EFFECT OF IMPURITIES ON PARTICLE COLLECTION STUDIES WITH A MODULAR PUMP LIMITER ON TORE SUPRA

Particle collection experiments with a modular pump limiter in Tore Supra, for ohmic and additional power heating, are reported. The essential feature of these experiments is that the pressure buildup in the pump limiter plenum is only driven by the hydrogen influx whereas the total ion influx in the throat is shown to be partly due to impurities. This is consistent with experimental results which show similar evolution of Z(eff) in the plasma and of the ratio GAMMA(T)/p of the total ion influx GAMMA(T) in the throat to the pressure p in the plenum. Particle collection efficiency, in terms of the hydrogen influx GAMMA(D) to the pressure ratio GAMMA(D)/p, is shown to be roughly constant over the density (ohmic) and additional power ranges studied.