Assessment of the JT-60SA divertor cryopump performance

The cryogenic pumping system is one of the key components that define the operational window of JT-60SA. It is envisaged to utilize condensation pumps that work at 3.8 K, and proper thermal shields cooled with water and 80 K gaseous helium are necessary to allow having them installed at short distance to the torus in order to exploit high pumping speeds. In this paper, one complete divertor cryopump unit in a 40 degrees sector is studied by Monte Carlo simulation. The pumping speeds of one cryopump unit for D-2 were found to be between 14.8 m(3)/s and 18.1 m(3)/s depending on the assumptions taken. In addition, the heat loads to the cryopump condensation pipes during steady state nominal operation, as well as the heat loads and transient behavior after massive gas injection events are assessed. The present design can fulfil the requirement of pumping, cooling and regeneration.