Design of the advanced divertor pump cryogenic system for DIII-D

Abstract

The design of the cryogenic system for the DIII-D advanced divertor cryocondensation pump is presented. The advanced divertor incorporates a baffle chamber and bias ring located near the bottom of the DIII-D vacuum vessel. A 50000-l/s cryocondensation pump will be installed underneath the baffle for plasma particle exhaust. The pump consists of a liquid-helium-cooled tube operating at 4.3 K and a liquid-nitrogen-cooled radiation shield. Liquid helium is fed by forced flow through the cryopump. Compressed helium gas flowing through the high-pressure side of a heat exchanger is regeneratively cooled by the two-phase helium leaving the pump. The cooled high-pressure gaseous helium is then liquefied by a Joule-Thomson expansion valve. The liquid is returned to a storage dewar. The liquid nitrogen for the radiation shield is supplied by forced flow from a bulk storage system. Control of the cryogenic system is accomplished by a programmable logic controller.<>