Magnetic refrigeration device and magnetic refrigeration method

Abstract

To provide a magnetic refrigeration device which suppresses an accumulated magnetic energy loss and reduces an induction voltage in an excitation / demagnetization process of a magnetic working material, and a magnetic refrigeration method.SOLUTION: A magnetic refrigeration device comprises: a magnetic working material having a magneto-caloric effect; a main superconducting electromagnet which applies a magnetic field to the magnetic working material; a sub superconducting electromagnet which is magnetically coupled with the main superconducting electromagnet; a current source which is connected to the main superconducting electromagnet; a heat exhaust mechanism which exhausts heat of the magnetic working material and performs heat exchange; and a control section which controls operations of the current source and the heat exhaust mechanism. The control section controls the operation of the current source so as to control the timing, magnitude and direction of flow of a current to each of the main superconducting electromagnet and the sub superconducting electromagnet and controls the operation of the heat exhaust mechanism so as to control the timing of heat exhaust and heat exchange of the magnetic working material.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a magnetic refrigeration apparatus and a magnetic refrigeration method. [Background technology]

[0002] When a magnetic field applied to a magnetic material at a certain temperature is increased or decreased, the temperature of the material changes due to an increase or decrease in entropy resulting from the magnetic moment. This is called the magnetocaloric effect; increasing the temperature allows it to be used as a heating device, and decreasing the temperature allows it to be used as a cooling device. In particular, refrigeration technology that applies the magnetocaloric effect is called magnetic refrigeration. Compared to refrigeration technology that achieves heat removal through a cycle involving the compression and expansion of refrigerant gas, magnetic refrigeration does not require a compressor or allows for the miniaturization of mechanical drive mechanisms, which is expected to solve problems related to noise and vibration, realize smaller devices, reduce labor, and improve maintainability.

[0003] Known methods of creating a low-temperature environment using magnetic refrigeration include adiabatic demagnetization refrigeration (ADR), Carnot magnetic refrigeration (CMR), and active magnetic regenerative refrigeration (AMRR).

[0004] In all of these magnetic refrigeration methods, the cooling effect is achieved by reducing the magnetic field felt by the magnetic material. Magnetic refrigeration systems are classified into mechanically driven magnetic refrigeration systems, which increase or decrease the magnetic field by mechanically changing the relative positions of the magnet and magnetic material, and static systems, which increase or decrease the magnetic field by energizing or demagnetizing an electromagnet without changing the relative positions of the magnet and magnetic material. In the latter system, to achieve practically effective refrigeration capacity, a strong magnetic field of several tesla must be demagnetized in a matter of seconds, which is technically difficult.

[0005] For example, in ADR, an excited superconducting magnet is demagnetized by connecting it in series with an external resistor and discharging it. This method is effective for obtaining low temperatures instantaneously, as in ADR, but when considering steady-state operation such as in a refrigerator (a device that generates or maintains low temperatures through a thermodynamic cycle), the energy lost each time the magnet discharges cannot be ignored from the perspective of refrigeration efficiency. On the other hand, regenerating stored magnetic energy requires a larger power supply and dedicated equipment, which increases costs. In other words, one of the challenges for practical use of refrigerators using magnetic refrigeration (magnetic refrigerators) is to obtain changes in the magnetic field applied to the magnetic material without losing the stored magnetic energy of the superconducting magnet as heat energy.

[0006] To address these issues, a method has been devised for demagnetizing a magnetic body by generating a steady strong magnetic field space using a superconducting magnet or the like, placing the magnetic body in this strong magnetic field space, and then using a magnetic shield to cancel out the magnetic field acting on the magnetic body (see, for example, Patent Documents 1 to 4).

[0007] According to Patent Documents 1 to 4, in all cases, a magnetic shield is placed between a superconducting magnet and a magnetic body, and the magnetic body is demagnetized by inserting and rotating the magnetic shield into the magnetic shield. However, these methods have the disadvantage that a complex driving mechanism and a large driving force are required to move the magnetic shield in a strong magnetic field.

[0008] A demagnetization method has been devised that reduces energy loss by preparing multiple superconducting magnets and using electrical means to use the energy discharged during demagnetization to excite other superconducting coils (see, for example, Patent Document 5). This method is completely electrical and does not have any driving parts, so it can significantly reduce energy loss and is also easy to maintain. However, when considering operation in a practical refrigeration cycle (a cycle of about a few seconds), the problem remains that electrical insulation with a considerable voltage resistance (equivalent to or greater than kilovolts) is required to prevent insulation breakdown due to the large induced voltage that occurs when the superconducting coils are excited or demagnetized.

[0009] When a superconducting magnet quenches, a sudden local temperature rise can cause the superconducting conductor to burn out or its characteristics to deteriorate. Therefore, measures to prevent such irreversible malfunctions are required, which are called quench protection. One quench protection technique is to rapidly demagnetize a quenched superconducting magnet. According to Non-Patent Document 1, a method has been considered in which a sub-coil magnetically coupled to the main magnetic field coil is used to rapidly reduce the current value of the main magnetic field coil through electromagnetic induction. However, there have been no reports on further applications of this technology. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 04-177065 [Patent Document 2] Japanese Patent Application Publication No. 04-240361 [Patent Document 3] Japanese Patent Application Publication No. 04-273956 [Patent Document 4] Japanese Patent Application Publication No. 06-151983 [Patent Document 5] Japanese Patent Publication No. 2022-068403 [Non-patent literature]

[0011] [Non-Patent Document 1] Shinnosuke Matsunaga, "Study on low-melting-point metal-impregnated uninsulated high-temperature superconducting coils and their quench protection", SOKENDAI No. 2392, Graduate School of Physical Sciences, 10, Department of Nuclear Fusion Science, 2023-03-24 Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic refrigeration apparatus and a magnetic refrigeration method that suppress the loss of accumulated magnetic energy and reduce induced voltage during the excitation and demagnetization process of a magnetic working material. [Means for solving the problem]

[0013] The magnetic refrigeration device according to the present invention for cooling a body to be cooled comprises a magnetic working material having a magnetocaloric effect, at least one main superconducting electromagnet that applies a magnetic field to the magnetic working material, at least one auxiliary superconducting electromagnet that is magnetically coupled to the at least one main superconducting electromagnet, a current source connected to the at least one main superconducting electromagnet, a heat dissipation mechanism that dissipates heat from the magnetic working material and exchanges heat, and a control unit that controls the operation of at least the current source and the heat dissipation mechanism, wherein the control unit controls the operation of the current source to control the timing, magnitude, and direction of current flow to each of the at least one main electromagnet and the at least one auxiliary superconducting electromagnet, and controls the operation of the heat dissipation mechanism to control the timing of heat dissipation and heat exchange of the magnetic working material, thereby solving the above-mentioned problem. The control unit may control the operation of the current source and the heat dissipation mechanism to pass a current through the at least one main superconducting electromagnet, apply a magnetic field to the magnetic working material, raise the temperature of the magnetic working material, dissipate heat from the magnetic working material using the heat dissipation mechanism, increase or decrease the current passed through the at least one main superconducting electromagnet and at least one auxiliary superconducting electromagnet magnetically coupled to the at least one main superconducting electromagnet so as to reduce the magnetic field applied to the magnetic working material, lower the temperature of the magnetic working material, maintain the current passed through the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet, and exchange heat between the magnetic working material and the cooled body. The control unit may further control the operation of the current source and the heat dissipation mechanism to increase or decrease the current flowing through the at least one main superconducting electromagnet and the at least one sub-superconducting electromagnet so as to increase the magnetic field applied to the magnetic working material, raise the temperature of the magnetic working material, maintain the current flowing through the at least one main superconducting electromagnet and the current flowing through the at least one sub-superconducting electromagnet, dissipate heat from the magnetic working material using the heat dissipation mechanism, lower the temperature of the magnetic working material, exchange heat with the cooled body, raise the temperature of the magnetic working material, and repeat the following in this order: The at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet may have a hollow cylindrical shape and be stacked. The at least one main superconducting electromagnet and the at least one secondary superconducting electromagnet may have a hollow cylindrical shape, and the at least one main superconducting electromagnet and the at least one secondary superconducting electromagnet may be positioned concentrically. The current source may be selected from the group consisting of a DC power supply, a bidirectional power supply, a regenerative power supply, and a flux pump device. The control unit may further include a control device electrically connected to the current source and the heat dissipation mechanism, and a control circuit electrically connected to the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet. The control circuit may include an element selected from the group consisting of a discharge resistor, a switch, a diode, and combinations thereof, and may discharge the stored magnetic energy of the at least one main superconducting electromagnet and the at least one secondary superconducting electromagnet. The at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet may each be selected from the group consisting of a superconducting coil with inter-turn insulation, an uninsulated superconducting coil, a partially uninsulated superconducting coil, and combinations thereof. The heat dissipation mechanism may further include a pre-cooling stage that dissipates heat from the magnetic working material, and a heat exchanger that dissipates heat from the pre-cooling stage. The magnetic refrigeration method for cooling a body to be cooled according to the present invention includes passing a current through the at least one main superconducting electromagnet, applying a magnetic field to the magnetic working material, and raising the temperature of the magnetic working material; dissipating heat from the magnetic working material using a heat dissipation mechanism; increasing or decreasing the current passed through the at least one main superconducting electromagnet and at least one auxiliary superconducting electromagnet magnetically coupled to the at least one main superconducting electromagnet so as to reduce the magnetic field applied to the magnetic working material, thereby lowering the temperature of the magnetic working material; maintaining the current passed through the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet, and exchanging heat between the magnetic working material and the body to be cooled, thereby solving the above-mentioned problem. Following the heat exchange with the cooled body, the method may further include increasing or decreasing the current flowing through the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet so as to increase the magnetic field applied to the magnetic working material, thereby raising the temperature of the magnetic working material; maintaining the current flowing through the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet, discharging heat from the magnetic working material using the heat dissipation mechanism, lowering the temperature of the magnetic working material, exchanging heat with the cooled body, raising the temperature of the magnetic working material, and discharging heat from the magnetic working material using the heat dissipation mechanism, in this order. [Effects of the Invention]

[0014] The magnetic refrigeration apparatus of the present invention comprises a magnetic working material having a magnetocaloric effect, a main electromagnet that applies a magnetic field to the magnetic working material, and a sub-electromagnet that is magnetically coupled to the main electromagnet, without any mechanical drive unit. It also comprises a current source connected to these elements, a heat dissipation mechanism that dissipates heat from the magnetic working material and exchanges heat, and a control unit that controls the operation of at least the current source and the heat dissipation mechanism. The control unit controls the operation of the current source to control the timing, magnitude, and direction of current flow to the electromagnets, the operation of the heat dissipation mechanism to control the timing of heat dissipation and heat exchange from the magnetic working material, and the opening and closing of switches. The control unit controls the timing, magnitude, and direction of current flow to the magnetically coupled main electromagnet and sub-electromagnet, thereby inducing induced voltages and induced currents through electromagnetic induction, and exchanging energy as magnetic energy between the main electromagnet and sub-electromagnet. As a result, losses associated with the process of converting stored magnetic energy into other forms of energy can be reduced. Furthermore, by minimizing induced voltages, large induced voltages due to high-speed operation can be suppressed. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart showing the steps of the magnetic refrigeration method of the present invention. [Figure 2] Schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention. [Figure 3] Another schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention. [Figure 4] 1 is a flow chart illustrating further steps of the magnetic refrigeration method of the present invention. [Figure 5] Another schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention. [Figure 6] Another schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention. [Figure 7] Schematic diagram showing a magnetic refrigeration device of the present invention. [Figure 8] Schematic diagram showing another arrangement of the main electromagnet and the auxiliary electromagnet [Figure 9] Circuit diagram showing the magnetic refrigeration device of Example 1 DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Like elements are designated by like numbers and their description will be omitted. The present inventors discovered that by using a main superconducting electromagnet (hereinafter simply referred to as the main electromagnet) that applies a magnetic field to a magnetic working material and a secondary superconducting electromagnet (hereinafter simply referred to as the secondary electromagnet) that is magnetically coupled to it, energy can be transferred as magnetic energy between the main electromagnet and the secondary electromagnet, creating a space in which the magnetic field increases and decreases, and they came up with the magnetic refrigeration apparatus and magnetic refrigeration method of the present invention.

[0017] FIG. 1 is a flowchart showing the steps of the magnetic refrigeration method of the present invention. FIG. 2 is a schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention. FIG. 3 is another schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention.

[0018] As described above, the magnetic refrigeration method of the present invention uses at least one main electromagnet 210 (FIG. 2) and at least one sub-electromagnet 220 (FIG. 2) magnetically coupled thereto, applies a magnetic field to a magnetic working material 230 (FIG. 2) to lower its temperature, and cools an object to be cooled 240 (FIG. 2) by heat exchange with the magnetic working material 230. The object to be cooled 240 applicable to the present invention may be a sample to be measured or a gas to be cooled (nitrogen, hydrogen, etc.).

[0019] The magnetic working material 230 may be any magnetic material that undergoes a paramagnetic-ferromagnetic transition when acted upon by an applied magnetic field, and may be a material having a magnetocaloric effect, and may be appropriately selected from known materials depending on the temperature range to which the cooled object 240 is to be cooled. For example, gadolinium may be selected for the magnetic working material 230 at room temperature, and holmium aluminum may be selected when hydrogen liquefaction (20 K) is to be achieved. Alternatively, a combination of these materials may be used depending on the temperature range to be cooled. Such a design can be easily accomplished by one skilled in the art.

[0020] 1 shows the steps of the magnetic refrigeration method of the present invention. Step S110: A current is applied to at least one main electromagnet 210 to apply a magnetic field to the magnetic working material 230, thereby increasing the temperature of the magnetic working material 230. Step S120: Heat is removed from the magnetic working material 230 by the heat removal mechanism. Step S130: The current flowing through at least one main electromagnet 210 and at least one sub-electromagnet 220 magnetically coupled to the at least one main electromagnet 210 is increased or decreased so as to reduce the magnetic field applied to the magnetic working material 230, thereby decreasing the temperature of the magnetic working material 230. Step S140: The current flowing through at least one main electromagnet 210 and the current flowing through at least one sub-electromagnet 220 are maintained, and heat is exchanged between the magnetic working material 230 and the body 240 to be cooled.

[0021] According to the present invention, the total amount of stored magnetic energy in the main electromagnet and the sub electromagnet becomes substantially constant through the above-mentioned step S130, and the magnetic working material 230 can be cooled while suppressing loss of stored magnetic energy and induced voltage.

[0022] Each step will be explained in detail. Steps S110 and S120 correspond to state I in Figures 2 and 3. In particular, when a current I is applied to the main electromagnet 210, main When the current I (FIG. 3) is passed through the magnetic field indicated by the solid arrow, a magnetic field B (FIG. 3) is generated, and the magnetic working material 230 is applied with the magnetic field B, and the magnetic working material 230 is excited. main 2 and 3, the magnitude of the current I is not particularly limited as long as the magnetic working material 230 is excited. sub However, there is no particular restriction. At this time, the total stored magnetic energy W total is expressed by the following equation: W total =W main +W sub +W couple =0.5×L main ×(I main ) 2 +0.5×L sub ×(I sub )2 +M×I main ×I sub

[0023] where W main is the stored magnetic energy of the main electromagnet 210, and W sub is the stored magnetic energy of the secondary electromagnet 220, and W couple is the stored magnetic energy resulting from magnetic coupling. L main is the self-inductance of the main electromagnet 210, and L sub is the self-inductance of the secondary electromagnet 220, and I main is the current in the main electromagnet 210, and I sub is the current of the secondary electromagnet 220, and M is the mutual inductance between the main electromagnet 210 and the secondary electromagnet 220. However, M is a positive value in the summation connection and a negative value in the differential connection. Note that the following explanation is for the summation connection.

[0024] In the above formula, I sub is zero, so W total ≒0.5×L main ×(I main ) 2 The stored magnetic energy W of the main electromagnet 210 main (Fig. 2, Fig. 3) are W main =0.5×L main ×(I main ) 2 Therefore, the stored magnetic energy W stored in the main electromagnet 210 is main and the total stored magnetic energy W total The relationship between total =W main This becomes:

[0025] Also, the induced voltage V of the main electromagnet 210 main (Figure 3) is L main ×(dI main / dt)+M×(dI sub / dt), and the induced voltage V sub (Figure 3) is L sub ×(dI sub / dt)+M×(dI main / dt). Here, the induced voltage V main and V sub are both zero.

[0026] Here, heat is dissipated from the magnetic working material 230 by a heat dissipation mechanism. Well-known methods such as a solid type and a fluid type can be used as the heat dissipation mechanism. For example, a gas gap type heat switch or a superconducting heat switch can be used as the solid type, and the heat is dissipated by bringing a pre-cooling stage (for example, the pre-cooling stage 731 in FIG. 7) into thermal contact with the magnetic working material 230. For example, for a fluid type, the heat is dissipated by spraying hydrogen gas or helium gas onto the magnetic working material 230 or by water cooling. This lowers the temperature of the magnetic working material 230, so that the temperature of the magnetic working material 230 can be lowered below that of the initial state by step S130, which will be described later. In state I, the temperature T of the magnetic working material 230 is mag is the temperature T of the cooled body 240 obj That is, the degree of heat removal in step S120 is not limited as long as the temperature of the magnetic working material 230, which was increased in step S110, is reduced.

[0027] Note that steps S110 and S120 may be performed simultaneously, or step S120 may be performed after step S110. Furthermore, while the magnetic working material 230 is being evacuated, the currents flowing through the main electromagnet 210 and the sub-electromagnet 220 are maintained at the values ​​of step S110.

[0028] Step S130 corresponds to the state II in FIGS. 2 and 3. The current I main (FIG. 3) is gradually reduced, and the current I sub 3 (solid line in FIG. 3 ) is gradually increased. As a result, the stored magnetic energy of the main electromagnet 210 is transferred to the sub-electromagnet 220 by electromagnetic induction, and a magnetic field is generated in the sub-electromagnet 220 indicated by the dotted arrow in FIG. 2(B), while the magnetic field generated by the main electromagnet 210 indicated by the solid arrow is reduced. As a result, the magnetic field B applied to the magnetic working material 230 in step S110 is reduced, and the temperature T mag decreases.

[0029] current I main may be reduced to zero or may be flowed in the opposite direction to step S110 until the magnetic working material 230 is demagnetized. main and L sub When the magnitudes L are the same, the current I main Until I sub When increasing the current I main Only the current equivalent to 2 × M / L times I sub Also, the current I sub There is no particular limitation on the size of the secondary electromagnet 220 as long as it can generate a magnetic field.

[0030] Again, the total stored magnetic energy W total satisfies the above equation, but I main With the decrease of the stored magnetic energy W of the main electromagnet 210 main decreases, and the I due to magnetic coupling sub With the increase of M, the stored magnetic energy M×I main ×I sub This results in the total stored magnetic energy W generated in step S110. total can be maintained substantially constant.

[0031] In Figure 2(B), the stored magnetic energy M×I main ×I sub W cоuple It is expressed as W total ≒W main +W cоuple +W sub By satisfying the above, the stored magnetic energy W of the main electromagnet 210 in state I main A part of the stored magnetic energy W of the secondary electromagnet 220 is generated by magnetic coupling. sub 2, the magnetic field applied to the magnetic working material 230 is reduced as the magnetic field moves from the magnetic working material 230 to the magnetic working material 230.

[0032] Also, the induced voltage V of the main electromagnet 210 main is V main =V mainL +V mainM=L main ×(dI main / dt)+M×(dI sub / dt), and the induced voltage V sub is V sub =V subL +V subM =L sub ×(dI sub / dt)+M×(dI main / dt), resulting in a smaller induced voltage. Here, V mainL , V mainM , V subL and V subM represent the self-induction voltage of the main electromagnet 210, the mutual induction voltage of the main electromagnet 210, the self-induction voltage of the secondary electromagnet 220, and the mutual induction voltage of the secondary electromagnet 220, respectively.

[0033] Step S140 corresponds to state III in Figures 2 and 3. In detail, the current I flowing through the main electromagnet 210, which was reduced in step S130, main (FIG. 3), and the current I flowing through the secondary electromagnet 220 increased in step S130 sub While maintaining the temperature T (solid line in FIG. 3), the object to be cooled 240 exchanges heat with the magnetic working material 230. As a result, the temperature T obj The temperature T mag rises, and the object to be cooled 240 can be cooled.

[0034] In FIG. 2(C), the magnetic field of the secondary electromagnet 220 (dotted arrow in FIG. 2) increases, and the current I main becomes a value smaller than that in step S110, zero, or a negative value, and the magnetic field applied to the magnetic working material 230 decreases (although it is demagnetized in FIG. 2(C) and FIG. 3, it is not limited to this). Also, the stored magnetic energy W of the main electromagnet 210 in state II main The total of the stored magnetic energy W of the secondary electromagnet 220 sub and the stored magnetic energy W total ≒W sub It shows how W cоuple =M×I main ×I subHowever, here, I main = 0, so W cоuple = 0. In this way, steps S110 to S130 achieve a magnetic field change with reduced loss of magnetic energy.

[0035] In FIG. 2(C), the stored magnetic energy W main All of the above is transferred to the auxiliary electromagnet 220, but this is not limited to this. total ≒W main +W sub As long as the above condition is satisfied, the stored magnetic energy W of the main electromagnet main If a larger change in the magnetic field is required, the current I main 2 in the direction opposite to the direction of state I in FIG. 2 to cancel the magnetic field created by the secondary electromagnet 220.

[0036] In step S110 and in state I of FIG. 2(A), the secondary electromagnet 220 does not generate a magnetic field, but this is not limited thereto and the secondary electromagnet 220 may generate a magnetic field.

[0037] A well-known method can be used to exchange heat between the magnetic working material 230 and the object to be cooled 240 in step S140. For example, heat exchange can be achieved by bringing the magnetic working material 230 and the object to be cooled 240 into thermal contact via a thermal switch.

[0038] 2 and 3, the explanation has been given for the summation connection, but in the differential connection, the current I sub In other words, in the case of a differential connection, as shown by the dotted line in FIG. sub Then, in step S130, a current I sub is gradually decreased, and in step S140, the current I sub In this case, the stored magnetic energy W total remains substantially unchanged and the induced voltage is also reduced.

[0039] In this way, by performing steps S110 to S140, it is possible to suppress the loss of stored magnetic energy and minimize the induced voltage while cooling the magnetic working material 230, and by heat exchange, cool the object to be cooled 240. Although steps S110 to S140 are a single-shot cooling operation, the above steps may be repeated to perform continuous cooling, as shown in Figs.

[0040] FIG. 4 is a flow chart illustrating further steps of the magnetic refrigeration method of the present invention. FIG. 5 is another schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention. FIG. 6 is another schematic diagram illustrating the principle of the magnetic refrigeration method of the present invention.

[0041] FIG. 4 is performed following step S140 in FIG. Step S150: The current flowing through at least one main electromagnet 210 and at least one sub-electromagnet 220 is increased or decreased so as to increase the magnetic field applied to the magnetic working material 230, thereby increasing the temperature of the magnetic working material 230. Step S160: The current flowing through at least one main superconducting electromagnet 210 and the current flowing through at least one sub-superconducting electromagnet 220 are maintained, and heat is removed from the magnetic working material 230 by the heat removal mechanism. Step S170: Reducing the temperature of the magnetic working material 230 (Step S130), exchanging heat with the cooled body 240 (Step S140), increasing the temperature of the magnetic working material 230 (Step S150), and dissipating heat from the magnetic working material 230 (Step S160) are repeated in this order.

[0042] According to the present invention, by performing the above-described steps S110 to S170, the cooling and temperature increase of the magnetic working material 230 can be repeated while suppressing the loss of the stored magnetic energy of the main electromagnet 210, thereby continuously cooling the object to be cooled 240.

[0043] Steps S110 to S130 are as described above, and therefore the explanation will be omitted. Steps S150 and S160 correspond to state IV in FIGS. 5 and 6. Here, too, the description will be given as a summing connection. More specifically, the current I main (FIG. 6) is gradually increased, and the current I sub 5B, the magnetic field generated by the main electromagnet 210, indicated by the solid arrow, increases, and the magnetic field B applied to the magnetic working material 230 also increases, causing the temperature T mag The current I main The magnitude of the magnetic field is not particularly limited as long as the magnetic working material 230 is excited.

[0044] Again, the total stored magnetic energy W total satisfies the above equation, but I main With the increase of main increases, and I sub With the decrease of sub decreases, and the stored magnetic energy M×I main ×I sub However, the stored magnetic energy W generated in step S110 total can be maintained substantially constant.

[0045] In Figure 5(B), the stored magnetic energy M×I main ×I sub W cоuple It is expressed as W total ≒W main +W cоuple +W sub By satisfying the above, the stored magnetic energy W of the secondary electromagnet 220 in state III sub A part of the stored magnetic energy W of the main electromagnet 210 main This shows how it has moved to

[0046] Also, the induced voltage V of the main electromagnet 210 main is V main =VmainL +V mainM =L main ×(dI main / dt)+M×(dI sub / dt), and the induced voltage V sub is V sub =V subL +V subM =L sub ×(dI sub / dt)+M×(dI main / dt), resulting in a smaller induced voltage.

[0047] Here, heat is dissipated from the magnetic working material 230 by a heat dissipation mechanism. Well-known methods such as a solid type and a fluid type can be used as the heat dissipation mechanism. For example, a gas gap type heat switch or a superconducting heat switch can be used as the solid type, and the heat is dissipated by bringing a pre-cooling stage (for example, the pre-cooling stage 731 in FIG. 7) into thermal contact with the magnetic working material 230. For example, for a fluid type, the heat is dissipated by spraying hydrogen gas or helium gas onto the magnetic working material 230 or by water cooling. This lowers the temperature of the magnetic working material 230, so that the temperature of the magnetic working material 230 can be lowered below that of the initial state. In state IV, the temperature T of the magnetic working material 230 mag Finally, the temperature T obj It is pre-cooled to a temperature similar to or slightly higher than that.

[0048] Steps S150 and S160 may be performed simultaneously, or step S160 may be performed after step S150. While the magnetic working material 230 is being evacuated, the currents flowing through the main electromagnet 210 and the sub-electromagnet 220 are maintained.

[0049] In step S170, the above steps S130 to S160 are repeated to continuously cool the object to be cooled 240. As described above, by employing the method of the present invention, it is possible to reduce the energy loss and the induced voltage of the electromagnet when exciting and demagnetizing the magnetic working material. As a result, it is possible to perform excitation and demagnetization at high speed, further reducing energy loss and achieving a high-speed, repeated cooling effect.

[0050] 5 and 6, the explanation has been given for the summation connection, but in the differential connection, the current I sub In other words, in the case of a differential connection, as shown by the dotted line in FIG. sub Then, in step S130, a current I sub is gradually decreased, and in step S140, the current I sub In this case, the stored magnetic energy W total remains substantially unchanged and the induced voltage is also reduced.

[0051] In the above explanation using Figures 1 to 6, the magnetic field created by the main electromagnet 210 and the magnetic field created by the sub-electromagnet 220 were in the same direction, but since a cooling effect can be obtained if the magnetic working material 230 is excited or demagnetized, the magnetic field created by the main electromagnet 210 and the magnetic field created by the sub-electromagnet 220 may be in opposite directions to cancel out the magnetic field created by the sub-electromagnet 220.

[0052] The principle of the magnetic refrigeration method of the present invention has been described with reference to FIGS. 1 to 6. Hereinafter, a magnetic refrigeration apparatus for implementing the magnetic refrigeration method of the present invention will be described.

[0053] FIG. 7 is a schematic diagram showing a magnetic refrigeration device of the present invention.

[0054] The magnetic refrigeration device 700 of the present invention for cooling a cooled body 240 comprises a magnetic working material 230 having a magnetocaloric effect, at least one main superconducting electromagnet (hereinafter simply referred to as a main electromagnet) 210 that applies a magnetic field to the magnetic working material 230, at least one secondary superconducting electromagnet (hereinafter simply referred to as a secondary electromagnet) 220 that is magnetically coupled to the main electromagnet 210, a current source 710 connected to the at least one main electromagnet 210, a heat dissipation mechanism 730 that dissipates heat from the magnetic working material 230 and exchanges heat, and a control unit 720 that controls the operation of at least the current source 710 and the heat dissipation mechanism 730.

[0055] Here, the control unit 720 controls the operation of the current source 710 to control the timing, magnitude, and direction of current flow to each of the at least one main electromagnet 210 and the at least one sub-electromagnet 220, and also controls the operation of the heat dissipation mechanism 730 to control the timing of heat dissipation and heat exchange of the magnetic working material 230.

[0056] Specifically, the control unit 720 controls the operation of the current source 710 to control the timing, magnitude, and direction of the current flowing through the main electromagnet 210 and the sub electromagnet 220, which are magnetically coupled to each other, so that the total stored magnetic energy of the main electromagnet 210 and the sub electromagnet 220 is substantially constant.

[0057] 7 preferably further includes a pre-cooling stage 731 and a heat exchanger 732, and is configured to cool the object to be cooled 240. The operation of cooling the object to be cooled 240 in the magnetic refrigeration device 700 in FIG. 7 will be described with reference to FIGS. 5 and 6.

[0058] The control unit 720 preferably: A current is passed through the main electromagnet 210 to apply a magnetic field B to the magnetic working material 230, and the temperature T mag Increase The heat dissipation mechanism 730 dissipates heat from the magnetic working material 230; The currents flowing through the main electromagnet 210 and the sub-electromagnet 220 are increased or decreased so as to reduce the magnetic field B applied to the magnetic working material 230, and the temperature T mag Lowering The current flowing through the main electromagnet 210 and the current flowing through the sub-electromagnet 220 are maintained to exchange heat between the magnetic working material 230 and the cooled body 240. It controls the operation of the current source 710 and the heat dissipation mechanism 730 .

[0059] 5 and 6. In detail, in state I, the control unit 720 controls the current source 710 so that the magnetic field B is applied to the magnetic working material 230 in advance, and the current source 710 outputs a current to the main electromagnet 210, and the temperature T mag is lower than the temperature that was previously increased by applying magnetic field B due to the heat dissipation by heat dissipation mechanism 730.

[0060] In state II, the control unit 720 controls the stored magnetic energy W of the main electromagnet 210. main At the same time, the control unit 720 reduces the current output from the current source 710 to the main electromagnet 210. However, the stored magnetic energy W main The discharge of the current I of the main electromagnet 210 may be performed by the operation of only one of the current source 710 and the control unit 720. If the main electromagnet 210 and the sub-electromagnet 220 are magnetically coupled in a summing connection, the current I of the main electromagnet 210 main Due to electromagnetic induction caused by the decrease in I sub If the main electromagnet 210 and the sub electromagnet 220 are magnetically coupled by a differential connection, the current in the main electromagnet 210 decreases due to electromagnetic induction, and the current in the sub electromagnet 220 increases as shown by the solid line in the figure. sub The current previously excited in the secondary electromagnet 220 decreases as shown by the dotted line. The stored magnetic energy W main is discharged, and the magnetic field B applied to the magnetic working material 230 is reduced, so that the temperature T mag decreases.

[0061] Then, as in state III, I main and I sub By maintaining the temperature T mag rises, and the temperature T оbj decreases.

[0062] The control unit 720 further The currents flowing through the main electromagnet 210 and the sub-electromagnet 220 are increased or decreased so as to increase the magnetic field B applied to the magnetic working material 230, and the temperature T mag Increase The current flowing through the main electromagnet 210 and the current flowing through the sub-electromagnet 220 are maintained, and heat is removed from the magnetic working material 230 by the heat removal mechanism 730. Temperature T of the magnetic working material 230 mag , and heat exchange with the cooled body 240, and the temperature T mag and then the heat is removed from the magnetic working material 230 by the heat removal mechanism 730, in this order. The operation of the current source 710 and the heat removal mechanism 730, as well as the main electromagnet 210 and the secondary electromagnet 220 may be controlled.

[0063] This allows repeated changes between states I, II, III, IV, and V in Figures 5 and 6, and the cooling and temperature increase of the magnetic working material 230 can be repeated while suppressing the loss of stored magnetic energy, thereby continuously cooling the cooled body 240.

[0064] Specifically, in state IV, the current source 710 outputs a current under the control of the control unit 720, and the current I main increases, a magnetic field is applied to the magnetic working material 230, and the temperature of the magnetic working material 230 increases. In state V, the current I main and the current I of the secondary electromagnet 220 sub The magnetic working material 230 is then heated by the heat dissipation mechanism 730.

[0065] As a method of heat exchange in state V, well-known methods such as a solid type and a fluid type can be adopted. As a solid type, for example, a gas gap type heat switch or a superconducting heat switch can be adopted, and heat is discharged by thermally contacting a pre-cooling stage (for example, pre-cooling stage 731 in FIG. 7) with the magnetic working material 230. As a gas type, for example, heat is discharged by spraying hydrogen gas or helium gas onto the magnetic working material 230 or by water cooling.

[0066] Control unit 720 controls the operation of current source 710 and heat dissipation mechanism 730 to repeat State I, State II, State III, State IV, and State V, thereby continuously cooling object 240. As described above, by employing the magnetic refrigeration device of the present invention, the induced voltage during magnetization and demagnetization is small, allowing for high-speed magnetization and demagnetization, and achieving a repeated refrigeration effect while suppressing magnetic energy loss.

[0067] In addition, in the excitation and demagnetization operations of the main electromagnet and the sub electromagnet, it is also possible to use the method of transferring energy between the electromagnets using the electrical method described in Patent Document 5. In this case, the strong magnetic coupling between the main electromagnet and the sub electromagnet suppresses induced voltage, and an improvement in the speed of operation of the magnetic refrigeration device described in Patent Document 5 is expected.

[0068] Next, each component will be described in detail. There are no particular limitations on the main electromagnet 210 and the sub-electromagnet 220 as long as they are each a coil wound with superconducting wire, but for example, they may be selected from the group consisting of a superconducting coil with inter-turn insulation, an uninsulated superconducting coil, a partially uninsulated superconducting coil, and combinations thereof.

[0069] The main electromagnet 210 and the sub electromagnet 220 have a hollow cylindrical shape, but may be stacked on top of each other as shown in Figures 2 and 5. This magnetically couples the main electromagnet 210 and the sub electromagnet 220. The hollow cylindrical shape may be a cylindrical shape whose cross section has a shape selected from the group consisting of a circle, a triangle, a rectangle, and a polygon.

[0070] FIG. 8 is a schematic diagram showing another arrangement of the main electromagnets and the sub electromagnets.

[0071] The number of main electromagnets 210 and sub-electromagnets 220 is not limited to one. For example, as shown in Fig. 8(A), one main electromagnet 210 and two sub-electromagnets 220a and 220b may be used.

[0072] Alternatively, as shown in Fig. 8(B), two main electromagnets 210a and 210b and two sub-electromagnets 220a and 220b may be used. In this way, the number of main electromagnets 210 and sub-electromagnets 220 may be multiple.

[0073] As shown in FIG. 8(C), the main electromagnet 210 and the sub-electromagnet 220 may have a hollow cylindrical shape and be positioned concentrically so that one electromagnet encloses the other. In this case, they can also be magnetically coupled to each other. In FIG. 8(C), the main electromagnet 210 is positioned inside and the sub-electromagnet 220 is positioned outside, but the positions may be reversed. However, in the reversed case, the magnetic working material 230 is positioned in the space between the main electromagnet 210 and the sub-electromagnet 220.

[0074] As shown in Fig. 8(D), the main electromagnet 210 may be located inside and the sub-electromagnet 220 may be located outside, and the magnetic working material 230 may be located both inside the main electromagnet 210 and in the space between the main electromagnet 210 and the sub-electromagnet 220. In this case, the roles and operations of the main electromagnet 210 and the sub-electromagnet 220 described in this specification may be interchanged during operation. The number and arrangement of the main electromagnets and sub-electromagnets may be appropriately combined from Figs. 8(A) to (D) as long as they are magnetically coupled to each other.

[0075] The magnetic working material 230 can be any material having a magnetocaloric effect, and is appropriately selected from known materials depending on the temperature range to which the object to be cooled 240 is to be cooled. For example, gadolinium can be used at room temperature, and holmium aluminum can be selected when hydrogen liquefaction (20 K) is to be achieved. Alternatively, a combination of these materials may be used depending on the temperature range to be cooled. Such a design can be easily accomplished by a person skilled in the art.

[0076] If the current source 710 is connected only to at least the main electromagnet 210, a current also flows in the sub-electromagnet 220 due to electromagnetic induction. In detail, when the main electromagnet 210 and the sub-electromagnet 220 are summatively connected, the current I main dI per time dt main When it is decreased, the current I sub(M / L main )×dI main Only the value changes.

[0077] The current sources 710 may be any current source capable of supplying current to each of them. The current sources 710 may be selected from the group consisting of a DC power supply, a bidirectional power supply, a regenerative power supply, and a flux pump device. Furthermore, any device having the function of supplying magnetic flux other than a flux pump device may be used. Furthermore, the current sources 710 may have the function of electrically transferring stored magnetic energy between electromagnets, as in Patent Document 5.

[0078] 7 shows a state in which one current source 710 is connected only to the main electromagnet 210, but the current source 710 may be connected to both the main electromagnet 210 and the sub electromagnet 220, or two or more current sources may be used, with one current source for the main electromagnet connected to the main electromagnet 210 and another current source for the sub electromagnet connected to the sub electromagnet 220. In this case as well, the control unit 720, which will be described later, may control the operation of two or more current sources.

[0079] The control unit 720 preferably includes a control device 721 and a control circuit 722. The control device 721 is electrically connected to the current source 710 and the heat dissipation mechanism 730 and controls the operations thereof. Such a control device 721 has computer functions and may include a central processing unit (CPU), and memories such as a read-only memory (ROM) and a random access memory (RAM) that store programs for operating the central processing unit (CPU).

[0080] The control circuit 722 is electrically connected to the main electromagnet 210 and the sub electromagnet 220, and has the function of discharging the magnetic energy stored in the main electromagnet 210 and the sub electromagnet 220, or has switches that open, short, or reconnect both ends of the main electromagnet 210 and the sub electromagnet 220 to the components, or both. In Fig. 7, the control circuit 722 is electrically connected to the control device 721, and discharges the stored magnetic energy automatically or at any timing in response to a signal from the control device 721. However, the control circuit 722 does not necessarily have to be connected to the sub electromagnet 220.

[0081] The control circuit 722 may be composed of an element selected from the group consisting of a discharge resistor, a switch, a diode, and a combination thereof. This protects the current source 710 and the control circuit 722 from unexpected reverse voltage. The resistance may be a known resistor, or the resistance of a superconducting wire inside the main electromagnet 210 or the sub electromagnet 220, or the contact resistance between turns. In FIG. 7, the control circuit 722 is located outside the magnetic refrigeration apparatus 700, but this is not limiting and the control circuit 722 may be located inside the magnetic refrigeration apparatus 700 or both inside and outside the magnetic refrigeration apparatus 700. If a regenerative power supply is used as the current source 710 and the current source 710 has the function and configuration of the control circuit 722, the control circuit 722 may be omitted.

[0082] The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples. [Example]

[0083] [Example 1] Example 1 relates to a magnetic refrigeration device including one main electromagnet, one sub-electromagnet, one current source connected to the main electromagnet, a heat dissipation mechanism, and a control unit.

[0084] FIG. 9 is a circuit diagram showing the magnetic refrigeration apparatus of Example 1. As shown in FIG.

[0085] The circuit diagram shows the main electromagnet L1, the secondary electromagnet L2, and the current source I connected to the main electromagnet L1. ps1The magnitude of the self-inductance of each of the main electromagnet L1 and the sub-electromagnet L2 is also represented by the same symbol. The mutual inductance M is a positive value, that is, we consider the case of a summation connection.

[0086] Current source I ps1 The magnitude of the current output by the resistor R is also expressed by the same symbol. e1 and R e2 , and switch SW e1 , S.W. t1 , S.W. p1 , S.W. e2 and S.W. t2 An electrical circuit is provided to allow the stored magnetic energy to be discharged.

[0087] Switch SW in Figure 9 e1 , S.W. t1 , S.W. p1 , S.W. e2 , S.W. t2 The open / closed state of the switch SW1 indicates the condition when the main electromagnet L1 is excited at the beginning of operation. e1 and SW e2 By combining the opening and closing of the other switches, the main electromagnet L1, the sub-electromagnet L2, or both can be discharged at any timing. The opening and closing of the switches is performed by computer-controlled circuits and power supplies (not shown).

[0088] Current source current I ps1 The main electromagnet L1 is excited by increasing the current I1 flowing through the main electromagnet L1, and a magnetic field is applied to the magnetic working material (step S110 in FIG. 1). This increases the temperature of the magnetic working material. Next, heat is removed from the magnetic working material by the heat removal mechanism (step S120 in FIG. 1). In detail, the current I ps1 Keep the switch SW t1 and SW e1 is changed from open to closed, and then the current I ps1 Set to zero and switch SW p1 In this way, the magnetic working material whose temperature has risen due to the application of a magnetic field is evacuated.

[0089] Then, the temperature of the magnetic working material is lowered (step S130 in FIG. 1). t2 and SW e2 Switch SW t1 By switching from closed to open, the resistance R e1 A discharge occurs due to the magnetic field, decreasing the current I1. At the same time, the sub-electromagnet L2 is excited by electromagnetic induction, increasing the current I2. The current I1 decreases, i.e., the main electromagnet L1 is demagnetized, so the magnetic field applied to the magnetic working material decreases, and the temperature of the magnetic working material drops. Next, heat exchange occurs between the object to be cooled and the magnetic working material, cooling the object to be cooled (step S140 in FIG. 1).

[0090] The above is the operation of S110 to S140 in Fig. 1, but continuous operation as shown in Fig. 4 is also possible. After the object to be cooled is cooled, the temperature of the magnetic working material is increased (step S150 in Fig. 4). The switch SW e1 is changed from closed to open, and then the current I ps1 By increasing the current I1 flowing through the main electromagnet L1, the main electromagnet L1 is excited and a magnetic field is applied to the magnetic working material, which increases the temperature of the magnetic working material.

[0091] At the same time, heat is removed from the magnetic working material by the heat removal mechanism (step S160 in FIG. 4). The sub-electromagnet L2 is demagnetized by electromagnetic induction, and the current I2 decreases. Next, the current I ps1 Keep the switch SW t1 and SW e1 is changed from open to closed, and then the current I ps1 Set to zero and switch SW p1 is switched from closed to open. In this way, the magnetic working material 230, whose temperature has risen due to the application of the magnetic field, is released. Next, by repeating the process of lowering the temperature of the magnetic working material, heat exchange, raising the temperature of the magnetic working material, and releasing the heat (step S170 in FIG. 4), a continuous cooling operation can be achieved. [Industrial Applicability]

[0092] In the magnetic refrigeration device of the present invention, the main electromagnet and the sub electromagnet are magnetically coupled, allowing magnetic energy to be exchanged between them as is, creating a space in which the magnetic field increases and decreases, dramatically reducing energy loss. Use of such a magnetic refrigeration device reduces losses and induced voltages associated with energy conversion, simplifies the insulation structure, speeds up the refrigeration cycle, and enables the device to be made more compact. [Explanation of symbols]

[0093] 210 Main electromagnet 220 Secondary electromagnet 230 Magnetic Working Materials 240 Cooled object 700 Magnetic Refrigeration Device 710 Current Source 720 Control Unit 721 Control Device 722 Control Circuit 730 Heat dissipation mechanism 731 Pre-cooling stage 732 Heat exchanger

Claims

1. A magnetic refrigeration device that cools an object to be cooled, a magnetic working material having a magnetocaloric effect; at least one main superconducting electromagnet that applies a magnetic field to the magnetic working material; at least one secondary superconducting electromagnet magnetically coupled to the at least one primary superconducting electromagnet; a current source connected to the at least one main superconducting electromagnet; a heat dissipation mechanism for dissipating heat from the magnetic working material and exchanging heat; a control unit that controls the operation of at least the current source and the heat dissipation mechanism; Equipped with The control unit controlling operation of the current source to control timing, magnitude, and direction of current flow through each of the at least one main electromagnet and the at least one secondary superconducting electromagnet; The magnetic refrigeration apparatus controls the operation of the heat rejection mechanism so as to control the timing of heat rejection and heat exchange of the magnetic working material.

2. The control unit Passing a current through the at least one main superconducting electromagnet to apply a magnetic field to the magnetic working material, thereby increasing the temperature of the magnetic working material; The heat dissipation mechanism dissipates heat from the magnetic working material; increasing or decreasing the current flowing through the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet magnetically coupled to the at least one main superconducting electromagnet so as to reduce the magnetic field applied to the magnetic working material, thereby reducing the temperature of the magnetic working material; maintaining a current flowing through the at least one main superconducting electromagnet and a current flowing through the at least one sub-superconducting electromagnet to exchange heat between the magnetic working material and the cooled body; The magnetic refrigeration apparatus according to claim 1 , wherein the operation of the current source and the heat removal mechanism is controlled.

3. The control unit further increasing or decreasing the current flowing through the at least one main superconducting electromagnet and the at least one sub superconducting electromagnet so as to increase the magnetic field applied to the magnetic working material, thereby increasing the temperature of the magnetic working material; maintaining a current flowing through the at least one main superconducting electromagnet and a current flowing through the at least one auxiliary superconducting electromagnet, and dissipating heat from the magnetic working material by the heat dissipation mechanism; a step of decreasing the temperature of the magnetic working material, exchanging heat with the cooled body, increasing the temperature of the magnetic working material, and discharging heat from the magnetic working material by the heat discharging mechanism, repeated in this order; The magnetic refrigeration apparatus according to claim 2 , wherein the operation of the current source and the heat removal mechanism is controlled.

4. 4. The magnetic refrigeration apparatus according to claim 1, wherein the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet have a hollow cylindrical shape and are stacked.

5. the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet have a hollow cylindrical shape, 4. The magnetic refrigeration apparatus according to claim 1, wherein the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet are positioned concentrically.

6. 6. The magnetic refrigeration apparatus according to claim 1, wherein the current source is selected from the group consisting of a DC power supply, a bidirectional power supply, a regenerative power supply, and a flux pump device.

7. The control unit a control device electrically connected to the current source and the heat dissipation mechanism; a control circuit electrically connected to the at least one primary superconducting electromagnet and the at least one secondary superconducting electromagnet; The magnetic refrigeration device according to any one of claims 1 to 6, further comprising:

8. 8. The magnetic refrigeration apparatus according to claim 7, wherein the control circuit includes an element selected from the group consisting of a discharge resistor, a switch, a diode, and combinations thereof, and discharges the stored magnetic energy of the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet.

9. 9. The magnetic refrigeration apparatus according to claim 1, wherein the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet are each selected from the group consisting of a superconducting coil with inter-turn insulation, an uninsulated superconducting coil, a partially uninsulated superconducting coil, and combinations thereof.

10. The heat dissipation mechanism includes: a pre-cooling stage for removing heat from the magnetic working material; a heat exchanger that rejects heat from the pre-cooling stage; The magnetic refrigeration device according to any one of claims 1 to 9, further comprising:

11. A magnetic refrigeration method for cooling an object to be cooled, comprising: applying a current to the at least one main superconducting electromagnet to apply a magnetic field to the magnetic working material, thereby increasing the temperature of the magnetic working material; dissipating heat from the magnetic working material by a heat dissipation mechanism; increasing or decreasing the current flowing through the at least one main superconducting electromagnet and the at least one auxiliary superconducting electromagnet magnetically coupled to the at least one main superconducting electromagnet so as to reduce the magnetic field applied to the magnetic working material, thereby reducing the temperature of the magnetic working material; maintaining a current flowing through the at least one main superconducting electromagnet and a current flowing through the at least one auxiliary superconducting electromagnet, and exchanging heat between the magnetic working material and the cooled body; A magnetic refrigeration method comprising:

12. Following the heat exchange with the cooled body, increasing or decreasing the current flowing through the at least one main superconducting electromagnet and the at least one sub superconducting electromagnet so as to increase the magnetic field applied to the magnetic working material, thereby increasing the temperature of the magnetic working material; maintaining a current flowing through the at least one main superconducting electromagnet and a current flowing through the at least one auxiliary superconducting electromagnet, and dissipating heat from the magnetic working material by the heat dissipation mechanism; Repeating the steps of lowering the temperature of the magnetic working material, exchanging heat with the cooled body, raising the temperature of the magnetic working material, and discharging heat from the magnetic working material by the heat discharging mechanism in this order. The magnetic refrigeration method of claim 11 further comprising:

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