Stability of Localized MHD Perturbations in Confinement Systems with Closed Magnetic Field Lines

Conditions are determined for the stability of a finite-pressure plasma against perturbations localized near a magnetic field line in a magnetic confinement system without average minimum-B. The marginal stability ((omega)[sup 2] = 0) is achieved at the pressure profile p(alpha)U[sup –5/3] (where U = [contour_integral_counter-clockwise]dl/B), provided that the pressure is lower than a certain critical value above which an unstable incompressible mode in which the displacement as a function of the coordinate along the field line has zeros appears at some magnetic field line.