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

This paper describes the cooling performance of a pulse tube stage extendin g to room temperature which is precooled by a single-stage GM refrigerator. With this system it was possible to reach liquid helium temperatures witho ut using rare earth compounds as regenerator material. Instead the regenera tor was filled with conventional lead spheres. With the regenerator warm en d being at a precooling temperature of about 31 K a minimum no-load tempera ture near 4.2 K at the cold end of the pulse tube was achieved. This no-loa d temperature is considerably lower than what has been achieved before by t wo-stage regenerative refrigerators which operate without rare earth materi al and attain typically no-load temperatures above 6 K when operated with l ead in the coldest regenerator section. In the presented hybrid system a co oling 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. (C) 2000 Elsevier Science Ltd. All rights r eserved.