Abstract
Recenty, regenerative refrigerators such as the Gifford-McMahon (GM) refrigerator achieve liquid helium temperature level by using magnetic regenerator materials, which have larger heat capacity below 10K than a conventional regenerator material of Pb. The purpose of this study is to investigate the heat characteristic of the regenerator, which is operated with liquid helium temperature level. In the present paper, we describe the experimental results of the regenerator performance in a two-stage GM refrigerator. Temperatures and pressure in the regenerator were measured and the stored heat in the regenerator was calculated from these data. The stored heat was divided between that stored in regenerator material and that stored in helium gas. The stored heat is compared between ideal gas operation and non-ideal gas operation. The regenerator efficiency was calculated from the stored heat. For ideal gas operation, the stored heat was equal at each position; however, for non-ideal gas operation, it was slight from the middle of the regenerator to the cold end. The multi-layered regenerator constructed using several magnetic materials which have different peaks of the specific heat increases the stored heat in the part in which heat capacity was increased, and achieves higher regenerator efficiency. Regenerator efficiency is higher at lower flow rates, and at higher the hot end temperatures of the regenerator. Therefore, the best condition for cryocooler operation changes with the temperature range in which the regenerator is used.
