J at 10 Hz (HiLASE). 6.5.3 The Development Path to High Repetition Rate, High Average Power IFE Drivers Diode-pumped solid-state lasers (DPSSLs) or ns-pulse high-energy pump laser of the HAPLS Energetic Excimer Lasers can be used for in- laser delivered to ELI Beamlines, or the DiPOLE direct and direct drive and fast ignition. The Laser. Currently DPSSL technology is estimat- fundamental physics and technology were al- ed to be at TRL 5, but due to the high capital ready developed for the National Ignition Fa- cost currently associated with diode arrays, cility [Spa2016]. To adapt these lasers for IFE, the overall TRL is set at TRL 4. To put this in certain modifications are required, such as perspective, a diode pumped NIF-like laser replacing flashlamps with semiconductor laser would need ~$20B (!) worth of diodes to to- diode arrays and high-efficiency pulse-form- day’s market price, plus its electrical drivers. ing circuits [FUL2015] to reduce heat input The required transition with respect to pulse and increase wall-plug efficiency. Active cool- energy and average power from state-of-the- ing of laser gain materials will replace convec- art lasers to an IFE beamline and a full-scale tive cooling [Bay2011]. New passive and active IFE laser drive is shown in Fig. 22. Each of the components and approaches will be needed to different technology gaps on this path is de- compensate for large thermo-optical aberra- scribed in more detail below. tions. Laser materials, such as ceramics or ad- vanced glasses, with improved thermo-optical Excimer lasers could be well suited for direct properties, longer storage time, or larger gain drive in the deep UV and with large bandwidth cross section will also be needed. Additional (<10THz for ArF, <3THz for KrF), but complexi- optical features such as large-aperture optical ties in multiplexing, pulse compression, beam switches, gain isolation, frequency conversion shaping, and optical damage require a de- [Bay2011], [Hae2016], spatial filtering, beam tailed model. The overall efficiency is estimat- image relaying [Che2019] at high average ed at 10% (ArF) and 7% (KrF) after accounting power will also be required. Advanced surface for various factors. The ASPEN KrF concept finishes and dielectric coatings are needed to promises to be simpler but is at an early stage increase damage threshold and lifetime. [Con2022]. Some of these architectural changes and tech- German startups in the field of fusion ener- nological advances have been realized in the gy are developing power plant architectures 97

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MEMORANDUM LASER INERTIAL FUSION ENERGY Fig. 22: Overview of high-energy laser systems and required scaling of pulse energy for an IFE laser driver (parameters of fusion plant according to the LIFE study). Scaling from the frontiers of DPSSL technology approximately x50 in performance improvement is needed, in addition to the necessary increase in wall-plug efficiency. that require high peak power laser pulses to fusion driver beamline. generate intensities exceeding 1019W/cm2 for secondary radiation source generation. Mar- An Integrated IFE Beamline vel Fusion GmbH requires laser pulses with Design is Needed durations less than 100 femtoseconds, while Understanding the target physics requires Focused Energy GmbH requires pulses with high precision, advanced lasers, diagnostics durations of a few picoseconds. Both require and simulation tools. Hence, the laser is a key high energy (incoherent pulse pedestal) and technology that must advance in TRL faster high-power contrast (coherent pulse pedes- to drive the other areas forward in capability, tal, 100dB or better). Estimates for the total as it is one of the critical elements in driving energy, peak power, and other requirements a fuel capsule to ignition. To achieve the in- are developed in ongoing target physics sim- tended pulse energy of ~2 MJ for an inertial ulations. Integrated experiments at ignition fusion power plant (energy requirement dif- scale have not yet been conducted. Both com- fers between direct drive and indirect drive panies underpin the need for efficient DPSSL approach), a minimum number of beam lines drive laser development that can be retro- is required to ensure homogenous illumina- fitted with chirped pulse amplification. Gain tion of the target while maintaining symme- media will have to support these very short try. However, the maximum number of beam pulses or adequate nonlinear pulse shortening lines is limited by the acceptable number of methods must be employed. apertures in the reaction chamber and the beam quality. Large aperture amplifiers can In the following, areas of R&D and technology reduce the total number of components and demonstrators are listed needed for develop- system complexity, while smaller apertures ing today’s laser technology jointly towards a ease laser-design, thermal management, and 98

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS mass-production of optical components. demonstrated for gas-cooled technology demonstrators like DiPOLE or HAPLS, both To demonstrate a credible path to an inertial operate at lower fluencies (DiPOLE ~2.5 J/cm2; confinement fusion power plant, an integrat- HAPLS ~8 J/cm2) than necessary to achieve ed design for an IFE laser beamline is needed high wall plug efficiencies. This achievement to identify potential risks, opportunities, tech- remains a critical research and development nology gaps, supply chain issues and necessary process that requires careful attention to de- developments, overall schedule and cost esti- sign details. Efficiency is determined by the mates for realizing a first-of-a-kind plant, and physical properties of the laser gain media, an estimate of the economy of scale. Design heat extraction method, heat exchange and studies must address not only the definition recirculation of the coolant and the optical of critical components, but also the scaling of design. High laser fluencies and low saturation these components with respect to aperture fluencies, as well as pump-pulse duration well and power. They would identify specific R&D below the upper-state lifetime, are ways to in- topics and enable a focus on the most prom- crease the extracted energy out of the active ising and urgent topics. Industry involvement laser medium. However, these methods are at this fundamental stage is essential for long- limited by laser-diode costs, optical damage, term success. threshold of optical materials and coatings used, amplifier cross-section, and choice of Pulse Energy laser material. For the latter, a trade-off be- Laser sources with even higher performance tween emission cross-section, energy levels levels than the DIPOLE or HAPLS laser (>1 kJ and upper-state lifetime, bandwidth, ther- and >10 kW for a single beamline) are required mos-optical properties, laser diode suitability, for an IFE power plant. These lasers have a and intrinsic efficiency must be found. The op- significantly lower market readiness level and tical path can be optimized by a homogeneous very long market horizons (7 years+). Chal- top-hat beam profile, adapted imaging, and lenges are aperture scaling of laser gain me- increasing the number of passes inside the dia, architectures for effective energy storage active medium while lowering the single-pass and extraction techniques, relay imaging and gain at the same time. Beam transport and ro- spatial filtering at very high intensities, gain bust high average power spatial filtering have isolation at large aperture and high fluence been addressed in HAPLS but scaling to full levels, and others. With adequate funding, aperture for high energy still must be demon- technology readiness levels (TRL) of 3-4 can strated. be achieved on an individual beamline level in a research environment. However, reach- Thermal Management ing TRL 5-6 and the production capability to The cooling of high-energy (>1 kJ) and high mass-produce hundreds of beamlines for an average power (>>10 kW) lasers is a challenge IFE power plant requires significant involve- due to the large amplifier cross-sections (>10 ment and investment from industry, which cm × 10 cm) and the limited ability to trans- needs to be incentivized and subsidized to port waste heat out of the optical aperture bridge these long market horizons. Developing over distances >1 cm without inducing serious a reliable and capable supply chain is another temperature gradients and thermo-optical challenging task. Despite the long market hori- aberrations. Face-cooling is the only possible zon for an IFE power plant, a large-scale coor- solution for solid-state lasers, demonstrated dinated laser development effort holds enor- with helium-cooled slabs at room-tempera- mous potential to drive spin-outs and uncover ture (HAPLS) and cryogenic temperatures (Di- novel market opportunities. POLE). Liquid cooling has been demonstrated at low repetition rates [Rus2017]. However, Efficiency scaling to very high average-power and ener- Achieving greater than 10% wall-plug effi- gies requires increasing the mass flow of the ciency (see above for definition) has not been coolant inducing increased perturbations and 99

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MEMORANDUM LASER INERTIAL FUSION ENERGY system complexity. Cooling outside the beam back reflection mitigation for 1ω short-pulse path in an active-mirror geometry and liq- drivers using the Pockels and/or Faraday ef- uid-cooling could be an alternative approach, fects is critical for high efficiency laser archi- but mounting-induced strain and scaling to tectures. However, the combination of high large apertures require new technical solu- average power and large aperture required tions. The same accounts for optically separat- for DPSSLs presents a significant challenge. ing the dominating waste power by dumping Currently, no gain isolation or polarization fluorescent radiation and ASE of the amplifier switching device or passive polarization con- from the heat generated by the laser process trol through half- and quarter waveplates is itself. available that can accommodate aperture siz- es >10 cm × 10 cm and operate at fluences >10 Gain Materials J/cm², and average power >100 W/cm². There- DPSSL designs suitable for laser indirect drive fore, there is a need to develop alternatives or offer a high level of technical readiness for the advancements to current plasma Pockels cells. near-term construction of a fusion pilot plant. Currently, most designs rely on Nd:Glass as Ultrashort Laser Pulse gain media, which is the only laser gain materi- Generation for Fast Ignition al produced at scale in large quantities and of Schemes sufficient optical quality. Nd:Glass is compati- To achieve high intensities for fast ignition ble with commercially available diode pump- schemes, laser drivers require short pulses ing. However, there are drawbacks such as the using chirped pulse amplification (CPA) mode. short gain lifetime, average power-induced This amplifies broadband, chirped pulses and phase distortions, and stress birefringence uses a grating pulse compressor to achieve in- that affect beam quality. These issues are tensities above 1019 W/cm2. Nd:glass and Yb: bypassed by cryo-cooled Yb:YAG in DiPOLE, CaF are gain materials for these type of lasers 2 however requiring a more complex amplifier due to their mature technology and broad cooling scheme to achieve cryo temperatures, bandwidth, while Yb:YAG at room temperature affecting efficiency along with the need for is also viable, but has not been demonstrated mitigating power caused by parametric lasing. at diameters consistent for energy extraction Another consideration for gain media is the of kilojoules and beyond. High wall-plug effi- need for mitigating laser-plasma instabilities ciency >5% for CPA lasers is difficult to achieve requiring broadening the frequency spectrum and inherently less than DPSSL driver lasers. of the laser pulse. Nd:Glass has a much larg- Furthermore, the use of diffraction gratings er gain-bandwidth than Yb:YAG. However, if to compress the pulse and focusing with re- a 100-200 GHz 3ω bandwidth would be suf- flective optics near-by the reaction chamber ficient for controlling plasma instabilities with is needed, which poses challenges for optics increasing laser drive power and energy, it may survival and integration into blanket systems. be possible to replace Nd:Glass with alterna- Despite presenting lower LPI problems, isolat- tive longer storage gain media. Increasing the ing the laser against 1ω back reflections from storage lifetime of the gain medium allows for a target remains a challenge that requires mit- the use of lower diode pump power, signifi- igation studies. It is recommended to develop cantly reducing the quantity of diode pumps conceptual system architectures and perfor- and therefore the total diode cost. Additional- mance studies for high wall-plug efficiency ly, increasing the gain cross-section allows for CPA lasers that align with the requirements of higher extraction efficiencies or lower inten- Fast Ignition while experiments are ongoing to sities inside the amplifier, increasing lifetime. validate the expected physics concepts for the However, an “optimal” solution will be derived various FI-fusion concepts. from target physics requirements. Cost & Mass Production Gain Isolation & Switching To achieve the most economic trade-off be- Achieving active gain isolation, switching, and tween pulse energy and number of beam- 100

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS lines, all system components must undergo failure rate. corresponding mass production cost optimization, and corresponding mass technology must be developed. Additionally, a production technology must be developed. large number of beamlines can offer addition- Additionally, a large number of beamlines can al functionalities such as independently deliv- offer additional functionalities such as inde- ering wavelengths or higher fault tolerance pendently delivering wavelengths or higher despite an increased statistical failure rate. fault tolerance despite an increased statistical 6.5.4 Capabilities and Competencies in Germany Germany has a strong research focus on pho- manufacturing technologies, laser material tonics including high-energy laser technology, processing and high power coatings. with several institutions and universities con- » Ludwig Maximilian University LMU Munich ducting research in applying these capabilities and Center for Advanced Laser Applica- to supporting experiments on shock-physics, tions (CALA): Research on high-energy and astrophysics, materials at extreme conditions, high-peak-power laser systems and the laser-particle acceleration, production engi- application to laser-particle acceleration, neering, EUV-generation, medicine and life X-ray generation and high-field physics. science, and more. Some notable examples » Max Planck Institute of Quantum Optics for institutions in Germany include: (MPQ): MPQ conducts research on high-in- tensity laser physics, including the develop- » GSI Helmholtz Centre for Heavy Ion Re- ment of high-power laser systems for parti- search in Germany and the Helmholtz-In- cle acceleration, laser-driven fusion energy, stitute Jena conduct research in laser and the study of extreme laser-matter in- development, particularly in the field of teractions. high-energy lasers for applications in high » Technical University of Munich (TUM): TUM energy density science, warm dense mat- has a strong focus on research in high-peak ter research, laser-driven secondary sourc- power laser physics, including the devel- es and their applications in medicine. opment of laser systems for fusion energy, » Helmholtz-Zentrum Dresden-Rossendorf laser-driven particle acceleration, and the (HZDR): The Institute of Radiation Physics study of ultrafast laser interactions with at HZDR conducts research on laser-driven matter. ion acceleration, laser-plasma interactions, » Ferdinand Braun Institute Berlin (FBH): and the development of high-power laser FBH’s main research activities include de- systems. sign of high power laser diodes, manufac- » Fraunhofer Institute for Laser Technology turing and packaging of laser diode bars (ILT): ILT focuses on the development of and packaging of micro optics high-power lasers and laser systems for » Institut für Strahlwerkzeuge (IFSW) Stutt- industrial applications, laser systems engi- gart: IFSW conducts research in the area of neering for aerospace, as well as research high power solid state lasers with a focus on laser material processing including la- on ThinDisk and fiber lasers. ser-based additive manufacturing and la- ser-based optics manufacturing. On the industrial side, Germany is one of the » Fraunhofer Institute of fine mechanics leading optics and lasers manufacturer, inte- (IOF): IOF focuses on the development of grator and system developer. Companies with fiber-based high-power lasers for industrial key expertise in fields relevant to fusion lasers applications, as well as research on preci- are: sion optics development » Laser Zentrum Hannover (LZH): LZH con- » TRUMPF: A leading global company in la- ducts research on laser systems for indus- ser technology for industrial applications, trial applications, as well as laser-based with headquarters in Ditzingen, Germany. 101

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MEMORANDUM LASER INERTIAL FUSION ENERGY TRUMPF offers a wide range of lasers for » Laser Components GmbH: a supplier of various industries, including manufactur- components for laser technology, including ing, aerospace, and electronics. optics and coatings. » Coherent: A global supplier of laser-based » Layertec is a German company that special- solutions for a wide range of industries, in- izes in optical components and coatings, cluding semiconductor, microelectronics, including high-precision thin-film coatings and medical. Coherent is headquartered in for laser optics. Layertec is considered a Santa Clara, California, but has a significant leading supplier of high-end optical coat- presence in Germany, with various loca- ings and has partnerships with several key tions in Germany. players in the laser industry. » Jenoptik: A German company with exper- » Laseroptik is a manufacturer of high LIDT tise in photonics and laser technology for (laser induced damage threshold) laser industrial applications, healthcare, and optics and coatings from VUV to IR for in- defense. Jenoptik offers a range of lasers, dustry, medical technology and scientific including high-power diode lasers and ul- research. trafast lasers. » AMS OSRAM is a global leader in high pow- » Laserline: A German manufacturer of er diode lasers with production capabilities high-power diode lasers for industrial ap- for large numbers of single emitter diodes plications, including welding, cutting, and as well as diode lasers arrays additive manufacturing. Laserline is head- » IPG is a global leader in industrial fiber la- quartered in Mülheim-Kärlich, Germany. sers providing the full value chain from di- » Heraeus: Provides materials and compo- ode laser emitters to industrial high power nents for lasers, such as laser crystals, fi- lasers up the multi-100 kW continuous out- bers, and optics. put power » Schott: Supplies glass materials for laser components, such as laser-glass, laser win- Both lists represent only a snapshot of private dows and lenses. laser- and optics industry and is by no means » ZEISS is a well-known company in the field considered complete. of optical manufacturing. The company has a long history of innovation in optical tech- These companies are leaders in the develop- nology and is considered a leading manu- ment and production of lasers and optics for facturer of optical components, systems, various applications, including industrial man- and solutions, as well as an innovator in the ufacturing, scientific research, and medical design and construction of complex optical applications. They have a significant impact instruments and systems. on the German economy and the global laser » OptoTech Optikmaschinen GmbH: a manu- market. facturer of machines and systems for preci- sion optics, including polishing and coating machines. 6.5.5 Industry Led R&D for IFE Germany is already a major player in the glob- provement of quality and productivity of large, al laser market with a market share of 40% in high quality optical components will boost the Europe. These companies, along with many development of optical materials and coat- more German companies leading in lasers, op- ings, automated production processes as well tical materials, optics manufacturing, produc- as sensing and inspection methods. The de- tion machines and other enabling technologies velopment of IFE laser drivers could further would benefit from an increased demand for strengthen Germany‘s position in the market high-power and high-energy lasers required by driving the development of new and more for IFE. The significant and simultaneous im- advanced laser technologies, as well as foster- 102

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS ing collaborations and partnerships between Overall, the development of laser drivers for companies, research institutions, and govern- IFE will have a significant impact on the pho- ment agencies. These activities can only be re- tonic and its supply chain industries, specifi- alized in close collaboration with industry and cally in Germany, providing new opportunities cannot be achieved by research institutions for growth and innovation, while also address- alone. This could spur further innovation and ing global energy and environmental challeng- advancement in laser technology, leading to es. It has the potential to position the country increased competitiveness in the global mar- as a leader in high-power laser technology, in ket. Additionally, the development of IFE tech- both academia and industry. nology could lead to new job opportunities within the laser industry in Germany, boosting the country‘s economy and contributing to its global leadership in the field of photonics. European photonicsmarket Market shareby country, 2019 Key figures, 2019 Key figuresGermany, 2019 Rest ofEurope Finland(1%) Photonicsmanufacturers Spain (2%) Sweden(2%) 10% Germany Photonicsproduction ca. 1,000 Switzerland €103 billion 4% Italy 5% 40% Numberofemployees Netherlands 6% Numberofemployees 161,000 > 390,000 15% 15% Sales France €40 billion Growth since2015 United Kingdom 7% / year Fig. 23: European Photonics Market 2019 and numbers of German Photonic Industry [Spe2021]. 6.5.6 Findings and Recommendations Germany and the EU have a strong presence in sources, which generate high-energy photons, the fields of optical component design, man- electrons, neutrons, or ions through the inter- ufacturing, and high-precision, high average action of high-peak power lasers with matter. power laser sources for commercial material These sources are now experiencing success- processing and metrology. While this provides ful commercial applications and expected to a solid foundation for laser source develop- transition from basic research to applied tech- ment in laser-driven inertial fusion power nology in the coming years. plants, there is a need for a functional engi- neering ecosystem that specifically addresses Developing IFE drive lasers requires advance- the requirements of lasers that combine high ments in various components and optical energies (>100 J) and high average powers technologies, such as optical materials, non- (>1 kW). However, the market for lasers with linear crystals, and coatings for reflectors and these parameters has only recently emerged, anti-reflection. To ensure their long-term per- primarily in the field of laser-driven secondary formance and reliability, accelerated lifetime 103

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MEMORANDUM LASER INERTIAL FUSION ENERGY testing is necessary, which involves exposing high wall-plug efficiencies. This facility should the laser components to higher stress levels complete within 4-5 years to support IFE and operating conditions to identify any po- beamline development. tential weaknesses or failures before deploy- ment. This testing helps in reducing the risk To make a design decision for laser beam- of costly failures and downtime in the future. lines for an IFE power plant in ten to twelve Therefore, it is recommended to develop an years, we propose implementing two identical accelerated lifetime test laser facility that can beamline demonstrators operating at similar scale from current high power laser architec- output characteristics. These demonstrators tures and known materials, without requiring should replicate the beamlines to be used in AcceleratedLifetime Test Capability Development Development ofFull-ScaleBeamline Development ofModeling Prototypes and Simulation Capabilities Target Experiment Beamline Laser Development Beamline 16.0 Bitte passen Sie die 5.20 Dokumenten-Klassifizierung mit 23 Hilfe des Add-ins an, siehe Folie 3 Seite 16.05. Bitte passen Sie die Dokumenten- 1 2023 Klassifizierung mit Hilfe des Add-ins an, siehe Folie 3 Start Year 5 Year 10+ 104 Design Decision Target Develop- ment ConceptualDesign Lasers Physics Basis Development Beamline Key Component operations Demonstrators Target Tracking and Beam Steering R&D and Demonstrators noitaulavE ecnamrofreP AcceleratedLifetime TestingofComponents Development ofKey Optical Components Short Pulse Laser Development Fusion Physics Advancement

1. FullScaleIgnitionExperiments ConceptualDesign IFE BeamlineDesign
2. LPI Mitigation Studies IFE Beamlines forPower Plant
3. Fast IgnitionPhysics
4. ….. Performance ScalingofPump Diode Technology ScalingofPump Diode ProductionCapability Development ofPower Plant ScaleTarget Tracking and Beam Steering Technology Laser Performance Scalingx5 Laser Performance Scalingx10 (Materials, Architecture) (aperturescaling, thermal) Legend: Development Effort Testbed/demonstrator capability Fig. 24: Recommended course of action for developing an IFE beamline concept for fu- sion power plants, building on a multi-pronged approach of technology development, testbeds and phased performance scaling.

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS the IFE power plant, including output energy, ments for an IFE power plant laser source (en- repetition rate, and efficiency. Depending on ergy, efficiency, beam quality, bandwidth,…). diode prize development, a smaller aperture This could start from a re-evaluation of LLNL’s may be used to lower costs, but all technol- LIFE study [Bay2011], [Erl2011] with respect to ogies used on the beamline must be capa- changing laser require¬ments due to recent ble of being aperture scaled for use in an IFE findings in fusion research (e.g. larger band- beamline. Consequently, any new technol- width require¬ments) and advances in laser ogies must have a well-defined and practi- and component technology. Moreover, an ex- cal development plan attached to them. The perimental verification of the feasibility of the first beamline, called the “Laser development laser design proposed in the LIFE study (very beamline,” will evaluate laser architectures, al- high fluences to reach required efficiencies) low for continued R&D, process development with a reduced aperture prototype operating and optimizing laser performance, as well as at similar fluence and efficiency is recommend- test laser components. The second beamline, ed. Implementation of the demonstrators will known as the “Target experiment beamline,” be followed by an experimental performance will have a scaled target chamber and will evaluation (years 8-9) succeeded by a design serve as a testbed for target experiments and review (year 10) based on the findings of the IFE diagnostics. The aim of this dual beamline evaluation phase, which allows for optimiza- approach is to create a testbed facility with tion of the beamline design prior to making a two beamlines: one for laser research and de- final design decision for beamlines for an IFE velopment, and the other for target develop- power plant. As similar development efforts ment and testing, which will be efficient and are expected to occur globally, it is crucial to effective. compete in terms of performance, reliability, availability, maintainability, and cost. The demonstrator implementation (years 4-8) will be preceded by a design study (years 1-3) In the following we list the core findings and evaluating different laser architectures (gain recommendations to achieve the final goal of material, active medium geometry, cooling delivering critical technologies is support of a architecture, pump architecture, amplifying cost competitive and industrially manufactur- beam path,…) with respect to the require- able IFE beamline: 6.5.6.1 Design Study Finding Worldwide, there hasn’t been an integrated laser system design study for driving IFE conducted since the LIFE study in 2012, while in Germany an integrated study has never been carried out. Recommendation Develop a comprehensive conceptual design study for a laser system(s) capable of driving an IFE powerplant including the physics case and a cost model for the architecture. Identify risk centers and potential R&D to buy down risk. The first step is to perform competitive sys- HAPLS in the US. High-level conceptual design tem engineering concept studies for an IFE studies are essential to identify and refine po- laser beamline, including transport and fo- tential paths forward and the most promising cusing systems. These studies should take the IFE concepts. tremendous progress made over the last de- cade in high energy (>100 J), high repetition The conceptual design study of the IFE driver rate (>10 Hz) and high average power (>1 kW) architecture aims to achieve total cost-effec- lasers such as Mercury, DiPOLE in the UK or tiveness. However, it is also important to re- 105

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MEMORANDUM LASER INERTIAL FUSION ENERGY view the different design prospects and limits, using off-the-shelf optical components could such as the supported bandwidth or control of spur competitive commercial development other beam parameters. Versatility is critical leading to economies of scale with high-vol- for alternative approaches to fusion energy, ume manufacturing that would benefit indus- such as direct drive and fast ignition, as well as trial and other applications for nanosecond for secondary applications in science and in- lasers of this scale. dustry for high-speed processing and extreme states of matter. Furthermore, the impact on design architec- ture by laser packaging, reliability, availabil- For example, laser direct drive (LDD) with ity, and maintainability must be considered. hot-spot ignition or shock ignition offers the The conceptual design must account for the potential for high-gain performance for com- reliability and longevity demands of continu- mercial power production, indicating a ~5× ous operation in a power plant environment. higher laser energy coupling compared to in- Thus, the laser system must be highly modu- direct drive schemes (see Sec. 5.2). However, lar – both on a beamline-level as well as on laser plasma instabilities pose a challenge to a subassembly-level. Each beamline must fit realizing the higher coupling efficiency poten- the standard maximum dimensions of trans- tial. Broadband laser irradiation may mitigate portation and need to be hot swappable with these plasma instabilities and improve target standardized interfaces. For fast service the irradiation uniformity. Besides new concepts beamlines of different suppliers should be in- like optical parametric amplification and sum terchangeable. Likewise, the beamlines should frequency generation of a single aperture, a be composed of as many modular subcompo- laser system consisting of more, but smaller nents as possible, easing off-line service at site aperture beamlines can deliver broadband and stock holding. The system design must irradiation by combining the output of lasers avoid all causes of component deterioration operating at many discrete wavelengths span- such as sputtering or radiation exposure of ning the required spectrum. The modular ap- optical components. Moreover, system design proach provides scalability across a range of should minimize interlinkage of component IFE facilities to enable complex pulse shapes, failures and damage to assure for fast resto- many wavelengths, and focal spot zooming to ration in case of component damage. optimize LDD drive. The large number of lasers 6.5.6.2 Simulation and Modelling for Design, Evaluation, and Control of the Laser System Finding The proposed high energy laser is a very complex technical system – with respect to design of the individual components, data evaluation for the overall system, and control of the adaptive elements during operation (de- formable mirrors, diode laser operation for adaptive pumping, …). Recommendation To design and operate such a complex cyber-physical system sophisti- cated simulation tools and models need to be employed and developed. The concept and design phase must be accompanied by modeling and numerical simulations. This includes the main components and process- es: High-power diode pumps, laser amplification, laser beam propagation, cryogenic cooling, nonlinear frequency conversion. Most of the numerical tools for the simula- ed and extended for the specific purpose. tions are available but may need to be adapt- Computational Fluid Dynamics (CFD) codes 106

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS (OpenSource and commercial) can be used turn control instructions, for example for the out of the box, but especially the modeling adaptive optics for wavefront correction. The of turbulence requires experience. A special overall system consisting of master oscillator, challenge for the simulation of optical prop- pump modules, amplifier, frequency conver- agation is the large apertures in the system. sion, focusing, etc. and many necessary sen- Besides software for multi-physics simulation sors reaches a level of complexity that needs of the laser operation, beam propagation, and active control. A large amount of sensor data fluid-dynamics (for the cooling concept), novel must be collected, evaluated in real time and concepts from the field of data science includ- fed back into the control system. ing solutions based on artificial intelligence (AI) are used to evaluate and process the data stream from a variety of sensors and re- 6.5.6.3 High-power Diode Pump Sources Finding The cost of semiconductor lasers for pumping an IFE powerplant size facil- ity is prohibitive currently. Recommendation Establish an R&D program to reduce the production costs of semiconduc- tor laser pump modules suitable for IFE-DPSSL technologies. To achieve an economically feasible fusion that rests on the following development areas: powerplant, the diode laser technology needs to provide robust, high reliability and long » Improving electro-optical efficiency to val- performing high-power pump sources at af- ues around 70% at high brightness through fordable price points. Compared to the state novel chip and epitaxial design and through of the art today (500 W/bar, lifetime of 2.2 enhanced thermal management technol- Gshots in QCW mode [Kou2021], cost of 0.4 ogy. Modeling the complex interplay of $/W,efficiencyof55provementsarenecessary,especiallyregard-withinthedevicesrepresentsakeymeth-inglifetime(7\times increase)andcost(50\times de-odtorapidlyidentifypromisingnewdesigncrease)[Hae2022].Toputthisinperspective,concepts.adiodepumped,NIFscaleimplosionfacility»Advancingdiodereliabilityandmean-time-pumpedwithdiodesinsteadofflashlampsto-failure(MTTF)assuranceviaimprovedwouldrequirediodesworth$20B at today’s crystal growth, advances in facet passiva- market price, plus the power forming net- tion technologies, optimized package de- work. To support the production of a single velopment, and establishing of test facili- fusion powerplant, the annual global output ties to validate the new designs. of high-power bars must increase by 25 times. » Reducing cost of diode production through This would require significant automation of the development of advanced manufac- the entire chip production process, with a par- turing processes and technologies that im- ticular focus on the assembly and packaging prove fabrication yields. steps, which currently account for the majori- » Developing a standardized industrial supply ty of the expenses (around 90%), Fig. 25 right. ecosystem that includes multiple sources The whitepaper [Hae2022] jointly developed of standardized pump diode components. by public research and private industry con- cludes that it is possible to achieve high power More information can be found in the afore- laser diode manufacturing costs of <$0.05/W mentioned whitepaper. 107

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MEMORANDUM LASER INERTIAL FUSION ENERGY 1 1000 0,1 100 0,01 10 0,001 1 2010 2015 2020 2025 2030 2035 108 ]W/$[tsoC]raeY/WM[emuloVnoitcudorPCostBreakdownofPumpmodul1008060TargetforIFE4020Year0noitazilateM,yxatipE0.4$/W tecaF,noitalugniS knistaeHhtiw edoiD eludompmuP ylbmessA 1 0.1 0.01 0.001 Fig. 25: Evolution of cost and production volume (left) and cost breakdown of high-power pump modules (right). Based on [Hae2022]. 6.5.6.4 Optical Components Finding A large number of optics and optical components are needed for an IFE laser system. Disruptive technologies for manufacturing those with high precision, high repeatability and consistent with high fluence laser opera- tion or consistent with the aggressive environment around the fusion tar- get chamber have to be developed, allowing economic and fast produc- tion of large optics in high volumes. Recommendation Establish an R&D initiative that leverages Germany’s extensive expertise in optics manufacturing to establish an IFE optics manufacturing center of excellence. The center will cultivate the skills and capacity to mass-pro- duce optics for IFE power plants. Disruptive technologies for manufacturing Besides the production process of the optical optical components have to be developed, al- components their surfaces and coatings must lowing economic and fast production of large fulfill high requirements in terms of absorp- optics (diameter >200 mm and larger) in high tion, optical damage thresholds and reliability. volumes and consistent with IFE laser specifi- Low absorption of passively cooled compo- cations. Approx. 10,000 optical components nents is critical due to the high average pow- of this size are required per facility, in addition er. A damage threshold as high as possible is to ~30,000 small optics. Innovative manu- an absolute must have for high laser efficiency facturing technologies like laser-based optics and small footprint. For reliable long-term op- manufacturing or precision molding combined eration, the density of defects must be as low with state-of-the-art grinding, polishing, MRF as possible. Critical defects, which can grow and IBF processes have the potential to form during operation, must be avoided in the final new process chains and overcome the limits optics. For mass production of the demanding of today’s optics manufacturing. For economi- surfaces and coatings on large aperture optics cal implementation and minimized down time with high yield intensive development of pro- during operation also novel packaging and cess, manufacturing techniques, automation alignment concepts need to be developed. and material sourcing is necessary.

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS In terms of passive amorphous materials used The frequency conversion of infrared laser ra- for beam delivery, only a few rad-hard glasses diation into the ultraviolet using energies >>10 like fused silica and cerium stabilized glasses J in combination with high repetition rates are available. While fused silica is highly trans- (about 10 Hz) and thus high average powers missive in the UV, stabilized glasses are avail- (>>100 W) is significantly limited by the avail- able with high index of refraction. New optical ability of suitable nonlinear crystals. In recent materials need to be developed which com- years, nonlinear media such as deuterated bine these properties. KDP, YCOB, and LBO have been identified and tested as potentially suitable nonlinear media, Neodymium doped phosphate glass is the although crystals made of these media have active laser medium for most high energy la- limitations in specific aspects in each case. For sers. The main benefits are comparably low example, the maximum allowable fluence ap- cost and availability in large dimensions and plied onto a crystal is limited by the laser-in- repeatable optical quality. Laser crystals on duced damage threshold of the material and the other hand have comparable high thermal optical coatings. Therefore, the maximum conductivity and lower induced thermo-op- available aperture of the crystal determines tical aberrations at the expense of time-con- the maximum achievable pulse energy in the suming crystal growth and limited apertures UV. For use in an IFE laser facility, nonlinear if conventionally grown. Edge-defined film- crystals must be fabricated with volumes or fed growth (EFG) offers the possibility to grow apertures scaled up by an order of magnitude crystal sheets with larger dimensions, but this while reducing the residual linear absorption technique was so far only demonstrated for to keep the thermal load low. In the case of limited materials. Laser ceramics are in be- LBO, high quality crystals with apertures well tween glass and monocrystalline materials, beyond the state of the art of 100 cm² have to they can be produced in larger apertures with be produced to be able to apply the full ener- almost the same performance compared to gy of a beamline at a fluence consistent with the base material. Research also needs to fo- the damage threshold. In addition, the cur- cus on the reduction of scattering losses and rent fabrication process must be refined, or a aligning of crystallites. To date Nd:Glass and new process developed, so that the number cryogenic cooled Yb:YAG/ceramic are the best (>1000) of large aperture, high quality nonlin- possible choices in terms of economical re- ear crystals required for an IFE laser facility is spective performance reasons. Overall, a suit- compatible with a production time of well un- able aperture and production scalable gain der one year. material must be developed. 6.5.6.5 Final Optics Finding For reliable long-term operation of IFE power plants, final optics near the reaction chamber are needed that withstand high neutron and UV fluenc- es. These components must be available in large size (approx. 500 to 1000 mm) and large volume. Recommendation Significant progress in the development of rad hard glasses is mandatory, e.g., developing of rad hard materials with high damage threshold, trans- mission and index of refraction. Economic mass production technologies of these materials and the optical components made of them shall be de- veloped, including low absorptive optical coatings which can withstand both high UV fluences and intensive neutron irradiation. 109

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MEMORANDUM LASER INERTIAL FUSION ENERGY To facilitate the advancement of high-ener- proving the performance of HEL systems. gy laser (HEL) systems, significant focus is re- quired in materials research for optics. This Furthermore, it is essential to develop auto- involves exploring novel materials such as ul- mated optical assembly and optomechanical tralow absorbing glasses and developing mass fixture methods that align with automated production methods for molded or 3D-print- optics placement and ensure consistency in ed optics. Additionally, it is crucial to conduct precision, repeatability, cost reduction, clean- research on self-healing optics, particularly for liness, and high RAMI of the systems. Hence, radiation resistance, to enhance the durability research and development in this area must of HEL optics. Tailored optics and active media be emphasized to advance the practicality development also hold great potential in im- and effectiveness of HEL. 6.5.6.6 Accelerated Lifetime Test Facility Finding A high repetition rate (minimum 10x of IFE pulse repetition rate) capability is needed to perform materials testing in IFE-powerplant-like conditions as well as establishing expertise and train talent. Germany operates only high energy laser systems that are low repetition rate and based on outdated technology not suitable for IFE. Recommendation A high power accelerated lifetime tester should be designed and built to explore, research, develop and gain experience in energetic high power laser operation as well as establishing essentially important science and technology testbed facilities: To provide accelerate lifetime testing capa- bility as a user facility to industry, public research institutions, and interna- tional partners. This capability would establish a Unique Selling Point for a capability no one else in the world has. Furthermore, these facilities are urgently needed to test concepts of big-data machine learning tools and train talent. In order to test the durability and reliability of erated by an increased repetition rate, which the materials and components, an accelerat- can be around 1 kHz. Thus, being much higher ed lifetime tester provides a faster and more compared to the power plant operation point. efficient way to simulate years of wear and This repetition rate should be increased by the tear in a shorter period of time, ultimately im- same factor by which the pulse energy (and proving their design and performance for the fluence) is reduced, yielding the same average IFE power plant while saving time and costs power as the power plant beamline. Since cost associated with long-term testing. is scaling with laser output energy strongly and with repetition rate only weakly, this laser This accelerated lifetime tester should be a will provide fundamental insights to high pow- beamline established to evaluate the optics er laser development for IFE at reduced cost degradation and estimate and validate the compared to an IFE beamline. Additionally, mean time between failures (MTTF) and mean there is the potential for spinouts/spin-offs, as time to resolve (MTTR) by the means of in- the prototype could serve as a high brilliance tense studies. The tester should be capable of secondary source driver or be relevant to a delivering fluence equivalent to power plant driver for a much more efficient EUV source beamline operation point, but in a reduced driver (compared to the only a few % efficient area compared to power plant beamline, typ- CO lasers). 2 ically around 0.5-5% (i.e., approximately 50- 500 J). The deterioration effects can be accel- 110

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS 6.5.6.7 Full Scale Beamline Prototypes Finding An IFE laser testbed facility is needed to study and optimize single-beam laser technologies, performance, target design, and diagnostics at rele- vant energy and pulse repetition rate. Recommendation A two-pronged approach should be taken to explore, research, develop and gain experience in energetic high power laser operation, as well as es- tablishing essentially important science and technology testbed facilities. Furthermore, these facilities are urgently needed to train talent. To reduce risks associated with both the driver ity, maintainability, and inspectability (RAMI) and target in the development of an IFE power models to ensure safe and efficient operation. plant, it is recommended that two demonstra- Economic evaluations will also be conducted tor facilities be established using a dual beam- to determine cost-effectiveness and scalabil- line approach. These facilities will provide ity. researchers with a test bed to study and op- timize laser performance, target design, con- The second demonstrator facility will focus on trol systems, and diagnostics at scale, which is target and diagnostic experiments and serve crucial for mitigating potential failure risks and as a specialized beamline dedicated to deliver- increasing the likelihood of success. ing a high-availability laser driver to the target. It will incorporate advanced technologies such The first facility will be a laser development as active target tracking and fast laser steer- beamline, designed at an IFE scale to demon- ing to enable precise targeting of high-veloc- strate the viability of various laser architec- ity moving targets, facilitating the acquisition tures and components for a fusion power of highly accurate and reliable experimental plant demonstrator. This facility will utilize a data. Additionally, the facility will facilitate single beamline with scalable components to various target studies, including target design, evaluate full packaged product (FPP) driver code validation, and diagnostics. performance and optimize reliability, availabil- 6.5.7 Conclusion and Summary Competitive R&D involving universities, re- Russia, and China, with growing investment search institutes, centers and industry fo- from the public sector and private-public cused on high energy and high-power lasers is partnerships. To avoid falling behind in the essential to create an ecosystem for the devel- field, particularly in inertial fusion, Germa- opment, production and supply chain of such ny needs to increase its commitment swiftly. lasers and beam delivery systems. Strength- Though needed for IFE research, creating in ening and complementing the optics and la- the short-term a NIF-scale implosion facility ser expertise in Germany through high-ener- for inertial fusion is unrealistic due to the re- gy laser engineering and science programs at quired resources and expertise. Instead, Ger- universities is a prerequisite. In addition, sub- many should focus on its existing expertise stantial and sustained development programs in laser and optics technology to achieve ICF allocated by scientific societies in Germany fusion research goals. To foster international are necessary. partnerships and establish USPs for Germany, an R&D program for an IFE drive laser is need- Inertial fusion is increasingly programmatic ed with strong participation and engagement in other countries like the USA, UK, France, from the private sector, including a technolo- 111

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MEMORANDUM LASER INERTIAL FUSION ENERGY gy roadmap and the realization of two beam- ties in the laser industry in Germany, as well as lines for IFE laser development and for target increase the country‘s competitiveness in the physics development. An accelerated lifetime global laser and optics market. This will spur test infrastructure must be built to enable ma- innovation and further advancements in laser- terials and component testing, as well as pro- and optics technology, which benefit not only viding training capability for next generation the IFE industry but also other industries that talent. The 10-year milestone is a beamline rely on lasers, specifically in manufacturing, design for an IFE power plant. security, and healthcare. Furthermore, the development of laser drivers for IFE expected to create new job opportuni- 6.6 Fusion Power Plant 6.6.1 Role of Fusion Power Plant in IFE This topic has been approached from two per- other options like production of hydrogen spectives: fuels can be attractive. » More generally, the term ‘Fusion Power » In the IFE onion, it is the outermost shell Plant’ is used to describe the FPP holisti- in which the high-grade heat generated by cally as an installation that converts fuels fusion processes is converted into a usable into usable energy. Such an overall picture end product, sometimes also referred to of an (IFE) FPP is important to both guide as Balance of Plant (BoP). The standard as- the integrated design on a conceptual level sumption is that this will be electricity, but as well as to characterize how the FPP will it was pointed out during several expert fit into the future energy market demands. hearings that in the future energy market, 6.6.2 R&D Status Worldwide Balance of plant: assuming that the primary IV fission), or start some dedicated research product of the FPP ‘engine’ is high grade heat since Helium cooling is not standard for large (i.e. neglecting direct conversion of charged plants today. This is even more pronounced particle energy into electricity), the balance of for other coolants. plant should have large similarities with that of a fission plant in that it converts the heat Holistic model: there is no standard ‘systems transported out of the reaction chamber in code’, i.e. a tool that combines in a consistent the form of a coolant into the final product integrated way the physics and technology as- (e.g. electricity). Thus, it is expected that the sumptions about the different shells of the on- needed technology is readily available and ion. Individual studies (such as LIFE) have cer- does not need targeted development specific tainly had such an approach to some degree, for IFE FPPs4. but it is not available. Such codes exist for MFE (e.g. the PROCESS code [Kov2014] which is the This statement is strictly only true for water standard tool used in the EU), and might, on a as a coolant, which is standard in other large conceptual level, be used as a model for set- power plants. Assuming Helium cooling, one ting up an equivalent IFE code. either has to assume that this technology will be developed for other customers (e.g. Gen Also, no description of an IFE plant as a part of 4 We note that this split of the onion means that all challenges of converting the fusion power into a heated coolant are dealt with by the blanket/reaction chamber section(s). 112

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS the energy system exists. Again, this is avail- power generation and shutdown in terms of able for MFE [Ker2023] and the basic approach timescales and energy flows) could serve as a (Characterization about start-up, steady state model. 6.6.3 Capabilities and Competencies in Germany and Europe Balance of plant: extensive infrastructure ex- fusion technology. ists with the Balance of Plant described above in industry in Germany and worldwide. In a Holistic model: the absence of such a model hearing of the Expert Group with one large was already pointed out above. The German German company, it was stressed that there is competence in Laser technology and target at present interest to engage in the Balance of fabrication could be used to give input to the plant part, but not in the building of a whole corresponding modules of a systems code. IFE FPP. It was also stressed that the present The same is true for elements that are com- environment in Germany is not viewed as fa- mon with MFE and for which expertise exists vorable to engage in a nuclear technology5. in Germany or the EU (MFE in Germany is well This goes together with a decline in educated embedded in the EU fusion program), such as (and educating) workforce in Germany in the outer fuel cycle or, to some degree, the blan- nuclear sector, which will have to be reverted ket. in case Germany enters as key player in any 6.6.4 Industry Led R&D for IFE Balance of plant: for water cooled solutions, Holistic model: since the elements of balance there is no specific need for industry led R&D. of plant exist in industry (with the caveats For He cooled concepts significant contribu- about the coolant choice made above), indus- tions could come from industry engaging in try can supply models to both the systems this area in the frame of other power plant code as well as the description of an FPP in an studies, such as Gen IV fission. It could be use- energy system. This will however not require ful to look for alliances in this area. substantial R&D. 6.6.5 Findings and Recommendations Balance of plant: as mentioned above, the gap Such a systems code is a must for any system- for He cooled balance of plant could be ad- atic study of IFE FPP options. We strongly rec- dressed together with partners (industry or ommend that Germany is an active partner in research) who have an interest there as well such a collaboration and brings in its expertise (e.g. Gen IV fission). outlined above. Holistic model: both the systems code and the This recommendation is consistent with BRN description in the energy system would ideal- PRO 6-5 “undertake a series of system-design ly be developed in international collaboration, studies to establish a suite of self-consistent involving the key players who have already quantitative IFE plant models”. engaged in IFE on a conceptual level (US, UK, Jp). This would ensure that existing expertise For completeness, we list here the findings is used, and might lead to a unified standard and recommendations of the section on tool that can be used by all involved parties. “Power Plant”. 5 For the supplier, this was a strong argument for the use of aneutronic fuels. 113

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MEMORANDUM LASER INERTIAL FUSION ENERGY Finding The readiness of the balance of plant depends crucially on the chosen coolant concept. Recommendation Establish a process for down-selection of the coolant concept and clarify the impact of the choice on the development needed for the Balance of Pant. Finding There is no openly available systems code for a description of the whole plant. This is needed to study various options and prepare their down-se- lection. Recommendation Establish a systems code, preferably in international collaboration with the aim to produce a standard that is used in studies worldwide. Finding There is no description of the characteristics of an IFE plant in the future energy system. This is needed in studies of how IFE plants would fit in there. Recommendation Establish a model of an IFE plant that can be used in energy systems stud- ies. 6.7 Diagnostics, Data Acquisition and Interpretation 6.7.1 Role of Diagnostics in IFE To examine the extreme conditions of ICF im- in scaling to such high gains from the current plosions, measure the subsequent output of state must be bridged. The NIF and other large energy and particles, and to understand and scale laser facilities (such as Omega or LMJ) quantify the input parameters, exquisite and possess a suite of diagnostics that exquisite- sophisticated measuring devices are required. ly measure x-rays, neutrons, gammas, optical Such diagnostics are highly specialized instru- light, and more, to infer plasma temperature, ments, that must operate in timescales down density, shape, stagnation time, hydrodynam- to nanoseconds (billionths of a second) or ic mix, pressure, hot spot velocity, uniformi- shorter, detect interactions often below the ty, yield, etc. There are over 100 diagnostic submicron level (millionth of a meter), and be instruments on the NIF, that played a pivotal capable of withstanding bombardment by in- role in providing the understanding required tense particle and electromagnetic radiation to achieve ignition. and debris. The more information obtained about the physical state of the plasmas pro- Even higher fidelity (spectral, temporal, duced, and the driver and systems surround- spaEven higher fidelity (spectral, temporal, ing the plasma, the more stringent the test of spatial, energy resolution) are necessary to theories, models, and codes can be leading to better understand the foundational physics predictive capability and understanding. in order to achieve the high gains (~50-100) required for IFE. As we learn more about the In order to develop target designs that achieve sensitivities of the fuel assembly and heating high gain for IFE, the physics knowledge gap process, new measurements and diagnostics 114

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS will be needed to probe and observe the im- be needed for: monitoring of laser delivery, pact of perturbations or imperfections on the target tracking and engagement, reactor wall fusion plasma. monitoring, neutron yield, and maintenance diagnostics. There may also need to be a num- Of note, measurements at interfaces are ber of other failure mode diagnostics to pro- particularly needed – both within the fusion vide information in the case things go wrong. plasma itself and at places where the various subsystems of an IFE power plant join. For Until that point, however, and to enable that example, precise measurements are needed point, the intermediate fusion pilot plant or at the interface between the capsule shell test facilities will have a set of diagnostic and and DT fuel as this is one of the key locations analysis requirements in-between. This will in- where hydrodynamic instability growth can clude: lead to mix and reduce the area of the “clean” hot spot. Diagnostics that can provide infor- » High repetition-rate (>Hz), radiation hard- mation at the interfaces can furthermore help ened diagnostics us understand the interplay between different » Automated analysis to keep pace with the components, technologies, and subsystems. shot rate, and preferably provide on-shot One example is at the final optics before the feedback laser is delivered into the target chamber – it » Edge computing to enable rapid analysis is here that the laser optics will be exposed to » On-shot metrology of the target (to make the largest amounts of debris and the highest decisions about the suitability of a target laser intensities, and continuous monitoring of for shot) damage and optics degradation will be crucial » On-shot characterization of the driver to ensuring good laser performance is main- » Measurement of target performance – this tained. will probably require a set of diagnostics on par or greater in number and capability In a fusion power plant, there should be min- than the set of diagnostics on the NIF imal diagnostics. It is envisioned that once » Measurements that allow for understand- things are up and running, at routine opera- ing of the tradeoffs between the various tions, only a small set of instrumentation will subsystems in a FPP (e.g., target imperfec- Fig. 26: There are over 100 diagnostic instruments on the NIF measuring a range of parameters related to the target physics. This diagnostic innovation has allowed for unparalleled view into the NIF implosion. Courtesy of LLNL. 115

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MEMORANDUM LASER INERTIAL FUSION ENERGY tions can potentially be compensated for ing with laser adjustments) » Transition between plasma control to reac- » Measurement of laser delivery, target tor control / machine protection tracking, neutron yield, and wall monitor- 6.7.2 R&D and Capability Status Worldwide In the U.S., ICF diagnostics are coordinated may often bring their own diagnostics for the through the National Diagnostics Working experiment, then remove them afterwards. Group which sets priorities for diagnostic de- Each laser will also have a small set of laser velopment in ICF across multiple ICF facilities characterization diagnostics, however, in most including NIF, Omega, and Z. This group pools cases they are insufficient to provide full on- resources and expertise from across multiple shot characterization. national laboratories and universities to devel- op and deploy increasingly sophisticated diag- Diagnostic modeling is an important capability nostics for new and higher fidelity measure- that is typically tied to an individual diagnos- ments. The group meets annually and also tic and can utilize a range of simulation and updates their plan to lay out how their mission modeling tools ranging from PIC modeling to space will be enhanced by new observables. GEANT to provide synthetic data. Synthetic Table 6 shows the ten transformational diag- data can aid in diagnostic development, cali- nostics identified by the group in 2021 that bration, validation, and machine learning train- the Working Group will collectively develop ing. Another variation on diagnostic modeling over the next few years. is the modeling of laser performance, such as with the Laser Performance Operations Mod- At the LMJ, the diagnostic set of mirrors the el (LPOM) at the NIF which uses diagnostic ones on NIF, but are currently more limited in feedback from previous NIF shots to maintain number. It is reported that over 80 diagnostics accurate energetics models. The LPOM model have been installed at the 100 kJ level laser also determines system setpoints required for facility Shen Guang-II and Shen Guang-III pro- requested shots and employs damage models totypes [Wan2020]. to minimize the probability of damage to the system. Similar models will be necessary for Each short-pulse, high-intensity laser facility IFE systems, but currently the NIF is the only has its own set of target physics diagnostics, laser to include such a comprehensive opera- centered around the types of HED and other tions model. experiments carried out there. Depending on the operations model, users of the facility 6.7.3 Commonalities with Magnetic Fusion There exist large discrepancies in parameter In IFE, the community has enormous exper- space between IFE and MFE: 12 orders of tise with fast measurements — there may be magnitude in confinement time, and 11 orders some application in MFE to measure insta- of magnitude in plasma density, but similar bility evolution or performance dynamics on temperatures. Thus, in most cases, the diag- nanosecond timescales. In MFE, the commu- nostics and measurements are quite different. nity has expertise with magnetic diagnostics However, conventional diagnostics such as – this could be applied to IFE for example with spectroscopy and polarimetry (X-ray, optical, the use of externally applied magnetic fields in electron, neutron, and magnetic), scattering HED plasmas. High resolution X-ray spectros- (Thomson and particle), fast ion diagnostics copy for identifying and calibrating high-Z im- and their absolute calibrations are being de- purities in the plasma for MFE, may be anoth- veloped in both IFE and MFE. er area that could be adapted to IFE, namely in 116

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS the monitoring impurities and wastes. plasma. This includes performance of materi- als in a fusion environment, tritium breeding In the realm of burning plasmas, there exists a blankets, tritium concerns including recovery, need to understand and quantify self-heating processing, accountability, and minimizing in- from alpha particles. An already-established ventory technique is measuring the signature alpha knock-on (AKN) tail in neutron spectra. Finally, as IFE will be pulsed while MFE contin- uous in its generation of fusion plasmas and There are of course more commonalities be- energy, there are different needs for irradia- tween MFE and IFE as we move away from the tion and testing facilities. Transformative Diagnos- New Capability tics Single LOS imaging (SLOS or DIXI-SLOS) Multi-dimensional shape ad spectra with unprecedented time and space resolution for fusion, Pu strength, and radiation effects sources Ultraviolet Thomson Scattering (UVTS) Localized plasma conditions and turbulences in hohlraum and Laser Direct Drive ablation plasm. Additional uses include plasma condi- tions at low density for rad flow studies and many discovery science applications 3D n/gamma imaging (NIS) 3D shape and size of both burning and cold compressed fuel as well as remaining carbon ablator Gamma spectroscopy (GCD) Fusion burn history allowing inferred pressure with increased preci- sion and measured truncation of burn from degradation mechanism such as mix and loss of confinement Time resolved neutron spectrum (MRS-time) Time evolution of the fusion burn temperature and areal density Hard x-ray imaging (Wolter) High energy source distribution and space-resolved plasma con- ditions in the hot plasma. Also enables high spatial and temporal resolution for radiography to infer material strength Time resolved diffraction (XRDt) Time evolution of material structure (including weapon materials) and compression at high pressure. Also enables more efficient facili- ty use through multiple measurements on a single shot High Resolution Velocimeter (HRV) Higher accuracy (<1%) time evolution of material EOS at high pressure. Also enables more efficient facility use through multiple high-fidelity measurements on a single shot >15 keV X-ray detection (DHEX) Multiple-frame resolved detection of high energy (>15 keV) x-rays with high detection efficiency hCMOS Multi-frame, burst mode imaging sensor capable pf capturing imag- es on the nanosecond timescale Table 6: The ten transformational diagnostics identified by the National Diagnostics Working Group in 2021. 117

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MEMORANDUM LASER INERTIAL FUSION ENERGY 6.7.4 Capabilities and Competencies in Germany Diagnostic capabilities in Germany and Europe area where Germany necessarily possesses are primarily tied to associated laser facilities. unique expertise. However, it should be noted As the experimental facilities tend to be mid- that diagnostics can be an avenue for relative- scale and university facilities, the diagnostics ly low investment for entry into partnership developed have typically been targeted to- on a facility. Also, diagnostic development is ward HED experiments and needs. a great tool for training of new experimental fusion scientists. Fusion experimental diagnostics are not an 6.7.5 Industry Led R&D for IFE Different ignition approaches will have slightly agnostic components, advanced manufactur- different requirements in the measurements ing or additive manufacturing of items such as of plasma conditions, interfaces, etc. For ex- novel materials for shielding or detection can ample, for the fast ignition approach, diag- be an area of exploration. nostics for particle acceleration, as well as their stopping and heating effectiveness are Industry may also play an important role in the required. Each test facility proposed by the calibration or diagnostics or diagnostic com- private companies will be quite different, and ponents. X-ray, neutron, or other radiation thus will require its own set of bespoke diag- sources with stable and uniform properties nostics. Industry will need to define these re- are often needed to correlate the readings of quirements and necessary measurements. It the diagnostic instruments with a standard in is expected that industry will at least to some order to check the instrument’s accuracy. extent want to develop some of the needed diagnostics in-house, to ensure integration Finally, while diagnostics for scientific discov- with the test facility and to ensure correct in- ery continue to be built in a bespoke fashion, terpretation of data generated. as the IFE industry accelerates, there will be increased demand for diagnostic instruments There are also many general diagnostic needs, in general. Industry may want to look for com- with common diagnostic technologies that in- mercialization opportunities with respect to dustry can play a role in providing. Technol- building, deploying, calibrating, and repairing ogies for high-repetition-rate (such as digital diagnostics. This is accompanied by oppor- recording media and scintillators for signal tunities to support the data acquisition and amplification and transfer), radiation harden- handling. ing, machine learning, and edge computing all require development. In the production of di- 6.7.6 Findings and Recommendations In the area of diagnostics and data acquisition These include: and interpretation, there are many gaps and » Laser plasma instabilities subsequent research opportunities – until a » Fuel or plasma or ablator density/temp/ full scale power plant is built that harnesses conditions vs. space & time the energy from high-rep-rate high-gain tar- » Opacity / opacity changes gets, diagnostics are the key to understanding » Imaging during explosive phase the physics and the IFE system. » Mix » Alpha heating/stopping, burn wave propa- New physics measurements are required to gation develop and test high gain target designs. 118

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS New technologies are required as well, these in real-time. Some level of standardization include: will furthermore accelerate progress for the » Target positioning determination/tracking full field as each private company and public » Target quality (capsule voids and defects, project centered around a “fusion engine” will microstructure, etc.) likely run into similar issues. In order to make » Chamber damage accumulation / materials fast progress, there also needs to be coupling monitoring of diagnostics and the data they provide to codes and systems. Diagnostic data that can As the paradigm for data acquisition moves validate codes will enable the development of toward high-repetition-rate experiments, and a predictive capability. thus high repetition rate diagnostics, very large data sets will become a reality. Big data and A major need is for diagnostics that can val- fast data handling and automation becomes a idate and verify claims and experimental re- challenge, but also an opportunity. Standard- sults. There should be a set of common diag- ization of data, controls, and system inter- nostics that can be brought to different laser faces is a need to allow the different subsys- facilities, to verify both public and private ap- tems to interact with each other as necessary, proaches. Calibration facilities and capabili- while building a framework where feedback ties are also needed. control can be used to optimize experiments Finding Diagnostics are key to understanding the physics of IFE and developing a viable integrated FPP. Recommendation Germany should establish a program to develop target, laser, control, and systems diagnostics. The diagnostic development program should mentation already developed for existing fa- be coordinated with and support the exper- cilities (such as NIF), but should furthermore imental program and facilities. This includes provide new insights into physics areas where facilities to be built in Germany, as well as there remain considerable uncertainties, and facilities outside of the country where collab- would benefit from improved temporal, spa- oration is to occur. These diagnostics should tial, and spectral resolution. build off of the extensive capability of instru- Finding High repetition rate diagnostics are needed for new facilities coming on- line with high repetition rate lasers, and for future IFE demonstration fa- cilities that will necessarily run at >Hz rates. There are currently only a limited set of relevant diagnostics worldwide capable of operating at these fast rates, capable of withstanding high fluence irradiation of radiation, EMP, and debris, and with automated analysis, and suitable data handling. Recommendation Germany should invest in high repetition rate diagnostic development. Development of HRR diagnostics is seen to would necessarily also incorporate big data be an area of high return on investment, and and machine learning approaches in order to a necessary step to make full use of the new process all the data effectively, so leans on an- high repetition rate laser facilities coming other strong competency of Germany. online around the world. This is an area that 119

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MEMORANDUM LASER INERTIAL FUSION ENERGY Finding A major gap in assessing viability of various approaches is the lack of diag- nostics that can validate and verify claims and experimental results. Recommendation There should be a set of common diagnostics that can be brought to dif- ferent laser facilities, to verify both public and private approaches. Calibra- tion facilities and capabilities are also needed. 6.8 Artificial Intelligence (AI) and High Performance Computing (HPC) 6.8.1 Role of AI and HPC in IFE AI and HPC will play a pivotal role in both de- ed through high-repetition-rate laser facilities. veloping the fundamental understanding re- R&D and capability status worldwide (where, quired to realize IFE, as well as transition tech- what). nologies to application space. Specifically, HPC is required to run and develop simulation There has been significant work worldwide in codes of increasing fidelity and complexity the development of AI and HPC capabilities. to fully capture the physics of the laser-tar- Use of both these tools for scientific comput- get interaction (from the atomistic scale up ing and scientific discovery has advanced at a to the hydro scale and beyond for the inter- tremendous pace as new HPC machines come action with the reactor system), to interpret online around the world, and as researchers data while in the R&D stage, to develop full develop new techniques for harnessing AI for systems models of the IFE reactor, and later everything from automation to controls to on to run the facility in an automated fashion feedback loops for self-driving optimization. and link an IFE-generated electricity source to a smart grid. AI is similarly needed to handle and utilize the large amounts of data generat- 6.8.2 Capabilities and Competencies in Germany Germany has substantial AI expertise spread pect demands will continue to grow for HPC across its many universities and research in- resources, so this is an area that Germany stitutes. The HPC capability in Germany for must ensure it keeps up. the moment has been mostly sufficient for the scale of science being done, however, we ex- 6.8.3 Industry Led R&D for IFE Industry has a role in developing AI tech- icant investment (both in capital cost and op- niques for the range of needs in IFE – this can erations), however, they can most surely drive include the use of AI for modeling and simula- demand and also provide hardware compo- tion, efficiencies in large-scale or high-volume nents that will be required in computational manufacturing, data handling, and more. It situations. is unlikely that the fusion industry will be the center of HPC, as supercomputers are a signif- 120

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EXPERTISE, COMPETENCE, AND CAPABILITIES ORGANIZED BY MODULAR TECHNOLOGIES/ RESEARCH AREAS 6.8.4 Findings and Recommendations Continued needs as AI and HPC grow in im- IFE reactors or components, and overall com- portance include improved techniques for puting resources to run simulations and mod- data analysis and interpretation, data stan- els. dardization, data handling, development of algorithms for the design and optimization of Finding Germany possesses enormous expertise in AI and HPC across its many universities and research institutions. Recommendation German AI expertise should be fostered and brought to bear on the IFE problem by opening up AI funding opportunities to IFE. Finding As new experimental and research facilities are brought online, integra- tion of AI and HPC will be necessary for full and optimal utilization of these facilities to provide new learning and knowledge acquisition. Recommendation Design and pursuit of new experimental capabilities should also consider AI and HPC. Finding Rapid and robust data analysis will be necessary for even a moderate rep- etition-rate facility. More data will require improved and automated data analysis, which can be enabled by AI and HPC. Recommendation Develop AI techniques to automate and improve data processing and anal- ysis. 121

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07 Education, Training, Outreach, Cooperation and Networking in Germany 122

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EDUCATION, TRAINING, OUTREACH, COOPERATION AND NETWORKING IN GERMANY 7.1 Status & Needs for Education & Training Germany has a broad research community responding resources in terms of high-perfor- in the areas of high-power laser and plasma mance computer capacities are also available. science, high power laser development and Major shortcomings are essentially that no la- other areas to develop a successful inertial ser/inertial fusion program has existed to sup- confinement fusion/inertial fusion energy port direct targeted cooperation with leading (ICF/IFE) strategy within the international con- nations in the field, both monetarily and pro- text. The key groups located at universities, grammatically. Thus, the technology exchange national research associations and industry was essentially focused on technical or meth- have expertise in experimental and theoret- odological individual aspects, but a holistic ical plasma science, laser target interactions, systemic processing was absent. diagnostics and the know-how to run success- ful even high-power short-pulse laser experi- This is also reflected in the low availabil- ments are rapidly transferable between high ity of experimental specific laser/inertial power laser and laser fusion communities. fusion facilities, even if the infrastructural Thus, a whole chain of human resources with prerequisites are given in Germany. Estab- both practical and theoretical knowledge is lishing laser fusion as a successful research ready to successfully establish and design a field in Germany and also to mobilize suc- laser fusion project in cooperation with oth- cessful industrial activity with respect to a er leading countries. The already existing ex- future power plant requires building also perimental facilities as well as the educational some laser/inertial fusion activity at universi- landscape enables the provision of appropri- ty level to complement the individual chairs. ately trained talent in the long term. The cor- Finding Funding scheme for high power laser fusion research doesn’t exist in Ger- many. There is vital high power laser community existent in Germany able to provide sufficiently large theoretical and experimental trained staff for a laser fusion power plant program. However an adequate funding scheme for laser fusion research is absent. A dedicated university education to- wards a laser fusion power plant is currently not existent. Recommendation Strengthen laser fusion specific education and funding program for edu- cation. Provision of a specific laser/inertial fusion program with a funding to train future staff. Strengthening laser fusion specific university education by provision of university chairs in: » high power pulsed optical beam sources, » beam shaping and guiding, » efficient optical components and conversion as well as » systems production technologies (from the optical systems to the tar- get itself where the fusion reaction takes place) by establishing dedi- cated chairs. Compared to the United States or the UK, fusion technology and plasma physics at uni- Germany currently has a minimal presence in versities, with a primary focus on magnetic 123

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MMEEMMOORRAANNDDUUMM LLAASSEERR IINNEERRTTIIAALL FFUUSSIIOONN EENNEERRGGYY fusion. Furthermore, related fields such as nu- tinued chairs at universities and a poor start- clear technology, nuclear materials, and diag- ing position. Disciplines such as nuclear pro- nostics have also been significantly impacted cess engineering no longer exist in Germany. by the nuclear phase-out, resulting in discon- Finding Germany has a lack of nuclear-qualified staff. Recommendation Provision of chairs and corresponding infrastructures in Germany. Regardless of which type of fusion power nology development within Germany, which is plant is realized, the provision of nuclear-qual- not focused on inertial fusion but takes Laser ified personnel for planning, construction, Fusion (IFE) as the most challenging use case operation and decommissioning is necessary and driver. These already existing sites can for both the licensor and the licensee, which act as hub to establish at nearby associated requires the consistent development of corre- universities professorships, the educational sponding expertise in training at universities basis to provide the personnel resources re- and other institutions of applied science. quired to establish not only an internationally competitive scientific basis but also providing Provision of chairs with corresponding infra- specialized staff for technology-oriented com- structures at German universities to stimulate panies. Naturally, the professorships require a this type of education in the following disci- research infrastructure targeting fusion, but plines also being competitive and attractive for in- dustry business to generate also an economic » Nuclear safety system engineering, frame which require for each an equipment » Nuclear process engineering, in the range of in average about two million » Nuclear physics (nuclei interaction with Euros given that they can access the nearby matter), infrastructures of the research centers. Since » Nuclear instrumentation/diagnostics. some of the identified topics are strongly in- terrelated it makes sense to cluster them at In the area of nuclear expertise can be used sites offering already pre-emptive know-how. synergistically in other research fields not only The hub concept is so attractive because the fusion (laser and/or magnetic fusion), but the established professorships can initially not occupation of this competence fields with the only synergistically access the laboratories of output of educated and trained staff is essen- the research centers until their own univer- tial for successful research and the construc- sity infrastructures are established, but can tion of a fusion facility. also develop existing industry contacts of the centers to further develop their own expertise The research centers at Fraunhofer, Max- and thus achieve productive results after a rel- Planck and Helmholtz already host some large- atively short time. scale infrastructures acting as a basis and seed for the development of future key tech- Finding A laser fusion network doesn’t exist in Germany until now.In Germany there is currently no laser fusion network but rather individual centers of expertise (laser sciences, plasma physics, fusion engineering, materials research, manufacturing technologies). The same applies, albeit to a lesser extent, to magnetic fusion, since most of the projects on integration with- in the European framework are bundled there. 112244

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EDUCATION, TRAINING, OUTREACH, COOPERATION AND NETWORKING IN GERMANY Recommendation Build a Laser Fusion network in Germany and strengthen the ecosystem for Laser technology development between industry and German Re- search Centers. It should be considered whether a German turn requires the establishment of a tangible laser fusion initiative jointly supported by the laser fusion project that manifests the cred- research centers (Fraunhofer, Max-Planck, ible will to design and, if necessary, realize a Helmholtz), the universities and industry could fusion power plant. represent laser fusion to the public. This in Finding Fusion research requires a wide range of expertise, infrastructure and or- ganizational mechanism. Any kind of fusion research requires the provision of a wide range of ex- pertise, technical infrastructures (laser facilities, thermal-hydraulic test stands, process engineering plants, material characterization sites in- cluding hot-cell, dedicated manufacturing techniques) and organizational mechanisms (program and project structures) that are difficult to master by any state alone. At the same time, a duplication of large infrastructures does not make sense, but rather synergetic effects in accessing large infra- structures should be used. Recommendation German Research institutions should collaborate with each other and with international experts in the field of IFE like LLNL (USA). Such collaboration could accelerate the time to market. In a first step in a cooperation agreement between the competent bodies (e.g. LLNL, other US laboratories and Fraunhofer ILT, IPP Garching, KIT and possibly others from Germany) of the laser fusion in the context of a laser power plant study should be envisaged. Such a measure would enable to pool all the the exchange of experts at the specialist level, expertise to identify a feasible power plant the mutual knowledge of the technical skills of concept by mutual exchange of information the partners and generates for the future also and to develop the necessary interface mech- the exchange of young scientists and students anisms for a long-term cooperation and dis- as well as practical training. tribution of tasks. This cooperation allows for Finding Germany has a great educational system in various fields which are need- ed for fusion technology. Recommendation Keep the research capabilities in Germany and continuously invest in up- grades of laser facilities. The mid-scale short-pulse, high-intensity sci- has been seen from the past three decades, entific laser facilities (such as DRACO, PENELO- besides being scientifically very productive, PE, PHELIX, CALA, POLARIS) provide an excel- these facilities serve as spawning grounds for lent training ground for young scientists. As the necessary plasma physics, laser engineer- 125

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MMEEMMOORRAANNDDUUMM LLAASSEERR IINNEERRTTIIAALL FFUUSSIIOONN EENNEERRGGYY ing, and high energy density science expertise needed for a growing IFE program. Further- more, the nature of the training on these fa- cilities sets up researchers well for translating to larger, more complex facilities, like what will be needed for IFE demonstration. Many of the current leaders in ICF around the world now were trained on these facilities and facilities like them. Germany needs to ensure the sustainment and upgrade of existing mid-scale laser fa- cilities, and furthermore pursue new high energy, ultra intense facilities. Such cutting edge facilities enable groundbreaking science, serve as an attractor of new talent to the field, and serve the very important mission of work- force development and training. 112266

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08 APPENDIX

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MEMORANDUM LASER INERTIAL FUSION ENERGY 8.1 References Abbreviation Full Citation [Abu2021] H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett., 129, 075001, 2022; Op cit. [Ale2015] D. Alessi, C. W. Carr, R. A. Negres, R. P. Hackel, K. A. Stanion, D. A. Cross, G. Guss, J. D. Nissen, R. Luthi, James E. Fair, J. A. Britten, and C. Haefner “Optical damage performance mea- surements of multilayer dielectric gratings for high energy short pulse lasers”, Proc. SPIE 9345, High Power Lasers for Fusion Research III, 934509 (26 February 2015); https://doi. org/10.1117/12.2084823. [Ale2020] Alessi, D.A., Prantil, M.A., Herriot, S.I., et al. (2020): High precision characterization of the kilojoule multi-ps advanced radiographic capability. Optics InfoBase Conference Papers, art. no. HTh2B.5. [Alek 2020] Irina Aleksandrova, Eugeniy Koshelev and Elena Koresheva, In-Line Target Production for Laser IFE, Appl. Sci. 2020, 10, 686; doi:10.3390/app10020686. [Alek2022] I. V. Aleksandrova, E. R. Koresheva, and E. L. Koshelev, A high-pinning-Type-II supercon-duct- ing maglev for ICF target delivery: main principles, material options and demonstration mod- els, High Power Laser Science and Engineering, (2022), Vol. 10, e11, 15 pages. doi:10.1017/ hpl.2022.1. [Alex2013] N. B. Alexander, R. W. Petzoldt, E. I. Valmianski, G. E. Lee, D. T. Frey, and J. T. Bousquet, Mass-Fabrication of Targets for Inertial Fusion Energy, Proceeding of 24th IAEA Fusion Energy Conference October 8-13, 2012, San Diego, USA, Online publication of IAEA http://www- naweb.iaea.org/napc/physics/FEC/FEC2012/html/fec12.htm, March 2013, pg 525. [Alv2011] Alvarez, J., Rivera, Gonzalez-Arrabal, R., Garoz, D., del Rio, E., & Perlado, J. (2011). Materi- als Research for HiPER Laser Fusion Facilities: Chamber Wall, Structural Material and Final Optics. Fusion Science and Technology, 60(2), pp. 565-569. doi:https://doi.org/10.13182/ FST11-A12443. [Bag2010] V. Bagnoud, B. Aurand, A. Blazevic, S. Borneis, C. Bruske, B. Ecker, U. Eisenbarth, J. Fils, A. Frank, E. Gaul, S. Goette, C. Haefner, T. Hahn, K. Harres, H.-M. Heuck, D. Hochhaus, D. H. H. Hoffmann, D. Javorkov´a, H.-J. Kluge, T. Kuehl, S. Kunzer, M. Kreutz, T. Merz-Mantwill, P. Neu- mayer, E. Onkels, D. Reemts, O. Rosmej, M. Roth, T. Stoehlker, A. Tauschwitz, B. Zielbauer, D. Zimmer, and K. Witte, Appl. Phys. B 100, 137 (2010). [Bar2004] C.P.J. Barty et al: Nucl. Fusion 44 S266 (2004). [Bay2006] A. J. Bayramian, R. J. Beach, C. Bibeau, R. Campbell, C. A. Ebbers, B. L. Freitas, R. Kent, D. Van Lue, Z. Liao, T. Ladran, S. A. Payne, K. I. Schaffers, S. Sutton, B. Chai, and Y. Fei, “High Average Power Frequency Conversion on the Mercury Laser,” in Advanced Solid-State Photonics, Tech- nical Digest (Optica Publishing Group, 2006), paper MB1. [Bay2011] A. Bayramian et al. “Compact, Efficient Laser Systems Required for Laser Inertial Fusion Ener- gy”, Fusion Science and Technology, vol. 60, 28-48 (2011). 128

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MEMORANDUM LASER INERTIAL FUSION ENERGY Abbreviation Full Citation [Con2022] Conner Galloway, Cliff Thomas, Mike Tobin, et al. “ASPEN Laser and A New IFE Power Plant Concept”, IFE Science & Technology Community Strategic Planning Workshop, 2022. https:// lasers.llnl.gov/content/assets/docs/nif-workshops/ife-workshop-2021/white-papers/gallo- way-xcimer-IFE-workshop-2022.pdf. [Coo1994] Robert Cook, Production of Hollow Microspheres for Inertial Confinement Fusion Experi- ments, MRS Online Proceedings Library (OPL), Volume 372: Symposium W1 – Hollow and Solid Spheres and Microspheres—Science and Technology, 1994, 101, DOI: https://doi. org/10.1557/PROC-372-101. [Coo2020] Cook, C. C., Fong, E. J., Schwartz, J. J., Porcincula, D. H., Kaczmarek, A. C., Oakdale, J. S., Moran, B. D., Champley, K. M., Rackson, C. M., Muralidharan, A., McLeod, R. R., Shusteff, M., Highly Tunable Thiol-Ene Photoresins for Volumetric Additive Manufacturing. Adv. Mater. 2020, 32, 2003376. https://doi.org/10.1002/adma.202003376. [Dan2004] C. N. Danson, P. A. Brummitt, R. J. Clarke, J. L. Collier, B. Fell, A. J. Frackiewicz, S. Hancock, S. Hawkes, C. Hernandez-Gomez, P. Holligan, M. H. R. Hutchinson, A. Kidd, W. J. Lester, I. O. Musgrave, D. Neely, D. R. Neville, P. A. Norreys, D. A. Pepler, C. J. Reason, W. Shaikh, T. B. Win- stone, R. W. W. Wyatt, and B. E. Wyborn, IAEA J. Nucl. Fusion 44, S239 (2004). [DiN2015] Di Nicola, J.M., Yang, S.T., et al.: The Commissioning of the advanced radiographic capability laser system: Experimental and modeling results at the main laser output. Proceedings of SPIE

• The International Society for Optical Engineering, 9345, art. no. 93450I. (2015) https://doi. org/10.1117/12.2080459. [Dit2021] T. Ditmire, M Roth, A. Stein, T. Forner, talk “ Focused Energy Perspective on Inertial Fusion Energy, to IFE Workshop, Nov. 16, 2021, https://lasers.llnl.gov/content/assets/docs/nif-work- shops/ife-workshop-2021/10_Ditmire-Focused-Energy-IFE-Workshop-Present.pdf. [Du2018] Kai Du, Meifang Liu, Tao Wang, Xiaoshan He, Zongwei Wang, Juan Zhang, Recent progress in ICF target fabrication at RCLF, Matter and Radiation at Extremes 3 (2018) 135 - 144. [Erl2011] A. Erlandson et al., “Comparison of Nd:phosphate glass, Yb:YAG and Yb:S-FAP Laser Beam- lines for Laser Inertial Fusion Energy (LIFE)”, Optical Material Express, vol. 1, 1341 (2011). [Fed2017] Federici, G., Biel, W., Gilbert, M., Kemp, R., & Taylor, N. (2017). European DEMO design strategy and consequences for materials. Nuclear Fusion, 57, p. 092002 (26pp). doi:DOI 10.1088/1741-4326/57/9/092002. [Fre2005] D.T. Frey, D.T. Goodin, R.W. Stemke, R.W. Petzoldt, T.J. Drake, W. Egli, B.A. Vermillion, R. Klasen & Cleary M.M. (2005) Rep-Rated Target Injection for Inertial Fusion Energy, Fusion Science and Technology, 47:4, 1143-1146, DOI: 10.13182/FST05-30. [FUL2015] E. S. Fulkerson et al., “Pulsed power system for the HAPLS Diode Pumped Laser System,” 2015 IEEE Pulsed Power Conference (PPC), 2015, pp. 1-6, doi: 10.1109/PPC.2015.7296854. [Gaf2019] Gaffney Phys. Plasmas 26, 082704 (2019), https://doi.org/10.1063/1.5108667. 130

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APPENDIX Abbreviation Full Citation [Lab2008] Labaune C, Hulin D, Galvanauskas A, Mourou G., “On the feasibility of a fiber-based in- ertial fusion laser driver”, Optics Communications. 281: 4075-4080. DOI: 10.1016/J.Opt- com.2008.04.012. [Lat2010] Latkowski et al., Chamber design for the Laser Inertial Fusion energy (LIFE) Engine, LL- NL-JRNL-463734. [Lat2017] Latkowski, J. F., Abbott, R. P., Aceves, S., Anklam, T., Cook, A. W., DeMuth, J., … al., e. (2017). Chamber Design for the Laser Inertial Fusion Energy (LIFE) Engine. Fusion Science and Tech- nology, 60(1), pp. 54-60. doi:https://doi.org/10.13182/FST10-318. [Law1957] J.D. Lawson, Proceedings of the Physical Society, Section B 70 (1), 6, 1957. [Lee2011] G. E. Lee, N. B. Alexander, E. Diaz, J. D. Sheliak, A Robotic System for High-Throughput-Rate Target Assembly, Fusion Sci. and Tech., 59 (1), January 2011, pg 227-233. [Lee2021] Lees, Phys. Rev. Lett. 127, 105001 (2021), https://journals.aps.org/prl/abstract/10.1103/Phys- RevLett.127.105001. [Li2021] Li, Y. (2021). Thermomechanical behvaiour of Tungsten under fusion relevant hydrogen plas- ma loads. University Eindhoven of Technology. [Lin2011] Linke, J., Löewenhoff, T., Massaut, V., Pintsuk, G., Ritz, G., Rödig, M., … Wirtz, M. (2011). Per- formance of different tungsten grades under transient thermal loads. Nuclear Fusion, 51(7), pp. 073017-8pages. doi:10.1088/0029-5515/51/7/073017. [Liu2016] Meifang Liu, Lin Su, Jie Li, Sufen Chen, Yiyang Liu, Jing Li, Bo Li, Yongping Chen, Zhanwen Zhang, Investigation of spherical and concentric mechanism of compound droplets, Matter and Radiation at Extremes 1 (2016) 213 - 223. [LLE2021] https://www.lle.rochester.edu/index.php/2022/11/16/2021-annual-report/. [LLN2022] https://www.llnl.gov/news/lawrence-livermore-national-laboratory-achieves-fusion-ignition [Ma2022] Ma, T. (2022). Basic research needs workshop on inertial Fusion Energy. Lawrence Livermore National Laboratory- US dept. of Energy. [Mar1976] Maroni, V. (1976). Patent No. Patent No 3,957,597. [Mar1988] A. J. Martin , R. J. Simms, R. B. Jacobs, Beta energy driven uniform deuterium—tritium ice lay- er in reactor-size cryogenic inertial fusion targets, Journal of Vacuum Science and Technology A 6, 1885 (1988, May 1, 1988); https://doi.org/10.1116/1.575234. [Mas2018] V. Masson-Delmotte et al, “Global Warming of 1.5C”, An IPCC Special Report, Tech. rep., IPCC (2018), https://www.ipcc.ch/sr15/. [Mei2008] W.R. Meier, J. of Physics: Conference Series 112, 032036 (2008). 133

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MEMORANDUM LASER INERTIAL FUSION ENERGY Abbreviation Full Citation [Mei2009] W.R. Meier, Fusion Science and Technology, 56, 647-651 (2009). [Mei2010] WR Meier et al., Integrated process modeling for the laser inertial fusion energy (LIFE) gener- ation system UCRL-JC-126817. [Mei2013] Meier, W., Dunne, A., Kramer, K., Reyes, S., & Anklam, T. (2013). Fusion Technology Aspects of Laser Inertial Fusion Energy (LIFE). Lawrence Livermore National Laboratory. [Mei2016] Meifang Liu, Lin Su, Jie Li, Sufen Chen, Yiyang Liu, Jing Li, Bo Li, Yongping Chen, Zhanwen Zhang, Investigation of spherical and concentric mechanism of compound droplets, Matter and Radiation at Extremes 1 (2016) 213 – 223. [Mer1994] Yu. A. Merkuliev, A. A. Akunets, V. S. Bushuev, V. M. Dorogotovtsev, A. I. Gromov, A. I. Isakov, A. I. Nikitenko, S. A. Startsev, S. M. Tolokonnikov, R. C. Cook, Study of Production and Quality of Large (1–2 MM) Polystyrene Hollow Microspheres, MRS Online Proceedings Library (OPL), Volume 372: Symposium W1 – Hollow and Solid Spheres and Microspheres—Science and Technology , 1994 , 119 DOI: https://doi.org/10.1557/PROC-372-119. [Mil2009] R. Miles, et al., 2009, “LIFE Target Fabrication Costs,” LLNL-TR-416932. [Mil2014] Robin Miles, Allan Chang, Francesco Fornasiero, Mark Havstad, Sergei Kucheyev, Mary Leb- lanc, Paul Rosso, and Greg Schebler (2014) Thermal and Structural Issues of Target Injection into a Laser-Driven Inertial Fusion Energy Chamber, Fusion Science and Technology, 66:2, 343- 348, DOI: 10.13182/FST14-779. [Miy2000] Miyanaga, N., et al., 2000. The GEKKO XII-HIPER (High Intensity Plasma Experimental Re- search) System Relevant to Ignition Targets. In: 18th IAEA Fusion Energy Conf. Sorrento, Italy [Mor1991] Moriyama, H., Asaoka, Y., & Ito, Y. (1991). Kinetics of Tritium Recovery from Liquid Lithium by Molten Salt Extraction. Fusion Technology, 19, pp. 1046-1050. doi:https://doi.org/10.13182/ FST91-A29481. [Mor1995] Moriyama, H., Tanaka, S., Sze, D. K., Reimann, J., & Terlain, A. (1995). Tritium recovery from liq- uid metals. Fusion Engineering and Design, 28, pp. 226-239. doi:https://doi.org/10.1016/0920- 3796(95)90043-8. [Mor2013] Mourou, G., Brlocklesby, B., Tajima, T. & Limpert, J. (2013). The future is fibre accelerators. Nature Photon. 7, 258–261. [MOS2002] E. Moses, “The National Ignition Facility: status and plans for laser fusion and high-ener- gy-density experimental studies”, Proceedings of the 19th IEEE/IPSS Symposium on Fusion Engineering. 19th SOFE (Cat. No.02CH37231), Atlantic City, NJ, USA, 2002, pp. 487-492, doi: 10.1109/FUSION.2002.1027741. [Mos2009] E.Moses, et al., LLNL Report LLNL-CONF-413798, 2009. 134

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APPENDIX Abbreviation Full Citation [NASEM2013] Assessment of Inertial Confinement Fusion Targets National Academies of Sciences, Engineering, and Medicine. 2013. Assessment of Inertial Confinement Fusion Targets. Washington, DC: The National Academies Press. https://doi. org/10.17226/18288. [NASEM2014] An Assessment of the Prospects for Inertial Fusion Energy, 2013 National Academies of Sciences, Engineering, and Medicine. 2013 https://nap.nationalacademies.org/catalog/18289/an-assessment-of-the-prospects-for-iner- tial-fusion-energy. [Neg2017] Raluca A. Negres, Christopher J. Stolz, Michael D. Thomas, Mark Caputo, “355-nm, nano-sec- ond laser mirror thin film damage competition”, SPIE Proceedings Vol 10447, Laser-Induced Damage in Optical Materials 2017; 104470X (2017) https://doi.org/10.1117/12.2279981. [Neu2022] Neugebauer, C. F. (2022). Investigation on the Semi-Continuous Separation of Hydrogen Iso- topes for Fusion. Faculty of Mechanical Engineering. Karlsruhe Germany: Karlsruhe Institute of Technology. [Norimat- T. Norimatsu, Y. Kozaki, H. Shiraga, H. Fujita, K. Okano and Members of LIFT Design Team, su2017] Conceptual design and issues of the laser inertial fusion test (LIFT) reactor – targets and chamber systems, Nucl. Fusion 57 116040 [Obe2015] Obenschain, S., et al., 2015. High-energy krypton fluoride lasers for inertial fusion. Applied Optics 54 (31), F103. https://doi.org/10.1364/ao.54.00f103. [Ols2021] R. E. Olson, M. J. Schmitt, B. M. Haines, G. E. Kemp, C. B. Yeamans, B. E. Blue, D. W. Schmidt, A. Haid, M. Farrell, P. A. Bradley, H. F. Robey, and R. J. Leeper, (2021), A polar direct drive liquid deuterium tritium wetted foam target concept for inertial confinement fusion, Physics of Plasmas, 28, 122704, doi: 10.1063/5.0062590. [PAT1976] Patent Nr. Patent No 3,957,597, 1976. J.P. Perin, E. Bouleau, and B. Rus, Pellet Injector for Inertial Fusion, Proceedings of 5th INTER- [Per2011] NATIONAL CONFERENCE ON THE FRONTIERS OF PLASMA PHYSICS AND TECHNOLOGY, 18-22 April 2011, Singapore, Republic of Singapore, https://www-pub.iaea.org/MTCD/publications/ PDF/TE-1713-CD/talks/posters/Perin-poster-paper.pdf. [Pet2015] Ronald Petzolt, Neil Alexander, Lane Carlson, Eric Cotner, Dan Goodin & Robert Kratz (2015) Linear Induction Accelerator with Magnetic Steering for Inertial Fusion Target Injection, Fu- sion Science and Technology, 68:2, 308-313, DOI: 10.13182/FST14-915. [Pet2020] Peters, B. (2020). Development of a Hydrogen-Selective Vacuum Pump on the Basis of Super- permeation. Faculty Mech. Engingeering . Karlsruhe Germany: Karslruhe Institute of Technol- ogy. doi:DOI: 10.5445/IR/1000122305. 135

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MEMORANDUM LASER INERTIAL FUSION ENERGY Abbreviation Full Citation [Pilar2018] J. Pilar, M. De Vido, M. Divoky, P. Manson, M. Hanus, K. Erfel, P. Navratil, Th. Butcher, O. Slezak, S. Banerjee, J. Phillips, J. Smith, A. Lucianetti, C. Hernandez-Gomez, Ch. Edwards, J. Col- lier, T. Mocek, “Characterization of Bivoj/DiPOLE100: HiLSAE 100-J/10-Hz diode pumped solid state laser,” Proc. of SPIE 10511, Solid State Lasers XXVII: Technology and Devices, 105110X (2018). [Pos1956] R.F. Post, Rev. Mod. Phys., 28, 338, 1956. [Puk1999] Pukhov et al J. Plasma Phys. 61, 425 (1999). [Put2019] S. Putvinski, D. Ryutov, and P. Yushmanov, Nuc. Fusion, 59 (7), 076018, 2019. [Ram1988] Ramis et al, Comp. Phys. Comm. 49, 475-505 (1988). [Ram2009] Ramis et al, Comp. Phys. Comm. 180, 977-994 (2009). [Rey2013] Reyes, S., Babineau, D., Davis, R., Taylor, C., Anklam, T., Dunne, M., … Willms, S. (2013). Overview of the LIFE fuel cycle. EPJ Web of Conferences, 59, p. 11002. doi:DOI: 10.1051/epj- conf/20135911002. [Rus2017] Rus B., Bakule P., Kramer D., Naylon J., Thoma J., “ELI-beamlines: progress in development of next generation short-pulse laser systems“. [Saw2004] Sawan, M., Sviatoslavsky, I., Raffray, A., & Wang, X. (2004). Comparison of neutronics features for candidate balnkets. Proc. HAPL Workshop, (p. 14). Lawrence Livermore National Laborato- ry, June 2021. [Saw2007] Sawan, M. E., Aplin, C., Svatoslavsky, G., & Raffray, A. (2007). Neutronics Analysis of a molten salt blanket for the HAPL Laser Fusion Power Plant with magnetic intervention. Madison , Wisconsin: Fusion technology Institute University Wisconsin. [Schr2007] Diana Schroen, Dan Goodin, Jared Hund, Reny Paguio, Barry McQuillan & Jonathan Streit (2007) The Challenge of an IFE Foam Capsule Overcoat, Fusion Science and Technology, 52:3, 468-472, DOI: 10.13182/FST07-A1532. [Schro1995] Diana Schroen-Carey, George E. Overturf III, Robert Reibold, Steven R. Buckley, Stephan A. Letts, and Robert Cook, Hollow foam microshells for liquid-layered cryogenic inertial confine- ment fusion targets, Journal of Vacuum Science & Technology A 13, 2564 (1995); https://doi. org/10.1116/1.579450. [Schw2003] Ana M. Schwendt, Arthur Nobile, Peter L. Gobby, Warren P. Steckle Jr., Denis G. Colombant, John D. Sethian, Daniel Thomas Goodin & Gottfried Ernst Besenbruch (2003) Tritium Invento- ry of Inertial Fusion Energy Target Fabrication Facilities: Effect of Foam Density and Consid- eration of Target Yield of Direct Drive Targets, Fusion Science and Technology, 43:2, 217-229, DOI: 10.13182/FST03-A262. [Sci2022] https://scientificrussia.ru/articles/akademik-sergej-garanin-idei-ng-basova-o-sozdanii-ter- moadernogo-reaktora-na-baze-lazernogo-termoadernogo-sinteza-vpolne-realizuemy 136

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APPENDIX Abbreviation Full Citation [Set2010] J.D. Sethian, D.G. Colombant, J.L. Giuliani Jr., R.H. Lehmberg, M.C. Myers, S. P. Obenschain, A.J. Schmitt, J. Weaver, M.F. Wolford, F. Hegeler, M. Friedman, A.E. Robson, A. Bayramian, J. Caird, C. Ebbers, J. Latkowski, W. Hogan, W.R. Meier, L.J. Perkins, K. Schaffers, S. Abdel Kahlik, K. Schoonover, B. Sadowski, K. Boehm, L Carlson, J. Pulsifer, F. Najmabadi, A.R. Raffray, M.S. Tillack, G. Kulcinishi, J.P. Blanchard, T. Heltemes, A. Ibrahim, E. Marriott, G. Moses, R. Radell, M. Sawan, J. Santarius, G. Sviatoslavsky, S. Zenobia, N. M. Ghoniem, S. Sharafat, J. Elll-Alwady, Q. Hu, C. Duty, K. Leonard, G. Romanoski, L.L. Snead, S.J. Zinkle, C. Gentile, W. Parsells, C. Prinksi, T. Kozub, T. Dodson, D.V. Rose, T. Renk, C. Olson, N. Alexander, A. Bozek, G. Flint, D.T. Goodin, J. Hund, R. Paguio, R.W. Petzoldt, D.G. Schroen, J. Sheliak, T. Bernat, D. Bittner, J. Karnes, N. Petta, J. Streit, D. Geller, J.K. Hoffer, M.W. McGeoch, S.C. Glidden, H. Sanders, D. Weidenheimer, D. Morton, I.D. Smith, M. Bobecia, D. Hardig, T. Lehecka, S.B. Gilliam, S.M. Gidcumb, D. Forsythe, N.R. Parikh, S. O’Dell, and M. Gorensek, The Science and Technologies for Fusion Energy With Lasers and Direct-Drive Targets, IEEE Transactions on Plasma Science, 38 No 3 (2010), pp 690-703. [Sha2012] H. D. Shay, P. Amendt, D. Clark, D. Ho, M. Key, J. Koning, M. Marinak, D. Strozzi, and M. Tabak, Implosion and burn of fast ignition capsules—Calculations with HYDRA, Physics of Plasmas 19, 092706 (2012); https://doi.org/10.1063/1.4751839. [Shc1983] Shcherbakov, V. A. Ignition of a laser-fusion target by a focusing shock wave.Sov. J. Plasma Phys. 9, 240 241 (1983). [SOM1994] SOMBRERO study (Final Report, WJSA-92-01). [Spa2016] M. L. Spaeth et al., “Description of the NIF Laser,” Fusion Science and Technology 69, 25-145, 2016. http://dx.doi.org/10.13182/FST15-144. [Spe2018] Spears Phys. Plasmas 25, 080901 (2018), https://doi.org/10.1063/1.5020791. [Spe2021] Trend Report Photonics, Industry Trends and Market Potential 2021/2022, Photonics in the Germany Industry Association SPECTARIS. [Sto2017] E. Storm, J. D. Lindl “Indirect-Drive Inertial Confinement Fusion,” in “Energy from the Nucleus: The Science and Engineering of Fission and Fusion.” 2017. 69-120. [Tak2015] Takaki, K., Kageyama, K., Sunahara, A., Yabuuchi, T., & Tanaka, K. (2015). Simulated ablation of carbon wall by alpha particles for a laser fusion reactor. Journal of Nuclear Materials, 459, pp. 77-80. doi:https://doi.org/10.1016/j.jnucmat.2015.01.005. Teichmann, T., & Day, C. (2021). Particle Simulation of Linear Diffusion Pumps or DEMO [Tei2021] Torus Exhaust Pumping. Fusion Engineeering & Design, 169, p. 112694. doi:https://doi. org/10.1016/j.fusengdes.2021.112694. [Tep2019] Teprovich, J. A., Colon Mercado, H. R., Olson, L., Ganesan, P., Babineau, D., & Garcia-Diaz, B. L. (2019). Electrochemical extraction of hydrogen isotopes from Li/LiT mixtures. Fusion Engi- neering and Design, 139, pp. 1-6. doi:https://doi.org/10.1016/j.fusengdes.2018.11.018. 137

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MEMORANDUM LASER INERTIAL FUSION ENERGY Abbreviation Full Citation [Uec2021] Ueckerdt et al., 2021 https://ariadneprojekt.de/publikation/eckpunkte-einer-anpassungsfaehigen-wasserstoffstrat- egie/. [Ver2007] B. VERMILLION, J. T. BOUSQUET, R.E. ANDREWS, M. THI, M.L. Hoppe, E.R. CASTILLO, A. Nikroo, G.T. GOODIN, G.E. BESENBRUCH, (2007). Development of a New Horizontal Rotary GDP Coater Enabling Increased Production. Fusion Science and Technology. 51. 10.13182/ FST07-A1481. [Wan2011] W. Wang, T.B. Jones, D. R. Harding, On-Chip Double Emulsion Droplet Assembly Using Elec- trowetting-on-Dielectric and Dielectrophoresis Fusion Sci. Technol. 2011, 59 (1). [Wan2017] Wang, K., Doerner, R. B., Meyer, F., Bannister, M., Darbal, A., Strout, R., & Parish, C. (2017). Morphologies of tungsten nanotendrils grown under helium exposure. Nature Scientific Re- ports, p. 7:42315. doi: DOI: 10.1038/srep4231. [Wan2020] Wang et al., Matter and Radiation at Extremes, 5, 035201 (2020). [Yu1994] Yu. A. Merkuliev, A. A. Akunets, V. S. Bushuev, V. M. Dorogotovtsev, A. I. Gromov, A. I. Isakov, A. I. Nikitenko, S. A. Startsev, S. M. Tolokonnikov, R. C. Cook, Study of Production and Quality of Large (1–2 MM) Polystyrene Hollow Microspheres, MRS Online Proceedings Library (OPL), Volume 372: Symposium W1 – Hollow and Solid Spheres and Microspheres-Science and Tech- nology , 1994 , 119 DOI: https://doi.org/10.1557/PROC-372-119. [Zen2010] Zenobia, S. J. (2010). Surface morphology of tungsten at high Temeprature for the first wall armor and divertor plates of fusion reactors. Madison Wisconsin: University of Wisonsin Mad- ision Fusion Technology Institute. [Zhe2016] Zheng, W., Wei, X., Zhu, Q., Jing, F., Hu, D., Su, J., Deng, X. (2016). Laser performance of the SG-III laser facility. High Power Laser Science and Engineering, 4, E21. doi:10.1017/ hpl.2016.20. [Zin2017] Zinkle, S., Boutard, J., Hoelzer, D., Kimura, A., Lindau, R., Odette, G., … Tan, L. T. (2017). Devel- opment of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications. (V. IAEA, Ed.) Nuclear Fusion, 57, pp. 092005-18pages. doi:DOI 10.1088/1741-4326/57/9/092005. [Zou2008] Zou, J.P., et al., 2008. Recent progress on LULI high power laser facilities. Journal of Physics Conference Series 112 (Part 3). https://doi.org/10.1088/1742-6596/112/3/032021. [Zyl2018] A.B. Zylstra, et al., Phys. Plasmas, 25, 056304, 2018. [Zyl2022] A.B. Zylstra, et al., Phys. Rev. E 106, 025202, 2022. 138

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APPENDIX 8.2 Abbreviations Abbreviation Full Term 1D One-Dimensional 2D Two-Dimensional 3He Helium-3 Isotope 2PP Two photon polymerization; a high-resolution additive manufacturing method AI Artificial Intelligence AM Additive Manufacturing appm atomic parts per million AWE Atomic Weapons Establishment, United Kingdom Be Berylium BMBF Bundesministerium für Bildung und Forschung BoP Balance of Plant BRN Basic Research Needs CALA Center for Advanced Laser Application, München CBET Cross-Beam Energy Transfer CEA Commissariat à l’énergie atomique et aux énergies alternatives, France CEA-SBT Service des Basses Températures of CEA, Grenoble, France CLF Central Laser Facility of Science, Technology, and Facilities Council, United Kingdom CR Convergence Rate D Deuterium DD direct drive DiPOLE 10 Hz Laser System at Rutherford Appleton Laboratory, Didcot DIR Direct internal recycle DLC Diamond Like carbon 139

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MEMORANDUM LASER INERTIAL FUSION ENERGY Abbreviation Full Term DOE Department of Energy dpa Displacements per Atom DPSSL Diode Pumped Solid State Laser DRACO Dresden laser acceleration source at HZDR DT Deuterium Tritium ELI Extreme Light Infrastructure ENEA Research Center in Frascati, of the Italian National Agency for New Technologies, Energy and Sustainable Economic Development EOS Equation of State F4E Fusion for Energy FOAK First of a Kind FESAC Fusion Energy Sciences Advisory Committee FI Fast Ignition FPP Fusion power plant FZJ Forschungszentrum Jülich g Acceleration of gravity, 9.8 m/s G Gain GA General Atomics, USA GDP an amorphic polymer plastic formed through Glow Discharge Polymerization in a plasma GEKKO Laser system at Institute for Laser Engineering, Osaka GLC Generalized Lawson Criterion GSI Helmholtz Zentrum – Gesellschaft für Schwerionenforschung mbH HAPL High Average Power Laser program; USA 2000 – 2008 HDC High density carbon (a nano-crystalline diamond material) HED High Energy Density 140

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APPENDIX Abbreviation Full Term High-Z Material of high atomic number HIJ Helmholtz-Zentrum Jena HIBEF Helmholtz International Beamline for Extreme Fields, HZDR HiPER High Power Laser Research, EU project 2008-2013 HPC High Performance Computing HZDR Helmholtz-Zentrum Dresden Rossendorf ICF Inertial confinement fusion IDD Indirect drive IFE Inertial Fusion Energy ILE Institute for Laser Engineering, Osaka INFUSE Innovation Network for Fusion Energy J Joule JET Joint European Torus KIT Karlsruhe Institute of Technology kJ KiloJoule kWh Kilowatt hour LLE Laboratory for Laser Energetics, Rochester LMJ Laser Megajoule, France LMU Ludwig-Maximillians-Universität München LANL Los Alamos National Laboratory, USA LIFE Laser Inertial Fusion Energy, LLNL reactor development effort, USA 2008 – 2013 LIGA Lithographie, Galvanoformung, Abformung – lithography, electroplating, and molding LLE Laboratory for Laser Energetics of the University of Rochester, USA LLNL Lawrence Livermore National Laboratory, USA 141

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MEMORANDUM LASER INERTIAL FUSION ENERGY Abbreviation Full Term LPI Laser-Plasma-Instabilities Nd Neodym MOPA Master Oscillator Power Amplifier MEMS Microelectromechanical systems MFE Magnetic Fusion Energy mg Milligram MINT Mathematik Informatik Naturwissenschaft und Technik MJ MegaJoule MPQ Max-Planck Institut für Quantenoptik, Garching mrad Milli-radian NIF National Ignition Facility, USA nm Nanometer NNSA National Nuclear Security Administration OMEGA Laser System at Laboratory for Laser Energetics, Rochester OSTP Office of Science and Technology PAM Preamplifier Modul PCS Power Conditioning System PE-CVD Plasma enhanced chemical vapor deposition PENELOPE Petawatt ENergy-Efficient Laser for Optical Plasma Experiments, project at HZDR PEPC Plasma-electrode Pockel cepp PHELIX Petawatt High-Energy Laser for Ion eXperiments, GSI Darmsadt PIC Particle in Cell, Code POLARIS Multi-hundred Terawatt laser system, operated at HIJ PPP Public Private Partnership 142

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APPENDIX Abbreviation Full Term PRO Priority research opportunity PW PetaWatt R&D Research and Development ROMP Ring opening metathesis polymerization SI Shock ignition T Tritium TBR Tritium breeding ratio TRL Technical Readiness Level TW Terrawatt TUD Technical University Darmstadt USP Unique Selling Point UPM Universidad Politécnica de Madrid YAG Yttrium-Aluminum-Garnet-Laser Yb Ytterbium Z Atomic number of an element 143

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MEMORANDUM LASER INERTIAL FUSION ENERGY 8.3 Terms of Reference Expert Group on Inertial Fusion: Terms Of Reference The fusion of light atomic nuclei is the primary Tasks: energy source of the universe. If we could de- velop this energy source for controlled energy » Summarized presentation and evaluation generation on earth, humanity would have ac- of the global state of the art of science cess to a climate-neutral, inexhaustible source and technology of energy almost entirely independent of any • of inertial fusion energy (IFE): location factors. The research and develop- • Approaches to inertial fusion ment of fusion energy is a grand scientific • Consideration of the required modular and technological challenge calling for differ- technologies ent approaches and paths to max-imize the probability of success. In view of major prog- » Expertise, competence and capabilities ress made in the past two years, a number of • Who are the scientific players who countries, including the USA, France, the UK play a key role in inertial fusion re- and China, are currently launching new initia- search worldwide? tives and investment to accelerate technology • Which scientific centers in Germany development for fusion-based energy pro- contribute what kind of expertise to duction, establish innovation ecosystems to- the research of inertial fusion? gether with industry and thus position them- • In which areas does Germany have selves favourably in international competition. outstanding scientific expertise, and where does it have any deficits? Germany is currently developing one of the • In which areas does German industry most promising approaches, magnetic fu- have outstanding know-how? sion, in the context of national and interna- • What capabilities or experimental fa- tional partnerships. The ITER fusion research cilities in Germany contribute to or facility, which is currently being constructed could be employed in the solving of in France, is intended to demonstrate posi- questions on inertial fusion? tive net energy production on the basis of an • In which technologies does Germany MFE concept. It is expected to facilitate first have unique advantages today? research experiments with fusion plasmas of deuterium and tritium in 2035 at the earliest. » Research needs • What are the biggest obstacles to in- The National Ignition Facility at Lawrence Liver- dustrial application of inertial fusion more National Laboratory in the USA pursues from a current perspective? a different approach, known as laser-based • What are the resulting research needs? inertial confinement fusion, and achieved an Which German universities or research energy yield of 1.3 megajoules (MJ) in 2021. institutions could make relevant con- This groundbreaking achievement together tributions to research based on exist- with the successful follow-up experiments, ing expertise (such as experiments, the possibility of modular development of the theory and simulation, artificial intelli- necessary technologies and the US decision to gence and machine learning, diagnos- once again launch an IFE program are all good tics, drivers, targets, materials, inte- reason to reassess the situation of inertial fu- grated plant or system engineering)? sion in Germany and create an overview of possible research needs. 144

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APPENDIX » Scaling and implementation • Germany‘s science and industry eco- system has unique features in some technologies. Which of them could enable accelerated market access in a partnership with leading countries in inertial fusion? • What needs exist in terms of train- ing and labor force development? » Evaluation of the role of industry, includ- ing the evaluation of public-private part- nerships in an IFE program • As far as is known, what is the status of technology development among the relevant enterprises in the field of inertial fusion? • What spin-out technologies can be ex- pected as far as is predictable today? • In which fields can collabora- tions between enterprises and universities or research institu- tions accelerate development? » Timeframe • In what timeframe can the above mentioned technological obstacles to the implementation of inertial fusion be overcome? • When can we expect an industrial use of inertial fusion (possibly broken down by different approaches)? » Recommendations • To what extent does it make sense for Germany to be involved in inertial fu- sion from a scientific, technological or economic perspective? • How should Germany position itself in terms of science/technology to be- come a major partner in the interna- tional development of inertial fusion? • What strategic international partner- ships should be envisaged, if any? 145

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MEMORANDUM LASER INERTIAL FUSION ENERGY 8.4 Expert Panel Prof. Dr. Constantin Leon Haefner » Head of the BMBF Inertial Fusion Energy Expert Panel » Commissary for Fusion Energy, Fraunhofer Gesellschaft » Head of Fraunhofer Institute for Laser Technology, » Ordinarius, Chair for Laser Technology, RWTH Aachen Members of the Inertial Fusion Expert Commission Neil Alexander, PhD » Director Inertial Fusion Energy at General Atomics, US Prof. Riccardo Betti, PhD » Chief Scientist, Laboratory for Laser Ener- getics » RL McCrory Professor, Depts. Mechani- cal Engineering and Physics, University of Rochester, US 146

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APPENDIX Omar Hurricane, PhD » Chief scientist of the Inertial Confinement Fusion Program » Distinguished Member of the Technical Staff, Design Physics (DP) Division » Lawrence Livermore National Laboratory LLNL Tammy Ma, PhD » Program Element Leader for High-Intensity Laser HED Science, Advanced Photon Tech- nologies » Lead, Inertial Fusion Energy (IFE) Institu- tional Initiative » Lawrence Livermore National Laboratory LLNL Prof. Dr. Robert Stieglitz » Head Institute for Neutron Physics and Re- actor Technology (INR) » Chair Institute for Applied Thermofluidics (IATF) » Director Frederic Joliot-Otto Hahn School (CEA-KIT) » Karlsruher Institute of Technology (KIT) Prof. Dr. Hartmut Zohm » Director at Max-Planck Institute, Max- Planck Institute for Plasmaphysics » Honorary Professor at Ludwig-Maximilians University Munich 147

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MEMORANDUM LASER INERTIAL FUSION ENERGY Impressum Herausgeber BMBF-Expertenkommission zur laserbasierten S. 92, Fig. 18: links Fraunhofer ILT Trägheitsfusion, vertreten durch ihren Spre- rechts LLNL cher Prof. Dr. Constantin Leon Häfner S. 94, Fig. 19: LLNL S. 96, Fig. 20: LLNL Stand S. 97, Fig. 21: links ELI beamlines Mai 2023 rechts STFC UKRI S. 98, Fig. 22: Fraunhofer ILT Text S.103,Fig. 23: Fraunhofer ThinkTank nach Expertenkommission [Spe2021] S. 104, Fig. 24: Prof. Dr. Constantin Haefner Gestaltung S. 108, Fig. 25: Prof. Dr. Constantin Haefner Coverbild: Fraunhofer ILT S. 114, Fig. 26: LLNL Rest: VDI Technologiezentrum GmbH Bildnachweise Coverbild: » Hintergrundgrafik: Tee_Photolive » Target: LLNL » Plasma: pixelparticle » Stromleitungen: peterschreiber.media » Diamantkugeln: Fraunhofer IAF » Laser: Prof. Dr. Constantin Haefner » Netzwerk: AdobeStock_ 162834039 » KI: AdobeStock_208569122 S.32, oben: wenjin chen S.32, unten: LLNL S. 37, Fig. 1: LLNL S. 38, Fig. 2: Prof. Dr. Constantin Haefner S. 41, Fig. 3: Prof. Dr. Hans-Martin Henning nach [Uec2021] S. 43, Fig. 4: Omar Hurrican, PhD S. 46, Fig. 5: LLNL S. 56, Fig. 6: LLNL S. 57, Fig. 7: General Atomics S. 58, Fig. 8: LLNL S. 59, Fig. 9: General Atomics S. 60, Fig. 10: General Atomics S. 61, Fig. 11: General Atomics S. 63, Fig. 12: General Atomics S. 68, Fig. 13: Neil Alexander, PhD S. 71, Fig. 14: Prof. Dr. Hartmut Zohm S. 73, Fig. 15: Prof. Dr. Robert Stieglitz S. 78, Fig. 16: Prof. Dr. Robert Stieglitz S. 90, Fig. 17: Prof. Dr. Robert Stieglitz