Plasma Confinement Studies in the ISX-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>Tokamak

Abstract

Gross-energy-confinement times (${\ensuremath{\tau}}_{E}$) 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 ${\ensuremath{\tau}}_{E}$ 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 ${\ensuremath{\tau}}_{E}$ increased with discharge current, in agreement with this interpretation.