Superconducting coil device and method for manufacturing the same

Abstract

A superconductive coil device according to this disclosure comprises: a superconductive tape material wound in a helical shape over a plurality of layers; and a metal sheet and an insulating sheet that are provided between the layers of the superconductive tape material. The superconductive coil device is characterized in that the superconductive tape material and the metal sheet are electrically connected, and that the superconductive tape material is fastened with an adhesive between turns of one layer. With this superconductive coil device, prevention of burn damage occurring during quenching, prevention of characteristic degradation caused by hoop stress and axial compressive stress, and prevention of characteristic degradation caused by thermal stress during cooling can be accomplished simultaneously.

Description

Technical Field

[0001] The present invention relates to a superconducting coil device and a method for manufacturing the same.

Background Art

[0002] By operating a coil device (high-temperature superconducting coil device) wound with a high-temperature superconducting tape wire at a high current density, it is possible to manufacture a compact coil device that generates a high magnetic field. In order to manufacture such a coil device, it is necessary to solve all of the following three problems.

[0003] First problem: A high-temperature superconducting coil device may be damaged by quenching (transition from the superconducting state to the normal conducting state and a rise in temperature), and a protection technique for preventing this is important.

[0004] Second problem: In a high-temperature superconducting coil device, strong electromagnetic stresses, that is, hoop stress and axial compression stress are generated. Therefore, it is important to prevent mechanical deterioration of the coil by preventing these stresses from becoming too high. In particular, in recent years, problems have become apparent in which the hoop stress increases or the high-temperature superconducting tape wire buckles due to a screening current (superconducting eddy current) peculiar to a high-temperature superconducting coil device, and countermeasures against this phenomenon are important.

[0005] Third problem: A high-temperature superconducting coil device may be mechanically deteriorated by thermal stress during cooling, and it is important to prevent this.

[0006] FIG. 9(A) is a diagram showing the configuration of a superconducting coil device A disclosed in Conventional Example 1 (Non-Patent Document 1). Cross-section 910 is a cross-sectional view by a plane perpendicular to the circumferential direction. As shown in the figure, the superconducting coil device A of Conventional Example 1 is a layer-wound coil in which a plurality of layers of high-temperature superconducting tape wires 912 are wound in a spiral shape, and a composite sheet of a metal sheet 913 and an insulating sheet 914 is sandwiched between the layers of the tape wires 912. This configuration is called the intra-Layer No-Insulation (LNI) method.

[0007] According to this configuration, the coil device can be protected from burnout during quenching. This is because the tape wire 912 and the metal sheet 913 are in electrical contact, so that the current bypasses to the metal sheet 913 during quenching. Also, since the tape wire 912, the metal sheet 913, and the insulating sheet 914 are not adhered to each other, mechanical degradation due to the difference in thermal stress during cooling does not occur.

[0008] However, in the superconducting coil device A of the conventional example 1, since the tape wire 912 is not fixed and is in a state where it is easily movable with respect to electromagnetic stress, it is impossible to prevent characteristic degradation due to hoop stress and axial compression stress, which are the second problems. As shown in FIG. 10, strong electromagnetic stress, that is, hoop stress and axial compression stress, is generated in the tape wire 912. Since a shielding current (superconducting eddy current) flows through the tape wire 912, problems such as an increase in hoop stress and buckling of the tape wire 912 have been clarified in recent years. Also, Lorentz forces in different directions, outward and inward in the radial direction, act depending on the location, causing the tape wire 912 to tilt, so that slippage of the tape wire 912 occurs due to axial compression stress. Thus, in the conventional example 1, the second problem cannot be solved.

[0009] FIG. 9(B) is a diagram showing the configuration of a superconducting coil device B disclosed in the conventional example 2 (Non-Patent Document 2). The cross section 920 is a cross-sectional view by a plane perpendicular to the circumferential direction. The difference from the conventional example 1 is that an impregnating material 915 such as an epoxy resin is infiltrated and cured between the layers to adhere the tape wire 912, the metal sheet 913, and the insulating sheet 914. As a result, the coil is rigidified, so that the effect of increasing hoop stress and the slippage of the tape wire 912 can be suppressed, and the second problem can be solved.

[0010] However, by using the impregnating material 915, the electrical contact between the tape wire 912 and the metal sheet 913 is lost or becomes insufficient. Therefore, it becomes impossible to achieve prevention of burnout during quenching. Furthermore, since the entire coil is rigidified, due to the difference in the thermal shrinkage rates of the tape wire 912 and the impregnating material 915 during cooling, an excessive thermal stress (tensile direction with respect to the tape wire surface) is applied in the radial direction, and the tape wire 912 deteriorates mechanically.

[0011] Thus, although the superconducting coil device B of the conventional example 2 can solve the second problem, it cannot solve the first and third problems.

Prior Art Documents

Non-Patent Documents

[0012]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] An object of the present invention is to provide a superconducting coil device capable of simultaneously achieving prevention of burnout during quenching, prevention of characteristic deterioration due to hoop stress and axial compression stress, and prevention of characteristic deterioration due to thermal stress during cooling.

Means for Solving the Problems

[0014] In order to solve the above problems, the present invention adopts a configuration in which superconducting tape wires in a layer are mechanically adhered by an adhesive, while at least a part of the superconducting tape wires and the metal sheet are not adhered but maintain electrical contact.

[0015] More specifically, a first aspect of the present invention is a superconducting coil device including superconducting tape wires wound spirally over a plurality of layers, and a metal sheet and an insulating sheet provided between the layers of the superconducting tape wires, wherein the superconducting tape wires and the metal sheet are electrically connected, and the superconducting tape wires are adhered between turns of one layer by an adhesive, characterized by a superconducting coil device.

[0016] A second aspect of the present invention is a step of winding superconducting tape wires spirally, a step of applying an adhesive between turns of the superconducting tape wires, a step of winding a metal sheet and an insulating sheet outside the superconducting tape wires, and repeating the above steps a plurality of times, which is a method for manufacturing a superconducting coil device.

Effects of the Invention

[0017] According to the present invention, it is possible to simultaneously achieve prevention of burnout during quenching, prevention of characteristic deterioration due to hoop stress and axial compression stress, and prevention of characteristic deterioration due to thermal stress during cooling.

Brief Description of the Drawings

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[0019] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The components of each embodiment described below can be combined as appropriate.

[0020] (Configuration) Figs. 1A to 1C are diagrams showing the configuration of the high-temperature superconducting coil device 100 according to the present embodiment. Fig. 1A shows a cross-section 110 of the superconducting coil device 100 by a plane perpendicular to the circumferential direction. Fig. 1B is an enlarged view of the cross-section 110. Fig. 1C is an enlarged view of a partial cross-section 120 in Fig. 1B. Figs. 1D and 1E are enlarged views of the partial cross-section 120 in a modified example. Note that it should be noted that these are schematic diagrams for explaining Figs. 1A to 1E and do not accurately depict the structure.

[0021] As shown in the figure, the high-temperature superconducting coil device 100 is a layer-wound coil in which a plurality of layers of non-insulated high-temperature superconducting tape wires 112 are wound in a spiral shape, and a composite sheet of a metal sheet 113 and an insulating sheet 114 is sandwiched between the layers of the tape wires 112. The composite sheet may be a structure in which the sheets are pasted together with an adhesive or the like, a structure in which an insulating material is electrodeposited on one side of the metal sheet, or a structure in which a metal material is plated on one side of the insulating sheet. Also, in each layer, an adhesive 116 is provided between the turns of the tape wire 112, and the tape wires 112 in the z-direction (coil axis direction) are adhered to each other. Further, since the adhesive 116 is provided only between the turns, the tape wire 112 and the metal sheet 113 are in electrical contact. Note that the metal sheet 113 and the insulating sheet 114 do not necessarily have to be a composite sheet, and a configuration in which individual metal sheets 113 and insulating sheets 114 are respectively sandwiched may also be used.

[0022] The high-temperature superconducting tape wire 112 is, for example, REBa 2 Cu 3 O x (REBCO wire) or Bi 2 Sr 2 Ca 2 Cu 3 O x(BSCCO wire). Here, RE is a rare earth element such as Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. The tape wire 112 generally has a multilayer structure composed of a plurality of materials for mechanical reinforcement and electrical protection. For example, the tape wire 112 has a superconducting layer provided via an intermediate layer on one side of a substrate such as Hastelloy, and has one or a plurality of stabilizing layers (for example, two layers of a copper stabilizing layer and a silver stabilizing layer) covering these. The size of the tape wire 112 is not particularly limited, but for example, those with a width of 4 mm and a wire thickness of about 0.1 mm (substrate 75 μm, stabilizing layer 20 μm) can be adopted.

[0023] The metal sheet 113 is copper in this embodiment, but may be other metals such as platinum, gold, silver, or a conductive material other than a metal. The thickness of the metal sheet 113 is, for example, 7 μm.

[0024] The insulating sheet 114 is polyimide in this embodiment, but any other material can be adopted as long as it has sufficient flexibility and can provide insulation. For example, polytetrafluoroethylene (PTFE, Teflon (registered trademark)) can be adopted. The thickness of the insulating sheet 114 is, for example, 12.5 μm.

[0025] The adhesive 116 is an epoxy resin in this embodiment, but may be any material as long as it can bond the tape wires 112 together. For example, as the adhesive 116, a thermosetting resin-based, thermoplastic resin-based, or elastomer-based adhesive can be adopted. Alternatively, the adhesive 116 may be a metal with a lower melting point than the tape wire 112, such as solder. Further, the adhesive 116 may be an adhesive containing ceramic powder.

[0026] As shown in FIG. 1C, the adhesive 116 may be provided between turns in one layer, and need not be provided between the tape wire 112 and the metal sheet 113 and between the tape wire 112 and the insulating sheet 114. Also, the adhesive 116 need not be provided at all between turns. For example, it may be provided in a portion of 50% or more per turn, preferably in a portion of 75% or more, and more preferably in a portion of 90% or more. Note that the above ratio may be adhered as an average of a plurality of turns, and even if the ratio is adhered only below the above ratio between one turn, it may be acceptable. For example, no adhesive 116 may be provided at all between a certain one turn.

[0027] Also, as shown in FIG. 1D, the adhesive 116 may be provided between the tape wire 112 and the insulating sheet 114 in addition to between turns. That is, the adhesive 116 may have a first portion 116a provided between turns and a second portion 116b provided between the tape wire 112 and the insulating sheet 114. Although FIG. 1D shows that the adhesive 116 is provided over the entire area between the tape wire 112 and the insulating sheet 114, there may be a portion where the adhesive 116 is not provided between them, and the tape wire 112 and the insulating sheet 114 may be in direct contact.

[0028] Also, as shown in FIG. 1E, the adhesive 116 may be further provided between the tape wire 112 and the metal sheet 113. That is, in addition to the first portion 116a provided between turns and the second portion 116b provided between the tape wire 112 and the insulating sheet 114, the adhesive 116 may have a third portion 116c provided between the tape wire 112 and the metal sheet 113. Here, the tape wire 112 and the metal sheet 113 must be at least partially in direct contact and electrically connected, and it is not preferable to provide the adhesive 116 over the entire area between the tape wire 112 and the metal sheet 113. For example, among the area per turn of the tape wire 112 and the metal sheet 113, it is preferable that 50% or more of the portion is in direct contact, more preferably 75% or more, and even more preferably 90% or more. Note that the above ratio may be in direct contact as an average of multiple turns, and even if less than the above ratio is in direct contact for one turn, it may be acceptable.

[0029] In addition, when the adhesive 116 is provided between the tape wire 112 and the insulating sheet 114, it is not necessarily the case that the adhesive 116 is required between the tape wire 112 and the insulating sheet 114, and it may be omitted. Also, the second portion 116b and the third portion 117c do not necessarily have to be continuous with the first portion 116a and may be separated from the first portion 116a. Also, in the above description, the tape wire 112 is wound over multiple layers, but the tape wire 112 may be only one layer.

[0030] (Manufacturing Method) A method for manufacturing the superconducting coil device 100 according to this embodiment will be described. Here, a manufacturing method for making the coil device 100 having the structure shown in FIG. 1C will be described. First, the tape wire 112 is wound in a spiral for one layer around the coil winding form. Then, an adhesive 116 such as an epoxy resin is applied to the space between the turns. The adhesive 116 protruding from between the turns is wiped off as appropriate. Then, a composite sheet composed of the metal sheet 113 and the insulating sheet 114 is wound, or the metal sheet 113 is wound and then the insulating sheet 114 is wound thereon. After that, the tape wire 112 is wound in a spiral for one more layer on the insulating sheet 114. Thereafter, the above-described process is repeated.

[0031] When making the coil device 100 having the structure shown in FIG. 1D, an adhesive 116 such as an epoxy resin is applied to the entire surface of the coil winding form, and then the tape wire 112 is wound in a spiral for one layer. The adhesive protruding from the space between the turns is wiped off as appropriate. Then, a composite sheet composed of the metal sheet 113 and the insulating sheet 114 is wound. After that, an adhesive 116 is applied to the entire surface of the insulating sheet 114, and then the tape wire 112 is wound in a spiral for one more layer. Thereafter, the above-described process is repeated.

[0032] If manufactured in this way, a coil device having the structure shown in FIG. 1C or FIG. 1D is made. Note that if the adhesive 116 protruding from between the turns is left unintentionally or intentionally, a coil device having the structure shown in FIG. 1E is made.

[0033] In the above description, a structure in which the superconducting tape wire 112, the metal sheet 113, and the insulating sheet 114 are provided in this order toward the outer side in the radial direction (r) of the coil has been described. However, a structure in which the insulating sheet 114, the metal sheet 113, and the superconducting tape wire 112 are provided in this order toward the outer side in the radial direction may also be used. The manufacturing method of the superconducting coil device having this structure is basically the same as the above, but it is necessary to wind the superconducting tape wire 112 without applying the adhesive to the metal sheet 113 and then apply the adhesive between the turns.

[0034] Regardless of the order of the superconducting tape wire 112, the metal sheet 113, and the insulating sheet 114, the superconducting coil device can be manufactured by repeating a plurality of steps including: winding the superconducting tape wire 112 in a spiral shape; applying an adhesive 116 between turns of the superconducting tape wire 112; and winding the metal sheet 113 and the insulating sheet 114 in this order or in the reverse order outside the superconducting tape wire 112.

[0035] (Performance Evaluation) The performance of the superconducting coil device 100 according to this embodiment was verified by experiments and numerical analysis.

[0036] [1. Protection Function during Quench Occurrence (First Problem)] First, a quench was forcibly generated using the superconducting coil device 100 according to this embodiment. FIG. 2A shows the experimental results using the coil device of Comparative Example 2 (Non-Patent Document 2), and FIG. 2B shows the experimental results using the coil device 100 according to this embodiment. These figures show the time variations of current, magnetic field, and coil voltage.

[0037] In the coil device according to Comparative Example 2 in which the tape wire and the metal sheet are insulated, as shown in FIG. 2A, the coil voltage rapidly increases due to quench occurrence and burnout occurs. On the other hand, in the coil device 100 according to this embodiment, since the electrical connection between the tape wire 112 and the metal sheet 113 is maintained, as shown in FIG. 2B, an automatic protection effect peculiar to the LNI type coil is obtained in which the current bypasses to the metal sheet 113 and the magnetic field decays when a quench occurs. Specifically, by eliminating the interlayer contact by the interlayer insulating sheet 114, the time constant of the excitation delay is shortened, and further, by connecting the turns by the metal sheet 113, a protection effect against thermal runaway can be obtained. Thus, according to this embodiment, the above-described first problem can be solved.

[0038] [2. Prevention of Deterioration due to Hoop Stress and Axial Compressive Stress (Second Problem)] Next, stress analysis was performed on one layer of the coil using the finite element method. Here, the electromagnetic force caused by the screening current peculiar to the high-temperature superconducting tape wire was considered. FIG. 3A shows the results for the coil device of Conventional Example 1 (Non-Patent Document 1), and FIG. 3B shows the results for the superconducting coil device 100 according to the present embodiment. These figures show the distribution of hoop stress and the displacement of the tape wire at each z position.

[0039] As shown in FIG. 3A, in the coil device of Conventional Example 1 in which the epoxy resin is not impregnated between the turns of the tape wire, the hoop stress ranges from a maximum of 556 MPa to a minimum of -300 MPa. Also, since the turns are not adhered to each other, a large displacement occurs in the tape wire. In this way, since the axial compressive stress is applied in a state where the tape wire is tilted, the wire slips. When slipping occurs, the tape wire is greatly deformed and deteriorated.

[0040] On the other hand, in the coil device according to the present embodiment, as shown in FIG. 3B, it can be seen that the absolute values of the maximum hoop stress and the minimum hoop stress applied to the tape wire are reduced. It has been found that buckling is likely to occur when hoop stress in the compression direction (negative hoop stress in the above) occurs, and the coil device according to the present embodiment can significantly suppress the hoop stress in the compression direction. For these reasons, it is possible to suppress the occurrence of deterioration of the tape wire and buckling. Also, since the deformation of the tape wire is suppressed by the impregnated epoxy resin between the turns, an effect of preventing the tape wire from slipping due to the axial compressive stress can also be obtained. That is, according to the present embodiment, the above-described second problem can be solved.

[0041] Similarly, a similar stress analysis was performed on a coil consisting of 60 layers. The analysis method is the same as described above. Fig. 4A shows the results for the coil device of Conventional Example 1 (Non-Patent Document 1), and Fig. 4B shows the results for the superconducting coil device 100 according to the present embodiment. In these figures, the distribution of hoop stress at each z position is shown together with the positions where the hoop stress takes the maximum and minimum values and their values. Fig. 5 shows the magnitude of the hoop stress at each position of the 28th layer from the center side. Graph 501 (circles) shows the results for the coil device of Conventional Example 1, and graph 502 (crosses) shows the results for the coil device of the present invention.

[0042] As shown in Fig. 4A, the hoop stress of the coil device of Conventional Example 1 is maximum 667 MPa and minimum -259 MPa. On the other hand, as shown in Fig. 4B, the hoop stress of the coil device according to the present embodiment is maximum 595 MPa and minimum -4 MPa, and it can be seen that both the maximum and minimum values are reduced. In particular, the hoop stress in the compression direction can be almost completely eliminated. Also, as shown in Fig. 5, the coil of the present embodiment can suppress the variation of the hoop stress within one layer compared with the coil of Conventional Example 1, and it can be seen that the hoop stress changes continuously. Thus, also in the case of a 60-layer coil, reduction of the absolute values of the maximum and minimum values of the hoop stress, and in particular reduction of the hoop stress in the compression direction can be achieved, so that deformation and buckling of the coil can be suppressed.

[0043] [3. Prevention of degradation due to thermal stress (third problem)] Next, the current-voltage characteristics of the coil before and after impregnation with epoxy resin were examined for the superconducting coil device 100 according to the present embodiment and the coil device of Conventional Example 2 (Non-Patent Document 2). Fig. 6A shows the measurement results for the coil device (multiple layers) according to Conventional Example 2, and Fig. 6B shows the measurement results for the coil device (single layer) according to the present embodiment.

[0044] As shown in Fig. 6A, in the coil device of Comparative Example 2, the critical current is decreased by the impregnation of epoxy resin. This is because the layers are adhered to each other by the epoxy resin (impregnating material), and the deterioration of the wire material is caused by the thermal stress generated by the difference in the thermal shrinkage rate during cooling.

[0045] On the other hand, in the coil device according to the present embodiment, the impregnation of epoxy resin is limited and the layers are not adhered to each other. Therefore, as shown in Fig. 6B, the decrease in the critical current does not occur before and after the impregnation of epoxy resin.

[0046] In this measurement, there is a difference that the coil device according to the present embodiment is a single layer, while the coil device according to Comparative Example 2 is a multi-layer. Due to this difference, the values of the critical currents of the two are different. However, since this measurement is for measuring the deterioration during cooling, the current value itself is not important. Also, it is obvious that if the deterioration prevention effect can be obtained in one layer in the coil of the present embodiment, the same effect can be obtained in multiple layers. However, for safety, the current-voltage characteristics were examined in a multi-layer coil.

[0047] Fig. 7A shows the measurement results of the coil device (multi-layer) according to Comparative Example 2, and Fig. 7B shows the measurement results of the coil device (multi-layer) according to the present embodiment. Note that the coil devices in Fig. 6A and Fig. 7A are different. In the coil device according to the comparative example, the critical current (the electric field standard is 1 μV / cm) decreases from 56 A to 40 A, while in the coil device according to the present embodiment, the decrease is from 44 A to 42 A, and almost no decrease in the critical current occurs before and after the impregnation of epoxy resin.

[0048] [Summary of the effects of the present embodiment] Fig. 8 is a diagram summarizing the effects of the superconducting coil device 100 according to the present embodiment in comparison with Comparative Examples 1 and 2. In Comparative Example 1, protection from burnout due to quench (the first problem) and prevention of characteristic deterioration due to thermal stress during cooling (the third problem) can be solved, but prevention of characteristic deterioration due to increased hoop stress and axial compressive stress (the second problem) cannot be solved. In Comparative Example 2, the second problem can be solved, but the first and third problems cannot be solved.

[0049] This embodiment can solve all of these three problems. The first problem is solved by electrically contacting the tape wire and the metal sheet within the layer. The second problem is solved by providing an adhesive between the turns of the tape wire within the layer to fix the tape wires to each other. The third problem is solved by not mechanically bonding the tape wire and the metal sheet, that is, by avoiding the adhesion between the tape wires between the layers.

[0050] According to this embodiment, a small coil device that generates a high magnetic field can be manufactured. The coil device of this embodiment can be applied to devices that require operation in a permanent current mode, such as NMR devices and MRI devices.

Explanation of Signs

[0051] 100: Superconducting coil device 112: High-temperature superconducting tape wire 113: Metal sheet 114: Insulating sheet 116: Adhesive

Claims

1. A superconducting coil device comprising a superconducting tape wire wound spirally over a plurality of layers, and a metal sheet and an insulating sheet provided between the layers of the superconducting tape wire, wherein the superconducting tape wire and the metal sheet are electrically connected, the turns of the superconducting tape wire wound spirally in the same layer are adhered by an adhesive, the adhesive is provided only (1) between the turns of the superconducting tape wire wound spirally in the same layer, or (2) between the turns of the superconducting tape wire wound spirally in the same layer and at least a part between the superconducting tape wire and the adjacent insulating sheet, or (3) between the turns of the superconducting tape wire wound spirally in the same layer, at least a part between the superconducting tape wire and the adjacent insulating sheet, and a part between the superconducting tape wire and the adjacent metal sheet, characterized in that it is a superconducting coil device.

2. In one layer, the superconducting tape wire, the metal sheet, and the insulating sheet are provided in the order of superconducting tape wire, metal sheet, insulating sheet, or insulating sheet, metal sheet, superconducting tape wire, toward the outside in the radial direction. The superconducting coil device according to claim 1.

3. The superconducting tape wire and the metal sheet are in direct contact at least partially without passing through the adhesive. The superconducting coil device according to claim 1 or 2.

4. The superconducting tape wire and the insulating sheet are adhered at least partially by the adhesive. The superconducting coil device according to any one of claims 1 to 3.

5. The adhesive is a thermosetting resin. The superconducting coil device according to any one of claims 1 to 4.

6. The adhesive is a metal having a lower melting point than the superconducting tape wire and the metal sheet. The superconducting coil device according to any one of claims 1 to 4.

7. The insulating sheet is polyimide. The superconducting coil device according to any one of claims 1 to 6.

8. The insulating sheet is polytetrafluoroethylene. The superconducting coil device according to any one of claims 1 to 6.

9. A method for manufacturing a superconducting coil device comprising a superconducting tape wire wound spirally over a plurality of layers, and a metal sheet and an insulating sheet provided between the layers of the superconducting tape wire, comprising: winding the superconducting tape wire spirally for one layer; applying an adhesive to the space between the turns of the superconducting tape wire wound spirally for one layer; wrapping a metal sheet and an insulating sheet around the outside of the superconducting tape wire wound spirally for one layer; repeating the above steps a plurality of times. A method for manufacturing a superconducting coil device, characterized by the above steps.

10. The method for manufacturing a superconducting coil device according to claim 9, further comprising wiping off the adhesive protruding from the space between the turns after applying the adhesive to the space between the turns of the superconducting tape wire wound spirally for one layer. A method for manufacturing a superconducting coil device according to claim 9, characterized by the above steps.

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