Ballooning optimized pressure profiles in toroidal Heliacs

The local 3-D ideal MHD stability properties for two different H-1 Heliac configurations with values of magnetic well of 1.3 and 3.2%, respectively, have been investigated. The pressure profile has been determined that approaches marginal stability to 3-D ballooning modes almost uniformly across the plasma radius for each case. In spite of the difference in well depths, the p limits for both configurations are almost the same (at 0 = 0.8%). The optimal pressure profile for the deep well configuration is slightly more peaked than that for the standard configuration. The ballooning imposed 0 limits are more stringent than those of the Mercier criterion (0 = 1 %) and the ballooning optimized pressure profiles are more peaked than the corresponding profiles which are marginal according to the Mercier criterion.