WO2015083291A1

WO2015083291A1 - Super-conducting wire material, production method therefor, and super-conducting coil using same

Info

Publication number: WO2015083291A1
Application number: PCT/JP2013/082857
Authority: WO
Inventors: 菅野　周一; 水上　貴彰; 楠　敏明; 田中　秀樹
Original assignee: 株式会社日立製作所
Priority date: 2013-12-06
Filing date: 2013-12-06
Publication date: 2015-06-11

Abstract

Provided are a super-conducting wire material accomplishing a more satisfactory critical current density than in prior art, a production method therefor, and a super-conducting coil using the same. In order to achieve this objective, a super-conducting wire material (10) is provided with a plurality of super-conducting materials (4), each comprising a magnesium diboride layer (2) immobilized on a substrate (1), in such a way that: in a cross-section orthogonal to the current-conduction direction, a plurality of the magnesium diboride layers (2) are disposed along at least two directions comprising an immobilization direction of the magnesium diboride layer (2) with respect to the substrate (1), and a direction intersecting with the immobilization direction; and the cross-sectional area of the magnesium diboride layer (2) that constitutes the super-conducting material (4) is the same among each of the super-conducting materials (4) in the cross-section.

Description

Superconducting wire, manufacturing method thereof and superconducting coil using the same

The present invention relates to a superconducting wire, a manufacturing method thereof, and a superconducting coil using the same.

Niobium-titanium alloys and the like are known as materials exhibiting superconducting properties. A superconducting coil is manufactured by winding a superconducting wire composed of this niobium-titanium alloy or the like spirally around a coil bobbin or the like. Such a superconducting coil is provided in medical diagnostic equipment such as a magnetic resonance imaging apparatus (MRI) and a nuclear magnetic resonance apparatus (NMR), and uses superconducting characteristics.

From the viewpoint of obtaining a superconducting wire having a higher critical current density, a material superior to a niobium-titanium alloy is required. In this regard, since the beginning of the 21st century, it has become clear that magnesium diboride (MgB ₂ ) exhibits superconducting properties at 40K, and various studies have been conducted on magnesium diboride. In particular, magnesium diboride has attracted attention as a superconducting material for medical diagnostic devices that require a stable magnetic field as a material to replace conventional niobium-titanium alloys. Since the magnetic anisotropy of magnesium diboride is sufficiently small, a good critical current density ( _Jc ) can be obtained even if the crystal orientation and the winding direction are not aligned.

A powder-in-tube method (PIT method) is known as a method for producing magnesium diboride. The powder-in-tube method is a method in which a raw material powder such as magnesium or boron is filled in a metal tube (sheath) and then drawn, and the metal tube is heat treated to generate magnesium diboride in the metal tube. By this method, a superconducting wire in which magnesium diboride is filled in a metal tube is obtained, and it is known that a good critical current density is exhibited particularly in a low magnetic field of about 2 T or less.

However, in a high magnetic field (for example, about 5T to 10T), the superconducting wire produced by the powder-in-tube method has room for improvement in the critical current density. Therefore, in order to obtain a superconducting wire having a good critical current density particularly in a high magnetic field, a method for obtaining a thin film of magnesium diboride has attracted attention. In this method, a raw material such as magnesium or boron is vapor-deposited on a substrate by an electron beam or the like, and a magnesium diboride thin film is formed on the substrate. Magnesium diboride thin film produced by this method exhibits a good critical current density in a high magnetic field, so it can be applied to high magnetic field applications such as medical diagnostic equipment such as high magnetic field MRI and superconducting equipment such as superconducting linear. There is expected.

A technique described in Patent Document 1 is known in relation to a technique for producing a superconducting coil using a thin film magnesium diboride. Patent Document 1 describes a probe coil for a nuclear magnetic resonance apparatus formed by winding a magnesium diboride superconducting wire or a thin film.

JP 2004-327593 A

When a thin film formed on a substrate is cut into a tape shape together with the substrate and wound on a coil bobbin to produce a superconducting coil, the tape-shaped thin film is distorted due to the winding. In particular, the smaller the coil bobbin being wound, the greater the distortion. If such strain increases, the thin film may peel off from the substrate or the flow resistance in the thin film may increase, and the critical current density of the superconducting coil may decrease. Therefore, in the conventional technique, the advantage of the thin film-like magnesium diboride that exhibits a good critical current density even in a high magnetic field is not fully utilized.

The present invention has been made in view of such problems, and the problem to be solved by the present invention is a superconducting wire material that exhibits a better critical current density than the conventional one, a method for manufacturing the same, and a method using the same. It is to provide a superconducting coil.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have arranged the superconducting material in which a magnesium diboride layer is formed on the surface of a base material in a superconducting wire in a predetermined direction. I found that it can be solved.

According to the present invention, it is possible to provide a superconducting wire having a better critical current density than the conventional one, a manufacturing method thereof, and a superconducting coil using the same.

It is a figure which shows the cross section of the superconducting wire of this embodiment. It is a figure which shows the superconducting material contained in the superconducting wire of this embodiment. It is a figure explaining the superconducting coil provided with the superconducting wire of this embodiment, (a) is the whole figure, (b) is the A section enlarged view of (a). It is a figure which shows the cross section of the modification about the superconducting wire of this embodiment. It is a figure which shows the cross section of another modification about the superconducting wire of this embodiment. It is a figure which shows the cross section of another modification about the superconducting wire of this embodiment. It is a figure which shows the cross section of another modification about the superconducting wire of this embodiment. It is a figure which shows the cross section of another modification about the superconducting wire of this embodiment.

Hereinafter, modes for carrying out the present invention (the present embodiment) will be described.

FIG. 1 is a view showing a cross section of the superconducting wire 10 of the present embodiment. The superconducting wire 10 has a circular cross section as shown in FIG. 1, and includes a base material 1, a magnesium diboride layer 2 formed on the surface of the base material 1, and an insulator 3 for insulating and fixing them. Has been. Note that the cross section of the superconducting wire 10 is maintained in a circular shape by the insulator 3. Although not shown in FIG. 1, the superconducting wire 10 includes a protective film 5 (see FIG. 2) that covers the magnesium diboride layer 2. Hereinafter, the base material 1 and the magnesium diboride layer 2 formed on the surface of the base material 1 are collectively referred to as “superconducting material 4” as appropriate.

The substrate 1 has a surface on which a magnesium diboride layer 2 is formed, and also supports the magnesium diboride layer 2. In the superconducting wire 10, the substrate 1 is made of a thermodynamically stable (not easily thermally reacted) metal, such as stainless steel, aluminum, duralumin, copper, iron, or the like. A ceramic material such as silicon is also suitable depending on the application of the superconducting wire 10.

The thickness of the substrate 1 is, for example, 10 μm or more and 1 mm or less. However, as the thickness of the base material 1 increases, the area of the magnesium diboride layer 2 in the cross section of the superconducting wire 10 becomes relatively small. Therefore, it is preferable that the base material 1 does not become excessively thick.

The magnesium diboride layer 2 is made of magnesium diboride, and is fixed (formed) on the surface of the substrate 1 by vapor deposition or the like. In the superconducting wire 10, a current flows in a direction perpendicular to the paper surface of FIG. 1. When a current flows through the magnesium diboride layer 2, a magnetic field is generated around the superconducting wire 10, and superconducting characteristics are exhibited.

The thickness of the magnesium diboride layer 2 is, for example, not less than 0.2 μm and not more than 30 μm. By setting the thickness of the magnesium diboride layer 2 within this range, the content of magnesium diboride in the superconducting wire 10 can be improved. Moreover, although it is preferable that the thickness of the magnesium diboride layer 2 is as thick as possible, the manufacturing time of the superconducting wire 10 can be shortened by setting it to 30 μm or less, for example.

In the superconducting wire 10, the superconducting material 4 (more specifically, the magnesium diboride layer 2) is in a cross section perpendicular to the current flow direction (that is, a cross section extending in the vertical and horizontal directions in FIG. 1). They are arranged in at least two directions. That is, in the superconducting wire 10, in the cross section, the stacking direction (fixing direction, FIG. 1) of the magnesium diboride layer 2 that intersects the vertical direction and intersects the vertical direction (orthogonal in FIG. 1). Another superconducting material 4 is arranged in two directions (left and right direction).

In other words, in the superconducting wire 10 of FIG. 1, a plurality of superconducting materials 4 are arranged in the vertical direction, and a plurality of superconducting materials 4 are arranged in the left-right direction orthogonal to the vertical direction. Yes. The number of superconducting materials 4 arranged in the vertical direction is 7 including the superconducting material 4A when the superconducting material 4A of FIG. 1 is used as a reference (two on the upper side of the superconducting material 4A and four on the lower side). become. The number of superconducting materials 4 arranged in the left-right direction is 7 including the superconducting material 4A (4 on the left side and 2 on the right side of the superconducting material 4A) with reference to the superconducting material 4A in FIG. )become. By arranging the superconducting material 4 in this way, the superconducting material 4 can be arranged not only in one direction but also in various directions. Therefore, the unevenness of the magnetic field formed around the superconducting wire 10 can be suppressed. Thereby, a good critical current density can be obtained.

In addition, since the superconducting material 4 is arranged in two orthogonal directions, the superconducting wire 10 having a vertically and horizontally symmetrical structure with respect to the center of the cross section of the superconducting wire 10 can be obtained. Thereby, the magnetic field formed around the superconducting wire 10 can be made uniform, and an even better critical current density can be obtained.

Further, for example, when the superconducting wire 10 having a diameter L is produced, not only one superconducting material 4 having a width (length in the vertical direction in FIG. 1) of the magnesium diboride layer 2 of L is used. By disposing a plurality of superconducting materials 4 finely divided as described above, strain generated in the magnesium diboride layer 2 when wound around the coil bobbin 20 (see FIG. 3) can be sufficiently suppressed. Thereby, the fall of a critical current density can be suppressed more reliably and a better critical current density can be obtained.

Furthermore, in the cross section, the cross sectional area of the magnesium diboride layer 2 is equal in each superconducting material 4 as shown in FIG. By forming the magnesium diboride layer 2 in this way, the flow resistance of each superconducting wire 4 can be made uniform, and the current flowing through each superconducting wire 4 can be made equal. Thereby, a good critical current density can be obtained.

Further, in the superconducting wire 10, the magnesium diboride layer 2 is densely formed on the surface of the substrate 1. That is, the magnesium diboride layer 2 has almost no pores. As a result, it is possible to suppress a decrease in the flow path of the current due to the presence of the pores, uniformize the current flowing through the magnesium diboride layer 2 and obtain a good critical current density. Whether or not the magnesium diboride layer 2 is densely formed can be determined by observing the cross section of the magnesium diboride layer 2 with an electron microscope or the like.

As a method for forming the magnesium diboride layer 2 densely, for example, the magnesium diboride layer 2 is formed by fixing the magnesium diboride to the surface of the substrate 1 by vapor deposition or sputtering. be able to. Specific methods such as vapor deposition and sputtering include a pulse laser ablation (PLD) method, an electron beam method, an ion beam method, and the like.

The insulator 3 bundles the superconducting material 4 and is insulated from the outside. That is, the superconducting material 4 is covered with the insulator 3, whereby the insulator material 4 is turned into a wire. The insulator 3 is, for example, enamel. Further, as described above, the superconducting material 4 constituting the superconducting wire 10 is covered with the insulator 3 so that the cross section of the superconducting wire 10 is circular. Thereby, when the superconducting wire 10 is wound around the coil bobbin 20 (see FIG. 3) in a coil shape, the strain applied to the superconducting wire 10 can be further reduced.

FIG. 2 is a diagram showing the superconducting material 4 included in the superconducting wire 10 of the present embodiment. A protective film 5 is formed on the magnesium diboride layer 2 included in the superconducting material 4 so as to cover the entire surface of the magnesium diboride layer 2 in the vertical and horizontal directions. Since the magnesium diboride layer 2 is easy to oxidize, the protective film 5 is formed to block the contact of oxygen to the magnesium diboride layer 2 and to prevent the magnesium diboride layer 2 from being oxidized.

The protective film 5 is preferably made of a material that functions as a pinning center from the viewpoint of improving the critical current density. Specifically, nickel is mentioned from a viewpoint of exhibiting the function as a pinning center, preventing the oxidation of the magnesium diboride layer 2 as mentioned above.

Further, the thickness of the protective film 5 depends on the thickness of the magnesium diboride layer 2 and cannot be generally specified, but is, for example, not less than 0.1 nm and not more than 0.3 nm. By making the thickness of the protective film 5 within this range, the thickness of the protective film 5 with respect to the magnesium diboride layer 2 can be set to a suitable thickness ratio, so that more reliable oxidation prevention can be achieved, and good A critical current density can be obtained. Moreover, when the superconducting wire 10 is wound around the coil bobbin 20, the deterioration associated with the mechanical operation of winding is more reliably prevented.

The superconducting wire 10 can be manufactured as follows, for example. First, the superconducting material 4 is obtained by forming the magnesium diboride layer 2 on the surface of the substrate 1 (superconducting material manufacturing step). As a method for forming the magnesium diboride layer 2, for example, a vapor deposition method or a sputtering method can be applied as described above. Moreover, the protective film 5 is formed by vapor deposition etc. as needed. And using the obtained superconducting material 4, at least two directions (two directions orthogonal in the example shown in FIG. 1) of the fixing direction of the magnesium diboride layer 2 with respect to the base material 1 and the direction crossing the fixing direction. ), The superconducting materials 4 having the same cross-sectional area of the magnesium diboride layer 2 are fixed by the insulator 3 to form a wire. Thereby, the superconducting wire 10 is obtained (wire material forming step).

Also, the superconducting wire 10 can be produced as follows, for example. First, a magnesium diboride layer 2 is formed on a rectangular substrate (which becomes a base material 1 by being cut into a tape shape). Moreover, the protective film 5 is formed by vapor deposition etc. as needed. Next, the substrate on which the magnesium diboride layer 2 is formed is cut together with the magnesium diboride layer 2 so as to have a desired width, whereby the base material 1 on which the magnesium diboride layer 2 is formed (that is, A superconducting material 4) is obtained (superconducting material manufacturing step). Then, the superconducting wire 10 is obtained in the same manner as in the wire forming step.

Furthermore, the superconducting wire 10 can be manufactured as follows, for example. First, the raw material which comprises the magnesium diboride layer 2 is fixed with respect to a rectangular-shaped board | substrate (it becomes the base material 1 by being cut | disconnected in tape shape). Examples of the raw material include magnesium powder, boron powder, and boron carbide powder. Next, the substrate is heat-treated, whereby the magnesium diboride layer 2 is formed on the substrate surface. The heat treatment temperature at this time is, for example, 500 ° C. to 900 ° C. By the above operation, a substrate on which the magnesium diboride layer 2 is formed is obtained.

And after forming the protective film 5 by vapor deposition etc. as needed, it cut | disconnects so that the cross-sectional area of the magnesium diboride layer 2 may become equal, The superconductivity by which the magnesium diboride layer was formed in the base material 1 Material 4 is obtained. Thereafter, in the superconducting material 4, the magnesium diboride layer 2 having the same cross-sectional area is formed so that the magnesium diboride layer 2 is arranged in at least two directions (two directions orthogonal in the example shown in FIG. 1). The base materials 1 thus fixed are fixed by the insulator 3. Thereby, the superconducting material 4 is turned into a wire in the same manner as in the wire forming step, and the superconducting wire 10 is obtained (superconducting material manufacturing step).

FIG. 3 is a diagram for explaining a superconducting coil 100 including the superconducting wire 10 of the present embodiment, where (a) is an overall view thereof, and (b) is an enlarged view of part A of (a). As shown in FIG. 3A, the superconducting coil 100 has a superconducting wire 10 spirally wound around a coil bobbin 20, and a power source 30 is connected to the superconducting wire 100. A magnetic field is generated along the central axis of the coil bobbin 20 by passing a current from the power supply 30 to the superconducting wire 10.

Further, as shown in FIG. 3B, the superconducting wire 10 is wound around the coil bobbin 20 so that the superconducting material 4 faces the coil bobbin 20 in a predetermined direction. Specifically, in each superconducting material 4, the superconducting wire 10 is wound around the coil bobbin 20 so that the base material 1 constituting the superconducting material 4 is disposed on the coil bobbin 20 side. In other words, the superconducting wire 10 is wound around the coil bobbin 20 so that the magnesium diboride layer 2 is disposed outside the base material 1.

By winding the superconducting wire 10 so as to have such a relative positional relationship, the strain of the magnesium diboride layer 2 accompanying the winding can be made as small as possible. In other words, since the magnesium diboride layer 2 is disposed on the outer side (the side far from the coil bobbin 20), the wound two layers are compared with the case where the magnesium diboride layer 2 is disposed on the inner side (the side closer to the coil bobbin 20). The radius of curvature of the magnesium boride layer 2 is increased. Therefore, the distortion accompanying winding can be reduced. In particular, FIG. 3 schematically shows a winding, but in reality, the winding is actually performed many times. Therefore, by reducing the strain generated in the magnesium diboride layer 2 as much as possible, the magnesium diboride layer 2 The flow resistance can be made as small as possible. Thereby, a higher critical current density can be achieved.

In FIG. 3B, the superconducting wire 10 is wound so that the central axis of the coil bobbin 20 and the base material 1 are parallel to each other. The superconducting wire 10 may be wound so as to be inclined. That is, since the superconducting wire 10 is spirally wound around the coil bobbin 20, it is difficult to wind the superconducting wire 10 so as to be strictly parallel. Therefore, the strain of the magnesium diboride layer 2 can be further suppressed by winding the superconducting wire 10 so as to be slightly inclined from the parallel state.

FIG. 4 is a view showing a cross section of a modification (superconducting wire 11) of the superconducting wire 10 of the present embodiment. In the superconducting wire 11, unlike the superconducting wire 10 of FIG. 1, the insulator 3 is covered with a metal. Specifically, as shown in FIG. 4, the superconducting wire 11 includes a superconducting material 4 and an insulator 3 that fixes the superconducting material 4 in a metal tube 6.

By using the superconducting wire 11 having such a configuration, the operation when fixing the superconducting material 4 with the insulator 3 becomes easy. Moreover, since the outer surface of the superconducting wire 11 is composed of the metal tube 6, the mechanical strength of the superconducting wire 11 can be further increased.

FIG. 5 is a view showing a cross section of another modified example (superconducting wire 12) of the superconducting wire 10 of the present embodiment. In the superconducting wire 12, as in the superconducting wire 10 of FIG. 1, the cross-sectional areas of the respective magnesium diboride layers 2 in the cross section are equal. However, in the superconducting wire 10 shown in FIG. 1, the dimensions of the magnesium diboride layer 2 of each superconducting material 4 are also equal, but in the superconducting wire 12 of FIG. 5, the magnesium diboride layer of each superconducting material 4. 2 have different dimensions (dimensions in the vertical and horizontal directions in FIG. 1).

Even if the superconducting wire 12 is configured in this manner, a good critical current density can be obtained as in the superconducting wire 10 of FIG. Further, when the superconducting wire 12 is produced, even when the thickness of the magnesium diboride layer 2 formed on each base material 1 is uneven, the superconducting wires 4 having the same cross-sectional area of the magnesium diboride layer 2 are connected to each other. Can be used to obtain a superconducting wire 12 having a good critical current density. Further, when the superconducting material 4 is obtained by cutting, for example, a rectangular substrate on which the magnesium diboride layer 2 is formed, even if the thickness of the formed magnesium diboride layer 2 is uneven. The superconducting wire 12 having the superconducting material 4 having the same cross-sectional area can be obtained by cutting with a width corresponding to the thickness.

FIG. 6 is a view showing a cross section of still another modified example (superconducting wire 13) of the superconducting wire 10 of the present embodiment. In the superconducting wire 10 of FIG. 1, one magnesium diboride layer 2 is formed on one base material 1. However, in the superconducting wire 13 of FIG. The magnesium diboride layer 2 is formed.

As described above, the superconducting wire 10 can be obtained by forming the rectangular magnesium diboride layer 2 on the rectangular substrate and then cutting these layers, and the superconducting wire 13 shown in FIG. Then, this cutting process can be omitted. Therefore, since no shear stress is applied to the magnesium diboride layer 2, it is possible to more reliably prevent the magnesium diboride 2 from being peeled from the substrate 1 in the vicinity of the cut surface.

In addition, as a method of disposing the plurality of magnesium diboride layers 2 on the surface of the base material 1, for example, after forming the magnesium diboride layer 2 on the entire surface of the base material 1, a plurality of diboride layers are formed by a method such as etching. What is necessary is just to divide into magnesium chloride 2. Since the magnesium diboride layer 2 is usually formed with a uniform thickness, the magnesium diboride layer 2 having the same thickness can be reliably formed on the surface of the single substrate 1.

FIG. 7 is a view showing a cross section of still another modified example (superconducting wire 14) of the superconducting wire 10 of the present embodiment. In the superconducting wire 10 shown in FIG. 1, the superconducting material 4 is arranged stepwise vertically and horizontally. In the superconducting wire 14 shown in FIG. 7, the superconducting material 4 is arranged vertically and horizontally and obliquely. . Even if the superconducting material 4 is arranged in this way, a good critical current density can be obtained. Therefore, when the superconducting wire 4 is fixed by the insulator 3, it is not necessary to strictly position and arrange the superconducting material 4, and the superconducting wire 14 can be easily manufactured while maintaining a good critical current density. .

FIG. 8 is a view showing a cross section of still another modified example (superconducting wire 15) of the superconducting wire 10 of the present embodiment. The superconducting wire 10 in FIG. 1 has a circular cross section, but the superconducting wire 15 in FIG. 8 has a rectangular cross section. By using the superconducting wire 15 having a rectangular cross section, when winding on the coil bobbin 20 (see FIG. 3), the space can be wound more efficiently than when the cross section is circular. Thereby, the number of windings can be increased.

Hereinafter, the present embodiment will be described more specifically with reference to examples.

<Example 1 and Comparative Example 1>
Example 1
The superconducting wire 10 of FIG. 1 was produced as follows.
First, magnesium powder (purity 99.9% by mass) and granular boron (purity 99.5% by mass) are weighed so that the molar ratio of magnesium and boron is 1: 2, and 120 minutes using a roughing machine. Mixed. Subsequently, the obtained mixture was heat-treated at 900 ° C. for 10 hours in an argon atmosphere to obtain magnesium diboride.

Using the obtained magnesium diboride, a magnesium diboride layer 2 was formed on the surface of the duralumin plate (base material 1) by a pulse laser ablation method (PLD method). Specifically, the tablets obtained magnesium diboride and pressed obtained as a target in an argon atmosphere and irradiated with laser light of ^{1J / cm 2 ~ 5J / cm} 2 at room temperature to this target. And the magnesium diboride was vapor-deposited on the surface of the 500-micrometer-thick duralumin board which attached the substrate holder with the vapor | steam of the generated magnesium diboride. The thickness of the evaporated magnesium diboride was 30 μm, the width was 0.2 cm, and the length was 10 cm. Here, the thickness represents the length in the left-right direction in FIG. 2, the width represents the length in the vertical direction in FIG. 2, and the length represents the length in the direction perpendicular to the paper in FIG. Hereinafter, when the same expression is used, the same length is expressed. After vapor deposition, annealing was performed for 1 hour while changing the temperature from 300 ° C. to 800 ° C., and then cooled to room temperature. This obtained the base material 1 (namely, superconducting material 4) in which the magnesium diboride layer 2 was formed in the surface.

Although it was not a clear diffraction peak by X-ray diffraction measurement, it was confirmed that the formed layer was composed of magnesium diboride. Moreover, when the critical current density was measured about the formed magnesium diboride layer 2, it was 1600 A / mm < ² > in 5T and 20K.

The base material 1 on which the magnesium diboride layer 2 is formed is arranged in a stepped shape as shown in FIG. 1, and is fixed with an insulator 3 (enamel) so that the cross section has a circular shape with a diameter of about 1 cm. A wire rod 10 was obtained. And in order to perform the characteristic evaluation of the superconducting coil using the obtained superconducting wire 10, the obtained superconducting wire 10 was transformed into a semicircular shape in a spiral shape. And when the superconducting wire 10 was energized and the critical current density was measured, it was 1500 A / mm ² at 5T and 20K.

This value (1500 A / mm ² ) is substantially the same value as the critical current density (1600 A / mm ² ) of the magnesium diboride layer 2 formed on the surface of the substrate 1. Therefore, even when thin-film magnesium diboride is formed into a wire, sufficient connectivity between the magnesium diboride layers in the magnesium diboride layer 2 is ensured, and good criticality of the thin-film magnesium diboride is ensured. It was found that the current density can be maintained.

(Comparative Example 1)
In Example 1, the magnesium diboride layer 2 having a thickness of 30 μm, a width of 0.2 cm, and a length of 10 cm was formed on the duralumin plate. In Comparative Example 1, except that the width was 1 cm, it was carried out. The same magnesium diboride layer 2 as in Example 1 was formed. When the critical current density of the formed magnesium diboride layer 2 was measured, it was 1600 A / mm ² at 5T and 20K.

Then, 10 base materials 1 (superconducting material 4) on which the magnesium diboride layer 2 is formed are arranged only in the formation direction of the magnesium diboride layer 2 with respect to the base material 1 (that is, only in one direction), A superconducting wire was obtained in the same manner as in Example 1. When the characteristics of the superconducting coil were evaluated in the same manner as in Example 1, the critical current density was 900 A / mm ² at 5T and 20K.

This value (900A / mm ^2), compared with the critical current density of the formed on the substrate 1 a magnesium diboride layer ² (1600A / mm 2), and a value of about 50% to 60%. Therefore, it was found that the critical current density is reduced when the coil is arranged in one direction as in Comparative Example 1, when the coil is formed. This is presumably because the connectivity between the magnesium diboride layers in the magnesium diboride layer 2 was reduced by coiling.

<Example 2>
Superconducting material 4 and the like were placed in metal tube 6 to produce superconducting wire 11 shown in FIG. Specifically, the superconducting material 4 was produced in the same manner as in Example 1, and the superconducting wire 11 was produced by being housed in the nickel metal tube 6 together with the enamel as the insulator 3. And about the obtained superconducting wire 11, when the characteristic evaluation of the superconducting coil was performed like Example 1, the critical current density was 1550 A / mm < ² > in 5T and 20K.

This value (1550 A / mm ² ) is almost the same value as the critical current density (1600 A / mm ² ) of the magnesium diboride layer 2 formed on the surface of the substrate 1. Therefore, even when the metal tube 6 is provided, it was found that the good critical current density of the thin film magnesium diboride can be maintained as in the first embodiment.

<Example 3>
A superconducting wire 12 was produced in the same manner as in Example 1 except that a superconducting material 4 having the same cross-sectional area but different dimensions of the magnesium diboride layer 2 as shown in FIG. 5 was used. And about the obtained superconducting wire 12, when the characteristic evaluation of the superconducting coil was performed like Example 1, the critical current density was 1500 A / mm < ² > at 5T and 20K.

This value (1500 A / mm ² ) is substantially the same value as the critical current density (1600 A / mm ² ) of the magnesium diboride layer 2 formed on the surface of the substrate 1. Therefore, even if the dimensions of the magnesium diboride layer 2 are different, as long as the cross-sectional areas of the magnesium diboride layer 2 are equal, the good critical current density of the thin film magnesium diboride can be obtained as in the first embodiment. I found that it can be maintained.

<Example 4>
A superconducting wire 13 was produced in the same manner as in Example 1 except that a plurality of magnesium diboride layers 2 were formed on one base 1 as shown in FIG. And about the obtained superconducting wire 13, when the characteristic evaluation of the superconducting coil was performed like Example 1, the critical current density was 1500 A / mm < ² > at 5T and 20K.

This value (1500 A / mm ² ) is substantially the same value as the critical current density (1600 A / mm ² ) of the magnesium diboride layer 2 formed on the surface of the substrate 1. Therefore, if the cross-sectional area of the magnesium diboride layer 2 is equal regardless of the number of the magnesium diboride layers 2 formed on one base material 1, as in the first embodiment, a thin-film magnesium diboride layer is formed. It was found that a good critical current density can be maintained.

DESCRIPTION OF SYMBOLS 1 Base material 2 Magnesium diboride layer 3 Insulator 4 Superconducting material 5 Protective film 6

Metal tube

10, 11, 12, 13, 14, 15 Superconducting wire 20 Coil bobbin 100 Superconducting coil

Claims

A plurality of superconducting materials in which a magnesium diboride layer is fixed to a base material,
In a cross section perpendicular to the direction of current flow, the magnesium diboride layer faces in at least two directions: a fixing direction of the magnesium diboride layer with respect to the substrate and a direction intersecting the fixing direction. Arranged,
A superconducting wire, wherein the cross-sectional area of the magnesium diboride layer constituting the superconducting material is equal in each of the superconducting materials.
The at least one part of the said magnesium diboride layer arrange | positioned toward the two directions in the said cross section is arrange | positioned toward the orthogonal direction, It is characterized by the above-mentioned. Superconducting wire.
The superconducting wire according to claim 1 or 2, wherein one magnesium diboride layer is fixed to the base material.
The superconducting wire according to claim 1 or 2, wherein a plurality of magnesium diboride layers are fixed to the base material.
The superconducting wire according to claim 1 or 2, wherein the substrate is made of a metal that is thermodynamically stable with respect to the magnesium diboride layer.
The superconducting wire according to claim 1 or 2, wherein the magnesium diboride layer is covered with a protective film.
The superconducting wire according to claim 1 or 2, wherein the magnesium diboride layer is densely formed on the surface of the base material.
Forming a superconducting material by forming a magnesium diboride layer on the substrate surface;
In a cross-section in a direction perpendicular to the direction of current flow, the magnesium diboride layer is oriented in at least two directions: a fixing direction of the magnesium diboride layer with respect to the substrate and a direction intersecting the fixing direction. A superconducting wire manufacturing method, comprising: a step of forming a wire by fixing the superconducting materials having the same cross-sectional area to each other.
The at least part of the said magnesium diboride layer arrange | positioned toward the two directions in the said cross section is arrange | positioned toward the orthogonal direction, It is characterized by the above-mentioned. Manufacturing method of superconducting wire.
A plurality of superconducting materials in which a magnesium diboride layer is fixed to a base material, and the cross section in a direction perpendicular to the direction of current flow, the magnesium diboride layer is the magnesium diboride layer with respect to the base material And the cross-sectional area of the magnesium diboride layer constituting the superconducting material is equal in each superconducting material in the cross section. A superconducting coil, comprising: a superconducting wire that is wound around and a coil bobbin around which the superconducting wire is wound.
The at least one part of the said magnesium diboride layer arrange | positioned toward two directions in the said cross section is arrange | positioned toward the orthogonal direction, It is characterized by the above-mentioned. Superconducting coil.
The superconducting coil according to claim 10 or 11, wherein the superconducting wire is wound around the coil bobbin so that the base material constituting the superconducting wire is disposed on the coil bobbin side.