High Beta Studies on Isx-B With Neutral Beam Injection

Abstract

Injection of E Q into D plasmas with beam power P, of up to 1.7 MW has produced rras betas of ^4X, volume-averaged betas of ^3%, and central betas of ^10% in the ISX-B tokamak. Although theoretical calculations indicate that the observed equilibria may be unstable to ballooning modes, no catastrophic loss of confinement has been observed, and beta continues to increase with injection power. In theje beam-dominated highbeta discharges the electron and ion energy confinement times are still similar to those obtained with ohmic heating: ion energy confinement is neoclassical within a factor of ^2, and electron energy confinement follows the usual Alcator scaling. In high-power injection discharges the character of the magnetohydrodynamic (MHD) behavior changes, the particle confinement time decreases, and the inward impurity transport appears to ba inhibited. These effects, however, may not be linked directly to beta.