Obtaining extremely high vacuum using sintered fine copper powder as a cryosorbent

Fine copper powder (FCP), sintered to the cryopanels of cryopumps, was evaluated as a cryosorbent for H₂. A Gifford–McMahon refrigerator cooled the tested cryopanel of a two‐stage cryopump. The third stage of a three‐stage cryopump that was tested was cooled by Joule–Thomson expansion of He. 30 g of FCP were sintered to the second stage panel (20 K) of the two‐stage bakeable cryopump, whereas 10 g of FCP were sintered to the third stage panel (4.3 K) of the three‐stage bakeable cryopump. Hydrogen pumping speed, capacity, and base pressure measurements are given as a function of temperature. Cryopanel preparation and system bakeout procedures, reliably leading to pressures <10⁻⁹ Pa, are given. Hydrogen thermal desorption peaks for the FCP sintered cryopanel are also reported.