PROTEAN : Neutral Entrainment Thruster Demonstration

Transcription

1 PROTEAN : Neutral Entrainment Thruster Demonstration Dr. David Kirtley Dr. George Votroubek Dr. Anthony Pancotti Mr. Michael Pfaff Mr. George Andexler MSNW LLC - Principle Investigator -Dynamic Accelerator Design -Test Lead -Student Labor/Modeler -Technical Staff Dr. John Slough Dr. Richard Milroy University of Washington -Thruster, MOQUI, Circuit Design -MOQUI and SEL-Hifi Distribution A; Public Release. This presentation contains MSNW proprietary information.

2 Why Neutral Entrainment? Electrothermal and fully ionized EP devices have significant, fundamental performance limits. Thermal systems are low Isp due to materials concerns T/P is limited by frozen flow (thermal, molecular) EP systems are high Isp due to plasma losses T/P is limited by frozen flow (ionization, wall losses) Neutral Entrainment is Revolutionary No Wall Thermal Issues No Plasma Performance Limitations u e e T P u 2c 2 e h P c T h h 2 c 2 u e 2e m e ion ion Thrust-to-power >> 200 mn/kw Xenon > 100 mn/kw on Lightweight propellants Huge performance envelope on all fuels

3 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. Thrust Isp Dynamic formation and acceleration of an FRC, shown with 4 field coils

4 Key Physics KEY: Momentum exchange within a magnetic field gradient that continues to apply a body force and add kinetic energy Critical Parameters: Plasma temperature Elastic processes radiation, excitation, wall interaction Charge exchange and ionization collision cross sections Ionization is not a loss mechanism! Basic Idea: 1. Form and accelerate an ion to high velocity 2. Charge exchange to create a fast-moving neutral and a slow ion 3. Charge-Exchange cross sections are much larger than Ionization cross sections 4. Add more kinetic energy and accelerate the slow ion to high velocity 5. Final product is two high velocity particles and one ionization cost Form Plasma in FRC thruster Charge Exchange with Neutral Gas Add more thrust/kinetic energy with no more ionization

5 SEL Implementation of Visco-Resistive MHD with a Dynamic Neutral Fluid Background Density Equations Momentum Equations Energy Equations Single-fluid plasma model which allows for Spitzer-Chodura resistivity, Braginskii thermal conduction, symmetric viscosity, and dissipation For readability, dissipative terms are excluded.

6 Numerical Calculation of Ion - Neutral Interaction Employing the SEL Code Initial conditions SEL-HiFi Visco-Resistive MHD Neutral and Ion Fluids added Flux-source form for inputs Completely implicit with an adaptive grid with high-order spectral elements Neutral fluid with resonant charge exchange, electron-impact ionization, and radiative recombination reactions Neutral density psuedocolor plots for baseline ELF simulation with a Gaussian radial neutral gas profile. Black and white arrows indicate the direction and magnitude of plasma and neutral momentum, respectively. Clear neutral entrainment is seen. Meier, E.T., et al. "Development and validation of a two-fluid plasma-neutral model", Innovative Confinement Concepts (2011).

7 Pressure psuedocolor plots for baseline ELF simulation. Clear neutral entrainment, pulse sharpening, and increase in external magnetic field pressure are seen. Temporal profiles of momentum-related quantities for ELF baseline simulation Distribution A: Approved for public release; distribution is unlimited.

8 Technical Approach Thruster 200 mm quartz thruster 5 kw RMF FRC thruster with 25 kw NET Accelerator Diagnostics Multi-MHz Double Langmuir, Magnetic TOF Neutral Doppler velocimetry Downstream ballistic force pendulum Combined Circuits Bias and accelerator coils, tightly integrated Innovative, high-q circuits Supersonic Injector On-axis injection with steady gas flow Combined low-velocity swirl and supersonic injection 1 kw EMPT Neutral Entrainment Dynamic Acceleration PROTEAN! MSNW Dielectric Facility

9 Neutral Entrainment as a Thruster 5 kw FRC thruster 25 kw of Neutral Entrainment Power 3-5 Stages of Neutral Injection STTR Overview PROTEAN DEMO: Joule FRC discharges at 2,000-3,000 Hz 10 Joule Neutral Entrainment Acceleration stage Average power kw with 100 V feed Specific impulse 800-5,000 s (Xenon) Operation on complex, lightweight gases Steady operation utilizing steady gas flow Key Scientific Challenges Optimization of entrainment with minimal ionization Molecular gases Theoretical thruster thrust-to-power for a Xenon thruster with various frozen flow losses. Also included is a PPU and divergence efficiency of 90% each.

10 PROTEAN Status On schedule Facilities designed and implemented Preliminary RMF source thruster design done Hardware being refurbished for use Long lead (3 month) quartz ordered and delivered Accelerator hardware procured and installed Neutral Injector designed and installed Circuit Model for coupled bias, ejector completed MOQUI model completed Thruster neutral testing underway

11 MOQUI Design Effort MOQUI Fluid, Resistive 2D MHD Used extensively in FRC modeling at UW Phase I Modeling Effort Underway Expanded PDA cylindrical model Conical Dynamic Accelerator FRC Increases lifetime Reduces wall interaction Increases coupling (M) Code complications Large expansion = unstable grid effects MOQUI modeling of a Conical acceleration section with an RMF FRC.

12 Facility and Test Design Thruster 12 degree quartz cone 0.2 m total length Radial injector ports End-mounted neutral injector port Diagnostic/Drift Section 0.25 m diameter cylindrical drift section with bias field magnets 2 axial, 2 azimuthal diagnostic ports MHz Double Langmuir, Magnetic TOF Neutral Doppler velocimetry Ballast Chamber 1 m diameter, quartz chamber with steady bias magnetic fields Ballistic Pendulum Fast Ion Gauge Hardware, flanges, and thruster completed

13 Innovative Combined Circuits Plot1 ICOIL1, ICOIL2 in amps Y3, Y8 in volts D Energy Recovery 16.0K 12.0K 1.60K 1.20K 1 ICOIL1 2 ICOIL2 3 Y3 4 Y8 Key to efficient theta-pinch acceleration 8.00K 4.00K MSNW considers it a requirement 0 0 Diode 25.0U 75.0U 125U 175U 225U TIME in secs Lswstart 124 Additional diodes, high-density capacitors Ibias 8 1 Lswbias 10 nh 7 Bias switch nh 11 Main switch 10 Imain Lmain 2 nh Icoil Lstray 2 nh Lcoil 3 Combined Bias/Acceleration Coils Steady axial bias fields (RMF) are not compatible with pulsed axial fields (PDA) K Vbias Cbias 400 µf I coil V bias V main 6 Vmain Cmain 30 µf Diode 12 Rload µh 4 Vcoil Combined axial field structure Long-duration pulsed slow field for RMF formation High-speed pulsed acceleration field for peristaltic acceleration Requires specific inductive isolation and secondary (low energy) pulsed circuit Fully integrated K K K U 15.0U 25.0U 35.0U 45.0U time in secs

14 Injector Neutral Injection is challenging in a steady operating, plasma environment Requirements Injection must be downstream Modeling results show on-axis is optimal to minimize secondary ionization and heating FRC requires slow moving, distributed gas flow Neutral flow must be ~5X more than source flow Solution AFOSR NE Phase I clearly showed axial injection required On axis supersonic nozzle 400:1 expansion -- Mach 18 Off-axis, radial injection for FRC gas With ideal swirl geometry Integrated pre-ionization

15 Key Results So Far MOQUI MHD Modeling of complete geometry, operation conditions Full circuit modeling of bias, accelerator switching and coils Thruster body, coil, interface constructed Accelerator, RMF, and bias field circuits constructed Install and initial testing underway Coaxial supersonic molecular beam injector and preionization. Spice model of bias, accelerator, and flux conserving circuits. Pressure psuedocolor plots for baseline ELF simulation. Clear neutral entrainment, pulse sharpening, and increase in external magnetic field pressure are seen.

16 MHD Modeling and Scaling Neutral Entrainment Demonstration Entrainment Argon, Xenon, Neon Axial Injection Bias Field Gauss Accelerator Coils 1-3 microsecond rise Gauss On-Going Work MOQUI modeling of a Conical acceleration section with an RMF FRC. 1. Neutral Injection - FIG 2. FRC Acceleration - TOF, Magnetic 3. Entrainment - Magnetic, Doppler 4. Thruster Operation - TOF, Impulse Photographs of thruster body, coil, interface, accelerator, RMF, and bias field circuits