Kinetic simulations of the formation and stability of the field-reversed configuration

The Field-Reversed Configuration (FRC) is a high-beta compact toroidal plas ma confined primarily by poloidal fields. In the FRC the external field is reversed on axis by the diamagnetic current carried by thermal plasma parti cles. A three-dimensional, hybrid, particle-in-cell (zero-inertia fluid ele ctrons, and kinetic ions), code FLAME, previously used to study ion rings [ Yu. A. Omelchenko and R. N. Sudan, J. Comp. Phys. 133, 146 (1997)], is appl ied to investigate FRC formation and tilt instability. Axisymmetric FRC equ ilibria are obtained by simulating the standard experimental reversed theta -pinch technique. These are used to study the nonlinear tilt mode in the "k inetic" and "fluid-like" cases characterized by "small" (similar to 3) and "large" (similar to 12) ratios of the characteristic radial plasma size to the mean ion gyro-radius, respectively. The formation simulations have reve aled the presence of a substantial toroidal (azimuthal) magnetic field insi de the separatrix, generated due to the stretching of the poloidal field by a sheared toroidal electron flow. This is shown to be an important tilt-st abilizing effect in both cases. On the other hand, the tilt mode stabilizat ion by finite Larmor radius effects has been found relatively insignificant for the chosen equilibria. (C) 2000 American Institute of Physics. [S1070- 664X(00)01505-6].