A regenerator of a regenerative refrigerator includes: a magnetic regenerator material used for cold storage; and a container that accommodates the magnetic regenerator material. A part of the container that accommodates the magnetic regenerator material includes: a first region that includes a temperature range in which a specific heat of the magnetic regenerator material reaches maximum during an operation of the regenerative refrigerator, and a second region that is in a temperature range different from that of the first region. A cross sectional area of a part of the first region that accommodates the magnetic regenerator material is smaller than a cross sectional area of a part of the second region that accommodates the magnetic regenerator material.

A cryocooler includes a second-stage cooling stage, a second cylinder which includes the second-stage cooling stage on a terminal of the second-stage cylinder, a second-stage displacer which includes a magnetic regenerator material and is accommodated in the second-stage cylinder so as to be able to reciprocate in the second-stage cylinder, and a tubular magnetic shield which is installed on the second-stage cooling stage and extends along the second-stage cylinder outside the second-stage cylinder. The magnetic shield is formed of a normal conductor and a product of an electrical conductivity in a temperature range of 10 K (Kelvin) or less and a thickness of the tubular magnetic shield is 60 MS (Mega-Siemens) to 1980 MS.

A regenerator accumulates cooling generated by expansion of refrigerant gas, and the regenerator includes a regenerator material which is made of a nonmagnetic material, a regenerator material which is made of a magnetic material, a container which includes a high temperature end and a low temperature end, and which accommodates the regenerator material made of the nonmagnetic material at the high temperature end side and the regenerator material made of the magnetic material at the low temperature end side. The container further accommodates an insertion member which narrows a passage area of the refrigerant gas flowing to a region accommodating the refrigerator material made of the magnetic material so that the passage area of the low temperature end side is narrower compared to the passage area of the high temperature end side.

A heat regenerating material particle according to an embodiment includes a plurality of heat regenerating substance particles having a maximum volume specific heat value of 0.3 J/cm.sup.3.Math.K or more at a temperature of 20 K or lower, and a binder bonding the heat regenerating substance particles, the binder containing water insoluble resin. The heat regenerating material particle has a particle diameter of 500 μm or less.

This invention provides a regenerator material having a high specific heat, particularly in the temperature range of 10 to 25K, and a regenerator and a refrigerator comprising the regenerator material. The present invention specifically provides an HoCu-based regenerator material represented by general formula (1): HoCu.sub.2-xM.sub.x (1), wherein x is 0<x≤1, and M is at least one member selected from the group consisting of Al and transition metal elements (excluding Cu), as well as a regenerator and a refrigerator comprising the regenerator material.

A heat regenerating material particle of an embodiment contains a heat regenerating substance having a maximum value of specific heat at a temperature of 20 K or less is 0.3 J/cm.sup.3.Math.K or more, and one metal element selected from the group consisting of calcium (Ca), magnesium (Mg), beryllium (Be), strontium (Sr), aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), and cobalt (Co). The heat regenerating material particle includes a first region and a second region, the second region is closer to an outer edge of the heat regenerating material particle than the first region, and the second region has a higher concentration of the metal element than the first region.

A cryocooler includes a second-stage cooling stage, a second cylinder which includes the second-stage cooling stage on a terminal of the second-stage cylinder, a second-stage displacer which includes a magnetic regenerator material and is accommodated in the second-stage cylinder so as to be able to reciprocate in the second-stage cylinder, and a tubular magnetic shield which is installed on the second-stage cooling stage and extends along the second-stage cylinder outside the second-stage cylinder. The magnetic shield is formed of a normal conductor and a product of an electrical conductivity in a temperature range of 10 K (Kelvin) or less and a thickness of the tubular magnetic shield is 60 MS (Mega-Siemens) to 1980 MS.

A regenerator of a cryo-cooler uses helium both as a working gas and as a heat storage material. The regenerator includes cells whose exterior sides form flow channels through which the working gas flows. Each cell has connected first and second cavities enclosed by a heat-conductive cell wall. The cavities contain helium that is used to store heat. Each cells is shaped as a disk. The working gas flows both through the flow channels and around the regenerator so as to exchange heat with the helium in the cavities via the heat conducting cell wall. Each cell has a pressure-equalizing opening through the cell wall whose diameter is smaller than the thickness of the cell wall. The diameter of the pressure-equalizing opening is dimensioned to permit the pressure of the helium contained in the cell to change by a maximum of 20% during any working cycle of the cryo-cooler.

A gas refrigerating machine having: an input for gas to be cooled; a recuperator; a compressor having a compressor input, the compressor input being coupled to a first recuperator output; a heat exchanger; a turbine; and a gas output, wherein the recuperator is rotationally symmetrical, wherein an axis of symmetry of the recuperator coincides with an axis of the compressor, or an axis of the turbine, or an axis of a rotor of a drive motor, or an axis of the gas output, or an axis of the input, or an axis of a suction region basically or within manufacturing tolerances.

A gas refrigerating machine having: an input for gas to be cooled; a recuperator; a compressor having a compressor input coupled to a first recuperator output; a heat exchanger; a turbine; and a gas output, wherein the gas refrigerating machine has a housing in the wall of which the input for gas to be cooled is located and in the wall of which the gas output is located, the recuperator, the compressor, the turbine and the heat exchanger arranged in the housing, and the gas refrigerating machine formed as an open system, wherein the input for gas is located in a region to be cooled and the gas output is located in the region to be cooled to suck warm gas from the region to be cooled via the input for gas and to discharge cold gas into the region to be cooled via the gas output.