Cryocoolers near their low-temperature limit.

This paper analyses the recently-observed temperature–time dependence in a GM-cooler near its low-temperature limit. The paper mainly focusses on GM-coolers with 4 He as the working fluid, but some attention is also paid to pulse-tube refrigerators (PTR’s) using 3 He and many features of the treatment equally apply to Stirling coolers. Ample attention is paid to the thermodynamics of the cycle by considering the isentropes in the Tp -diagrams of 4 He and 3 He. The role of the line, where the thermal expansion coefficient is zero, is emphasized. Some fundamental thermodynamic relationships are derived. [ABSTRACT FROM AUTHOR]