A superfluid ~3He-~4He compressor, that utilizes a bellows piston design and low dissipation suction and discharge valves, has been developed at the Cryogenic Engineering Laboratory at MIT. This compressor has a superleak bypass around the suction valve, which allows the superfluid ~4He part of the working fluid to flow freely out of the compressor when the valves are closed during the compression stroke. Since the ~3He component of the mixture cannot flow through the superleak, the ~3He concentration of the mixture increases during the compression process. This compressor is suitable for use in a new class of sub-Kelvin refrigerators including the superfluid Joule-Thomson refrigerator. The design and predicted performance of this compressor is presented.
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