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Characterization of Magnetohydrodynamic Transport in a Field Reversed Configuration
Marco Onofri, P. Yushmanov, S. Dettrick, D. Barnes, K. Hubbard, T. Tajima and the TAE team
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
Abstract
Transport in a Field Reversed Configuration (FRC) is studied by using the two-dimensional code Q2D, which couples a magnetohydrodynamic code with a Monte Carlo code for the beam component. The simulation by Q2D of the parallel transport in the simple open q-pinch fields and its associated outflow shows an excellent agreement with one of the existing theories, providing a benchmark for Q2D and simultaneously deepening the theoretical understanding of this fundamental process. We find a sharp distinction between the evolved radial density profiles of the FRC and mirror plasmas as a result of the transport processes, showing that the closed flux surfaces of an FRC enhance the confinement over that of a mirror. The Q2D code is also used to study the formation of the electrostatic potential in the divertor.
Reference
M. Onofri at el., “Magnetohydrodynamic Transport Characterization of a Field-Reversed Configuration”, Phys. of Plasmas 24, 092518 (2017).
Q2D model
MHD code (Lamy Ridge) coupled with Monte Carlo code
Benchmark
Confinement in linear systems with open field lines: parallel transport. Q2D compared with parallel transport theory (Brunel and Tajima, Phys. Fluids , 1983).
Initial conditions
§ Uniform Bz, n
§ Plasma lost from the ends
§ Initial condition pressure balance
= B2 0e
0i
Results
§ Plasma accelerates near the ends
Global transport simulation of C-2
Density profiles evolution at midplane
Initial conditions
§ Anomalous transport coefficients (From Q1D).
§ Resistivity=5 x classical
§ Electron perpendicular thermal conductivity=20 x
classical
§ Other transport coefficients: classical
Results
Density gradient evolution
FRC t=6L/Cs
§ Density decays quickly in mirror
§ In FRC, density decays in SOL; confined in core § Maximum density on axis in mirror
Vz at r=0
FRC
mirror
FRC
mirror
§ FRC outflow velocity> mirror
§ When normalized to local Cs, FRC ≈ mirror
§ FRC and mirror behave the same in open field line region
§ C-2 geometry
§ Formation sections § Mirror plugs
§ Neutral beams
0i P + B2
Mirror
t=6L/C s
0 2μ0
B0e= external magnetic field
2μ0
B = internal magnetic field
§ Vz =Cs
at the ends
n
e(
m- 3)
Gradient length vs. time
experiment
Plug field=2T
Plug field=4T
Radial density profile t=0.6 ms
experiment
Plug field=2T
Plug field=4T
§ kinetic mirror confinement important in parallel transport in SOL
Monte Carlo Code
NBI H (source)
CX/ionize
FRC H+
CX
H
Wall (sink)
Lamy Ridge
§ Q2D agrees with theory in Brunel and Tajima, Phys. Fluids , 1983 (solid line).
Parallel transport comparison of FRC and mirror
§ Plugs improve parallel confinement § Ln larger with stronger mirrors
Effects of fueling on electrostatic potential in C-2W divertor
Gas puff will be used for fueling
• MHD
• realistic wall geometry
• external coils and
conductors
• neutral gas from wall
recycling and warm
neutrals
• Different ion and
electron temperatures
B, E, n, Ti, Te CX/ionize
§ Gas puff near mirror coils § Plasma slows down
§ Acceleration in divertor
Potential for different gas puff locations
Gas after coil
No gas
Gas before coil
Gas at coil
Initial conditions for FRC and mirror simulations
Jf, nf, energy, momentum
FRC
Mirror:
No closed field lines
Number of particles, momentum and energy conserved between fast particles and thermal plasma
§ Electrostatic confinement is not lost with gas puff
§ Gas must be injected before mirror coils
§ Simulation results were used to design the C-2W gas puff system
prompt loss
shine through
Ln (cm)
ne (m-3)
ne


































































































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