Regenerator material and regenerative refrigerator

A first-stage regenerator material and a second-stage regenerator material are regenerator materials each having a laminated structure for use in a GM refrigerator. Each layer of the regenerator material is provided with a plurality of holes to allow gas to pass therethrough along a laminating direction. At least one layer includes a base material and a coating covering the base material. Volumetric specific heat of the coating is larger than volumetric specific heat of the base material in a temperature range from 20 K to 40 K.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a regenerator material and a regenerative refrigerator including the regenerator material.

2. Description of the Related Art

Regenerative refrigerators such as a Gifford-McMahon (GM) refrigerator, a pulse tube refrigerator, a Stirling refrigerator, and a Solvay refrigerator can cool an object in a range from a low temperature of about 100 K (kelvin) to a cryogenic temperature of 4 K. Such a regenerative refrigerator is used for cooling a superconducting magnet, a detector, and the like, a cryopump, and the like.

For example, in the GM refrigerator, working gas such as helium gas compressed in a compressor unit is guided to a regenerator unit and is precooled by a regenerator material in the regenerator unit. The precooled working gas is adiabatically expanded in an expansion chamber thus to further lower a temperature thereof. The low temperature working gas passes through the regenerator unit again and returns to the compressor unit. At this time, the working gas passes through the regenerator unit while cooling the regenerator material in the regenerator unit for working gas to be guided subsequently. With this procedure as one cycle, cyclic cooling is performed.

SUMMARY OF THE INVENTION

One embodiment of the present invention relates to a regenerator material for use in a regenerative refrigerator. The regenerator material comprising a laminated structure, each layer of the laminated structure provided with a plurality of holes to allow gas to pass therethrough along a laminating direction. At least one layer of the laminated structure includes a base material and a coating covering the base material. Volumetric specific heat of the coating is larger than volumetric specific heat of the base material in a temperature range from 20 K to 40 K, except a case in which the coating consists primarily of bismuth.

Another embodiment of the present invention also relates to a regenerator material for use in a regenerative refrigerator. The regenerator material comprising a laminated structure, each layer of the laminated structure provided with a plurality of holes to allow gas to pass therethrough along a laminating direction. At least one layer of the laminated structure is provided with a coating made of an alloy of bismuth and tin, an alloy of antimony and tin, or an alloy of bismuth, antimony, and tin.

Still another embodiment of the present invention relates to a regenerative refrigerator including the aforementioned regenerator material.

Optional combinations of the aforementioned constituting elements, and implementations of the invention in the form of methods, apparatuses, and systems, may also be practiced as additional modes of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, similar or identical components and members illustrated in respective drawings may be shown with the same reference numerals, and description of the duplicate components and members may be omitted as needed. And also, dimensions of the members in the respective drawings may be shown to be enlarged or shrunk as needed to facilitate understanding. In addition, in the respective drawings, some of the members that may not be important in description of embodiments may be omitted.

In the regenerative refrigerator, a heat exchange efficiency of the regenerator material significantly influences refrigerating capacity of the refrigerator. For example, the present applicant conventionally proposed, in Japanese Patent Application Laid-Open No. 2006-242484, forming of a regenerator material by laminating metal meshes to which bismuth is applied or plated.

Since volumetric specific heat of the bismuth in a low temperature range is relatively large, using the bismuth can enlarge heat capacity of the regenerator material in the low temperature range. However, plating the bismuth is technically difficult or would require trouble and cost if it were successful.

An exemplary purpose of an embodiment of the present invention is to provide a regenerator material enabling to increase a heat exchange efficiency and a regenerative refrigerator including the regenerator material.

FIG. 1is a schematic configuration of a GM refrigerator1having built therein a regenerator material according to an embodiment. The GM refrigerator1includes a gas compressor unit3and a two-stage cold head10functioning as a refrigerator. The cold head10includes a first-stage cooling section15and a second-stage cooling section50, and these cooling sections are connected to be coaxial with a flange12.

The first-stage cooling section15includes a hollow-centered first-stage cylinder20, a first-stage displacer22provided to enable reciprocating movement in an axial direction Q in this first-stage cylinder20, a first-stage regenerator material30according to the embodiment filled in the first-stage displacer22, a first-stage expansion chamber31provided inside the first-stage cylinder20on a side of a low temperature end23band changing a volume thereof by the reciprocating movement of the first-stage displacer22, and a first-stage cooling stage35provided around the low temperature end23bof the first-stage cylinder20. Between an inner wall of the first-stage cylinder20and an outer wall of the first-stage displacer22is provided a first-stage seal39.

A high temperature end23aof the first-stage cylinder20is provided with a plurality of first-stage high-temperature-side flow paths40-1to let helium gas flow in and out of the first-stage regenerator material30. In addition, the low temperature end23bof the first-stage cylinder20is provided with a plurality of first-stage low-temperature-side flow paths40-2to let helium gas flow in and out of the first-stage regenerator material30and the first-stage expansion chamber31.

The second-stage cooling section50has an approximately similar configuration to that of the first-stage cooling section15and includes a hollow-centered second-stage cylinder51, a second-stage displacer52provided to enable reciprocating movement in the axial direction Q in the second-stage cylinder51, a second-stage regenerator material60according to the embodiment filled in the second-stage displacer52, a second-stage expansion chamber55provided inside the second-stage cylinder51on a side of a low temperature end53band changing a volume thereof by the reciprocating movement of the second-stage displacer52, and a second-stage cooling stage85provided around the low temperature end53bof the second-stage cylinder51. Between an inner wall of the second-stage cylinder51and an outer wall of the second-stage displacer52is provided a second-stage seal59. A high temperature end53aof the second-stage cylinder51is provided with a second-stage high-temperature-side flow path40-3to let helium gas flow in and out of the second-stage regenerator material60. In addition, the low temperature end53bof the second-stage cylinder51is provided with a plurality of second-stage low-temperature-side flow paths54-2to let helium gas flow in and out of the second-stage expansion chamber55.

In the GM refrigerator1, high-pressure helium gas from the gas compressor unit3is supplied via a high-pressure valve5and a pipe7to the first-stage cooling section15while low-pressure helium gas is exhausted from the first-stage cooling section15via the pipe7and a low-pressure valve6to the gas compressor unit3. The first-stage displacer22and the second-stage displacer52perform reciprocating movement along the axial direction Q by a driving motor8. And also, interlocking with this, opening/closing of the high-pressure valve5and the low-pressure valve6is performed to control timing of intake and exhaust of helium gas.

The high temperature end23aof the first-stage cylinder20is set at a room temperature, for example, and the low temperature end23bis set at 20 K to 40 K, for example. The high temperature end53aof the second-stage cylinder51is set at 20 K to 40 K, for example, and the low temperature end53bis set at 4 K, for example.

Operations of the GM refrigerator1configured as above will be described. Suppose the first-stage displacer22and the second-stage displacer52are at bottom dead centers respectively in the first-stage cylinder20and the second-stage cylinder51in a state in which the high-pressure valve5is closed, and in which the low-pressure valve6is closed.

In this state, when the high-pressure valve5becomes in an open state, and the valve6remains in a closed state, high-pressure helium gas flows from the gas compressor unit3into the first-stage cooling section15. The high-pressure helium gas flows from the first-stage high-temperature-side flow paths40-1into an inside of the first-stage displacer22and is cooled to reach a certain temperature by the first-stage regenerator material30. The cooled helium gas flows from the first-stage low-temperature-side flow paths40-2into the first-stage expansion chamber31.

Some of the high-pressure helium gas having flowed into the first-stage expansion chamber31flows from the second-stage high-temperature-side flow path40-3into an inside of the second-stage displacer52. This helium gas is cooled to a lower predetermined temperature by the second-stage regenerator material60and flows from the second-stage low-temperature-side flow paths54-2into the second-stage expansion chamber55. As a result of these, the first-stage expansion chamber31and the second-stage expansion chamber55become in high-pressure states.

Subsequently, the first-stage displacer22and the second-stage displacer52move to top dead centers, and the high-pressure valve5is closed. And also, the valve6is opened. Hence, the helium gas in the first-stage expansion chamber31and the second-stage expansion chamber55becomes in a low-pressure state from the high-pressure state, and a volume thereof expands. As a result, a temperature of the helium gas in the first-stage expansion chamber31and the second-stage expansion chamber55is further lowered. In addition, by doing so, the first-stage cooling stage35and the second-stage cooling stage85are respectively cooled.

Subsequently, the first-stage displacer22and the second-stage displacer52move toward the bottom dead centers. Along with this, the low-pressure helium gas follows a reverse route of the above and returns via the valve6and the pipe7to the gas compressor unit3while respectively cooling the first-stage regenerator material30and the second-stage regenerator material60. The valve6is thereafter closed.

The above operations are regarded as one cycle. By repeating the above operations, heat is absorbed from cooled objects (not illustrated) respectively thermally-connected to the first-stage cooling stage35and the second-stage cooling stage85to enable the cooled objects to be cooled.

FIG. 2is a schematic view illustrating a configuration of the first-stage regenerator material30. The first-stage regenerator material30has a laminated structure in which N (N is a natural number of at least 2) sheet-like metal meshes32-1to32-N are laminated along a laminating direction P. The laminating direction P is approximately parallel to the axial direction Q of the cold head10or the moving direction of the first-stage displacer22. The cold head10is configured so that the helium gas may move along the moving direction of the first-stage displacer22in the first-stage displacer22. Thus, the laminating direction P is approximately parallel to the moving direction of the helium gas. In other words, the helium gas moves along the laminating direction P through the first-stage regenerator material30.

Each of the metal meshes32-1to32-N constituting each layer of the laminated structure is formed by weaving a wire member having a predetermined wire diameter and made of a predetermined material. A plane defined by each of the metal meshes32-1to32-N constituting each layer is approximately orthogonal to the laminating direction P. When the helium gas flows along the laminating direction P through the first-stage regenerator material30, the helium gas passes through a plurality of openings33of each of the metal meshes32-1to32-N constituting each layer.

High-temperature-side metal meshes out of the N metal meshes32-1to32-N are formed by weaving a copper or stainless steel wire member37. Low-temperature-side metal meshes out of the N metal meshes32-1to32-N are formed by weaving a different wire member34from the wire member37of the high-temperature-side metal meshes. The low-temperature-side metal meshes are metal meshes that are at 50 K or less at the time of normal operations of the GM refrigerator1, for example.

FIG. 3is a cross-sectional view of the wire member34of the low-temperature-side metal meshes. The wire member34includes a base material34aand a coating34bcovering the base material34a. The base material34ais made of a copper-based material or stainless steel. The copper-based material may be phosphor bronze, red brass, pure copper, tough pitch copper, or oxygen-free copper, for example. The coating34bis made of any one of zinc, tin, silver, indium, and gold, or an alloy containing at least two out of zinc, tin, silver, indium, and gold. Especially, the coating34bis formed by a plating treatment of the base material34a.

Ideas in selecting materials for the base material34aand the coating34bare as follows.

(1) To make volumetric specific heat of the coating34blarger than volumetric specific heat of the base material34ain a temperature range from 20 K to 40 K. Also, to make volumetric specific heat of the coating34bat 50 K larger than volumetric specific heat of the base material34aat 50 K.

FIGS. 4A and 4Bare graphs each illustrating relationship between volumetric specific heat and a temperature of each of various metals. Referring to these graphs, respective volumetric specific heat of zinc, tin, silver, indium, and gold is larger than volumetric specific heat of copper in the temperature range from 20 K to 40 K. And also, respective volumetric specific heat of zinc, tin, silver, indium, and gold at 50 K is larger than volumetric specific heat of copper at 50 K, and volumetric specific heat of bismuth at 50 K is smaller than volumetric specific heat of copper at 50 K.

(2) To make heat conductivity of the base material34alarger than heat conductivity of the coating34bin the temperature range from 20 K to 40 K.

(3) To make malleability or ductility or both (that is, malleability-and-ductility) of the coating34bhigher than that of bismuth. Malleability-and-ductility is a kind of mechanical property (plasticity) of a solidmaterial and represents a limit of an ability of a material to be flexibly deformed without fracture. Malleability-and-ductility is classified into malleability and ductility. In materials science, ductility is especially an ability of a material to deform under tensile stress and is often characterized by an ability of the material to be stretched into a wire. On the other hand, malleability is an ability of a material to deform under compressive stress and is often characterized by an ability of the material to form a thin sheet by hammering or rolling. Malleability of bismuth is relatively low, and bismuth is weak in tensile stress. Conversely, zinc, tin, silver, indium, and gold have relatively high malleability and ductility.

The coating34bis preferably formed by tin plating. Tin is one of traditionally well-known and familiar metal materials. Molten tin plating on sheet iron is known as a tinplate, and an alloy with lead is traditionally used as solder for intermetallic connection. In recent year, with advanced improvement of plating bath, bright tin plating further excellent in brightness, solderability, and an anti-corrosion property is obtained. Hardness of tin plating is shown in the following table.

As shown in this table, hardness of bright tin is 30 to 60 Hv and is higher than that of non-bright tin, which is 3 to 8 Hv. Accordingly, forming the coating34bby bright-plating the base material34awith tin can increase hardness of the coating34b, which is preferable.

FIG. 5is a schematic view illustrating a configuration of the second-stage regenerator material60. The second-stage regenerator material60has different configurations between a high-temperature-side part62and a low-temperature-side part64. The high-temperature-side part62is configured in a similar manner to that of the low temperature side of the first-stage regenerator material30. That is, the high-temperature-side part62has a laminated structure in which a plurality of sheet-like metal meshes are laminated along a laminating direction (that is, the axial direction Q). A wire member of each of these metal meshes includes a base material corresponding to the base material34aand a coating corresponding to the coating34b.

The low-temperature-side part64is configured to include a plurality of balls of bismuth, lead, and/or a magnetic material such as HoCu2. The second-stage regenerator material60is configured so that a temperature of a boundary66between the high-temperature-side part62and the low-temperature-side part64may be approximately 10 K at the time of normal operations of the GM refrigerator1.

With the GM refrigerator1including the regenerator materials30and60according to the present embodiment, specific heat of the regenerator materials30and60, which are at 10 K to 50 K at the time of normal operations of the GM refrigerator1, can be increased. Thus, a heat exchange efficiency at the regenerator materials30and60can be increased. Consequently, refrigerating capacity of the GM refrigerator1can be increased.

FIG. 6is a graph illustrating relationship between a temperature of the first-stage cooling stage35and refrigerating capacity actually measured in the GM refrigerator1. In the graph illustrated inFIG. 6, black-filled triangles represent data in a case in which the metal meshes of the first-stage regenerator material are not tin-plated while black-filled squares represent data in a case in which the metal meshes on the low temperature side of the first-stage regenerator material30are tin-plated. It is apparent from this graph that, in a temperature range of 50 K or less, first-stage refrigerating capacity in the case with tin plating significantly exceeds first-stage refrigerating capacity in the case without tin plating. Especially, the first-stage refrigerating capacity at 40K is increased from 46.8 W in the case without plating to 53.4 W in the case with plating, which is an approximately 14% increase. And also, the first-stage refrigerating capacity at 30K is increased from 19.0 W in the case without plating to 36.4 W in the case with plating, which is an approximately 91% increase.

FIG. 7is a graph illustrating relationship between the refrigerating capacity of the first-stage cooling stage35at 40 K actually measured in the GM refrigerator1and a ratio of diameters of the wire member34. When a diameter of the base material34aon a cross-section of the wire member34is referred to as d1 while an outside diameter of the coating34bis referred to as d2 (refer toFIG. 3), a ratio of diameters of the wire member34is given as d2/d1. The refrigerating capacity draws a peak with d2/d1=1.4 approximately at a center thereof. The reason for this is that a too thin coating34bimpairs the specific heat increase effect by the coating34bwhile a too thick coating34breduces the sizes of the openings of the metal meshes to increase flow path resistance or thins the base material34ato make heat conduction worse. Accordingly, it is more preferable to set d2/d1 in a range from 1.3 to 1.5 so that these influences may be balanced.

Also, in the GM refrigerator1including the regenerator materials30and60according to the present embodiment, heat conductivity of the base material34ais larger than heat conductivity of the coating34bin the temperature range from 20 K to 40 K. Thus, relatively increasing the heat conductivity of the base material34acan facilitate heat conduction through the base material34aand reduce a temperature difference in a radial direction (a direction orthogonal to the laminating direction P) of the regenerator materials30and60. This contributes to improvement in the heat exchange efficiency at the regenerator materials30and60.

That is, with the regenerator materials30and60according to the present embodiment, heat conduction as well as heat capacity of the regenerator materials30and60can be increased to reduce a temperature gradient. Meanwhile, it is preferable to adopt a material with larger heat conductivity among the copper-based materials, such as red brass, pure copper, tough pitch copper, and oxygen-free copper, which have larger heat conductivity than phosphor bronze.

Also, in the GM refrigerator1including the regenerator materials30and60according to the present embodiment, the coating34bis made of a material relatively excellent in malleability-and-ductility. Thus, when the metal meshes are filled in the displacers22and52, a possibility of breakage of the coating34bof the metal meshes caused by mechanical contact, stress, a scrape, or the like can be reduced. In addition, when the regenerator materials30and60perform reciprocating movement together with the displacers22and52during normal operations of the GM refrigerator1, a possibility of breakage of the coating34bcaused by vibration can be reduced.

Also, in the GM refrigerator1including the regenerator materials30and60according to the present embodiment, the first-stage regenerator material30has a laminated structure in which the N sheet-like metal meshes32-1to32-N are laminated along the laminating direction P. Accordingly, a pressure loss can be reduced further than in a case of adopting a plurality of balls as a regenerator material.

The configuration and operations of the GM refrigerator1including the regenerator materials30and60according to the embodiment have been described above. Those skilled in the art would understand that the present embodiment is illustrative only, that various variant embodiments for combination of the respective components are available, and that such variant embodiments are within the scope of the present invention.

In the present embodiment, as for the wire member34of the low-temperature-side metal meshes among the N metal meshes32-1to32-N, a case in which the coating34bis an outermost layer has been described. However, the present invention is not limited to this.FIG. 8is a cross-sectional view of a wire member134of the metal meshes according to a first variant embodiment. The metal mesh wire member134includes a base material134acorresponding to the base material34a, a coating134bcorresponding to the coating34b, and a protecting layer134ccovering the coating134b. The protecting layer134cis made of bismuth, antimony, or an alloy of these. Alternatively, the protecting layer134cmay be made of bright tin or chromium.

With the present variant embodiment, since the relatively soft coating134bis covered with the relatively hard protecting layer134c, damage of the coating134bcan be reduced. Meanwhile, antimony or bismuth may be mixed with a material for the coating134bto coat these at the same time. In this case, a volumetric mixing ratio of antimony or bismuth is preferably 0.01% to 49.99%.

In the present embodiment, although a case in which the cross-section of the wire member34is isotropic or circular has been described, the present invention is not limited to this.FIG. 9is a cross-sectional view of a wire member234of the metal meshes according to a second variant embodiment. The wire member234includes a base material234aand a coating234bcovering the base material234a. The base material234ais made of a copper-based material or stainless steel. The copper-based material may be phosphor bronze, red brass, pure copper, tough pitch copper, or oxygen-free copper, for example. The coating234bis made of an alloy containing any one or at least two out of zinc, tin, silver, indium, and gold.

A width W1 of the cross-section of the wire member234in the laminating direction P is smaller than a width W2 in an orthogonal direction R intersecting with, especially, orthogonal to, the laminating direction P in the cross-section. Especially, a surface of the wire member234has two flat portions236and238opposed to each other in the laminating direction P. Such a wire member234may be formed by rolling a base material having a circular cross-section and tin-plating the rolled base material, for example.

FIG. 10is a cross-sectional view when the two metal meshes according to the second variant embodiment are laminated. When the metal meshes made of the wire member234are laminated along the laminating direction P, the lower flat portion238of the wire member234of the upper metal mesh is brought into contact with the upper flat portion236of the wire member234of the lower metal mesh. At this time, a contact area thereof is larger than that in a case where the cross-section of the wire member is circular, for example. Accordingly, contact stress at the time of filling can be distributed, and damage of the coating can be reduced.

In the present embodiment, although a case in which tin is used as a material for the coating34b, but in which the coating34bdoes not consist primarily of bismuth, has been described, the present invention is not limited to this. For example, the coating may be an alloy of bismuth and tin, an alloy of antimony and tin, or an alloy of bismuth, antimony, and tin.

Tin has a transition point between beta tin and alpha tin at a temperature close to a room temperature. In transition to alpha tin, malleability is lost, and at the same time, volume largely increases. Although this transition seldom progresses in a normal temperature range due to an effect of impurities or the like, the transition may progress in a frigid environment as in the Arctic region, in which case a phenomenon occurs in which a tin product is swollen and deteriorated. This phenomenon is called tin pest by an analogy to the epidemic since it starts at a part of a tin product and eventually spreads into the entirety.

Tin significantly changes a physical property thereof by this allotropic transformation. Tin physically transforms from beta tin to alpha tin at 13.2 degrees Celsius, but an actual reaction progresses in a low temperature range of −10 degrees Celsius or below, and reaction speed thereof is maximum at −45 degrees Celsius. In the present variant embodiment, the coating is formed by adding antimony, bismuth, or both as impurities to beta tin. Thus, the above allotropic transformation can be restricted. Meanwhile, a volumetric mixing ratio of antimony, bismuth, or both is preferably 0.01% to 49.99%.

In the present embodiment, although a case in which the first-stage regenerator material30and/or the second-stage regenerator material60have/has on the low temperature side different metal meshes from those on the high temperature side (that is, a case in which two kinds of metal meshes are laminated) has been described, the present invention is not limited to this. In an embodiment, the first-stage regenerator material30and/or the second-stage regenerator material60may have three or more kinds of metal meshes, and different kinds of metal meshes may be laminated in respective temperature regions.

For example, as illustrated inFIG. 11, a first-stage regenerator material100may include a first part101furthest on the high temperature side, a second part102at a middle temperature, and a third part103furthest on the low temperature side. The low temperature side of the first part101is adjacent to the high temperature side of the second part102, and the low temperature side of the second part102is adjacent to the high temperature side of the third part103.

Each of the first part101, the second part102, and the third part103has at least one metal mesh, or normally, a plurality of metal meshes. In the first part101, first metal meshes made of a first wire member are laminated. Similarly, in the second part102, second metal meshes made of a second wire member are laminated, and in the third part103, third metal meshes made of a third wire member are laminated. The first wire member, the second wire member, and the third wire member are different from one another as several specific examples thereof will be described below, and the first metal meshes, the second metal meshes, and the third metal meshes are thus different kinds of metal meshes from one another.

The first wire member, the second wire member, and the third wire member have different volume ratios of the coating to the base material from one another. Specifically, the volume ratio is larger further on the low temperature side. For example, the metal meshes made of different kinds of wire members are laminated in the respective temperature regions so that an area ratio of the coating to the base material on a cross-section (to be precise, a cross-section by a plane perpendicular to a longitudinal direction of the wire member) of the wire member may be larger further on the low temperature side, to constitute the first-stage regenerator material100. For example, in a case where the cross-section of the wire member is circular, the aforementioned d2/d1 is larger further on the low temperature side. Accordingly, in the first-stage regenerator material100, further on the low temperature side, the amount of the coating material per layer is larger, and heat capacity per layer is larger. In this manner, a heat exchange efficiency on the low temperature side can be increased, and refrigerating capacity of the GM refrigerator1can be improved.

FIG. 12A,FIG. 12B, andFIG. 12Cillustrate examples of a first wire member104, a second wire member105, and a third wire member106, respectively. Respective cross-sections of the first wire member104, the second wire member105, and the third wire member106are illustrated.

The first wire member104includes a base material. The first wire member104does not include coating. The second wire member105includes a base material105aand a coating105bcovering the base material105a. The third wire member106includes a base material106aand a coating106bcovering the base material106a.

The first wire member104, the base material105aof the second wire member105, and the base material106aof the third wire member106have equal cross-sectional dimensions. Hence, the first wire member104, the base material105aof the second wire member105, and the base material106aof the third wire member106have equal outside diameters. On the other hand, the coating106bof the third wire member106is thicker than the coating105bof the second wire member105. Thus, the second wire member105is thicker than the first wire member104, and the third wire member106is thicker than the second wire member105.

Since the third wire member106is thicker than the second wire member105, openings surrounded by the wire member of the third metal meshes can be smaller than those of the second metal meshes. However, since the third metal meshes are arranged further on the low temperature side than the second metal meshes, and viscosity of helium gas on the low temperature side is low, an increase of a pressure loss in the third part103(and also lowering of refrigerating capacity) can be restricted. Thus, it can be thought that improvement of a heat exchange efficiency by making the coating thicker exceeds an increase of a pressure loss. Accordingly, refrigerating capacity of the GM refrigerator1can be improved.

FIG. 13A,FIG. 13B, andFIG. 13Cillustrate other examples of the first wire member104, the second wire member105, and the third wire member106, respectively. As illustrated in the figures, while the first wire member104and the base material105aof the second wire member105have equal cross-sectional dimensions, the base material106aof the third wire member106is thinner than the base material105aof the second wire member105. Hence, the coating106bof the third wire member106can be thicker than the coating105bof the second wire member105. And also, since the base material106aof the third wire member106is thin, the third wire member106can have an equal thickness to that of the second wire member105. Accordingly, an increase of a pressure loss in the third part103can be restricted further than in the example illustrated inFIG. 12C. Meanwhile, in this case, the third wire member106may be thicker than the second wire member105to make the coating106bthicker.

FIG. 14A,FIG. 14B, andFIG. 14Cillustrate still other examples of the first wire member104, the second wire member105, and the third wire member106, respectively. As illustrated in the figures, the base material105aof the second wire member105is thinner than the first wire member104, and the base material106aof the third wire member106is as thick as the base material105aof the second wire member105. By doing so, an increase of a pressure loss in the second part102can be restricted. In this case, the second wire member105may be as thick as or thicker than the first wire member104.

In the present embodiment, although a case in which the first-stage regenerator material30has a laminated structure in which the N sheet-like metal meshes32-1to32-N are laminated along the laminating direction P has been described, the present invention is not limited to this. For example, the first-stage regenerator material may have a laminated structure in which a plurality of metal plates provided with a plurality of holes or porous metal plates are laminated. In this case, each of the metal plates on the low temperature side may be provided with a coating by plating. The same is true of the second-stage regenerator material60.

Although the present embodiment has been described taking the GM refrigerator1as an example, the present invention is not limited to this, and the regenerator material according to the present embodiment may be built in another kind of regenerative refrigerator such as a GM-type or Stirling-type pulse tube refrigerator, a Stirling refrigerator, and a Solvay refrigerator.

The GM refrigerator1having built therein the regenerator material according to the present embodiment may be used as a cooling means or a liquefying means in a superconducting magnet, a cryopump, an X-ray detector, an infrared sensor, a quantum photon detector, a semiconductor detector, a dilution refrigerator, an He3 refrigerator, an adiabatic demagnetization refrigerator, a helium liquefier, a cryostat, and the like.

Priority is claimed to Japanese Patent Application No. 2013-129461, filed on Jun. 20, 2013 and Japanese Patent Application No. 2013-257721, filed on Dec. 13, 2013, the entire contents of which are incorporated herein by reference.