Cryogenic refrigerator and control method therefor

Abstract

A cryogenic refrigerator ( 10 ) which generates a cryogenic temperature by compressing and expanding a working gas in a closed loop ( 11 ). The cryogenic refrigerator comprises a bypass line ( 22 ) allowing a high-pressure portion and a low-pressure portion to communicate with each other, a gas storage tank ( 24 ) located midway in the bypass line and having pressure regulation valves ( 23 a , 23 b ) on the high-pressure side and the low-pressure side, respectively, and a pressure control unit ( 26 ) controlling the pressure regulation valves. The pressure control unit ( 26 ) controls the pressure regulation valves ( 23 a , 23 b ) so that the pressure in the gas storage tank ( 24 ) is equal to the pressure in the closed loop at room temperature and in a stopped state and so that the pressure in the gas storage tank ( 24 ) is between the pressures in the high-pressure portion and in the low-pressure portion and is close to the pressure in the low-pressure portion in an operating state.

1 . A cryogenic refrigerator which generates a cryogenic temperature by compressing a working gas in a closed loop and expanding the compressed working gas, the cryogenic refrigerator comprising:
 a bypass line which allows a high-pressure portion and a low-pressure portion in the closed loop to communicate with each other;   a gas storage tank which is located midway in the bypass line and has pressure regulation valves on the high-pressure side and the low-pressure side, respectively; and   a pressure control unit which controls the pressure regulation valves,   wherein the pressure control unit controls the pressure regulation valves so that the pressure in the gas storage tank is equal to the pressure in the closed loop at room temperature and in a stopped state and controls the pressure regulation valves so that the pressure in the high-pressure portion is equal to a predetermined pressure in an operating state in which a cryogenic temperature is generated.   
     
     
         2 . The cryogenic refrigerator according to  claim 1 , wherein the capacity of the gas storage tank is set so as to enable the pressure in the gas storage tank to be maintained at a predetermined reference pressure or lower at room temperature and in the stopped state and so as to enable the pressure in the high-pressure portion to be maintained at a predetermined operating pressure in the operating state in which the cryogenic temperature is generated. 
     
     
         3 . The cryogenic refrigerator according to  claim 1 , wherein the pressure control unit:
 maintains the pressure regulation valves to be fully opened in the stopped state of the cryogenic refrigerator; and   opens the pressure regulation valve connected to the high-pressure side in the case where the pressure in the high-pressure portion exceeds a predetermined maximum pressure and opens the pressure regulation valve connected to the low-pressure side in the case where the pressure in the high-pressure portion is equal to or lower than a predetermined minimum pressure.   
     
     
         4 . The cryogenic refrigerator according to  claim 1 , further comprising:
 a room-temperature compressor which is installed in a room temperature portion in the closed loop to compress the working gas from a predetermined low pressure to a predetermined high-pressure;   a first intermediate heat exchanger which is located between a cryogenic temperature portion in the closed loop and the room temperature portion to perform a heat exchange between the working gases; and   an expander which is installed on the cryogenic temperature portion side from the first intermediate heat exchanger to isentropically expand the working gas.   
     
     
         5 . The cryogenic refrigerator according to  claim 4 , wherein:
 the room-temperature compressor includes a plurality of turbo compressors which compress the working gas in multiple stages from the predetermined low pressure to the high pressure;   the expander includes a plurality of expansion turbines which expand the working gas in multiple stages from the high pressure to the low pressure; and   a plurality of intermediate heat exchangers which perform a heat exchange between the working gases are disposed in the middle of the plurality of expansion turbines.   
     
     
         6 . A control method for a cryogenic refrigerator which generates a cryogenic temperature by compressing a working gas in a closed loop and expanding the compressed working gas, the control method comprising:
 providing the cryogenic refrigerator with a bypass line which allows a high-pressure portion and a low-pressure portion in the closed loop to communicate with each other and a gas storage tank which is located midway in the bypass line and has pressure regulation valves on the high-pressure side and the low-pressure side, respectively; and   controlling the pressure regulation valves so that the pressure in the gas storage tank is equal to the pressure in the closed loop at room temperature and in a stopped state and controlling the pressure regulation valves so that the pressure in the high-pressure portion is equal to a predetermined pressure in an operating state in which a cryogenic temperature is generated.   
     
     
         7 . The control method for the cryogenic refrigerator according to  claim 6 , wherein the capacity of the gas storage tank is set so as to enable the pressure in the gas storage tank to be maintained at a predetermined reference pressure or lower at room temperature in the stopped state and so as to enable the pressure in the high-pressure portion to be maintained at a predetermined operating pressure in the operating state in which the cryogenic temperature is generated.