| 摘要 |
PURPOSE:To facilitate repair and replacement at the time of a fault of the freezer by extending the freezing part of the freezer by a helium gas cooling zigzag pipe and constituting the freezing part so that it can be mounted on a material to be cooled in a freely attachable and detachable manner. CONSTITUTION:A part of a helium gas in a compressor 22 flows in the pipeline of each heat exchanger whereby cold air obtained by expansion cylinders 4 and 5 is carried to extended heat exchangers 14 and 15, and sucked of its heat therein and is heat exchanged with an inflowing helium gas of room temperature in a first stage heat exchanger 12, thus cold air returning to the compressor substantially in the form of a helium gas of room temperature. Accordingly, the outer surface temperatures of first stage and second stage extended heat exchangers 14 and 15 can be set at a temperature at which a nitrogen gas and a neon gas sealed in cooling vessels 16 and 17 are liquefied. Since the gas sealed cooling vessels 16 and 17 are held at predetermined temperature and pressure because the sealed gas is liquefied therein, if these vessels are thermally connected to a radiation shield or other material to be cooled, the radiation shield or other material to be cooled can be cooled in a manner of easily attaching or detaching the freezer. Thereby, cooling of the heat radiation shield of a superconductive magnet becomes easy and the repair and replacement at the time of a fault of the freezer are facilitated.
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