An Interesting Poster to look at from the Tri Alpha Energy Team in California

High power electron beam for plasma heating
A. Tkachev1,2, S. Korepanov1, I. Isakov1, A. Korepanov1, K. Pirogov1,2, V. Matvienko1, I. Karnavskiy1,2, L. Tagney1, K. Knapp1 and the TAE Team
1 TAE Technologies Inc., 19631 Pauling, Foothill Ranch, CA 92610 Electron beam design[2]
2 University of California Irvine, Irvine, CA, 92697
atkachev@tae.com
APS-DPP 2020 / Online / November 9-13, 2020
Normal shot
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Abstract
A high power electron beam for plasma heating has been developed at TAE Technologies. The electron beam is designed to provide up to 200 A electron current at 30 kV accelerating voltage with pulse duration up to 6 ms. Electrons are extracted from a plasma emitter and accelerated by multi-aperture accelerating grids. The e-beam source was optimized for operation in high magnetic field. Near nominal beam parameters were achieved (although, not all simultaneously): 30 kV, 200 A, 5.7 MW, 5 ms. Extracted electron current density of more than 4.5 A/cm2 was demonstrated. Additionally, we observed virtual cathode formation and beam pinching caused by the lack of space charge compensation in the beam, i.e. lack of the ambient gas.
Introduction
Shot with virtual cathode
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Multi-aperture grid, that forms the plasma emitter for the electron beam, assembled on the connecting flange
Virtual cathode formation is observed
View at the target plate inside vacuum during the shot 1. Virtual cathode regime – low light conditions
2. Normal beam operation – much more light
Maximum achieved beam parameters
~30 kV ~190 A
3600 μs
Typical shots with near nominal parameters
References
1. Seidl, Miloš. Review of electron-beam heating of magnetic-mirror confined plasmas, with application to the Tandem Mirror Experiment. No. UCRL-52759. California Univ., Livermore (USA). Lawrence Livermore Lab., 1979.
2. Deichuli, P., et al. "Low energy, high power hydrogen neutral beam for plasma heating." Review of Scientific Instruments 86.11 (2015): 113509.
3. Sorokin, A., et al. "Characterization of 1 MW, 40 keV, 1 s neutral beam for plasma heating." Review of Scientific Instruments 81.2 (2010): 02B108.
Section view of the e-beam installed at the test stand
1. Electrostatic screen
2. Plasma expansion chamber
3. Accelerating grids
4. Beam emitter magnetic coil
5. Beamline transport magnetic coils
6. Beam dump with diagnostics
Accelerating cell simulation in PBGUNS[3]
Beam formation in an elementary accelerating cell
Voltage
Current X-ray signal
Accel. voltage HVPS current X-ray signal (a.u.)
General view of C2-W
C2-W is a plasma confinement device designed to produce and sustain FRC plasma. Field reversed configuration (FRC) is achieved with the help of two fast-coils formation sections and sustained by the neutral beam injection system. The e-beam will be injected axially into C2-W for additional plasma heating.
A shot with varying gas conditions, see description:
Electron beam design requirements[1]
Accelerating voltage Electron current Beam power
Pulse duration
30 kV 200 A 6 MW 6 ms
j3/2 = 25 A / cm2 j = 5.5 A / cm2 ‹θ2› = 56 mrad ~ 1 A
 Child’s law limit
 Extracted current density
 Optimal beam divergence
 Expected current per cell
 This can be achieved with ~200 accelerating cells
 First bunch – virtual cathode regime
 insufficient ambient gas for neutralization
 virtual cathode forms due to high space charge  X-ray intensity at the target plate is low
 Strong high-frequency noise due to VC
 Second bunch – normal beam operation
 space charge compensation becomes sufficient  X-ray intensity at the target plate is twice as high
1. 0 – 1.4 ms 2. 1.4 – 2.4 ms 3. 2.4 – 5.2 ms
Virtual cathode is formed Breakdown and recovery Normal shot conditions
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