The DIII-D divertor cryopump system: Design and operational experience

A high throughput cryocondensation pump has been installed inside the DIII-D plasma chamber as part of the Advanced Divertor Program. During normal plasma discharges the pumping surface temperature must remain sufficiently low (<6.3 K) to pump deuterium while the pump is subjected to transient Joule heating induced by the Ohmic heating coils as well as energetic particles from the plasma. A cryogenic cooling system was specifically designed to handle pulsed heat loads up to 100 W lasting for 10 S. Prototype testing was carried out to verify and develop pulsed capability. During characterization tests, deuterium pumping speeds of 42,000 {ell}/s at 0.66 Pa pressure were achieved. This speed was maintained during 300 W, 8 s long test heat pulses. Physics experiments with the cryopump have been very successful showing a 50% plasma density reduction during H-mode. The design of the advanced divertor cryosystem and cryosystem operational experience are presented.