Study Of A Separated Two-stage Pulse Tube Cooler Working Below Liquefied Helium Temperature

Pulse tube cooler has no moving parts at the cold head, thus it has considerable advantages of higher reliability, lower mechanical vibration, lower magnetic noise and longer lifetime than other types of refrigerators. More and more people have focused on this new kind of cryocooler because it has potential to be applied to cryogenic electronics, space and superconductor cooling. As people know more and more about its working mechanism, pulse tube cooler has become more and more competitive in many applications which need it to work around 80 K and can displace any other kinds of cryocooler such as Stirling and G-M cooler. Up to now, the lowest no-load temperature was 2.07 K obtained by Thummes with a liquid nitrogen precooled two-stage pulse tube cooler using ⁴He as working fluid. Recently, 1.27 K was obtained by Jiang ning at a separate two-stage pulse tube with ³He as working fluid, which is the lowest temperature reached by a regenerative refrigerator. However, more effort is needed to improve the performance of multi-stage pulse tube cooler working below liquid helium temperature. In order to increase cooling capacity of a two-stage pulse tube, a new-designed pulse tube cooler consisting of two separate single-stage pulse tubes was built. The heat exchanger in the middle of the second stage regenerator is thermally connected to the cold head of the first stage for precooling. As compared to that of coolers with common gas supply, such design presents higher flexibility in distribution of cooling capacity of the stages and easier adjustment of DC-Flow. The two stages are possible to operate at different frequencies, timing, working pressures and compressors, even at different working fluids. Of course, it can also operate with only one compressor for both stages. The two stages are both operated in orifice and double-inlet mode with the phase-shifting components located at ambient temperature. The coldest end of the second stage regenerator is filled with magnetic material HoCu₂ and ErNiCo for better...