Development of cryopump to evacuate large throughput under high heat load condition for SST-1

Cryopump is an ultra-high vacuum pump and finds application in space, fusion research, and semi-conductor industry, etc. In space and fusion research, large volume cryo-vac chambers are maintained in the UHV range which requires a pump with high pumping speed. Cryopump is the solution to such requirements. It's a cryogenic pump with its sub components operating at cryogenic temperature, i.e., < 123K. The pumping speed of the pump is the geometric function of surfaces area and their orientation, temperature of the surfaces, the temperature of gases, and type of gases to be pumped. Therefore, a customized sorption pump considering high radiation heat load is designed to cater for the baking cycle operation of SST-1 Tokamak. During baking, temperatures of Plasma Facing Components is 250°C and that of vacuum vessel is 150°C. The major gas that evolved during baking is water vapour. The pump was analysed for temperature of different components like baffles, shield and charcoal coated panels using ANSYS and pumping speed of water vapour and nitrogen gas using Molflow simulations. The fabricated pump is tested for leak tightness, temperature and pressure. The vacuum of r' 1 x 10-8 mbar is achieved with no gas load condition. The outgassing rate of the pump and pumping speed of nitrogen is analysed and measured experimentally. The pumping speed for nitrogen is found to be r' 3300 litre/sec. This pump will be tested for the designed pumping speed of nitrogen gas and water vapour with variable dosing and heat load. (author)