Introduction

Abstract

The development of the superconducting machines, such as superconducting magnets for nuclear fusion, electric machines, high energy physics, magnetically levitated train, and the Josephson Junction, should be a driving force for a technical innovation. The reliable helium refrigerator system is indispensable for practical utilization of these superconducting machine. The requirements for a practical use of the helium refrigerator system are considered as follows.
(1) A long and continuous operation is required.
(2) The contamination in the circulating helium should be avoided.
(3) The efficiency of the refrigerator system should be as high as possible.
(4) The control method must be established.
The helium compressor-one part of helium refrigerator system-should be required the above condition. However, the helium compressor is a week point of the helium refrigeration system and the many type of compressor have been developed.
In this special issue, the construction, characteristics and performance of the helium compressors, which is used the helium refrigerator system in Japan as shown Table, is reported.
Table Helium Compressor