Patent ID: 7523618

Claim:
A cryo pump including: a cryogenic refrigerator; a first-stage panel and a generally cylindrically-shaped heat shield plate that are cooled in a first stage of the cryogenic refrigerator; and a second-stage panel that is surrounded by the heat shield plate, is cooled by a second stage of the cryogenic refrigerator, and has an absorbent, the cryo pump further comprising: a notch, provided in and extending circumferentially about the heat shield plate, for allowing for entrance of gas molecules; and an additional shield disposed apart from the heat shield plate and adjacent the notch for preventing entrance of heat due to radiation from a room-temperature cryo pump chamber to the second-stage panel, the additional shield being sized relative to the notch such that the gas molecules outside the second-stage panel meander through the notch and around at the additional shield in order to enter into the second- stage panel.