PARTICLE EXHAUST ABOVE THE OHMIC DENSITY LIMIT IN TEXTOR

Experiments have been carried out in the TEXTOR tokamak to investigate the performance of the pump limiter ALT-II at the highest achievable core densities. Neutral beam heating allows the density to be extended beyond the ohmic limit. The use of one beam raises the line-averaged density limit by approximately 50%. Results from discharges with co- and balanced injection are shown. Plasma fluxes to the pump limiter increase with density. Up to 4.5 X 10(21) ions/s (720 A) are collected in the eight segment belt, with pumped particle fluxes of up to 3 X 10(21) atoms/s (60 mbarl/s). Exhaust efficiency determination requires knowledge of the efflux of plasma from the core, which can be estimated from SOL profiles and from D(alpha) emission. Both exhaust efficiency estimates increase with density. Experimental results are discussed in terms of predictions from the neutral transport code EIRENE.