STABILIZATION OF KINK INSTABILITIES BY EDDY CURRENTS IN A SEGMENTED WALL AND COMPARISON WITH IDEAL MHD THEORY

The characteristics of external kink instabilities observed during wal l stabilization studies in the HBT-EP tokamak have been compared with the predictions of ideal MHD theory, in order to examine the stabilizi ng role of a resistive wall that is segmented both toroidally and polo idally. The reconstructed equilibria, for discharges with different pl asma-wall configurations, are consistent with external and internal ma gnetic measurements, measured soft X ray profiles and measured equilib rium wall eddy currents. The stability analysis of these equilibria pr edicts patterns of instability induced eddy currents for a model wall that is continuous and perfectly conducting, and these patterns are in good agreement with the ones observed on the HBT-EP segmented nail. T hese eddy currents account for the observed stabilization of fast idea l modes when the wall is fully inserted, consistent with the predictio n of marginal stability.