Cryogenic system and control method for cryogenic system

Abstract

A cryogenic system includes a cryocooler and a controller. The cryocooler includes a first cylinder, a second cylinder including a heat absorbing portion, a first temperature sensor measuring a first measurement temperature, a second temperature sensor measuring a second measurement temperature, and a third temperature sensor measuring a third measurement temperature. The controller is configured to acquire a first measurement temperature from the first temperature sensor, a second measurement temperature from the second temperature sensor, and a third measurement temperature from the third temperature sensor, to set an upper limit temperature of the heat absorbing portion, based on the first measurement temperature, the second measurement temperature, and an axial position of the heat absorbing portion, and to control the heat source such that the third measurement temperature is equal to or lower than the upper limit temperature of the heat absorbing portion.

What is claimed is: 
     
         1 . A cryogenic system comprising:
 a cryocooler including
 a first cylinder, 
 a second cylinder provided in series with the first cylinder in an axial direction and including a heat absorbing portion thermally connected to a heat source in an axial intermediate portion of the second cylinder, 
 a first temperature sensor measuring a first measurement temperature in one axial end portion of the second cylinder close to the first cylinder, 
 a second temperature sensor measuring a second measurement temperature in the other axial end portion of the second cylinder far from the first cylinder, and 
 a third temperature sensor measuring a third measurement temperature in the heat absorbing portion; and 
   a controller configured to:
 acquire the first measurement temperature from the first temperature sensor, the second measurement temperature from the second temperature sensor, and the third measurement temperature from the third temperature sensor, 
 set an upper limit temperature of the heat absorbing portion, based on the first measurement temperature, the second measurement temperature, and an axial position of the heat absorbing portion, and 
 control the heat source such that the third measurement temperature is equal to or lower than the upper limit temperature of the heat absorbing portion. 
   
     
     
         2 . The cryogenic system according to  claim 1 ,
 wherein the controller is configured to:
 determine a reference temperature distribution of the second cylinder having the first measurement temperature in the one axial end portion of the second cylinder and having the second measurement temperature in the other axial end portion of the second cylinder and linearly changed depending on an axial position in the second cylinder, and 
 set the upper limit temperature of the heat absorbing portion, based on the reference temperature distribution and the axial position of the heat absorbing portion. 
   
     
     
         3 . The cryogenic system according to  claim 1 ,
 wherein the one axial end portion of the second cylinder is thermally connected to a first portion of the heat source, the other axial end portion of the second cylinder is thermally connected to a second portion of the heat source, and   the heat absorbing portion is thermally connected to a third portion of the heat source connecting the first portion and the second portion.   
     
     
         4 . The cryogenic system according to  claim 3 ,
 wherein the heat source includes a refrigerant gas line that passes through the first portion, the third portion, and the second portion, in this order, and   the controller is configured to control a refrigerant gas flow rate of the refrigerant gas line such that the third measurement temperature is equal to or lower than the upper limit temperature.   
     
     
         5 . The cryogenic system according to  claim 3 ,
 wherein the heat source includes a current lead that passes through the first portion, the third portion, and the second portion in this order, and   the controller is configured to control a current of the current lead such that the third measurement temperature is equal to or lower than the upper limit temperature.   
     
     
         6 . A control method for a cryogenic system, the cryogenic system including a cryocooler including a first cylinder and a second cylinder which are provided in series in an axial direction, the second cylinder including a heat absorbing portion thermally connected to a heat source in an axial intermediate portion of the second cylinder, the method comprising:
 measuring a first measurement temperature in one axial end portion of the second cylinder close to the first cylinder;   measuring a second measurement temperature in the other axial end portion of the second cylinder far from the first cylinder;   measuring a third measurement temperature in the heat absorbing portion;   setting an upper limit temperature of the heat absorbing portion, based on the first measurement temperature, the second measurement temperature, and an axial position of the heat absorbing portion; and   controlling the heat source such that the third measurement temperature is equal to or lower than the upper limit temperature of the heat absorbing portion.