Cooling scheme for W7-X divertor cryo-vacuum pumps

Ten divertor cryo-vacuum pumps (CVP) will be installed in the plasma vessel of Wendelstein 7-X stellarator. The inner part of CVP is used for the condensation of hydrogen, deuterium, etc. and chevrons are used to protect the inner part from the radiation and gas loads. The inner part is cooled with cold helium (He) and operated at 3.4 K and 3.9 K during peak power and standard modes of operation. The chevrons are operated at 80 K and supplied with liquid nitrogen (LN2). Three different helium cooling schemes were worked out using forced flow supercritical helium, namely, parallel flow, parallel flow with intermediate sub-cooling and series flow with intermediate sub-cooling. For the chevrons, three cooling schemes, i.e. bath cooling, forced flow two phase and single phase with pump, were worked out. The analysis involved the process calculations and thermo-hydraulic calculations considering the operational requirements of CVP. The optimisation was also coupled with the LN2 heat exchangers of the helium refrigerator to find the optimum flow scheme. The regeneration of inner part up to LN2 temperatures and the complete CVP up to ambient conditions is foreseen without affecting the other cooling applications connected to refrigerator.