Pulse tube refrigerator cryostat with an intrinsic top-loading system

The authors have undertaken basic research and prototype developments of four-valve pulse-tube refrigerators (FVPTR) since several years. Two single-stage FVPTR in coaxial and U-shaped arrangement have been designed for maximum refrigeration power at cooling temperatures below 30 K. The heat flow through a thermal link between the pulse tube and the regenerator is the determining difference between the U-shaped and the coaxial configuration. The intrinsic heat flux has a complex influence on the cooler performance, e.g. the cooling power, the temperature distribution within the pulse tube and the dynamic losses. Based on these results we propose a design study of a coaxial FVPTR with an intrinsic top-loading system. This cryostat is most suitable for measurements and analytical applications with even low maintenance costs. The main advantage for the operator is the rapid sample exchange while the refrigerator is operating. The process takes only a matter of minutes. Thus the time to cool successive samples is greatly reduced over cold finger cryostats.