Equilibrium and Ideal MHD Stability Analysis of Wall-Stabilized Tokamak Plasmas.(^* )

The characteristics of external kink instabilities observed during wall stabilization studies in HBT-EP are compared with the predictions of ideal MHD theory. Equilibrium reconstructions have been performed for discharges with various plasma-wall configurations and plasma formation techniques, using external and internal magnetic measurements and an eigenmode representation of the equilibrium shell eddy current distribution. The stability analysis of these equilibria predicts, for a model continuous shell, patterns of instability-induced eddy currents that agree closely with the measurements for our segmented shell. The presence of the wall close to the plasma results in a reduction of the growth rates of about an order of magnitude for (m=3), (n=1) external instabilities. (^*)Work supported by US DOE Grant DE--FG02--86ER--53222