Cryopump of 60,000 l/sec for hydrogen gas

In neutral beam injection for the JT-60, the condensation cryopumps of 106 l/sec for hydrogen will be used. In development of the cryopumps a small scale cryopump of 60,000 l/sec has been constructed following on that of 12,000 l/sec. It consists of a pair of liquid-helium cooled panels (60 cm x 60 cm), liquid-nitrogen cooled chevrons and radiation shields. The measured pumping speed agrees with the design one and after condensation of 13 Torr.l/cm2 no drop in the pumping speed is observed. The rate of liquid helium consumption was obtained and the sources of heat loading to the cryopanels were investigated. The heat loading due to hydrogen gas in particular is 0.12 +- 0.02 J/Torr.l, which is explainable by the energy difference of normal hydrogen between 80 K and 4.2 K; this energy difference is not internal energy nor enthalpy. (author)