Fast local mode properties in field-reversed configurations

Abstract

Local eigenmodes of field-reversed configurations (FRCs) were previously computed using ideal magnetohydrodynamics, including compressibility and double adiabaticity. Here the eigenmodes are compared with earlier analytic models. In equilibria, as initially generated in θ pinches, the rigid displacements of the analytic models are similar to actual eigenmodes in structure and growth rate; moreover, the growth rates are similar to those of global modes. In equilibria that naturally arise later in the quiescent FRC, the analytic models fail to predict features of the eigenmode behavior: ballooning-like structure, and much faster growth rate than global modes. This suggests explanations for the difficulty of forming large FRCs in θ pinches, and for the appearance of characteristic profiles in quiescent FRCs.