A seven-Watts G-M/J-T 4K helium refigerator

A seven-watts G-M/J-T helium refrigerator at 4K was designed and fabricated at the Institute of Cryogenics and Superconductivity Technology (ICST) in Harbin Institute of Technology (HIT). The refrigerator uses two single-stage Gifford-McMahon (G-M) cryocoolers for precooling the Joule-Thomson (J-T) flow circuit. It mainly consists of five Linde-type heat exchangers and an adjustable J-T valve. The compression system utilizes the G-M type helium compressors to supply the helium flow for the G-M cryocoolers and the J-T circuit. This paper describes the design and optimization of the 4K G-M/J-T refrigerator in detail. The refrigerator can also be operated as a helium liquefier with the production of 36 liter per day.