Magnetic regenerator material particles, regenerator, refrigerator, cryopump, superconducting magnet, nuclear magnetic resonance imaging device, nuclear magnetic resonance device, magnetic field-applied single crystal pulling device, and helium recondensing device

Abstract

To provide magnetic regenerator material particles that exhibit a reduced breakage rate even under long-term vibrations due to operation of a refrigerator in an extremely low-temperature region, a regenerator and a refrigerator whose refrigeration performance does not decrease even after long-term operation by virtue of including the magnetic regenerator material particles, and a device such as a superconducting magnet that includes the refrigerator.SOLUTION: Magnetic regenerator material particles of an embodiment are composed of an intermetallic compound containing a rare earth element, and a proportion of an area of voids present in a cross section thereof is 0.0001% or more and 15% or less. A regenerator, a refrigerator, and a device such as a superconducting magnet including the refrigerator according to embodiments include the magnetic regenerator material particles of the embodiment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to magnetic regenerator particles, a regenerator, a refrigerator, a cryopump, a superconducting magnet, a nuclear magnetic resonance imaging (MRI) device, a nuclear magnetic resonance device, a magnetic field application type single crystal pulling device, and a helium recondensation device. [Background technology]

[0002] In recent years, superconducting technology has made remarkable progress, and as its application fields expand, the development of high-performance and highly reliable cryogenic refrigerators has become essential. Such cryogenic refrigerators are required to maintain high thermal efficiency for a long period of time.

[0003] In a cryogenic refrigerator, multiple regenerators are placed inside a regenerator. For example, cold is generated by heat exchange between the regenerators and helium gas passing through the regenerator. For example, superconducting MRI devices and cryopumps use refrigerators with refrigeration cycles such as the Gifford-McMahon (GM) system, Stirling system, or pulse tube system.

[0004] High-performance refrigerators are also essential for magnetic levitation trains, which use superconducting magnets to generate magnetic force. Furthermore, high-performance refrigerators are now being used in superconducting energy storage systems (SMES) and magnetic field-applied single crystal growing systems for producing high-quality silicon wafers. Active efforts are also being made to develop and commercialize pulse tube refrigerators, which are expected to offer even higher reliability.

[0005] Furthermore, in the superconducting magnets and MRI devices mentioned above, the liquid helium used evaporates, making replenishing it a problem. In recent years, the helium depletion problem has become more serious, making it difficult to obtain, and affecting the industrial sector.

[0006] To reduce the consumption of liquid helium and ease the burden of maintenance such as replenishment, helium recondensing devices that recondense evaporated helium have been put into practical use and are in high demand. These helium recondensing devices also use GM refrigerators or pulse tube refrigerators to cool the helium to a temperature of 4K in order to liquefy it.

[0007] In addition, GM refrigerators and pulse tube refrigerators can be used to liquefy gases other than helium or to prevent evaporation when storing liquefied gases. An example of a gas other than helium is hydrogen. Since the boiling point of liquefied hydrogen is approximately 20 K, evaporation of liquefied hydrogen can be reduced by keeping the temperature below 20 K.

[0008] In refrigerators equipped with a regenerator, a working medium such as compressed helium (He) gas flows in one direction through a regenerator housing the regenerator material, supplying its thermal energy to the regenerator material. The expanded working medium then flows in the opposite direction through the regenerator, receiving thermal energy from the regenerator material. As the heat recovery effect in this process improves, the thermal efficiency of the working medium cycle improves, making it possible to achieve lower temperatures.

[0009] The higher the specific heat per unit volume of the regenerator material, the more heat energy the regenerator material can store, improving the refrigeration capacity of the refrigerator. Therefore, it is desirable to install a regenerator material with a high specific heat at low temperatures on the low-temperature side of the regenerator, and a regenerator material with a high specific heat at high temperatures on the high-temperature side.

[0010] Depending on the composition of the regenerator material, it exhibits a high volumetric specific heat in a specific temperature range. Therefore, by combining regenerator materials with different compositions that exhibit a high volumetric specific heat in the target temperature range, the regenerator capacity can be increased, and the refrigeration capacity of the refrigerator can be improved.

[0011] In conventional refrigerators, freezing at 4K has been achieved by combining metallic regenerator materials such as lead (Pb), bismuth (Bi) and tin (Sn) on the high-temperature side with metallic magnetic regenerator materials such as Er3Ni, ErNi and HoCu2 on the low-temperature side below 20K. Non-metallic magnetic regenerator materials such as Gd2O2S are also sometimes used in combination with the metallic magnetic regenerator materials mentioned above.

[0012] In recent years, superconducting equipment using high-temperature superconducting wires has also been developed. Operation of these equipment at temperatures between 10K and 30K is being considered. For refrigerators operating at these temperatures, it is desirable to use a regenerator material that exhibits a high volumetric specific heat between 10K and 30K.

[0013] When refrigerators are used to prevent the evaporation of superconducting equipment or liquefied gases, they are required to maintain high thermal efficiency for a long period of time. During the cycle of heat exchange between the regenerator material and the working substance, mechanical vibrations are applied to the regenerator material. For this reason, while the refrigerator is operating, the regenerator material is constantly vibrating at the refrigerator's operating temperature. If the amount of regenerator material damaged by this vibration exceeds a certain level, the flow of the working medium, such as helium (He) gas, becomes poor, and thermal efficiency decreases. If the regenerator material is severely damaged, the flow of the working medium, such as He gas, will stop, and the refrigerator will stop.

[0014] Therefore, to improve the long-term reliability of refrigerators, the regenerator material must be able to withstand long-term vibrations at temperatures that the refrigerator operates at, and the amount of destruction that occurs must be below a certain level. For example, refrigerators operate at temperatures that are liquid helium temperatures (approximately 4 K) for MRIs that use low-temperature superconducting wires, 10 to 30 K for devices that use high-temperature superconducting wires, and liquefied hydrogen temperatures (approximately 20 K) for cooling liquefied hydrogen. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-73661 [Patent Document 2] International Publication No. 96 / 006315 [Patent Document 3] International Publication No. 2014 / 057657 Summary of the Invention [Problem to be solved by the invention]

[0016] The problem that the present invention aims to solve is to provide magnetic regenerator particles that have a low breakage rate even when subjected to vibration at extremely low temperatures for a long period of time, and to provide a regenerator equipped with such particles that does not lose its refrigeration performance even when operated for a long period of time. [Means for solving the problem]

[0017] The magnetic regenerator particles of the embodiment are made of an intermetallic compound containing a rare earth element represented by RMz (R represents at least one rare earth element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, M represents at least one metal element selected from Ni, Co, Cu, Ag, Si, Ga, Bi, Al and Ru, and z is a number in the range of 0.001 to 9.0), and the area ratio of voids in the particles present in the cross section is 0.0001% or more and 15% or less, the ratio of particles having an aspect ratio of 1 is 70% or more, and when the perimeter of the projected image is L and the actual area of ​​the projected image is A, the area ratio is 4πA / L 2 The ratio of magnetic regenerator particles having a circularity R of 0.4 or less is 10% or less.

[0018] The regenerator of the embodiment is characterized in that, among the magnetic regenerator particles containing a rare earth element represented by RMz mounted in the regenerator, the proportion of magnetic regenerator particles having an area ratio of voids present in the cross section of 0.0001% or more and 15% or less is 70% or more. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 3 is a schematic cross-sectional view showing the main configuration of the magnetic regenerator particle of the first embodiment and the refrigerator of the third embodiment. [Figure 2]FIG. 10 is a cross-sectional view showing a schematic configuration of a cryopump according to a fourth embodiment. [Figure 3] FIG. 10 is a perspective view showing a schematic configuration of a superconducting magnet according to a fifth embodiment. [Figure 4] FIG. 10 is a cross-sectional view showing a schematic configuration of a nuclear magnetic resonance imaging apparatus according to a sixth embodiment. [Figure 5] FIG. 13 is a cross-sectional view showing a schematic configuration of a nuclear magnetic resonance spectrometer according to a seventh embodiment. [Figure 6] FIG. 13 is a perspective view showing a schematic configuration of a magnetic field application type single crystal pulling apparatus according to an eighth embodiment. [Figure 7] FIG. 13 is a perspective view showing a schematic configuration of a helium recondensation device according to a ninth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same or similar components will be designated by the same reference numerals, and the description of components that have already been described may be omitted as appropriate.

[0021] In this specification, cryogenic temperatures refer to, for example, a temperature range of 30 K or less. In the temperature range of 30 K or less, superconducting equipment can operate and helium or hydrogen can be liquefied.

[0022] (First embodiment) The magnetic regenerator particles of the first embodiment are made of an intermetallic compound containing a rare earth element represented by RMz (R represents at least one rare earth element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, M represents at least one metal element selected from Ni, Co, Cu, Ga, Bi, Ag, Si, Al and Ru, and z is a number in the range of 0.001 to 9.0).

[0023] In the magnetic regenerator particles of the first embodiment, the ratio of the area occupied by voids in the cross section is 0.0001% or more and 15% or less.

[0024] The cross-sectional area of ​​the magnetic regenerator particle of the first embodiment and the area occupied by voids present in the cross-section can be determined by image analysis of an optical microscope image or a scanning electron microscope (SEM) image. In the image analysis of an SEM image, a backscattered electron image is used. For example, ImageJ can be used as image analysis software.

[0025] From the brightness of the backscattered electron image, it is possible to extract from the image the areas corresponding to voids and the areas corresponding to non-voids in the regenerator particles. When extracting the corresponding areas, for example, the brightness is binarized. For example, if the extracted areas are compared with the original image with the naked eye and it is clear that the voids have not been properly extracted, the binarization conditions are adjusted and then the particle cross section and the area of ​​the voids are evaluated.

[0026] When observing the cross section of the magnetic regenerator particle of the first embodiment, it is desirable to use a sample in which the magnetic regenerator particle is impregnated in a resin and then polished by ion milling to expose the cross section. In this case, if polishing is performed using abrasive paper, weak parts in the regenerator material will fall off, making it impossible to accurately evaluate the voids. For this reason, it is desirable to polish using ion milling, which is less likely to cause falling off.

[0027] The cross section of the exposed sample is observed using an optical microscope or a scanning electron microscope (SEM). At this time, it is desirable to identify voids by comparing the SEM secondary electron image with the backscattered electron image, excluding any dust adhering to the measurement surface.

[0028] Furthermore, it is desirable to select magnetic regenerator particles to be evaluated whose cross-sectional equivalent circle diameter is within ±10% of the median value of the particle size distribution, and observe the voids. Particles whose cross-sectional equivalent circle diameter is outside the range of ±10% of the median value of the particle size distribution mean that the cross-section is outside the center of the particle, and it may not be possible to accurately evaluate the proportion of voids present in the particle.

[0029] The particle size distribution of the magnetic regenerator particles can be measured by evaluating the distribution of diameters of perfect circles corresponding to the area of ​​the shapes observed in images of the magnetic regenerator particles, such as optical microscope images or scanning electron microscope images (SEM images). When evaluating the diameter distribution, it is desirable to evaluate the diameters of, for example, 50 or more particles.

[0030] The detection of elements contained in the magnetic regenerator particles of the first embodiment and the measurement of the atomic concentration of the elements can be performed, for example, by dissolving the magnetic regenerator particles in a liquid and using inductively coupled plasma atomic emission spectroscopy (ICP-AES).Furthermore, the detection can also be performed using energy dispersive X-ray spectroscopy (EDX) or wavelength dispersive X-ray spectroscopy (WDX).

[0031] The magnetic regenerator particles according to the first embodiment have a particle size of 50 μm or more and 3 mm or less. The aspect ratio of the magnetic regenerator particles is, for example, 1 or more and 5 or less. The aspect ratio of the magnetic regenerator particles is the ratio of the major axis to the minor axis of the magnetic regenerator particles. The shape of the magnetic regenerator particles is, for example, spherical.

[0032] The particle size of the magnetic regenerator particles is the 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 of the magnetic regenerator particles, such as an optical microscope image or a scanning electron microscope image (SEM image). The particle size of the magnetic regenerator particles can be determined, for example, by image analysis of the optical microscope image or the SEM image.

[0033] The method for producing the magnetic regenerator particles of the first embodiment is not particularly limited, and various production methods can be applied. For example, a method in which a molten base alloy of a predetermined composition is rapidly cooled and solidified to form granules by centrifugal atomization, plasma rotating electrode method, gas atomization method, rotating electrode method, etc. can be applied.

[0034] The base alloy can be produced by melting the raw materials using a high-frequency melting method or the like and pouring the molten metal into a mold. Alternatively, the base alloy can be produced by, for example, mixing raw material powders to prepare a raw material mixture, molding the resulting raw material mixture, and sintering it in a vacuum furnace. Furthermore, by optimizing the manufacturing conditions or performing shape classification using a tilt vibration method, for example, magnetic regenerator particles with an aspect ratio of 1 to 5 can be obtained.

[0035] In addition, by optimizing the manufacturing conditions and performing shape classification such as the inclined vibration method, when the perimeter of the projected image of the magnetic regenerator particle is L and the actual area of ​​the projected image is A, the following equation can be obtained: 4πA / L 2 The circularity R expressed by the following formula can be made to exceed 0.4.

[0036] The magnetic regenerator particles of the first embodiment can be manufactured by subjecting the obtained magnetic regenerator particles to a pressure heat treatment. In the pressure heat treatment, the voids can be controlled by controlling the pressure applied to the sample and the heat treatment temperature. When the HIP method is used in the pressure heat treatment, the voids can be controlled by controlling the gas pressure and the sintering temperature. The HIP treatment is performed, for example, in a pressurized inert gas atmosphere. Argon or nitrogen can be used as the inert gas. The gas pressure is, for example, 1 MPa or more and 200 MPa or less. The heat treatment temperature is, for example, 500°C or more and 2000°C or less. The heat treatment temperature is adjusted depending on the melting point of the sample. The heat treatment time is, for example, 1 hour or more and 48 hours or less.

[0037] Next, the function and effect of the magnetic regenerator particles of the first embodiment will be described.

[0038] In cryogenic refrigerators, the process of filling the regenerator with regenerator particles is generally performed at room temperature. Therefore, even if the regenerator is tightly packed at room temperature, thermal contraction in a cryogenic environment increases voids between the regenerator particles or between the regenerator and the regenerator, changing the packing properties. When voids between the regenerator particles increase, the regenerator particles may move within the regenerator, causing collisions and other problems. Operating a refrigerator with this void can cause wear and cracks in the regenerator particles due to vibrations during operation and the back-and-forth movement of the working gas inside the regenerator, resulting in reduced refrigeration performance.

[0039] The smaller the thermal expansion coefficient of the cold storage material particles, the more effectively they can suppress the generation of voids between the cold storage material particles due to thermal contraction in an extremely low temperature environment, stabilizing the filling of the cold storage material particles in the cold storage unit and reducing the frequency of rattles. This reduces the frequency of wear and cracks in the cold storage material particles during operation of the refrigerator, and allows the refrigerator's refrigeration performance to be stable for a long period of time.

[0040] In the embodiment, the area ratio of voids present in the magnetic regenerator particles is 0.0001% or more, preferably 0.0005% or more, and more preferably 0.001% or more. When the area ratio of voids is 0.0001% or more, the voids present within the particles absorb the particle shrinkage, and the thermal shrinkage of the regenerator particles is smaller than that of regenerator particles with a void area ratio of less than 0.0001%, suppressing changes in packing properties in an extremely low temperature environment and reducing the frequency of rattle. As a result, the frequency of wear and cracks in the magnetic regenerator particles is reduced, and refrigeration performance can be maintained even when the refrigerator is operated for a long time.

[0041] In the embodiment, the area ratio of voids present in the magnetic regenerator particles is 15% or less, preferably 10% or less. As the amount of voids present in the magnetic regenerator particles increases, the strength of the magnetic regenerator particles tends to decrease, but when the area ratio of voids is 15% or less, rattling due to changes in packing is reduced, so the amount of damage to the magnetic regenerator particles caused by vibrations during operation of the refrigerator is reduced, and the refrigerator performance can be maintained for a long period of time.

[0042] The particle size of the magnetic regenerator particles in the first embodiment is preferably 50 μm or more and 3 mm or less. It is more preferably 1 mm or less, and even more preferably 500 μm or less. When the particle size of the magnetic regenerator particles is 50 μm or more, the packing density of the magnetic regenerator particles in the regenerator is low, reducing the pressure loss of the working medium such as helium and improving the refrigeration performance of the refrigerator. On the other hand, when the particle size of the magnetic regenerator particles is 3 mm or less, the distance from the surface of the magnetic regenerator particle to the center of the particle is short, making it easier for heat to be transferred between the working medium and the magnetic regenerator particles to the center of the regenerator, improving the refrigeration performance of the refrigerator.

[0043] The aspect ratio of the magnetic regenerator particles in the embodiment is preferably 5 or less, and more preferably 2 or less. When the aspect ratio of the magnetic regenerator particles is 5 or less, the voids become uniform when the magnetic regenerator particles are filled into a regenerator, and the refrigeration performance of the refrigerator is improved.

[0044] The circularity R of the magnetic regenerator particles of the embodiment is preferably more than 0.4, and more preferably 0.6 or more. When the circularity R of the magnetic regenerator particles approaches 1, the shape approaches a sphere, and the voids when the magnetic regenerator particles are filled into a regenerator become uniform, and the filling property becomes stable, thereby improving the refrigeration performance of the refrigerator.

[0045] (Second embodiment) The regenerator of the second embodiment is a regenerator filled with a plurality of single or multiple types of regenerator particles. The regenerator of the second embodiment is filled with a plurality of magnetic regenerator particles represented by RMz, and the proportion of the magnetic regenerator particles of the first embodiment among the magnetic regenerator particles represented by RMz is 70% or more. In addition, the regenerator of the second embodiment has a perimeter of 4πA / L, for example, where L is the perimeter of the projected image of the magnetic regenerator particle of the first embodiment filled in the regenerator and A is the actual area of ​​the projected image. 2 The ratio of magnetic regenerator particles having a circularity R of 0.4 or less is 15% or less.

[0046] If the proportion of the magnetic regenerator particles of the first embodiment among the magnetic regenerator particles represented by RMz filled in the regenerator of the second embodiment is less than 70%, the contribution of the magnetic regenerator particles of the first embodiment is reduced, and the frequency of rattle occurring in an extremely low temperature environment cannot be reduced. The proportion of the magnetic regenerator particles of the first embodiment is 70% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 100%. The proportion of the magnetic regenerator particles of the first embodiment installed in the regenerator can be determined by taking a certain number of particles from the magnetic regenerator particles represented by RMz installed in the regenerator, observing the cross-sections of those particles, and calculating the proportion of particles with a void area ratio of 0.0001% to 15%. In this case, the average value of the void area ratio of particles with a void area ratio of 0.0001% to 15% is the void area ratio of the magnetic regenerator particles of the first embodiment installed in the regenerator. When evaluating the proportion of the magnetic regenerator particles of the first embodiment, it is desirable to observe and evaluate the cross sections of, for example, 10 or more particles.

[0047] The circularity R of magnetic regenerator particles can be determined by image processing of the shapes of multiple magnetic regenerator particles using an optical microscope. Magnetic regenerator particles with a circularity R of 0.4 or less exhibit a shape with irregularities on the surface. If such magnetic regenerator particles account for more than 15% of the magnetic regenerator particles represented by RMz, the porosity formed by the magnetic regenerator particles in the regenerator becomes non-uniform and the packing becomes unstable. This causes rattles at extremely low temperatures even when the magnetic regenerator particles according to the first embodiment are used, reducing the refrigeration performance and long-term reliability of the refrigerator during long-term operation. The magnetic regenerator particles with a circularity R of 0.4 or less are preferably 15% or less, more preferably 10% or less. More preferably, it is 5% or less, even more preferably 2% or less, and even more preferably 0%. When evaluating the proportion of magnetic regenerator particles with a circularity R of 0.4 or less, it is desirable to evaluate, for example, 50 or more particles.

[0048] (Third embodiment) The refrigerator of the third embodiment is a refrigerator equipped with the regenerator of the second embodiment filled with a plurality of magnetic regenerator particles of the first embodiment. Hereinafter, some of the descriptions overlapping with the first and second embodiments will be omitted.

[0049] 1 is a schematic cross-sectional view showing the main configuration of a refrigerator according to a third embodiment, which includes the regenerator of the second embodiment filled with a plurality of magnetic regenerator particles according to the first embodiment. The refrigerator according to the third embodiment is a two-stage regenerator-type cryogenic refrigerator 100 used for cooling superconducting equipment and the like.

[0050] The regenerative cryogenic refrigerator 100 includes a first cylinder 111, a second cylinder 112, a vacuum vessel 113, a first regenerator 114, a second regenerator 115, a first seal ring 116, a second seal ring 117, a first regenerator material 118, a second regenerator material 119, a first expansion chamber 120, a second expansion chamber 121, a first cooling stage 122, a second cooling stage 123, and a compressor 124.

[0051] The regenerative cryogenic refrigerator 100 has a vacuum vessel 113 in which a large-diameter first cylinder 111 and a small-diameter second cylinder 112 coaxially connected to the first cylinder 111 are installed. A first regenerator 114 is arranged in the first cylinder 111 so as to be able to reciprocate. A second regenerator 115, which is an example of the regenerator of the second embodiment, is arranged in the second cylinder 112 so as to be able to reciprocate.

[0052] A first seal ring 116 is disposed between the first cylinder 111 and the first regenerator 114. A second seal ring 117 is disposed between the second cylinder 112 and the second regenerator 115.

[0053] The first regenerator 114 contains a first regenerator material 118 such as a Cu mesh. The second regenerator 115 contains a second regenerator material 119.

[0054] The first regenerator 114 and the second regenerator 115 each have a passage for the working medium provided in the gap between the first regenerator material 118 and the second regenerator material 119. The working medium is helium gas.

[0055] A first expansion chamber 120 is provided between the first regenerator 114 and the second regenerator 115. A second expansion chamber 121 is provided between the second regenerator 115 and the front end wall of the second cylinder 112. A first cooling stage 122 is provided at the bottom of the first expansion chamber 120. A second cooling stage 123, which has a lower temperature than the first cooling stage 122, is formed at the bottom of the second expansion chamber 121.

[0056] The two-stage regenerative cryogenic refrigerator 100 described above is supplied with a high-pressure working medium from a compressor 124. The supplied working medium passes between first regenerator materials 118 housed in the first regenerator 114 and reaches the first expansion chamber 120. Then, it passes between second regenerator materials 119 housed in the second regenerator 115 and reaches the second expansion chamber 121.

[0057] At this time, the working medium is cooled by supplying thermal energy to the first cold storage material 118 and the second cold storage material 119. The working medium that has passed between the first cold storage material 118 and the second cold storage material 119 expands in the first expansion chamber 120 and the second expansion chamber 121 to generate cold. Then, the first cooling stage 122 and the second cooling stage 123 are cooled.

[0058] The expanded working medium flows in the opposite direction between the first and second cold storage materials 118 and 119. The working medium is discharged after receiving thermal energy from the first and second cold storage materials 118 and 119. The regenerative cryogenic refrigerator 100 is configured to improve the thermal efficiency of the working medium cycle as the heat recovery effect improves during this process, thereby achieving even lower temperatures.

[0059] In the regenerator of the refrigerator of the third embodiment, the second regenerator 115 is the regenerator of the second embodiment, and contains a plurality of magnetic regenerator particles of the first embodiment as at least a part of the second regenerator material 119. The plurality of magnetic regenerator particles of the first embodiment have a perimeter of 4πA / L, where L is the perimeter of the projected image of each magnetic regenerator particle and A is the actual area of ​​the projected image. 2 It is preferable that the circularity R of 0.4 or less is 15% or less.

[0060] In the third embodiment, the regenerator of the second embodiment may include, for example, a plurality of regenerator material filled layers of different types of regenerator material. The different types of regenerator material may be separated by a mesh. The mesh is, for example, a metal mesh. At least one of the plurality of regenerator material filled layers is the magnetic regenerator material particles of the first embodiment. In the refrigerator of the third embodiment, when the magnetic regenerator material particles of the first embodiment are combined with regenerator material particles having a maximum specific heat value lower than that of the magnetic regenerator material particles of the first embodiment, the plurality of magnetic regenerator material particles of the first embodiment are filled, for example, on the high temperature side of the regenerator.

[0061] When the magnetic regenerator particles of the first embodiment are combined with regenerator particles having a maximum specific heat value at a higher temperature than the magnetic regenerator particles of the first embodiment, multiple magnetic regenerator particles of the first embodiment are filled, for example, on the low-temperature side of a regenerator.

[0062] When the magnetic regenerator particles of the first embodiment are combined with regenerator particles having a specific heat maximum at a higher temperature than the magnetic regenerator particles of the first embodiment and with regenerator particles having a specific heat maximum at a lower temperature, the magnetic regenerator particles of the first embodiment are filled, for example, sandwiched between two regenerator particles of the first embodiment. When the magnetic regenerator particles of the first embodiment and different compositions are combined, it can be determined whether they are placed on the low temperature side or the high temperature side of the regenerator depending on the temperature at which they show a specific heat maximum.

[0063] To improve the reliability of the refrigerator, it is desirable that the amount of destruction of the regenerator particles be kept below a certain level even when subjected to vibration for a long period of time in an extremely low temperature environment. The refrigerator of the third embodiment is equipped with the regenerator of the second embodiment that includes the magnetic regenerator particles of the first embodiment.

[0064] By using the refrigerator of the third embodiment in a magnetic levitation train, a helium recondenser, or the like, it is possible to improve the long-term reliability of the magnetic levitation train and the helium recondenser.

[0065] According to the third embodiment, by using magnetic regenerator particles with excellent properties in which the amount of destruction of the magnetic regenerator particles is reduced, a refrigerator with excellent long-term reliability can be realized.

[0066] (Fourth embodiment) The cryopump of the fourth embodiment includes the refrigerator of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0067] 2 is a cross-sectional view showing a schematic configuration of a cryopump according to the fourth embodiment. The cryopump according to the fourth embodiment is a cryopump 500 including the regenerative cryogenic refrigerator 100 according to the third embodiment.

[0068] The cryopump 500 includes a cryopanel 501 that condenses or adsorbs gas molecules, a regenerative cryogenic refrigerator 100 that cools the cryopanel 501 to a predetermined cryogenic temperature, a shield 503 installed between the cryopanel 501 and the regenerative cryogenic refrigerator 100, a baffle 504 installed at the intake port, and a ring 505 that changes the pumping speed of argon, nitrogen, hydrogen, etc.

[0069] According to the fourth embodiment, a cryopump with excellent long-term reliability can be realized by using a refrigerator with excellent long-term reliability.

[0070] (Fifth embodiment) The superconducting magnet of the fifth embodiment includes the refrigerator of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0071] 3 is a perspective view showing a schematic configuration of a superconducting magnet according to a fifth embodiment. The superconducting magnet according to the fifth embodiment is a superconducting magnet 600 for a magnetic levitation train that includes the regenerative cryogenic refrigerator 100 according to the third embodiment.

[0072] The superconducting magnet 600 for a magnetic levitation train includes a superconducting coil 601, a liquid helium tank 602 for cooling the superconducting coil 601, a liquid nitrogen tank 603 for preventing the evaporation of the liquid helium, a laminated insulation material 605, a power lead 606, a persistent current switch 607, and a regenerative cryogenic refrigerator 100.

[0073] According to the fifth embodiment, a superconducting magnet with excellent long-term reliability can be realized by using a refrigerator with excellent long-term reliability.

[0074] (Sixth embodiment) The nuclear magnetic resonance imaging apparatus of the sixth embodiment includes the refrigerator of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0075] 4 is a cross-sectional view showing a schematic configuration of a nuclear magnetic resonance imaging apparatus according to the sixth embodiment. The nuclear magnetic resonance imaging (MRI) apparatus according to the sixth embodiment is a nuclear magnetic resonance imaging apparatus 700 equipped with the regenerative cryogenic refrigerator 100 according to the third embodiment.

[0076] The nuclear magnetic resonance imaging apparatus 700 includes a superconducting static magnetic field coil 701 that applies a spatially uniform and temporally stable static magnetic field to the human body, a correction coil (not shown) that corrects non-uniformity of the generated magnetic field, a gradient magnetic field coil 702 that applies a magnetic field gradient to the measurement region, a radio frequency wave transmitting / receiving probe 703, a cryostat 705, and a radiation heat insulating shield 706. A regenerative cryogenic refrigerator 100 is used to cool the superconducting static magnetic field coil 701.

[0077] According to the sixth embodiment, a nuclear magnetic resonance imaging apparatus with excellent long-term reliability can be realized by using a refrigerator with excellent long-term reliability.

[0078] (Seventh embodiment) The nuclear magnetic resonance apparatus of the seventh embodiment includes the refrigerator of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0079] 5 is a cross-sectional view showing a schematic configuration of a nuclear magnetic resonance (NMR) apparatus according to the seventh embodiment. The NMR apparatus according to the seventh embodiment is a nuclear magnetic resonance apparatus 800 equipped with the regenerative cryogenic refrigerator 100 according to the third embodiment.

[0080] The nuclear magnetic resonance apparatus 800 includes a superconducting static magnetic field coil 802 that applies a magnetic field to a sample such as an organic substance placed in a sample tube 801, a high-frequency oscillator 803 that applies radio waves to the sample tube 801 in the magnetic field, and an amplifier 804 that amplifies an induced current generated in a coil (not shown) around the sample tube 801. The apparatus also includes a regenerative cryogenic refrigerator 100 that cools the superconducting static magnetic field coil 802.

[0081] According to the seventh embodiment, a nuclear magnetic resonance apparatus with excellent long-term reliability can be realized by using a refrigerator with excellent long-term reliability.

[0082] (Eighth embodiment) The magnetic field application type single crystal pulling apparatus of the eighth embodiment includes the refrigerator of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0083] 6 is a perspective view showing a schematic configuration of a magnetic field application type single crystal pulling apparatus according to the eighth embodiment. The magnetic field application type single crystal pulling apparatus according to the eighth embodiment is a magnetic field application type single crystal pulling apparatus 900 equipped with the regenerative cryogenic refrigerator 100 according to the third embodiment.

[0084] The magnetic field application type single crystal pulling apparatus 900 includes a single crystal pulling section 901 having a crucible for melting raw material, a heater, a single crystal pulling mechanism, etc., a superconducting coil 902 for applying a static magnetic field to the raw material melt, a lifting mechanism 903 for the single crystal pulling section 901, a current lead 905, a heat shield plate 906, and a helium container 907. A regenerative cryogenic refrigerator 100 is used to cool the superconducting coil 902.

[0085] According to the eighth embodiment, a magnetic field application type single crystal pulling apparatus with excellent long-term reliability can be realized by using a refrigerator with excellent long-term reliability.

[0086] (Ninth embodiment) The helium recondensing device of the ninth embodiment includes the refrigerator of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0087] 7 is a schematic diagram showing the general configuration of a helium recondensation apparatus according to the ninth embodiment. The helium recondensation apparatus according to the ninth embodiment is a helium recondensation apparatus 1000 equipped with the regenerative cryogenic refrigerator 100 according to the third embodiment.

[0088] The helium recondensation device 1000 includes a regenerative cryogenic refrigerator 100 , an evaporation pipe 1001 , and a liquefaction pipe 1002 .

[0089] The helium recondensation device 1000 can recondense helium gas that evaporates from a liquid helium device provided in a device that uses liquid helium, such as a superconducting magnet, a nuclear magnetic resonance (NMR) device, a nuclear magnetic resonance imaging (MRI) device, a physical property measurement system (PPMS), or a magnetic property measurement system, to produce liquid helium.

[0090] Helium gas is introduced into the helium recondenser 1000 from a liquid helium device (not shown) through evaporation piping 1001. The helium gas is cooled to 4 K, which is below the liquefaction temperature of helium, by the regenerative cryogenic refrigerator 100. The condensed and liquefied liquid helium returns to the liquid helium device through liquefaction piping 1002.

[0091] According to the ninth embodiment, a refrigerator with excellent long-term reliability is used, thereby realizing a helium recondensing device with excellent long-term reliability.

[0092] The refrigerator of the third embodiment can improve long-term reliability by being used in a magnetic levitation train. [Example]

[0093] Examples and comparative examples of the magnetic regenerator particles of the first embodiment and their evaluation results will be described below.

[0094] Example 1 An Er3Ni master alloy was prepared by high-frequency melting. The Er3Ni master alloy was melted at approximately 800°C, and the molten metal was dropped onto a rotating disk in an Ar atmosphere (pressure approximately 101 kPa) and rapidly solidified. The resulting particles were classified by shape and sieved to obtain Er3Ni spherical particles.

[0095] The Er3Ni spherical particles were subjected to HIP treatment using nitrogen gas as the pressurizing gas at a pressure of 50 MPa and a heat treatment temperature of 600°C.

[0096] The Er3Ni spherical particles of Example 1 had an aspect ratio of 1.1, and the area ratio of voids was 0.0012%.

[0097] In order to evaluate the reliability when the magnetic regenerator particles are filled in a regenerator and a refrigerator is operated, the magnetic regenerator particles of Example 1 are filled in a cylindrical container of φ15 mm and height 5 mm at room temperature, and the container is cooled to a cryogenic temperature, and an amplitude of 2 mm and a maximum acceleration of 400 m / s are measured. 2 Simple harmonic motion of 2×10 9The weight percentage of the regenerator particles that were destroyed after the vibration test was 0.014%.

[0098] The refrigeration capacity of the regenerator material of Example 1 at 4.2 K was evaluated when it was installed in a refrigerator before and after the vibration test. The regenerator was filled at room temperature to create a cryogenic regenerator. A two-stage GM refrigerator was used as the refrigerator, and a Cu mesh was installed in the first-stage regenerator, Pb was installed on the high-temperature side of the second-stage regenerator, and the regenerator was filled with the regenerator material of each Example and Comparative Example at room temperature on the low-temperature side. Note that the regenerator particles after the vibration test included regenerator particles that had been destroyed by the vibration test, and a thermal load was applied to the first-stage regenerator so that the temperature reached 50 K.

[0099] In the following examples and comparative examples, the synthesis conditions of the magnetic regenerator particles and the HIP treatment conditions were adjusted to be appropriate conditions. The vibration test at a very low temperature and the capacity test of the refrigerator were carried out under the same conditions as in Example 1.

[0100] Example 2 Magnetic regenerator particles were produced in the same manner as in Example 1, except that the composition was Er3Co.

[0101] Example 3 Magnetic regenerator particles were produced in the same manner as in Example 1, except that the composition was ErAg.

[0102] Example 4 Magnetic regenerator particles were produced in the same manner as in Example 1, except that the composition was ErNi.

[0103] Example 5 Magnetic regenerator particles were produced in the same manner as in Example 1, except that the composition was HoCu2.

[0104] Example 6 Magnetic regenerator particles were produced in the same manner as in Example 1, except that the composition was HoCu.

[0105] Example 7 Magnetic regenerator particles were produced in the same manner as in Example 1, except that the composition was Ho2Al.

[0106] Example 8 The composition is Dy(Cu 0.5 Si 0.5 Magnetic regenerator particles were produced in the same manner as in Example 1, except that 2) was used.

[0107] Example 9 The composition is Dy(Cu 0.5 Ge 0.5 Magnetic regenerator particles were produced in the same manner as in Example 1, except that 2) was used.

[0108] (Examples 10 to 14) Magnetic regenerator particles were produced in the same manner as in Example 1, except that the gas pressure in the HIP treatment was changed.

[0109] Examples 15 to 20 Magnetic regenerator particles were produced in the same manner as in Example 5, except that the conditions for shape classification, such as the tilt angle and vibration strength, were adjusted.

[0110] (Examples 21 to 24, Comparative Example 3) The magnetic regenerator particles of Example 1 and Comparative Example 3 were used as the regenerator particles filled in the regenerator, and vibration tests and refrigerator tests were carried out using regenerators in which the ratio of these particles was changed.

[0111] (Examples 25 to 27, Comparative Example 4) Vibration tests and refrigerator tests were conducted using magnetic refrigerant particles that exhibit the same properties as Example 5 except for containing particles with a circularity of 0.4 or less, which were obtained by manufacturing in the same manner as Example 5 except for adjusting the shape classification conditions, such as the inclination angle, and using refrigerant units that used the magnetic refrigerant particles of Example 5 and varied their ratios.

[0112] Table 1 shows the weight percentage of broken particles and the refrigeration capacity of the magnetic regenerator particles according to each Example and Comparative Example after the vibration test.

[0113] [Table 1]

[0114] As in Examples 1 to 27, when the ratio of the void area in the cross section of the magnetic regenerator particles is 0.0001% or more, the ratio of particles broken in the vibration test decreases, and the rate of change in the refrigeration capacity of the refrigerator also becomes smaller. This is thought to be because the presence of a certain amount of voids or more suppresses the thermal contraction of the particles, reducing rattling caused by changes in the packing of the particles due to contraction during cooling.

[0115] As in Examples 10 to 14, when the ratio of the void area in the cross section of the magnetic regenerator particle is less than 15%, the ratio of particles broken in the vibration test decreases and the rate of change in the refrigeration capacity of the refrigerator also becomes smaller. This is thought to be because when the voids are below a certain amount, the thermal contraction of the particles is suppressed while the strength of the magnetic regenerator particle is maintained.

[0116] From Table 1, it can be seen that when the particle size of the magnetic regenerator particles is in the range of 50 μm or more and 3000 μm or less, the refrigeration capacity at 4.2 K is significantly improved.

[0117] Table 1 shows that when the aspect ratio of the magnetic regenerator particles is 5 or less, the refrigeration capacity at 4.2K is significantly improved.

[0118] Table 1 shows that when the proportion of magnetic regenerator particles represented by RMz contained in the regenerator, in which the void area ratio is 0.0001% or more and 15% or less, is 70% or more, the proportion of particles destroyed after the vibration test decreases and the extent of decline in refrigeration capacity becomes smaller. Furthermore, when the proportion of magnetic regenerator particles in which the void area ratio is 0.001% or more and 10% or less, is 70% or more, the proportion of particles destroyed after the vibration test further decreases and the extent of decline in refrigeration capacity becomes even smaller.

[0119] Table 1 shows that if the magnetic regenerator particles, represented by RMz, contained in the regenerator contain more than 15% magnetic regenerator particles with a circularity R of 0.4 or less, the proportion of broken particles after the vibration test increases and the refrigeration capacity also decreases.

[0120] From Table 1, it can be seen that even if the composition of the magnetic regenerator particles is different, as long as the void ratio is 0.0001% or more and 15% or less, the particle destruction rate when vibration is applied at extremely low temperatures is low.

[0121] The above examples confirmed the effects of the magnetic regenerator particles of the first embodiment and the regenerator of the second embodiment.

[0122] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. For example, components of one embodiment may be replaced or changed with components of another embodiment. These embodiments and modifications thereof are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0123] 100 Regenerative cryogenic refrigerator 114, 115 Regenerator 118, 119 Cold storage material 500 Cryopump 600 Superconducting Magnet 700 Nuclear Magnetic Resonance Imaging Device 800 Nuclear Magnetic Resonance Spectrometer 900 Magnetic Field Application Type Single Crystal Pulling Apparatus

Claims

1. the intermetallic compound is composed of an intermetallic compound containing a rare earth element represented by RMz (R represents at least one rare earth element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, M represents at least one metal element selected from Ni, Co, Cu, Ag, Ga, Bi, Si, Al, and Ru, and z is a number in the range of 0.001 to 9.0), and the ratio of the area of ​​voids in the particles present in the cross section is 0.0001% or more and 15% or less, and the ratio of particles having an aspect ratio of 1 is 70% or more, When the perimeter of the projected image is L and the actual area of ​​the projected image is A, 4πA / L 2 The magnetic regenerator particles have a circularity R of 0.4 or less, and the ratio of the magnetic regenerator particles is 10% or less.

2. 2. The magnetic regenerator particles according to claim 1, which are granular and have a particle size of 50 [mu]m to 3 mm.

3. A regenerator filled with the magnetic regenerator particles according to claim 1 or 2.

4. A refrigerator comprising the regenerator according to claim 3.

5. A cryopump comprising the refrigerator according to claim 4.

6. A superconducting magnet comprising the refrigerator according to claim 4.

7. A nuclear magnetic resonance imaging apparatus comprising the refrigerator according to claim 4.

8. A nuclear magnetic resonance apparatus comprising the refrigerator according to claim 4.

9. A magnetic field application type single crystal pulling apparatus comprising the refrigerator according to claim 4.

10. A helium recondensing device comprising the refrigerator according to claim 4.

Images