The design and fabrication of a toroidally continuous cryocondensation pump for the DIII-D advanced divertor

A cryocondensation pump will be installed in the baffle chamber of the DIII-D tokamak in the spring of 1992. The design is complete and fabrication of this pump is in progress. The purpose of the pump is to study plasma density control by pumping the divertor. The pump is toroidally continuous, approximately 10 m long, in the lower outer corner of the vacuum vessel interior. It consists of a 1-m/sup 2/ liquid-helium-cooled surface surrounded by a liquid-nitrogen-cooled shield to limit the heat load on the helium-cooled surface. The stainless steel liquid nitrogen shell has a copper coating on it to enhance thermal conductivity but the coating is broken to keep the toroidal electrical resistance high. The liquid-nitrogen-cooled surface is surrounded by a radiation/particle shield to prevent energetic particles from impacting and releasing condensed water molecules. The whole pump is supported off the water-cooled vacuum vessel wall. A testing program was used to develop coating techniques to enhance heat transfer and emissivity of the various surfaces. Fabrication tests were done to determine the best method of attaching the liquid nitrogen flow tubes to their shield surfaces. A prototype sector of the pump was built to verify fabrication and assembly techniques.<
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