WO2016031283A1

WO2016031283A1 - Connection part of superconducting wire rods and method for connecting superconducting wire rods

Info

Publication number: WO2016031283A1
Application number: PCT/JP2015/059017
Authority: WO
Inventors: 洋太一木
Original assignee: 株式会社日立製作所
Priority date: 2014-08-29
Filing date: 2015-03-25
Publication date: 2016-03-03
Also published as: JP2017208156A

Abstract

In order to realize a superconducting connection part having uniform and highly conductive properties, a solution is provided as follows. In the connection part of superconducting wire rods according to the present invention, a plurality of superconducting wire rods are integrated in a metal container by means of an MgB₂-containing sintered body, and the superconducting wire rods are connected to the metal container through Mg.

Description

Connecting part of superconducting wire and method of connecting superconducting wire

The present invention relates to a connection structure of a connection portion of a superconducting wire (MgB ₂ wire) using magnesium diboride (MgB ₂ ), and a connection method of the MgB 2 wire.

The critical temperature (transition temperature) of magnesium diboride (MgB ₂ ) is 39 K, which is higher than the critical temperature of conventional superconductors (eg niobium titanium (NbTi), niobium tritin (Nb ₃ Sn), etc.). Further, unlike a wire using an oxide superconductor, a wire using MgB ₂ has a feature of high magnetic field stability when operated in a permanent current mode in a closed circuit using it.

The permanent current mode is an operation method in which a current is continuously supplied to a closed circuit formed using a superconductor. That is, since the superconducting wire has zero resistance, once the current flows in the closed circuit, the current continues to flow without being attenuated. In order to realize such a permanent current mode, it is important to connect the ends of the superconducting wire or the superconducting wire constituting the permanent current switch with a superconductor.

For example, among MgB ₂ wire material, or a MgB ₂ wire material, as a technique for connecting the other wires, such as NbTi wire and Nb ₃ Sn wire, the following techniques are known.

Patent Document 1 describes a method of connecting MgB ₂ wires using a superconducting solder. The connection method of a superconducting wire using a superconducting solder is also used for the connection of other superconducting wires such as NbTi wires.

In Patent Document 2, the tip of a wire containing a mixed powder of magnesium (Mg) and boron (B), or an MgB ₂ wire, is polished to expose the MgB ₂ core, and inserted into a container. A method is described in which a mixed powder of Mg and B is filled and pressed from orthogonal directions, and heat treatment is performed. A heat treatment produces a sintered body of MgB ₂ and the wires are connected to each other.

Non-Patent Document 1 describes a method of connecting MgB ₂ wires in the following process. A mixed powder of Mg and B is filled in a cylindrical stainless steel container, and after inserting a copper plug, an unreacted MgB ₂ wire (a wire containing mixed powder of Mg and B) in which the core is exposed is inserted. Thereafter, the powder is pressurized with a copper plug, and the container is sealed with a ceramic bond, followed by heat treatment to form a MgB ₂ sintered body, and the wires are connected to each other.

JP, 2006-174546, A JP, 2012-094413, A

In the technology described in Patent Document 1, since the critical temperature of the superconducting solder is about 9 K or less, it can not be used at an operating temperature of 10 K or more. That is, even in the case of a superconducting magnet using MgB ₂ having a relatively high critical temperature (39 K), it has to be cooled to 10 K or less, and its characteristics can not be fully utilized.

In the techniques described in Patent Document 2 and Non-patent Document 1, the core (MgB ₂ or the mixed powder containing Mg and B) at the tip of the wire is exposed in the metal container and connected via the MgB ₂ sintered body Be done. In Patent Document 1, the wire end to be connected is fixed by superconducting solder over the entire length in the metal container, whereas in Patent Document 2 and Non-Patent Document 1, the vicinity of the container opening for inserting the wire, also only by the MgB ₂ sintered body produced by heat treatment, it is fixed to the metal container. Therefore, there is a portion where the wire is not fixed in the container. When the connection is energized, the current and the magnetic field exert an electromagnetic force on the wire. When an electromagnetic force is applied to the non-fixed portion, a load is applied to the fixed portions at both ends. The bonding interface between the wire core and the MgB ₂ sintered body is mechanically brittle and easily broken, resulting in deterioration of the current-carrying characteristics at the interface. In FIG. 2 of Non-Patent Document 1, the variation of the conduction characteristic among the samples is shown, and it can be seen that the sample with the lowest critical current (Ic) is about 1⁄3 of the highest sample. This variation is considered to be caused by insufficient fixing of the wire, as described above.

An object of the present invention is to solve the above-mentioned problems regarding the connection of MgB ₂ superconducting wire, and to realize a connection portion having a small variation between samples and having high current-carrying characteristics.

As a result of investigations to solve the above-mentioned problems, the present inventors have found that the problems can be solved by the structure of the connecting portion and the method of processing the end, and completed the present invention. In the connection portion of the superconducting wire according to the present invention, a plurality of superconducting wires are integrated by a sintered body containing MgB ₂ in a metal container, and the superconducting wire is connected to the metal container via Mg. .

According to the present invention, it is possible to realize a connection portion of a superconducting wire rod having a small variation and high conduction characteristics.

Configuration example of superconducting magnet Method of connecting superconducting wire of Example 1 Method of connecting superconducting wire of Example 2 Method of connecting superconducting wire of Example 3 Method of connecting superconducting wire of Example 4 Method of connecting superconducting wire of Example 5 Method of connecting superconducting wire of Example 6

The connection structure in the present invention is as described below. First, the tip of a wire having a core containing Mg and B or a compound containing them constituting the superconducting coil or permanent current switch to be connected is polished to expose the wire core. The ends of the wires are inserted into the metal container, and the raw material (Mg, B, or a compound containing them) of the MgB ₂ sintered body formed around the ends of the wires is filled into the metal container. The MgB ₂ sintered body is formed by pressurizing and heat treating it, and the wires inserted into the metal container are connected to each other. The present invention is intended to improve fixing of the wire by filling Mg excessively before heat treatment and pouring in solder after heat treatment.

The superconducting magnet is used in an MRI (Magnetic Resonance Imaging: magnetic resonance imaging) apparatus, an NMR (Nuclear Magnetic Resonance: nuclear magnetic resonance) apparatus, and the like. Since such a device requires high magnetic field stability, the superconducting magnet forms a closed circuit with only a superconductor and is operated in a "permanent current mode" in which current flows continuously. For that purpose, the technology which connects a superconducting coil, a permanent current switch, and wiring which connects them via a superconductor is essential.

In a conventional superconducting magnet apparatus, superconducting wires of NbTi or Nb3Sn are used, and many of them are operated by cooling to 4.2 K by liquid helium. In such a superconducting magnet, a connection technique using a superconducting solder represented by a PbBi alloy has been established.

Magnesium diboride (MgB ₂ ) is expected to be put to practical use as a superconducting magnet by refrigerator cooling that does not use liquid helium, because the critical temperature for transition to superconductivity is higher than that of conventional metal-based materials. In this case, since it is required to operate at 10 K or more, the conventional superconducting solder connection having a critical temperature of 10 K or less can not be applied. Therefore, it is necessary to establish a technique for connecting MgB ₂ wires with MgB ₂ .
(Overview)
A connecting portion of a superconducting wire in which a plurality of superconducting wires are integrated by a sintered body containing MgB ₂ in a metal case, wherein the superconducting wire is the inside of the metal case, Mg and solder with the metal case It is connected through. Fixing of the wire is improved, and the movement of the wire when the electromagnetic force works during current conduction is suppressed, so that it is possible to realize a superconducting joint having high current conduction characteristics with small variation.
(Superconducting magnet)
The superconducting magnet having the above-described superconducting wire connection structure has high reliability of the connection portion and stable operation without quenching is possible. FIG. 1 shows an example of the configuration of a superconducting magnet. In the superconducting magnet of FIG. 1, a superconducting coil 22 and a permanent current switch 23 are disposed inside a cooling vessel 26, and these are cooled by a refrigerator (not shown) via a support plate 25. When the superconducting coil 22 is excited, current is supplied via a current lead 24 connecting a power supply at room temperature (not shown) and the superconducting coil 22 at low temperature. The superconducting connection portion 21 is provided at two positions between the superconducting coil 22 and the permanent current switch 23.

Here, as a superconducting wire to be connected, a single-core wire composed of a metal sheath and an MgB ₂ core will be described as an example. Metal sheaths generally prevent stabilizers from reacting with stabilizers such as stabilizers to ensure high electrical and thermal stability and heat treatments to Mg and B to MgB ₂ The barrier material for The superconducting wire to be connected is not limited to MgB ₂ , and the present invention is applicable to NbTi and Nb 3 Sn used in conventional superconducting magnets. Since connection is made via (39 K) MgB _2, which has a high critical temperature, higher stability can be expected compared to connection with a conventional superconducting solder (critical temperature: 9 K). In addition, although a superconducting wire is generally used as a multifilamentary wire having a plurality of cores from the viewpoint of current capacity, wire length, magnetic stability, and AC loss, the configuration of the connection part is the same whether single or multifilamentary wire. Therefore, only the connection structure of a single core wire will be described here. The number of superconducting wires to be connected is not limited to two, and may be three or more.

FIG. 2 shows the connection procedure of this embodiment. Although only one wire is shown in the drawing, another wire is present in the depth direction of the drawing. First, the ends of the two wires 1 to be connected are polished to expose the cores 2 of the wires. At this time, the core 2 may be either in an unreacted state of Mg and B or in a state where MgB _{2 has been} formed. When Mg and B are in an unreacted state, the wire portion may be simultaneously heat treated at the time of the heat treatment for connection to make MgB ₂ . The wire with the core 2 exposed at the end is inserted into the metal container 4. As a material of the metal container 4, it is desirable to use Fe, Ni, Nb, Ta or alloys thereof which hardly react with Mg and B during heat treatment.
<(A) Mg + B filling>
After the wire 1 is inserted, the raw material of the MgB ₂ sintered body 8 is filled and pressurized. In this embodiment, a mixed powder (mixture) 5 of Mg and B is filled. A ball mill is usually used for mixing, but the method is not limited. In order to improve the current-carrying characteristics of the MgB ₂ sintered body 8, carbon or the like may be added, or MgB ₂ powder may be mixed. After filling the mixed powder 5 of Mg and B, the metal pin 6 is pressed by a press machine or the like.
<(B) Mg filling>
In the prior art, after filling the mixed powder 5 of Mg and B, sealing and heat treatment are performed, but in the present invention, Mg 7 is further added after this. The form of the Mg 7 powder may be powder or lump because it melts during heat treatment (in the case of powder, pressurization is required).

<(C) After heat treatment>
After that, the MgB ₂ sintered body 8 is formed at the end of the wire 1 by heat treatment, and the ends of the wire 1 are connected. In order to produce the MgB ₂ sintered body 8, heating is usually performed at 500 ° C. to 900 ° C. in an inert gas such as argon and nitrogen using an electric furnace. In the present embodiment, the melting point of Mg is heated to 650 ° C. or higher to dissolve Mg and fix the wire rod 1 and the metal container 4. However, if the temperature is high, the amount of evaporation of Mg increases, so a heat treatment at about 650 ° C. to 850 ° C. is desirable. Conventionally, in order to prevent evaporation of Mg, sealing is performed with a heat-resistant adhesive such as a ceramic bond before heat treatment, but in the present embodiment, sealing is not performed before heat treatment because solder fixation described later is performed. Therefore, in order to suppress the evaporation of Mg, heat treatment is performed in a state in which there is no gap at the opening of the metal container 4 as much as possible. That is, the gap between the metal pin 6 and the wire 1 is designed to be small, and heat treatment is performed in a state in which the metal pin 6 is inserted. The presence of Mg in the upper part of the mixed powder 5 of Mg and B not only fixes the wire, but also has the effect of suppressing the evaporation of Mg from the mixed powder mixed at Mg: B = 1: 2.

<(D) Solder filling>
After the heat treatment, while heating the metal container 4 to 150 ° C. to 300 ° C., solder is poured from the opening of the metal container 4 to fix the wire 1 and the metal container 4. The solder 9 may be a general PbSn solder or lead-free solder, but it is desirable that the viscosity be low. In this embodiment, both of the fixing by Mg 7 and the solder 9 are performed, but only one of them may be used. However, since Mg 7 may fix only the periphery of the MgB ₂ sintered body 8 and solder may flow only to the periphery of the opening of the metal container 4, it is preferable to carry out both. When soldering is not performed, the evaporation of Mg can be prevented by sealing the opening of the metal container 4 with a heat-resistant adhesive such as ceramic bond or screw before heat treatment, and only in the inert gas Also, heat treatment in vacuum is possible. In this example, the conduction characteristic of the connection portion is about 10% of the wire performance, but by fixing the wire with Mg and the solder, it becomes possible to suppress the variation within ± 10%. .

FIG. 3 shows the connection procedure of this embodiment. It is basically the same as Example 1, but the method of filling the raw materials is different. When the mixed powder 5 of Mg and B is heat-treated as in Example 1 to produce the MgB ₂ sintered body 8, the portion where Mg was present becomes a void, so the density of the generated MgB ₂ is the theory The maximum is about 50% of the density.
<(A) B filling><(b) Mg filling>
In this embodiment, after inserting the wire rod 1 into the metal container 4, first, only the B10 powder is filled and pressurized, and then the Mg7 powder is filled. As a result, an MgB ₂ sintered body 8 having a density of 70% or more with respect to the theoretical density is formed around the end of the wire 1, and high current conduction characteristics can be realized. In addition, since B10 and Mg7 melt | dissolve at the time of heat processing, the form may be powder or lump (in the case of powder, pressurization is required).
<(C) After heat treatment>
If the filling amount of Mg with respect to B is 0.5 mol or more, excess Mg will remain after heat treatment, which contributes to fixing of the superconducting wire.
<(D) Solder filling>
The fixing by the solder 9 is the same as in the first embodiment. According to this example, since the MgB ₂ sintered body having a density higher than that of Example 1 is formed, the conduction characteristic of the connection portion is improved to about 20% with respect to the wire performance.

4 to 7 show the connection procedure of the third to sixth embodiments. The basic flow is the same as in Example 2, but the feature of each example is that the wire insertion direction and the powder pressing direction are different, desirably, substantially orthogonal (80 ° to 100 °). . When the “insertion direction of the wire” and the “pressing direction of the mixed powder of Mg and B (or B powder)” are the same as in Examples 1 and 2, the force applied to the powder is applied to the cross section of the wire core. However, it is difficult to improve the adhesion between the wire core and the powder because a powder density gradient is generated in parallel to the pressing direction.

On the other hand, if the “insertion direction of the wire” and the “pressing direction of the mixed powder of B (or B powder)” are orthogonal as in Examples 3 to 6, the applied pressure is directly applied to the cross section of the wire core. In addition, since the cross-sections of the pressing surface and the wire core can be made close to each other, high adhesion between the powder and the wire core can be realized. Therefore, in these embodiments, in order to fill and press the mixed powder (or B powder) of B in the direction orthogonal to the opening for inserting the wire, as viewed from one end of the superconducting wire located inside the metal container Provide an opening in the metal container. Here, only the case of two-layer filling of B and Mg described in Example 2 will be mentioned, but even when the mixed powder of Mg and B described in Example 1 is filled, the super electric wire material according to the present invention The connection can be manufactured.

<(A) B filling><(b) Mg filling>
In this embodiment, after inserting the wire rod 1 into the metal container 4, first, only the B10 powder is filled and pressurized, and then the Mg7 powder is filled. As a result, an MgB ₂ sintered body 8 having a density of 70% or more with respect to the theoretical density is formed around the end of the wire 1, and high current conduction characteristics can be realized.

In the third embodiment, as in the second embodiment, the wire rod 1 and the metal container 4 are fixed by being filled with excess Mg 7 powder. In this case, if the gap between the opening of the metal container 4 and the wire 1 is not sealed by the ceramic bond 11, molten Mg flows out from the opening of the metal container 4 for inserting the wire, so sealing is performed. Stop is essential. Therefore, it is not possible to carry out the fixing by the solder after the heat treatment.
<(C) After heat treatment>
If the filling amount of Mg with respect to B is 0.5 mol or more, excess Mg will remain after heat treatment, which contributes to fixing of the superconducting wire. As shown in FIG. 4, Mg 7 exists between one end of the superconducting wire positioned inside the metal container and the opening.

FIG. 5 is an example in which the fixation by Mg is abandoned contrary to FIG. 4 and is fixed by solder.
<(A) B filling><(b) Mg filling>
In this embodiment, after inserting the wire rod 1 into the metal container 4, first, only the B10 powder is filled and pressurized, and then the Mg7 powder is filled. As a result, an MgB ₂ sintered body 8 having a density of 70% or more with respect to the theoretical density is formed around the end of the wire 1, and high current conduction characteristics can be realized.

In the fourth embodiment, as in the second embodiment, the wire rod 1 and the metal container 4 are fixed by being filled with excess Mg 7 powder. Here, the gap between the opening of the metal container 4 and the wire 1 is not sealed by the ceramic bond 11.
<(C) After heat treatment>
Before heat treatment, the metal pin 6 was fixed by the ceramic bond 11, and (b) the Mg-filled connection portion was rotated about 90 degrees to the left to heat the metal pin 6 so that it was on the lower side. Make sure that Mg does not flow out. As shown in FIG. 5, Mg 7 exists between one end of the superconducting wire positioned inside the metal container and the opening.
<(D) Solder filling>
In this case, since molten Mg 7 accumulates on the metal pin 6 side, fixation of the wire 1 by Mg 7 can not be expected, but the opening for inserting the wire of the metal container 4 is not sealed. It is possible. After the heat treatment, while heating the metal container 4 to 150 ° C. to 300 ° C., the solder 9 is poured from the opening of the metal container 4 to fix the wire 1 and the metal container 4.

Example 5 is an example in which “insertion direction of wire rod” and “pressing direction of mixed powder of Mg and B (or B powder)” are almost orthogonal to each other as shown in FIG. It is. <(A) B filling><(b) Mg filling>
B10 powder is filled, pressed by metal pin 6, and metal pin 6 is fixed and sealed by ceramic bond 11, and then excess Mg 7 is filled from the wire insertion direction. Thereby, the excess Mg 7 contributes to the wire fixation, and the fixation by the solder 9 can be performed after the heat treatment.

In Example 5, as in Examples 3 and 4, “insertion direction of wire rod” and “pressing direction of mixed powder of Mg and B (or B powder)” are different, preferably substantially orthogonal (80 In addition to the fact that the angle is in the range of 100 ° to 100 °, it is also characterized in that the metal pin 6 applies pressure from substantially the same direction as the wire insertion direction.
<(C) After heat treatment>
After the heat treatment, excess Mg 7 is present at a position adjacent to the wire 1. There is a space between the metal pin 6 and Mg 7 located in the same direction as the wire insertion direction. As shown in FIG. 6, Mg 7 exists between one end of the superconducting wire positioned inside the metal container and the opening of the metal container 4 in which the wire 1 is present.
<(D) Solder filling>
After the heat treatment, while heating the metal container 4 to 150 ° C. to 300 ° C., the solder 9 is poured from the opening of the metal container 4 (the side where the wire 1 exists) to fix the wire 1 and the metal container 4.

In the sixth embodiment, as shown in FIG. 7, the wire insertion direction and the powder pressing direction are orthogonal to each other, and further, the fixation with Mg and solder is realized. It is not necessary for the filling of Mg to be the same opening as the wire, and as shown in FIG. 7, an opening for filling Mg may be provided, and the workability of filling is better. For example, it is preferable that an angle between the insertion direction of the plurality of superconducting wires into the metal container and the direction from one end of the superconducting wire located inside the metal container to the opening for Mg filling be 10 to 80 °.
<(A) B filling><(b) Mg filling>
In the metal container 4, an opening for filling Mg is provided between “wire insertion direction”, “wire insertion direction”, and “pressure direction of mixed powder of Mg and B (or B powder)”.

B10 powder is filled, pressed by metal pin 6, excess Mg 7 is filled from the opening for Mg filling. Thereby, the excess Mg 7 contributes to the wire fixation, and the fixation by the solder 9 can be performed after the heat treatment.
<(C) After heat treatment>
After the heat treatment, excess Mg 7 is present inside the Mg filling opening of the metal container 4 and adjacent to the wire 1. There is a space between the metal pin 6 and the Mg 7 in the opening for Mg filling. As shown in FIG. 7, Mg 7 exists between one end of the superconducting wire positioned inside the metal container and the opening for Mg filling.
<(D) Solder filling>
After the heat treatment, while heating the metal container 4 to 150 ° C. to 300 ° C., the solder 9 is poured from the opening of the metal container 4 (the side where the wire 1 exists) to fix the wire 1 and the metal container 4.

The maximum values of the conduction characteristics of the connection portions obtained in Examples 3 to 6 were all as high as about 50% with respect to the wire performance. Furthermore, in Examples 5 to 6 in which Mg and solder are fixed, the variation can be suppressed to within ± 10%.

1: Wire 2: Core 3: Sheath 4: Metal container 5: Mixed powder of Mg and B 6: Metal pin 7: Mg
8: MgB ₂ sintered body 9: solder 10: B
11: ceramic bond 21: superconducting connection 22: superconducting coil 23: permanent current switch 24: current lead 25: support plate 26: cooling vessel

Claims

A connecting portion of a superconducting wire in which a plurality of superconducting wires are integrated by a sintered body containing MgB 2 in a metal container,
A connection portion of a superconducting wire characterized in that Mg is present inside the metal container and adjacent to the superconducting wire.
A connecting portion of the superconducting wire according to claim 1, wherein
The connecting portion of a superconducting wire characterized in that the superconducting wire is connected to the metal case via solder inside the metal case.
A connecting portion of the superconducting wire according to claim 1 or 2, wherein
The connection portion of a superconducting wire characterized in that the density of the sintered body is 70% or more of the theoretical density of MgB 2 .
It is a connection part of the superconducting wire rod according to any one of claims 1 to 3,
A superconducting wire characterized in that the metal container has an opening in a direction different from the insertion direction of the plurality of superconducting wires into the metal container as viewed from one end of the superconducting wire located inside the metal container. Connection part.
A connecting portion of the superconducting wire according to claim 4, wherein
An angle between an inserting direction of the plurality of superconducting wires into the metal container and a direction from one end of the superconducting wire positioned inside the metal container to the opening is 80 to 100 °. Superconductor wire connection.
A connecting portion of the superconducting wire according to claim 4, wherein
An angle between an inserting direction of the plurality of superconducting wires into the metal container and a direction from one end of the superconducting wire located inside the metal container to the opening is 10 to 80 °. Superconductor wire connection.
A connecting portion of the superconducting wire according to any one of claims 4 to 6, wherein
A connecting portion of a superconducting wire characterized in that Mg is present between one end of the superconducting wire located inside the metal container and the opening.
A method of connecting superconducting wires,
Inserting the plurality of superconducting wires into the opening of the metal container;
Filling the raw material of the MgB 2 sintered body in the vicinity of the plurality of superconducting wires;
And d) heating the filled raw material.
In a raw material of the MgB 2 sintered body, a molar ratio of Mg to B is larger than 0.5, and a method of connecting a superconducting wire.
It is a connection method of the superconducting wire according to claim 8,
The method of connecting superconducting wires, wherein the filling step includes a first filling step of filling a mixture of Mg and B, and a second filling step of filling Mg after the first filling step.
It is a connection method of the superconducting wire according to claim 8,
The method of connecting superconducting wires, wherein the filling step includes a first filling step of filling B and a second filling step of filling Mg after the first filling step.
10. The method of connecting superconducting wires according to claim 9, wherein
An angle between the filling direction in the first filling step and the second filling step and the insertion direction of the plurality of superconducting wires into the metal container is 80 to 100 °.
A method of connecting superconducting wires according to claim 10, wherein
An angle between the filling direction in the first filling step and the second filling step and the insertion direction of the plurality of superconducting wires into the metal container is 80 to 100 °.
10. The method of connecting superconducting wires according to claim 9, wherein
The angle between the filling direction of the first filling step and the inserting direction of the plurality of superconducting wires into the metal container is 80 to 100 °.
An angle between a filling direction of the second filling step and an inserting direction of the plurality of superconducting wires into the metal container is -10 to 10 °.
A method of connecting superconducting wires according to claim 10, wherein
The angle between the filling direction of the first filling step and the inserting direction of the plurality of superconducting wires into the metal container is 80 to 100 °.
An angle between a filling direction of the second filling step and an inserting direction of the plurality of superconducting wires into the metal container is -10 to 10 °.
10. The method of connecting superconducting wires according to claim 9, wherein
The angle between the filling direction of the first filling step and the inserting direction of the plurality of superconducting wires into the metal container is 80 to 100 °.
An angle between the filling direction of the second filling step and the inserting direction of the plurality of superconducting wires into the metal container is 10 to 80 °.
A method of connecting superconducting wires according to claim 10, wherein
The angle between the filling direction of the first filling step and the inserting direction of the plurality of superconducting wires into the metal container is 80 to 100 °.
An angle between the filling direction of the second filling step and the inserting direction of the plurality of superconducting wires into the metal container is 10 to 80 °.
The method of connecting superconducting wires according to any one of claims 8 to 16, wherein
A method of connecting a superconducting wire, the method comprising: a soldering step of pouring solder into the opening of the metal container from the gap between the plurality of superconducting wires after the heating step.