Experiment and m.h.d. theory of stability and relaxation in toroidal discharges

Abstract

The experimental behaviour of plasma instabilities in high-current discharges is found to be in good agreement with the predictions of linear and nonlinear magnetohydrodynamic theory. Observations show that on time-scales comparable with the Alfven transit time there are rapidly growing ideal magnetohydrodynamic perturbations whereas experiments on longer time-scales show the growth and saturation of resistive instabilities which involve changes in field line topology. The plasmas are observed to exhibit self-control mechanisms which are related to the relaxation of configurations to states of lower magnetic energy. Rapid magnetic field line reconnection phenomena, as in solar flares, are observed.