Masakazu Okamoto

Numerical and experimental study of a 4 K modified-Solvay cycle cryocooler

A two-stage 4 K Modified-Solvay cycle cryocooler1, which is a pneumatically driven Gifford — McMahon cryocooler and will be used for the conduction-cooled low temperature superconducting magnets, has been optimized by numerical and experimental study. After the optimization, the maximum cooling capacity of 36.5 W at 35 K on the first stage and 1.08 W at 4.2 K on the second stage with 6.7 kW input power has been obtained. This is the world’s first pneumatically driven G-M cryocooler which has over 1 W cooling capacity at 4.2 K. In this paper, experimental and numerical results of the influence of the valve opening timing and the displacer motion concerning the cooling capacity are described. The experimentally obtained optimum P-V diagram and valve timing are in good agreement with the numerical simulation results. And the reliability tests (over 100 times of cool-down and warm-up cycle, and over 3,000 hours continuous operation) were successfully conducted. It can be expected that this 4 K cryocooler has a high reliability equivalent to the commercial G-M cryocoolers which operate above 10 K on the 2nd stage temperature.