A refrigerator‐cooled cryopump is applied to an ultrahigh vacuum system made of aluminum alloys. This system is easy to bakeout and to achieve a pressure around 2–6×10−9 Pa. A pressure in the 10−9 Pa range is obtained without the baking process being repeated, if only dry nitrogen gas, instead of air, is introduced into the vacuum chamber. Some different regeneration procedures are also studied.

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