Feasibility analysis of HoCu2 and Gd2O2S as regenerative materials around 4-20 K

Stirling type pulse tube refrigerators have great application potentials in terahertz detection, deep space mid/ long infrared detection and so on. It is still hard for Stirling type pulse tube refrigerators to work at liquid helium temperatures efficiently. One of the reasons is the large regenerative heat loss under such low temperatures. In this paper, the cooling performance of the regenerative materials HoCu2 and Gd2O2S at liquid helium temperatures are investigated. Focused on the heat exchange between gas and matrix and the axial heat conduction, Sage simulations indicate that with high specific heat capacity and high thermal conductivity, Gd2O2S is able to improve the regenerator performance when the temperature is below 5.6 K since the Gd2O2S's specific heat capacity is higher than that of HoCu2 at these temperatures. As the refrigeration temperature increases, the optimal length of Gd2O2S decreases and too much Gd2O2S may deteriorate the performance, even causing the temperature to rise slightly at the cold end. This is because heat is released from matrix to gas and the axial heat conduction decreases even to negative value, which causes an increase in temperature gradient in the Gd2O2S part. Experimental results verify that the no-load refrigeration temperature can decrease from 4.75 to 4.57 K with 5 mm Gd2O2S instead of pure HoCu2 at the cold end, and the refrigeration temperatures at the cooling powers of 20 mW and 40 mW also decrease. Experiments show that Gd2O2S is capable of improving the performance when the refrigeration temperature is below 6.1 K, which agrees well with the findings from the simulations.

Automated summary

The study investigated the cooling performance of regenerative materials HoCu2 and Gd2O2S at liquid helium temperatures, finding that Gd2O2S can improve regenerator performance below 5.6K temperature. Experimental results demonstrated that Gd2O2S can enhance performance, but excessive use may deteriorate performance.