Attaining the liquid helium temperature with a compact pulse tube cryocooler for space applications

Recent breakthroughs in space science have motivated space exploration programs in many countries including China. Cryocoolers, which provide the mandatory low-temperature environment for many sensitive yet delicate space detectors, are crucial for the proper functioning of various systems. One benchmark for the cryocooler performance is attaining the liquid helium temperature. However, even with complex configurations and multiple driving sources, only a few cryocoolers to date can achieve this goal. Here we report a high-frequency pulse tube cryocooler(HPTC) driven by a single non-oil-lubrication compressor which is capable of reaching the liquid helium temperature while offering other advantages such as high compactness, excellent reliability and high efficiency. The HPTC obtains a no-load temperature of 4.4 K, which is the first realization of cooling below the4 He critical point with a gas-coupled two-stage arrangement. The prototype can provide a cooling power of 87 mW at 8 K, and 5.2 mW at 5 K with a 425 W input electric power, showing leading-level efficiency. Moreover, we demonstrate the ability of the cryocooler to simultaneously provide cooling power at different temperature levels to meet different requirements. Therefore, the prototype developed here could be a promising cryocooler for space applications and beyond.

Temperature Fluctuation of a Closed-Cycle Helium Joule-Thomson Cryocooler with Two-Stage Precooling

For quantum communications,single-photon detection,millimeter wave detection and other space projects,all of them need to work at liquid helium temperatures to achieve excellent performance.The closed-cycle helium Joule-Thomson cryocooler(JTC)is currently one of the mainstream solutions to realize the liquid helium temperature.While realizing the liquid helium temperature,the detector has strict requirements on the temperature fluctuation of the JTC,because the thermal noise caused by the JTC temperature fluctuation will have a critical impact on the detection performance.The typical closed-cycle helium JTC is precooling by a two-stage precooler.When the operating parameters of the JTC compressor remain unchanged,the change of the precooler is the main factor that affects the temperature fluctuation of the JTC.To explore the influence mechanism of JTC temperature fluctuations,experimental and theoretical studies are carried out.Based on the real gas equation of state,the influence of various parameters on the evaporator temperature fluctuations is explained.Research results show that the increase in temperature of each stage will cause the temperature of the JTC to increase.Especially,the change of the secondary precooling temperature(T_(pre2))has the most obvious influence on JTC temperature.Furthermore,the influence of the JT compressor’s buffer tank volume Vb on temperature fluctuation is studied.By increasing the Vb,the JTC temperature fluctuation caused by the temperature change of the precooler can be effectively reduced.

Thermal Performance of a 4 K High-Frequency Pulse Tube Cryocooler with Different Working Fluids

The high-frequency pulse tube cryocooler(HPTC)represents a promising miniature cryocooling technology due to its compact structure and the absence of low-temperature moving components.However,limited to the non-ideal gas effect of4He,the HPTC is hard to obtain high cooling performance in the liquid helium temperature range.3He as the working fluid can effectively improve the cooling performance of the HPTC,but the high cost hinders its wide application.In consideration of both cooling performance and cost-effectiveness,this paper explores the feasibility of utilizing^(3)He-^(4)He mixtures as the working fluid for HPTCs.Firstly,the experimental results of a developed HPTC based4He are reported.With a total power consumption of 575 W,the lowest temperature of 3.26 K was observed.And the measured cooling power at 4.2 K was 20.8 mW.Then the theoretical utmost efficiency of the cryocooler was calculated in terms of the thermophysical properties of the working fluids,using ^(3)He-^(4)He mixtures with different compositions as the working fluids.The whole machine modeling of the HPTC was further carried out,and the influence of the working fluids with different components on the structural parameters such as double-inlet and inertance tube,and operating parameters such as pressure and frequency were analyzed.The calculated results show that the cooling power is expected to be increased to36 mW and 53 mW if the equimolar ^(3)He-^(4)He mixture and pure ^(3)He are used,respectively.