A 70 K J-T cryocooler based on the fractional mixed-refrigerant cycle**This work is financially supported by the National Natural Sciences Foundation of China under the contract number of 50206024

Publisher Summary This chapter illustrates an experiment, with detailed analysis of mixture properties and cycle configuration, to reach about 65 to 70 K temperature range by using a mixed-gases Joule-Thomson system. A special cycle configuration is disclosed utilizing a newly developed fractional phase-separator with inner heat and mass transfer. This separator avoids cold clogging essentially. An optimal mixture is used to improve the system performance. A stable lowest temperature at 66 K and 1.06 W cooling capacities at 70 K are achieved with an input power of 0.5 kW, driven by a commercial single-stage hermetic compressor with a nominal input power of 500 W. The results obtained in this investigation show that with optimal mixed-refrigerant and cycle configuration, the mixed-refrigerant J-T cryocooler can provide refrigeration at 70 K temperature properly. This provides a low cost, high reliability refrigerator for 70 K temperature range application, especially for cooling high temperature superconductivity devices.