JP2003086265A - Connection part of superconducting line and its connecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection part and its connecting method of the MgB2 superconducting line which does not spoil the critical current. SOLUTION: Exposing the connection part of the superconducting line 1 to make it as a MgB2 superconductor 2, and making it locate in a vacuum chamber 10 through a vacuum corresponding lead introducing terminal 11, MgB2 superconductors 2 are contacted mutually. By exposing the portion, where these MgB2 superconductors 2 themselves have been contacted, in Mg-vapor atmosphere of about 900 deg.C, the MgB2 superconductor is formed in the contact portion. After that, taking it out from the vacuum chamber 10, putting the connection portion of these superconductors 2 into a small copper cup, and pouring lead-tin solder in it, makes the connection portion of the MgB2 superconductors fix. When connection resistance of the MgB2 superconducting line containing this connection portion is measured, it is 1 n Ω or less, which is considered to be superconductivity connection. Moreover, by the measurement of the critical current containing the connection portion, it shows the same value with the critical current of at the time of a MgB2 superconducting-line simple substance, that is, fall of the superconductivity characteristic is not seen, either.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a connecting portion (joint) between MgB ₂ superconducting wires and a connecting method thereof.

[0002]

2. Description of the Related Art Generally, a metal-based low-temperature superconducting wire, a Bi-based metal sheath oxide-based high-temperature superconducting wire (oxide superconducting wire), Y
As shown in FIG. 4, the connection of superconducting wires such as a system oxide superconducting wire is performed by directly connecting the superconducting wires 21 with each other by soldering 22. This is the length of the soldering region 22, and the energizing current value and The connection resistance value changed. As a method of reducing the connection (joint) resistance of the superconducting wire, in the connection of the metal-based low temperature superconducting wire, as shown in FIG. 5, the stabilizing metal of the superconducting wire 21 is melted to expose the superconductor (filament) 23. A method of connecting the superconductors 23 to each other by soldering 22, or yes, copper plating is applied to the exposed superconductor 23 from which the stabilizing metal is removed, and the copper-plated superconductors are connected to each other by soldering 22. The method is known. Further, as shown in FIG. 6 by connecting the oxide-based metal sheath superconducting wire, the filaments 25 of the oxide-based superconducting conductor exposed by peeling off a part of the sheath of the oxide-based metallic sheath superconducting wire 24 are brought into contact with each other. A heat treatment method for regenerating the oxide superconducting filament 26 in an oxygen atmosphere is known.

By the way, the MgB ₂ superconductor is Nb ₃ S
It is an intermetallic compound like n, and its superconducting property was recently discovered. In connecting the MgB ₂ superconductor, the lead-based solder does not directly contact the MgB ₂ superconductor between the filaments, so a method is adopted in which the filaments are plated with copper and then the filaments are soldered together. . In addition, as a method of not plating the MgB ₂ superconductor with copper, a low melting point solder (solder containing Bi) may be used to directly connect the filaments.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, MgB
_{In 2} superconductors, the filaments are plated with copper and soldered, or low melting point solders are used for connection. However, since MgB ₂ superconductors are compounds, they are distorted and thus have superconducting characteristics (criticality). There is a problem that the electric current) decreases, and further, the boron core wire that constitutes the filament is easily broken, and there is a problem that the filament is broken in the step of bringing the filaments into contact with each other. If even a part of such filament breakage occurs, the cross-sectional area of the superconducting wire decreases and the critical current decreases.
Also, even if the breakage of the filament could be prevented,
There is a problem that the critical current decreases due to the strain applied to the filament, and it is difficult to make a sound connection (without a decrease in the critical current).

[0005]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and in a connecting portion between MgB ₂ superconducting wires, MgB ₂ superconductors are brought into contact with each other and heat treated in Mg vapor. MgB ₂ characterized in that
It is a connection part of a superconducting wire. Further, the present invention is, MgB _2, characterized in that MgB in ₂ superconducting wire connecting portions of each other were subjected to heat treatment at Mg vapor wrapped boron foil that portion in contact with each other MgB ₂ superconductor It is a connection part of a superconducting wire. In addition, the above-mentioned MgB ₂ of the present invention
The connecting portion of the superconducting wire is characterized in that the MgB ₂ superconductors are brought into contact with each other, and the contact portion is coated with MgB ₂ powder.

[0006] The present invention also provides a method of connecting between MgB ₂ superconductive wire, contacting the MgB ₂ superconductor bodies of MgB ₂ superconducting wire, heat-treated by exposure in Mg vapor atmosphere, MgB ₂ a contact portion It is a method of connecting a MgB ₂ superconducting wire, which comprises forming a superconductor and fixing a connecting portion with lead-tin solder. Further, the present invention provides a method of connecting MgB ₂ superconducting wires to each other, wherein the M of the MgB ₂ superconducting wires is
gB ₂ superconductors are brought into contact with each other, boron foil is wrapped around the contacted portions, exposed to a Mg vapor atmosphere, and subjected to heat treatment,
It is a method of connecting MgB ₂ superconducting wire, characterized in that to form a MgB ₂ superconductor contact portion. Furthermore, the connection method of the MgB ₂ superconducting wire of the present invention is characterized in applying the MgB ₂ powder contact portion of MgB ₂ superconductor.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention, by contacting the MgB ₂ superconductor bodies of MgB ₂ superconducting wire subjected to a heat treatment in Mg vapor, in that connection, or applied strain, even if some broken occurs, the connection site Since the deterioration of the superconducting property due to the strain of the MgB ₂ superconductor can be recovered, the fractured part can be regenerated, and a new electrical bypass circuit can be formed, it is possible to make a connection without impairing the critical current. It is possible.

[0008]

The connection between MgB ₂ superconducting wires according to the present invention is carried out by exposing the connecting portions of the superconducting wires covered with insulation to form MgB ₂ superconductors and contacting the MgB ₂ superconductors with each other in a Mg vapor atmosphere. Heat treatment is performed therein to form a MgB ₂ superconductor in the contact portion. MgB ₂
As the superconductor, for example, a superconducting element wire in which MgB ₂ is generated is twisted on the surface of a boron wire, or a material containing MgB _{2 as} a part of the substance can be connected.

[0009]

[Embodiment 1] Embodiment 1 of the present invention will be described with reference to Table 1 and FIGS. FIG. 1 shows a vacuum chamber 10 for performing a step of connecting a MgB ₂ superconducting wire, which includes a vacuum-compatible lead introduction terminal 11, a pump 12, and a valve 13,
There is provided a crucible 14 for converting steam into steam. In FIG. 2, the connection (joint) portion of the MgB ₂ superconductor after being taken out from the Mg vapor atmosphere is fixed, and the lead-tin solder 17 is poured into the small copper cup 16. Table 1 shows
In the MgB ₂ superconductor for connection in Example 1, a boron wire φ
A superconducting element wire in which MgB ₂ is generated is twisted on the surface of 0.2 mm. The critical current column in Table 1
Liquid helium temperature is 4.2K, 10A flows under self magnetic field, and 7 × 7 × 7 strands in the column of superconducting wire means 7 strands twisted and 7 strands twisted together. Further, 7 pieces of the combined strands are twisted and 7 pieces of them are combined and twisted together, and the total number of strands is 343.

[Table 1]

The glass braid (insulating coating) of the superconducting wire 1 shown in Table 1 is removed from the coating at the portion to be connected to expose the MgB ₂ superconductor 2. As shown in FIG. 1, this is fixed through the vacuum-compatible lead introduction terminal 11, and the vacuum chamber 1
0, and the MgB ₂ superconductors 2 are brought into contact with each other. The portion where the MgB ₂ superconductors 2 are in contact with each other,
It is exposed to a Mg vapor atmosphere at about 900 ° C, and the contact area is exposed to M
A gB ₂ superconductor was formed. The Mg vapor atmosphere was formed by heating the crucible 14 with an electric heater to evaporate Mg in the chamber 10 which was evacuated.

Then, it is taken out of the vacuum chamber 10 and the MgB ₂ superconductor 2 of the superconducting wire 1 is taken out as shown in FIG.
After putting the connecting part 3 of each other in the small copper cup 16,
Lead-tin solder 17 was poured in to fix the connection (joint) portion 3 of the MgB ₂ superconductor. When the MgB ₂ superconductor 2 including this connection portion 3 was cooled in liquid helium and the connection resistance was measured, the connection was 1 nΩ or less, which is considered to be a superconducting connection, and even when the critical current including the connection portion was measured, MgB ₂ It showed the same value as the critical current when the superconducting wire was used alone, and no deterioration in superconducting properties was observed. On the other hand, for comparison, the connection resistances of the ones connected by copper plating using the same MgB ₂ wire and the ones connected by low melting point solder are each about 100 nΩ, but the critical current including the connection part In measurement, 60% to 70% when used alone
In the example 1, the MgB ₂ superconductors of Example 1 were brought into contact with each other, heat-treated in Mg vapor, and lead tin solder was poured in to fix the connection (joint) portion, which showed excellent characteristics. .

In addition, a glass braided (insulated coating) superconductor
Exposing the connecting portion of the lead wire 1 to MgB ₂ Superconductor 2
MgB on this connection (joint) part 3₂ Apply powder
Then, as shown in FIG.
I made an unconnected connection. In this connection method,
There is no decrease and above MgB₂ Connection method without applying powder
Connection resistance is halved compared to the method, and superconducting connection
As was excellent. In addition, in Example 1, M shown in Table 1
gB₂ I used a superconductor, but regarding the shape and size,
May be other than this, and MgB may be used as a part of the substance.₂ But
It would have been better if it was included and was better at such a connection
A superconducting connection is obtained.

[0013]

Example 2 Example 2 is a method for heat treatment with a boron foil, which will be described with reference to Table 1 and FIGS. As shown in FIG. 3, the connection portion of the glass braid (insulating coating) of the superconducting wire 1 in Table 1 is exposed to form the MgB ₂ superconductor 2, and M
The gB ₂ superconductors 2 are brought into contact with each other. A boron foil (thickness 30 mm × width 50 mm) 4 having a thickness of 0.03 mm is wrapped around the portion where the MgB ₂ superconductors 2 are in contact with each other. The thickness and dimensions of the boron foil vary depending on the size of the connecting portion and other conditions. This MgB ₂ superconductor 2 was brought into contact with each other, and the portion covered with the boron foil 4 was wrapped,
As shown in FIG. 1, it is located in a vacuum chamber 10 and exposed to a Mg vapor atmosphere at about 900 ° C.
A gB ₂ superconductor was formed. MgB including this connection
_{2 When the} superconductor was cooled in liquid helium and the connection resistance was measured, the connection was considered to be superconducting connection 1n.
Ω or less, even when measuring the critical current including the connection part, M
It showed the same value as the critical current when the gB ₂ superconducting wire was used alone, and no deterioration in superconducting properties was observed.

[0014]

As described above, according to the present invention,
By contacting the MgB ₂ superconductor bodies of MgB ₂ superconducting wire subjected to a heat treatment in Mg vapor, the distortion of the connecting portions or joined by distortion, even if some broken occurs, MgB ₂ superconductor connecting portion It is possible to recover the deterioration of the superconducting characteristics due to, regenerate the broken part, and form a new electric bypass circuit, so that it is possible to make a connection without impairing the critical current. is there.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a second embodiment of the present invention.

FIG. 4 is a diagram showing a conventional example.

FIG. 5 is a diagram showing a conventional example.

FIG. 6 is a diagram showing a conventional example.

[Explanation of symbols]

1 Superconducting Wire 2 MgB ₂ Superconductor 3 Connection Part 4 Boron Foil 10 Chamber 11 Vacuum Compatible Lead Introducing Terminal 12 Pump 12 13 Valve 13 14 Mg Crucible 16 Small Copper Cup 17 Lead Tin Solder 21 Superconducting Wire 22 Soldering 23 Superconductor ( Filament) 24 Oxide-based metal sheath superconducting wire 25, 26 Filament of oxide superconductor

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) H01B 12/04 ZAA H01B 12/04 ZAA 13/00 563 13/00 563Z

Claims (6)

[Claims] 1. A connecting portion between the MgB ₂ superconductive wire connecting portion of the MgB ₂ superconducting wire, characterized in that were subjected to heat treatment in a Mg vapor is brought into contact with each other MgB ₂ superconductor. 2. A connecting portion between the MgB ₂ superconductive wire, MgB ₂ superconductor, characterized in that were subjected to heat treatment at Mg vapor wrapped boron foil that portion in contact with each other MgB ₂ superconductor Line connection. 3. The MgB ₂ superconducting wire connecting portion according to claim 1, wherein the MgB ₂ superconductors are contacted with each other, and MgB ₂ powder is applied to the contact portions. 4. A MgB ₂ superconducting wire connection between contacting a MgB ₂ superconductor bodies of MgB ₂ superconducting wire, heat-treated by exposure in Mg vapor atmosphere, the MgB ₂ superconductor contact portion formed A method of connecting a MgB ₂ superconducting wire, characterized in that the connecting portion is fixed with lead-tin solder. 5. A method of connecting MgB ₂ superconducting wires to each other, wherein the MgB ₂ superconducting wires of the MgB ₂ superconducting wires are brought into contact with each other, a boron foil is wrapped around the contact portion, exposed to an atmosphere of Mg vapor, and subjected to heat treatment. connection of MgB ₂ superconducting wire, characterized in that to form a MgB ₂ superconductor portion. 6. The MgB ₂ superconductor is contacted with MgB _{2 at} a contact portion.
The method for connecting MgB ₂ superconducting wires according to claim 4 or 5, wherein powder is applied.