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Overview of FRC Propulsion and Materials Research

Overview of FRC Propulsion and Materials Research. David Kirtley and George Votroubek MSNW LLC, Redmond, WA 98052, USA John Slough , Samuel Andreason, and Chris Pihl Plasma Dynamics Laboratory, University of Washington Aydin Tankut and Fumio Ohichi

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Overview of FRC Propulsion and Materials Research

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  1. Overview of FRC Propulsion and Materials Research David Kirtley and George Votroubek MSNW LLC, Redmond, WA 98052, USA John Slough, Samuel Andreason, and Chris Pihl Plasma Dynamics Laboratory, University of Washington Aydin Tankut and Fumio Ohichi Materials Science Department, University of Washington Richard Milroy, Brian Nelson and Eric Meier Plasma Science and Innovation Center, University of Washington Alan Hoffman, Kenneth Miller and Daniel Lotz Redmond Plasma Physics Laboratory, University of Washington AFOSR Propulsion Materials Workshop November 4, 2010

  2. Discussion Index • Basic of FRC Physics • Summary of Propulsion Activities • Summary of Related DOE Activities • Related Materials Interests • Current Materials Research Program • Needs and Discussion

  3. R – null radius rs – separatrix radius rc – coil radius xs – rs/rc EXTERNAL FIELD FRC CLOSED POLOIDAL FIELD Radial Pressure Balance Equilibrium Relations: Axial Pressure Balance Flux conservation Physics of Pulsed Plasmoid Propulsion - The FRC

  4. Rotating Magnetic Field Formation m=1, “saddle” coils positioned radially external to axial field coils. Two oscillators phased at 90 produce constant amplitude B. Synchronous electron motion  j(r) = e ne  r • Decreases circuit requirements (100 % solid state) • Decreases radiation losses (operation on heavy gases) • Increases plasma currents and acceleration force • Minimizes wall interaction

  5. RMF generated plasma current from synchronous electrons Steady magnetic field in conical geometry The Generic RMF-Based Thruster 3 2 ELF J 1 (1) Rotating Magnetic Fields (RMF) form high-density, FRC plasmoid (2) FRC grows and accelerates driven by RMF generated currents & steady field (3) FRC expands as ejected, converting any thermal to directed energy

  6. Electrodeless Lorentz Force (ELF) Thruster RMF Generation of the Field Reversed Configuration (FRC) * Advantages • Vast Operating Range- 10-100 kW, 1000-6000 s Isp in a single thruster • Technology Scalable- 0.1-1000’s of kWs, 1018-1020 operating densities • Low Mass Thruster and PPU- 1-2 kW/kg including PPU • Efficient Ionization- Rapid, high-temperature , and magnetically isolated • COTS Electronics- Low voltage, solid-state switching • Long Life and Any Propellant- Electrodeless and magnetically isolated Status • Basic operation and performance demonstrated with earlier ELF program • Current program aims to develop from 6.1 to 6.2 and prove a steady state thruster • Initial design and advanced antenna geometry demonstrated • Neutral entrainment chamber constructed and passive operation underway • Modeling effort contracting is underway *Started October 2010

  7. Fundamental Science Neutral Entrainment * ISSUE: Plasma formation is the primary loss mechanism for ALL electrostatic or electromagnetic propulsion systems. It prevents operation at lower specific impulse, lowers efficiency at all exit velocities, and requires high mass propellants. Solution: Entrain neutrals in an acceleration field after formation. • Benefit: Dramatic Increases in T/P across all specific impulses and propellants, including Air. Thrust Isp Dynamic formation and acceleration of an FRC, shown with 4 field coils *Started October 2010

  8. ElectroMagnetic Plasmoid Thruster (EMPT)* A 1 kW-scale FRC thruster for deep space missions • EMPT Thruster: • 200-2000 Watt FRC thruster (3”diameter, 4” long, 0.2-2 Joule) • Very long lifetime, throttle-able power, deep space propulsion • Dramatically lower mass than existing EP • In-situ operation on ambient propellants ELF • First Demonstration of FRC formation at <1 Joule • Plasmoid Achieved 1000-6000s Isp in Xenon, Hydrazine (simulant) • Revolutionary step in both scale and performance • First demonstration of steady state operation (50 plasmoids at 2 kHz) • Demonstrated technology scaling and circuit efficiencies (10 nH stray ) *Phase II awarded November 2010

  9. High Energy FRC Programs • Plasma Liner Compression (PLC) • High energy magnetic compression • Xenon plasma ions at > 2 keV at end regions • Pulsed High Density (PHD) • FRC formation and collision, >10 MW plasma • > 10 GW/m2 transient energy loading • Foil Liner Compression (FLC) • Metallic liner implosion • Intense transient neutron and UV radiation pulse • Translation Compression and Sustainment (TCSU) • Steady State RMF-Formed FRCs at 10 MW energies • Low density, requires low recycle/impurity rates High speed photography of Foil Liner Compression 500 Joule Xenon RMF FRC - PLC 1m diameter colliding FRC- PHD

  10. LSX/mod (formation & acceleration) TCS Chamber (confinement & RMF drive) RMF Antennas RMF Translation, Compression, and Sustainment, Experiment (TCS) • Study Formation & Sustainment ofRMF driven FRCs. • Either form FRCs directly using RMF alone, or translate and expand theta-pinch formed FRCs from LSX/mod.

  11. FRC/RMF Materials Issues Fundamentally Non-Equilibrium Transient loading • Pulsed devices have transient wall loading of optical radiation, electric fields, and perhaps some ions. • What are the equilibrium temperature and sputtering effects of pulsed wall loading? • Sputtering rates are non-linear, how is this affected? • Gas deposition and recycling are key to fusion plasmas. Wall chemistry for reactive gases • FRC thrusters and fusion devices operate on chemically reactive gases. • What effects do high-temperature ion-wall interactions (even if they are very reduced) create if the ions are Oxygen, Nitrogen, or Hydrogen? In fusion plasmas the chemical sputtering rate can be more important than the purely kinetic energy sputtering rates. Effects of magnetized plasma • FRC thrusters run with magnetically confined ions. This means pulsed, large magnetic fields (300-3000 Gauss), large gyroradii (possibly greater than the device), and very large electric fields at the wall (measured up to kV). • How does pulsed magnetic fields this change the wall interaction and lifetime picture? Optical and Nuclear Radiation • A pulsed, high-temperature device will deliver pulsed optical radiation to the wall. This has effects for both contamination as well as the sputtering. • What are the effects of pulsed optical radiation on a thruster wall, both in terms of thermal loading and interaction with a neutral gas at the wall boundary.

  12. FRC Propulsion Specific Interests • Magnetic Isolation dramatically limits plasma-wall interaction – • To what degree? • RMF – FRC Propulsion Materials Interests • Very long lifetimes must be demonstrated • ELF, EMPT development programs • Erosion of insulator. How small? Is an insulator needed? • RF coupling to high-temperature insulators (dissipation) • Quartz is great, but low thermal conductivity • BN, AlO, SiN FRC wall materials are unknown • Transient thermal and electromagnetic radiation loading is new for propulsion, must be studied • Fundamentally non-equilibrium • FRC Thruster Elements • Wall : Quartz, SiN, Other Insulators • Magnet: Aluminum Flux Conservers • RMF: Copper Antenna Quartz Insulator Backplate Aluminum Flux Conservers Reflectors, and Heatsinks

  13. Current DOE Plasma-Wall Research 1 • First Wall Material Coatings and Preparation • Ta, SiO2, coating for surface gas loading • Steel and Quartz Chemistry during reversals • Siliconization, atomic oxygen loading • Ti-Gettering • Diagnostics (SAS) • Cylindrical Mirror Analyzer (CMA) • Energy Dispersive X-Ray Spectroscopy (XPS) • Plasma Chemical Vapor Deposition (PCVD, RGA) • Aurger Electron Spectroscopy (AES) • Vacuum materials handling capabilities • Diagnostics (TCS and UW) • He-GDC • Scanning Electron Microscopy (SEM) • Multi-point Thompson Scattering (MTS) • In-situ Optical First Wall Diagnostic • Scrape-off layer Langmuir Materials Concerns Impurities from Wall Materials Impurities from Gaseous Wall Loading Chemical and Kinetic Sputtering Gas Implantation – Recycling, Embrittlement Neutron Activation, Embrittlement

  14. Current DOE Research Program 2 • UW Experimental Efforts • Wall Materials Selection • First Wall Processing • High Energy Diverter Studies • Neutron Studies, DPA limits • PSI-Center Modeling Efforts • NIMROD FRC modeling of scrape-off and wall layer • NIMROD modeling of diverter flow • First wall interaction * • A. Tankut, G. Vlases, K.E. Miller, et al. “Wall conditioning in TCSU and its effect on plasma performance”, Journal of Fusion Materials, 2010 • A. Tankut, K.E. Miller, et al. “An XPS study on the evolution of type 304 stainless steel surface during routine TCSU operation”, JFM, 2010 • AydinTankut “Surface Analysis Studies in the Translation, Confinement, and Sustainment Upgrade (TCSU) Experiment”, Doctoral Thesis, 2009 • A. Tankut, F. S. Ohuchi . “SurfaceAnalysis Studies of TCS-U Components”, Innovative Confinement Concepts Meeting, 2008 • A. Tankut, F.S. Ohuchi.” Surface Analysis Studies on the Wall Conditioning of TCSU”, APS 2008

  15. Needs and Discussion Fundamental Science Question: What are the average temperature and sputtering effects of, non-equilibrium, chemically-reactive, transient plasma-wall interaction in a highly magnetized plasma? Experimental effort to demonstrate FRC lifetimes and identify erosion concerns Empirical quantification of erosion, deposition, chemistry in pulsed, magnetically confined plasmas Modeling effort to determine transient plasma radiation and thermal transport Modeling effort to assess optimal geometries and materials

  16. Proposed Effort Extension • Leverage University of Washington DOE programs for propulsion efforts • UW MSE, RPPL experience, diagnostics, and hardware • UW Personnel* • PSI-Center Modeling • Add interface to the Neutral Entrainment experiment to utilize existing SAS Hardware • MSE post doc runs investigation (Dr. Tankut), supervised by Shumlak, Nelson • MSE diagnostic package • Erosion • Deposition • Surface Chemistry • Materials Selection • PSI-Center Boundary Condition and Geometry Group modeling effort • NIMROD runs for ELF • Implement UEDGE Tokamak code Questions to Answer What and where is the erosion on a steady state ELF thruster What is the erosion, deposition, and chemical interaction for NE and reactive propellants What are the steady state temperature and erosion rates of non-equilibrium, chemically-reactive pulsed plasma-wall interaction in a highly magnetized plasma?

  17. TCSU Surface Analysis System Equipped With: - Analysis Chamber: X-Ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) - Glow Discharge Test Chamber: Ta-electrode, Residual Gas Analyzer (RGA) - Sample Transfer Device Glow Discharge Test Chamber Pbase: high 10-8 - low 10-7 Torrs RGA Glow Gas Inlets Ta electrode Sample Transfer Device Pbase: low 10-8 Torrs Additional (Campus) Facility Scanning Electron Microscopy (SEM) + Energy Dispersive X-ray Spectroscopy (EDS) Analysis Chamber Pbase: low 10-9 Torrs Electron Energy Analyzer X-ray Source Ion Pump Turbomolecular Pump Transportable P-supply

  18. Impurity problem in TCS Radiated Power vs. Total Input Power Significant fraction of the input power was radiated Impurities prevented the study of FRC physics in TCS

  19. After Standard Cleaning After He-GDC After Up to atmospheric N2 Summary of the evolution of SS in TCSU After Plasma Plasma GDC Up to N2 atm. O2 N2 e- H+ He+ H2O e- CxHy, H2O OH Fe-O , Cr-O O Bulk: Fe0, Cr0, Ni0 Fe Fe Fe0, Cr0, Ni0 Fe0, Cr0, Ni0 Fe0, Cr0, Ni0 Fe Fe O O O O C C

  20. Preliminary Ti-gettering tests: • - Basic understanding of processing parameters; SEM/EDS system was used. • Morphology was similar for Ti-film deposited on SS and quartz. • Increasing the substrate temperature from RT to 100oC did not result in an observable change in morphology or deposition rate. • Reducing the filament current b y ~15% reduced the deposition rate significantly. ON SS ON Quartz High temp (100oC) Low current (~15% lower) Ti O C O Fe Ti C O O Si Ni C C Ti/SiO2 T: RT, I: 16.5A, D: 60 min. Ti/SS T: RT, I: 16.5A, D: 60 min. Ti/SiO2 T: RT, I: 14.2A, D: 60 min. Ti/SS T: 100oC, I: 16.5A, D: 60 min.

  21. Surface analysis: Ti-gettering in TCSU (Phase I): e- Reduction of Fe by Ti on Ti-coated sample surface hν e- SS 1 SS 2 +16 Plasma shots 1st Ti-gettering Pre Ti-gettering Ti (few nm) 54% Fe0 38% Fe0 30% Fe0 XPS on Ti-coated surface (SS1) Intensity (au) Intensity (au) Intensity (au) Plasma shots lead to oxidation of Ti and reduction of Fe: - Volatiles from SS were trapped in Ti Binding Energy (eV) Binding Energy (eV) Binding Energy (eV) Fe-O was reduced by Ti: -∆GoTiO2 > -∆GoFe2O3 H+ H+ 24% Ti0 20% Ti0 H2O Ti film X H2O H+ X Intensity (au) Intensity (au) Fe-O , Cr-O Bulk: Fe0, Cr0, Ni0 Bulk: Fe0, Cr0, Ni0 Binding Energy (eV) Binding Energy (eV)

  22. 3. Ti-gettering - Summary • Preliminary Tests: Deposition rate can be controlled by filament current • Ti-gettering in TCSU: • 1st Ti-gettering: Improved vacuum, pumping H-species, reduced Fe-O • Plasma shots: Inhibited release of H2O • Plasma Performance: • Drastic reduction in impurity radiation (Ti on N and S bellows) • Drastic reduction in H-recycling

  23. FRC Generation Employing a Rotating Magnetic Field (RMF) RMF in R- plane generated by two sets of axial conductors (Helmholtz-like pair) placed orthogonal to each other. Oscillating currents, phased 90 apart creates a rotating field of constant magnitude

  24. Field Reversed Configuration (FRC) I0sin(t) Rotating Magnetic Field B rs rw Separatrix I0cos(t) L ~ 5rs Synchronous electron motion  j(r) = e ne  r m=1, “saddle” antenna coils are positioned radially external to the axial field coils. Two oscillators phased at 90 produce a constant amplitude rotating field B. 3 B B a a B a r r r r w w w w - - 3 B B t = 0 t > 0 a a Initial axial magnetic field Ba is reversed by synchronous J current driven by RMF RF Antenna Configuration for RMF FRC (ce >> ei) {Helicon (ce < ei)}

  25. Steady State Operation RF-capacitor circuit is charged through pulsed-charging or steady DC current Bias fields are steady or fed through similar pulsed-inductive network Gas flow is steady or synchronously chopped for high-throttled flow, no puff RMF discharge is timed to power flow and neutral density distribution Thermal/Ionization energy is added to plasmoid through current drive (Ohmic) Kinetic energy is transferred to plasmoid through inductive transfer (reactive)

  26. Downstream FRC Characteristics

  27. General Scaling Laws • Increasing neutral fill leads to larger, slower plasmoids • Decreasing neutral fill leads to hotter, faster plasmoids • Below 1E19 m-3current drive suffers and both thrust and velocity decrease • 5-10 Joule FRCs yield 20-30 km/s • 25-50 Joule FRCs yield 30-50 km/s Increasing ← Neutral Fill → Decreasing Increasing ← Neutral Fill → Decreasing Increasing ← Neutral Fill → Decreasing

  28. Task 1: ELF Thruster Program Plan Technology Development • Year 1 - Initial thruster design • Develop a thruster prototype that can demonstrate several pulse operation in a representative testing environment. • Full thruster design using existing hardware and infrastructure • Operate in a pseudo-steady state mode with extended operation • Investigate chamber effects • Validate performance goals and identify thruster design issues • Multiple Discharge, single gas puff Testing • Investigate chamber effects • Initial testing at AFRL to validate MSNW LLC results • High-Q power processing and circuit design • Year 2 - Demonstration thruster and electronics package • Develop a nose-to-tail thruster and electronics package for wide testing • Implement upgrades from Year 1 into a complete thruster package • Complete in-situ performance validation effort • Full thruster testing at AFRL • Validation testing at MSNW, UM

  29. Key Results to Date • First Demonstration of Non-Inductive Formation, Acceleration, and Ejection of FRC Plasmoids • Plasmoid Achieved 1000-6000s Isp in Air, Xenon, Monopropellant • Isp Measurement- Langmuir, B-probes track FRC acceleration, ejection • Produced > 1 mN-s /pulse (Air propellant) • Direct Thrust Measurement- via ballistic impulse pendulum developed at MSNW, • calibrated at NASA GRC • Average Power 50 kW, 5-50 J discharges • Nitrogen and Air Results • Initial testing of multiple FRC discharges • No noticeable erosion or thruster damage • Xenon Results • Demonstrated Kinetic >>Thermal Energy (impulse and magnetic pressure • balance) • Hydrazine (Simulant), Nitrous Oxide Results • Demonstrated ionization and electromagnetic acceleration of a monopropellant

  30. Fundamental Science Task 2: Neutral Entrainment ISSUE: Plasma formation is the primary loss mechanism for ALL electrostatic or electromagnetic propulsion systems. It prevents operation at lower specific impulse, lowers efficiency at all exit velocities, and requires high mass propellants. Solution: Entrain neutrals in an acceleration field after formation. • Benefit: Specific impulse can be tailored to the mission, while the thruster operated at its maximum efficiency, even on light propellants. • Basic Idea: An FRC will ‘injest’ large quantities of neutral gas through charge exchange collisions, not ionization. If you accelerate an FRC while providing upstream neutral gas, Isp can be specified and mass/thrust added with very high efficiency [1]. • ṁ Thrust Isp [1] Matsuzawa, Y., et. al, “Effects of background neutral particles on a field-reversed configuration plasma in the translation process”. Phys. Plasmas 15, (2008). Dynamic formation and acceleration of an FRC, shown with 4 field coils

  31. Task 2: Neutral Entrainment Program • Year 1 - Feasibility • Initial feasibility, interaction, and systems-level study • Neutral interaction modeling • Manifold and neutral flow design • Dynamic neutral interaction SEL implementation • AFRL numerical support • Neutral interaction experimental effort • Neutral entrainment chamber construction (ELF chamber mod) • FRC-Neutral drag and ingestion investigations • Neutral flow testing and puff valve modification • Neutral beam diagnostics investigations • Year 2 - Neutral Entrainment Demonstration • Demonstrate and quantify neutral entrainment • Neutral low modeling • AFRL numerical support • Neutral entrainment experimental investigation • Dynamic acceleration system design • Couple neutral injection and dynamic acceleration

  32. We have developed an advanced thruster concept that works and has wide-reaching payoffs • The ELF thruster is a major improvement over traditional electric propulsion, for most power levels and missions • Neutral entrainment could make it revolutionary – dramatically extending the specific impulse, thrust-to-power, and power ranges. • Direct innovative application to hypersonic vehicles, air-breathing space propulsion, in-situ propellant utilization, high-altitude recon, propellant sharing (multi mode), and ???. Fundamental Questions: Are there unforeseen technology development challenges to a pulsed inductive thruster? What are the power, specific impulse, geometry and density limits of neutral entrainment?

  33. Single Shot Electrodeless Lorentz Force Thruster Operation Successfully Demonstrated at MSNW Slough / Kirtley (MSNW), Milroy (University of Washington) • Field Reverse Configuration used to create Plasmoids in fusion community, combined with Rotating Magnetic Fields promise a breakthrough in high power (1 kW and up) space propulsion J Rotating Magnetic Field generated plasma current from synchronous electrons Steady magnetic field in conical geometry Input Power = 50 J (25-50 kW steady state) Propellant = Air, Argon, Xenon, Nitrous Oxide Measured Thrust impulse = 1mN-s per plasmoid ejection Measured Specific Impulse = 1,000-6,000 s depending mass flow rate Measured Peak Efficiency = ~50% (Xenon), theoretical = 87% RMF Antenna Steady Field Coil • Full Scale tests and optimization will be conducted at AFRL/RZSS (Haas, Brown ), modeling and Simulation AFRL RZSA / RZSS (Cambier)

  34. Dynamic Behavior with Rotating B - Thruster Configuration a) b) c) d) Helicon Thruster: With no significant diamagnetic current and negligible magnetic gradient, thruster relies on electrothermal heating and nozzle expansion at exit. Two fluid effects (double layer) enhance Isp, and efficiency . Concerns are efficiency, plasma detachment from thruster fields and beam spread. High Power Helicon Thruster: Larger RF field amplitude at lower frequency leads to a much larger high density, high  plasma. Plasma is lost from stationary plasma through axial JBr as well as electro-thermal expansion. Detachment and beam spread problems greatly reduced. Electrodeless Lorentz Force (ELF) Thruster: An even larger, lower frequency rotating field imposes synchronous  motion of all electrons. The resultant field producing a completely isolated, magnetized plasmoid (FRC). The strong axial JBr force rapidly drives the plasmoid out of the thruster. FRC expansion during ejection converts remnant thermal energy into directed energy. No detachment issues. Magnetically Accelerated Plasmoid Propulsion: With the FRC formed in ELF, further thrust or Isp can be obtained with peristaltic sequencing of axial array of flux coils. Large JBr force can be maintained throughout FRC passage enabling neutral gas entrainment significantly increasing thruster efficiency at optimal Isp. Br FjxB zc Br(vac) Br FjxB zc Br FjxB zc Br FjxB zc

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