Abstract: A Group I gas cryopumping system includes a compressor throttle cycle refrigerator using mixed refrigerants. Cold refrigerant flows through a cryopumping surface located in a vacuum chamber, whereon vapor freezes. The refrigerant then passes through a heat exchanger in cross flow with refrigerant from the compressor. Refrigerant flow entering and leaving the heat exchanger is in uninsulated lines at substantially room temperature. All exposed cold lines are eliminated. The throttle device and cold cryopumping surface are an integral unit that connects directly to the flow paths of the heat exchanger without intermediate lines. The compressor/aftercooler unit may be located at any convenient distance from the heat exchanger and cryopumping surface, and the heat exchanger is located immediately adjacent to the pumping surface in a separate housing outside the vacuum chamber. The heat exchanger housing may share or be isolated from the vacuum of the vacuum chamber.