Feedback suppression of resistive wall modes in a tokamak

The possibility of feedback suppression of the external kink modes in a tok amak with a resistive wall is studied theoretically, assuming that the stab ilizing conductors are located at a certain distance from the wall and with out making any assumptions regarding the locations of the magnetic sensors that close the feedback circuit and the parameters (i.e., the particular co mponents of the perturbed magnetic field or magnetic fluxes) measured by th e sensors. It is shown that the efficiency of the stabilizing system can ge nerally be analyzed within a two-parameter model. The parameters of the pro blem are the jump in the logarithmic derivative of the radial magnetic fiel d in the region where the stabilizing conductors are positioned and the rat io of the minor radius of the torus on which the conductors are wound to th e radius of the wall. However, specific calculations should be carried out with at least a three-parameter model: the final results should depend on t he currents in the conductors and the locations of the conductors and magne tic sensors. The relation between the magnetic parameter in the criterion f or the suppression of the resistive wall modes and the currents in the stab ilizing conductors is clarified, and the current magnitudes required for th e suppression are estimated. (C) 2000 MAIK "Nauka/Interperiodica".