Abstract
A 1.5W-class 4K GM (Gifford-McMahon) cryocooler has been developed. The regenerator material ErNi0·9Co0·1, the cold end of the second cylinder made on copper and intake/exhaust valve having original timing and interval are used in the cryocooler. In this study, four sizes of cylinders and two types of compressor units were prepared and the cooling capacities were measured. As a result, cooling capacity of the first and the second stage depended on the ratio between the first and the second cylinder's volume. When the compressor was fixed and cylinders were changed, the bigger the second stage cooling capacity became and the smaller the first stage cooling capacity became. The maximum cooling capacity of the first stage at 40K was 53.7W, and that of the second stage at 4.2K was 1.74W.
