LOCAL STABILITY IN HELIAC TYPE STELLARATORS

A study of the stability limits for ideal ballooning modes in helical axis stellarators (heliac type stellarators) has been performed. Speci fic configurations similar to those of the TJ-II heliac have been take n, having a deep magnetic well and almost zero shear, which is charact eristic for a heliac. The stability limits are those imposed by the de stabilization of ideal ballooning and local interchange modes. The num ber of periods is varied in order to make a progressive approximation to helical symmetry as the aspect ratio increases. The very high stabi lity limits for straight heliacs are recovered as the aspect ratio ten ds to infinity.