Pump Limiter Experiments and Engineering

Particle removal from tokamak plasmas is essential to achieve density control and some measure of impurity control. This requirement can be satisfied by pump limiters, the present status of which is reviewed here. Modular experiments have recently achieved particle removal rates over 10 torr-1/sec. Studies of impurity removal by pump limiters have demonstrated He and N₂ (moderate Z) exhaust. Successful modeling of the pump limiter performance using Monte-Carlo neutral gas codes has expanded the understanding of the physics of pump limiters. The heat flux to the surface of limiters in tokamaks has been studied in detail. The rapid progress in the engineering, theory, and experimental results of pump limiters has led to plans for the application of these devices in new experiments in the next few years.