Small cryocooler system for superconducting devices

A compact closed-cycle refrigeration system (RS), incorporates a two-stage expander with regenerators and a JT circuit, is described. The RS uses three new compact heat exchangers (HEs) in which aluminum perforated plates and plastic film spacers are stacked alternately, and each HE has scrool-shaped gas channels in both the high and low pressure sides. The diameter of the expander is 7 cm at the first stage and 3.5 cm at the second, with the stroke set at 2 cm. The refrigeration capacity of 50 W at 77 K and 3.5 W at 4.5 K is attained, taking 4 hr to cool down to 4.5 K. With closed evaporation gas lines of liquid He and N constant internal pressure of both gases was maintained. The RS description is illustrated with diagrams and performance graphs.