Global ideal MHD stability of plasmas with toroidal, helical and vertical field coils

A simple configuration that consists of a set of toroidal, helical and vertical field coils is used to calculate free boundary equilibria with non-zero plasma current and approximately helically symmetric plasma boundary shape. The amount of helical boundary deformation is controlled by the ratio of the current in the helical field coils to the current in the toroidal field coils. When this ratio is increased, the (m, n) = (2, 1) external kink is stabilized at beta similar or equal to 1% for inverse rotational transform profiles in the region q < 2 and an aspect ratio A similar or equal to 10.