| Reduction of the net wall particle inventory has been achieved in the DIII-D
tokamak by the use of a divertor cryopump for the particle exhaust. A sequence
of 12 discharges was conducted without helium glow discharge cleaning (HeGDC)
and without active cryopump exhaust, resulting in a net wall loading of 1250
torr.L (8.8*1022 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 loading was reduced to its initial value or less, i.e.
the wall loading state for the reference discharges with HeGDC. Plasma
performance did not suffer without the HeGDC in that the stored energy during
the ELMy phase was restored to the reference discharge level during the
discharges with the active cryopump. Hence, with continuous particle exhaust
(provided, for example, by a pumped divertor), next generation, long pulse
devices, such as ITER, will not require interdischarge HeGDC for particle
control, which would require turning off superconducting coils between
discharges |
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