Recent progress of advanced refrigeration systems R&D in Japan.

This paper describes recent progress on cryocoolers and their applications in Japan. The main progress in cryocoolers in the past decade is a 4 K cryocooler using magnetic regenerator materials. In 1998, two Japanese research groups achieved almost simultaneously a minimum temperature of 4 K by use of a Gifford McMahon (GM) cryocooler. Now 4 K-GM cryocoolers are commercially available from several Japanese cryocooler companies. Spherical magnetic regenerator materials, such as Er3Ni or HoCu2, are also distributed from Japan. By using a 4 K-GM cryocooler and a high Tc superconducting current lead, developed around 1990, a conductive cooled superconducting magnet (SCM) has been produced. The SCM, which does not use any liquid cryogen, is now quite popular for both research and industrial use. The magnetic regenerator materials were also applied to a 4 K-pulse tube cryocooler and to a GM/Joule-Thomson cryocooler for the magnetically levitated train.