Transport studies in high-performance field reversed configuration plasmas

Abstract

A significant improvement of field reversed configuration (FRC) lifetime and plasma confinement times in the C-2 plasma, called High Performance FRC regime, has been observed with neutral beam injection (NBI), improved edge stability, and better wall conditioning [Binderbauer et al., Phys. Plasmas 22, 056110 (2015)]. A Quasi-1D (Q1D) fluid transport code has been developed and employed to carry out transport analysis of such C-2 plasma conditions. The Q1D code is coupled to a Monte-Carlo code to incorporate the effect of fast ions, due to NBI, on the background FRC plasma. Numerically, the Q1D transport behavior with enhanced transport coefficients (but with otherwise classical parametric dependencies) such as 5 times classical resistive diffusion, classical thermal ion conductivity, 20 times classical electron thermal conductivity, and classical fast ion behavior fit with the experimentally measured time evolution of the excluded flux radius, line-integrated density, and electron/ion temperature. The numerical study shows near sustainment of poloidal flux for nearly 1 ms in the presence of NBI.

Suppressed ion-scale turbulence in a hot high-β plasma

“…1), resulting in an inverted toroidal wavenumber spectrum. This observation is consistent with essentially classical ion thermal confinement, with the radial ion thermal diffusivity evaluated from 1-D and 2-D transport analysis19, where is the classical collisional ion thermal diffusivity. Finite ion Larmor radius (FLR) effects9101112 are found to contribute crucially to the observed stability of long wavelength modes, as confirmed by gyrokinetic stability calculations2021.…”

Achievement of field-reversed configuration plasma sustainment via 10 MW neutral-beam injection on the C-2U device

“…Under these well-confined, stable and long-lived HPF conditions in C-2, we observed a clear correlation between NB input power and FRC performance, particularly in the improved energy decay time and FRC plasma lifetime. 1 and 2D transport simulations, Q1D [22] and Q2D [16,17], also indicated a high probability of FRC plasma sustainment with an appropriate upgrade of the NB injector systems. This was the initial motivation for the C-2U project to demonstrate FRC plasma sustainment with upgraded NB systems.…”

Cross-separatrix simulations of turbulent transport in the field-reversed configuration

“…While there is also ongoing work towards understanding FRC transport with hybrid kinetic/fluid transport codes, namely Q1D [16] and Q2D [17], the present work is the first global nonlinear gyrokinetic transport study of turbulence in the FRC. We expand on the past linear physics simulations mentioned above [13] to push into the nonlinear kinetic simulations required for understanding turbulence-driven transport.…”