Systematic Investigations of Regenerators for 4.2K-Refrigerators

Abstract

Using Rare Earth materials and compounds as regenerator, several groups have reached temperatures below T=4.2K with Gifford-McMahon (GM), as well as with pulse tube refrigerators. Their performance is substantially determined by the choice of Rare Earth material, especially its specific heat. Based on measured pressures and displacements of an existing mechanically driven GM coldhead, cooling capacities are predicted theoretically for different regenerator matrices. This will be compared with corresponding experimental results which include measurements of the temperature profile in the regenerator. The results are discussed in terms of mass flow rate through the regenerator and the influence of different loss mechanisms. So far, an optimum capacity of >1W was achieved at T=4.2 K, using a 6 kW compressor unit for operation. Different modifications of the displacer design however were necessary in order to achieve a very good repeatability of results and high stability during operation.