JPH04177065A - Magnetic refrigerator - Google Patents

Abstract

PURPOSE:To put the above refrigerator close to an ideal refrigerating cycle by enlarging the variation of a magnetic flux density in processes of excitation and demagnetization and by the demagnetization at zero magnetic field, by repeating one process wherein a magnetic actuation substance is placed in a strong magnetic field and is excited, and the other process wherein the magnetic actuation substance is inserted or held in a hollow part on a magnetic shield substance and is demagnetized. CONSTITUTION:A magnetic actuation substance 2 exists in a strong magnetic field at the end of the rising thereof and radiates heat by exciting. This heat is cooled until a temperature reaches a definite value by a heat bath 4 on the side of high temperature. After that, when quickly lowered and held in a hollow part 33 on a magnetic shield substance 3, the magnetic actuation substance 2 is adiabatically demagnetized, radiates cold, absorbs heat from a cold bath 5 and cools the cold bath 5. After that, when the magnetic actuation substance 2 is raised and held in the central part of a coil 1 by the escape from the hollow part 33 on the magnetic shield substance 3, heat generation by adiabatic excitation and cooling by the hot bath 4 on the side of the high temperature are performed. By a course of these processes, heat is transferred from the cold bath 5 to the hot bath 4 and the cold bath 5 is cooled.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a magnetic refrigeration system that generates cold in a magnetic working body by interposing a magnetic shield between a magnet for generating a strong magnetic field and a magnetic working body. Regarding machines.

(Prior technology) The adiabatic demagnetization method, which is a conventional cooling method for ultra-low temperature regions, is widely used for research purposes, but magnetic refrigerators using the adiabatic demagnetization method have not yet reached the practical stage for industrial use. This has not yet been achieved. A magnetic refrigerator basically consists of a magnet that generates a large magnetic field, a magnetic working body to be cooled, and an insulated vacuum container that houses the magnetic working body. Nowadays, it is possible to use superconducting wire coils, and while the magnetic flux density of electromagnets is generally limited to 2T, the use of superconducting coils has made it possible to generate strong magnetic fields of 5T or more. It has become possible. In addition, various materials are being considered for the magnetic actuating body, including garnet-type gadolinium/gallium oxide and chromium alum. Methods using gas or liquid, contact heat conduction in solids, and heat pipe methods are being considered.

Magnetic refrigerators require a mechanism to excite and demagnetize the magnetic actuating body. Conventionally, two methods have been used: controlling the generated magnetic field itself by continuously interrupting the current of an electromagnet or superconducting coil, and controlling the generated magnetic field itself under a constant strong magnetic field. There is a method of changing the magnetic flux density in the magnetic actuator by moving the magnetic actuator from a strong magnetic field region to a weak magnetic field area. The method of intermittent coil current is
It is difficult to open and close large currents, and even if superconducting coils are used, large currents flow through the wires connecting the coils to the external power supply and the power supply itself when the current starts and stops, causing Joule heating and freezing. It is only applied to small refrigerators because it reduces the efficiency of the machine, but in ordinary practical refrigerators, it is widely considered to adopt a method in which the magnetic actuating body itself makes reciprocating or rotating motion. ing.

(Problem to be solved by the invention) In the method of moving the magnetic actuating body itself between a strong magnetic field and a zero magnetic field, if a superconducting coil is used as the magnetic field coil, it is possible to maintain a strong magnetic field at all times in persistent current mode. However, it requires a complicated mechanism for reciprocating or rotating the magnetic actuating body, and it is difficult to move the magnetic actuating body into a completely zero magnetic field without crossing the return line of the magnetic field lines from the magnetic field coil during the demagnetization process. In this case, the distance of reciprocating or rotational movement must be significantly large, resulting in a large device. Therefore, the conventional technology was satisfied with a practical moving distance, but in this case, the demagnetization process ends in a residual magnetic field, and the magnetic flux density during the demagnetization process does not become zero, leaving a dissatisfaction in terms of thermal efficiency. was.

In addition, the thermal efficiency of the refrigerator is deteriorated due to the generation of frictional heat in bearings and sliding parts due to mechanical motion.Furthermore, the temperature rise of the magnetic actuating body in the excitation region is reduced by a cooling medium, and a magnetic actuating body in the demagnetization region. As the temperature decreases, it is necessary to circulate the cooling medium, but in this case, the thermal efficiency of the refrigerator inevitably decreases due to leakage of the medium around the rotating or sliding magnetic actuating body.

The present invention was made in view of the above problems, and
The present invention aims to provide a magnetic refrigerator with high thermal efficiency by using a superconducting coil in a constant current mode to fix the magnetic actuating body, or to shorten the moving distance as much as possible if it is moved.

(Means for Solving the Problems) The magnetic refrigerator of the present invention includes a magnet that generates a strong magnetic field, a cylindrical superconducting magnetic shield, a magnetic actuator, and the magnetic actuator or the magnetic shield. It consists of a reciprocating mechanism for reciprocating movement.

The reciprocating mechanism repeats a process in which the magnetic actuating body is excited in the strong magnetic field and a process in which the magnetic actuating body is inserted or housed in the hollow part of the magnetic shield and demagnetized. This is a magnetic refrigerator whose working body generates cold.

The magnet used in the present invention is a ferrous core electromagnet or a permanent magnet when a relatively weak magnetic field of 2T or less is used, but usually a superconducting coil is used at liquid helium temperature. Nb-Ti alloy or Nb
A wire made of a 3Sn compound is used, and a strong magnetic field is constantly generated from the coil in constant current mode.

For the magnetic actuator that generates cold, a material with large changes in magnetic flux density and large entropy changes with respect to temperature changes is used at the operating temperature, but at temperatures below 20 degrees, garnet-type gadolinium gallium oxide is used.
Furthermore, at temperatures above 20°C, the ferromagnetic material 1, for example, Dy
Al2 Aluminum compounds of other rare earth metals RA1
2 etc. can be used.

In order to effectively block the surrounding magnetic field, the magnetic shield has the following characteristics:
A laminate in which superconductor original plates and normal conductor original plates are stacked alternately is preferably used. A magnetic shield made of a superconductor layer needs to be cooled to below a critical temperature under an ambient magnetic field before use, and when a Nb-Ti alloy plate is used, it is immersed in liquefied helium.

The reciprocating mechanism causes the magnetic actuating body to reciprocate;
There is one that makes the magnetic shield move back and forth. In a magnetic cooler that moves a magnetic working body, the magnetic working body is connected to a drive rod of a reciprocating mechanism so as to be movable along the hollow center axis of the superconducting coil, and the magnetic working body is disposed close to the superconducting coil. The magnetic operating body reciprocates between the hollow part of the fixed cylindrical magnetic shield and the strong magnetic field.

Another method is to fix the magnetic actuating body in a strong magnetic field from a superconducting coil, and move the magnetic shield connected to the drive rod of the reciprocating mechanism so that the hollow part of the magnetic shield is connected to the magnetic actuating body. It is designed to move reciprocatingly so that it can be accommodated.

As this reciprocating mechanism, a method of connecting the other end of the drive rod to a rotating crank or a method of connecting it to a piston of a hydraulic cylinder is used, and when the movement stroke is small, a cam mechanism can be used.

In addition, the stroke of the magnetic shield or magnetic actuator is rapid, and it is preferable to delay or rest at both end positions, so a cam mechanism or hydraulic control that rests at both ends of the stroke is adopted. .

The present invention also provides a magnet that generates a strong magnetic field, a cylindrical superconducting magnetic shield placed in the magnetic field, a magnetic actuator placed in a hollow part of the magnetic shield, and a magnetic shield. A magnetic refrigerator comprising a liquid level control mechanism that controls the liquid level of a cooling liquid in which the body is immersed, and the superconducting magnetic shield is permeable to magnetism at a temperature higher than the temperature of the liquid. , a process in which the magnetic actuating body is excited by a part of the magnetic shield being exposed above the liquid surface by the liquid level control mechanism, and a process in which the magnetic shield is immersed in the liquid and the magnetic actuating body is excited. This includes a magnetic refrigerator in which the magnetic operating body generates cold by repeating the process of demagnetizing the body.

The difference from the above-mentioned magnetic refrigerator with a reciprocating mechanism is that the liquid level control mechanism changes the liquid level of the liquid in which the magnetic shield is immersed, usually in the vertical direction, so that the magnetic shield is completely immersed in the liquid. This method realizes a process in which the magnetic shield is cooled, and a process in which the temperature of the magnetic shield increases by exposing a part of it to the vacuum or vapor above the liquid surface. As a control mechanism, the container housing the magnetic shielding body has a siphon structure, and the pressure on the upper surface of the liquid in the container is adjusted. In this system, both the magnetic actuating body and the magnetic shielding body are fixed relative to the magnetic field coil, and no special moving mechanism is required.

In a magnetic refrigerator with a liquid level control mechanism, when liquid helium is used as the liquid in the magnetic shield,
As mentioned above, a laminate of an Nb-Ti alloy annular plate that exhibits superconductivity at the normal pressure boiling temperature of liquid helium and a normal conductor annular plate is used. An alloy composition that exhibits normal conductivity is required.

For both refrigerators with a reciprocating mechanism and refrigerators with a liquid level control mechanism, the magnetic shield is a laminate made by wrapping and forming a strip of a thin layer of superconductor and a thin layer of non-magnetic metal into a cylindrical shape. A sintered body, a powder-molded sintered body of an oxide superconductor, or a sintered body formed by winding and forming a band of an oxide superconductor thin layer and a nonmagnetic metal thin layer into a cylindrical shape is preferably used. The oxide superconductor is Y-Ba-Cu-0 type or B1-5r-C
A u-0 type superconducting material is used, and the magnetic shielding material containing this oxide is used by being immersed in liquid nitrogen or liquid helium.

(Function) In a magnetic refrigerator, a magnetic operating body excited in a strong magnetic field is adiabatically demagnetized by rapidly removing the magnetic field, generates cold, and cools itself. By applying a strong magnetic field, it is adiabatically excited, generates heat, and heats itself. In the present invention, the process of adiabatic demagnetization is applied to the hollow part of the cylindrical magnetic shield. This is achieved by housing the operating body. That is, the third
As shown in the figure, when the cylindrical superconducting laminate 3 is placed in a magnetic field, the magnetic lines of force 9 from the outside do not penetrate into the hollow portion 33 of the superconducting laminate 3, and the magnetic field strength becomes zero. Therefore, by transferring the magnetic actuator in a strong magnetic field to the hollow part of a magnetic shield placed near the strong magnetic field, the demagnetized state of the magnetic actuator can be easily obtained. Magnetic shielding is possible using ferromagnetic materials, but magnetic shields made of ferromagnetic materials cannot completely shield magnetism under magnetic fields as strong as those applied to magnetic refrigerators. This requires a considerably large thickness of the cylinder, and the weight of the magnetic shield itself increases, making it impractical. In the present invention, as shown in FIG. 2, the annular superconductor plate is composed of a cylindrical laminate 3 consisting of an annular superconductor plate 31 and a normal conductor plate 32, and the annular superconductor plate is A closed current that generates its own magnetic field so as to cancel out the invading external magnetic field is passed through the plate surface and its interior.

If we stack these superconductor plates without allowing external magnetic fields to penetrate,
Since the ability to block strong magnetic fields increases, even if this magnetic shield is placed fixedly or movably in a strong magnetic field near the superconducting coil for magnetic field generation, the hollow part A magnetic field can be obtained, thus making it possible to reduce the relative movement distance of the magnetic actuator or the magnetic shield for adiabatic demagnetization. This means that complete demagnetization can be achieved in a completely zero magnetic field, so the refrigeration cycle can be brought closer to the ideal cycle based on magnetothermodynamics, and it is expected that the refrigeration thermal efficiency will be improved. This means that cryogenic temperatures below IK can be practically achieved in refrigerators that operate below IK.

Further, the magnetic refrigerator of the present invention has a reciprocating mechanism for reciprocating the magnetic operating body or the magnetic shielding body, and
As shown in figures c) and d), the magnetic shield 3 is fixed,
By reciprocating the magnetic actuating body 2 between the strong magnetic field and the hollow portion 33 of the magnetic shielding body 3 using the reciprocating mechanism, it is possible to realize alternating changes between adiabatic excitation and adiabatic demagnetization of the magnetic actuating body 2. . Similarly, the magnetic actuating body 2 is fixed in the maximum magnetic field on the central axis of the superconducting coil 1, and the magnetic actuating body is accommodated in the hollow part 33 of the magnetic shielding body 3 and then released. Furthermore, by reciprocating the magnetic shield 3, it is possible to alternate between adiabatic excitation and adiabatic demagnetization.

Next, in the method of controlling the liquid level of the liquid in which the magnetic shield is immersed, when the magnetic shield is completely immersed in the liquid and is at the liquid temperature, the magnetic shield is in a superconducting state. In this case, lines of magnetic force from the magnet do not pass through the hollow part, and the magnetic actuating body fixed in the hollow part is in a demagnetized state.

Next, when the liquid level of the liquid is lowered and a part of the magnetic shield is exposed above the liquid surface and the temperature rises due to receiving radiant heat from the outside, the criticality of the superconductor under the magnetic field strength increases. When the temperature exceeds the temperature, the superconducting state of the magnetic shield changes to the normal conducting state, and the lines of magnetic force penetrate into the hollow part,
The magnetic actuating body inside the hollow part obtains an excited state. When the liquid level is raised again, the magnetic shield is cooled below the critical temperature and restored to the superconducting state, and the magnetic operating body in the hollow is demagnetized again. By the above liquid level operation, the magnetic actuating body can repeat the process of excitation and demagnetization.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 6 shows a superconducting coil 1 cooled with liquid helium, a magnetic shield 3 of a superconducting laminate fixed to the lower part inside the hollow part of the coil 1, and a support rod 71 of an elevating device 7 that can be lifted up and down. As shown in figure a), the magnetic actuator 2 is located at the center of the hollow part of the coil 1 at its upper limit, and the upper surface of the magnetic actuator 2 is located at the center of the hollow part of the coil 1. , is cooled by contacting the surface of the high-temperature side hot bath 4, and as shown in FIG. This is an embodiment in which the cold side heat bath 5 is in contact with the target solid 5 to be cooled. The device itself is housed in a vacuum chamber and is thermally shielded. Further, the high temperature side hot bath 4 is cooled by circulating gaseous helium as a cooling medium between it and a cooler (not shown). In the low temperature side heat bath 5, that is, the cold bath 5,
Sapphire is preferred because of its good thermal conductivity.

At the upper limit, the magnetic actuating body 2 is in a strong magnetic field, is excited, and generates heat, but this heat is cooled down to a constant temperature by the hot bath 4 on the high temperature side. Then, when the magnetic actuating body 2 is rapidly lowered and accommodated in the hollow part 33 of the magnetic shielding body 3, it is adiabatically demagnetized and generates cold, but at the same time it takes away heat from the cold bath 5. The cold bath 5 is cooled. Furthermore,
When the magnetic actuating body 2 rises, escapes the hollow part 33 of the magnetic shield 3, and is accommodated in the center of the coil 1, heat generation due to adiabatic excitation and high-temperature side hot bath 4 occur as described above.
Cooling is performed by Through this series of steps, heat transfer occurs from the cold bath 5 to the hot bath 4, and the cold bath 5 is cooled.

In this magnetic refrigerator, it is desirable that the magnetic actuating body 2 be raised and lowered rapidly, and at the upper and lower limits, a process of stopping the hot bath 4 and the cold bath 5 to ensure contact time is provided. In addition, since a completely zero magnetic field can be obtained at a position close to the superconducting coil 1 where the magnetic field strength is relatively large, the moving distance of the magnetic actuator 2 is short, and the excitation and demagnetization process approaches an ideal adiabatic process. I'm going to give it to you.

FIG. 6C) is an embodiment in which magnetic shielding bodies 3 having an inner diameter comparable to the inner diameter of the coil are arranged coaxially at the lower end of the superconducting coil 1, and in the hollow part of the superconducting coil 1, Since the magnetic shield 3 is not inserted, the inner diameter of the coil can be reduced. Furthermore, there is an advantage that the entire strong magnetic field in the hollow part of the coil 1 can be used for the magnetic actuating body 2. In this example, the low-temperature side heat bath 5 to be cooled is a gaseous helium bath, and the sliding surface in contact with the magnetic actuating body 2 is given flexibility to improve heat transfer, and the gaseous helium is circulated. A pump 6 is provided to equalize the temperature inside the tank.

In FIG. 7, a magnetic actuating body 2 is fixed in a strong magnetic field of a superconducting coil 1, and a superconducting cylindrical magnetic shield 3 can be raised and lowered so that the magnetic actuating body 2 can be accommodated in its hollow part 33. This is an embodiment in which the magnetic actuating body 2 is arranged as follows.
is porous and is housed in a container 21, and helium, which is a cooling medium, passes through the switching valve V1 and piping 23 from the cooler 41 and the cold bath 51 to the inside of the magnetic actuating body 2. A path is provided for the tube to pass through and return from the inside of the container 21 to the cooler 41 and the cold bath 51 via the piping 24 and the switching valve v2.

In Figure a), the magnetic shield 3 is at its lower limit, the magnetic operating body 2 is excited in the strong magnetic field of the coil 1, and the generated heat is transferred to the cooler by the switching valves v1 and V2. 41
The magnetic actuating body 2 is cooled by the circulation of gaseous helium between the two. Next, as shown in FIG.
When raised by a support rod 71 connected to a lifting device, the magnetic actuating body 2 moves into the hollow part 33 of the magnetic shielding body 3.
The magnetic actuating body 2 is housed in the magnetic body, is demagnetized, and generates cold. However, by switching the switching valves ■1 and ■2, gaseous helium is circulated between the magnetic actuating body 2 and the cold bath type 1 to cool it. The cold bath 51 for the desired purpose is cooled.

FIG. 8 shows that the magnetic operating body 2 fixed inside the superconducting coil 1 is arranged and fixed concentrically in the hollow part 33 of the magnetic shield 3, and the superconducting magnetic shield 2 is immersed in the liquid. An embodiment of a magnetic refrigerator is shown in which the liquid level 35 is controlled to excite and demagnetize the magnetic actuating body 2. Figure a) shows the closed container 34 housing the magnetic shield 3 and the superconductor 3. It communicates with the closed container 14 housing the coil 1 at its lowest part, and pipes 18 and 38 are connected to the containers 14 and 34 from the top, respectively, and a slight pressure difference is generated through the switching valve 61. High pressure side piping 39 and low pressure side piping 19 set
It is connected to the. The same container 14.34 is filled with five liquids, leaving an appropriate space at the top.

50 on the superconductor plate 31 constituting the magnetic shield 3.
%Nb-50%Ti alloy, helium can be used as the liquid, and in this case, it is superconducting at a temperature below the boiling point of helium and in a high magnetic field, so the boiling point is lower than the boiling point of helium. It becomes normal conductive even at a temperature only 2 to 3 times higher than the temperature.

FIG. 8a) shows that the liquid helium in the container 34 of the magnetic shield 3 completely covers the magnetic shield 3, and the liquid level is almost at the same level as the other superconducting coil 1. Since the magnetic shielding body 3 is cooled by the liquid and is in a magnetic shielding state, the magnetic operating body 2 is demagnetized. Next, as shown in Figure b), when the pipe 38 is set to the high pressure side by the switching valve 61, the liquid level in the container 34 of the magnetic shield 3 is lowered, and the liquid helium is transmitted through the communication part 16. The liquid level 15 on the side of the container 14 of the coil 1 is raised, but as a result, the upper half of the magnetic shield 3 is exposed from the liquid level 35 and is heated by radiant heat from the surroundings, raising the critical temperature. If it exceeds the magnetic field, the superconductivity is lost, and the magnetic field lines from the coil penetrate the exposed magnetic shield 3,
The magnetic actuating body 2 in the hollow portion 33 is excited.

As described above, by operating the switching valve 61, the liquid level 35 of the container 34 of the magnetic shield 3 is controlled, and the magnetic shield 3 is
By repeating exposing and dipping the upper part of the magnetic actuating body, the excitation and demagnetization of the magnetic actuating body can be repeated.

In this embodiment, the magnetic actuator 2 is immersed in liquid helium in a container 21, and a super leak 25 through which only superfluid helium passes is interposed in the lower part of the container, and a cold bath 27 is provided. is connected. When the magnetic actuating body 2 is excited, the liquid helium evaporates, is cooled by latent heat, and is maintained at approximately 4.1 K under atmospheric pressure, and in the next adiabatic demagnetization process, the liquid helium is rapidly evaporated. When the liquid helium cools and reaches a temperature of 2, only the superfluid helium in the liquid helium passes through the super leak 25.
The equilibrium temperature of this superfluid helium, housed in the container of the cold bath 26, is 1.9. That is, the magnetic refrigerator constantly obtains a cold bath temperature of 1.9 K from the boiling point temperature of 4.1 K of the liquid helium containing the magnetic working body 2.

In the above embodiment, a laminate of an annular superconductor plate 31 and a normal conductor plate 32 is used as the magnetic shield 3, but a superconductor band and a normal conductor band are used. It can also be carried out using a superconducting cylindrical body formed by winding bonded strips into a cylindrical shape.

FIG. 4 shows an example of a layered body in which layers of a superconductor 31 and a normal conductor 32 are wound coaxially around a cylindrical axis to form a cylindrical body, and the magnetic force M9 perpendicular to the cylindrical axis is Since the magnetic lines of force 9 do not bypass the cylindrical body and penetrate into the hollow portion 33,
The magnetic field strength becomes zero, and it can be used as a demagnetizing space for the magnetic actuating body 2. In addition, Y-Ba-Cu is added to the superconductor.
If a sintered body of -0 series oxide is used, a refrigerator that operates at liquid nitrogen temperature is also possible, and with the advent of room temperature superconductors, a refrigerator for room temperature operation is also possible.

Figure 5 shows two coils 1, 1 whose central axes coincide.
' is placed to create a strong magnetic field, and in the magnetic field, the magnetic actuating body 2 and the magnetic shielding body 3 shown in FIG. 4 are placed,
In Figure a), the magnetic shielding body 3 is fixed in a weak magnetic field position away from the central axis between the two coils 1°1', and the magnetic actuating body 2 is placed between the two coils 1, 1'. The magnet is excited on the central axis of the magnetic shield 3, and then, as shown in FIG.

In Fig. 5C), the magnetic operating body 2 is fixed at an intermediate position on the center axis of both coils 1 and 1' and is excited, and then, as shown in Fig. 5D), the magnetic stepping body 3 is moved to demagnetize the magnetic operating body 2 so as to be accommodated in the hollow part 33, and if the magnetic shielding body 3 is repeatedly raised and lowered by the lifting mechanism, it becomes a magnetic refrigerator. . If two coils are coaxially arranged in parallel, the magnetic field passing through the inner diameter of the two coils will be stabilized.In particular, if a Helmholtz coil is arranged, the magnetic field strength between the coils will be approximately constant, and the above It is advantageous to use a layered superconducting magnetic shield coaxially wound around a cylindrical shaft.

(Effects of the Invention) By implementing the magnetic refrigerator of the present invention, the following effects can be achieved.

1) A magnetic shield is a laminate of a superconductor plate and a normal conductor plate, and even if the external magnetic field is strong, the magnetic field lines do not penetrate into the hollow part and the magnetic field becomes zero. Because I can,
The magnetic actuating body excited in the magnetic field generated by the superconducting coil can be inserted into the hollow part of the magnetic shield and completely demagnetized. Therefore, the amount of change in magnetic flux density during the excitation and demagnetization process is large and zero. By demagnetizing with a magnetic field, the cooling cycle can be approximated to an ideal one, resulting in high thermal efficiency of the refrigerator. Furthermore, the magnetic shielding body can be movably arranged inside the superconducting coil, making it possible to shorten the reciprocating distance of the magnetic shielding body or the magnetic working body during the excitation-demagnetization process as much as possible. The machine itself can be made smaller and lighter.

2) Due to the complete shielding effect of the magnetic shield, the superconducting coil can be used in persistent current mode, and there is no power loss due to intermittent coil current, and the amount of heat absorbed by the zero magnetic field is large during the demagnetization process. Since it can be secured, a magnetic refrigerator with high thermal efficiency can be realized. Also, since it is possible to use a magnetic actuator with a relatively large volume,
Achieves high cooling power.

3) Control the liquid level of the immersion liquid of the superconducting magnetic shield,
In a refrigerator that repeatedly excite and demagnetize the magnetic operating body by cooling and heating the magnetic shield, there are no moving mechanical parts other than the valve for controlling the liquid level, and the refrigerator is Since it operates extremely quietly, it is highly useful as a cooling section for precision equipment.

[Brief explanation of drawings]

Figures 1 (a), (b) and (c) and (d) are conceptual cross-sectional views of the present magnetic refrigerator, and Figure 2 is a perspective view of the magnetic shield used in the present magnetic refrigerator. 3 is a magnetic field line diagram showing the behavior of the external magnetic field in the vicinity of the magnetic shield, and FIG. 4 is an external magnetic field line distribution diagram of the magnetic shield layered coaxially around the central axis. FIG. 5 is a view similar to FIG. 1 of a refrigerator according to another embodiment, and FIG. 6 is a sectional view of a magnetic refrigerator according to an embodiment of the present invention. Figure 7 shows the state in which the magnetic actuator is at the upper limit and is excited, the figure (b) shows the state in which the magnetic actuator is at the lower limit and is demagnetized, and Figure 7 shows the state in which the magnetic shield is movable. FIG. 8 shows a sectional view of a magnetic refrigerator of a type that controls the liquid level of a cooling liquid in a magnetic shield. (Explanation of symbols) 1... Superconducting coil, 2... Magnetic operating body, 3...
Magnetic shield, 4... High temperature side heat bath, 5... Low temperature side heat bath,
6...Circulation pump, 7...Elevating device. one or more one

Claims (1)

[Scope of Claims] 1. Consisting of a magnet that generates a strong magnetic field, a cylindrical superconducting magnetic shield, a magnetic operating body, and a reciprocating mechanism that reciprocates the magnetic operating body or the magnetic shield, By repeating a process in which the magnetic actuating body is excited in the strong magnetic field by the reciprocating mechanism, and a process in which the magnetic actuating body is inserted or housed in the hollow part of the magnetic shielding body and demagnetized, A magnetic refrigerator in which the magnetic operating body generates cold. 2. A magnet that generates a strong magnetic field, a cylindrical superconducting magnetic shield placed in the magnetic field, a magnetic actuator placed in the hollow part of the magnetic shield, and a magnetic shield in which the magnetic shield is immersed. a liquid level control mechanism for controlling the liquid level of the cooling liquid; the superconducting magnetic shield is permeable to magnetism at a temperature higher than the temperature of the liquid; , a process in which a part of the magnetic shield is exposed from the liquid surface to excite the magnetic actuating body, and a process in which the magnetic shield is immersed in the liquid to demagnetize the magnetic actuator. A magnetic refrigerator in which the magnetic operating body generates cold by repeating . 3. The magnetic refrigerator according to claim 1 or 2, wherein the cylindrical superconducting magnetic shield is a laminate of a superconducting ring plate exhibiting superconductivity and a ring plate exhibiting normal conductivity or insulation. 4. The magnetic material according to claim 1 or 2, wherein the cylindrical superconducting magnetic shield is a laminate formed by winding and forming a strip of a superconductor thin layer and a nonmagnetic metal thin layer into a cylindrical shape. refrigerator,. 5. The cylindrical superconducting magnetic shield is formed by winding and molding a powder-molded sintered body of an oxide superconductor or a strip of a thin oxide superconductor layer and a thin nonmagnetic metal layer into a cylindrical shape. The magnetic refrigerator according to claim 1 or 2, which is a sintered body.