Gifford-mcmahon (gm) cryocooler first-stage displacer, first-stage displacer assembly, and gifford-mcmahon cryocooler

A first-stage displacer of a Gifford-McMahon (GM) cryocooler, comprising:

• a first-stage displacer main body including a regenerator material and a first-stage displacer cylinder that accommodates the regenerator material;
• a metal upper cap attached to an upper end of the first-stage displacer main body and formed of a metal material;
• at least one piston seal mounted on a side surface of the metal upper cap;
• and
• an additional contact seal member mounted between the metal upper cap and the first-stage displacer cylinder, the contact seal member including a sealing ring and a back ring, the sealing ring formed of a synthetic resin material, the back ring adjacent to a radially inner side of the sealing ring and formed of synthetic rubber,
• wherein the piston seal includes a piston ring and a tension ring, the piston ring formed of a synthetic resin material, the tension ring adjacent to a radially inner side of the piston ring and formed of a metal material.