A Linear-Drive Pulse Tube Cooler for Applications Below 6K

Various planned NASA missions depend on the availability of reliable and efficient coolers that achieve temperatures below 6K. These coolers are needed as the upper stage for lower temperature coolers such as dilution refrigerators or adiabatic demagnetization refrigerators. Astronomical missions utilize such low temperatures to enhance infrared detector sensitivity and to cool optics. Low temperature cryocoolers form an indispensable part of astronomical missions which require long-term cooling of detectors (e.g. bolometers). Without active coolers the duration of cryogenic missions is limited by the size of the cryogen that can be incorporated in the respective space missions.A pulse tube cooler (PTC) driven by a long-life linear compressor embodies the high reliability and low vibration required in space missions. The absence of cold moving parts reduces wear and vibration and increases reliability which makes PTCs ultimately suited for space. Single-stage PTCs, driven by linear compressors and with a porous, stainless steel regenerator matrix, have achieved no-load temperatures below 50K. To provide cooling at lower temperatures the PTC requires additional stages with regenerators made from high heat capacity materials. The innovation we propose involves development of a multistage PTC driven by a linear compressor that achieves temperatures below 6K.