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

Abstract

• Sage indicates that Gd 2 O 2 S would result in temperature rise at 5.8 K. • Gd 2 O 2 S effects on the heat exchange and the axial heat conduction are analyzed. • Gd 2 O 2 S experimentally reduces the no-load temperature from 4.75 to 4.57 K. • Gd 2 O 2 S can improve the performance if the cooling temperature is below 6.1 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 HoCu 2 and Gd 2 O 2 S 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, Gd 2 O 2 S is able to improve the regenerator performance when the temperature is below 5.6 K since the Gd 2 O 2 S’s specific heat capacity is higher than that of HoCu 2 at these temperatures. As the refrigeration temperature increases, the optimal length of Gd 2 O 2 S decreases and too much Gd 2 O 2 S 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 Gd 2 O 2 S part. Experimental results verify that the no-load refrigeration temperature can decrease from 4.75 to 4.57 K with 5 mm Gd 2 O 2 S instead of pure HoCu 2 at the cold end, and the refrigeration temperatures at the cooling powers of 20 mW and 40 mW also decrease. Experiments show that Gd 2 O 2 S is capable of improving the performance when the refrigeration temperature is below 6.1 K, which agrees well with the findings from the simulations.