Regenerator material and regenerative refrigerator

A regenerative refrigerator comprising:

• a two-stage cold head comprising a second-stage cooling stage and a second-stage cylinder, the second-stage cooling stage provided around a low temperature end of the second-stage cylinder, the second-stage cylinder extending along an axial direction of the cold head from the low temperature end to a high temperature end, opposite to the low temperature end, of the second-stage cylinder;
• and
• a second-stage regenerator material arranged in the second-stage cylinder, the second-stage regenerator material comprising a laminated structure comprising a plurality of porous metal layers layered along a laminating direction from the high temperature end to an intermediate axial position between the high temperature end and the low temperature end of the second-stage cylinder and a plurality of balls arranged in a volume from the intermediate axial position to the low temperature end of the second-stage cylinder, each porous metal layer extending along a plane perpendicular to the laminating direction, the laminating direction is parallel to an axial direction of the cold head,
• wherein each porous metal layer of the laminated structure comprises a metal mesh or metal plate provided with a plurality of holes to allow gas to pass through the laminated structure along the laminating direction,
• wherein each porous metal layer of the laminated structure includes a base material made of metal and a metal coating made of metal, the metal coating covers the base material.

A regenerative refrigerator comprising:

• a cold head comprising a first-stage cooling stage and a first-stage cylinder, the first-stage cooling stage provided around a low temperature end of the first-stage cylinder, the first-stage cylinder extending along an axial direction of the cold head from the low temperature end to a high temperature end, opposite to the low temperature end, of the first-stage cylinder;
• and
• a first-stage regenerator material arranged in the first-stage cylinder, the first-stage regenerator material comprising a laminated structure comprising a plurality of first porous metal layers layered along a laminating direction from the high temperature end to a first axial position between the high temperature end and the low temperature end of the first-stage cylinder and a plurality of second porous metal layers layered along the laminating direction from the first axial position to a second axial position, closer to the low temperature end than the first axial position, of the first-stage cylinder, each of the first and second porous metal layers extending along a plane perpendicular to the laminating direction, the laminating direction is parallel to the axial direction of the cold head,
• wherein each of the first and second porous metal layers of the laminated structure comprises a metal mesh or metal plate provided with a plurality of holes to allow gas to pass through the laminated structure along the laminating direction,
• wherein each of the first porous metal layers of the laminated structure includes a base material made of metal and does not include coating,
• wherein each of the second porous metal layers of the laminated structure is provided with the base material made of metal and a coating covering the base material of that second porous metal layer,
• wherein the coating is made of an alloy of bismuth and tin, an alloy of antimony and tin, or an alloy of bismuth, antimony, and tin.