Refrigeration system of a large superconducting spectrometer magnet

A sector type superconducting spectrometer magnet, SKS, for nuclear physics experiments is under construction by the Institute for Nuclear Study, University of Tokyo with collaboration from KEK. The central magnetic field is 3 tesla with a magnet gap of 50 cm. The stored energy is 11.2 MJ at the maximum operation current of 500 A. Easy operation and maintenance have been taken into consideration. It is intended to make the heat leak as small as 3 W at 4 K. A small refrigerator is to be used for thermal insulation at 80 and 20 K in combination with a medium size refrigerator at 4 K. (author)