Design of the JT-60SA divertor cryopumps

JT-60SA is the largest tokamak before ITER, and operation is due to start in 2020. F4E (in the framework of the Broader Approach) and EUROfusion do contribute with several enhancement projects to the JT-60SA tokamak. The JT-60SA divertor cryopump system is one of such enhancements. The cryopump is separated into 9 identical units, distributed equally along the circumference and located in the volume in-vessel underneath the divertor dome. Each cryopump unit consists of four cryosorption panels cooled by 3.7 K supercritical helium, and a thermal radiation shield surrounding the cryopanels made of a base plate and an inlet baffle cooled at about 80 K. To have sufficient pumping capacity for helium, the cryopanels will be coated with activated charcoal. Daily regeneration of the cryopumps at 100 K is foreseen overnight. The paper will present the detailed design of the cryopumps and highlight the main results of the supporting design development. Thermo-mechanical analyses have covered a variety of load cases, reflecting operation and regeneration conditions, low cycle fatigue, electromagnetic forces under plasma disruption conditions, and accelerations under seismic events. Particularly challenging was to maximize performance in a given space limited by the size of the existing divertor cassettes. Vacuum flow simulations have been performed to predict pumping speed and capacities for hydrogenic gases and helium. It will be shown how the requirements put on the cryopumps have been considered in the final design.