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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

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

  • 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

R – null radius

rs – separatrix radius

rc – coil radius

xs – rs/rc





Radial Pressure Balance



Axial Pressure Balance

Flux conservation

Physics of Pulsed Plasmoid

Propulsion - The FRC

Rotating magnetic field formation
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

RMF generated plasma current from synchronous electrons

Steady magnetic field in conical geometry

The Generic RMF-Based Thruster






(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

Electrodeless Lorentz Force (ELF) Thruster

RMF Generation of the Field Reversed Configuration (FRC) *


  • 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


  • 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

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.



Dynamic formation and acceleration of an FRC, shown with 4 field coils

*Started October 2010

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


  • 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

High energy frc programs
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

Rmf translation compression and sustainment experiment tcs


(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.

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.

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


Aluminum Flux Conservers Reflectors, and Heatsinks

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

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

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

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?

Tcsu surface analysis system
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


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










Impurity problem in tcs
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

After Standard Cleaning

After He-GDC

After Up to atmospheric N2

Summary of the evolution of SS in TCSU

After Plasma



Up to N2 atm.








CxHy, H2O


Fe-O , Cr-O


Bulk: Fe0, Cr0, Ni0



Fe0, Cr0, Ni0

Fe0, Cr0, Ni0

Fe0, Cr0, Ni0









  • - 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 Quartz

High temp (100oC)

Low current (~15% lower)















T: RT, I: 16.5A, D: 60 min.


T: RT, I: 16.5A, D: 60 min.


T: RT, I: 14.2A, D: 60 min.


T: 100oC, I: 16.5A, D: 60 min.

Surface analysis: Ti-gettering in TCSU (Phase I):


Reduction of Fe by Ti on Ti-coated sample surface


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



24% Ti0

20% Ti0


Ti film





Intensity (au)

Intensity (au)

Fe-O , Cr-O

Bulk: Fe0, Cr0, Ni0

Bulk: Fe0, Cr0, Ni0

Binding Energy (eV)

Binding Energy (eV)

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

  • 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

    Field Reversed

    Configuration (FRC)


    Rotating Magnetic

    Field B

    rs rw



    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.





















    t = 0 t > 0



    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)}

    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)

    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

    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

  • 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

    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].



    [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

    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

    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?

    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


    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)

    Dynamic Behavior with Rotating

    B - Thruster Configuration





    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.