Stability analysis of a cylindrical surface current plasma confined by a force-free magnetic field with perfectly conducting tenuous plasma

Abstract

A force-free magnetic field satisfies a relation Del *B= alpha B, where alpha is assumed a constant in space. For a surface current cylindrical main plasma confined by force-free fields with perfectly conducting tenuous plasma, the stability is investigated in detail numerically by evaluating the stable region and the growth rate of the unstable mode for parameters k, m, R0/r0, alpha r0, beta and ( mu 0r0)-1 from dispersion relation, where k is a real wave number, m is an integer, r0 and R0 are the radii of the main plasma and the conducting wall, respectively, and beta and mu 0 are the plasma beta and reciprocal pitch on the main plasma surface, respectively. For negative ( mu 0r0)-1, positive k and m=1, the stable region is larger expanded by introducing the force-free magnetic field with tenuous plasma of perfect conductivity than that of small resistivity, because of virtual wall effect in the perfectly conducting tenuous plasma. The marginal stability curve for R0/r0=1.5, alpha r0<or approximately=-2.0 almost agrees with the curve for the vacuum field with the wall of R0/r0=1.