Pumping Performance Evaluation of HL-2M In-Vessel Cryopump With Monte Carlo Method

Abstract

Sufficient pumping speed and good pumping performance should be guaranteed for the HL-2M tokamak. In order to provide sufficient pumping capacity, two in-vessel cryopumps will be installed at outer floor and ceiling, respectively. Pumping performance of HL-2M in-vessel cryopump has been estimated by direct simulation Monte Carlo program and test particle Monte Carlo program under free molecular flow condition. The predicted pumping speeds of each bare cryopump are 51.29 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s for H2, 38.04 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s for D2, and 24.94 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s for He. An advanced divertor system will be installed, located on the floor of the HL-2M vessel. When the conductance of the divertor is taken into account, the pumping speeds of the floor ring are 20.11 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s for H2, 15.14 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s for D2, and 12.50 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s for He. This shows that the effective pumping speed of the cryopump is greatly affected by the conductance of the divertor. A parametric study has been carried out, allowing the sticking coefficients of some different gases to vary within a +/-0.05 range with respect to the corresponding reference values. The results indicate that the He pumping speeds may be significantly affected by a small change of the sticking coefficient, while negligible effects are predicted to occur, as far as H2 and D2 are concerned. The results of the dynamic evaluation of the pumping process indicate that the cryopump has a quick time response.