Performance improvement of magnetized coaxial plasma gun by magnetic circuit on a bias coil

Introduction to C-2U
n Advanced Beam-Driven Field-Reversed Configuration (FRC); Campaign timeline: March 2015- March 2016
Motivations
2University of California, Irvine, CA 92697
A New Code (ANC)
Drift-kinetic e- at Field Nulls
n Numerical growth at field nulls can be a problem for DK
electrons due to 1/B dependence of ExB drift.
n Growth is artificially suppressed at field nulls and outside desired particle boundary by applying a masking coefficient to the weight advance (w-dot) equation of drift-kinetic particles.
masking coefficient
DC magnets
confinement vessel
neutral-beam injectors
mirror plug
FRC (core)
n Advanced beam driven FRCs at TAE are macroscopically stable, and transport limited.
n Core and SOL transport likely coupled, requiring global geometry simulation.
n Goal 1: reduced transport model.
n Goal 2: quantitative predictions of experimental transport
Local Flux-Surface Model
n Simulations carried out using the Gyrokinetic Toroidal Code (GTC)
n First-principles, integrated PIC simulation code.
Full feature list of GTC at [http://phoenix.ps.uci.edu/gtc]
n Gyrokinetic ions and drift-kinetic electrons used.
n Electrostatic model used.
n Perturbative model.
n Simulations on single flux surfaces; separately in FRC
n First-principles, PIC code designed for FRC magnetic geometry, to capture large-orbit ion dynamics, and cross-separatrix transport.
n Code physics features:
n Fully-kinetic or drift-kinetic ions.
n Drift-kinetic or Boltzmann electrons.
n Electrostatic field solver.
n Perturbative model.
n Cylindrical coordinates (not as efficient as magnetic coordinates, but span magnetic separatrix).
n Algorithms and Libraries:
n Group decomposition of particles by MPI task, OpenMP
parallelization of particle loops.
n Spectral decomposition of electrostatic Poisson solver into toroidal modes, by MPI task. Laplace matrix inversian by PETSc.
scrape-off layer (SOL)
plasma gun
n FRC Sustainment on C-2U
n 5 ms sustainment achieved June 2015.
n Sustainment correlated with beam pulse duration.
n Confinement Time Exceeds Classical FRC Scaling n Record particle
confinement times for FRC!
n Qualitatively different physics?
core and the scrape-off layer (SOL).
core
530
n Written in Fortran 2003 (mostly), some C++, Python calls. Global Simulation with ANC
n Fully kinetic ions sample both core and SOL.
Summary
Simulation of drift wave instability in field-reversed configurations
n Local Model Conclusions:
using global magnetic geometry
D. P. Fulton1, C. K. Lau2, Z. Lin2, T. Tajima1, I. Holod2, and the TAE Team1
1TRI ALPHA ENERGY, INC., P.O. Box 7010, Rancho Santa Margarita, CA 92688-7010
S. Divertor S.Formation N.Formation N. Divertor
n FRC core strongly stable! SOL turbulence weak but finite.
n Both FLR and gradient-B effects stabilizing.
n Good qualitative agreement with doppler backscattering measurements in experiment. (See poster by L. Schmitz).
n Field is solved on a cylindrical domain, with particle weight suppressed outside of a prescribed flux surface.
nonlinear measured R0/ Ln crit
linear instability threshold (GTC)
core : kζρs ≈ 0.9-17.5 SOL : kζρs ≈ 1.4-16.4
gradient drive : R0/Ln
r-R ~ 4 cm s
:SOL
r ~ Rs :separatrix 0.4 r-Rs ~ -6 cm :core
(Core)
kθρe ~ 0.07-0.28 0.2
0
ñ/n [au]
growth rate : γ R0/Cs
246
246
gradient drive : R0/Ln R/Ln
B0 (G) ⇢i (cm)
n 5 ms sustainment on C-2U heralds transport limited confinement in advanced beam driven FRCs.
n Local gyrokinetic model indicates ion mode stability in FRC core; qualitative agreement with experimental.
n Cross-separatrix fully-kinetic ion model has been implemented and tested. Simulations are ongoing.
Future Work
n Parameter scans/ non-linear simulations with global geometry model (ongoing).
n Realistic axial boundary conditions. n Electromagnetic field solver.
References
See posters by C. K. Lau, L. Schmitz
D. P. Fulton et al, Phys. Plasmas 23, 012509 (2016). D. P. Fulton et al, Phys. Plasmas 23, 056111 (2016). http://www.trialphaenergy.com/research-library/
5.3 ⇢e (cm) 0.039
R0 /Cs (μs) 4.4
SOL
B0 (G) 1260 ⇢i (cm) 2.3
⇢e (cm) 0.017 R0 /Cs (μs) 6.2