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Highlights • The mechanism of multi-bypass was numerical studied. • Multi-bypass has the functions of orifice and double-inlet, making it like two-stage cryocooler. • A minimum no-load temperature 3.7 K was obtained, and the cooling power was 14 mW@4.2 K. • New mK cooling chain for HUBS satellite was proposed and analyzed. Abstract The Vuilleumier (VM) type pulse tube cryocooler (VPTC) is a new kind of 4 K cryocooler which had been experimentally verified. This paper presents the recent advances on a 4 K VPTC in our laboratory. First, the mechanism of multi-bypass was numerically studied using Sage software. The results showed that the function of the multi-bypass is not only similar to a double-inlet, but also to an orifice, which makes the VPTC work like a two-stage cryocooler. Based on the simulation results, the performance of VPTC was experimentally studied. Under its optimal operating conditions, a no-load temperature of 3.7 K has been obtained, which is the first demonstration of a single-stage VPTC obtaining temperatures below 4 K. It can supply about 14mW cooling power at 4.2 K and about 100 mW cooling power at 35 K simultaneously, which has potential application as the pre-cooler for an adiabatic demagnetization refrigerator (ADR). Finally, based on this VPTC, a new mK cooling chain for HUBS (Hot Universe Baryon Surveyor) satellite is proposed and its prospect has also been theoretically analyzed. [ABSTRACT FROM AUTHOR]

VM type pulse tube cryocooler is a new type pulse tube cryocooler driven by the thermal-compressor. This paper presented the recent experimental results on a novel single-stage VM type pulse tube cryocooler with multi-bypass. The low temperature double-inlet, orifice and gas reservoir, and multi-bypass were used as phase shifters. With the optimal operating frequency of 1.6 Hz and optimal average pressure of 1.4 MPa, a no-load temperature of 4.9 K has been obtained and 30 mW@5.6 K cooling power has been achieved. It was the first time for the single-stage VM-PTC obtaining liquid helium temperature reported so far. Moreover, it was also the first time for the multi-bypass being used in the low-frequency Stirling type pulse tube cryocooler. [ABSTRACT FROM AUTHOR]

This paper presents experimental results on a novel two-stage gas-coupled VM-PT cryocooler, which is a one-stage VM cooler coupled a pulse tube cooler. In order to reach temperatures below the critical point of helium-4, a one-stage coaxial pulse tube cryocooler was gas-coupled on the cold end of the former VM cryocooler. The low temperature inertance tube and room temperature gas reservoir were used as phase shifters. The influence of room temperature double-inlet was first investigated, and the results showed that it added excessive heat loss. Then the inertance tube, regenerator and the length of the pulse tube were researched experimentally. Especially, the DC flow, whose function is similar to the double-orifice, was experimentally studied, and shown to contribute about 0.2 K for the no-load temperature. The minimum no-load temperature of 4.4 K was obtained with a pressure ratio near 1.5, working frequency of 2.2 Hz, and average pressure of 1.73 MPa. [ABSTRACT FROM AUTHOR]

A high-frequency coaxial multi-bypass pulse tube refrigerator (MBPTR) was designed, manufactured, and tested. The cold finger is driven by a linear compressor through a connection tube to reduce the vibrations coming from the compressor. The pulse tube refrigerator adopts a coaxial configuration with a double-inlet and a single multi-bypass to improve the performance. With Er 3 Ni spheres at the cold end of the regenerator, the refrigerator can reach a no-load temperature of 13.9 K with 250 W electric input power, which is the lowest temperature for this kind of refrigerator reported so far. Especially, the interplay of double-inlet and multi-bypass was observed experimentally. An Er 3 Ni spheres regenerator was found to be a potential substitution for stainless steel wire mesh (SSWM) regenerator for this kind of refrigerator. [ABSTRACT FROM AUTHOR]