| 摘要 |
PROBLEM TO BE SOLVED: To improve cooling performance in a multi-step freezer for cooling a superconductor magnet by providing a thermal switch connected between a first cooling end having higher cooling capability and a second cooling end having lower cooling capability, and encapsulating gas having a boiling point between lowest arrival temperatures of the cooling ends in the thermal switch. SOLUTION: This mullet-step freezer 1 is adapted such that there is protruded into a vacuum container 2 a most part of a freezer body 1a including first and second cooling ends 5a, 6a where cooling plates 5a, 6a and cooling parts 21a, 21b are connected, and a radiation shield 3 is connected with the first cooling plate 5a to form a cooling space 8. The second cooling end 6 is disposed in the cooling space 8, and an article 7 to be cooled is connected with the second cooling plate 6a. There is further connected with both cooling plates 5a, 6a a thermal switch 4 which is on in thermal connection by evaporation of encapsulated gas and is off in thermal connection by liquefaction of the gas. There is used a gas having a boiling point between lowest arrival temperatures of the cooling ends 5, 6 for the encapsulated gas whereby required time for cooling is shortened. |
