JPH0737445A - Compound superconductive wire - Google Patents

Abstract

PURPOSE:To provide a compound superconductive wire with excellent superconductive properties in highly magnetic field. CONSTITUTION:A compound superconductive wire is composed by uniting a large number of basic cluster wires 3 prepared by reciprocally layering a compound superconductor layer 1 and a silver layer 2. The thickness of the silver layer 2 is made 0.3-5 times the coherence length of the compound superconductor layer 1. As a result, the finely distributed silver layer 2 has pinning function, so that the superconductive properties in a highly magnetic field are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound superconducting wire having excellent superconducting properties especially under a high magnetic field.

[0002]

2. Description of the Related Art Nb ₃ Sn, Nb ₃ are used for compound superconductors.
Examples include Al and V ₃ Ga. Since these are inferior in workability, its generation, for example, after processing the composite of the Nb metal and the Cu-Sn alloy to the final shape, the heat treatment by diffusing the Sn into Nb and Nb ₃ Sn compound superconducting It was carried out by a method of producing a reaction. Specifically, bronze (Cu
-Sn-based alloy) pipe is filled with Nb rod, and this is drawn to form a composite wire rod. The step of filling this copper wire pipe into a copper pipe and drawing it is performed a desired number of times to obtain a predetermined wire diameter. Finishing, bronze method of heat-treating this, or internal diffusion method (eg, tube method) of drawing a composite wire rod in which Nb layer or Nb alloy layer is arranged around Sn-rich alloy core material, and finally heat-treating There is.

[0003]

In the method of producing a compound superconductor as described above, the production rate is in bronze and N.
It is limited by the diffusion rate of Sn in the b ₃ Sn layer. When the heating temperature is raised to increase the production rate, the grain boundaries effective for pinning are reduced, and a non-superconductor compound is produced.
On the other hand, when the heating temperature is lowered, Sn is insufficient in the central portion of the Nb layer, and the stoichiometric composition of the Nb ₃ Sn superconductor cannot be obtained. Thus, there has been a limit to improving the characteristics of the conventional compound superconducting wire such as Nb ₃ Sn.

[0004]

The present invention has conducted intensive studies in view of such a situation. The normal conductor has a pinning effect equal to or higher than that of a grain boundary. Among normal conductors, silver is Nb or Nb. The present inventors have found that they can be a good pinning point even after heat treatment because they are non-reactive with alloys and the like, and have further researched to complete the present invention. That is, the present invention provides a compound superconducting wire in which a large number of basic cluster lines in which a compound superconductor layer and a silver layer are alternately laminated are combined, and the thickness of the silver layer is the coherence length of the compound superconductor layer. It is a compound superconducting wire characterized by being in the range of 0.3 to 5 times the length.

In the present invention, the thickness of the silver layer is limited to a range of 0.3 to 5 times the coherence length of the compound superconductor layer (ξ: a transitional distance until the number of superconductors reaches the equilibrium value). When the thickness of the copper layer is less than 0.3 times the coherence length of the compound superconductor layer, leaching of superconducting conductors into the silver layer occurs, and when it exceeds 5 times, the pinning effect decreases and the silver layer This is because the space factor increases and the characteristics of the entire superconducting wire deteriorate. In the present invention, the spacing of the silver layers within the basic cluster line is the lattice spacing a _f (a _f of the quantized magnetic flux lines _).
= 1.07 × (φ ₀ / B) ^1/2 , where φ ₀ is a magnetic flux quantum and B is a magnetic flux density) is desirable from the viewpoint of pinning efficiency.

The compound superconducting wire of the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged cross-sectional view showing an embodiment of the compound superconducting wire of the present invention. Compound superconductor layer 1 and silver layer 2
A large number of basic cluster lines 3 in which and are alternately laminated are united.

Next, a method for producing the compound superconducting wire of the present invention will be described with reference to the drawings. Figure 2 b-Chi are process explanatory views showing an embodiment of the production method of Nb ₃ Sn compound superconducting wire. N
The b plate 4 and the silver plate 5 are alternately laminated and filled in the silver tube 6 to form the primary billet 7 (Fig. A).
Was extruded and integrated, and then cold drawn to form a primary wire rod 8 (Fig. B). The primary wire rod 8 was filled again in the silver pipe 6 to form a secondary billet 17 (Fig. C). , This secondary billet 17 is hot-worked and cold-drawn again to form a secondary wire rod 18 (Fig. 2), and this secondary wire rod 18 is filled into the copper pipe 10 again to form a tertiary billet 27 (Fig. (Fig. E), the tertiary billet 27 is hot worked and cold drawn again to form the multilayer composite wire 9 (Fig. F), and Sn is plated on the outer peripheral surface of the multilayer composite wire 9 (Fig.). The multilayered composite wire plated with Sn is subjected to a predetermined heat treatment to react the Nb in the Nb layer with the Nb ₃ Sn superconductor to form an Nb ₃ Sn compound superconducting wire (Fig. H).
In addition to the hot extrusion and the cold wire drawing, the drawing process of the composite billet includes drawing and swaging.

In this manufacturing method, since Sn is supplied by plating, the required amount of Sn can be supplied without waste.
Since Sn is supplied immediately before the heat treatment, S is added during the stretching process.
A non-superconductor compound containing n is not generated. N
Since b and silver are excellent in processability and do not react with each other, the final multilayer composite wire can be processed well. In the heat treatment step of the Sn-plated multilayer composite wire, Sn diffuses the copper layer and the silver layer, so that the diffusion rate is high. Since the Nb layer is thin, Nb ₃ having a stoichiometric composition is extended to the inside of the Nb layer.
The Sn superconductor is formed at a low temperature in a short time. Nb ₃ S
Since n superconductors are formed in a short time at low temperature,
Generation of non-superconductor compounds is suppressed. The size, shape, distribution form, volume fraction, etc. of the silver layer that forms the pinning point can be freely designed when the primary billet is assembled. There are various advantages such as.

[0009]

The compound superconducting wire of the present invention is a combination of basic cluster wires in which compound superconducting layers and silver layers are alternately laminated, and the thickness of the silver layer is equal to the coherence length of the compound superconducting layer. Since it is in the range of 0.3 to 5 times, the normal-conducting silver layer efficiently pins the magnetic flux lines, and the superconducting property under a high magnetic field is improved.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 Nb-1 wt% Ti alloy plates having a thickness of 4.5 mm and silver plates having a thickness of 1 mm were alternately laminated and filled in a silver tube having an outer diameter of 45 mmφ and an inner diameter of 42 mmφ to form a primary billet. . Next, this primary billet was hot extruded into an extruded material having an outer diameter of 11 mmφ, and this extruded material was subjected to cold drawing to obtain a 1.3 mmφ primary wire material. Next, 650 pieces of this primary wire rod were filled into a silver tube with an outer diameter of 45 mmφ and an inner diameter of 38.5 mmφ to form a secondary billet. Made into a wire rod. This secondary wire rod is again used with an outer diameter of 45 mm and an inner diameter of 38.5
Filling 650 pieces in a mmφ copper tube to form a third billet,
This tertiary billet was again subjected to hot extrusion and cold wire drawing.
Made into a multi-layer composite wire rod with various wire diameters within the range of 06 to 1 mmφ. Next, Sn was deposited on the surface of this multilayer composite wire by hot dip plating, and this was held in an Ar atmosphere at a temperature near the melting point of Sn for 24 hours, then heated to 600 ° C. for 48 hours, and further.
The temperature was raised to 700 ° C. and kept for 24 hours to diffuse Sn into the Nb layer, and reacted with the Nb to form an Nb ₃ Sn compound superconductor, and an Nb ₃ Sn compound superconducting wire was manufactured. The amount of Sn deposited by hot-dip plating was 20 wt% of the amount of silver in the compound superconducting wire.

Comparative Example 1 In Example 1, the wire diameter of the multilayer composite wire was 0.05 mmφ or
Nb _{3 in the} same manner as in Example 1 except that 1.18 mmφ was used.
A Sn compound superconducting wire was manufactured.

Comparative Example 2 Bronze having an outer diameter of 45 mmφ and an inner diameter of 38 mmφ (Cu-14.3 wt% S
n) A Nb-1wt% Ti alloy rod is filled in a pipe and subjected to hot extrusion and cold drawing to form a composite element wire with an outer diameter of 1.3 mmφ. This composite element wire has an outer diameter of 45 mmφ, For copper tubes with an inner diameter of 38.5 mmφ
650 pieces were filled, and hot extrusion and cold drawing were performed again on this to obtain a final wire rod having an outer diameter of 0.3 mmφ. Next this is Ar
The Nb ₃ Sn compound superconducting wire was manufactured by keeping the temperature at 700 ° C. for 24 hours.

The critical current density (Jc) of the Nb ₃ Sn compound superconducting wire thus obtained was measured in liquid He under a magnetic field of 10 to 16T. The results are shown in Table 1. The coherence length ξ of the obtained compound superconductor layer was about 4 nm.

[0014]

[Table 1] * Critical current density per unit cross-sectional area (including silver layer) of Nb ₃ Sn filament.

As is clear from Table 1, the products of the present invention (No.
1 to 5) all showed high Jc under a high magnetic field. This is because the silver layer pinned the magnetic flux. On the other hand, No. 6 of the comparative example product had the silver layer too thin to reduce its pinning effect, and No. 7 had a large proportion of the silver layer in the cross section of the compound superconducting wire.
No. 8 had a low Jc due to the lack of pinning points and the formation of non-superconductor compounds.

Example 2 Nb plates having a thickness of 4.5 mm and silver plates having a thickness of 1 mm were alternately laminated and filled in a silver tube having an outer diameter of 45 mmφ and an inner diameter of 42 mmφ to form a primary billet. Next, this primary billet was hot extruded to form an extruded material having an outer diameter of 11 mmφ, which was cold drawn to 1.3 mmφ to form a primary wire rod. Next, this primary composite wire
650 pieces were filled in a silver tube having an outer diameter of 45 mmφ and an inner diameter of 38.5 mmφ to form a secondary billet, and this secondary billet was again subjected to hot extrusion and cold drawing to form a secondary wire rod of 1.3 mmφ. Next, 650 pieces of this secondary wire were again filled into a copper tube with an outer diameter of 45 mmφ and an inner diameter of 38.5 mmφ to form a tertiary billet. The tertiary billet was hot extruded and cold drawn again to 0.06 to 1 mmφ.
The multi-layer composite wire rod has various wire diameters within the range. Next, Al was deposited on the surface of this multilayer composite wire by hot dip plating, kept at 380 ° C for 24 hours in an Ar atmosphere, and subsequently heated to 570 ° C for 48 hours and further heated to 850 ° C. It was kept for 48 hours to diffuse Al into the Nb layer and reacted with the Nb to form an Nb ₃ Al compound superconductor, thereby manufacturing an Nb ₃ Al compound superconducting wire. In the above, the amount of Al deposited by hot dipping was set to 30 wt% of the amount of silver in the compound superconducting wire.

Comparative Example 3 In Example 2, the wire diameter of the multi-layer composite wire was 0.05 mmφ or
Nb _{3 in the} same manner as in Example 1 except that 1.18 mmφ was used.
An Al compound superconducting wire was manufactured.

Comparative Example 4 Nb was applied to an Al-Mn alloy pipe having an outer diameter of 45 mmφ and an inner diameter of 38 mmφ.
The rod is filled, hot extruded and drawn to form a composite wire with an outer diameter of 1 mmφ. This composite wire has an outer diameter of 45 mmφ,
A copper tube having an inner diameter of 38 mmφ was filled with 1000 pieces, and hot extrusion and cold drawing were performed again on this to obtain a final wire rod having an outer diameter of 0.2 mmφ. Next, this was kept in an Ar atmosphere at 850 ° C. for 48 hours to produce a Nb ₃ Al compound superconducting wire.

The critical current density (Jc) of the Nb ₃ Al compound superconducting wire thus obtained was measured in liquid He under a magnetic field of 10 to 16T. The results are shown in Table 1. The coherence length ξ of the obtained compound superconductor phase was about 4 nm.

[0020]

[Table 2] * Critical current density per unit cross-sectional area (including silver layer) of Nb ₃ Al filament.

As is clear from Table 1, the products of the present invention (No.
9 to 13) all showed high Jc values under a high magnetic field. This is because the silver layer pinned the magnetic flux. On the other hand, No. 14 of the comparative example product has a too thin silver layer to reduce its pinning effect, and No. 15 has a too large proportion of the silver layer in the cross section of the compound superconducting wire.
No. 16 had a low Jc value due to a lack of pinning points and the formation of non-superconductor compounds.

Although the Nb ₃ Sn and Nb ₃ Al compound superconducting wires have been described above, the same effects can be obtained by applying the present invention to other compound superconducting wires such as V ₃ Ga.

[0023]

As described above, in the compound superconducting wire of the present invention, the silver layer having the pinning effect is finely distributed, so that the Jc value in a high magnetic field is improved, and a remarkable effect is industrially exhibited.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional explanatory view showing an embodiment of a compound superconducting wire of the present invention.

FIG. 2 is a process explanatory view showing an embodiment of a method for producing a compound superconducting wire of the present invention.

[Explanation of symbols] 1 compound superconductor layer 2 silver layer 3 basic cluster wire 4 Nb plate 5 silver plate 6 silver pipe 7,17,27 composite billet 8,18 composite wire rod 9 multi-layer composite wire rod 10 copper pipe

Claims (1)

[Claims] 1. A compound superconducting wire in which a large number of basic cluster lines in which a compound superconductor layer and a silver layer are alternately laminated are united, and the thickness of the silver layer is the coherence length of the compound superconductor layer. The compound superconducting wire is characterized by being in the range of 0.3 to 5 times.