JPH0450719B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a method for connecting compound-based superconducting wires having superconducting intermetallic compounds.

"Prior art" Compound-based superconductors such as Nb ₃ Sn have very brittle properties, and it is difficult to process compound rods, etc., so when manufacturing superconducting wires using the above compounds, Usually, the material is processed in a composite state that has not yet become a final intermetallic compound, and after that processing, a diffusion heat treatment is performed to generate an intermetallic compound.

Conventionally, as a connection method for compound-based superconducting wires manufactured as described above, Figs.
Methods of configuring the connection structures shown in the figures are known. In the structure shown in FIG. 4, superconducting wires 1 and 2 are manufactured by overlapping the ends of a pair of compound superconducting wires 1 and 2, and applying solder 3 to the overlapping portion. In the structure shown in Fig. 5, the tip surfaces of the superconducting wires 3 and 4 formed by twisting into a tape are butted against each other, and a tape-shaped superconducting element of a predetermined length is placed above and below the butted part. The superconducting wires 3, 4 are connected by a method such as covering the superconducting wires 5, 6 and half-attaching the superconducting wires 3, 4 and the superconducting wires 5, 6,
In the structure shown in FIG. 6, the tip surfaces of the single-wire superconducting wires 7 and 8 are butted against each other, and both sides of the butted portion are sandwiched between superconducting wires 9 and 10 of a predetermined length. By soldering the wires 9 and 10, the superconducting strands 7 and 8 are
is connected.

"Problems to be Solved by the Invention" When superconducting wires are connected by each of the above methods, the superconducting wires are connected through solder and contact connection, and the superconducting wires are connected without any gaps. It becomes virtually impossible to join.
Then, when a large current is passed through the superconducting wire, the current flows through the solder layer and the contact area, and there is a risk of heat generation in the solder layer and the contact area. This is an undesirable phenomenon. Note that the heat generation in the solder layer causes the superconducting state to transition to the normal conducting state. There is a problem that this may cause a so-called quench phenomenon.

``Object of the Invention'' The present invention has been made in view of the above-mentioned circumstances, and allows compound superconducting wires to be integrally and easily connected to each other without any gaps. The purpose is to provide a connection method with high strength.

"Means for Solving the Problems" The present invention provides a method for disposing a large number of filaments of at least one metal element among two or more metal elements constituting a superconducting intermetallic compound, and Among the elements, the base containing the remaining elements is
A compound obtained by applying diffusion heat treatment to a superconducting wire with a circular cross section and covered with a stabilizing base material consisting of a copper alloy or substantially copper to form a filament-shaped superconducting intermetallic compound within the base. In the method for connecting system superconducting wires, the diffusion heat treatment temperature is set to a temperature range of 650 ° C to 850 ° C lower than the melting temperature of the stabilizing base material made of copper or copper alloy,
Stabilizing the superconducting wire before diffusion heat treatment Diffusion heat treatment is performed to heat the stabilized base materials for 20 to 150 hours in a vacuum atmosphere or inert gas atmosphere while keeping the surfaces of the base materials in contact with each other. Only the parts are welded by solid-phase diffusion of copper atoms, and a pair of recesses separated by the surface of the stabilizing base material are formed on both sides of the welded part, and each of these pair of recesses is filled with solder to close the recesses. This is used to connect superconducting wires together.

"Action" 650℃~850℃ lower than the melting temperature of the stabilizing base material
By applying diffusion heat treatment, which is heated for 20 to 150 hours,
Mutual diffusion of copper atoms occurs at the surfaces where the stabilizing base materials of the superconducting wire are in contact with each other, and the stabilizing base materials are welded together. At this time, since the diffusion heat treatment is performed at a temperature lower than the melting temperature of the stabilizing base material, only the surface parts of the stabilizing base material that are in contact with each other and their surrounding areas are welded by diffusion of copper atoms, and both sides of the welded part A recess defined by the surface of the stabilizing base material having a circular cross section is formed in the recess. Here, by performing diffusion heat treatment at the above temperature, the welded part is joined without spreading greatly from the contact part, so the above-mentioned recess is reliably formed, and the welded part is joined near the base arranged inside the superconducting wire. The welded part will not spread.

Then, by applying solder to fill the recesses, the superconducting wires are integrally connected without forming any recesses between the superconducting wires.

Furthermore, if the superconducting wires are brought into contact with each other and subjected to diffusion heat treatment, and solder is applied to the recesses formed between the superconductor wires, the position of the solder can be easily determined due to the presence of the recesses. It is possible to perform reliable solder application, and to connect superconducting wires reliably and firmly.

``Example'' Figures 1 to 3 show an example of the present invention. In the figures, 1 indicates a superconducting wire, and this superconducting wire 1 is a cylindrical stabilizer made of oxygen-free copper. Base material 1A
A thin cylindrical diffusion barrier layer 1B made of Ta or Nb is provided inside the stabilizing base material 1A, and a large number of Nb filaments 1c are provided inside the barrier layer 1B. This is a well-known structure consisting of a rod-shaped base 1D made of a Cu-Sn alloy.

In order to connect the superconducting wires 1, 1, diffusion heat treatment is performed while the ends of the superconducting wires 1, 1 to be connected are kept in contact with each other as shown in FIG. This diffusion heat treatment is performed at a temperature of about 650 to 850℃ in a vacuum or in an inert gas atmosphere for 20 minutes.
This is done by heating for about 150 hours. In addition,
It is preferable that the superconducting wires 1, 1 to be brought into contact be thoroughly cleaned, and it is also preferable that they be sandwiched or tied with metal fittings, metal wires, etc. so that the mutual contact force is strengthened. Here, the temperature at which the above-mentioned diffusion heat treatment is performed is lower than the melting temperature of the stabilizing base material 1A, but the surface portion of the stabilized base material 1A that has been brought into contact is exposed to the high temperature during the heat treatment, in an inert gas atmosphere, or,
Since it is heated for a long time in a vacuum atmosphere, copper atoms diffuse actively in the surface contact areas, and as a result, the surface contact areas and their surrounding areas are welded together as shown in FIG. By this welding, a recess 1a is formed on both sides of the welded portion, which is defined by the surfaces of the stabilizing base materials 1A, 1A each having a circular cross section. In addition, by diffusion heat treatment, Nb filament 1c is
The Nb ₃ Sn superconducting intermetallic compound filament 1E is formed, and the superconducting wire 1 becomes a superconducting wire 1'. Then,
Concave portion 1a on the surface of welded superconducting wires 1', 1'
A solder layer 2 is formed by applying solder so as to fill it up, as shown in FIG. 3, and the welded portion is reinforced by the solder layer 2, thereby completing the connection of the superconducting wires 1', 1'.

Superconducting wires 1' connected by the method described above,
1', the stabilizing base materials 1A and 1A are welded together and integrated, so unlike the connection structure using the conventional connection method, which connects through a solder layer, it does not generate heat even when a large current is applied. There is no danger. Therefore, if the superconducting wires are connected by the method described above, the conventional problem of breaking the superconducting state at the connection part and transitioning to the normal conducting state does not occur. Further, the above-described method is carried out using the heat of the diffusion heat treatment conventionally carried out when forming superconducting wires, so it can be easily carried out without requiring any special treatment or process for connection. Furthermore, as mentioned above, by applying diffusion heat treatment at 650 to 850°C for 20 to 150 hours, the stabilized base material 1A
Since the diffusion heat treatment is performed at a temperature lower than the melting temperature of A defined recess 1a is formed on the surface of the stabilizing base materials 1, 1 each having a circular cross section. Here, by carrying out the diffusion heat treatment at the above-mentioned temperature, the welded part is joined without greatly expanding from the contact part, so that the recess 1a is reliably formed, and the base 1D disposed inside the superconducting wire 1 is The welded area will not spread to nearby areas.

Then, solder 2 is applied to fill this recess 1a.
By stacking the superconducting wires 1', 1', the superconducting wires 1', 1' can be integrally connected without leaving any recesses 1a between the superconducting wires 1', 1'.

In addition, if the superconducting wires 1, 1 are brought into contact with each other, a diffusion heat treatment is applied to both, and then solder 2 is applied to the recess 1a formed between the superconducting wires 1, 1, the solder 2 is Set the filling position to concave part 1
Due to the presence of a, the solder can be easily determined, and the solder can be deposited reliably, and the circular superconducting wires can be connected reliably and firmly.

In the above embodiments, the method of the present invention was applied to a Nb ₃ Sn-based superconducting wire having a diffusion barrier layer 1B, but a superconducting wire having no diffusion barrier layer 1B, or Nb ₃ Ga, Nb ₃ Ge, Of course, the present invention may be applied to superconducting wires such as Nb ₃ Al, V ₃ Ga, etc.

"Experiment example" A structure equivalent to superconducting wire 1 shown in Figure 1.
Five Nb ₃ Sn superconducting strands (1.0 mmφ) were molded and twisted to make a conductor. Two of these conductors were prepared, their ends overlapped with a length of 50 mm, and the overlapped part was made of stainless steel. Tie with steel wire. Diffusion heat treatment (800℃×
50H, _N2 gas atmosphere), and after treatment, apply solder to the overlapping parts in air to complete the connection.
The superconducting properties of this superconducting wire were investigated. In addition, we prepared two conductors with the same configuration as the above conductor, performed diffusion heat treatment without overlapping them, and investigated the superconducting properties of a superconducting wire in which the two conductors were overlapped and soldered after the diffusion heat treatment. Investigation of superconducting properties is
A current of 4.2 k, 10 T (Tesla) was passed through each superconducting wire.

A critical current value of 1000A was obtained for the superconducting wire that was subjected to diffusion heat treatment after stacking. This value is almost the same as that of a general superconducting stranded wire that does not have a connection part. On the other hand, superconducting wires that were subjected to diffusion heat treatment and soldered without overlapping became normal conductive and generated voltage at a current value exceeding 600A. When the superconducting wire was later taken out and examined, it was found that almost no solder remained.

From the above results, it is clear that the superconducting wires connected using the method of the present invention are perfectly bonded.

``Effects of the Invention'' As explained above, according to the present invention, the superconducting wires are connected by diffusion heat treatment while they are in contact with each other, and the contacting surface portions of the superconducting wires are welded and connected. Unlike the connection through solder, the superconducting wires are connected integrally. Therefore, no heat is generated at the connection part,
The quench phenomenon that conventionally occurs due to heat generation at the connection part does not occur. Furthermore, since the heat during the diffusion heat treatment is used for connection, no special process or treatment is required for connection, making the connection work easy. In addition, by applying diffusion heat treatment at 650 to 850℃ for 20 to 150 hours, the diffusion heat treatment is performed at a temperature lower than the welding temperature of the stabilizing base material, so the surfaces of the stabilizing base materials that are in contact with each other Only the portion and its surrounding portion are welded, and recesses defined in the surface of the stabilizing base material having a circular cross section are formed on both sides of the welded portion. Here, by performing diffusion heat treatment at the above temperature, the welded part is joined without greatly spreading from the contact part, so the recess is reliably formed, and the welding reaches close to the base arranged inside the superconducting wire. The parts do not expand.

Then, by applying solder to fill the recesses, the superconducting wires can be integrally connected without leaving any recesses between the superconducting wires.

Also, if the superconducting strands are brought into contact with each other, a diffusion heat treatment is applied to both, and then solder is applied to the recesses formed between the superconducting strands,
The presence of the recess allows for easy determination of the position where the solder is to be applied, ensuring reliable solder application, and the ability to reliably and firmly connect the circular superconducting wires.

[Brief explanation of the drawing]

Figures 1 to 3 show the method of the present invention; Figure 1 is a cross-sectional view showing superconducting wires in contact with each other, and Figure 2 is a cross-sectional view showing how superconducting wires are welded together. Figure 3 is a cross-sectional view showing the solder applied to the welded part, Figure 4 is a cross-sectional view showing the connection state by the first conventional method, and Figure 5 is the second
Cross-sectional view showing the connection state by the conventional method shown in Fig. 6.
The figure is a side view showing a connection state according to the third conventional method. 1...Superconducting strand, 1'...Superconducting wire, 1a...
...Concavity, 1A...Stabilizing base material, 1C...Nb filament, 1D...Base.

Claims (1)

[Scope of Claims] 1. A large number of filaments of at least one metal element among the two or more metal elements constituting the superconducting intermetallic compound, and the remaining elements among the two or more metal elements A superconducting wire with a circular cross section is covered with a copper alloy or a stabilizing base material consisting essentially of copper, and a filament-shaped superconducting intermetallic compound is generated within the base by performing diffusion heat treatment. In the method for connecting compound-based superconducting wires, the diffusion heat treatment temperature is set at 650°C to 850°C, which is lower than the melting temperature of the stabilizing base material made of copper or copper alloy.
The stabilizing base materials of the superconducting wire before diffusion heat treatment are heated in a vacuum atmosphere or an inert gas atmosphere for 20 minutes with the surfaces of the stabilized base materials in contact with each other.
Diffusion heat treatment is applied to heat for ~150 hours, and the contact areas and the vicinity of the stabilizing base materials are welded by solid-phase diffusion of copper atoms, and a pair is formed on both sides of the welded area, separated by the surface of the stabilizing base materials. A method for connecting compound-based superconducting wires, the method comprising: forming recesses, filling each of the pair of recesses with solder after diffusion heat treatment, and connecting the superconducting wires by filling the recesses.