Tilt Mode, Turbulence and Transport in Field-Reversed Configurations.

摘要

An outstanding theoretical problem of great importance in research on field-reversed configurations (FRCs) is the explanation of the observed stability of FRCs to the internal tilt mode. For example, in the Los Alamos FRX-C experiment, FRCs showed no evidence of the internal tilt mode during experimental lifetimes of up to 300 mu s, which is over an order of magnitude longer than the expected ideal MHD growth time. Finite-Larmor-radius (FLR) theory is inappropriate for the FRC configuration and the observed stability has not been explained by FLR theory. We are engaged in MHD and kinetic studies of the tilt mode that are aimed at explaining the observed stability in FRC experiments. These studies are within the contexts of two physical models: resistive MHD and the Vlasov-fluid model (collisionless ions, massless fluid electrons). Computer codes that implement both linearized and fully nonlinear versions of these models are being used. Our results do not yet provide an adequate explanation of the observed stability, although a strongly stabilizing tendency due to kinetic ion effects has been observed. The effects of plasma rotation appear to be unimportant. It seems most likely that a combination of profile effects, ion kinetic effects and nonlinear effects will be required to understand the gross stability of FRCs. The theoretical and simulational evidence for interior turbulence in FRCs is overwhelming. For investigating the important subject of turbulence and transport in FRCs, we use both analytic studies and numerical simulation. A conclusion of our investigations is that FRC transport laws should not be based on lower-hybrid-drift (LHD) modes localized near the separatrix, but should be based on low-frequency turbulence occurring throughout the FRC profile. 18 refs., 1 fig. (ERA citation 13:058148)