Kinetic Effects on the Stability Properties of Field-reversed Configurations: II. Nonlinear Evolution
Authors: Elena V. Belova, Ronald C. Davidson, Hantao Ji, and Masaaki Yamada
Date of PPPL Report: November 2003
Published in: Physics of Plasmas 2:5 (May 2004) 2523-2531
Results of three-dimensional hybrid simulations of the field-reversed configuration (FRC) are presented. Emphasis of this work is on the nonlinear evolution of magnetohydrodynamic (MHD) instabilities in kinetic FRCs. A wide range of s values is considered, where the s is the FRC kinetic parameter that measures the number of ion gyroradii in the configuration. The linear and nonlinear stability of MHD modes with toroidal mode numbers n greater than or equal to 1 is investigated, including the effects of ion rotation, finite electron pressure, and weak toroidal field. Low-s simulations show nonlinear saturation of the n = 1 tilt mode. The n greater than or equal to 2 rotational modes are observed to grow during the nonlinear phase of the tilt instability due to ion spin-up in the toroidal direction. Large-s simulations show no saturation of the tilt mode, and there is a slow nonlinear evolution of the instability after the initial fast linear growth. Overall, the hybrid simulations demonstrate the importance of nonlinear effects, which are responsible for the saturation of instabilities in low-s configurations, and also for the increase in FRC life-time compared to MHD models in high-s configurations.