Refrigerator and cryopump

Abstract

A refrigerator includes: a refrigerator cylinder including a cylindrical first-stage cylinder and a cylindrical second-stage cylinder configured to have a smaller inner diameter than the first-stage cylinder and coupled to the first-stage cylinder; a cylindrical first-stage displacer disposed inside the first-stage cylinder; a first-stage cold storage device disposed inside the first-stage displacer; a cylindrical second-stage displacer configured to have a smaller outer diameter than the first-stage displacer, disposed inside the second-stage cylinder, and coupled to the first-stage displacer; a second-stage cold storage device disposed inside the second-stage displacer; and a reciprocating mechanism that reciprocates, in the refrigerator cylinder into which a coolant gas is introduced, the first- and second-stage displacers in a direction along a central axis line of the refrigerator cylinder. A non-fluorine coating layer is formed on an outer circumferential surface of the second-stage displacer, and a clearance is provided between the coating layer and the second-stage cylinder.

What is claimed is: 
     
         1 . A refrigerator, comprising:
 a refrigerator cylinder including a cylindrical first-stage cylinder and a cylindrical second-stage cylinder, the second-stage cylinder being configured to have a smaller inner diameter than the first-stage cylinder and being coupled to the first-stage cylinder;   a cylindrical first-stage displacer disposed inside the first-stage cylinder;   a first-stage cold storage device disposed inside the first-stage displacer;   a cylindrical second-stage displacer configured to have a smaller outer diameter than the first-stage displacer, disposed inside the second-stage cylinder, and coupled to the first-stage displacer;   a second-stage cold storage device disposed inside the second-stage displacer; and   a reciprocating mechanism that reciprocates the first-stage displacer and the second-stage displacer in a direction along a central axis line of the refrigerator cylinder in the refrigerator cylinder into which a coolant gas is introduced, wherein   a non-fluorine coating layer is formed on an outer circumferential surface of the second-stage displacer, and   a clearance is provided between the coating layer and the second-stage cylinder.   
     
     
         2 . The refrigerator according to  claim 1 , wherein
 the coating layer includes at least one of a diamond-like carbon (DLC), titanium nitride, titanium carbide, ceramics, polyimide (PI), or polyetheretherketone (PEEK).   
     
     
         3 . A cryopump that evacuates gas inside a vacuum chamber, comprising:
 the refrigerator according to  claim 1 , and   a cooling plate that is cooled by the refrigerator and condenses or adsorbs the gas inside the vacuum chamber to remove the gas.