Method for manufacturing a superconducting coil and superconducting coil

Abstract

This invention provides a method for manufacturing a superconducting coil that allows for adjustment of the inter-winding contact resistance in a superconducting coil formed by winding high-temperature superconducting wire, even after winding, and a superconducting coil adjusted in this manner. [Solution] The method for manufacturing a superconducting coil 10 according to the present invention is characterized by comprising: a resistance measurement step S51 for measuring the inter-winding contact resistance value of a superconducting coil 10 made by winding a rare-earth oxide superconducting wire (high-temperature superconducting wire 1) having copper 3a on its surface; and a correction step S53 for correcting the inter-winding contact resistance value by holding the superconducting coil 10 at 100°C to 200°C if the inter-winding contact resistance value in the resistance measurement step S51 is outside a desired range.

Description

Technical Field

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

Background Art

[0002] The development of rare-earth-based high-temperature superconducting wires (hereinafter, REBCO wires) has progressed, and superconducting coils that generate strong magnetic fields, which were not achievable with conventional low-temperature superconducting wires, can now be fabricated. The critical temperature of REBCO wires is as high as about 95 Kelvin (K), and they can be used in a superconducting state even at the liquid nitrogen temperature of 77K. Although there are advantages such as less energy required for cooling due to the high operating temperature, there are also issues to be addressed for effective use. Generally, the specific heat of metal materials such as copper tends to increase with increasing temperature. Based on the operating temperature of 4.2K for conventional low-temperature superconducting NbTi, at 20K, it has a specific heat approximately 10 times that at 4.2K, and at 77K, it has a specific heat approximately 100 times that at 4.2K. The fact that a large specific heat makes it difficult for the temperature of the superconducting wire to rise with a certain amount of heat generation / input is an advantage in terms of keeping the superconducting wire below the critical temperature, but on the other hand, it also causes disadvantages. In a superconducting coil using REBCO wires (hereinafter, REBCO coil), when local normal conduction and heat generation called hot spots occur, compared to extremely low temperatures such as 4.2K, the temperature rise of the superconducting wire is extremely slow. Therefore, the normal conduction associated with the temperature rise of the surrounding wires does not spread, and only the hot spots consume and generate heat from the stored energy of the coil, which may lead to burnout.

[0003] As a countermeasure against local normal conduction and heat generation in REBCO coils, a coil manufacturing method called a non-insulated coil is considered promising. In conventional superconducting coils, it is common to electrically insulate between coil windings. However, in a non-insulated coil, for example, by means such as impregnating the coil wire with solder, electrical conductivity is ensured while having a certain electrical resistance without electrically insulating between the windings. Thereby, when local normal conduction occurs, the current flowing through that winding can be diverted to the adjacent winding, preventing burnout at the hot spot.

[0004] When an uninsulated coil is excited by increasing the current, current flows not only through the superconducting section but also through the conductive parts between the windings, resulting in a phenomenon called excitation lag, where the strength of the magnetic field generated by the REBCO coil is not proportional to the current value. In extreme cases, this delay can last for several days. In some applications using REBCO coils, it is essential to excite the coil within a specified time, so there is a lower limit to the inter-winding contact resistance. In such applications, it is necessary to eliminate the excitation lag by increasing the inter-winding contact resistance.

[0005] On the other hand, there is an upper limit to the inter-winding contact resistance. If the inter-winding contact resistance is too high when the aforementioned hot spot occurs, the amount of current commutating from the REBCO wire to the conductive part between the windings decreases, increasing the energy consumed within the REBCO wire. As a result, the temperature of the REBCO wire rises, and the purpose of protecting the REBCO coil is not achieved.

[0006] A technique for protecting the REBCO coil is disclosed, for example, in Patent Document 1. Specifically, Patent Document 1 discloses an HTS field coil (i.e., a superconducting coil) comprising a plurality of windings (i.e., high-temperature superconducting wires) containing a high-temperature superconductor (HTS) material and a metal stabilizer, and a partial insulating layer that separates the windings so that current can be shared between the windings via the partial insulating layer. The partial insulating layer includes a conductive layer coated on one side with a first insulating layer and on the other side with a second insulating layer. Each insulating layer has one or more windows through which electrical contact can be formed between the windings and the conductive layer. The windows of the first insulating layer are offset in the plane of the conductive flakes (conductive layer) from the windows of the second insulating layer. With this structure, the HTS field coil described in Patent Document 1 shares current between the windings via the partial insulating layer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 2021-513219 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in the technique described in Patent Document 1, which uses the aforementioned windowed partial insulating layer, if an issue occurs such as the inter-winding contact resistance in a superconducting coil formed by winding high-temperature superconducting wire not having the desired performance, it is not possible to adjust the inter-winding contact resistance after winding.

[0009] The present invention has been made in view of the above circumstances. The object of the present invention is to provide a method for manufacturing a superconducting coil that allows for adjustment of the inter-winding contact resistance in a superconducting coil formed by winding a high-temperature superconducting wire even after winding, and a superconducting coil manufactured by this method. [Means for solving the problem]

[0010] The present invention, which solves the aforementioned problems, is characterized by comprising: a resistance measurement step of measuring the inter-winding contact resistance value of a superconducting coil made by winding a rare-earth oxide superconducting wire having copper on its surface; and, if the inter-winding contact resistance value in the resistance measurement step is outside a desired range, a correction step of correcting the inter-winding contact resistance value by holding the superconducting coil at 100°C to 200°C. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for manufacturing a superconducting coil that allows for adjustment of the inter-winding contact resistance in a superconducting coil formed by winding a high-temperature superconducting wire, even after winding, and a superconducting coil manufactured by this method. Other issues, configurations, and effects not mentioned above will be revealed by the following description of embodiments. Further features related to the present invention will be revealed by the description herein and the accompanying drawings. [Brief explanation of the drawing]

[0012] [Figure 1] This is a flowchart illustrating the method for manufacturing the superconducting coil 10 according to the first embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a part of the superconducting coil 10 according to the first embodiment. [Figure 3] This is a schematic cross-sectional view of the high-temperature superconducting wire 1 in the second embodiment. [Figure 4] This is a schematic cross-sectional view of a part of the superconducting coil 10 according to the third embodiment. [Figure 5] This is a flowchart illustrating the method for manufacturing the superconducting coil 10 according to the fourth embodiment of the present invention. [Figure 6] This is a schematic cross-sectional view of a part of the superconducting coil 10 according to the fourth embodiment. [Modes for carrying out the invention]

[0013] Hereinafter, a method for manufacturing a superconducting coil and a superconducting coil according to one embodiment of the present invention will be described with reference to the drawings as appropriate. Note that common components in the following description and drawings may be denoted by the same reference numerals, and redundant descriptions may be omitted. Furthermore, the present invention is not limited to the following embodiments. Moreover, the description herein is merely a typical example and does not limit the claims or applications in any sense.

[0014] In the following embodiments, where necessary for convenience, the description will be divided into multiple sections or embodiments. Unless otherwise specified, these are not unrelated, and one may be a modification, detail, or supplementary explanation of part or all of the other. Furthermore, in the following embodiments, when referring to the number of elements (including quantity, numerical value, amount, range, etc.), unless otherwise specified or clearly limited to a specific number in principle, it is not limited to that specific number, and may be greater than or less than that number.

[0015] Furthermore, in the following embodiments, it goes without saying that the components are not necessarily essential unless otherwise explicitly stated or considered to be fundamentally essential. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc., of the components, etc., it shall include those that are substantially similar or analogous to their shape, etc., unless otherwise explicitly stated or considered to be fundamentally essential. The same applies to the numerical values ​​and ranges mentioned above. In addition, the size and number of each component etc. in the illustrations have been exaggerated or simplified as appropriate to make the illustrations easier to understand.

[0016] [First Embodiment] A method for manufacturing a superconducting coil 10 (Figure 2) according to the first embodiment of the present invention (hereinafter sometimes referred to as "this manufacturing method") involves winding a rare-earth oxide superconducting wire having copper on its surface to produce a superconducting coil 10. This rare-earth oxide superconducting wire is sometimes called a high-temperature superconducting wire because its critical temperature is high, around 95 Kelvin (K), or it is sometimes called a REBCO wire due to its material. In the following description, the rare-earth oxide superconducting wire may be referred to as the high-temperature superconducting wire 1 (Figure 2). Known high-temperature superconducting wires can be used. The high-temperature superconducting wire 1 is not particularly limited, but for example, a substrate 5 (Figure 2) such as Hastelloy may be provided with an orientation layer and a barrier layer as needed (neither shown), a superconducting layer (not shown) on top of that, and a copper 3a film (copper oxide film 3 (Figure 2)) on top of that as a stabilizing layer. That is, the high-temperature superconducting wire 1 has copper 3a on its surface as described above. The substrate 5 only needs to have mechanical properties against bending and other forces in the high-temperature superconducting wire 1, and a rolled and oriented Ni-W substrate can also be used. The orientation layer is deposited to obtain oriented crystals, improve the degree of orientation, and reduce lattice misfit with the superconducting layer. As the orientation layer, for example, a CeO2 layer deposited by the IBAD (Ion Beam Assisted Deposition) method can be used. The barrier layer is laminated between the substrate 5 and the orientation layer to prevent the diffusion of impurity metals from the substrate 5. The superconducting layer is formed by aligning oxide crystals (REBCO) composed of RE, Ba, Cu, and O in a plane such that the crystal axes are aligned in one direction. RE stands for rare earth elements, and includes scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), eurobium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).The superconducting layer can be formed by, for example, the PLD (Pulsed laser deposition) method, the MOCVD (Metal Organic Chemical Vapor Deposition) method, the MOD (Metal Organic Deposition) method, the LPE (Liquid Phase Epitaxy) method, etc.

[0017] FIG. 1 is a flowchart for explaining the content of a method for manufacturing a superconducting coil 10 according to a first embodiment of the present invention. As shown in FIG. 1, this manufacturing method has a resistance measurement step S51 and a correction step S53. Further, this manufacturing method has a winding step S50 before the resistance measurement step S51. Further, this manufacturing method has a determination step S52 after the resistance measurement step S51. Hereinafter, the winding step S50, the resistance measurement step S51, the determination step S52, and the correction step S53 will be described in accordance with the flow order shown in FIG. 1.

[0018] In the winding step S50, the high-temperature superconducting wire 1 is wound in a coil shape to form the shape of the superconducting coil 10. The high-temperature superconducting wire 1 can be formed into a coil shape by winding it around a bobbin (not shown). The bobbin may be, for example, made of stainless steel, fiber-reinforced plastic (FRP), ceramic, etc.

[0019] In the resistance measurement step S51, the measurement of the contact resistance value between windings in the superconducting coil 10 formed by winding the high-temperature superconducting wire 1 is performed. The simplest method for measuring the contact resistance value between windings in the superconducting coil 10 is measurement by the four-terminal method at room temperature. By measuring the generated voltage at both ends of the coil when energized from both ends of the coil winding, the resistance of the entire coil is confirmed. Next, the contact resistance measurement by current source interruption is shown. The superconducting coil 10 is cooled to the temperature at which the high-temperature superconducting wire 1 exhibits superconducting characteristics, for example, the liquid nitrogen temperature of 77K, and the superconducting coil 10 is energized using a current source to obtain a certain value of current. Next, a switch or the like is used to interrupt the current source and attenuate the current. The contact resistance value between windings can be measured from this decay time constant and the inductance value of the coil.

[0020] In the determination step S52, it is determined whether the inter-winding contact resistance value measured in the resistance measurement step S51 is within the desired range. If the inter-winding contact resistance value is outside the desired range (No in determination step S52), the correction step S53 is performed. If the inter-winding contact resistance value is within the desired range, the correction step S53 is skipped and manufacturing (adjustment) is completed (Yes in determination step S52). The desired range for the inter-winding contact resistance value is, for example, 0.1 mΩ·cm. 2 ~100mΩ·cm 2 For example, a winding contact resistance value outside the desired range is 0.1 mΩ·cm. 2 One example is that it is less than [a certain value]. However, the desired range of the inter-winding contact resistance value in this embodiment can be arbitrarily set according to the specifications required for the product, and is not limited to those described above.

[0021] In the correction step S53, the superconducting coil 10 is maintained at a temperature between 100°C and 200°C to correct the inter-winding contact resistance value. For example, in the correction step S53, after drying the superconducting coil 10, the temperature of the superconducting coil 10 is maintained at a temperature between 100°C and 200°C using a constant temperature bath or the like. The maintenance time is arbitrary. The atmosphere around the superconducting coil 10 may be air or a mixed gas with controlled oxygen concentration. After the desired time has elapsed, the superconducting coil 10 is left to cool or left to cool until its temperature reaches room temperature. The superconducting coil 10 that has gone through this step is returned to the resistance measurement step S51. Note that if the temperature in the correction step S53 is below 100°C, the process may take too long or the process may not be sufficient, which is undesirable. If the temperature in the correction step S53 exceeds 200°C, the superconducting properties of the high-temperature superconducting wire 1 may deteriorate, which is undesirable. If the temperature in the modification process S53 is between 100°C and 200°C, it is possible to form the copper oxide film 3 while preventing a decrease in the performance of the high-temperature superconducting wire 1.

[0022] This manufacturing method allows for the production of a suitable superconducting coil 10 by performing the above steps. In particular, since this manufacturing method includes a resistance measurement step S51 and a correction step S53, the inter-winding contact resistance of the superconducting coil 10, which is formed by winding a high-temperature superconducting wire 1, can be adjusted even after winding. Because this manufacturing method allows for the adjustment of the inter-winding contact resistance of the superconducting coil 10 even after winding, it is possible to provide a superconducting coil 10 that can be excited within a desired time and that prevents coil damage due to partial normal conduction.

[0023] Figure 2 is a schematic cross-sectional view of a superconducting coil 10 according to the first embodiment. In Figure 2, the superconducting coil 10 shows an example in which a high-temperature superconducting wire 1, manufactured as a tape wire with a rectangular cross-section, is wound in a pancake coil shape. The superconducting coil 10 can be wound by winding the high-temperature superconducting wire 1, which is wound on the inner circumference without changing the wire width direction 2, around the coil axis 8, thereby creating a coil with the configuration shown in the schematic cross-sectional view of Figure 2. It is preferable that the high-temperature superconducting wire 1 is a tape wire with a rectangular cross-section, but it can also be a wire with a circular cross-section or a wire with a hexagonal cross-section.

[0024] A film of copper 3a (preferably oxygen-free copper) is placed on the outer surface of the high-temperature superconducting wire 1, and a copper oxide film 3 is formed on the outermost surface of the copper 3a by oxidation. If the aforementioned modification step S53 is not performed, the thickness of the copper oxide film 3 on the surface of the high-temperature superconducting wire 1 is often 3 to 4 nm. This has been confirmed, for example, in Reference 1 (Qualtec Co., Ltd., "Copper Oxide Film and Solderability Supplement) Solder Wettability and Voids", [URL]https: / / www.qualtec.co.jp / new_qualtec / wp-content / themes / qualtec_theme / pdf / copper_oxide_solder.pdf, p. 5). If the aforementioned modification step S53 is not performed (i.e., if the thickness of the copper oxide film 3 is 3 to 4 nm), an excitation delay occurs, as explained in the background technology section. The occurrence of an excitation delay in this case is supported, for example, by Reference 2 (Atsushi Ishiyama, "Protection Techniques for REBCO Coils - Including Comparisons with Low-Temperature Metallic Superconducting Coils," Cryogenic Engineering, Vol. 57, No. 5, 2022, pp. 281 to 292, Fig. 10).

[0025] On the other hand, by performing the aforementioned modification step S53, the thickness of the copper oxide film 3 exceeds 6 nm. Since the copper oxide film 3, which has a higher resistivity than when the aforementioned modification step S53 is not performed, becomes thicker, specifically, the thickness of the copper oxide film 3 exceeds 6 nm, so the resistivity of the surface of the high-temperature superconducting wire 1 increases sufficiently, and as a result, the contact resistance between windings also increases. Furthermore, if the thickness of the copper oxide film 3 becomes too thick, coil damage due to partial normal conduction may occur, although this is not always the case due to its relationship with other factors. There is no particular upper limit to the thickness of the copper oxide film 3, but for example, it can be set to 20 nm. Even if the thickness of the copper oxide film 3 exceeds 20 nm, the inter-winding contact resistance does not increase significantly, so the effect of being able to excite within the desired time or the effect of preventing coil damage due to partial normal conduction does not increase significantly. In other words, if the thickness of the copper oxide film 3 exceeds 20 nm, the effect is not commensurate with the time and cost required for processing, and is therefore undesirable. For this reason, when specifying the upper limit of the thickness of the copper oxide film 3, it is best to set it to 20 nm as described above. The thickness of the copper oxide film 3 can be measured, for example, using a measuring device employing the SERA method (continuous electrochemical reduction method), but the means for measuring the thickness of the copper oxide film 3 are not limited to this.

[0026] In the first embodiment, since the reinforcing tape wire 6 (see Figure 4), which will be described later, is not included, the packing factor of the high-temperature superconducting wire 1 in the coil cross-section increases, making it possible to manufacture a compact superconducting coil 10.

[0027] [Second Embodiment] The embodiments described below will focus on the differences from the first embodiment. Figure 3 is a schematic cross-sectional view of the high-temperature superconducting wire 1 in the second embodiment. In the present invention, since the modification process S53 is performed after the winding process S50, the environment of the high-temperature superconducting wire 1 in the modification process S53 differs depending on the part. For example, as shown in Figure 2 above, when viewed from the high-temperature superconducting wire 1, the high-temperature superconducting wire 1 is often stacked without gaps on both sides in the wire thickness direction 4, while there is space on the outside in the wire width direction 2. When the temperature of the superconducting coil 10 is raised in this state, the surface of the copper 3a at both ends in the wire width direction 2 is easily oxidized, but the copper 3a in the center of the wire width direction 2 is hardly in contact with the atmosphere and is therefore less likely to be oxidized. Therefore, the thickness of the former copper oxide film 3 becomes thicker than the thickness of the latter copper oxide film 3, and a thick oxide film portion 31 and a thin oxide film portion 32 are formed. In other words, as shown in Figure 3, the high-temperature superconducting wire 1 is a tape wire with a rectangular cross-section. When the longer side of the cross-section is defined as the wire width direction 2 and the shorter side is defined as the wire thickness direction 4, the thickness of the copper oxide film 3 at both end faces in the wire width direction 2 (thick oxide film portion 31) is greater than the thickness of the copper oxide film 3 at the center of the wire width direction 2 (thin oxide film portion 32). In this case, the statement "the thickness of the copper oxide film 3 exceeds 6 nm" means that the thickness of the thick oxide film portion 31 (the thickness of the copper oxide film 3 at both end faces in the wire width direction 2) exceeds 6 nm.

[0028] On the other hand, as shown in Figure 3, the substrate 5, such as Hastelloy, occupies most of the cross-section of the high-temperature superconducting wire 1, and the copper 3a is arranged on the outer periphery of the substrate 5. Functional layers 9, such as an orientation layer, a barrier layer, and a superconducting layer, are arranged between the substrate 5 and the copper 3a. Since the resistivity of copper 3a (copper oxide film 3) is lower than that of the substrate 5, the resistance in the wire thickness direction 4 is strongly influenced by the copper 3a (copper oxide film 3) at both ends in the wire width direction 2. Therefore, even in such localized areas, it is possible to increase the resistance value by changing the thickness of the copper oxide film 3. Even when the thickness of the copper oxide film 3 differs depending on the location, as in this embodiment, fine adjustment of the contact resistance is possible. In this case, the aforementioned statement that "the thickness of the copper oxide film 3 exceeds 6 nm" can be understood to mean that the thickness of the thick oxide film portion 31 (the thickness of the copper oxide film 3 at both end faces in the wire width direction 2) exceeds 6 nm.

[0029] [Third Embodiment] Figure 4 is a schematic cross-sectional view of a superconducting coil 10 according to the third embodiment. This embodiment is an example in which a reinforcing tape wire 6 is wound together with a high-temperature superconducting wire 1 manufactured as a tape wire. Since superconducting coils 10 are generally used in strong magnetic fields, they need to be strong enough to withstand electromagnetic forces. As shown in Figure 4, the superconducting coil 10 has a reinforcing tape wire 6, such as stainless steel tape, wound together with the high-temperature superconducting wire 1, so it can withstand higher electromagnetic forces. The width dimension of the reinforcing tape wire 6 is preferably the same as the width dimension of the high-temperature superconducting wire 1 manufactured as a tape wire, as this makes it easier to handle. Although not shown in the figure, a high-temperature superconducting wire 1 with a circular or hexagonal cross-section may also be wound around the reinforcing tape wire 6.

[0030] [Fourth Embodiment] Figure 5 is a flowchart illustrating the manufacturing method of the superconducting coil 10 according to the fourth embodiment of the present invention. Figure 6 is a schematic partial cross-sectional view of the superconducting coil 10 according to the fourth embodiment. As shown in Figure 5, the manufacturing method of the superconducting coil 10 according to the fourth embodiment differs from the manufacturing method of the superconducting coil 10 according to the first embodiment shown in Figure 1 in that it includes a resin impregnation step S54. In the manufacturing method of the superconducting coil 10 according to the fourth embodiment, the winding step S50, resistance measurement step S51, determination step S52, and correction step S53 are performed, similar to the first embodiment. However, in the manufacturing method of the superconducting coil 10 according to the fourth embodiment, if the inter-winding contact resistance value is within the desired range in the determination step S52 (Yes in the determination step S52), the manufacturing (adjustment) is not terminated, but the resin impregnation step S54 is performed immediately following the determination step S52.

[0031] In the resin impregnation process S54, the superconducting coil 10, whose inter-winding contact resistance value is within a desired range, is impregnated with resin 7. The resin 7 is not particularly limited and any resin can be used as long as it can impregnate the superconducting coil 10. The curing temperature of the resin 7 varies, but since the contact resistance between windings changes when the temperature of the superconducting coil 10 is raised again, it is desirable to use a resin that cures at room temperature or below 100°C. Examples of such resins 7 include epoxy and cyanoacrylate, but are not limited to these. As shown in Figures 5 and 6, the superconducting coil 10 is mechanically reinforced by being impregnated with resin and fixed (cured).

[0032] In this embodiment, the superconducting coil 10 and a cooling copper plate 11 for cooling the superconducting coil 10 by conduction may be impregnated with resin together. Figure 6 also shows the cooling copper plate 11 used for cooling the superconducting coil 10.

[0033] The contact resistance between the high-temperature superconducting wires 1, and the contact resistance between the high-temperature superconducting wires 1 and the reinforcing tape wires 6, both change depending on the degree of contact between them. Therefore, in the four-terminal measurement method, it is desirable that the relative distance between the measurement terminals at a certain temperature takes a constant value. In this embodiment, since resin impregnation is performed after correcting the contact resistance, it is desirable that the resin 7 does not impregnate between the high-temperature superconducting wires 1 or between the high-temperature superconducting wires 1 and the reinforcing tape wires 6.

[0034] The method for manufacturing the superconducting coil 10 and the superconducting coil 10 according to the present invention have been described in detail above with reference to embodiments. However, the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail for the purpose of explaining the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add a configuration from another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0035] 10 Superconducting Coils 1. High-temperature superconducting wire 2 Wire width direction 3a copper 3 Copper oxide film 5 circuit boards 4. Wire thickness direction 6. Reinforcement tape wire 7 resin 8 Coil shaft 9 Functional Layers S50 Winding Process S51 Resistance measurement process S52 Judgment process S53 Correction process S54 Resin impregnation process

Claims

1. A resistance measurement step for measuring the inter-winding contact resistance value in a superconducting coil formed by winding a rare-earth oxide superconducting wire having copper on its surface, If the inter-winding contact resistance value is outside the desired range in the resistance measurement step, a correction step is performed to correct the inter-winding contact resistance value by holding the superconducting coil at 100°C to 200°C. A method for manufacturing a superconducting coil, characterized by having the following features.

2. A method for manufacturing a superconducting coil according to claim 1, After the aforementioned correction process, A method for manufacturing a superconducting coil, characterized by having a resin impregnation step of impregnating the superconducting coil with resin if the inter-winding contact resistance value is within a desired range in the resistance measurement step.

3. This is a superconducting coil made by winding a rare-earth oxide superconducting wire having copper on its surface. A superconducting coil characterized in that the thickness of the copper oxide film on the surface of the rare-earth oxide superconducting wire exceeds 6 nm.

4. A superconducting coil according to claim 3, The superconducting coil is characterized in that the rare-earth oxide superconducting wire is a tape wire with a rectangular cross-section, and when the long side of the cross-section is defined as the wire width direction and the short side of the cross-section as the wire thickness direction, the thickness of the copper oxide film at both end faces in the wire width direction is greater than the thickness of the copper oxide film at the center in the wire width direction.

5. A superconducting coil according to claim 4, A superconducting coil characterized in that reinforcing tape wire is inserted between the windings of the rare-earth oxide superconducting wire.

6. A superconducting coil according to any one of claims 3 to 5, A superconducting coil characterized in that the superconducting coil is impregnated with a resin.

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