Superconducting magnet device

Abstract

Provided is a superconducting magnet device comprising: a winding frame; a superconducting coil that is configured by winding a tape-shaped superconducting wire on the winding frame; and a buffer member that suppresses torsional deformation which is caused by flow of a transport current to the superconducting coil.

Description

Superconducting magnet device

[0001] The present invention relates to a superconducting magnet device.

[0002] The measurement performance of nuclear magnetic resonance (NMR) devices improves as the magnetic field becomes stronger, and therefore, development of superconducting magnet devices (superconducting coil devices) capable of generating high magnetic fields is underway (Patent Documents 1-3, Non-Patent Document 1). x , RE is rare earth elements such as Y, Gd, Eu, etc.) and Bi-2223 (Bi2Sr2Ca2Cu3O x High-temperature superconducting materials such as CrNb 2 O 4 can achieve high critical current densities even in high magnetic fields, so high-temperature superconducting materials are often used for the innermost coil.

[0003] High-temperature superconducting coils are susceptible to mechanical deterioration due to the strong electromagnetic stresses, i.e., hoop stress and axial compressive stress, and it is important to prevent this. In particular, a research group including the present inventors has recently discovered that the shielding current specific to high-temperature superconducting coils causes twisting deformation of high-temperature superconducting wires, resulting in increased hoop stress and buckling of high-temperature superconducting tape wires. They are currently investigating countermeasures to this phenomenon in order to ensure stable operation (Non-Patent Document 2).

[0004] Furthermore, if the circuit resistance of the high-temperature superconducting coil is high, the decrease (drift) of the central magnetic field will become large. Therefore, in order to enable long-term continuous operation over several years to several decades, it is also necessary to suppress the attenuation of the central magnetic field.

[0005] International Publication No. 2021 / 172276 Japanese Patent Application Laid-Open No. 2019-169626 Japanese Patent Application Laid-Open No. 2016-6825

[0006] Suetomi, Y., et al. "A novel winding method for a no-insulation layer-wound REBCO coil to provide a short magnetic field delay and self-protect characteristics." Superconductor Science and Technology 32 (2019): 045003 (13pp).S. Takahashi et al., "Hoop Stress Modification, Stress Hysteresis and Degradation of a REBCO Coil Due to the Screening Current Under External Magnetic Field Cycling," in IEEE Transactions on Applied Superconductivity, vol. 30, no. 4, pp. 1-7, June 2020, Art no. 4602607, doi: 10.1109 / TASC.2020.2974837.

[0007] An object of the present invention is to provide a superconducting magnet device that can be operated stably.

[0008] A first aspect of the present invention is a superconducting magnet device comprising: a reel; a superconducting coil formed by winding a tape-shaped superconducting wire around the reel; and a buffer member that suppresses torsional deformation that occurs when a transport current flows through the superconducting coil.

[0009] A second aspect of the present invention is a superconducting magnet device comprising: a reel; and a first superconducting coil and a second superconducting coil formed by winding a tape-shaped superconducting wire around the reel; the first superconducting coil and the second superconducting coil are not electrically connected except for an earth connection, but are magnetically coupled; and the second superconducting coil generates a magnetic field that compensates for the decrease in magnetic field in response to the decrease in magnetic field that accompanies the attenuation of the current flowing through the first superconducting coil.

[0010] A third aspect of the present invention is a superconducting magnet device comprising: a reel; a first superconducting coil configured by winding a tape-shaped superconducting wire around the reel; and a second superconducting coil configured by winding the superconducting wire around the reel; wherein the second superconducting coil is not electrically connected to the first superconducting coil except for a ground connection, and the second superconducting coil is provided between the reel and the innermost layer of the first superconducting coil.

[0011] According to the present invention, a superconducting magnet device capable of stable operation can be provided.

[0012] FIG. 1 is a diagram illustrating the configuration of a superconducting magnet device according to Embodiment 1. FIG. 2 is a diagram illustrating the configuration of coils included in the superconducting magnet device according to Embodiment 1. FIG. 3 is a diagram illustrating the configuration of coils included in the superconducting magnet device according to Embodiment 1. FIGS. 4A and 4B are diagrams illustrating deformation when a transport current is passed through the superconducting magnet device according to Embodiment 1. FIGS. 5A and 5B are diagrams illustrating deformation when a transport current is passed through the superconducting magnet device according to Embodiment 1. FIGS. 6A to 6D are diagrams illustrating the configuration of a superconducting magnet device according to Embodiment 2. FIGS. 7A to 7D are diagrams illustrating the central magnetic field attenuation of the superconducting magnet device according to Embodiment 2. FIGS. 8A to 8D are diagrams illustrating the central magnetic field attenuation of the superconducting magnet device according to Embodiment 2. FIGS. 9A and 9B are diagrams illustrating the configuration of a superconducting magnet device according to a modification of Embodiment 2. FIGS. 10A to 10C are diagrams illustrating the torsional floating phenomenon.

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The components of the embodiments described below can be combined as appropriate.

[0014] [First Embodiment] The first embodiment relates to a superconducting magnet device that can suppress the torsional floating phenomenon that occurs in the coil wire and avoid physical damage to the coil.

[0015] (Twist Floating Phenomenon) Before describing this embodiment, the torsion floating phenomenon will be described with reference to FIGS. 10A to 10C. FIG. 10A is a diagram showing the appearance of a superconducting coil 1000 that constitutes a superconducting magnet device. In the superconducting coil 1000, a superconducting coil wire 1001 is wound in multiple layers around a bobbin 1002. The superconducting coil wire 1001 is a tape-shaped wire such as REBCO or Bi-2223, and is wound in an aligned spiral manner with layers overlapping each other, as shown in FIG. 10B. This winding method is also called layer winding.

[0016] FIG. 10C is a diagram illustrating the shielding current and Lorentz force generated when a transport current It flows through the superconducting coil 1000. The magnetic field B generated by the transport current It includes an axial component Bz and a radial component Br. The radial magnetic field component Br is perpendicular to the tape surface of the superconducting coil wire 1001, and application of this magnetic field generates a shielding current Is in the superconducting coil wire 1001 that cancels out the magnetic field. When a circumferential shielding current Is is generated in the axial magnetic field component Bz, a radial Lorentz force Fr is generated. Here, because the shielding current flows in different directions above and below the tape, an outward force is applied to the upper side of the tape and an inward force is applied to the lower side of the tape, resulting in a torsional force being applied to the tape. This torsional force causes the superconducting coil wire 1001 to twist (tilt) and deform. This phenomenon is referred to herein as the torsional floating phenomenon. Furthermore, the Lorentz force generated by the interaction between the radial magnetic field component Br and the transport current It acts to compress the superconducting coil 1000 in the axial direction. If a torsional floating phenomenon occurs and an axial compressive force is applied when there is a gap between the coil wire and the bobbin or between the coil wires, buckling may occur, in which the tape material slides between adjacent tape materials. If buckling occurs, the superconducting coil 1000 may be physically damaged.

[0017] (Configuration) The configuration of a superconducting magnet device 10 according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 is a schematic diagram showing the appearance and cross section of the superconducting magnet device 10, Figure 2 is a schematic diagram showing the structure near the upper end of the innermost coil 11, and Figure 3 is a schematic diagram showing an enlarged view of part of the structure of the inner layer side of the coil 11.

[0018] The superconducting magnet device 10 is a main coil used in an NMR device, and is made up of multiple concentric coils 11 to 15 connected in series. Here, since the central magnetic field is high, the central coils 11 and 12 are made of high-temperature superconducting material (HTS), and the outer coils 13 to 15 are made of low-temperature superconducting material (LTS). As an example, coil 11 is made of REBCO, coil 12 is made of Bi-2223, and coil 13 is made of Nb ３ The coil 11 is made of Sn, and the coils 14 and 15 are made of NbTi. Note that the configuration shown in Fig. 1 is merely an example, and the number of coils constituting the main coil and the material of each coil are not particularly limited. For example, the coils 11 and 12 may both be made of REBCO, that is, a configuration without using Bi-2223 may be used.

[0019] Each coil has a structure in which a coil wire is wound around a bobbin. REBCO and Bi-2223 are tape-shaped wires, and coils 11 and 12 are layer-wound as shown in FIG. 10B. By employing layer winding, it is possible to reduce the number of joints between superconducting wires by using long wires. When superconductingly joining wires together, it is advisable to extend the wire to a position away from the coil and then join it in order to reduce the effect of the coil's leakage magnetic field.

[0020] In this embodiment, the coil 11 has a structure in which a reinforcing material (bind) is provided between multiple coil layers. For example, the reinforcing material is made of stainless steel (SUS). The number of coil layers and the number of reinforcing material layers are designed so that the stress distribution is at the same level. Figure 2 is a diagram showing an example of the configuration of the coil 11. Note that Figure 2 is an enlarged view of the vicinity of the upper end of the coil 11.

[0021] As shown in Figure 2, the winding of the coil 11 is divided into multiple sections. The innermost section 22-1 includes, in that order from the inside, two dummy layers, ten layers of superconducting coil wire, and two layers of reinforcing material. Section 22-2 is composed of eight layers of superconducting coil wire and two layers of reinforcing material on the outside. Section 22-3 is composed of eight layers of superconducting coil wire and three layers of reinforcing material on the outside, repeated four times. Section 22-4 is composed of eight layers of superconducting coil wire and four layers of reinforcing material on the outside, repeated six times. Section 22-5 is composed of eight layers of superconducting coil wire and five layers of reinforcing material on the outside, repeated three times. Section 22-6 is composed of eight layers of superconducting coil wire and six layers of reinforcing material on the outside. By increasing the proportion of reinforcing material toward the outside in this way, the resulting hoop stress distribution is made uniform.

[0022] Figure 3 shows the configuration of coil 11 in more detail, and is an enlarged view of sections 22-1 and 22-2 in Figure 2. On bobbin 31, from the inside out, are provided an insulating layer 32, two dummy layers 33, ten superconducting coil layers 34, an insulating layer 35, and two reinforcing layers 36. These constitute section 22-1. Similarly, section 22-2 is composed of an insulating layer 37, eight superconducting coil layers 38, an insulating layer 39, and two reinforcing layers 40.

[0023] The insulating layers 32, 35, 37, and 39 are made of an insulating material such as a polyimide sheet or a PET sheet. The dummy layer 33 and the superconducting coil layers 34 and 38 are each formed by winding a tape-shaped REBCO wire around a bobbin. In this embodiment, the dummy layer 33 is provided between the bobbin 31 and the innermost superconducting coil layer 34. The superconducting coil layers 34 and 38 (and the superconducting coil layers in other sections) are connected in series, but the dummy layer 33 is not electrically connected to (separated from) the superconducting coil layers. Therefore, when a current is applied to the superconducting magnet device 10, a transport current flows through the superconducting coil layers 34 and 38, but no transport current flows through the dummy layer 33.

[0024] The dummy layer 33 can be formed by winding a superconducting wire made of the same material as the wire constituting the coil layer, for example, a REBCO tape wire, in a layer winding manner around the bobbin 31. The dummy layer 33 may or may not be a closed circuit.

[0025] (Verification of Effects) The effects of the dummy layer 33 will be described with reference to FIGS. 4A, 4B, 5A, and 5B.

[0026] 4A and 4B show the results of numerical experiments on the radial component (shown in shading) of the electromagnetic force acting on the superconducting wire when a transport current is passed through it, and the resulting deformation, with and without a dummy layer. Note that these figures are magnified six times in the radial direction.

[0027] 4A shows the results when there is no dummy layer 33. As is evident at the point indicated by the dotted line 41, a large radial force is applied to the coil wire in the innermost layer, causing a torsional floating phenomenon in which the tape-shaped wire tilts. The torsional floating phenomenon creates gaps between the coil layers, making it easy for the electromagnetic force that displaces the wire axially toward the center of the coil to cause buckling, in which the coil wire slides into its neighboring coil.

[0028] 4B shows the results for the coil 11 of this embodiment, which includes a dummy layer 33. Because no transport current flows through the dummy layer 33, no electromagnetic force (volume force) is generated that displaces the wire axially toward the center of the coil. Although an electromagnetic force (volume force) acts on the coil layer 34, the dummy layer 33 functions as a buffer, preventing the coil layer from tipping over due to its elastic force (springiness). This effect is due to the shielding current induced in the wire in the dummy layer 33 and the Lorentz force generated by an external magnetic field. This suppresses the torsional floating phenomenon in the innermost layer of the coil (e.g., the area indicated by the dotted line 42).

[0029] Figures 5A and 5B show the results of numerical experiments to determine the misalignment Δx between adjacent turns of the coil wire when a transport current is applied, with and without a dummy layer. The horizontal axis represents the turn (axial position), and the vertical axis represents the misalignment. Here, the misalignment Δx is the difference in the radial position of the center line of the coil wire thickness direction between adjacent turns in the coil axial direction. Note that the wire thickness in this numerical experiment is approximately 130 μm. Also, in the graph, the type of plot marker indicates the layer, with an open circle representing the first layer (dummy layers are not counted).

[0030] Figure 5A shows the results for the case where no dummy layer 33 is provided, with many misalignments exceeding 40 μm, with a maximum misalignment of 80 μm. On the other hand, Figure 5B shows the results for the coil 11 of this embodiment, with the dummy layer 33 provided, and it can be seen that the misalignment amount is suppressed to a maximum of 30 μm. It is believed that damage is unlikely to occur if the misalignment amount is less than 1 / 3 or 1 / 4 of the wire thickness, and this method can meet both criteria.

[0031] As described above, according to this embodiment, by providing a dummy layer between the bobbin and the innermost coil layer, which is electrically isolated from the coil layer and does not allow a transport current to flow, the dummy layer functions as a buffer member and can suppress the torsional floating phenomenon, thereby suppressing physical damage to the coil and enabling stable operation of the superconducting magnet device.

[0032] (Modifications of the dummy layer) In the above description, the dummy layer 33 is formed by winding one superconducting wire, but since the dummy layer does not need to function as a coil, the dummy layer may be formed by winding a plurality of discontinuous superconducting wires. Also, one superconducting wire does not need to wrap around the bobbin once, and one turn may be formed by multiple superconducting wires.

[0033] Furthermore, although the dummy layer 33 is formed of two layers, it may be formed of one layer or three or more layers.

[0034] Furthermore, the dummy layer 33 may be configured by non-inductively winding the superconducting wire. That is, the dummy layer 33 may be configured so that the inductance is cancelled out as a whole by reversing the winding direction depending on the layer.

[0035] In this embodiment, the dummy layer 33 is provided in the innermost layer of the innermost coil 11, but it may be provided in other locations. For example, the dummy layer may be provided in a location other than the innermost layer (inside or outside the coil layer 34) of the innermost section 22-1 of the coil 11. Alternatively, the dummy layer may be provided in a section other than the innermost layer, such as section 22-2. Furthermore, the dummy layer may be provided in a coil other than the innermost coil 11, such as coil 12.

[0036] According to this embodiment, it is possible to provide a superconducting magnet device that can stably generate a high magnetic field. The superconducting magnet device of this embodiment can be applied to equipment that requires operation in a persistent current mode, such as an NMR device or an MRI device.

[0037] [Embodiment 2] Embodiment 2 relates to a superconducting magnet device that can suppress attenuation (drift) of the central magnetic field strength due to electrical resistance.

[0038] (Configuration) Fig. 6A shows the circuit configuration of a superconducting magnet device 60 according to this embodiment. In addition to the configuration of embodiment 1, the superconducting magnet device 60 according to this embodiment includes a compensation coil 66 that is not electrically connected to the main coil 61 (except for connection via ground) but is magnetically coupled to it. Note that the main coil 61 and the compensation coil 66 do not have to be directly electrically connected, and may be connected to ground and electrically connected via the ground. In other words, the main coil 61 and the compensation coil 66 are not electrically connected except through the ground connection.

[0039] The main coil 61 and the compensation coil 66 are wound in the same direction, and the mutual inductance M is positive. In response to the decrease in the magnetic field that accompanies the attenuation of the transport current flowing through the main coil 61, the compensation coil 66 generates a magnetic field that compensates for the decrease in the magnetic field. Specifically, as shown in FIG. 6B, the current I flowing through the main coil 61 ｍａｉｎis reduced by the circuit resistance, and the magnetic field B generated by the main coil 61 ｍａｉｎ When the magnetic field decreases, a current I is supplied to the compensation coil 66 to compensate for the decreased magnetic field. ｃｏｍｐ flows and magnetic field B ｃｏｍｐ This generates a central magnetic field B ｍａｉｎ +B ｃｏｍｐ The degree of attenuation can be suppressed.

[0040] 6C and 6D are diagrams showing an example of a superconducting magnet device according to this embodiment.

[0041] 6C includes a main coil 61 consisting of coils 62-65 and a compensation coil 66A. Coil 62 is made of REBCO or Bi-2223, and coil 63 is made of Nb ３ The coils 64 and 65 are wound with Sn, and NbTi, respectively, and these coils are connected in series. Note that the coil configuration shown in FIG. 6C is merely an example, and the same configuration as that of the first embodiment (FIG. 1) or other configurations may be used. In the superconducting magnet device 60A, the compensation coil 66A is provided in the coil 63. The compensation coil 66A may be provided in the innermost layer, the outermost layer, or an intermediate layer of the coil 63. The coil wire used for the compensation coil 66A is made of the same material as the coil 63, Nb ３ It may be Sn, or other superconducting materials such as REBCO, Bi-2223, or NbTi.

[0042] The superconducting magnet device 60B shown in Figure 6D includes a main coil 61 consisting of coils 62-65, and a compensation coil 66B. In this example, the compensation coil 66B is provided in the innermost coil 62. As above, the compensation coil 66B may be provided in any of the innermost, outermost, or intermediate layers of the coil 62. The coil wire used for the compensation coil 22B may be made of the same material as the coil 62, such as REBCO or Bi-2223, or may be made of Nb ３ Other superconducting materials such as Sn, NbTi, etc. may also be used.

[0043] (Effect Verification) The effect of this embodiment will be described. The change over time of the magnetic field generated in the superconducting magnet device 60A shown in Fig. 6C under the following conditions was calculated.

[0044] Main circuit current value (initial value) I ｍａｉｎ = 220.541A Current value of the compensation circuit (initial value) I ｃｏｍｐ = 0A Self-inductance of main circuit L ｍａｉｎ = 230H Self-inductance of the compensation circuit L ｃｏｍｐ = 0.02H Mutual inductance between main circuit and compensation circuit M = 1.25H Resistance value of main circuit R ｍａｉｎ = 1.91 x 10 －９ Ω Resistance value of compensation circuit R ｃｏｍｐ =10 －１２ Ω Magnetic field generated by the main coil (per 1A) B ｍａｉｎ = 0.1086 T / A Magnetic field generated by the compensation coil (per 1 A) B ｃｏｍｐ =0.0014T / A

[0045] 7A to 7D show the calculation results. 7A and 7B show the current value and generated magnetic field when a compensation circuit is not used, and 7C and 7D show the current value and generated magnetic field when a compensation circuit is used. When a compensation coil is not used, the current I flowing through the main circuit ｍａｉｎ On the other hand, when a compensation coil is used, the current I flowing through the main coil decreases. ｍａｉｎ The current I that flows through the compensation circuit as the ｃｏｍｐ increases. ｍａｉｎ The magnetic field strength B created by ｍａｉｎ decreases, but I ｃｏｍｐ The magnetic field strength B created by ｃｏｍｐ is added, so the central magnetic field B ｍａｉｎ +B ｃｏｍｐ The attenuation can be suppressed to about one-third, 0.01 ppm / h.

[0046] Similarly, the change in magnetic field over time was calculated for the superconducting magnet device 60B shown in Fig. 6D under the following conditions.

[0047] Main circuit current value (initial value) I ｍａｉｎ = 220.541A Current value of the compensation circuit (initial value) I ｃｏｍｐ = 0A Self-inductance of main circuit L ｍａｉｎ = 230H Self-inductance of the compensation circuit L ｃｏｍｐ = 0.00092H Mutual inductance between main circuit and compensation circuit M = 0.167H Resistance value of main circuit R ｍａｉｎ = 1.91 x 10 －９ Ω Resistance value of compensation circuit R ｃｏｍｐ =10 －１２ Ω Magnetic field generated by the main coil (per 1A) B ｍａｉｎ = 0.1086 T / A Magnetic field generated by the compensation coil (per 1 A) B ｃｏｍｐ =0.0006T / A

[0048] Figures 8A to 8D show the calculation results. Figures 8A and 8B show the current value and generated magnetic field when a compensation circuit is not used, and are similar to Figures 7A and 7B. Figures 8C and 8D show the current value and generated magnetic field when a compensation circuit is used. In this example, the decay rate of the central magnetic field can be further suppressed, with the decay rate averaging 0.006 ppm / h over 10 years and 0.01 ppm / h after 10 years. Thus, the compensation effect is greater when the compensation coil is placed on the innermost coil of the multiple coils that make up the main coil, and the greatest effect is obtained when the compensation coil is placed on the innermost coil.

[0049] The compensation coil in this embodiment can also function as the dummy layer (buffer material) in embodiment 1. The fact that it functions as a dummy layer is also a reason why it is preferable to provide the compensation coil in the innermost coil layer. In other words, it is preferable to provide a second coil between the bobbin of the innermost coil 11 and the innermost coil layer, so that it has the functions of both the dummy layer in embodiment 1 and the compensation coil in embodiment 2.

[0050] (Variation of Embodiment 2) A further variation of the superconducting magnet device using the above compensation circuit is shown below. If the main coil quenches and the current flowing through the main circuit attenuates, the current flowing through the compensation coil may increase dramatically due to electromagnetic induction, potentially damaging the coil. Therefore, in this variation, a current limiting circuit is provided in the compensation coil circuit to suppress the increase in current flowing through the compensation coil circuit even when a quench occurs, thereby avoiding damage to the compensation coil.

[0051] 9A shows the circuit configuration of a superconducting magnet device 60C according to this modification. As shown in the figure, a current limiting circuit 67 is provided in a compensation coil 66. The current limiting circuit 67 is made of a superconducting material. Heat generated when a quench occurs in the main coil 61 is transferred to the current limiting circuit 67, and this heat causes the current limiting circuit 67 to transition to a normal conductor, generating resistance. As a result, an increase in the current flowing through the compensation circuit due to electromagnetic induction can be suppressed, and damage to the compensation coil can be avoided.

[0052] The current limiting circuit 67 is, for example, a non-inductive coil in which superconducting wire is non-inductively wound. The reason why the current limiting circuit 67 is a non-inductive coil is so that it does not interfere with the operation of the compensation coil. Furthermore, since the current limiting circuit needs to be in thermal contact with the main coil 61 so that it transitions to normal conduction when a quench occurs, it is preferable to wind it within the coil layer of the main coil. In particular, it is preferable to provide a current limiting circuit in a coil made of low-temperature superconducting material that easily transitions to normal conduction with little heat. Furthermore, the superconducting material that makes up the current limiting circuit 68 may have a lower critical temperature than the superconducting material that makes up the compensation coil 66, or it may have the same critical temperature.

[0053] FIG. 9B is a diagram showing an example of a superconducting magnet device 60C according to this modification. This superconducting magnet device 60C has a configuration in which a current limiting circuit 67 is added to the superconducting magnet device 60B ( FIG. 6D ). A compensation coil 66B is provided in the innermost layer of the innermost coil 62 of the main coils. The current limiting circuit 67 is provided in a coil 64 made of NbTi. Similar to the coil 64, the current limiting circuit 67 has a configuration in which an NbTi wire is wound into the layers of the coil 64. The current limiting circuit 67 is non-inductively wound as described above. For example, the current limiting circuit has two layers of NbTi wire wound, with the first and second layers wound in opposite directions, resulting in no inductance overall.

[0054] As mentioned above, the current limiting circuit 67 does not have to be provided inside the coil 64, but may be provided anywhere inside, inside, or outside the other coils, and the material thereof is not particularly limited.

[0055] According to this modification, the compensation coil can suppress the attenuation of the central magnetic field and can also prevent damage to the circuit when a quench occurs. Furthermore, since the compensation coil also functions as a buffer member, physical damage due to the torsional floating phenomenon can also be avoided.

[0056] 11, 12, 13, 14: Coil 31: Winding frame 32: Insulating layer 33: Dummy layer 34: Coil layer 35: Insulating layer 36: Reinforcing layer 37: Insulating layer 38: Coil layer 39: Insulating layer 40: Reinforcing layer

Claims

1. A superconducting magnet device comprising: a reel; a superconducting coil formed by winding a tape-shaped superconducting wire around the reel; and a buffer member that suppresses torsional deformation that occurs when a transport current flows through the superconducting coil.

2. The superconducting magnet device according to claim 1, wherein the buffer member is provided between the bobbin and the innermost layer of the superconducting coil.

3. A superconducting magnet device according to claim 1 or 2, characterized in that the buffer member is constructed by winding superconducting wire around the reel, and is not electrically connected to the superconducting coil except via earth.

4. A superconducting magnet device according to any one of claims 1 to 3, characterized in that the superconducting wire constituting the superconducting coil and the superconducting wire constituting the buffer member are made of the same material.

5. A superconducting magnet device according to any one of claims 1 to 3, characterized in that the buffer member is formed by non-inductively winding the superconducting wire.

6. The superconducting magnet device according to any one of claims 1 to 5, characterized in that the superconducting wire is a high-temperature superconducting wire containing REBCO or Bi-2223.

7. A superconducting magnet device comprising: a reel; and a first superconducting coil and a second superconducting coil formed by winding a tape-shaped superconducting wire around the reel; wherein the first superconducting coil and the second superconducting coil are not electrically connected except via earth, but are magnetically coupled; and the second superconducting coil generates a magnetic field that compensates for the decrease in magnetic field in response to the decrease in magnetic field that accompanies the attenuation of the current flowing through the first superconducting coil.

8. The superconducting magnet device according to claim 7, wherein the second superconducting coil is provided between the bobbin and the innermost layer of the first superconducting coil.

9. A superconducting magnet device according to claim 7 or 8, characterized in that the superconducting wire constituting the first superconducting coil and the superconducting wire constituting the second superconducting coil are made of the same material.

10. A superconducting magnet device as described in any one of claims 7 to 9, characterized in that a current limiting circuit made of superconducting wire having a lower critical temperature than the superconducting wire making up the second superconducting coil is connected to the second superconducting coil, and the current limiting circuit is configured so that the heat generated when a quench occurs causes the current limiting circuit to undergo a normal conducting transition.

11. A superconducting magnet device according to claim 10, characterized in that the second superconducting coil is made of high-temperature superconducting wire, and the current-limiting circuit is made of low-temperature superconducting wire.

12. The superconducting magnet device according to claim 10 or 11, characterized in that the current limiting circuit is a coil in which superconducting wire is wound non-inductively.

13. A superconducting magnet device according to any one of claims 10 to 12, characterized in that the current limiting circuit is wound inside the first superconducting coil.

14. A superconducting magnet device comprising: a reel; a first superconducting coil formed by winding a tape-shaped superconducting wire around the reel; and a second superconducting coil formed by winding the superconducting wire around the reel; wherein the second superconducting coil is not electrically connected to the first superconducting coil except via a ground, and the second superconducting coil is provided between the reel and the innermost layer of the first superconducting coil.

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