A reduction in a permeability of refrigerant gas is suppressed while increasing a filling factor of regenerator material particles with respect to a stage of a cold head. A cold head includes a stage including regenerator material particle groups, and a metal mesh material partitioning the regenerator material particle groups. The metal mesh material has quadrangular mesh holes each having a length of a long side of 1/10 or more and ½ or less of each of average particle sizes of the regenerator material particle groups.

A cryocooler includes a cold head including a displacer movable in an axial direction, a drive piston connected to the displacer to move the displacer in the axial direction, an expansion chamber formed with the displacer, a piston drive chamber formed with the drive piston, a spool valve including a valve drive chamber, a spool that moves between a first position and a second position in response to a pressure of the valve drive chamber, and a pressure control mechanism configured to control a pressure of the valve drive chamber so that the spool reciprocates between the first position and the second position, and to generate a pressure fluctuation having an opposite phase to the pressure fluctuation in the expansion chamber in the piston drive chamber in synchronization with the reciprocation of the spool.

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 double-inlet valve for a Gifford-McMahon (GM) type double-inlet pulse tube cryocooler system for providing cooling at cryogenic temperatures includes a fixed restrictor and a needle valve coupled to the fixed restrictor in parallel. The needle valve produces asymmetric flow. The combination of the fixed restrictor and the needle valve having an asymmetric flow provides improved alternating current (AC) flow characteristics and adjustability of direct current (DC) flow to increase the available cooling.

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.

The subject of this invention is a method of heat transfer in the embedded structure of a heat regenerator and the design thereof. It regards the related heat regenerators, which operate on the principle of the described method and enable a reduction of the pressure drop due to the fluid flow through the heat regenerator and consequently an increase of the power density. The concept of the operation of the heat regenerator by this invention, in which for the oscillation of the flow of the primary (first) fluid (P), electromechanical elements are applied. In the housing (1) between the elements (2) for the oscillation of the primary (first) fluid (P), there are positioned a primary hot heat exchanger (PT) and a primary cold heat exchanger (PH). In the direction of the arrow (A) the unidirectional flow of the secondary (second) fluid (S) flows from the heat sink into the primary cold heat exchanger (PH). In the direction of the arrow (B) the unidirectional flow of the secondary (second) fluid (S) exits from the primary cold heat exchanger (PH) and flows towards the heat source. Meanwhile, in the direction of the arrow (C), the unidirectional flow of the secondary (second) fluid S enters the primary hot heat exchanger (PT) and exits in the direction of the arrow (D) as the unidirectional flow of the secondary (second) fluid S of the primary hot heat exchanger (PT) towards the heat sink. Between both primary heat exchangers, (PT) and (PH), the porous regenerative material is positioned, which is part of the regenerator 4, with the hydraulically separated segments.

A cold storage material particle of an embodiment includes at least one first element selected from the group consisting of a rare earth element, silver (Ag), and copper (Cu) and a second element that is different from the first element and forms a multivalent metal ion in an aqueous solution, in which an atomic concentration of the second element is 0.001 atomic % or more and 60 atomic % or less, and a maximum value of volume specific heat at a temperature of 20K or less is 0.3 J/cm.sup.3.Math.K or more.

A regenerator for a cryocooler includes a cell, a flow passage, a capillary and supporting elements. A cell wall encloses a cavity with sub-cavities. A connecting passage connects a first sub-cavity to a second sub-cavity. A first cell partition is disposed between the first and second sub-cavities. The flow passage is also disposed between the first and second sub-cavities. During operation of the regenerator, helium in the cavity functions as a heat-storing material, while helium that flows through the flow passage functions as a working gas. The capillary forms a pressure-equalizing opening in the cell wall and connects the helium that functions as the heat-storing material inside the cavity to the helium that functions as the working gas outside the cavity. The supporting elements are inside the first sub-cavity and separate the first cell partition from a second cell partition. The first and second cell partitions enclose the first sub-cavity.

An apparatus includes a heat exchanger configured to transfer heat to a fluid and to absorb heat from the fluid as the fluid flows between a warm end and a cold end of a cryocooler. The heat exchanger includes at least one section having a substrate of at least one allotropic form of carbon and a layer of nanoparticles on or over the substrate. The heat exchanger could include multiple sections, and each section could include one of multiple substrates and one of multiple layers of nanoparticles. The heat exchanger can further include pores through the multiple sections of the heat exchanger, where the pores are configured to allow the fluid to flow through the heat exchanger and to contact the substrates and the layers of nanoparticles. The nanoparticles could include at least one lanthanide element or alloy, and the substrate could include carbon nanotubes or graphene.

A pulse tube cryocooler which includes a pulse tube having a pulse tube high-temperature end and a pulse tube low-temperature end, and extending in an axial direction from the pulse tube high-temperature end to the pulse tube low-temperature end. The pulse tube cryocooler further includes a regenerator having a regenerator high-temperature end and a regenerator low-temperature end, and being disposed rowed alongside the pulse tube, with the regenerator high-temperature end being positioned displaced, in terms of the axial direction, from the pulse tube high-temperature end toward the cryocooler low-temperature side, and the regenerator low-temperature end being fluid-passage linked with the pulse tube low-temperature end and a pressure-switching valve for connecting the regenerator high-temperature end to a high-pressure source and to a low-pressure source in alternation, and being disposed between the pulse tube high-temperature end and the regenerator high-temperature end in terms of the axial direction.