Heat transfer enhancement of NBI vacuum pump cryopanels

Huge cryogenic pumps are installed inside neutral beam injectors in order to manage the typically very large gas flows. This paper deals with the aspect of passive cooling in NBI cryopump design development and discusses design considerations in two example areas. One is the design of cryopanels consisting of a pipe, centrally supplied with cryogenic helium, and a welded fin, passively cooled, to provide the necessary pumping surface below a given maximum temperature. The results of several parametric simulations in ANSYS are presented using different copper thicknesses and cryopanel geometries to discuss the thermal capability (heat transfer characteristics and heat capacities) of a number of design variants. The optimum design solution is based on copper-coated fins, using an electroplating technique, and thereby improving the heat transfer of the cryopanels while attaining an overall reduction in weight. The other area is the sound design of the manifold shielding system with a weld contact between copper and stainless steel. Weld samples were manufactured and investigated to raise awareness of the demands and risks during manufacturing and to demonstrate that readily applicable weld procedures exist.

► Cryopanel is optimized minimizing its maximal temperature rise and heat capacity.
► Copper coating on the cryopanels is necessary to reach a high thermal efficiency.
► The copper coating is achieved using an electroplating technique.
► A thermal shield for the cryopump 4 K manifold would reduce heat leaks down to 10%.
► The manufacturability and operation of the thermal shield is discussed.