Global simulation of field-reversed configuration using fully kinetic ion and drift kinetic electron

Possible Role of External Radial Electric Field on Ion Heating in an FRC
Deepak K. Gupta, E. Trask, S. Korepanov, E. Granstedt, D. Osin, B. Deng, M. Beall, K. Zhai and the TAE Team
TRI ALPHA ENERGY, INC., P.O. Box 7010, Rancho Santa Margarita, CA 92688-7010 , USA
Introduction
n C-2U has achieved steady-state operation of advanced beam- driven FRCs using neutral beam injection and edge biasing.
n Edge biasing, which provides a radial electric field, is applied by either plasma guns or biased electrodes located in diverters at both ends of the machine.
n This cross-field external radial electric field helps stabilizing the FRC, and thus, provides a favorable target condition for coupling with neutral beam injection.
n In addition, an ion heating is observed due to edge biasing.
Effect on O4+ Ion Temperature (Ti) Due to Gas Puff in Necking Region C-2 – Electrode Biasing Campaign
Correlation with Edge Biasing
n C-2U had long (>7ms) shots with higher (~700eV) as well as lower (~400eV ) pressure balanced temperature (Ttotal).
n Thermal energy changes nearly 50 to 75% for similar particle inventory.
Effect of Biasing on Ion Heating
n Magnetic mirror-plug strength was changed by varying the charging voltage of the plug power supply (Vplug).
n Higher ion heating rate at lower mirror-plug field strength (or plug voltages) are observed.
n Available power from the biasing system is more than sufficient for the ‘auxiliary’ power (Paux,i) for observed ion heating
n Inferred auxiliary power even has similar time history to bias power
No Puff
20 psi Puff
40 psi Puff
n Both, total temperature, Ttotal, & Ion temperature, Ti are higher, which indicate...
èincrease in thermal energy, and
ènot only in fast ion pressure.
n Similar beam power input. No significant change in formation.
n What controls this plasma heating ?
n Correlation Matrix for relevant plasma gun parameters & plasma parameters.
Correlation Matrix
n O4+ Ion heating matches total temperature behavior, but with more stronger effect.
n Evidence of ion mass or charge dependent heating process.
n O4+ ion rotational velocity decreases with increase in plug strength.
n Reduction in average density in open field lines plasma is consistent with reduced axial mirror confinement at lower field (or Vplug).
Low Mirror-Plug Field
High Mirror-Plug Field
Cross-Field Impedance in Open Field-Lines Changes with Plug Field Strength
Courtesy: Sean Dettrick
Deepak K Gupta et.al., Tri Alpha Energy, Inc., “Possible role of external radial electric field on ion heating in an FRC ” Poster CP10.00081: 58th APS-DPP Conference, San Jose, California, October 31–November 4, 2016
Initial
sustained
sustained
Initial
n Total temperature, Ttotal and thermal energy, Eth show strong correlation with Plasma Gun Voltages.
n No correlation with plasma density.
n è Biased voltage plays role in ion heating.
R & τRC (=RC)
R & τ (=RC)
n n
n n
n
VBias
PowBias
At low Vplug, less sustained bias power but more Ion heating
=> Higher heating efficiency, or higher power/particle.
Higher initial capacitance & sustained resistivity at lower Vplug.
Conclusion
Bias current flows along multiple paths.
Higher resistivity in open field-line with low plugs allows more radial current in SOL region in confinement section.
Higher radial bias current in confinement region, and possibly voltage too, leads to higher ion heating.
IBias
RC