クライオポンプの特性

概要

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Some characteristics of a newly developed cryopump were studied, which makes a step of our serial investigations of the application of cryogenics to high-vacuum ; as a pumping method of the ultra-high vacuum thin film evaporator. The cryogenerator is composed of six heat exchangers, an expansion engine (reciprocating type), and two Joule-Thomson valves, as shown in Fig. 1. Cold generated by this apparatus was measured as 10 watts at 4.2°K. The generator can also be used as a helium liquefier adapting a helium container shown in Fig. 5. The cryopanel of which diameter is 200mm, colded by the cryogenerator, can be refrigerated down to 812°K, within two hours after starting, and the ultimate pressure was measured as 9.8×10-9 torr by B-A gauge, and 1.13×10-8 torr by RH gauge. The relation between pressure and cryopanel temperature is shown in Fig. 10, and composition of the residual gas was analized as shown in Fig. 11. By this analysis, the ultimate pressure seemed to be decided principally by the hydrogen, in ultra-high vacuum region. The pumping speed was measured as 3.0 l/sec cm2 for nitrogen gas in pressure range of10-710-4 torr, shown in Fig. 12. The pumping speed did not be affected by the deposited solid nitrogen film even its thickness assumed 1.7mm.