Method for operating cryocooler and cryocooler

Abstract

A method for operating a cryocooler includes: connecting a second compressor in series with a first compressor on a high pressure line or a low pressure line; connecting a buffer volume to the low pressure line via a supply valve; executing initial cooling for cooling an expander from an initial temperature to a cryogenic temperature in a state where the second compressor and the buffer volume are connected to the cryocooler; and executing a steady operation of maintaining the expander at the cryogenic temperature after the initial cooling. The execution of the initial cooling includes supplying a working gas to the expander by using the first compressor and the second compressor, and controlling the supply valve to keep a pressure of the high pressure line within a preset appropriate pressure range based on the measured pressure of the high pressure line.

What is claimed is: 
     
         1 . A method for operating a cryocooler in which the cryocooler includes a first compressor, an expander, and a high pressure line and a low pressure line connecting the first compressor to the expander, the method comprising:
 connecting a second compressor in series with the first compressor on the high pressure line or the low pressure line;   connecting a buffer volume to the low pressure line via a supply valve;   executing initial cooling for cooling the expander from an initial temperature to a cryogenic temperature in a state where the second compressor and the buffer volume are connected to the cryocooler; and   executing a steady operation of maintaining the expander at the cryogenic temperature after the initial cooling, wherein   the execution of the initial cooling includes:
 supplying a working gas to the expander by using the first compressor and the second compressor, and 
 controlling the supply valve to keep a pressure of the high pressure line within a preset appropriate pressure range based on a measured pressure of the high pressure line. 
   
     
     
         2 . The method according to  claim 1 , further comprising:
 removing the second compressor after the initial cooling.   
     
     
         3 . The method according to  claim 1 , further comprising:
 removing the buffer volume after the initial cooling.   
     
     
         4 . The method according to  claim 1 , wherein
 the execution of the initial cooling includes
 discontinuing control of the supply valve based on the measured pressure of the high pressure line when a measured pressure of the low pressure line falls below a preset low pressure threshold, and 
 controlling the supply valve to restore a pressure of the low pressure line to the low pressure threshold based on the measured pressure of the low pressure line. 
   
     
     
         5 . The method according to  claim 4 , wherein
 the execution of the initial cooling includes
 discontinuing control of the supply valve based on the measured pressure of the low pressure line when the measured pressure of the high pressure line falls below a high pressure threshold, and 
 controlling the supply valve to restore the pressure of the high pressure line to the high pressure threshold based on the measured pressure of the high pressure line. 
   
     
     
         6 . A method for operating a cryocooler in which the cryocooler includes a first compressor, an expander, and a high pressure line and a low pressure line connecting the first compressor to the expander, the method comprising:
 connecting a second compressor in series with the first compressor on the high pressure line or the low pressure line;   executing initial cooling for cooling the expander from an initial temperature to a cryogenic temperature in a state where the second compressor is connected to the cryocooler; and   executing a steady operation of maintaining the expander at the cryogenic temperature after the initial cooling, wherein   the first compressor or the second compressor includes a compressor motor with a variable operating frequency, and   the execution of the initial cooling includes:
 supplying a working gas to the expander by using the first compressor and the second compressor, and 
 controlling the operating frequency of the compressor motor to keep a pressure of the high pressure line within a preset appropriate pressure range based on a measured pressure of the high pressure line. 
   
     
     
         7 . The method according to  claim 6 , further comprising:
 removing the second compressor after the initial cooling.   
     
     
         8 . The method according to  claim 6 , further comprising:
 connecting a buffer volume to the low pressure line via a supply valve, wherein   the execution of the initial cooling includes   controlling the supply valve to keep the pressure of the high pressure line within the preset appropriate pressure range based on the measured pressure of the high pressure line.   
     
     
         9 . The method according to  claim 8 , further comprising:
 removing the buffer volume after the initial cooling.   
     
     
         10 . A cryocooler comprising:
 an expander capable of executing initial cooling for cooling from an initial temperature to a cryogenic temperature and a steady operation of maintaining the cryogenic temperature after the initial cooling;   a high pressure line and a low pressure line connected to the expander;   a first pressure sensor that measures a pressure of the high pressure line;   a second pressure sensor that measures a pressure of the low pressure line;   a buffer volume for storing a working gas;   a supply valve that connects the buffer volume to the low pressure line; and   a controller configured to control the supply valve to keep the pressure of the high pressure line within a preset appropriate pressure range based on the pressure of the high pressure line measured by the first pressure sensor during the initial cooling, wherein   the controller is further configured to:
 discontinue control of the supply valve based on the pressure of the high pressure line when the pressure of the low pressure line measured by the second pressure sensor falls below a preset low pressure threshold, and 
 control the supply valve to restore the pressure of the low pressure line to the low pressure threshold based on the pressure of the low pressure line measured by the second pressure sensor. 
   
     
     
         11 . The cryocooler according to  claim 10 , wherein
 the controller is further configured to:
 discontinue control of the supply valve based on the pressure of the low pressure line when the pressure of the high pressure line measured by the first pressure sensor falls below a high pressure threshold, and 
 control the supply valve to restore the pressure of the high pressure line to the high pressure threshold based on the pressure of the high pressure line measured by the first pressure sensor. 
   
     
     
         12 . The cryocooler according to  claim 10 , further comprising:
 a first compressor connected to the expander through the high pressure line and the low pressure line; and   a second compressor connected in series with the first compressor on the high pressure line or the low pressure line.