Experimental studies on pump limiters

Pump limiters are mechanical devices for He-ash removal, fuel particle control, and possibly impurity control. Different designs have been suggested by various authors over the past decade. However, the magnetic divertor concepts seemed to be more promising, mainly because of their remote plasma-material interactions. All of the characteristics of magnetic divertors have been proven experimentally, but the overall performance and complexity cause concern about their application to tokamak reactors. Consequently, it is time now to explore the potential of mechanical particle control devices, i.e. pump limiters. Because of the high recycling at the limiter, it is sufficient to exhaust only a small fraction, about 1 to 10%, of the limiter particle flux to remove e.g. He at its rate of production. Pump limiter experiments have been conducted so far on Alcator, PDX, Macrotor, and ISX. Depending on the experimental design, a pressure build-up of between 1 mTorr and 50 mTorr has been reported