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 including a body part and a heat conducting part, wherein a 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 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,   wherein the heat conducting part faces the cooling stage across the clearance channel.   
     
     
         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 heat conducting part includes an overlapping part that overlaps the body part in stroke directions of the displacer, and
 the body part includes an overlapped part corresponding to the overlapping part.   
     
     
         4 . The cryogenic refrigerator as claimed in  claim 3 , wherein the heat conducting part has a bottomed tube shape. 
     
     
         5 . The cryogenic refrigerator as claimed in  claim 3 , wherein the overlapping part and the overlapped part form a screw part. 
     
     
         6 . The cryogenic refrigerator as claimed in  claim 3 , further comprising:
 an insertion member inserted into a first hole part formed in the overlapping part and a second hole part formed in the overlapped part so as to connect the body part and the heat conducting part.   
     
     
         7 . The cryogenic refrigerator as claimed in  claim 1 , wherein the heat conducting part has a tubular shape with a slit that makes the heat conducting part discontinuous in a circumferential direction thereof. 
     
     
         8 . The cryogenic refrigerator as claimed in  claim 1 , wherein the material of the heat conducting part is selected from the group consisting of copper, aluminum, and stainless steel. 
     
     
         9 . A displacer, comprising:
 a body part; and   a heat conducting part,   wherein the heat conducting part is positioned at a low temperature end of the displacer, and   a material of the heat conducting part has a higher thermal conductivity than the body part.   
     
     
         10 . The displacer as claimed in  claim 9 , wherein an outside diameter of the heat conducting part is smaller than an outside diameter of the body part at normal temperature.