Abstract: Disclosed is a multiple stage cryogenerator including a cryopump system in which a thermally conductive bridge between a pumping assembly and a low temperature stage is somewhat lengthened in order to reduce the length of a conductive bridge between a higher temperature stage and a radiation shield for the pumping assembly. The thermal gains produced by reducing the length of the latter bridge outweighs considerably the thermal losses caused by lengthening the first bridge so as to substantially improve the overall thermal efficiency of the system.