Cryogenic refrigerator

Abstract

In a cryogenic refrigerator, a displacer includes a low temperature end and a high temperature end. A cylinder accommodates the displacer to be reciprocated in a longitudinal direction, and forms an expansion space which is an expansion space of a refrigerant gas between the low temperature end of the second displacer and the cylinder. The damper portion is disposed to be adjacent to the expansion space and communicates with the expansion space. A volume of the damper portion is 30% or less of a volume of the expansion space.

What is claimed is: 
     
         1 . A cryogenic refrigerator comprising:
 a displacer which includes a low temperature end and a high temperature end;   a cylinder which accommodates the displacer to be reciprocated in a longitudinal direction and forms an expansion space of a refrigerant gas between the low temperature end of the displacer and the cylinder; and   a damper portion which is disposed to be adjacent to the expansion space and communicates with the expansion space,   wherein a volume of the damper portion is 30% or less of a volume of the expansion space.   
     
     
         2 . The cryogenic refrigerator according to  claim 1 ,
 wherein the damper portion is included in the displacer.   
     
     
         3 . The cryogenic refrigerator according to  claim 2 ,
 wherein the displacer includes a cover portion at the low temperature end, and   wherein the damper portion has a short pipe shape in which one end is opened and the other end is closed, the one end is directed to a side adjacent to the expansion space, and the other end is closed by the cover portion.   
     
     
         4 . The cryogenic refrigerator according to  claim 1 ,
 wherein the damper portion is provided on the cylinder.   
     
     
         5 . The cryogenic refrigerator according to  claim 4 ,
 wherein the cylinder includes a flanged cooling stage having a protruding portion which extends in a direction perpendicular to a long axis of the cylinder, at a bottom portion and a position corresponding to the expansion space on an outer periphery, and   wherein the damper portion is provided in the protruding portion of the cooling stage.   
     
     
         6 . The cryogenic refrigerator according to  claim 1 ,
 wherein the cryogenic refrigerator is a multistage cryogenic refrigerator which includes a plurality of the displacers, and   wherein the damper portion is installed to be adjacent to the expansion space which is formed between the lowest temperature side displacer and the cylinder.