Design Study of Small Efficient Cryocoolers.

A triple-expansion Stirling-cycle refrigerator driven by a linear mechanism was the configuration selected to best meet the requirements of this Phase I design study for a small, low-power, light-weight, efficient, closed-cycle cryocooler. The specifications for the cooling of superconductive magnetometers require the cryogenic refrigerator to operate at 10 degrees K or less with a heat load of 50 mW, have an electrical input power not exceeding 250 W, and have minimum mechanical motion and magnetic signatures. The results of this design study indicate that the 50 mW of refrigeration at 10 degrees K with a maximum power input of 250 W can be readily met with a free-displacer, free-piston system. Three problem areas were identified and analyzed, viz., the lead regenerator matrix, piston seals, and output-temperature fluctuations. An analysis was also made of the magnetic effects of mechanical motion. This report concludes with an outline of the proposed efforts for a Phase II program. Author