Generation of liquid helium temperatures using a lead regenerator in a GM precooled pulse tube stage Original Research Article

This paper describes the cooling performance of a pulse tube stage extending to room temperature which is precooled by a single-stage GM refrigerator. With this system it was possible to reach liquid helium temperatures without using rare earth compounds as regenerator material. Instead the regenerator was filled with conventional lead spheres. With the regenerator warm end being at a precooling temperature of about 31 K a minimum no-load temperature near 4.2 K at the cold end of the pulse tube was achieved. This no-load temperature is considerably lower than what has been achieved before by two-stage regenerative refrigerators which operate without rare earth material and attain typically no-load temperatures above 6 K when operated with lead in the coldest regenerator section. In the presented hybrid system a cooling power of 10 mW at 4.6 K, 100 mW at 6 K and 1 W at 9.2 K was achieved using a 6 kW helium compressor.