Plasma stability control in a toroidal system by feedback and HF fields

The theoretical and experimental aspects of controlling MHD stability in toroidal systems by feedback systems and HF fields are presented. Results of theoretical studies of resonant excitation of helical MHD oscillations in a current-carrying plasma column by the multipole HF field are given, and the effect of such oscillation buildup on the evolution of unstable helical modes is discussed. The conditions for exciting helical oscillations, the main stabilization criteria, and the results of experimental studies of kink instability stabilization by a feedback system are presented. A stabilizing effect is only provided by introducing a phase shift into the feedback circuit and choosing the amplifier gains; stabilization improves the plasma thermal insulation and increases its energy content.