PROBLEM TO BE SOLVED: To provide a pressurized superfluid helium cryostat which can elevate the cooling efficiency of a cooler, in comparison with a cooling system cooling liquid helium by a precooling heat exchanger.;SOLUTION: A first flow regulating valve 7 and a precooler 8 are located between a liquid helium inlet 6 at the bottom of 4.2 K liquid helium bath 2 and a JT valve 9, a second flow regulating valve. The precooler is depressurized by a vacuum pump and cooled. Then, in order to make the liquid helium flow, from the 4.2 K liquid helium bath into the cooler, the temperature of the precooler is kept at a temperature slightly higher than the temperature of the cooler. The liquid helium, taken out from the 4.2 K liquid helium bath is subjected to JT (Joule-Thomson)-expansion and cooling down to a precooler temperature by the first flow regulating valve 7 and accumulates in the precooler. Since the liquid helium in the precooler can be cooled to lower than 2.2 K and it can be further subjected to JT-expansion by the JT valve 9, the efficiency of the cooler can be increased further than when the precooling heat exchanger is installed.;COPYRIGHT: (C)2008,JPO&INPIT
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