In the area of space astronomy, some electronic detectors should be cooled to liquid helium temperature level to improve their sensitivity and reduce the background noise. A hybrid J-T cooler has been developed for future space application by our laboratory. The J-T loop is precooled by two-stage thermally coupled pulse tube cooler. There is no moving part at low temperature in this system which features low vibration electromagnetic interference. The hybrid J-T cooler has been experimental tested and cooling capacity of about 34.5mW@4.32K is achieved when supply pressure is 1.97MPa. Besides, when sufficient precooling power is provided for the J-T loop cooling capacity of 102.3mW at 5.02K is achieved. In this experiment, three oil free linear compressors are used to drive the J-T loop and a GM cooler is used to provide the precooling power for the J-T cooler. This J-T cooler will be the potential cryocooler for the future space detectors requiring cooling power of 100mW at < 6K.
Integration of optics inside a detector-dewar-cooled-assembly (DDCA) is a good strategy to miniaturized infrared cameras in order to provide small payload systems with thermal vision capability for both military and civilian applications. The optical additional mass has to be very small in order to limit the cool-down time of the DDCA. However, reducing the mass of these optical systems results in a decrease of the resolution and impaction on the image quality, making them difficult to use in the high-performance and high sensitivity applications. In order to achieve better optical performances, a classical optical system which consisted of four lenses was integrated in the DDCA. By optimizing the heat transfer of the lens mount and using a miniature pulse tube cryocooler(MPTC) as the cooling source, the cooling time of the system was reduced. The lens mount and the lenses were cooled down to 80K in an hour by the MPTC with 45W input power. The total mass to be cooled is 100 g, where the mass of the lenses is 15 g. In the later prototypes, the mass of the lens mount can be greatly reduced by optimizing the installation of the detector and the lens mount, and the cooling time of the cryogenic camera integrated with the high-performance optical system can be reduced to an acceptable range by using the lens mount heat transfer optimization method described in this paper.
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