Verification test for helium panel of cryopump for DIII-D advanced divertor

It is planned to install a cryogenic pump, in the lower divertor portion of the DIII-D tokamak with a pumping speed of 50000 l/s and an exhaust of 2670 Pa-l/s (20 torr-l/s). A coaxial counterflow configuration has been chosen for the helium panel of this cryogenic pump. The cool-down rates and fluid stability of this configuration are evaluated. A prototypic test was performed to increase confidence in the design. That the helium panel cooldown rate agreed quite well with analytical prediction and was within acceptable limits. The design flow rate proved stable and two-phase pressure drop can be predicted quite accurately. Results confirm that a cooldown of the helium panel from 300 K to liquid helium temperature can be achieved in the few minutes available between plasma shots. Helium flow results indicate that, at the design flow rate of 5 g/s, flow will be stable for heat loads up to 54 W. The expected heat load on the helium panel during operation is about 10 W.<>