JP3340152B2 - Superconducting magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet formed by using an oxide superconducting tape wire.

[0002]

2. Description of the Related Art As a method of forming an oxide superconductor into a wire, a metal sheath method is considered promising. in this way,
A superconducting tape wire having a high critical current density has been obtained by repeatedly filling a metal pipe such as silver with an oxide superconductor powder and then repeatedly performing processing such as drawing, rolling and pressing and heat treatment. In the superconducting tape wire produced by such a metal sheath method, the c-axis of the crystal of the superconductor is aligned perpendicular to the tape surface, and the external magnetic field dependence of the critical current density has a very large anisotropy. When the magnetic field is applied in parallel to the tape surface, the critical current density decreases little, but when the magnetic field is applied perpendicular to the tape surface, the critical current density sharply decreases. Japanese Unexamined Patent Publication No. 1-246801 discloses a superconducting magnet prepared by using the above-described superconducting wire. FIG. 7 is a cross-sectional view of a conventional solenoid type magnet formed using such a superconducting tape wire.

[0003] By reducing the magnetic field perpendicular to the superconducting wire by winding the superconducting wire at the end so that the crystal direction showing a high critical current density follows the bending of the magnetic field, the critical current density can be prevented from lowering. Can be. However, when a tape-shaped superconducting wire is wound around the structure shown in FIG.
There is a problem that a large strain is generated in the wire, the crystal orientation of the superconductor in the superconducting wire is broken, and the critical current density is greatly reduced. Therefore, it has not been possible to provide a superconducting magnet capable of sufficiently extracting the high critical current density of the superconducting wire. Along with this, the conventional superconducting magnet critical magnetic field has been low.

[0004]

When a superconducting wire having crystal anisotropy as described above is wound so as to follow a magnetic field in which a crystal orientation is generated at an end portion, a large strain is generated in the wire, and the superconducting wire is formed. However, there is a problem that the crystal orientation of the superconductor collapses and the critical current density is greatly reduced.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a superconducting magnet which is free from the influence of a magnetic field at the end and has a significantly improved critical current density and critical magnetic field.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a superconducting magnet comprising a coil wound with a superconducting wire rod in which a crystal plane exhibiting a high critical current density is preferentially oriented in the direction of current flow. Wherein the inner diameter of the coil is larger at the end than at the center of the coil.

As a superconductor constituting a superconducting wire, a superconductor having a crystal anisotropy in critical current density is used, and many such superconductors are known. For example,
Rare earth element-containing perovskite oxide superconductors, Bi-Sr-Ca-Cu-O-based oxide superconductors, T
For example, a 1-Ba-Ca-Cu-O-based oxide superconductor is used. The oxide superconductor containing a rare earth element and having a perovskite structure may be any as long as it can realize a superconducting state. For example, a ReM ₂ Cu ₃ O _{7 -d-} based (Re is Y, La, Sc, Nd, Sm , Eu, Gd, Dy, H
At least one element selected from rare earth elements such as o, Er, Tm, Yb, and Lu; M is at least one element selected from Ba, Sr, and Ca; In the following numbers, part of Cu is Ti, V, Cr, M
oxides of n, Fe, Co, Ni, Zn, etc.). The rare earth elements are defined in a broad sense and include Sc, Y and La-based elements. Also, B
The i-Sr-Ca-Cu-O-based oxide superconductor has a chemical formula: Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x (1): Bi ₂ (Sr, Ca) ₃ Cu ₂ O _x (2) (formula in, some Bi are those represented by such substitutable) such as Pb, T1-Ba-Ca- Cu-O based oxide superconductor of the _{formula: T1 2 Ba 2 Ca 2 Cu} 3 O _x (3): T1 ₂ (Ba, Ca) ₃ Cu ₂ O _x (4)

[0008]

The magnetic field at the end can be made smaller than the magnetic field at the center by making the inner diameter of the coil larger at the end than at the center. Therefore, even if the magnetic field at the end is applied in a direction deviated from the direction parallel to the tape surface of the superconducting wire, the magnetic field component applied in the direction perpendicular to the tape surface can be reduced compared to the case where the inner diameter is the same, so the critical current density of the superconducting wire is Of the superconducting wire can be sufficiently utilized, and a strong magnetic field can be generated. Also, since all superconducting wires are wound in parallel with one axis, the superconducting wire is disclosed in
Disorder in the crystal orientation of the superconductor due to distortion due to winding as described in JP-A-6801 can be prevented.

[0009]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a superconducting magnet according to a first embodiment of the present invention. Reference numeral 1 denotes a superconducting wire having anisotropy in the dependence of the critical current density on the external magnetic field, and its direction is aligned so that the tape surface is parallel to the direction of the magnetic field generated at the center. By doing so, a sufficiently large magnetic field can be generated at the center. On the other hand, it is wound so that the inner diameter R2 at the end is larger than the inner diameter R1 at the center. At the end, the magnetic field component applied to the superconducting wire in the direction perpendicular to the plane can be suppressed low, and the critical current density and the critical magnetic field of the superconducting magnet in this embodiment can be improved. Further, since the winding direction of the superconducting wire is not forcibly changed, there is no disturbance in the crystal direction due to strain. The superconducting magnet having the above configuration was manufactured by the following method.

First, Bi ₂ O ₃ , SrCO ₃ , CaCO
_The powders of ₃ , PbO and CuO are weighed in predetermined amounts so that the ratio of each metal element satisfies the composition of the above formula (1), and after sufficient mixing, the mixed powder is quenched in air for 800 hours. The mixture was baked under the conditions of 48 ° C. × 48 hours, and the baked product was repeatedly pulverized and mixed by a ball mill to obtain the composition having the above (1).
Was satisfied, and a Bi-based oxide superconductor powder satisfying the following conditions was produced.

Next, a superconducting wire was manufactured using the Bi-based oxide superconductor powder. First, a Bi-based oxide superconductor powder was filled in a silver tube having an outer diameter of 20 mm, an inner diameter of 15 mm, and a length of 300 mm, and this was subjected to surface reduction to produce a wire rod having an outer diameter of 1.5 mm. Then, the wire was subjected to rolling to produce a tape-shaped wire having a cross-sectional shape of 3 mm in width and 0.2 mm in thickness.

This tape-shaped wire was heat-treated in an oxidizing atmosphere at 800 to 850 ° C. for 48 hours, and the superconducting properties of the superconducting wire were measured. And the critical current density at 77K is 50,000 A / cm ² Met.

Thereafter, as shown in the cross-sectional view of FIG. 2, the superconducting wire is wound around a winding jig whose ends are thicker in order from the thinnest portion so as to fill the steps, and the inner diameter is reduced to 5 mm.
A 0 mm superconducting magnet was produced. This winding jig
In order to make the outer diameter at both ends 1.5 times or more at the center, the length of the entire length L is gradually increased in steps from L / 20 to L / 2 from both ends.

When the superconducting characteristics of the superconducting magnet thus obtained were measured, the critical current density was 10 at 77K.
000A / cm ² And 3000 in the magnet
A Gaussian magnetic field was generated.

As a comparative example of the first embodiment, the superconducting wire 1 produced in the first embodiment is wound around a winding jig having the same length as that of the above-mentioned embodiment and a constant outer diameter of 50 mm. To produce a superconducting magnet. When the superconducting properties of the superconducting magnet thus manufactured were measured, the critical current density was 1000 A / cm ^2. The generated magnetic field was 300 gauss, drastically reduced to 1/10 of the generated magnetic field of the first embodiment.

As described above, according to this embodiment, a high magnetic field can be generated. In addition, since the direction of the superconducting wire was not changed, no disturbance in the crystal orientation of the superconductor was observed, and the critical current and the critical magnetic field did not decrease due to the disorder in the crystal direction. If necessary, heat treatment, for example, annealing in an oxygen-containing atmosphere may be performed after winding. Next, a second embodiment of the present invention will be described.

A tape-shaped superconducting wire was manufactured under the same conditions as in the first embodiment. The superconducting properties of this wire were as shown in FIG. As shown in the cross-sectional view of FIG. 4, this tape-shaped wire is wound around a winding jig having both ends thick and has an inner diameter of 1 mm.
An 8 mm superconducting magnet was produced. This winding jig has a total length of 500 mm, an outer diameter near the center of 20 mm, and is thickened in steps from 230 mm from both ends, and the outer diameter at both ends is 60 mm. The winding method was to start winding from the thinnest part in the center and wind in order to fill the steps.

When the superconducting properties of the superconducting magnet thus obtained were measured, the critical current density was 10 at 77K.
000A / cm ² And 250 near the center of the coil.
A magnetic field of 0 Gauss was generated.

In the vicinity of 230 mm from both ends of the magnet,
The superconducting wire has a magnetic field of 2500 Gauss inclined about 5 degrees from the tape surface. However, in this case, the magnetic field component in the direction perpendicular to the tape surface is about 250 Gauss, as shown the characteristics of FIG. 3, 10000 A / cm ² It can be seen that it is possible to maintain the critical current density of By the way, it is considered that the magnetic field spreads considerably at the end of the magnet and is applied to the tape surface at an angle of 5 degrees or more. However, the inner diameter is tripled, and the magnetic field at this portion is 1/9 of the magnetic field at the center, that is, about 278 gauss. Even if the magnetic field is applied to the tape surface at an angle of 60 degrees, it is 1
0000A / cm ² It can be seen that it is possible to maintain the critical current density of As described above, it is possible to design a superconducting magnet using the characteristics of the superconducting wire shown in FIG. 3, and it is possible to sufficiently bring out the characteristics of the superconducting wire.

As a comparative example of the second embodiment, the superconducting wire prepared in the second embodiment is wound around a winding jig having the same length as that of the above-mentioned embodiment and a constant outer diameter of 20 mm. A magnet was made. When the superconducting properties of the superconducting magnet thus manufactured were measured, the critical current density was 1000 A / cm ^2. The generated magnetic field was 200 gauss, which was drastically reduced to 1/10 or less of the generated magnetic field of this embodiment. Thus, according to the present embodiment, a high magnetic field can be generated. In addition, since the direction of the superconducting wire was not changed, no disorder in crystallinity was observed, and there was no decrease in critical current and critical field due to disorder in crystal orientation. Also, the position where the lead is taken out is important, and FIG.
It is preferable to take it out from the center of the coil as shown in FIG.

In FIG. 5B, reference numeral 51 denotes a superconducting wire having a critical current density dependent on an external magnetic field. The superconducting wire 51 is wound from the center of the winding jig 54 so that the power leads 52 and 53 are located near the center of the coil. It ends around the center at the beginning.

The magnitude of the magnetic field leaking to the outside is smaller near the center of the side surface of the coil than at the end of the magnet. For this reason, in the power lead portions 52 and 53, even if the magnetic field is applied in a direction deviated from the direction parallel to the tape surface, the leakage magnetic field is weak, so that the decrease in the critical current density of the superconducting wire at this portion is small.
For this reason, it is possible to prevent a decrease in the critical current density in the power lead portion, and to make full use of the maximum critical current density of the superconducting wire to generate a strong magnetic field.

As shown in FIG. 5A, the critical current density and the generated magnetic field can be improved by several to ten times as compared with the superconducting magnet in which the power lead portion is taken out from the coil end as in the conventional case.

[0025]

As described above, in the superconducting magnet of the present invention, the strength of the magnetic field spread at the coil end is suppressed by making the inner diameter of the end of the coil larger than the inner diameter of the center of the coil. It is possible to generate a high magnetic field by utilizing the critical current density of the superconducting wire when the magnetic field is parallel to the tape surface without determining the overall critical current density at the coil end. For example, the critical current density and the critical magnetic field of the superconducting magnet can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a superconducting magnet according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a winding jig used in the first embodiment.

FIG. 3 is a diagram showing the external magnetic field dependence of the critical current density of the oxide superconducting tape wire used in the superconducting magnet according to the second embodiment of the present invention.

FIG. 4 is a sectional view of a winding jig used in a second embodiment.

FIG. 5 is a perspective view of a superconducting coil according to an embodiment of the present invention and a conventional example.

FIG. 6 is a view showing the external magnetic field dependence of the critical current density of an oxide superconducting tape wire having anisotropy in the critical current density dependence on the external magnetic field.

FIG. 7 is a sectional view of a conventional superconducting magnet.

[Explanation of symbols]

 1 .... Superconducting wire

────────────────────────────────────────────────── (5) References JP-A-63-274116 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 6/00 ZAA

Claims (3)

(57) [Claims] 1. A superconducting magnet comprising a coil wound with a superconducting wire in which the c-axis of the crystal is oriented perpendicular to the direction of conduction , wherein the inner diameter of the coil is smaller at the end than at the center of the coil. A superconducting magnet characterized in that it is larger. 2. The internal diameter of the coil is L / 20 from both ends of the coil, where L is the total axial length of the coil.
2. The superconducting magnet according to claim 1, wherein the size of the superconducting magnet increases from L / 2 or less. 3. The superconducting magnet according to claim 1, wherein the superconducting wire starts winding near the center of the coil and ends winding near the center.