High-beta experiments with neutral-beam injection on PDX

Abstract

We report experimental investigations of high-beta plasmas produced in PDX with near perpendicular neutral-beam injection. Systematic power scans have been performed over a wide range of toroidal fields (0.7T < B/sub T/ < 2.2T) and plasma currents (200 kA < I/sub p/ < 500 kA). At high toroidal fields, the change in total stored energy due to beam injection increases linearly with input power and also increases with plasma current. At lower toroidal fields and low injection-power levels, the stored energy also increases with power and plasma current. However, at high power and low toroidal fields, a saturation in heating is observed. This result suggests the onset of a ..beta../sub T/ limit for circular cross-sectional tokamaks with near-perpendicular injection. Scaling experiments indicate that this ..beta../sub T/ limit increases with rising (1/q). Values of ..beta../sub T/ approx. = 3% at q/sub Psi/ = 1.8 have been achieved.