JP7438533B2 - Ultra-low resistance connection method between high-temperature oxide superconducting wire and metallic superconducting wire - Google Patents

Description

The present invention relates to an ultra-low resistance connection method for high-temperature oxide superconducting wire and metallic superconducting wire.

Rare earth (RE)-based oxide superconducting wires have high superconducting critical temperatures and high critical magnetic fields, and are used in high-field NMR (nuclear magnetic resonator) devices, magnetic resonance imaging (MRI), and superconducting magnetic energy storage. Various applications are expected, such as (SMES) and power transmission cables. In particular, in a 1 GHz super strong magnetic field NMR device, the generated magnetic field exceeds 23.5 T, so high-temperature superconducting wires such as RE-based superconducting wires are essential.

In such a super strong magnetic field NMR apparatus, due to size and cost constraints, it is necessary to construct the outer layer not only with an RE-based superconducting coil but also with a metal-based superconducting coil such as NbTi or Nb ₃ Sn. Therefore, in order to operate such a super strong magnetic field NMR device with persistent current, it is essential not only to connect RE-based superconducting wires to each other, but also to make superconducting connections between RE-based superconducting wires and metallic low-temperature superconducting wires. .

However, due to the difficulty in controlling the interlayer structure of the two materials, which have completely different properties and manufacturing methods, a superconducting connection between an RE-based oxide superconducting wire and a metal-based superconducting wire has not been achieved so far. Therefore, in order to realize a pseudo-superconducting connection between the two wires, it is necessary to increase the bond length and area and reduce the connection resistance between the two wires, but it is possible to realize persistent current operation of the connection resistance. In order to reduce the resistance value to less than 5 m, a connection length of 5 m or more is required. Considering the arrangement of the connections in the magnetic system, securing such space is extremely impractical. In order to solve this space problem, a co-wound connection structure was proposed as described in Patent Document 1. In this proposal, a high-temperature superconducting tape wire and a metal-based low-temperature superconducting tape wire are brought into surface contact in the longitudinal direction, and by winding them up like a spring with solder interposed between them, they are integrated into a relatively compact low-temperature superconducting tape wire. A resistive connection is realized.

The first problem with the above method is that a metallic low-temperature superconducting tape wire is required for connection. Usually, the metallic superconducting wire used in magnets is a round wire or a rectangular wire, and it is rare that a tape wire is used to construct a magnet. Therefore, in order to use the above connection method, a metal-based superconducting tape wire is separately prepared for connection, and this tape wire is pre-wired into a round wire or It is necessary to form a superconducting connection with the rectangular wire.

Other problems include interposing solder between the mechanically brittle high-temperature superconducting tape wire and the metallic low-temperature superconducting tape wire, winding them up like a spring at the same time, and integrating them, which requires delicate work. The problem is that it is complicated. Here, since it is necessary to wind up the metal-based superconducting tape wire, flexibility is essential for the metal-based superconducting tape wire, and it can be used for connection with brittle compound-based superconducting wires such as Nb ₃ Sn. Can not.
Therefore, when connecting a rare earth superconducting wire and a Nb ₃ Sn compound superconducting wire, the Nb ₃ Sn wire is first bonded to flexible NbTi by the method shown in Non-Patent Document 1 and Patent Document 2, for example. A two-step connection process is required, in which the rare earth superconducting wire is connected to the wire and then the rare earth superconducting wire is connected to the flexible NbTi tape wire using the method described above.
This situation similarly applies to Bi-based oxide superconducting wires in which superconducting connections with metal-based superconducting wires have not been established.

Special Publication No. 2016-535431 USP No. Publication No. 4907338

IEEE TAS, DOI: 10.1109/77.783267 SUST paper, doi:10.1088/0953-2048/23/8/085013 fig. 3 Introduction to rare earth-based high-temperature superconducting wires Fujikura Co., Ltd. p. 5 https://www.fujikura.co.jp/products/newbusiness/superconductors/01/superconductor.pdf

The purpose of the present invention is to develop high-temperature oxide superconducting wires and metallic superconducting wires with ultra-low resistance, which are space-saving, simple, versatile, and capable of realizing ultra-strong magnetic field NMR of over 1 GHz capable of persistent current operation. The purpose is to provide a connection structure.

As a result of intensive research in order to solve the above problems, the present inventors have discovered that a direct reduction in resistance between a round or rectangular metallic superconducting wire and an oxide superconducting wire can be achieved without using an NbTi tape wire. We believed that if resistance connection technology were developed, it would be possible to dramatically simplify the work and further save space, and specifically, we developed the present invention with the goal of realizing a connection resistance of 10 ^-9 Ω or less. Completed.

[1] The ultra-low resistance connection method of the present invention between a high-temperature oxide superconducting wire and a metallic superconducting wire includes coating the surface of a high-temperature oxide superconducting tape wire with surface coating solder, as shown in FIG. 5, for example. (S100) The high temperature oxide superconducting tape wire is compactly wound and housed in a metal case while suppressing the maximum strain experienced by the oxide superconducting layer within the range of -1.5% to 0.2%. S102), molten superconducting solder is poured into the metal case (S104), and maintained at a temperature higher than the melting point of the superconducting solder and the surface coating solder for a certain period of time to create superconductivity between the high temperature oxide superconducting tape wires. The solder is mutually diffused (S106), and the metallic superconducting wire, in which the filament at the end of the metallic superconducting wire is coated with superconducting solder, is immersed in the superconducting solder in a molten state in the metal case. (S108), the superconducting solder is cooled and solidified, and the high temperature oxide superconducting tape wire and the metallic superconducting wire are integrated via the superconducting solder (S110).

[2] Preferably, in the ultra-low-resistance connection method for high-temperature oxide superconducting wire and metallic superconducting wire of the present invention [1], the high-temperature oxide superconducting tape wire is a rare earth-based oxide superconducting tape wire. When the rare earth oxide superconducting tape wire is wound inside the metal case, the oxide superconducting layer of the rare earth oxide superconducting tape wire becomes the rare earth oxide superconductor. It is preferable to wind the tape wire in such a direction that it is located on the compression side when viewed from the mechanical neutral plane of the tape wire.
[3] Preferably, in the ultra-low resistance connection method of the present invention between a high-temperature oxide superconducting wire and a metallic superconducting wire, compressive strain of the oxide superconducting layer of the rare earth-based oxide superconducting tape wire is applied. The range is preferably -1.5% or more and 0% or less.
[4] Preferably, in the ultra-low-resistance connection method for high-temperature oxide superconducting wire and metallic superconducting wire of the present invention [1], the high-temperature oxide superconducting tape wire is a bismuth-based superconducting wire; When the bismuth-based superconducting wire is wound inside the metal case, the maximum strain experienced by the oxide superconducting layer of the bismuth-based superconducting wire is preferably 0.2% or less.

[5] Preferably, in the ultra-low resistance connection method of high temperature oxide superconducting wire and metallic superconducting wire of the present invention [1] to [4], the surface coating solder is Sn, Pb-Sn, Pb- It is preferable to use one of Sn--Bi, Sn--Ag, and Pb--Bi alloys.
[6] Preferably, in the ultra-low resistance connection method of high temperature oxide superconducting wire and metallic superconducting wire of the present invention [1] to [4], the superconducting solder is Pb-Bi, In-Sn- It is preferable to use one type of Bi alloy.
[7] Preferably, in the ultra-low resistance connection method for high temperature oxide superconducting wire and metallic superconducting wire of the present invention [1] to [6], the metal case is configured to connect the high temperature oxide superconducting tape wire to The high-temperature oxide superconducting tape wire is curved at least once and accommodated, and one end of the high-temperature oxide superconducting tape wire is pulled out, and the metallic superconducting wire is integrated with the superconducting solder accommodated in the metal case. It would be nice to be connected.

[8] For example, as shown in FIG. 4, the present invention provides a high-temperature oxide superconducting wire comprising an oxide superconducting tape wire 20, a metallic superconducting wire 30, a superconducting solder 40, and a metal case 10. and a metal-based superconducting wire, in which an oxide superconducting tape wire 20 is housed in a metal case 10 in a wound state, and the oxide of the oxide superconducting tape wire 20 is The maximum strain experienced by the superconducting layer is suppressed within the range of -1.5% to 0.2%, and the superconducting solder 40 is interdiffused between the oxide superconducting tape wires 20, and the oxidation One end of the oxide superconducting tape wire 20 is pulled out from the metal case 10, and the metal superconducting wire 30 and the superconducting solder 40 are joined while maintaining the superconducting state, and the oxide superconducting tape wire 20 and This structure ensures a contact area between the superconducting solders 40 necessary to obtain a resistance of 10 ⁻⁸ Ω or less.

[9] The present invention is an NMR, MRI, or superconducting transport device using the ultra-low resistance connection body of the oxide superconducting tape wire and metallic superconducting wire described in [8].

According to the ultra-low resistance connection method of the present invention between a high-temperature oxide superconducting wire and a metallic superconducting wire, it is possible to realize an ultra-low resistance connection between the two wires that is compact and has an extremely small installation area, and allows for a more general-purpose persistent current connection. Operable ultra-strong magnetic field NMR exceeding 1 GHz can be realized.

FIG. 1 is a configuration diagram illustrating how a rare earth-based oxide superconducting tape wire according to an embodiment of the present invention is housed in a metal case, in which (A) is a plan view and (B) is shown in FIG. 1(A). It is a sectional view taken along the line BB. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural perspective view illustrating the appearance of a metal case for a connecting portion, showing an embodiment of the present invention. FIG. 1 is a configuration diagram of a metallic superconducting wire in which a superconducting filament is coated with superconducting solder, showing an embodiment of the present invention. FIG. 1 is a conceptual diagram of a connection portion in which a rare earth-based oxide superconducting tape wire and a metal-based superconducting wire are integrated via superconducting solder, showing an embodiment of the present invention. 1 is a flowchart showing an embodiment of a method for connecting a high-temperature oxide superconducting wire and a metallic superconducting wire with ultra-low resistance according to the present invention. 1 is a cross-sectional photograph of a rare earth superconducting wire showing an embodiment of the present invention. FIG. 2 is a diagram illustrating the connection resistance between a rare earth-based oxide superconducting tape wire and a metal-based superconducting wire when the length inside the case is 15 cm, showing an embodiment of the present invention. FIG. 2 is a diagram illustrating the connection resistance between a rare earth-based oxide superconducting tape wire and a metal-based superconducting wire when the length inside the case is 50 cm, showing an embodiment of the present invention. Approximation of the connection resistance between a rare earth oxide superconducting tape wire and a metal superconducting wire, using the length inside the case of the rare earth oxide superconducting tape wire as a variable, showing an embodiment of the present invention It is a curve. 1 is a cross-sectional photograph of a bismuth-based superconducting wire showing an embodiment of the present invention.

The present invention will be explained below using the drawings.
FIG. 1 is a configuration diagram illustrating how a rare earth-based oxide superconducting tape wire according to an embodiment of the present invention is accommodated in a metal case, where (A) is a plan view and (B) is a FIG. 3 is a cross-sectional view taken along line BB shown in FIG. FIG. 2 is a structural perspective view illustrating the appearance of a metal case for a connecting portion, showing an embodiment of the present invention.
In the figure, a metal case 10 is a dish-shaped container with an oval-shaped outline, and is manufactured using, for example, stainless steel. The type of stainless steel may be one commonly used as a structural corrosion-resistant steel, such as SUS316 and SUS304. The metal case 10 has a slit 12 and a curved portion 14. The slit 12 is an opening for pulling out the end of the rare earth oxide superconducting tape wire 20. The curved portion 14 is a portion having a curvature necessary to bend the rare earth oxide superconducting tape wire 20. The shape of the metal case 10 is a boat-shaped case with a rounded tip, for example, the length inside the case is 5 cm, the width is 1 cm, and the radius of curvature on both sides of the case is 5 mm, but the shape is not limited to this.

The rare earth-based oxide superconducting tape wire 20 is constructed by laminating a metal substrate 22, an oxide superconducting layer 24, an Ag protective layer 26, and a Cu coating layer 28, and has a superconducting critical temperature of liquid nitrogen. This wire is a so-called high-temperature superconducting wire that exceeds the temperature. As the rare earth-based oxide superconducting tape wire 20, for example, model name FYSC-SCH04 manufactured by Fujikura Corporation, which is described in Non-Patent Document 3, may be used, but the present invention is not limited thereto. The rare earth oxide superconducting tape wire 20 has a winding part 20a that is integrated with the metal superconducting wire 30 and superconducting solder 40 inside the metal case 10, and a lead wire part 20b pulled out from the slit 12. Consists of.

The metal substrate 22 is made of a nickel-based alloy or a cobalt-based alloy such as Hastelloy (registered trademark), Inconel (registered trademark), or Monel (registered trademark), and has a coefficient of thermal expansion similar to that of the oxide superconducting layer 24. The plate thickness is, for example, 75 μm.
The oxide superconducting layer 24 is made by epitaxially growing an RE-based oxide superconducting phase (eg, YBaCuO, GdBaCuO, etc.) on the metal substrate 22 as an alignment tape substrate, and has a film thickness of, for example, 2 to 5 μm.
The Ag protective layer 26 protects the brittle oxide superconducting layer 24, and has a thickness of, for example, 2 μm.
The Cu coating layer 28 is formed by coating the Ag protective layer 26 with a highly conductive metal such as Cu to form a wire, and the thickness of the wire is, for example, 20 μm. The Cu covering layer 28 is formed around the Ag protective layer 26 using, for example, plating.

The surface coating solder layer (not shown) coats the surface of the end of the oxide superconducting tape wire 20, and the coating length is suitable for superconducting connection, for example, from 15 cm to 50 cm from the end. Define within the range. The thickness of the surface coating solder layer is preferably 15 to 25 μm, for example. Examples of the material of the surface coating solder layer 29 include Sn, Sn-based alloys such as Pb-Sn, Pb-Sn-Bi, and Sn-Ag, and Pb-based alloys such as Pb-Bi.

The rare earth-based oxide superconducting tape wire 20 is constructed such that the oxide superconducting layer 24 is located on the compression side when viewed from the mechanical neutral plane 25 when the tape wire 20 is wound inside the metal case 10. Wind it in the correct direction (Figure 1 (B)).
This is because strain deterioration of the critical current in rare earth oxide superconducting tape wires is suppressed on the compression side at low temperatures of 40K or less (see Non-Patent Document 2). The range of strain at this time is preferably -1.5% or more and 0% or less. If it is less than that, the oxide superconducting layer may be mechanically deteriorated. More preferably, it is −1.0% or more.

If the oxide superconducting tape wire is a bismuth-based superconducting wire, the oxide superconducting layers exist on both sides of the mechanical neutral plane, so be especially careful about the orientation when winding it into the metal case. There's no need. However, during winding, it is desirable that the maximum strain experienced by the oxide superconducting layer be 0.2% or less. If it exceeds 0.2%, the oxide superconducting layer may be mechanically deteriorated.

The length of the tape wire to be wound is preferably as long as possible, and in the case of rare earth oxide superconducting wires, in order to achieve a resistance of 10 ^-8 Ω or less, it is desirable to have a length of at least 20 cm. Further, in order to achieve a resistance of 10 ⁻⁹ Ω or less, a length of 2 m or more is desirable. In the case of bismuth-based superconducting wires, in order to achieve a resistance of 10 ^-9 Ω or less, it is desirable that the wire be at least 5 cm long, and furthermore, in order to achieve a resistance of 10 ^-9 Ω or less, a length of 50 cm or more is required. is desirable.

Here, one reason why bismuth-based superconducting wire requires a shorter winding length than rare earth-based superconducting wire to obtain the same low resistance value is that the cross-sectional configuration of the wire is significantly different. It's for a reason. Rare earth wires have a single oxide superconducting layer epitaxially grown on a substrate, whereas bismuth wires have an ultrafine multicore structure in which many oxide superconducting filaments are embedded. Therefore, in the bismuth-based superconducting wire, the contact area between the oxide superconducting layer and the matrix is significantly larger than the area of the interface between the oxide superconducting layer and the sheath in the rare earth-based superconducting wire. Therefore, with the bismuth-based wire, the contribution of the interfacial resistance between the oxide superconducting layer and the matrix to the connection resistance can be extremely small, and this means that even with the same winding length, the bismuth-based superconducting wire has a lower resistance. This is the reason why the value is obtained.

As a guideline for the conditions to maintain the temperature above the melting point of the superconducting solder and the surface coating solder, for example, when the superconducting solder is Pb-56wt%Bi and the surface coating solder is Pb-60wt%Sn, the temperature is 200°C to 300°C. , for a period of at least 1 minute and no more than 1 hour. At temperatures below 200°C, the superconducting solder cannot sufficiently diffuse between the wires, and at temperatures above 300°C, the oxide superconducting layer may deteriorate. Furthermore, if the heating time is less than 1 minute, the superconducting solder will not be able to diffuse sufficiently between the wires, and if the heating time is longer than 1 hour, the oxide superconducting layer may deteriorate.

FIG. 3 is a configuration diagram of a metallic superconducting wire in which a superconducting filament is coated with superconducting solder, showing an embodiment of the present invention.
The metallic superconducting wire 30 is composed of a metallic superconducting filament 32 and a Cu sheath 34, and has a superconducting solder 40. The metallic superconducting filament 32 is made of a metallic superconducting material such as NbTi or Nb ₃ Sn, and is composed of, for example, about 3 to 49 filaments with a wire diameter of 0.6 to 1.5 mm. There is.
The Cu sheath 34 is a cylindrical cover that bundles the metallic superconducting filaments 32 and mechanically protects the metallic superconducting filaments 32. At the end of the Cu sheath 34, several centimeters of the metallic superconducting filament 32 are exposed.
Examples of the superconducting solder 40 include Pb-based and Sn-based alloys such as Pb-Bi and In-Sn-Bi. The superconducting solder 40 covers the area of the metallic superconducting filament 32 exposed from the end of the Cu sheath 34 .

The length of the superconducting solder coating on the metallic superconducting filament and the length of the case immersed in the superconducting solder are preferably 2 cm or more. Below that, when a large current is passed through the metallic superconducting wire, the current density passing through the interface between the metallic superconducting filament and the superconducting solder exceeds the critical current density of the superconducting solder, resulting in a large This will cause conductive resistance.

The manufacturing process for superconducting solder coating on metallic superconducting filaments is, for example, the process disclosed in Non-Patent Document 1 and Patent Document 2.
First, the tip of the metallic superconducting wire 30 is immersed in molten Sn (250 to 260° C.) for 90 minutes to replace the Cu matrix surrounding the metallic superconducting filament 32 with Sn.
Next, it is immersed in molten PbBi (250 to 260° C.) for 5 minutes to replace Sn with PbBi. In this way, the metallic superconducting filament 32 is coated with the superconducting solder 40 such as PbBi.

FIG. 4 is a conceptual diagram of a connection portion in which a rare earth-based oxide superconducting tape wire and a metal-based superconducting wire are integrated via superconducting solder, showing an embodiment of the present invention.
The ultra-low resistance connection body of a high-temperature oxide superconducting wire and a metallic superconducting wire is composed of a metal case 10, an oxide superconducting tape wire 20, a metallic superconducting wire 30, and a superconducting solder 40.
The oxide superconducting tape wire 20 is a rare earth superconducting wire or a bismuth superconducting wire.

The manufacturing process of an ultra-low resistance connection body of a high-temperature oxide superconducting wire and a metallic superconducting wire as shown in FIG. 4 is as shown in a flow chart shown in FIG. FIG. 5 is a flowchart showing an embodiment of a method for connecting a high-temperature oxide superconducting wire and a metallic superconducting wire with ultra-low resistance according to the present invention.
First, the surface of the oxide superconducting tape wire 20 is coated with surface coating solder (S100). Next, the oxide superconducting tape wire 20 is compactly wound and housed in the metal case 10 while suppressing the maximum strain experienced by the oxide superconducting layer 24 within the range of -1.5% to 0.2% ( S102). Next, the molten superconducting solder 40 is poured into the metal case 10 (S104) and held at a temperature higher than the melting point of the superconducting solder 40 and the surface coating solder for a certain period of time, so that the superconducting solder is formed between the oxide superconducting tape wires 20. 40 are mutually diffused (S106).
Next, the metallic superconducting wire 30 in which the metallic superconducting filament 32 at the end of the metallic superconducting wire 30 is coated with the superconducting solder 40 is placed inside the metal case 10 using the superconducting solder 40 in a molten state. (S108), the superconducting solder 40 is cooled and solidified, and the oxide superconducting tape wire 20 and the metallic superconducting wire 30 are integrated via the superconducting solder 40 (S110).
In this way, the superconducting solder 40 is cooled and solidified, and is integrated into the oxide superconducting tape wire 20 and the metallic superconducting wire 30. The metal case 10 acts as a holder that holds the superconducting solder 40 in a molten state.

With this configuration, the metallic superconducting wire 30 and the superconducting solder 40 are joined while maintaining the superconducting state, and a sufficiently large contact area is created between the oxide superconducting tape wire 20 and the superconducting solder 40. is ensured, extremely low resistance can be obtained, and an ultra-low resistance connection between the high-temperature oxide superconducting wire and the metallic superconducting wire can be realized.

A GdBCO tape wire manufactured by Fujikura (4 mm width, 0.13 mm thickness) was prepared as a rare earth-based oxide superconducting tape wire. A cross-sectional photograph is shown in FIG. Using this 20 cm wire, both sides were coated with commercially available Pb-60Sn solder over a distance of 15 cm from one end. At this time, the thickness of the solder layer was about 20 μm.

Next, as shown in FIG. 2, a stainless steel plate with a length of 5.2 cm, a width of 1.2 cm, and a height of 8 mm is processed to form a boat-shaped metal case 10 in which the tape wire is wound. Got ready. The length of the inside of the metal case is 5 cm, the width is 1 cm, and the radius of curvature on both sides of the case is 5 mm. A slit 12 for passing the tape wire is provided at the end of the metal case. A solder-coated high-temperature oxide superconducting tape wire was wound into a metal case so that compressive strain was applied to the oxide superconducting layer, as shown in FIG. 1(B). The length of the solder-coated high-temperature oxide superconducting tape wire inside the metal case was 15 cm. At this time, the oxide superconducting layer in the superconducting tape wire is located at a distance of 38 μm from the mechanical neutral plane, and the maximum strain experienced by the oxide superconducting layer is estimated to be −0.76%.

Next, the metal case in which the solder-coated superconducting tape wire was wound was held at 200° C., and Pb-56wt%Bi superconducting solder was inserted. At this time, Pb-56wt%Bi was completely melted and filled in the metal case.
This state was maintained for 30 minutes so that the Pb--Bi superconducting solder would interdiffuse between the superconducting tape wires.

Next, by the method shown in Non-Patent Document 1 and Patent Document 2, a NbTi metal-based superconducting wire whose end superconducting filament is coated with Pb-Bi superconducting solder as shown in FIG. - Bi was inserted into the metal case in a molten state. This was cooled, and a connecting portion between the high-temperature oxide superconducting wire and the metallic superconducting wire having the shape shown in FIG. 4 was produced.

Next, electrodes were attached to the high-temperature oxide superconducting wire and the metallic superconducting wire, and the wires were immersed in liquid helium, and resistance was measured using a four-probe method in a magnetic field using a magnet. The applied current was 100A. The results are shown in FIG. For example, at 0.2T, the connection resistance was 1.1×10 ⁻⁸ Ω. The reason why the resistance value increases rapidly above 1.2 T is because the Pb--Bi superconducting solder reaches a critical magnetic field and undergoes a normal conduction transition.

In Example 1, the connection resistance was 1.1×10 ⁻⁸ Ω, so to further reduce the resistance, the length of the superconducting tape wire wound into the metal case was increased to 50 cm.
In the same manner as in Example 1, a connecting portion between a high-temperature oxide superconducting wire and a metallic superconducting wire having a shape as shown in FIG. 4 was produced. At this time, the tape wire will be wound 4 turns, and the minimum radius of curvature of the neutral plane of the tape wire will be 4.44 mm, so the maximum strain experienced by the oxide superconducting layer will be -0.85%. It is estimated that.

As in Example 1, electrodes were attached to the high-temperature oxide superconducting wire and the metallic superconducting wire, immersed in liquid helium, and the resistance was measured using a four-probe method in a magnetic field using a magnet. The results are shown in FIG. For example, at 0.2T, the connection resistance was 2.6×10 ⁻⁹ Ω, and it was confirmed that the connection resistance decreased approximately in proportion to the length wound around the metal case.

Since the connection between the metallic superconducting wire and the superconducting solder is in a superconducting state, the overall connection resistance value is determined by the interfacial resistance between the high-temperature superconducting wire and the superconducting solder, and the resistance value is determined by the interfacial resistance between the high-temperature superconducting wire and the superconducting solder. It can be assumed that it is simply inversely proportional to the length of insertion. Therefore, an approximate curve of the connection resistance value (y=1.3×10 ⁻⁹ x ⁻¹ (Ω)) was calculated using the resistance value of 50 cm as a reference, and is shown in FIG. According to this, the connection resistance value is estimated to be 0.65 nΩ if the length wound around the metal case is 2 m, and 6.5×10 ⁻¹¹ Ω if the length is 20 m. However, at this time, in order to fit the 2 m and 20 m long oxide superconducting tape wires into the metal case, the size of the metal case was changed so that the maximum strain experienced by the oxide superconducting layer was -1.5%. Needless to say, the design must be designed to meet the above requirements.

If we were to use the same method to wind a 5 m long tape wire while suppressing the maximum strain experienced by the oxide superconducting layer to -1%, the inner dimensions would be 7 cm long, 2 cm wide, and high. A container with a diameter of 7 mm and a radius of curvature at both ends of 5 mm may be prepared. At this time, assuming that the thickness of the solder-coated tape wire is 0.17 mm, the tape wire will be wound around 30 turns in the metal case, and the minimum radius of curvature will be 5 mm. The maximum strain experienced by the oxide superconducting layer at that time is -0.76%. Furthermore, if the length and width of the inner metal case are increased by 10 mm each, it is possible to wind up an additional 5 m, and if each is further increased by 10 mm, it is possible to wind the inner metal case by an additional 5 m.

As a bismuth-based superconducting tape wire, DI-BSCCO-H tape wire (4.5 mm width, 0.23 mm thickness) manufactured by Sumitomo Electric was prepared. FIG. 10 is a cross-sectional photograph of a bismuth-based superconducting wire showing one embodiment of the present invention. Using this 55 cm wire, both sides were coated with commercially available Pb-60Sn solder over a distance of 50 cm from one end. At this time, the thickness of the solder layer was about 20 μm.

Next, a stainless steel plate with a thickness of 8 mm was processed to prepare a circular metal case with a diameter of 15 cm and a depth of 6 mm into which the tape wire was wound. A slit is provided at one location on the outer periphery of the metal case, parallel to the tangential direction of the outer periphery, for passing the tape wire through. 50 cm of the solder-coated high-temperature oxide superconducting tape wire was wound into this metal case. The maximum strain experienced by the oxide superconducting layer at this time is 0.153%.

Next, in the same manner as in Example 1, a connecting portion between a high-temperature oxide superconducting wire and a metallic superconducting wire having a shape as shown in FIG. 4 was produced.
As in Example 1, electrodes were attached to the high-temperature oxide superconducting wire and the metallic superconducting wire, immersed in liquid helium, and the resistance was measured using a four-probe method in a magnetic field using a magnet. As a result, a connection resistance value of 5×10 ⁻¹⁰ Ω at 0.2T was obtained.

Although Examples 1 to 3 are shown as examples of the present invention, the present invention is not limited thereto, and various embodiments can be considered within the scope obvious to those skilled in the art. Such an obvious scope is also included in the scope of the present invention.
For example, if a second high-temperature superconducting wire is incorporated into a metal case in the same manner as shown in Figure 4 instead of the metallic superconducting wire, a compact and simple ultra-low resistance high-temperature oxide superconducting tape can be created. Wire-to-wire connections can also be obtained.

As explained in detail above, according to the ultra-low resistance connection body of the present invention of high-temperature oxide superconducting wire and metallic superconducting wire, compact and simple ultra-low resistance high-temperature oxide superconducting There is no technology for connecting conductive tape wires and metallic superconducting wires, and this work is expected to make a significant contribution to the development and spread of high-field magnet systems that require persistent current operation, such as high-field NMR devices.
The high-field NMR device using the ultra-low-resistance connection of high-temperature oxide superconducting wire and metallic superconducting wire of the present invention realizes general-purpose ultra-high magnetic field NMR of over 1 GHz capable of persistent current operation. can do.

10 Metal sheath 12 Slit 14 Curved portions 20, 20a, 20b Rare earth-based oxide superconducting tape wire 22 Orientation tape substrate 23 Bismuth-based superconducting wire (BSCCO)
24 RE-based oxide superconducting phase 25 Mechanical neutral plane 26 Ag protective layer 28 Cu well-conducting metal layer 30 Metal-based superconducting wire 32 Metal-based superconducting filament 34 Cu sheath 40 Superconducting solder

Claims (7)

The surface of the high-temperature oxide superconducting tape wire is coated with surface coating solder,
The high-temperature oxide superconducting tape wire is wound and housed in a metal case while suppressing the maximum strain experienced by the oxide superconducting layer within a range of -1.5% to 0.2%;
Pour molten superconducting solder into the metal case,
Holding the temperature above the melting point of the superconducting solder and the surface coating solder for a certain period of time to interdiffuse the superconducting solder between the high temperature oxide superconducting tape wires;
immersing the metal-based superconducting wire in which the filament at the end of the metal-based superconducting wire is coated with superconducting solder in the superconducting solder in a molten state in the metal case;
The superconducting solder is cooled and solidified, and the high-temperature oxide superconducting tape wire and the metallic superconducting wire are integrated through the superconducting solder to form a high-temperature oxide superconducting wire and metallic superconducting wire. Ultra-low resistance connection method for wires. The high-temperature oxide superconducting tape wire is a rare earth-based oxide superconducting tape wire,
When the rare earth-based oxide superconducting tape wire is wound inside the metal case, the oxide superconducting layer of the rare earth-based oxide superconducting tape wire is removed from the surface of the rare earth-based oxide superconducting tape wire. 2. The ultra-low-resistance connection method of a high-temperature oxide superconducting wire and a metallic superconducting wire according to claim 1, wherein the wire is wound in such a direction as to be located on the compression side when viewed from a mechanical neutral plane. The high-temperature oxide superconductor according to claim 2, wherein the range of compressive strain of the oxide superconducting layer of the rare earth-based oxide superconductor tape wire is -1.5% or more and 0% or less. Ultra-low resistance connection method between conductive wire and metallic superconducting wire. The high temperature oxide superconducting tape wire is a bismuth-based superconducting wire,
Claim characterized in that when the bismuth-based superconducting wire is wound inside the metal case, the maximum strain experienced by the oxide superconducting layer of the bismuth-based superconducting wire is 0.2% or less. 1. An ultra-low resistance connection method between a high-temperature oxide superconducting wire and a metallic superconducting wire according to 1. The high-temperature oxide superstructure according to any one of claims 1 to 4, wherein the surface coating solder is any one of Sn, Pb-Sn, Pb-Sn-Bi, Sn-Ag, and Pb-Bi alloy. Ultra-low resistance connection method between conductive wire and metallic superconducting wire. The superconducting solder of the high temperature oxide superconducting wire and the metallic superconducting wire according to any one of claims 1 to 4, wherein the superconducting solder is one of Pb-Bi and In-Sn-Bi alloy. Low resistance connection method. The metal case has a shape in which the high-temperature oxide superconducting tape wire is curved at least once and accommodated therein, and one end of the high-temperature oxide superconducting tape wire is pulled out;
The high-temperature oxide superconducting wire and metal-based superconductor according to any one of claims 1 to 6, wherein the metal-based superconducting wire is integrally connected to the superconducting solder housed in the metal case. Ultra-low resistance connection method for wires.