Cryogenic refrigerator and displacer

Abstract

A cryogenic refrigerator includes a displacer including a body part and a heat conducting part, wherein the material of the heat conducting part has a higher thermal conductivity than the body part; a cylinder accommodating the displacer in such a manner as to allow the displacer to reciprocate in the axial directions of the cylinder, wherein an expansion space is formed between the cylinder and a low temperature end of the displacer; a clearance channel formed between the displacer and the cylinder so as to allow a refrigerant gas to flow into the expansion space; and a cooling stage positioned adjacent to the expansion space. The heat conducting part faces the cooling stage across the clearance channel.

What is claimed is: 
     
         1 . A cryogenic refrigerator, comprising:
 a displacer having a cylindrical shape extending between a low temperature end and a high temperature end thereof, and including:
 a body part made of phenol containing cloth, 
 a heat conducting part provided at a lower temperature side relative to the body part, said heat conducting part including a diameter smaller than an overlapped part of the body part so as to be inserted into an inner circumference of the overlapped part of the body part that overlaps the overlapping part in a stroke direction of the displacer, said heat conducting part being made of copper or aluminum, 
 a regenerator material within an inner space thereof, and 
 an opening provided at an outer peripheral surface of the displacer at the low temperature end so as to be connected to the inner space; 
   a cylinder accommodating the displacer in such a manner as to allow the displacer to reciprocate in axial directions of the cylinder, wherein an expansion space is formed between the cylinder and a low temperature end of the displacer;   a clearance channel formed between the outer peripheral surface of the displacer and an inner peripheral surface of the cylinder so as to allow a refrigerant gas to flow into the expansion space from the opening of the displacer; and   a cooling stage positioned adjacent to the expansion space and having a hollow portion provided around an outer peripheral surface of the cylinder so as to enclose the expansion space and a bottom portion provided so as to face a bottom portion of the cylinder so as to enclose the expansion space,   wherein the heat conducting part faces the hollow portion of the cooling stage across the clearance channel,   wherein the cylinder and the high temperature end of the displacer define a room temperature chamber that changes its volume according to a reciprocating movement of the displacer in the axial directions of the cylinder, and   wherein the cylinder and the displacer defines the expansion space that changes its volume according to the reciprocal movement of the displacer.   
     
     
         2 . The cryogenic refrigerator as claimed in  claim 1 , wherein the heat conducting part has a lower coefficient of thermal expansion than the body part. 
     
     
         3 . The cryogenic refrigerator as claimed in  claim 1 , wherein the entire part of the bottom portion of the heat conducting part directly faces the bottom portion of the cylinder. 
     
     
         4 . The cryogenic refrigerator as claimed in  claim 1 , wherein the heat conducting part and the body part are fixed to each other by inserting a pin into the overlapped part and the overlapping part. 
     
     
         5 . The cryogenic refrigerator as claimed in  claim 1 , wherein the heat conducting part has a lower coefficient of linear thermal expansion than the body part. 
     
     
         6 . The cryogenic refrigerator as claimed in  claim 4 , wherein the pin is made of the phenol containing cloth.