A Wide Temperature Range, Reliable, Compact Cryogenic Thermal Switch

Nuclear explosion monitoring systems need an effective cryogenic xenon sampling system to monitor the concentration of the radioactive xenon isotopes in the atmosphere. The cryogenic xenon trap needs to operate over a large temperature range (-150°C to 300°C) during each gas absorption and desorption cycle. The xenon trap requires a thermal switch that allows a cryocooler to cool the trap during the collection stage, and then thermally disconnect the cryocooler from the trap during the xenon removal stage. This paper reports a preliminary study to develop a compact, reliable thermal switch that has an adjustable thermal conductance and can operate over a wide temperature range. The thermal switch is a thermosyphon that uses a unique fluid mixture and a unique configuration to enable it to operate over a wide temperature range (20°C to -150°C). The thermal switch automatically turns off during the high-temperature xenon desorption process. This thermally disconnects the xenon trap from the cryocooler cold head and thus prevents the cold head from overheating. This passive thermal switch simplifies the integration of a xenon trap with a cryocooler and significantly reduces the size, mass and power consumption of a xenon collection system. This paper presents a preliminary design of the thermal switch and the test results of a proof-of-concept prototype with a refrigerant mixture.