Heat regenerating material, regenerator, refrigerator, superconducting magnet, nuclear magnetic resonance imaging apparatus, nuclear magnetic resonance apparatus, cryopump, and magnetic field application type single crystal pulling apparatus

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/cm3·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.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-174316, filed on Sep. 18, 2018, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to heat regenerating material particle, regenerator, refrigerator, superconducting magnet, nuclear magnetic resonance imaging apparatus, nuclear magnetic resonance apparatus, cryopump, and magnetic field application type single crystal pulling apparatus.

BACKGROUND

For a cryogenic refrigerator used for cooling a superconducting device or the like, heat regenerating material particles having a high volume specific heat value in a low temperature range are used. Here, specific heat per unit volume is defined as volume specific heat. Examples of the heat regenerating material particles include a metal such as lead (Pb) or bismuth (Bi), a rare earth compound such as HoCu2or Er3Ni, and an oxide such as Ag2O, Cu2O, or Gd2O2S.

For example, in a case of manufacturing oxide heat regenerating material particles, multistage processes such as granulation of a powder raw material, sintering at high temperature, and spheroidizing by polishing are required. Therefore, a manufacturing process is complicated and manufacturing cost is high.

DETAILED DESCRIPTION

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/cm3·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.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Incidentally, in the following description, the same sign will be given to the same or a similar member or the like, and description of a member or the like described once will be omitted appropriately.

Here, a cryogenic temperature means, for example, a temperature range in which a superconducting phenomenon can be usefully utilized industrially. For example, the cryogenic temperature is in a temperature range of 20 K or lower.

First Embodiment

A heat regenerating material particle according to a first embodiment includes a plurality of heat regenerating substance particles having a maximum volume specific heat value of 0.3 J/cm−3·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.

FIG. 1is a schematic cross-sectional view of the heat regenerating material particle according to the first embodiment. A heat regenerating material particle10according to the first embodiment is used, for example, for a refrigerator achieving a cryogenic temperature of 5 K or lower.

The shape of the heat regenerating material particle10is, for example, a spherical shape, a bale shape, a spheroid shape, or an irregular shape, and is not particularly limited.FIG. 1illustrates a case where the heat regenerating material particle10has a spherical shape.

The heat regenerating material particle10has a particle diameter (d inFIG. 1) of 500 μm or less. The particle diameter d of the heat regenerating material particle10is, for example, 100 μm or more and 500 μm or less. The particle diameter d is more preferably 150 μm or more and 300 μm or less. The particle diameter d is still more preferably 180 μm or more and 250 μm or less.

The particle diameter d of the heat regenerating material particle10is a circle equivalent diameter. The circle equivalent diameter is the diameter of a perfect circle corresponding to the area of a figure observed in an image such as an optical microscope image or a scanning electron microscope image (SEM image). The particle diameter d of the heat regenerating material particle10can be determined by image analysis of an optical microscope image or an SEM image, for example.

The heat regenerating material particle10includes a plurality of heat regenerating substance particles11and a binder12. The heat regenerating substance particles11and the binder12have different compositions from each other, and therefore can be distinguished from each other, for example, with a scanning electron microscope-backscattered electron composition image (SEM-BSE COMP image) or by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX).

The heat regenerating substance particles11have a maximum volume specific heat value of 0.3 J/cm3·K or more at a temperature of 20 K or lower. The number of the heat regenerating substance particles11in the heat regenerating material particle10is, for example, 10 or more and 10,000 or less.

The shape of each of the heat regenerating substance particles11is, for example, a spherical shape, a bale shape, a spheroid shape, or an irregular shape, and is not particularly limited.FIG. 1illustrates a case where each of the heat regenerating substance particles11has an irregular shape.

The particle diameter of each of the heat regenerating substance particles11is, for example, 0.01 μm or more and 10 μm or less. The median particle diameter of each of the heat regenerating substance particles11is, for example, 0.01 μm or more and 50 μm or less.

FIG. 2is an explanatory diagram of a method for measuring the particle diameter of each of the heat regenerating substance particles11according to the first embodiment.FIG. 2particularly illustrates a case where there is a portion where the adjacent heat regenerating substance particles11are in direct contact with each other without the binder12between the particles.

The median particle diameter of the heat regenerating substance particles11is determined, for example, by selecting any 10 points of the heat regenerating substance particles11in the heat regenerating material particle10in an observation image and determining a median value of the diameters of maximum circles (C inFIG. 2) including these points (P inFIG. 2) but not including the binder12. In case the selected points of the heat regenerating substance particles11is an even number, the median value may be an arithmetic mean of two values of the diameters of maximum circles closest to center of a distribution of the diameters of maximum circles. For example, by image analysis of an SEM image, it is possible to determine the particle diameters and a median value of the particle diameters of the heat regenerating substance particles11.

Incidentally, even when a grain boundary of the adjacent heat regenerating substance particles11is not necessarily clear, the particle diameter of each of the heat regenerating substance particles11can be determined as illustrated inFIG. 2, for example, in accordance with the above definition.

The heat regenerating substance particles11contain, for example, an oxide as a main component. The oxide contained in the heat regenerating substance particles11contains, for example, at least one of silver (Ag) and copper (Cu). Examples of the oxide contained in the heat regenerating substance particles11include Ag2O and Cu2O. Ag2O and Cu2O are nonmagnetic materials.

The oxide contained in the heat regenerating substance particles11contains, for example, gadolinium (Gd) and sulfur (S). Examples of the oxide contained in the heat regenerating substance particles11include Gd2O2S. Gd2O2S is a magnetic material.

The heat regenerating substance particles11contain, for example, a rare earth compound as a main component. Examples of the rare earth compound contained in the heat regenerating substance particles11include HoCu2and Er3Ni. HoCu2and Er3Ni are magnetic materials.

Composition analysis of the heat regenerating substance particles11can be performed by energy dispersive X-ray spectroscopy, for example.

The binder12contains a water insoluble resin as a main component. The binder12is a resin binder. The binder12bonds the heat regenerating substance particles11to each other.

Examples of the water insoluble resin contained in the binder12include a polyvinyl butyral resin (PVB), a polyamide resin, and an epoxy resin. The polyvinyl butyral resin (PVB) is preferable because of having high temperature cycle resistance. The epoxy resin is preferable because of having high mechanical strength.

The heat regenerating substance particles11contained in the heat regenerating material particle10have an occupancy ratio of 60% by volume or more and 95% by volume or less, for example. The binder12contained in the heat regenerating material particle10has an occupancy ratio of 5% by volume or more and 40% by volume or less, for example.

The heat regenerating material particle10has a porosity of less than 20% by volume, for example. The porosity of the heat regenerating material particle10is the occupancy ratio of voids present in the heat regenerating material particle10.

The occupancy ratio of the heat regenerating substance particles11contained in the heat regenerating material particle10, the occupancy ratio of the binder12contained in the heat regenerating material particle10, and the porosity of the heat regenerating material particle10are represented, for example, by the area ratios occupied by the heat regenerating substance particles11, the binder12, and voids observed in an optical microscope image or an SEM image, respectively. The occupancy ratio of the heat regenerating substance particles11contained in the heat regenerating material particle10, the occupancy ratio of the binder12contained in the heat regenerating material particle10, and the porosity of the heat regenerating material particle10can be determined, for example, by image analysis of an optical microscope image or an SEM image.

Next, a first example of a method for manufacturing the heat regenerating material particle10according to the first embodiment will be described. Hereinafter, a case where the heat regenerating substance particles11are formed of Ag2O and the binder12is formed of a polyvinyl butyral resin (PVB) will be exemplified.

FIGS. 3A, 3B, 3C, and 3Dare explanatory diagrams of the first example of the method for manufacturing the heat regenerating material particle according to the first embodiment.FIGS. 4A and 4Bare top views of a punching sheet used in the first example of the method for manufacturing the heat regenerating material particle according to the first embodiment.

First, Ag2O powder is synthesized in a wet manner.

Next, a polyvinyl butyral resin and an organic solvent are each weighed and mixed to dissolve the polyvinyl butyral resin in the organic solvent.

Hereinafter, this solution is referred to as a binder solution.

The amount of the polyvinyl butyral resin in the binder solution is, for example, 5% by weight. Examples of the organic solvent include acetone and ethanol.

Next, Ag2O powder and the binder solution are each weighed and mixed to prepare a slurry28. Next, the slurry28is mixed while the solvent in the slurry28is volatilized. As the solvent in the slurry28is volatilized, the viscosity of the slurry28increases.

Next, a punching sheet32is disposed on a pedestal30(FIG. 3A). Next, in a stage when the viscosity of the slurry28increases and the slurry28becomes clay-like, the slurry28is embedded in the punching sheet32(FIG. 3B).

As illustrated inFIGS. 4A and 4B, for example, the punching sheet32is a flat plate in which a large number of holes34each having a predetermined size are provided. The punching sheet32preferably has high resistance to a solvent and preferably easily removes particles formed by solidification of the slurry28.

Next, the slurry28embedded in the punching sheet32is pressurized using a die36(FIGS. 3C and 3D). Pressurizing the slurry28increases the density of the particles formed by solidification of the slurry28.

For example, the slurry28embedded in the punching sheet32may be pushed and pressurized with a rod-shaped member instead of the die36. For example, the slurry28may be pressurized together with the punching sheet32.

Next, the particles formed by solidification of the slurry28are removed from the punching sheet32. For example, the particles are pushed and removed with a rod-shaped member.

Next, the removed particles are polished by barrel polishing or the like to round corners for spheroidizing and reduction in diameter. The heat regenerating material particle10having a desired shape and particle diameter is manufactured by polishing.

Next, a second example of the method for manufacturing the heat regenerating material particle10according to the first embodiment will be described. FIGS.5A,5B, and5C are explanatory diagrams of the second example of the method for manufacturing the heat regenerating material particle according to the first embodiment.

The procedure is similar to that in the first example until the slurry28is mixed while the solvent in the slurry28is volatilized.

In a stage when the viscosity of the slurry28increases and the slurry28becomes clay-like, the slurry28is disposed on a lower die40(FIG. 5A). Hemispherical grooves are lined up in the lower die40.

Next, the slurry28is sandwiched between the lower die40and an upper die42(FIG. 5B). Recessed hemispherical grooves are formed at a tip of the upper die42.

The slurry28is pushed into the hemispherical grooves of the lower die40by the upper die42to form spherical particles (FIG. 5C).

Next, a third example of the method for manufacturing the heat regenerating material particle10according to the first embodiment will be described.FIG. 6is an explanatory diagram of the third example of the method for manufacturing the heat regenerating material particle according to the first embodiment.

The procedure is similar to that in the first example until the slurry28is mixed while the solvent in the slurry28is volatilized.

In a stage when the viscosity of the slurry28increases and the slurry28becomes clay-like, the slurry28is filled into a container50. The slurry28filled in the container50is pressed against a plate52with a hole, for example, using an extruding plate (not illustrated) in the container50. The slurry28is discharged in a rod shape from the hole.

As another method, for example, pressure is applied to the plate52with a hole while the slurry28is continuously supplied by rotating a screw structure member (not illustrated) provided in the container50. As a result, the slurry28shaped in a rod shape is continuously discharged from the hole.

Incidentally, as illustrated inFIG. 6, the plate52may have one hole or a plurality of holes. The plate52may be flat or spherical.

By cutting the rod-shaped slurry28, for example, with a cutter54, a columnar particle having an arbitrary length is obtained. For example, a spherical particle is obtained by applying a force to the particle or rounding corners of the particle.

Next, a fourth example of the method for manufacturing the heat regenerating material particle10according to the first embodiment will be described. Hereinafter, a case where the heat regenerating substance particles11are formed of Ag2O and the binder12is formed of an epoxy resin will be exemplified.

First, Ag2O powder is synthesized in a wet manner.

Next, the Ag2O powder is dispersed in at least one of a main agent and a curing agent of the epoxy resin. Next, the main agent and the curing agent are mixed.

Next, the mixture of the main agent and the curing agent is defoamed by evacuation. The mixture of the main agent and the curing agent is embedded in a punching sheet.

The mixture of the main agent and the curing agent is allowed to stand to be cured. It is also possible to shorten curing time by heating.

The mixture of the main agent and the curing agent acts to form particles, and then the particles are removed from the punching sheet.

Next, the removed particles are polished by barrel polishing or the like to round corners for spheroidizing and downsizing. The heat regenerating material particle10having a desired shape and particle diameter is manufactured by polishing.

Hereinafter, functions and effects of the heat regenerating material particle10according to the first embodiment will be described.

For a cryogenic refrigerator used for cooling a superconducting device, a heat regenerating material particle having a high volume specific heat value in a low temperature range is used. Examples of the heat regenerating material particle include a metal such as lead (Pb) or bismuth (Bi), a rare earth compound such as HoCu2or Er3Ni, and an oxide such as Ag2O, Cu2O, or Gd2O2S.

For example, in a case of manufacturing an oxide heat regenerating material particle, multistage processes such as granulation of a powder raw material, sintering at high temperature, and spheroidizing by polishing are required. Therefore, a manufacturing process is complicated. Therefore, manufacturing cost of the heat regenerating material particle increases, and the heat regenerating material particle is expensive.

For example, in a case of manufacturing a heat regenerating material particle, the chemical composition or the crystal structure of a heat regenerating substance may change due to a reaction at the time of sintering at a high temperature, and it may be impossible to obtain desired characteristics. For example, in a case where the heat regenerating substance particles11are formed of Gd2O2S, sulfur (S) escapes due to a too high temperature disadvantageously. In a case where the heat regenerating substance particles11are formed of Ag2O, oxygen (O) escapes due to a too high temperature disadvantageously. Therefore, in a portion where the composition has changed or a different compound has been generated, the characteristics may be deteriorated to make the characteristics of the heat regenerating material particle10unstable.

In the heat regenerating material particle10according to the first embodiment, the heat regenerating substance particles11are bonded using the resin binder12. Therefore, at the time of manufacturing the heat regenerating material particle10, at least sintering at a high temperature is unnecessary. Therefore, it is possible to manufacture the heat regenerating material particle10by a simple manufacturing process. Therefore, manufacturing cost of a heat regenerating material particle is reduced, and the heat regenerating material particle is inexpensive.

In addition, since sintering at a high temperature is unnecessary at the time of manufacturing the heat regenerating material particle10, a change in the chemical composition or the crystal structure of a heat regenerating substance is suppressed. Therefore, the heat regenerating material particle10with stable characteristics is achieved.

The water insoluble resin contained in the binder12is preferably a polyvinyl butyral resin (PVB), a polyamide resin, or an epoxy resin.

Table 1 illustrates an evaluation result of a resin used for the binder12. A result of a temperature cycle test on a resin as a candidate of the binder12, an evaluation result of the mechanical strength of a heat regenerating material particle, and an overall evaluation result based on these results are illustrated.

In the temperature cycle test, the temperature of a resin alone was repeatedly changed at room temperature or at 77 K, and the number of cycles before breakage was evaluated. A case where the number of cycles before breakage was large was evaluated to be “good”. A case where the number of cycles before breakage was particularly large was evaluated to be “excellent”.

Regarding the mechanical strength of a heat regenerating material particle, the compression strength and the vibration strength of the heat regenerating material particle were evaluated. For the compression strength, the strength at which a heat regenerating material particle was broken by compression was measured. For the vibration strength, heat regenerating material particles were put in container and vibrated, and evaluation was made by the ratio of the number of broken heat regenerating material particles. A case where the compression strength and the vibration strength were high was evaluated to be “good”. A case where the compressive strength and the vibration strength were particularly high was evaluated to be “excellent”.

As illustrated in Table 1, good results were obtained for a polyvinyl butyral resin, a polyamide resin, and an epoxy resin. Very good results were obtained particularly for a polyvinyl butyral resin and an epoxy resin.

By using a polyvinyl butyral resin, a polyamide resin, or an epoxy resin for the binder12, it is possible to achieve the heat regenerating material particle10having high resistance to thermal stress due to a temperature cycle and high mechanical strength. Therefore, by using a polyvinyl butyral resin, a polyamide resin, or an epoxy resin for the binder12, reliability of the heat regenerating material particle10is improved.

The heat regenerating material particle10according to the first embodiment contains a water insoluble resin in the binder12. For example, the heat regenerating material particle10may be exposed to the atmosphere when the heat regenerating material particle10is filled into a regenerator or maintenance of the regenerator is performed while the heat regenerating material particle10is filled in the regenerator.

If a water soluble resin is used for the binder12, the heat regenerating material particle10easily absorbs moisture when being exposed to the atmosphere. While the temperature is lowered from room temperature to a cryogenic temperature by starting a refrigerator, the heat regenerating material particle10which has absorbed moisture may be broken because the moisture absorbed is frozen to cause volume expansion. In addition, if a water soluble resin is used for the binder12, the resin may be dissolved in a case where the heat regenerating material particle10absorbs much moisture.

By using a water insoluble resin for the binder12, the heat regenerating material particle10according to the first embodiment suppresses moisture absorption when being exposed to the atmosphere.

The heat regenerating substance particles11contained in the heat regenerating material particle10have an occupancy ratio preferably of 60% by volume or more, more preferably of 70% by volume or more, still more preferably of 80% by volume or more. By satisfying the above range, a high heat regenerating function can be achieved.

The occupancy ratio of the heat regenerating substance particles11contained in the heat regenerating material particle10is preferably 95% by volume or less. By satisfying the above range, the mechanical strength of the heat regenerating material particle10is increased.

The binder12contained in the heat regenerating material particle10has an occupancy ratio preferably of 5% by volume or more, more preferably of 8% by volume or more, still more preferably of 10% by volume or more. By satisfying the above range, the mechanical strength of the heat regenerating material particle10is increased.

The occupancy ratio of the binder12contained in the heat regenerating material particle10is preferably 40% by volume or less, more preferably 30% by volume or less, still more preferably 20% by volume or less, and particularly preferably 10% by volume or less. By satisfying the above range, the occupancy ratio of the heat regenerating substance particles11is increased, and a high heat regenerating function can be achieved.

The heat regenerating material particle10has a porosity preferably of less than 20% by volume, more preferably of less than 15% by volume, still more preferably of less than 12% by volume, particularly preferably of less than 10% by volume. By satisfying the above range, the occupancy ratio of the heat regenerating substance particles11is increased, and a high heat regenerating function can be achieved.

As described above, according to the first embodiment, a heat regenerating material particle that can be manufactured by a simple manufacturing process can be achieved. Therefore, manufacturing cost of a heat regenerating material particle is reduced, and an inexpensive heat regenerating material particle can be achieved. In addition, since a heat regenerating material particle can be formed at a low temperature, a heat regenerating material particle with stable characteristics can be achieved.

Second Embodiment

A heat regenerating material particle according to a second embodiment is different from that according to the first embodiment in that a plurality of heat regenerating substance particles contains a first particle and a second particle having a chemical composition different from the first particle. Hereinafter, matters overlapping with the first embodiment will be partially omitted.

FIG. 7is a schematic cross-sectional view of a heat regenerating material particle according to the second embodiment.

A heat regenerating material particle20includes a plurality of heat regenerating substance particles11and a binder12. The heat regenerating substance particles11contain a first particle11aand a second particle11b. The chemical composition of the second particle11bis different from that of the first particle11a.

The first particle11acontains, for example, an oxide as a main component. The second particle11bcontains, for example, a rare earth compound as a main component.

In addition, the first particle11acontains, for example, a rare earth compound as a main component. The second particle11bcontains, for example, a metal as a main component.

In addition, the first particle11acontains, for example, a rare earth compound as a main component. The second particle11bcontains, for example, a rare earth compound different from the first particle11aas a main component.

The heat regenerating material particle20according to the second embodiment contains the first particle11aand the second particle11bhaving different chemical compositions. In other words, the heat regenerating material particle20contains the first particle11aand the second particle11bexhibiting a heat regenerating function in different temperature ranges. Therefore, the heat regenerating material particle20having a heat regenerating function in a wide temperature range can be achieved.

For example, the temperature at which volume specific heat is maximum is different between the first particle11aand the second particle11b.

The heat regenerating material particle20according to the second embodiment easily contains the first particle11aand the second particle11bhaving different chemical compositions in one heat regenerating material particle20by using the resin binder12.

As described above, according to the second embodiment, a heat regenerating material particle that can be manufactured by a simple manufacturing process can be achieved as in the first embodiment. Therefore, manufacturing cost of a heat regenerating material particle is reduced, and an inexpensive heat regenerating material particle can be achieved. In addition, since a heat regenerating material particle can be formed at a low temperature, a heat regenerating material particle with stable characteristics can be achieved. In addition, a heat regenerating material particle having a heat regenerating function in a wide temperature range can be achieved.

Third Embodiment

A refrigerator according to a third embodiment includes a regenerator in which the heat regenerating material particles according to the first or second embodiment are filled. Hereinafter, description of matters overlapping with the first or second embodiment will be partially omitted.

FIG. 8is a schematic cross-sectional view illustrating a configuration of a main part of the refrigerator according to the third embodiment. The refrigerator according to the third embodiment is a two-stage heat regenerating cryogenic refrigerator100used for cooling a superconducting device or the like.

The heat regenerating cryogenic refrigerator100includes a first cylinder111, a second cylinder112, a vacuum container113, a first regenerator114, a second regenerator115, a first seal ring116, a second seal ring117, a first heat regenerating material118, a second heat regenerating material119, a first expansion chamber120, a second expansion chamber121, a first cooling stage122, a second cooling stage123, and a compressor124.

The heat regenerating cryogenic refrigerator100includes the vacuum container113in which the large diameter first cylinder111and the small diameter second cylinder112coaxially connected to the first cylinder111are disposed. In the first cylinder111, the first regenerator114is disposed so as to freely reciprocate. In the second cylinder112, the second regenerator115as an example of the regenerator according to the third embodiment is disposed so as to freely reciprocate.

The first seal ring116is disposed between the first cylinder111and the first regenerator114. The second seal ring117is disposed between the second cylinder112and the second regenerator115.

The first heat regenerating material118such as a Cu mesh is housed in the first regenerator114. The heat regenerating material particles10according to the first embodiment or the heat regenerating material particles20according to the second embodiment are filled in the second regenerator115as the second heat regenerating material119.

The first regenerator114and the second regenerator115each have a passage of a working medium provided in a gap or the like of the first heat regenerating material118or the second heat regenerating material119. The working medium is helium gas.

The first expansion chamber120is provided between the first regenerator114and the second regenerator115. The second expansion chamber121is provided between the second regenerator115and a tip wall of the second cylinder112. The first cooling stage122is provided at a bottom of the first expansion chamber120. The second cooling stage123having a temperature lower than the first cooling stage122is formed at a bottom of the second expansion chamber121.

The first expansion chamber120is provided between the first regenerator114and the second regenerator115. The second expansion chamber121is provided between the second regenerator115and a tip wall of the second cylinder112. The first cooling stage122is provided at a bottom of the first expansion chamber120. The second cooling stage123having a temperature lower than the first cooling stage122is formed at a bottom of the second expansion chamber121.

To the two-stage heat regenerating cryogenic refrigerator100described above, a high-pressure working medium is supplied from the compressor124. The supplied working medium passes through the first heat regenerating material118housed in the first regenerator114and reaches the first expansion chamber120. Then, the working medium passes through the second heat regenerating material119housed in the second regenerator115and reaches the second expansion chamber121.

At this time, the working medium is cooled by supplying thermal energy to the first heat regenerating material118and the second heat regenerating material119. The working medium that has passed through the first heat regenerating material118and the second heat regenerating material119expands in the first expansion chamber120and the second expansion chamber121to generate cold. Then, the first cooling stage122and the second cooling stage123are cooled.

The working medium that has expanded flows in the opposite direction through the first heat regenerating material118and the second heat regenerating material119. The working medium receives thermal energy from the first heat regenerating material118and the second heat regenerating material119and is then discharged. The heat regenerating cryogenic refrigerator100is configured such that the thermal efficiency of a working medium cycle is improved to achieve a lower temperature as a recuperative effect becomes better in this process.

As described above, according to the third embodiment, an inexpensive refrigerator can be achieved by using an inexpensive heat regenerating material particle. In addition, by using a heat regenerating material particle with stable characteristics against a cycle of a large temperature change reaching a cryogenic temperature, a highly reliable cryogenic refrigerator capable of stably providing high efficiency cooling performance for a long time can be achieved.

Fourth Embodiment

A superconducting magnet according to a fourth embodiment includes the refrigerator according to the third embodiment. Hereinafter, matters overlapping with the third embodiment will be partially omitted.

FIG. 9is a perspective view illustrating a schematic configuration of the superconducting magnet according to the fourth embodiment. The superconducting magnet according to the fourth embodiment is a magnetically levitated train superconducting magnet400including the heat regenerating cryogenic refrigerator100according to the third embodiment.

The magnetically levitated train superconducting magnet400includes a superconducting coil401, a liquid helium tank402for cooling the superconducting coil401, a liquid nitrogen tank403for preventing volatilization of the liquid helium tank402, a laminated thermal insulator405, a power lead406, a permanent current switch407, and the heat regenerating cryogenic refrigerator100.

According to the fourth embodiment, by using an inexpensive refrigerator, an inexpensive superconducting magnet can be achieved. In addition, by using a refrigerator with stable characteristics, a superconducting magnet with stable characteristics can be achieved.

Fifth Embodiment

A nuclear magnetic resonance imaging apparatus according to a fifth embodiment includes the refrigerator according to the third embodiment. Hereinafter, matters overlapping with the third embodiment will be partially omitted.

FIG. 10is a cross-sectional view illustrating a schematic configuration of the nuclear magnetic resonance imaging apparatus according to the fifth embodiment. The nuclear magnetic resonance imaging (MRI) apparatus according to the fifth embodiment is a nuclear magnetic resonance imaging apparatus500including the heat regenerating cryogenic refrigerator100according to the third embodiment.

The nuclear magnetic resonance imaging apparatus500using a nuclear magnetic resonance (NMR) phenomenon is an example of a nuclear magnetic resonance apparatus.

The nuclear magnetic resonance imaging apparatus500includes a superconducting static magnetic field coil501for applying a spatially uniform and temporally stable static magnetic field to a human body, a correction coil (not illustrated) for correcting nonuniformity of a generated magnetic field, a gradient magnetic field coil502for imparting a magnetic field gradient to a measurement region, a radio wave transmitting/receiving probe503, a cryostat505, and a radiant heat insulation shield506. The heat regenerating cryogenic refrigerator100is used for cooling the superconducting static magnetic field coil501.

According to the fifth embodiment, by using an inexpensive refrigerator, an inexpensive nuclear magnetic resonance imaging apparatus and nuclear magnetic resonance apparatus can be achieved. In addition, by using a refrigerator with stable characteristics, a nuclear magnetic resonance imaging apparatus and a nuclear magnetic resonance apparatus with stable characteristics can be achieved.

Sixth Embodiment

A cryopump according to a sixth embodiment includes the refrigerator according to the third embodiment. Hereinafter, matters overlapping with the third embodiment will be partially omitted.

FIG. 11is a cross-sectional view illustrating a schematic configuration of the cryopump according to the sixth embodiment. The cryopump according to the sixth embodiment is a cryopump600including the heat regenerating cryogenic refrigerator100according to the third embodiment.

The cryopump600includes a cryopanel601for condensing or adsorbing a gas molecule, the heat regenerating cryogenic refrigerator100for cooling the cryopanel601to a predetermined cryogenic temperature, a shield603provided between the cryopanel601and the heat regenerating cryogenic refrigerator100, a baffle604provided in an inlet, and a ring605for changing a discharge speed of argon, nitrogen, hydrogen, or the like.

According to the sixth embodiment, by using an inexpensive refrigerator, an inexpensive cryopump can be achieved. In addition, by using a refrigerator with stable characteristics, a cryopump with stable characteristics can be achieved.

Seventh Embodiment

A magnetic field application type single crystal pulling apparatus according to a seventh embodiment includes the refrigerator according to the third embodiment. Hereinafter, matters overlapping with the third embodiment will be partially omitted.

FIG. 12is a perspective view illustrating a schematic configuration of the magnetic field application type single crystal pulling apparatus according to the seventh embodiment. The magnetic field application type single crystal pulling apparatus according to the seventh embodiment is a magnetic field application type single crystal pulling apparatus700including the heat regenerating cryogenic refrigerator100according to third embodiment.

The magnetic field application type single crystal pulling apparatus700includes a single crystal pulling unit701including a raw material melting crucible, a heater, a single crystal pulling mechanism, and the like, a superconducting coil702for applying a static magnetic field to a raw material melt, a lifting mechanism703for the single crystal pulling unit701, a current lead705, a heat shield plate706, and a helium container707. The heat regenerating cryogenic refrigerator100is used for cooling the superconducting coil702.

According to the seventh embodiment, by using an inexpensive refrigerator, an inexpensive magnetic field application type single crystal pulling apparatus can be achieved. In addition, by using a refrigerator with stable characteristics, a magnetic field application type single crystal pulling apparatus with stable characteristics can be achieved.

Incidentally, as in the fourth, fifth, and seventh embodiments, in a case of using a refrigerator for cooling a superconducting magnet, the heat regenerating substance particles11are particularly preferably formed of a nonmagnetic material. The reason for this is that, in the fourth and seventh embodiments, a shaft of a refrigerator may be bent by reception of a force by a magnetic material in a magnetic field. In addition, the reason is that, in the fifth embodiment, a magnetic material reciprocates in a magnetic field to generate a magnetic noise, and a nuclear magnetic resonance signal may be hindered.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, heat regenerating material particle, regenerator, refrigerator, superconducting magnet, nuclear magnetic resonance imaging apparatus, nuclear magnetic resonance apparatus, cryopump, and magnetic field application type single crystal pulling apparatus described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the devices and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.