Toroidal pump limiter experiments in the TEXTOR tokamak

The Advanced Limiter Test-II (ALT-II) is a large area toroidal pump limiter in the TEXTOR tokamak. Discrete target plates located in channels at eight toroidal positions behind the main limiter surface neutralize a portion of the plasma efflux from the core. The resulting gas is exhausted by eight external pumps. The primary experimental goals of ALT-II are aimed at power loading studies and plasma density control during long pulse (4 s), high power (6 MW) tokamak discharges. It is found that both the power and the plasma flow to the limiter are asymmetric and depend on line density. Peak neutral pressures of 0.8 m torr and removal rates of up to 0.15 torr·L/s per pump station are achieved in the Ohmic phase. The projected exhaust efficiency of ALT-II with full pumping is 5-10%. During ion cyclotron resonance frequency heating, the particle removal rate exceeds 0.4 torr·L/s per blade, and the exhaust efficiency is 4-5% for power levels up to 2.6 MW. (author). 46 refs, 10 figs