Pressurized Superfluid Helium Cryostat

Abstract

In a pressurized superfluid helium cryostat, a first flow rate control valve and a preliminary cooler are installed between a liquid helium inlet at a bottom portion of a 4.2K liquid helium bath and a J-T valve which is a second flow rate control valve. The preliminary cooler is cooled by depressurization by a vacuum pump. The liquid taken in from the 4.2K liquid helium bath is cooled to a temperature of the preliminary cooler by J-T expansion in the first flow rate control valve, and stored in the preliminary cooler. The liquid helium in the preliminary cooler can be cooled below 2.2K, and further subjected to J-T expansion in the J-T valve. By installation of the preliminary cooler, the efficiency of the superfluid cooler can be increased as compared to a conventional type.

1 . A pressurized superfluid helium cooled cryostat, comprising:
 a first liquid helium bath which stores liquid helium;   a second liquid helium bath which stores superfluid liquid helium, the temperature of which is lower than that of the liquid helium in the first liquid helium bath;   a vacuum chamber which contains the first liquid helium bath and the second liquid helium bath, and insulates heat from room temperature; and   a superfluid cooler provided in the second liquid helium bath, which communicates with the first liquid helium bath via a passage and generates the superfluid helium to cool the second liquid helium bath, wherein   the pressurized superfluid helium cooled cryostat comprises a preliminary cooler provided between the first liquid helium bath and the superfluid cooler for lowering the temperature of the liquid helium by lowering vapor pressure, and the first liquid helium bath and the superfluid cooler communicate with each other via the preliminary cooler.   
     
     
         2 . The pressurized superfluid helium cooled cryostat according to  claim 1 , further comprising:
 a first flow rate control valve which controls the flow rate of the liquid helium flowing through the passage communicating the first liquid helium bath and the superfluid cooler; and   a second flow rate control valve which controls the flow rate of the liquid helium flowing through a passage communicating the preliminary cooler and the superfluid cooler.   
     
     
         3 . The pressurized superfluid helium cooled cryostat according to  claim 2 , wherein the first flow rate control valve is composed of a valve which causes J-T expansion of the liquid helium. 
     
     
         4 . The pressurized superfluid helium cooled cryostat according to  claim 2 , wherein the second flow rate control valve is composed of a valve which causes J-T expansion of the liquid helium. 
     
     
         5 . The pressurized superfluid helium cooled cryostat according to  claim 1 , further comprising a pumping line for the preliminary cooler for depressurizing the preliminary cooler by a vacuum pump provided outside the vacuum chamber. 
     
     
         6 . The pressurized superfluid helium cooled cryostat according to  claim 1 , further comprising a pumping line for the superfluid cooler for depressurizing the superfluid cooler by a vacuum pump provided outside the vacuum chamber. 
     
     
         7 . The pressurized superfluid helium cooled cryostat according to  claim 1 , further comprising a safety valve between the first liquid helium bath and the second liquid helium bath.