CONTROL OF WALL PARTICLE INVENTORY WITH DIVERTOR PUMPING ON DIII-D

Reduction of the net wall particle inventory has been achieved in the DIII-D tokamak by the use of a divertor cryopump for the panicle exhau st. A sequence of 12 discharges was conducted without helium glow disc harge cleaning (HeGDC) and without active cryopump exhaust, resulting in a net wall loading of 1250 torr . L (8.8 x 10(22) atoms) by the end of the sequence. The cryopump was activated for the subsequent set of 10 discharges. At the end of this set of discharges, the net wall loa ding was reduced to its initial value or less, i.e. the wall loading s tate for the reference discharges with HeGDC. plasma performance did n or suffer without the HeGDC in that the stored energy during the ELMy phase was restored to the reference discharge level during the dischar ges with the active cryopump. Hence, with continuous particle exhaust (provided, for example, by a pumped divertor), next generation, long p ulse devices, such as ITER, will nor require interdischarge HeGDC for panicle control, which would require turning off superconducting coils between discharges.