Observations of spheromak equilibria which differ from the minimum-energy state and have internal kink distortions

Abstract

Experimental spheromak magnetic equilibria are measured which differ significantly from the minimum-energy state, and are well described by a numerical model where ${j}_{?}$/B has a linear dependence on the poloidal flux function. Equilibria are determined in a nonperturbing manner by the combination of measurements of flux-conserver image currents with calculations from this model. These equilibria are corroborated by the observation of nondisruptive rotating internal kink distortions (with toroidal mode numbers n=1, 2, and 3), coupled with theoretical thresholds for the onset of these modes.