Plasma Confinement Studies in the ISX-ATokamak

Abstract

Gross-energy-confinement times (${\tau }_E$) in the ISX-$A$ (Impurity Study Experiment) tokamak exceeded predictions of the usual empirical scaling relations. We attribute this performance to reductions of impurity radiation and magnetohydrodynamically driven loss channels. The value of ${\tau }_E$ reached a limit as a function of plasma density. We suggest that this limit is due to a transition from electron- to ion-dominated loss regimes. Maximum attainable values of ${\tau }_E$ increased with discharge current, in agreement with this interpretation.