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.
The Hot Universe Baryon Surveyor (HUBS) mission is proposed to study “missing” baryons in the universe. Unlike dark matter, baryonic matter is made of elements in the periodic table, and can be directly observed through the electromagnetic signals that it produces. Stars contain only a tiny fraction of the baryonic matter known to be present in the universe. Additional baryons are found to be in diffuse (gaseous) form, in or between galaxies, but a significant fraction has not yet been seen. The latter (“missing” baryons) are thought to be hiding in low-density warm-hot ionized medium (WHIM), based on results from theoretical studies and recent observations, and be distributed in the vicinity of galaxies (i.e., circumgalactic medium) and between galaxies (i.e., intergalactic medium). Such gas would radiate mainly in the soft X-ray band and the emission would be very weak, due to its very low density. HUBS is optimized to detect the X-ray emission from the hot baryons in the circumgalactic medium, and thus fill a void in observational astronomy. The goal is not only to detect the “missing” baryons, but to characterize their physical and chemical properties, as well as to measure their spatial distribution. The results would establish the boundary conditions for understanding galaxy evolution. Though highly challenging, detecting “missing” baryons in the intergalactic medium could be attempted, perhaps in the outskirts of galaxy clusters, and could shed significant light on the large-scale structures of the universe. The current design of HUBS will be presented, along with the status of technology development.
Transition Edge Sensor (TES) is a key component for Hot Universe Baryon Survey (HUBS), which is proposed in China to address the so-called “missing baryon problem”. A stable heat sink below 100 mK is needed for the detector’s noise suppression and high resolution. Since HUBS is a satellite based observation mission, a complicated cooling system suitable for space application becomes an important supporting sub-system. A compounded cooling system, including a mechanical cryocooler and an adiabatic magnetization refrigerator (ADR), has been proposed for HUBS. The mechanical cryocooler is used as the pre-cooling 4 K stage, and the ADR is responsible for further reducing the temperature to below 100 mK. High-frequency pulse tube cryocooler (HPTC) and HPTC combined with Joule Thompson cooler (J-T) are two candidates for the mechanical pre-cooling stage, both of which are currently under development. The ADR is being designed and processed. In this paper, we will present the preliminary architecture of the HUBS cooling system, as well as the latest states of HPTC, J-T, and ADR.
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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