Development of a linear drive cryocooler system incorporating both stirling and orifice pulse tube refrigeration cycles

This paper describes the development, testing, and field trial results of a free-piston, linear drive cryocooler system designed to meet various commercial market requirements. The cryocooler units are used to cool high performance computer system microprocessors, high temperature superconductor (HTS) devices, and macromolecular X-ray crystallography equipment. Three distinct cold head configurations are utilized: 1) a Stirling cycle unit for HTS applications in the 60 to 65 K temperature range with a capacity up to 10 watts, 2) a Stirling cycle computer cooling unit providing approximately 25 watts capacity at 90 K, and 3) an orifice Pulse Tube refrigeration cycle operating over a temperature range of 75 to 90 K with a nominal capacity of 7.5 watts. All of these coolers incorporate a common free-piston, linear drive gas compressor utilizing flexural bearings to eliminate potential degradation due to contamination or seal wear and insure a long, maintenance-free operating life. A description of the cooler operating requirements along with mechanical details of the gas compressor, cold heads, heat rejection system, and supporting power electronics is provided. Issues concerning the use of a common gas compressor for both Stirling and Pulse Tube coolers are discussed. An emphasis is placed on cooler test results gathered under the unique operating conditions experienced by the coolers when integrated into their respective system configurations. A detailed comparison between actual cooler operating characteristics and predicted values based on refrigeration cycle simulation models developed at Stirling Technology Company (STC) is presented.