Pulsed Fission Fusion (PuFF) Propulsion System Project PI: Robert B. Adams, Ph.D. NASA Project PI: Robert B. Adams, Ph.D. Teammates and Acknowledgements • Current • Jason Cassibry, Ph.D. – Associate Professor, UAH • Glen Doughty, NASA-MSFC/ER24 • Brian Taylor, NASA-MSFC/ER23 • Patrick Giddens – Graduate Student, UAH • Bill Seidler, Ph.D. – Research Professor, UAH • Past • Leo Fabisinski – Senior Engineer, ISSI • David Bradley – Senior Engineer, Yetispace • Erin Gish, Engineer – Boeing Project PI: Robert B. Adams, Ph.D. Fission and Fusion Energy Release • Mass Defect = Mass of free nucleons – mass of assembled nucleus • Nuclear force (residual strong force) stronger than electrostatic • Nuclear Binding Energy • E/A = (Δm/A) * c^2 • Fusion: Energy release by combining nuclei • Fission: Energy release by splitting nuclei E = mc^2 Average binding energy per nucleon (MeV) vs Number of nucleons in nucleus Coulomb (repulsive) vs Residual Strong (attractive) Project PI: Robert B. Adams, Ph.D. Fission/Fusion Reaction Space • Fission: Fissile Nucleus (U-235) + Neutron -> Product Nuclei (KE ~ 168 MeV) + Neutrons (v ~ 2.2) + 180 MeV gamma; Fission fragments yield curve vs mass number A. • Fusion: Deuterium + Tritium -> Helium + Neutron + Energy; Nuclear fusion reaction equations (D-T, D-D, D-He3, etc.) Project PI: Robert B. Adams, Ph.D. Fission/Fusion Ignition Requirements • Fission • Criticality is a function of: fission cross section, Number density, And geometry • Neutrons must balance: Lost outside reactor, Absorbed through photon capture, Fission events • Fusion • Breakeven is a function of: Fusion cross section, temperature distribution, density • Lawson Criterion: n_e * tau_E >= (12 * k_B * T) / (E_ch * <sigma*v>) Project PI: Robert B. Adams, Ph.D. Advanced Nuclear Crewed Mars Mission Concept Pulsed Fission Fusion (PUFF) Propulsion System • Propulsion concept with significant performance capability with potential to open the solar system for human exploration and near interstellar space for robotic probes • Concept focus was toward a single design suitable to enabling wide range of missions. For Mars mission performance sufficient to carry Space Habitat, CEV, Lander, Surface Habitat and ISRU facility. • Engine system provides a propulsive impulse operating on the principle of a pulsed two stage nuclear reaction triggered by the compression of a fuel target by means of an intense electrical pulse • Resultant charged particles, emitted by the impulse, are deflected by magnetic nozzle, also serving as a energy capture device to energize the primary power system capacitors for subsequent pulse Reference: Polsgrove, T. et al. Design of Z-Pinch and Dense Plasma Focus Powered Vehicles, 2010 AIAA Aerospace Sciences Meeting Project PI: Robert B. Adams, Ph.D. Two Stage Nuclear Reaction Sequence • Pre-reaction: • Lithium (Li) shell/cone is injected to bridge the power system anode to target holder (providing a complete circuit) • 2 mega-amps (at 2 mega-volts) travels along the liquid lithium cone to target. • Lorentz force (jxB) produced by the flowing current and generated magnetic field compresses hybrid target of uranium and Deuterium-Tritium (D-T) to 1/10 original size, reaching criticality for the Uranium. • First Stage (Fission): • Uranium criticality produces spontaneous fission reaction (heating) • Fission heats the D-T fuel creating fusion conditions (interaction cross-section) • Second Stage (Fission - Fusion Cascade): • Fusion produces additional neutron which in turn ignite more fission • Additional fission reactions generate more heat, boosting fusion rate • Fission to D-T fusion cycle cascades until burnout. • Expansion: • Plasma produced during impulse expands outward against magnetic nozzle • Magnetic nozzle directs the particles generating thrust & captures energy necessary to initiate the next pulse • Single target impulse event requires several microseconds; repeat up to 100 Hz Project PI: Robert B. Adams, Ph.D. Criticality • Dials for successful implosion: • Target composition • Target geometry • Compression level • Duration • Instabilities • Energy release • Shock propagation • Starting neutron flux • Tamper geometry Graph: Criticality vs. Radius for Various Compression Ratios (Spherical Target Radius 2 to 6 cm, compression ratios 2, 3, 4). Project PI: Robert B. Adams, Ph.D. SPFMax Plots showing: 1. Neutrons vs Time (ns) for Neutrons from fusion and Neutrons from fission (ranging 10^12 to 10^16). 2. Energy (J) vs Time (ns) for Energy from fusion and Energy from fission (0 to 5000 J over 100 ns). 3D SPH / particle simulation visualization of target compression. Project PI: Robert B. Adams, Ph.D. PuFF Mission Analysis • Engine Performance: • Based on previous fusion designs • Much analysis and experimentation to be made to lock down pulse frequency and target size • Specific impulse and thrust are variable, can be modified by amount of lithium injected • Future Performance: • Introduction of LTD's can increase specific power by factor of 10 Parameters and Values Table: - Isp (vac): 20,000 sec - Thrust: 29,400 N (6.5 klbf) - Specific Power: 96 kW/kg - g's: 0.015-0.027 Project PI: Robert B. Adams, Ph.D. Mars High Speed Mission • Earth to Mars in 37 days • 0.6 Earth escape • 2.6 day TMI • 31.4 day coast • 0.8 day Mars deceleration • 2.1 day Mars capture • Payload: • 25 mT crew compartment Project PI: Robert B. Adams, Ph.D. Interstellar Precursor Mission Analysis • Interstellar Space • Termination shock in 5 years (pass Voyager I) • 275 AU in 10 years • Solar gravitational lens in 20 years • 1000 AU in 36 years • Burn profile • 0.4 days Earth escape • 1.4 days deorbit • 48 day inbound coast • 2.5 day solar burnout Project PI: Robert B. Adams, Ph.D. Mass Breakout Subsystem | Mars Express | TAU Mission - Magnetic Nozzle: 14.83 mT | 14.83 mT - Radiation Shielding: 14.01 | 14.01 - D-T Tankage: 5.0 | 5.0 - Li Tankage: 1.45 | 0.94 - Truss: 2.71 | 2.09 - Other Primary Structures: 0.64 | 0.49 - Secondary Structures: 0.13 | 0.10 - Capacitor Banks: 2.10 | 2.10 - Marx Generator Circuitry: 0.13 | 0.13 - RCS Wet Mass: 1.03 | 0.79 - Low Temp Heat Rejection: 1.30 | 1.30 - Medium Temp Heat Rejection: 14.82 | 14.82 - High Temp Heat Rejection: 1.26 | 1.26 - LN2 Seed Coil Cooling: 8.41 | 8.41 - Auxiliary Power: 4.40 | 4.40 - Avionics: 0.39 | 0.39 - Payload: 25.00 | 10.00 - Dry Mass (without MGL): 94.87 | 77.57 - Mass Growth Allowance (30%): 40.66 | 35.21 - Total Dry Mass: 135.53 | 112.78 - Fuel: 56.02 | 37.03 - Total Wet Mass: 191.55 | 149.81 Project PI: Robert B. Adams, Ph.D. Activities Supporting Pulsed Fission Fusion (PuFF) Propulsion Three primary areas of focus advanced basic research for PUFF concept. • Charger – 1 – UAH led program, NASA-MSFC and Boeing participation – High Power/Pulsed Power Facility - ONGOING • A test facility for high power and thermonuclear fusion propulsion concepts, astrophysics modeling, radiation physics • Located in the UAH Aerophysics Lab at Redstone • The highest instantaneous pulsed power facility in academia – 572 kJ (1 TW at 100 ns) (1 MA at 1 MV) • Original equipment received from DTRA in 2012 • Resource to evaluate PUFF target underlying impulse physics • Linear Transformer Drivers (LTD’s) – Enabling Power System Component (Mass/Pulse) - ONGOING • Originally developed in Russia, several purchased by DOE (Sandia Nat. Labs) • Ring of capacitors discharge into central ring, inducing current in conductors running through center • Much higher efficiency and mass savings relative to current Marx bank technology • Sandia baselining LTD’s for next generation Z-machine ($3-4 B national facility) • NASA-MSFC developing smaller versions for pulsed plasma propulsion use • Larger system concepts envisioned as flight weight option for PuFF • Enabling technology significantly reduces mass of overall vehicle Project PI: Robert B. Adams, Ph.D. Charger - 1 • A test facility for high power and thermonuclear fusion propulsion concepts, astrophysics modeling, radiation physics • Located in the UAH Aerophysics Lab at Redstone • The highest instantaneous pulsed power facility in academia – 572 kJ (1 TW at 100 ns) Aerophysics Research Center UAH Project PI: Robert B. Adams, Ph.D. Charger - 1 • Progress on Control System • Hooking up 55 different GHz connections through fiber optics to monitor and control Charger – 1 • LabView Control panels being programmed • Control Loop • Data Acquisition • Communication established from Test Control Center to Decade Module Project PI: Robert B. Adams, Ph.D. Triggering System • Trigger System Installation • Fiber optic signal triggers 501B transformer – procured, waiting for arrival • 501B triggers PT55 thyratron – being rebuilt in lab • PT55 triggering PA80 capacitor/switch – PT55 found/tested • PA80 creating 80kV bridge voltage for mini-Marx – under testing • Mini-Marx triggering Marx Bank – under refurbishment by UAH/NASA • Refurb being assisted by recent location of original DECADE Quad hardware • Difficult to find some 20 yr old technology Project PI: Robert B. Adams, Ph.D. Linear Transformer Driver - Concept • Factor of 10 weight reduction in capacitor banks, structure, and associated power management. • Enables faster pulsing giving higher thrust Diagrams: Comparison of traditional Marx generator vs. Linear Transformer Driver (Primary consisting of individual loops that are self-powered and very low inductance, secondary consisting of a single bar of steel/single wire loop). Project PI: Robert B. Adams, Ph.D. Current LTD Technology • High Current Electronic Institute • Single Cavity • 0.5 MA @ 100kV • 70-100 ns rise time • 0.1 Hz pulse rate • 2 m diameter • 4 constructed • 3 at Sandia • 1 at Univ. Michigan Project PI: Robert B. Adams, Ph.D. Current LTD Technology • LTD II – Sandia National Labs • Five Cavity Experiment • Reached 400 kV, 1 MA over 100 ns Project PI: Robert B. Adams, Ph.D. Future LTD Technology • Next Generation Z – Machine • The current Z-machine operates with Marx Bank technologies • Sandia has conceived two replacement options: • Z-300: 300 TW system that would fit in current Z-machine building • Z-800: 800 TW system that, combined with Mag-LIF, is projected to reach engineering break even fusion Diagram: linear-transformer-driver (LTD) modules (210 total), radial-transmission-line impedance transformers, system of self-magnetically insulated vacuum transmission lines. Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - base assembly] Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - upper plate assembly] Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - inner ring integration] Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - trigger module mounting] Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - multi-switch assembly] Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - casing ring] Project PI: Robert B. Adams, Ph.D. LTD Version 5 [CAD rendering of LTD cavity structure - fully enclosed single cavity unit with ports] Project PI: Robert B. Adams, Ph.D. LTD Version 6 Exploded diagram showing: - Metglas Ferrite Cores - High Permittivity BaTiO3 Capacitors - High Voltage-Fast Gas Switches Project PI: Robert B. Adams, Ph.D. LTD Stack • Develop Linear Transform Driver (LTD) Stack that can be used in pulsed plasma and fusion propulsion systems Diagram components: - LTD Cavity - High Voltage Charge Lines - Trigger Lines Project PI: Robert B. Adams, Ph.D. LTD Version 7 [CAD views and exploded assembly diagram of LTD Version 7 layout and individual brick components] Project PI: Robert B. Adams, Ph.D. Research and Development Support for PuFF, Charger – 1, LTDs Historical timeline for basic R&D activities related to PUFF: • Charger-1, PuFF and LTD development provides a unique high power research and development capability for MSFC • Limited funding from varied sources and partners – focused on small hardware evaluations • Striving to maintain forward momentum Timeline Milestones: - April 2012: UAH receives DM2 from DTRA - June 2012: CSDWG awards 130K to effort - September 2012: MSFC Chief Technologist awards 0.58 FTE, 57k - December 2012: UAH receives 300k from AL Innov. Fund - February 2013: Initial mating of Charger-1 components - July 2013: NIAC Phase 1 granted for PuFF concept - May 2014: First implosion of Li wire - October 2014: CIF awarded – LTD Development - April 2015: First firing of LTD cavity - July 2015: Boeing, UAH, MSFC CSDWG commits 300k, 0.8 FTE to Charger-1 - October 2015: CIF continuation – LTD Development - Jan 2016: CSDWG commits 0.6 FTE - March 2016: ZP Advanced Propulsion FTEs - October 2016: CIF – Nuclear target/Mat'l mgmt. Project PI: Robert B. Adams, Ph.D. Key Technologies – Progression from Physics to Engineering Maturation map from Physics / R&D to Engineering across six subsystems: A - Target: Implosion Capsule -> Implosion Physics, instabilities and burn-up -> Target detailed design, enrichment and containment -> Target burn-up/yield (model/experiment) -> Manufacturing approach for Target Quantities -> Handling and Storage limitations & restrictions B - Linear Transformer Drivers (LTD): Pulsed power storage, discharge and compression system -> Physics of LTD super-cavity operation, power density and pulse compression -> LTD system material and component science to meet energy requirements -> Performance physics of integrated multiple super-cavities to yield necessary pulse with and timing -> LTD Manufacturing approaches and hardware integration -> Power / Liner system integration with structure to conduct energy pulse C - Magnetic Nozzle (MN): Directs fission/fusion products and recovers energy for next pulse -> High temperature magnetic nozzle topology, field strength, plasma coupling -> Power recovery approach methodology and design to maximize efficiency -> Superconductor type and design for minimal cooling and cooling requirements/subsystems -> Magnet integrated cooling and operations control system -> Manufacture approach and integration technique with power systems D - Recharge System: Pulse generation and onboard power storage/generation -> Power system topology to couple MN coupled energy recovery to LTD array -> Power system topology to process LTD energy for Liner/target implosion -> Onboard power generation to provide initial start / restart capability of system (solar/nuclear) -> Integrated design and power balance incorporating subsystems -> Manufacturing approach/methodology for high power components E - Lithium Injectors: Lithium tankage / distribution systems to provide target liner and power conduction path -> Linear physics interaction with implosion and power system -> Vessel/internal heating design for solid material storage - liquid dispensing -> Liquid lithium feed system with pumps supplying implosion site -> Liquid lithium liner generator design and testing -> Liner recovery process and demo between pulses F - Target Storage / Dispenser: Maintains targets in non-critical configuration, injects into nozzle -> Vessel /internal dispensing hardware design -> Target loading and containment protection -> Feed tube(s) / conveyance design for dispensing to implosion location(s) -> Target holding design at use location suitable for multi pulse operations Project PI: Robert B. Adams, Ph.D. Backup Charts Project PI: Robert B. Adams, Ph.D. LTD versions 1 and 2 [Photographs of lab bench testing setup and CAD geometry model of early LTD prototypes] Project PI: Robert B. Adams, Ph.D. LTD version 3 • Larger shell • Testing at +/- 1 kV • Still using 1 brick • Measuring induced current in central shaft Project PI: Robert B. Adams, Ph.D. LTD version 4 • Tested V6 Cavity with individual triggers for each brick. • Each of these triggers was isolated with a 500uH inductor. • Resulting pulse had 50% shorter rise time due to much shorter (and hence lower inductance) circuit path. Circuit schematic: Current Through Core, Charge Lines, 2 kV Trigger, Each of 8 Bricks. Oscilloscope trace showing measured pulse.