The first phase of the Radiative Divertor Program (RDP) for DIII D at General Atomics was completed in February 1997. The addition of this RDP first phase divertor and cryopump system has given DIII D the capability of pumping the upper, outer strike point for a double null, high triangularity plasma. The new water-cooled divertor baffle structure and cryopump installed during this phase have been operational during the 1997 experimental campaign. With both the new cryopump and the existing advanced divertor cryopump that was installed in 1992, the total divertor pumping speed is approximately 64,000 l/s at a 2 mTorr baffle pressure.
The 3600 torodially continuous RDP cryopump is located on the outboard ceiling inside the vessel. It is approximately 10 m in circumference and has 0.8 m2 of 4.3 K liquid helium-cooled pumping surface made of 25.4 mm diameter Inconel tubing. The liquid helium-cooled surface is surrounded by two concentric liquid nitrogen-cooled shields, which are surrounded by a particle shield. Both the new and existing cryopumps have a similar design with an overall cross section diameter of 9.5 cm.
The cryopump fabrication included laser cutting of the nitrogen and particle shields, wire EDM cutting of the helium feedline spacers, plasma spray coating of the outer nitrogen shield, and various other hardware processes. Most of the installation work took place outside of the vacuum vessel on the DIII D site. The in-vessel installation took only two and one-half weeks to complete. This is due to the pump hardware being designed to accommodate quick and easy in-vessel welding and fastening. In addition, tooling was designed specifically for the RDP installation to easily locate the pump and its support structures.
*Work supported by U.S. Department of Energy Contract DE-AC03-89ER51114.