| abstract |
A cooling system for cooling, preferably a superconducting magnet, to a low temperature, comprises a main refrigerator, an auxiliary refrigerator connected to the main refrigerator, and switch control means (14,23) for controlling the supply of refrigerant used in the main refrigerator to the auxiliary refrigerator. Preferably the main refrigerator employs the Gifford-McMahon cycle and the auxiliary refrigerator is a pulse tube refrigerator. The control means enables helium gas in the main refrigerator to be guided to the pulse tube refrigerator at the time of pre-cooling the thermal shield (4) and the superconducting coil (5). Pre-cooling continues until nitrogen gas contained in the thermal switches (28,29) is frozen. Electromotive valve (23) is then closed separating the main refrigerator from the auxiliary refrigerator. The pulse tube refrigerator comprises the pulse tube (26), a heat absorption tube (25), a refrigerant-filled chamber (24) including a copper net for cold-accumulating purposes, and a capillary tube (27). The main refrigerator has a first stage cooling section (15) for cooling thermal shield (4) and a second stage cooling section (16) for cooling a thermally conductive copper member (6) attached to the superconducting coil (5). |