SAND2007-2984P PULSED POWER at Sandia National Laboratories: the first forty years Anne Van Arsdall WHAT IS PULSED POWER . . . In the early days, this technology was often called 'pulse power' instead of pulsed power. In a pulsed power machine, low-power electrical energy from a wall plug is stored in a bank of capacitors and leaves them as a compressed pulse of power. The duration of the pulse is increasingly shortened until it is only billionths of a second long. With each shortening of the pulse, the power increases. The final result is a very short pulse with enormous power, whose energy can be released in several ways. The original intent of this technology was to use the pulse to simulate the bursts of radiation from exploding nuclear weapons. Pulsed Power Timeline (over) iv ACKNOWLEDGMENTS Jeff Quintenz initiated this history project while serving as director of the Pulsed Power Sciences Center. Keith Matzen, who took over the Center in 2005, continued funding and support for the project. The author is grateful to the following people for their assistance with this history: Staff in the Sandia History Project and Records Management Department, in particular Myra O'Canna, Rebecca Ullrich, and Laura Martinez. Also Ramona Abeyta, Shirley Aleman, Anna Nusbaum, Michael Ann Sullivan, and Peggy Warner. For her careful review of technical content and helpful suggestions: Mary Ann Sweeney. For their insightful reviews and comments: Everet Beckner, Don Cook, Mike Cuneo, Tom Martin, Al Narath, Ken Prestwich, Jeff Quintenz, Marshall Sluyter, Ian Smith, Pace VanDevender, and Gerry Yonas. For their assistance with and comments on content: Malcolm Buttram, Jim Lee, Ray Leeper, Keith Matzen, Tom Mehlhorn, Tom Sanford, and Charles Shirley. Scientists and engineers for information provided: Ray Clark, Ellis Dawson, Steve Downie, Mike Desjarlais, Mark Kiefer, Dan Jobe, David L. Johnson, Barbara Lewis, John Maenchen, Dillon McDaniel, Cliff Mendel, Craig Olson, Charlie Robinson, Johann Seamen, Dave Seidel, Steve Shope, and A.W. Snyder. CONTENTS CHAPTER ONE from 1960-1970 . . . 1 Technical Sidebars: - Atomic Energy Commission to National Nuclear Security Administration . . . 2 - Weapons Effects Simulation and Radiation Effects . . . 4 - The Cable Pulser . . . 6 - Pulsed Power Technology . . . 9 - Spastic . . . 10 - Hermes I and II . . . 14-15 - REBA . . . 17 - Hydra and SLIM . . . 20-21 - Lasers . . . 22 CHAPTER TWO from 1970-1980 . . . 27 Technical Sidebars: - Fusion . . . 28 - Beckner, Yonas, Narath . . . 32 - Wire-On-Axis Research . . . 34 - Early Codes . . . 40-41 - Proto I and Proto II . . . 42-43 - Countdown to EBFA/PBFA I . . . 48 - Particle Beam Weapons Make Headlines . . . 50 - Magnetically Self-Insulated Transmission Lines . . . 53 - EBFA-PBFA: Electron Beams vs. Ion Beams . . . 54-55 - PBFA II Funding . . . 56 CHAPTER THREE from 1980-1990 . . . 63 Technical Sidebars: - Recollections of the First Shot on PBFA I . . . 65 - PBFA I . . . 66-67 - Major Strategic Defense Initiative Work at Sandia . . . 74-76 - A 1984 Perspective of the Strategic Defense Initiative . . . 77 - PBFA II: Technical Timeline . . . 80-83 - PBFA II . . . 84-85 - Later Computer Codes for Fusion . . . 86-88 - On the Scene at PBFA II . . . 92 - Saturn . . . 94-95 - Hermes III . . . 96-97 - New Record on PBFA II . . . 99 - Prestwich and Martin Awards . . . 100 CHAPTER FOUR from 1990 to ZR . . . 105 Technical Sidebars: - The Proposed Microfusion Facility . . . 108-110 - Fusion Concepts-direct and indirect drive . . . 111 - International Collaborations . . . 112-113 - The Fusion Policy Advisory Committee . . . 115 - PBFA II Target Experiments, 1991 . . . 117 - The National Ignition Facility . . . 120-121 - Science-Based Stockpile Stewardship . . . 122-123 - Sculpture Honors Pulsed Power Researchers . . . 126 - Z Pinch . . . 127 - Sandia's 1995 Breakthrough with Z Pinches . . . 128-129 - Final Results of Sandia's Ion Beam Research . . . 132-133 - Highlights from Z . . . 134-135 - VanDevender, Yonas Pulsed Power Awards . . . 136 - Z-Pinch Inertial Fusion Energy . . . 140-141 - ZR . . . 142-143 - Z-Beamlet . . . 144-146 INTRODUCTION Pulsed power accelerators store electrical energy, compress it in time and space, and deliver it to a target as strong, short, fast-rising pulses of power. How the energy is delivered determines the type of radiation, or the beam, that will be produced. Sandia needed such capability beginning in the 1960s for one of its traditional responsibilities, weapons effects simulations. The military was building new kinds of electronics into warheads, and the United States needed to test their vulnerability to radiation from an enemy's nuclear weapons. The accelerators could simulate the effects of those weapons and harden US warheads against them. Chapter one of this history outlines the early years of pulsed power at Sandia, the 1960s and early 1970s, when collaborations with the Atomic Weapons Research Establishment in the United Kingdom resulted in Sandia's building relatively small machines capable of simulating gamma rays and then x rays. At the same time, the Department of Defense was building competing accelerators for the same purpose, some of them attempting to create controlled fusion events in the laboratory in classified experiments. (Uncontrolled fusion reactions are used as the secondaries in nuclear weapons.) In parallel with accelerator development, the newly invented laser was being established as an important technology for many of the same applications as accelerators at Lawrence Livermore, Los Alamos, and Sandia laboratories, and at the Naval Research Laboratory. During the 1960s, Sandia established a basic research program to support its traditional engineering design work. Al Narath and Everet Beckner, two new staff members who rose quickly into higher management, spearheaded this effort, and out of this program came the push to get Sandia into the inertial confinement nuclear fusion arena. Nuclear fusion was at the time dominated by Livermore and Los Alamos, using lasers as drivers. Realizing that pulsed power accelerators might be suited to fusion research, Narath and Beckner saw a fusion program as one way to attract new talent to Sandia. In addition, fusion research would help bolster Sandia's role in national defense and other areas and also had the potential for development as a source of energy, which greatly added to its appeal. Chapter two covers roughly the decade of the 1970s. In the early years of that decade, Narath and Beckner hired Gerry Yonas into Sandia because of his expertise at Physics International with large accelerators and fusion work. Very soon after coming to Sandia, Yonas began to champion Sandia's accelerators as potential drivers for inertial confinement fusion to the Department of Energy and Congress. Because lasers were seen as the frontrunner technology for fusion, the proposal to consider accelerators for the same purpose was viewed with some skepticism. Indeed, Livermore and Los Alamos did not welcome what they considered a dark-horse contender in the fusion arena. Pulsed power accelerators and their particle beams did not seem to them well suited to this work because the beams were difficult to focus to a small area. (Tight focusing, which lasers do easily, is crucial to compressing and heating the fusion pellet.) Moreover, Sandia would be competing for funding in an area the other laboratories had dominated. Chapter two also relates how various test beds and increasingly powerful accelerators were developed in the pulsed power area for weapons effects simulations, as the inertial confinement fusion program grew. It was during this time that Sandia changed its approach from using electron beams to light ions for fusion. Reflecting the increasing complexity of fusion and weapons effects studies, the new field of computers and computer codes began to aid understanding and predictions. Chapter three covers the 1980s and the beginning of Sandia's large complex accelerators designed specifically to ignite an inertial confinement fusion reaction. Teams of experts were brought together for this effort, which requires interdependent elements to make fusion work. The elements include designing the machines (such as PBFA I and PBFA II) and diodes to create particle beams or other mechanisms for delivering power onto a target, fabricating fusion pellets inside specially designed targets, implementing detailed diagnostics for experiments, and creating computer codes to understand and then predict what the diagnostics revealed. In 1984, Pace VanDevender took leadership of what had grown into a Pulsed Power Program. Yonas left to become chief scientist in the national Strategic Defense Initiative (Star Wars), and, in fact, Sandia was assessing the use of pulsed power capabilities as beam weapons. As earlier, Sandia's particle beams were competing with the lasers at Livermore and Los Alamos in the areas of fusion and beam weapons. Chapter three outlines how simulation of weapons effects continued to be a mainstay of the Pulsed Power Program and subsequently began to vie with fusion in importance. At the national level, defense requirements necessitated a facility capable of high-yield fusion that could deliver levels of energy beyond simple ignition, and plans were formulated around even more powerful lasers and/or accelerators as drivers. Meanwhile, controlled fusion ignition continued to be assessed by computer calculations, but eluded laboratory experimenters everywhere. Sandia's main approach during this period was to use lithium ion beams as the driver for fusion. The final chapter in this history, chapter four, spans the 1990s and the early years of the twenty-first century. Using PBFA II, Sandia tried a variety of techniques to get its light-ion beams to deliver the power on target needed to prove this technology was capable of igniting a fusion reaction in a pellet. The caveat was that even if the technique were shown to be successful, a bigger machine would actually be required to deliver enough power to ignite fusion in a pellet. VanDevender led the program through this time, which involved a number of focused national reviews, and in 1993 turned the reins over to Don Cook, who had been the program manager under him. As difficulties with the ion-beam approach were slowly being overcome, another long-time candidate for fusion, called the z pinch, scored unexpected successes on Saturn, one of Sandia's large accelerators (formerly PBFA I). Z-pinch technology—used in the target area to produce non-thermal x rays for testing nuclear weapons effects and for x-ray laser experiments—had been in the weapons programs for many years (harking back to the 1960s). It had been sidelined at Sandia in favor of ion beams because particle beams were considered at the time more suited for use in a fusion power plant. The upshot was that PBFA II was reconfigured for z pinches in 1996 and light-ion-beam work for fusion ceased. The new accelerator was renamed Z to emphasize the commitment to z-pinch research, and with Z, Sandia achieved an impressive series of scientific breakthroughs. Cook left the Pulsed Power Program in 1999 to head up the new Microsystems and Engineering Science Applications (MESA) program. Succeeding him was Jeff Quintenz, a theorist who had been with pulsed power since coming to Sandia in 1975. A major event under Quintenz was obtaining approval and funding to refurbish and upgrade Z into the more powerful ZR. In 2004, soon after the funding for ZR was approved, Quintenz accepted a position outside pulsed power, and in January 2005 Keith Matzen took over the Pulsed Power Sciences Center. Matzen, a high-energy-density physicist, had been Quintenz's deputy and had long been a key player in the z-pinch program. The spectacular Z, which prompted a story in Esquire in 1999, has continued to be a major tool in Sandia weapons effects, weapons physics, and fusion technologies (now more often called high-energy-density physics than fusion). Z and other capabilities in the pulsed power area are major contributors to Sandia's traditional mission of verifying the safety and reliability of the nation's stockpile of nuclear weapons. In addition, Z contributes to the development of the National Ignition Facility, just as the refurbished Z will when succeeding Z. Although the research on Z has been the most visible and best-known part of pulsed power work at Sandia, other long-term capabilities continue to be strong. These capabilities include directed energy technologies and repetitive-rate high-energy pulsed power, and, harking to its beginning, weapons effects simulations and radiography. Because the emphasis in pulsed power at Sandia has been on building and operating accelerators, this history only briefly touches on theoretical and computational aspects, particularly before the late 1970s. While reading this history, it must be kept in mind that the majority of activities at the Department of Energy/National Nuclear Security Administration weapons laboratories, such as Sandia, are government-funded. Proposals for new projects, requests for funds for ongoing projects, and project reviews to determine funding levels are part of life in the nuclear weapons complex. Without approval far in advance, very large projects, such as Sandia's accelerators PBFA I (Saturn), PBFA II (Z) and the Z-Machine Refurbishment (ZR), would not be possible. Even with projects planned and often funded months or years ahead, shifting national priorities and unforeseen budget constraints quite often enter into play and are reflected in reductions, less often increases, in the amount of funding certain projects receive. For this reason, an ongoing thread of discussion in the history is funding. In this work, 'fusion' refers to inertial confinement fusion, meaning a controlled microfusion event in the laboratory involving a driver (such as a particle accelerator or a laser) and a fusion target. Where magnetic confinement fusion is meant, it is so named. The goal of both techniques is the same—to compress and heat a plasma to a temperature that will spark a fusion reaction within it. Magnetic confinement fusion is the technology being pursued in the international fusion energy effort named ITER. Inertial confinement fusion, on the other hand, has been sought primarily for weapons effects simulations, weapons physics, and other scientific reasons, and secondarily as a source of energy production. This history is drawn from written archives and from the memories of many who contributed to pulsed power at Sandia. The historic illustrations, schematics, and photos come directly from archival materials and were intentionally left unchanged. By the end of 1953, the United States had a capability no other nation had: both fission and fusion devices in its stockpile of atomic weapons. Live field tests of nuclear weapons were being conducted, with each test heavily instrumented to capture minute details of the event. In the aftermath of each test, data were studied to improve the device, maximize yield, and more fully understand the underlying physics of the weapons. Allies of the United States, notably Great Britain, were also making advances in nuclear weapons development at this time, but so was the Soviet Union. The arms race with Russia escalated steadily during the 1950s, highlighted by the first Soviet fusion device being tested in 1955, closely followed by the launch of Sputnik I two years later. Although Sputnik was not a weapon but a satellite that orbited the Earth, its daily orbits and electronic signals were a constant reminder that US arms might not be supreme. With Sputnik II in the skies in November 1957 and the successful launch of a Soviet intercontinental ballistic missile that same year, the Cold War and the space race between the United States and Russia gained momentum. This tense environment generated new responsibilities for the weapons laboratories in the United States during the 1950s. Realizing the Soviet Union had missile capability, possibly rivaling that of the United States, there were concerns about the effects of radiation from an enemy's exploding atomic weapons on US military equipment. New electronic systems were being deployed in US weapons control systems, and Sandia needed to test their vulnerability to radiation, especially to gamma rays. As vacuum tubes gave way to semiconductors, Sandia was responsible for hardening all the arming, fusing, and other systems it was developing against radiation from a nuclear explosion. In 1957, basic research responsibilities were added to Sandia's Systems Research organization to probe the complex subatomic world behind radiation effects. This research laid the foundation for what would become the fledgling Pulsed Power Program within less than a decade. Established in 1952, Systems Research initially had the goal of promoting specialization in the areas of engineering associated with ordnance development. To begin the basic research effort, a high-voltage Van de Graaff accelerator was installed in Area I, and a Sandia Lab News story of March 22, 1957, said the accelerator would 'establish the scientific basis for understanding and interpreting the effects of radiation environments.' The Van de Graaff could accelerate single types of particles at selected intensities, allowing their effects on materials to be studied individually. The high-energy particles could also be used to produce x rays or neutrons. Global concerns about radioactive fallout from international weapons testing prompted an agreement between the United States and Soviet Union suspending nuclear tests and prompting investigations into laboratory simulations to replace them. The moratorium on testing lasted from October 1958 to August 1961 and, for a time, put a brake on weapons design; however, weapons effects simulation studies in the laboratory continued unabated. In fact, such simulations had always been attractive since live tests were expensive and therefore limited in number. Great interest was sparked at this time in the United States in building a variety of machines to emulate a variety of weapons effects, and Sandia began building and/or acquiring new facilities to respond to this need. In March 1961, as a companion piece to the Van de Graaff at Sandia, a newly acquired Cockcroft-Walton accelerator began creating positively charged ions and ion beams for various experiments and studies. A junior-size Cockcroft-Walton, the Microbevatron, joined the Systems Research organization in October 1961 to produce low-current electron and ion beams for this basic research. X rays and neutrons could be generated with these accelerators but at very low dose and dose rate levels and over very small volumes compared to the levels desired for the military's weapons effects studies. Planned since 1957, the Sandia Engineering Pulsed Reactor Facility opened in 1961 in Area III, providing intense bursts of fast neutrons and gamma rays to use in radiation effects studies, in particular the effect of bursts and total doses of radiation on equipment. In the early 1960s weapons scientists began to realize that gamma rays and a broad spectrum of radio frequencies (electromagnetic radiation caused by gamma rays) had the potential to harm the operation of weapons systems at long distance from the explosion. As a consequence, the Department of Defense and the Atomic Energy Commission requested investigations of this phenomenon to ascertain where their electronic systems would fail. Thus, the weapons community and various Department of Defense agencies became very interested in the concept of high-current accelerators to generate x rays to simulate the effects of gamma rays. The unique aspect of weapons effects simulators was the requirement for very high dose rate over a relatively large volume compared to what could be produced with commercially available x-ray sources or government research accelerators. Because x rays are not as deeply penetrating as gamma rays, in the early days of weapons effects testing they were not considered to be of great importance for simulations. Some x-ray sources are high-voltage accelerators designed to produce an electron beam that bombards a metallic target. When the electrons are stopped in the target, a few percent of the kinetic energy of the beam is converted to x rays. The remainder of the energy heats the target. The x rays produced in this way are named Bremsstrahlung, a German term for braking radiation, because the x rays are formed by rapidly stopping the electron beam. If the electron beam is accelerated to energies in the 10 million electron volts to 15 million electron volts range, the Bremsstrahlung emission gives a good simulation of some weapons effects. Field Emission Corporation was founded in 1958 to develop and market x-ray sources for commercial radiography and beam physics research studies. These devices, known as Febetrons, were high-impedance pulsed power sources that produced 30-nanosecond pulses up to 2.3 megavolts driving unique x-ray tubes that produced about two rads at one meter. Sandia purchased one of their first high-voltage machines. A.W. 'Bill' Snyder, head of radiation effects then, said there was suddenly a huge market in the United States for these machines. Sandia started to develop pulsed power sources at the same time it acquired the Febetron, exploring in the laboratory how to build better radiation simulators. A machine called the cable pulser was the result, an effort that dates to the early 1960s. Researchers realized that the machine would not be able to produce adequate Bremsstrahlung x-ray intensities and dose rates over a large enough area to simulate gamma rays, and they began to look for a better way to produce the high voltage with the power needed. The requirement for high dose rate and the 15-megavolt limit meant high-current beams (100s-1000s kiloamps) and a pulse duration less than 100 billionths of a second were needed. Technology to satisfy these beam requirements was not available at this time, and as a result, Sandia and private companies interested in developing simulators for Department of Defense agencies began to seek new approaches. One interesting approach was being developed in Great Britain by a group headed by J.C. 'Charlie' Martin at the Atomic Weapons Research Establishment (AWRE), Aldermaston. This group was exploring unique ways to create high-voltage, high-current pulses and new techniques to convert these pulses to high-current electron beams with short pulse duration. Such a technology was needed to make the high x-ray dose rates required to simulate gamma rays. The work at AWRE was the start of what was later termed pulse power or pulsed power technology and pulsed power accelerators. From 1961 to early 1963, information about the initial flash of radiation from a nuclear explosion and the effects of x-ray radiation had been obtained from aboveground and underground tests of nuclear weapons, supplemented by laboratory simulations using reactors and accelerators at weapons laboratories such as Sandia. However, radioactive fallout from aboveground testing and renewed popular concern about the global effects of radiation from weapons tests by an increasing number of countries led to a Limited Test Ban Treaty being signed in August 1963 by the United States, the United Kingdom, and the USSR. The treaty prohibited testing of nuclear devices in the atmosphere, in outer space, and underwater. With full-scale aboveground tests no longer possible, weapons effects work would henceforth be laboratory simulations, supplemented by underground testing. Nuclear detonations produce a spectrum of radiation and radiation effects, so the machines used to emulate them had to be capable of producing similar spectra. Sandia and other weapons laboratories as well as private industry began a stepped-up effort to develop machines capable of producing the effects needed to understand how to harden US weapons absent any aboveground testing. In 1963, Sandia began to investigate the work Charlie Martin and his group were doing at AWRE. The highest energy, highest dose machine they had developed was called SMOG, said to stand for 'Six Megavolts or Good-Bye.' (However, SMOG produced 4 megavolts and they did not give up.) AWRE needed flash x-ray radiography, but could not afford the enormous sums Los Alamos had spent for this purpose on PHERMEX, a linear electron accelerator built for flash radiographic studies of explosively driven metal systems such as imploding nuclear weapons. Built in 1957, the Pulsed High Energy Radiation Machine Emitting X Rays (PHERMEX) at Los Alamos represented a unique—and expensive—diagnostics capability in flash radiography at the time. The AWRE pulsed power radiography approach was less expensive than PHERMEX technology, and used lower energy, higher current electron beams. The lower voltage, higher current aspect promised to better satisfy simulation requirements. These positive aspects factored into Sandia's decision to try to adopt the new pulsed power technology. Collaboration with AWRE was enabled by the Mutual Defense Agreement of 1958, which provided the basis for extensive nuclear collaboration between the United States and Britain. Ken Haynes, a reactor specialist in Snyder's group, went with several other engineers to AWRE in 1963 and 1964 to learn their technology. The contact with Martin's work convinced Sandia's staff that, with the help of Charlie Martin and his UK engineers, they could build a machine similar to SMOG to do the experiments needed for radiation hardening. Sandia opted to sign an agreement with AWRE to build a machine to create a large x-ray output. Tommy Storr and Ian Smith came over from the UK to work with Haynes in Area V in the basement of the reactor building where they built Spastic, Sandia's version of SMOG. Because of Sandia's interest in studying radiation effects using extremely high doses of Bremsstrahlung, the primary reason for building Spastic was to simulate gamma radiation. Using high doses of x rays from the machine, transient radiation effects on electrical components, electronic circuits, and systems could be analyzed. The Sandia Lab News of January 15, 1965, reported 'Sandia Laboratory Team Develops New Flash-X Ray Machine—World's Largest,' though in the story the machine remains nameless. Haynes is listed as project leader with Ray Clark and Paul Beeson as his team, and the success is attributed to international cooperation that began the previous April in England. The cooperation culminated in the first test of the device in November 1964. The 1970s and 1980s are the Cold War era, marked by competition between the United States and the Soviet Union over supremacy in strategic nuclear weapons. With their responsibilities for national defense, the Department of Defense and the Atomic Energy Commission had overlapping requirements for weapons-related programs, and they both funded work at a number of laboratories throughout the country to try to find the best solutions. Of the Atomic Energy Commission's nuclear weapons laboratories, Sandia had developed a special skill in designing pulsed power accelerators for the many types of radiation simulations needed by the weapons community. Lawrence Livermore and Los Alamos, on the other hand, had pioneered laser development to study the physics of inertial confinement fusion in addition to weapons physics. In the opening years of the 1970s, Al Narath was director of Solid State Sciences in Sandia's research organization and Everet Beckner was manager of Plasma and Laser Physics Research. Beckner's group was studying the production and output of dense plasmas. Both men recognized the importance of Sandia's high-power electron accelerators for weapons effects because of their ability to provide intense x-ray sources. In time, they became convinced that fusion research also suited Sandia's accelerator capabilities and, in addition, that an inertial confinement fusion program would greatly benefit the Labs. In spite of the opposition, Narath and Beckner relentlessly insisted upon Sandia's capabilities to do fusion and their intent to establish a program at the Labs. In 1971, the nation's fusion programs went under a Controlled Thermonuclear Research Division within the Atomic Energy Commission. At the conclusion of the review, the committee determined that electron-beam accelerators were as viable as lasers in the quest to create a controlled fusion reaction in small pellets of deuterium-tritium. Soon after the review (mid-1972), Beckner and Narath hired Gerry Yonas into Sandia's research organization. Yonas had managed electron-beam physics work at Physics International. In Yonas, Narath and Beckner found the ideal champion for Sandia's fusion program; however, not for laser fusion, but using the accelerators that he knew so well. As manager of a new Electron Beam Physics Division, Yonas joined Narath and Beckner in insisting to Livermore and Los Alamos that Sandia merited a place at the fusion table. Promoted quickly into increasingly higher management positions, Yonas would champion and lead the fusion effort inside the Labs and at the national level throughout the 1970s and into the 1980s. In 1973, an international oil crisis made energy a rallying cry in the United States and brought additional pressure on the national laboratories to identify secure, environmentally safe sources of energy. In January 1973, Sandia researchers published a paper titled 'Electron Beam Focusing Using Current Carrying Plasmas in High-nu/gamma Diodes' in Physical Review Letters. In 1974 Sandia outlined to the Atomic Energy Commission a long-range program to develop a new Electron Beam Fusion Facility. The estimated cost was $15 million, and Sandia wanted it included in the FY 1976 Congressional budget. Sandia outlined plans for Proto I (operational 1974) and Proto II (operational 1977). In late 1979, the decision was made to switch from electron beams to ion beams, renaming EBFA to Particle Beam Fusion Accelerator (PBFA). In the early 1980s, the new Particle Beam Fusion Accelerator (PBFA I) began to operate, while its more powerful successor, PBFA II, was being designed. Teams of specialists were assembled, including theorists and computer code designers, as well as traditional machine designers and target specialists. PBFA I fired its first shot on June 28, 1980, producing 840 kilojoules of energy and 20 trillion watts of power in a 40-nanosecond pulse. By January 1981, the pulsed power team could report advances in its two approaches to inertial confinement fusion: imploding foils and ion beams. During the early 1980s, Sandia developed PBFA II with 36 modules delivering 100 terawatts. Ground was broken in March 1981 for a high bay building. In 1983, the Strategic Defense Initiative ('Star Wars') was announced by President Reagan, engaging Sandia's expertise in linear accelerators (RADLAC I & II) and beam propagation (EPOCH). In 1984, Pace VanDevender was named director of Pulsed Power Sciences, and Don Cook took over the Fusion Research Department. In December 1985, PBFA II was completed ahead of schedule and successfully fired. In the fall of 1987, PBFA I was converted to Saturn, becoming the world's most powerful x-ray source. In 1988, Hermes III became operational as the world's most powerful gamma-ray simulator. In March 1989, the PBFA II team achieved a record 5.4 TW/cm2 focused ion beam, surpassing the Davidson Committee milestone. In 1985 and 1989 respectively, Tom Martin and Ken Prestwich received the IEEE Erwin Marx Award. The 1990s brought an end to the Cold War, the cessation of underground nuclear testing in 1992, and the launch of Science-Based Stockpile Stewardship. Reviews by the Koonin Committee (1990) and Fusion Policy Advisory Committee evaluated the role of pulsed power and laser fusion. In 1991, target experiments on PBFA II demonstrated successful hydrodynamic implosion of fuel capsules. In June 1995, Tom Sanford and his team achieved a dramatic breakthrough on Saturn by using large numbers of fine wires in z-pinch arrays, producing over 40 terawatts of x-rays. This led to reconfiguring PBFA II into PBFA-Z in 1996, which subsequently achieved 1.8 to 2.0 megajoules of x-rays and power levels over 200 terawatts. In 1997, Sandia formally committed its fusion program to z-pinch technology, discontinuing light-ion beam research. In 1998, Livermore's Beamlet laser was transferred to Sandia and resurrected as Z-Beamlet to provide x-ray backlighting diagnostics for Z. In March 2003, Z produced thermonuclear fusion neutrons in dynamic hohlraum experiments. Between 2004 and 2007, the $61.7 million Z Refurbishment Project (ZR) was executed to upgrade the machine to 26 megamperes and 350 terawatts, providing a premier platform for stockpile stewardship, materials physics under extreme conditions, and inertial fusion energy concepts.