GM cryocooler

A GM cryocooler comprising:

• a displacer that is reciprocatable in an axial direction;
• a displacer cylinder that houses the displacer;
• a drive piston that is coupled to the displacer so as to drive the displacer in the axial direction;
• and
• a piston cylinder that houses the drive piston and that includes a drive chamber of which a pressure is controlled to drive the drive piston, and a gas spring chamber which is airtightly formed with respect to the displacer cylinder and is partitioned from the drive chamber by the drive piston,
• wherein the drive chamber is formed at a first end of the piston cylinder away from the displacer cylinder in the axial direction and the gas spring chamber is formed at a second end of the piston cylinder toward the displacer cylinder in the axial direction,
• wherein the drive piston is configured to increase a pressure of the gas spring chamber upon movement of the drive piston widening the drive chamber and narrowing the gas spring chamber such that the increased pressure of the gas spring chamber generates a gas spring force that resists the movement of the drive piston toward the gas spring chamber.