JPH0696629A - Composite superconductive and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent deterioration of a mechanical property while preventing deterioration of superconductivity due to thermal strain. CONSTITUTION:For example, Nb3Sn is used for a superconductor. A first portion 11a made of titanium, having a thermal contraction coefficient near that of a wire bundle 11 and a second portion 11b made of austenitic stainless steel which is easy to be joined to a refrigerant terminal tube are joined to each other in the conductor length direction, thus constituting a conduit 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite superconducting conductor used in, for example, a superconducting coil and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 8 is a sectional view of a conventional internal forced cooling type superconducting conductor disclosed in Japanese Patent Laid-Open No. 63-81707. In the figure, 1 is a wire bundle containing a superconducting element wire, and 2 is a stainless steel conduit containing the wire bundle 1.

FIG. 9 is a perspective view showing an example of a conventional superconducting coil. In the figure, 3 is a superconducting coil formed by winding the superconducting conductor as shown in FIG. 8, 4 is a current supply terminal provided at the end of the coiled superconducting conductor, and 5 are provided at a plurality of positions of the superconducting coil 3. It is a refrigerant terminal tube.

Next, the operation will be described. For example Nb
₃ Superconducting conductors using compound superconductors such as Sn are
It is coiled at room temperature without the Nb ₃ Sn formation chemical reaction. The coiled superconducting conductor is N
In order to cause the b ₃ Sn forming chemical reaction, heat treatment is performed at a high temperature of about 700 ° C. for several tens of hours. After such heat treatment,
The superconducting coil 3 is completed by applying electrical insulation.

The superconducting coil 3 as described above is used after being cooled to a cryogenic temperature of about -269 ° C. by a refrigerant such as helium. Helium, which is a refrigerant, is supplied from the refrigerant terminal tube 5 and flows through the inside of the superconducting coil 3.
More discharged.

By the way, the Nb ₃ Sn compound-based superconductor is extremely vulnerable to mechanical strain, and its superconducting property is significantly deteriorated by applying a slight strain of, for example, 0.5%, and the critical current density which is an index of current capacity is about. It will be reduced to 50%.

The largest element of the strain generated in the superconducting conductor is the thermal strain generated during cooling due to the difference in the material forming the conductor. Usually, the material used for the conduit 2 is, for example, austenitic stainless steel such as SUS304L, but this material has a Nb ₃ Sn generation heat treatment temperature of about 700 ° C. to a superconducting coil 3 usage temperature of about -269. Thermal shrinkage up to ℃ is about 1.6%, N
The thermal contraction rate of b ₃ Sn in the same temperature range is larger than about 0.7%. That is, a maximum of about 0.9% of thermal strain, which is the difference in thermal contraction rate, acts on Nb ₃ Sn which is a superconductor.

Recently, in order to prevent deterioration of superconducting properties due to this thermal strain, the use of titanium as a conduit material has been studied and prototyped as an advanced technology. Here, in the manufacturing process of the normal superconducting coil 3, the current supply terminal 4 and the refrigerant terminal tube 5 made of titanium are attached to the conduit 2. A refrigerant pipe (not shown) is connected to the refrigerant terminal pipe 5 when the superconducting coil 3 is installed in an operating device such as an adiabatic vacuum container at the installation site.

As a method of mounting the above-mentioned refrigerant terminal tube 5,
In order to ensure airtightness at extremely low temperatures, metallurgical joining methods such as welding are usually used. However, at high temperatures, titanium combines with oxygen and becomes brittle at high temperatures, so it is necessary to shield it with argon gas or the like in order to eliminate oxygen from the surroundings when welding.

[0010]

In the conventional superconducting conductor as described above, when titanium is used for the conduit 2, even if a slight amount of oxygen is present when the refrigerant terminal pipe 5 is welded, the ductility of the welded portion is reduced. Although it will be significantly reduced, it is difficult to completely shield the weld with argon gas etc. in the field pipe welding work, and the weld has a problem in mechanical properties at cryogenic temperature, that is, the weld is brittle. There was a problem that

The present invention has been made to solve the above problems, and it is a composite that can prevent deterioration of mechanical properties while preventing deterioration of superconducting properties due to thermal strain. An object is to obtain a superconducting conductor and a method for manufacturing the same.

[0012]

According to a first aspect of the present invention, there is provided a composite superconducting conductor, wherein first and second portions made of metal tubes made of different materials are joined to each other in a conductor length direction to form a conduit. In addition, the first portion is made of a metal having a heat shrinkage rate closer to that of the wire bundle than the second portion.

The composite superconducting conductor according to the invention of claim 2 is
First and second parts made of metal pipes of different materials are joined to each other at the same position in the conductor length direction to form a conduit for each layer, and the first part has a second part. A metal having a heat shrinkage rate closer to that of the wire bundle than that of the part is used.

In the method for manufacturing the composite superconducting conductor according to the third aspect of the present invention, the first and second portions made of metal tubes made of different materials are joined to each other in the conductor length direction so that the diameter is larger than the finished size. After manufacturing a large conduit, a wire bundle containing a superconducting element wire is put into the conduit, and then plastic working is performed to form the conduit into a desired shape and size.

[0015]

In the present invention, the first portion having a heat shrinkage ratio close to that of the wire bundle reduces the thermal strain, and the second portion has a metal which is excellent in airtightness and mechanical characteristics and which is easy to perform terminal treatment. Is independently selected to prevent deterioration of the mechanical properties of the weld.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. Example 1. FIG. 1 is a side view showing an internal forced cooling type composite superconducting conductor according to an embodiment of the present invention. In the figure, reference numeral 11 denotes a metal conduit containing the wire bundle 1, and the conduit 11 includes first and second portions 11a and 11b made of metal pipes made of different materials.
Are joined to each other in the conductor length direction.

Here, as the material of the first portion 11a, which is the main portion of the conduit 11, a metal having a heat shrinkage that substantially matches the heat shrinkage of the wire bundle 1 is selected. The material of the second portion 11b is the first portion 11
A metal that is mechanically and airtightly joined to a and is also joined to the refrigerant terminal pipe 5 is selected. For example, when the superconductor is Nb ₃ Sn, titanium is suitable as the material of the first portion 11a and austenitic stainless steel is suitable as the material of the second portion 11b. The state in which the superconducting conductor of this embodiment is wound is the same as that of the conventional superconducting coil 3 shown in FIG.

Next, the operation will be described. For example Nb
₃ Superconducting conductors using compound superconductors such as Sn are
It is coiled at room temperature without the Nb ₃ Sn formation chemical reaction. The coiled superconducting conductor is N
In order to cause the b ₃ Sn forming chemical reaction, heat treatment is performed at a high temperature of about 700 ° C. for several tens of hours. After such heat treatment,
The superconducting coil 3 is completed by applying electrical insulation.

The superconducting coil 3 as described above is used after being cooled to a cryogenic temperature of about -269 ° C. by a coolant such as helium. Helium, which is a refrigerant, is supplied from the refrigerant terminal tube 5 and flows through the inside of the superconducting coil 3.
More discharged.

As explained in the conventional example, the largest element of the strain generated in the superconducting conductor is usually the thermal strain generated during cooling due to the difference in the material forming the conductor. On the other hand, the main portion 1 of the conduit 11 of the first embodiment
The metal used for 1a is, for example, titanium,
This material has a Nb ₃ Sn formation heat treatment temperature of about 700
℃ from a -269 thermal shrinkage of about 0.8% to ℃ the use temperature of the superconducting coil, very close to the thermal shrinkage of about 0.7% at the same temperature range of Nb ₃ Sn. Therefore, thermal strain hardly acts on Nb ₃ Sn, which is a superconductor, and there is almost no deterioration in superconducting characteristics.

Further, the conduit 11 is provided with a current supply terminal 4 and a refrigerant terminal tube 5 in the coil manufacturing process, and when the refrigerant terminal tube 5 is installed with a refrigerant pipe on the spot when the conduit 11 is installed in an operating device such as an adiabatic vacuum container. It is attached. This terminal is attached by the second portion 11b, and the material of the attached article is also the second
Since it is the same austenitic stainless steel as the portion 11b, the gas shield at the time of welding for mounting is
Oxygen concentration control does not have to be strict compared with titanium welding, and it is easy to secure mechanical properties and airtightness at extremely low temperatures.

Example 2. Next, FIG. 2 is a sectional view of a composite superconducting conductor according to an embodiment of the invention of claim 2, and FIG. 3 is a side view showing the composite superconducting conductor of FIG. In the first embodiment described above, the case where the conduit is a single layer has been described. However, depending on the application of the superconducting coil, as shown in FIG. 2, the conduit 12 of the second layer may be provided on the outer circumference of the conduit 11 of the first layer. It may have a layered structure.

By providing such a conduit 12 of the second layer, the space 13 between the first layer and the second layer can be used as a flow path for the refrigerant. That is, in the conductor of the type of the first embodiment described above, the fluid resistance of the gap in the wire bundle body 1 is large and the refrigerant is difficult to flow, so that the cooling may not be sufficiently performed. The layered structure can compensate for such insufficient cooling capacity.

The conduits 11 and 12 of each layer are made of metal pipes made of different materials from each other.
1a, 12a and the second portions 11b, 12b are joined to each other at the same position in the conductor length direction, and the first portions 11a, 12a are the second portions 11b, 12b.
It is made of a metal that has a thermal contraction rate close to that of a wire bundle. For example, when the superconductor is Nb ₃ Sn, titanium is suitable as the material of the first portions 11a and 12a, and the second portions 11b and 1 are the same as in the first embodiment.
Austenitic stainless steel is suitable as the material of 2b.

In such a composite superconducting conductor, the conduit 11 of the first layer is not subjected to thermal strain due to the difference in thermal shrinkage from the conduit 12 of the second layer, and the thermal strain acting on the superconductor is reduced. It is possible to prevent deterioration of superconducting properties. Further, if the terminal is attached to the second portion 12b of the conduit 12 of the second layer, it is easy to secure the mechanical characteristics and the airtightness at an extremely low temperature as in the first embodiment.
Furthermore, as described above, according to the second embodiment, the shortage of the cooling capacity, which is the drawback of the first embodiment, can be compensated.

Example 3. Next, FIG. 4 is a side view showing a composite superconducting conductor according to another embodiment of the invention of claim 1.
A conduit 13 made of a single material around the conductor of FIG.
Is provided. In the second embodiment, the same material was used in the same section in the conductor length direction for both of the two-layer conduits. However, when the required superconducting property of the conductor has a little margin, the same as in the third embodiment. Alternatively, a conduit 13 made of a single material may be used for the second layer.

That is, the conduit 13 of the second layer indirectly gives a thermal strain to the wire bundle 1 through the conduit 11 of the first layer, but the heat shrinkage of the conduit 13 of the second layer affects the first layer. Since it is slight compared to the effect of heat shrinkage of the conduit 11, the second layer of the conduit 13 is a single layer which is easy to weld when the superconducting characteristics have a margin. A material made of only austenitic stainless steel may be used. Like this, 2
By forming the conduit 13 of the first layer from a single material, there is an advantage that the composite superconducting conductor can be manufactured economically and at low cost as compared with the second embodiment.

Example 4. Next, an example of a method of manufacturing the conduits 11 and 12 shown in each of the above examples will be described.
In each of the above embodiments, the method of joining different kinds of metal of the conduit material is not particularly limited, but the method of making different kinds of metals is important in actual production. The simplest method for joining dissimilar metals is mechanical fastening such as screwing, but with this method, it is extremely difficult to achieve the hermeticity of helium used as a refrigerant in a narrow space required for a conduit.

As shown in FIG. 5, for example, a titanium tube 2
When joining 1a and the austenitic stainless steel pipe 21b, that is, when titanium and austenitic stainless steel are selected as the different metals, diffusion joining is more joining strength and airtightness than welding as the joining method. Both sex is excellent. Generally, since diffusion bonding is performed in a furnace, as shown in FIG. 5, a joint between short pipes of dissimilar metals is manufactured in the furnace as a component, and this joint is welded to a long product made of each material. It may be joined by a method such as.

It should be noted that Nb ₃ Sn is currently put into practical use as a superconductor for high magnetic fields, but in the future, other compound superconductors currently in the research stage will show superior superconducting properties. And, it is considered that it will be possible to industrially produce. In that case, there is a possibility that strain sensitivity, heat shrinkage, and the like are different from those of Nb ₃ Sn, and it is expected that a suitable conduit material will also be different from that of the above-mentioned embodiment. In such cases, dissimilar metal bonding methods include diffusion bonding, welding, brazing, pressure welding, and other currently used dissimilar metal bonding methods. It is only necessary to select and adopt a material that is excellent in airtightness.

Example 5. Next, a method of manufacturing the composite superconducting conductor according to the third embodiment of the invention will be described.
Usually, a long tube made of a single material is mass-produced by a method of welding and stitching a long strip such as a continuously formed thin steel plate, that is, a continuous process such as roll forming. However, when the dissimilar metals are joined together, the processing characteristics differ in the length direction and the welding conditions also differ.Therefore, in conventional roll forming, stable welding strength, weld airtightness, and forming dimensions can be obtained. You cannot get the superconducting conductor you have.

Therefore, in the method of the fifth embodiment, as shown in FIG. 6, first, the wire bundle 1 is drawn into the conduit 11 made of the dissimilar metal junction pipe manufactured by the method of the fifth embodiment. At this time, as shown in the cross section of the intermediate product in FIG. 7A, the diameter of the conduit 11 is slightly larger than the finished size. Thereafter, the conduit 11 is subjected to plastic working such as rolling, edging or forging.
By reducing the cross section of to the desired shape and size,
A long composite superconducting conductor having a cross section shown in FIG. 7B is obtained.

By manufacturing the composite superconducting conductor by such a method, a large amount of high quality composite superconducting conductors without deterioration of superconducting characteristics and mechanical properties due to thermal strain as shown in Examples 1 to 3 can be obtained. And it can be obtained at low cost.

[0034]

As described above, in the composite superconducting conductor of the invention of claim 1, the first and second portions made of metal tubes of different materials are joined to each other in the conductor length direction to form a conduit. Since the first part is made of a metal having a heat shrinkage ratio closer to that of the wire bundle than the second part, the second part is made of a metal having excellent airtightness and mechanical properties. As a result, it is possible to prevent deterioration of the superconducting characteristics due to thermal strain while preventing deterioration of the mechanical properties.

In the composite superconducting conductor according to the second aspect of the present invention, the first and second portions made of metal tubes made of different materials are joined to each other at the same position in the conductor length direction. In addition to the effect of the invention of claim 1, the first part is made of a metal having a heat shrinkage rate closer to that of the wire bundle than the second part. By forming the refrigerant flow path between the conduits, the cooling capacity can be improved.

Further, in the method for manufacturing the composite superconducting conductor according to the third aspect of the present invention, the first method comprises the metal tubes of different materials.
And the second portion are joined to each other in the conductor length direction to manufacture a conduit having a diameter larger than the finished size, and then the wire bundle including the superconducting element wires is put into the conduit,
Since the conduit was then formed into the desired shape and dimensions by applying plastic working after this, it was possible to obtain a large amount of high-quality composite superconducting conductors with excellent superconducting properties and mechanical properties at low cost. Play.

[Brief description of drawings]

FIG. 1 is a side view showing a composite superconducting conductor according to an embodiment of the present invention.

FIG. 2 is a sectional view of a composite superconducting conductor according to an embodiment of the present invention.

FIG. 3 is a side view showing the composite superconducting conductor of FIG.

FIG. 4 is a side view showing a composite superconducting conductor according to another embodiment of the present invention.

5 is a perspective view showing components in the process of manufacturing the conduit shown in FIGS. 1 to 4. FIG.

FIG. 6 is a perspective view showing a method for manufacturing a composite superconducting conductor according to an embodiment of the invention of claim 3;

7A and 7B are cross-sectional views showing a state during and after manufacturing the composite superconducting conductor of FIG.

FIG. 8 is a sectional view of an example of a conventional superconducting conductor.

FIG. 9 is a perspective view showing an example of a conventional superconducting coil.

[Explanation of symbols]

 1 Wire bundle body 11 Conduit 11a 1st part 11b 2nd part 12 Conduit 12a 1st part 12b 2nd part

Claims (3)

[Claims] 1. A composite superconducting conductor of an internal forced cooling type in which a wire bundle containing a superconducting element wire is housed in a metal conduit, wherein the conduits are metal pipes of different materials. Are joined to each other in the conductor length direction, and the first portion is made of a metal having a heat shrinkage rate closer to that of the wire bundle body than that of the second portion. Characteristic composite superconducting conductor. 2. In a forced supercooling type composite superconducting conductor in which a wire bundle containing a superconducting element wire is housed in a plurality of layers of metal conduits, the conduits of each layer are made of metal pipes of different materials. The first and second parts,
All layers are joined to each other at the same position in the conductor length direction, and the first portion is made of a metal having a heat shrinkage rate closer to that of the wire bundle body than that of the second portion. A composite superconducting conductor characterized in that 3. A first tube comprising metal tubes made of different materials.
And the second portion are joined to each other in the length direction of the conductor to manufacture a conduit having a diameter larger than the finished size, and then the wire bundle including the superconducting element wire is put into the conduit and then subjected to plastic working. A method for manufacturing a composite superconducting conductor, characterized in that the above conduit is molded into a desired shape and size according to.