The Conceptual Design Of Toroidal Cryopump For HL-2M

The pumping system of divertor is important to tokomak. The purpose of the system is to pump helium ash, unburned fuels and the impurities to enhance the performance of divertor. Now, cryopumps are used on most of the tokomaks all over the world. HL-2A is to be modified with an efficient divertor (HL-2M), which needs powerful divertor pumping system and design a toroidal cryopump for HL-2M is necessity. The structure design, thermal calculation, cooling system, electromagnetic analysis and structural analysis are given.The toroidal cryopump of HL-2M is refrigerated cryopump with special cryopanel, which composed of many concentric tubes. Cannula is used to enhance the two-phase heat transfer, and the surface of outer tube is cryopanel. Liquid helium is boiling in the outer tube to cool the cryopanel. Many slits are settled on the top of inner tube to reduce the temperature difference and enhance the pumping properties. The calculations of heat transfer coefficient, flow conductance and effective pumping speed show that structure of the toroidal cryopump is successful. The calculation of heat load of liquid helium system is another key point of the paper. There are many coils in the vacuum and variable currents of the coils and plasma will produce induced electric current and Joule heat on the cryopump. The calculation of joule heat is also detailed on the paper.Electromagnetic field and temperature field are analyzed by method of finite element during the plasma rupturing to identify the structure design of the cryopump. When the plasma ruptures, there is electrodynamic force on the toroidal tubes, which will generate large stress on the braces. At first, the electrodynamic force of the cryopump is calculated, then, analysis the stress of the braces by coupling the electrodynamic field and structural field. At last, the result shows that the stress is less than the allowable stress of the material of braces. The design of cooling system is the last part of the paper. 100W, 4.3K liquid helium is available from helium refrigeration cycle of the cooling system that composed of three turbo-expanders, a two-stage compression screw compressor.