Design and performance characteristics of refrigerator-cooled cryopumps for the RIKEN ring cyclotron

Abstract

A 20 K cryopump with an 80 K baffle which differs from conventional cryopumps, particularly with respect to the cryopanel geometry with glued charcoal grains, was designed and its performance experimentally investigated. In the design, special emphasis was given to a high pumping speed for water vapour and a large pumping (or sorption) capacity for hydrogen gas. The experimental results were in good agreement with the design pumping speeds for hydrogen and nitrogen of 2×10 4 and 1.2×10 4 l s −1 respectively. The design value of the pumping speed for water vapour was 2.7×10 4 l s −1. The experimental results showed that the pumping capacity for hydrogen, being defined for a given throughput as the quantity of gas causing a 2x increase in the equilibrium pressure while pumping this throughput, is dependent on the initial equilibrium pumping pressure, being reduced with a decrease of the pressure: ∼2×10 3 Pa m 3 at 1×10 −5 Pa and ∼7.5×10 3 Pa M 3 at 1×10 −2 The experimental results are discussed with special emphasis on the pumping capacity for hydrogen.