| 摘要 |
<p>PURPOSE:To prevent a freezing mixture from its evaporation even if the supply of cold gas to a heat-shield plate is stopped, by providing a plurality of heat- shield plate-heat exchangers in the heat-shield plate placed in vacuum heat-insulating layers and transferring the cold gas to be fed from the outside of a low temperature vessel to said heat exchangers. CONSTITUTION:A freezing mixture reservoir part 16, placed in the case of a low temperature vessel and maintained to a high vacuum by vacuum heat-insulating layers 15a, 15b, provides a heat-shield plate 2 so that heat from the case 1 may be not directly radiated into said layers. The heat-shield plate 2, even if a cold- cooling transfer circuit or a refrigerator for cooling said plate causes a trouble, can be cooled in every heat-shield plate-heat exchanger 3A, 4B, enabling evaporation of a freezing mixture to be prevented by opening cold gas injection valves 6, 8 and cold-cooling discharge valves 12, 14 so as to transfer cold-cooling to the heat-sheidl plate 2 from cold gas injection lines 5, 7 to be discharged from cold gas discharge lines 11, 13.</p> |
