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• A gas-coupled two-stage high-frequency pulse tube refrigerator was developed. • A no-load temperature of 5.7 K was achieved. • The prototype achieves a cooling capacity of 80 mW/8 K with 400 W electric power. • The prototype can output the cooling capacity of 0.1 W/9.3 K and 1000 mW/40 K simultaneously. • The pre-cooling stage can obtain a cooling capacity of 4.3 W/40 K@330 W electric power before gas-coupling. High-frequency pulse tube refrigerator (HPTR) has significant advantages in terms of compactness and high reliability, but it is difficult to obtain very low cooling temperatures. To obtain temperatures below 10 K, multi-stage structures driven by more than one compressor are currently used. This paper reports a two-stage gas-coupled HPTR driven by a single compressor that is extremely compact and even comparable to a single-stage structure. The pre-cooling temperature influences and gas distribution characteristics, which are two important issues in the research of gas-coupled structure refrigerator, were first numerically calculated and analyzed. Then the calculation results were verified by experiments and the cooling performance was tested. Before gas-coupling with the lower stage, the pre-cooling stage can obtain 4.3 W/40 K cooling capacity with 330 W electric input power, which belongs to a high-efficiency 40 K refrigerator that has been reported so far. With an electric power of 400 W, the gas-coupled HPTR taking the developed 40 K refrigerator as the pre-cooling stage achieves a no-load temperature as low as 5.7 K, which is the lowest record of the current two-stage gas-coupled structure in HPTCs. The developed two-stage HPTR can obtain a cooling capacity as high as 80 mW/8 K, and the two stages can also output the cooling capacity of 100 mW/9.3 K and 1000 mW/40 K simultaneously. [ABSTRACT FROM AUTHOR]

High-frequency pulse tube cryocooler (HPTC) has advantages of compact structure, low vibration, high reliability and long operation time. In this study, Theoretical analysis and experimental tests have been conducted in four aspects based on a developed 4 K HPTC. Firstly, a compressor with larger power output capability was employed and the impedance match between the cold head and the compressor was discussed. Secondly, simply using inertance tube configuration to replace the traditional inertance tube-gas reservoir structure. Then, the type and the size of the regenerator materials working at 4–20 K have been experimentally optimized. Finally, the performance of double-inlet working at as low as 20 K has also been tested for the first time for the HPTC. The present prototype achieved a no-load temperature of 3.6 K, which is the lowest temperature record ever reported for HPTC using helium-4 as working gas. A cooling power of 6 mW/4.2 K was also obtained with 250 W input power and a precooling power of 12.1 W/77 K. [ABSTRACT FROM AUTHOR]

A high frequency pulse tube cryocooler with precooling (HPTCP) has been developed and tested to meet the requirement of weak magnetic signals measurement, and the performance characteristics are presented in this article. The HPTCP is a two-stage pulse tube cryocooler with the precooling-stage replaced by liquid nitrogen. Two regenerators completely filled with stainless steel (SS) meshes are used in the cooler. Together with cold inertance tubes and cold gas reservoir, a cold double-inlet configuration is used to control the phase relationship of the HPTCP. The experimental result shows that the cold double-inlet configuration has improved the performance of the cooler obviously. The effects of operation parameters on the performance of the cooler are also studied. With a precooling temperature of 78.5 K, the maximum refrigeration capacity is 0.26 W at 15 K and 0.92 W at 20 K when the input electric power are 174 W and 248 W respectively, and the minimum no-load temperature obtained is 10.3 K, which is a new record on refrigeration temperature for high frequency pulse tube cryocooler reported with SS completely used as regenerative matrix. [ABSTRACT FROM AUTHOR]