JPH08190817A - Superconducting device, permanent current switch element used in superconducting device, superconducting wire therefor, and method for manufacturing superconducting wire - Google Patents

Abstract

PURPOSE: To provide a superconducting wire in which electromagnetic stability is excellent and the resistant value of the wire can be large when a super conducting state is broken, and which is used for a highly reliable permanent current switch. CONSTITUTION: In a superconducting wire which is formed by embedding a superconducting filament 1 in a linear base material 2 with large electrical specific resistance, the electrical specific resistance of the linear base material 2 is set to be 10μΩcm or more, a low resistance base material 3 with the electrical specific resistance of 0.1μΩcm or less is coated on the periphery thereof, and an insulating coating 5 is formed further on the periphery thereof. The wire rod is formed so that the average value of the electrical specific resistance in the lengthwise direction of the wire rod is 1μΩcm or more in the normal conductive state of the wire rod. That is, a metal coating 3 with the small electrical specific resistance is provided on the periphery of the linear base material 2, and the metal coating 3 are formed discontinuously in the lengthwise direction of the linear base material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device, a permanent current switch element used in the superconducting device, and a superconducting wire for the permanent current switch element.

[0002]

2. Description of the Related Art Conventionally, a persistent current switch has been used in a superconducting magnet operated in a persistent current mode used in an MRI (magnetic resonance imaging medical diagnostic system) and a magnetic field generator for physical property research. When the superconducting magnet is operated in the permanent current mode, the exciting power supply can be disconnected, so that the superconducting magnet can be used as an electromagnet without power supply. Further, in the superconducting magnet for MRI or for studying physical properties, when the permanent current mode is set, a stable magnetic field with a very small magnetic field fluctuation can be obtained, and highly accurate measurement becomes possible.

The permanent current switch used in these devices is a thermal type which changes the temperature of the superconducting wire with a heater to switch between a superconducting state (ON state) and a normal conducting state (OFF state). There are known switches such as a current type that breaks the superconducting state by passing a current through the coil, or a magnetic field type that breaks the superconducting state by applying a magnetic field above the critical magnetic field to the superconducting wire.

Of these permanent current switches, the operation method will be described by taking as an example the case of incorporating a thermal type permanent current switch. In order to generate a magnetic field in the permanent current mode,
First, with the permanent current switch connected so as to short-circuit both ends of the superconducting coil being turned off, a current is passed from the exciting power supply to the superconducting coil. When the predetermined magnetic field is generated, the permanent current switch is turned on to make the current of the exciting power source zero.
In this state, current continues to flow in the closed circuit of the superconducting coil and the persistent current switch, and the persistent current mode is set.

As described above, it is necessary for the permanent current switch to have a high resistance in the OFF state so that no current flows in the permanent current switch itself when the coil is excited. Therefore, generally, for example, a superconducting wire rod having a length of several tens of meters and having a structure in which a Nb-Ti superconducting filament is embedded in a Cu-Ni alloy base material having a high electric resistivity is used in a coil shape. At this time, the heater wire is wound together and impregnated with resin.

In addition, when connecting the superconducting coil and the permanent current switch, attention should be paid to even the finest points such as using solder so as to have the lowest electric resistance or connecting the superconducting filaments to each other by spot welding. It is being appreciated.

[0007]

The cause of the instability of this kind of persistent current switch is not always clear at present, but the cause is that the base material of the superconducting wire to be used is Cu- which has a high electrical resistivity. Since it is a Ni alloy, it is considered that the electromagnetic instability due to the flux jump is large, or that the current distribution between the superconducting filaments is biased and the disturbance from the outside causes Joule heat generation and quenching during current redistribution. There is.

As a method for eliminating the instability of a superconducting wire used in a superconducting magnet for generating a magnetic field,
Conventionally, a method of incorporating or coating Cu having a low electric resistivity has been adopted, and it has a great effect on a wire rod of a superconducting magnet.

However, in the permanent current switch element, since it is necessary to increase the resistance value when the superconducting state is broken, if Cu is built in or coated like the above-mentioned measure, the resistance of the element is increased. Such a measure cannot be taken because the value is significantly reduced and the function of the persistent current switch is impaired, which is one of the factors of instability. Therefore, in order to improve such instability, conventionally, the winding wire including the connecting portion is fixed so as not to move, or a plurality of permanent current switches are used in parallel to have a margin, Measures were taken, but they were not always fully resolved.

The present invention has been made in view of the above circumstances, and an object thereof is to eliminate the above-mentioned problems and to have excellent electromagnetic stability of the wire, and to provide resistance in the longitudinal direction of the wire when the superconducting state is broken. It is an object of the present invention to provide a highly reliable persistent current switch that can increase the value and a superconducting wire used therefor.

[0011]

That is, according to the present invention, in a superconducting wire formed by embedding a superconducting filament in a linear base material having a large electric resistivity, the electric resistance of the linear base material is 10 μΩcm. In addition to the above, a low resistance base material having an electrical resistivity of 0.1 μΩcm or less is coated on the outer periphery thereof, and an insulating coating is further formed on the outer periphery thereof, and the electrical resistivity of this wire rod in the normal conducting state is this wire rod. Is formed so that the average value is 1 μΩcm or more in the longitudinal direction, and the initial purpose is achieved.

Specifically, specifically, a metal coating having a small electric resistivity is provided on the outer periphery of the linear base material,
This metallic coating is formed discontinuously in the longitudinal direction of the linear base material.

When a compound superconducting filament is used as a constituent element, the superconducting filament is embedded in at least a base material having a large electric resistivity, and a diffusion barrier material is formed on the outer periphery of the base material. In a superconducting wire, a metal coating having a small electric resistivity is discontinuously formed on the outer circumference of the diffusion barrier material in the lengthwise direction of the wire, and an insulating coating is formed on the outer circumference.

Further, as a superconducting wire used for a persistent current switch of a superconducting device operating in a persistent current mode, a superconducting wire having a structure in which a superconducting filament is embedded in a base material having a large electric resistivity, The superconducting wire rod is formed by disposing a metal coating having a small electric resistivity on the outer periphery of the base material discontinuously in the length direction of the wire rod and forming an insulating coating on the outer periphery thereof.

[0015]

In other words, in the superconducting wire thus formed, the combined resistance (R) per unit length (L) in the normal conducting state is, as shown in Equation 1, the cross-sectional area (S) of each constituent element. And the specific resistance value (ρ).

[0016]

[Number 1] _{1 / R = 1 / R 1} + 1 / R 2 + ... + 1 / R n ... (1) here,

[0017]

As Equation 2] _{R n = ρ n · L /} S n ... (2) example, the high-resistance base material of Cu-30% Ni, Nb-
Calculation is performed on a wire in which a superconducting filament of 46.5% Ti is embedded. If the cross-sectional area ratio between the base material and the superconducting filament is 2: 1, the specific resistance of the base material is 3.6 × ¹⁰ −5.
Ωcm, normal superconducting resistivity of superconductor is 6 just above the critical temperature
because it is x10- ⁵ Ωcm, the wire rod 1 having a 0.5mm diameter
cm resistance per length becomes 2.1x10- ² Ω. When the specific resistance is calculated by standardizing this over the entire cross section of the wire, 4.
It becomes 2 × ¹⁰ −5 Ωcm. Therefore, the switch resistance in the normal conducting state as a permanent current switch is, for example, 50Ω.
When using, a wire rod having a length of about 25 m is required.

Now, consider the case where Cu having a low electric resistivity is formed as a stabilizing material in order to improve the stability of the wire. In the above-described wire rod, trial calculation is performed with a wire rod in which a quarter of the Cu-Ni base material is replaced with Cu.
The electrical resistivity of Cu is 2 × ¹⁰ -8 Ωcm, Cu-30%
Since it is 1/1800 of Ni, the synthetic resistance per wire length of 1 cm is as small as 6 × ¹⁰ −5 Ω, which is 50 Ω.
In order to obtain the switch resistance of, the wire length becomes about 8 km, and it is practically impossible to obtain the permanent current switch.

In the present invention, Cu is divided in the length direction.
Therefore, the resistance value (R) of the wire rod per unit length is, as shown in the equation (3), the resistance value (R) of the portion formed of Cu.
11) and the resistance (R22) of the portion that does not form Cu.

[0020]

## EQU00003 ## R = R11 + R22 (3) That is, the above-mentioned part that constitutes Cu and the part that does not constitute Cu are connected in series in the length direction of the wire rod, and resistance becomes 1.1x10- ² Ω. When setting the switch resistance to 50Ω, for example, about 5
It requires a wire rod with a length of 0 m, which is twice as large as when Cu is not used. However, since Cu is used as the wire rod, electromagnetic stability is greatly improved, so that it functions effectively. It is possible to use a permanent current switch.

Further, by adopting this permanent current switch in the superconducting device, electromagnetic instability can be solved and the device can be made stable and highly reliable.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiments.

[First Embodiment] FIG. 7 is a cutaway view of the superconducting wire. The superconducting wire is formed by embedding a superconducting filament 1 in a linear base material 2 having a large electric resistivity. The electrical resistivity of this linear base material 2 is 10 μΩc
It is designed to be over m. Further, the outer periphery thereof is coated with a low-resistance base material 3 having an electric resistivity of 0.1 μΩcm or less.

What is important here is that the low-resistance base material 3 coated on the wire-shaped base material 2 has an average electrical resistivity in the normal direction of the wire material in the normal conducting state. 1 μΩ
It is formed so as to have a large resistance in the longitudinal direction so that it becomes cm or more. An insulating coating 5 is formed on the outer periphery of the low resistance base material 3.

When the superconducting wire is formed in this way, the outer periphery of the linear base material 2 is covered with the low-resistance base material 3 having an electric resistivity of 0.1 μΩcm or less, so that the wire is electromagnetically stable. And the electrical resistivity of this wire in the normal conducting state has an average value of 1 μΩ in the longitudinal direction of the wire.
Since it is formed to have a thickness of 10 cm or more, it is possible to increase the resistance value in the longitudinal direction of the wire when the superconducting state is broken, and thus to provide a switching element that is electromagnetically stable and highly reliable. You can

As the superconductor used in the present invention, conventionally used alloy-based materials such as Nb-Ti and compound-based materials such as NbSn and NbAl are used. For the high resistance base material, an appropriate material is selected in combination with the superconducting material used or in combination with the manufacturing process. For example, when an Nb-Ti superconductor is used, a Cu-Ni alloy is generally used, and when NbSn is used, a Cu-Sn alloy is desirable when manufactured by the bronze method.

In the case of NbAl, C is obtained by the jellyroll method.
u-Ni alloy can be used, but Nb tube method produces N
It is also possible to use a metal such as b or Ta, or an alloy having these as a base. In either case, if the electrical resistivity of the high-resistance base material is 1 μΩcm or more, it is acceptable.

Since the low-resistance base material is formed for the purpose of improving electromagnetic stability in the superconducting wire, it is desirable that the electrical resistivity be small, and metals such as Cu, Ag and Al are used. Furthermore, as a method for producing a superconducting wire according to the present invention, a superconductor is embedded in a high resistance base material,
After forming a composite body composed of low resistance metal on the outer periphery and thinning it, it is melted and removed so that the low resistance metal layer is formed, for example, discontinuously in the longitudinal direction of the wire, and an insulating coating is applied. Manufacturing method, or after making a composite in which a superconductor is embedded in a high-resistance base material and thinning it, coating is performed so that the low-resistance metal layer is discontinuous in the longitudinal direction of the wire, and insulation is performed. A manufacturing method including coating is adopted.

When Cu is formed in the wire, it is effective in improving the stability. At this time, although the composition ratio of Cu in the cross section of the wire varies depending on the purpose of use, it should be 10% or more of the base material. desirable. In the wire rod of the present invention, the electrical resistance of the wire rod in the normal conducting state is formed so that Cu does not continue in the length direction as a means for forming an average value of 1 μΩcm or more in the longitudinal direction of the wire rod. At this time, the ratio of the portion where Cu is constituted and the portion where Cu is not constituted is related to the resistance value of the wire rod as shown in the above formula 3, and it is possible if it is within the allowable range of the wire rod length. : 9 or less, preferably about 1: 1 is used. The length is 1 mm
A spacing of about 10 mm is desirable from the viewpoint of the stability of the wire rod in the length direction.

In the above description, the Nb-Ti wire is used as an example, but the present invention is also applicable to A15 type compound wire such as NbSn and NbAl. In the case of a compound wire, the high-resistance base material is a Cu-Sn alloy and the Nb tube method is NbA by the bronze method.
In the l-wire material, the high resistance base material may be Nb or Nb alloy. Since the compound wire is produced by heat treatment at 650 ° C. or higher, Nb, Ta or their alloys are used as a diffusion barrier in order to avoid Cu contamination when Cu is formed.

When manufacturing the wire of the present invention, the method can be roughly classified into two types. One is a method in which Cu is formed on the surface of a wire by a composite processing method, wire drawing is performed, and Cu is partially dissolved and removed with nitric acid. The other is a method in which the surface is coated with Cu, for example, by chemical plating after wire drawing. Both are easy to manufacture. Usually, the coil winding is performed after the insulation treatment, but it is effective to lightly work through a die to eliminate the unevenness in the length direction of the wire before the insulation treatment. An organic insulating material such as enamel is generally used as the insulating material, but a compound-based wire often requires high-temperature heat treatment after winding. At that time, an inorganic insulating material such as alumina glass is used.

[Second Embodiment] FIG. 1 shows another embodiment of the present invention.
This will be described below. This figure is a schematic view of a superconducting wire according to an embodiment of the present invention. A superconducting filament 1 is embedded in a high resistance base material 2, and a low resistance metal coating 3 is formed on the outer periphery of the wire material in a discontinuous manner in the longitudinal direction of the wire. The insulating coating 5 is applied to the outermost circumference. In this schematic diagram, the insulation coating is shown as a watermark.

In this embodiment, the superconducting filament 1 has a φ
There were 955 10 μm Nb-56.5% Ti alloys. A Cu-30% Ni alloy was used for the high resistance base material 2, and the cross-sectional area ratio between the base material and the superconductor was set to 1.5. Using the manufacturing process of FIG. 4, the low resistance metal coating 3 is formed by Cu plating to a thickness of 50 μm. Cu plating length is 5
mm, the length of the portion without Cu plating was 5 mm, and the outer diameter was 0.5 mm through a die. Polyimide is used for the insulation 5 and has a thickness of 20 μm.

In order to confirm the effect of the present invention, the diameter 30
A coil-shaped sample wound around a bobbin of 10 mm for 10 turns was set in a superconducting magnet, and a stabilizing current in a magnetic field was obtained. As a comparative sample, a conventional wire material having no Cu coating and a wire material in which all the base materials were Cu were used. The result is shown in FIG.
The applied magnetic field is shown on the horizontal axis, and the critical current or stabilizing current of the wire is shown on the vertical axis. In the sample of the Cu base material, the curve 63 shows the magnetic field dependence of the critical current, and in the conventional wire, the curve 62 cannot energize to the critical current of the superconducting filament, and the stabilizing current is about 100 to 200 A, which is higher than the critical current. It has dropped significantly.

With the wire of the present invention, it was possible to pass a critical current in a magnetic field of 4 T or more, and the stabilizing current in the low magnetic field region was about twice that of the conventional wire. Therefore, it can be seen that instability is significantly improved in the wire rod of the present invention.

[Embodiment 3] FIG. 2 shows another embodiment of the superconducting wire according to the present invention. The superconducting filament 11 is embedded in the high resistance base material 22, and the low resistance metal coating 3 is discontinuously formed on the outer circumference in the longitudinal direction of the wire. Insulation coating 5
Is applied to the outermost circumference. Also in this schematic diagram, the insulating coating is shown as a watermark. In this embodiment, the superconducting filament 11 is made of NbSn filament having a diameter of 3 μm of 14,000.
It was a book. A Cu-Sn alloy is used for the high resistance base material 22,
The cross-sectional area ratio between the base material and the superconductor was set to 1.5.

Using the manufacturing process shown in FIG. 5, the low resistance coating was performed by immersing the wire in nitric acid and locally dissolving and removing Cu. The diameter of the Cu coating portion is 0.7 mm, and the diameter of the portion without Cu coating is 0.56 mm. Moreover, the length of the Cu-coated portion is 5 mm, and the length of the portion without the Cu coating is 5 m.
m. For the insulation 5, a sleeve of alumina fiber having a thickness of 0.1 mm was used. In this embodiment, the NbSn superconducting compound has a high critical temperature of 17.5 K and a high critical magnetic field of 24 T, and thus can be used in a high magnetic field.

[Embodiment 4] Another embodiment of the superconducting wire according to the present invention will be described with reference to FIG. A superconducting filament 1 is embedded in a high resistance base material 2, and a low resistance metal coating 3 is formed on the outer periphery of the wire material in a discontinuous manner in the longitudinal direction of the wire. The insulating coating 5 is applied to the outermost circumference. In this schematic diagram, the insulation coating is shown as a watermark. In this embodiment, the superconducting filament 1 is made of NbAl filament of φ20 μm.
It was a book. Nb was used for the high-resistance base material 2, and the cross-sectional area ratio between the base material and the superconductor was 1.5.

Using the manufacturing process shown in FIG. 3, the so-called Nb tube method was used to incorporate the composite, and the low resistance coating was performed by immersing the wire in nitric acid and locally dissolving and removing Cu. The length of the Cu coating portion was 5 mm, and the length of the portion without Cu coating was 5 mm. For the insulation 5, a sleeve having a thickness of 0.1 mm, which was woven by bagging of alumina fibers, was used as in Example 2.

Although the example of the superconducting wire has been described above, if the superconducting wire is used in a superconducting application device incorporated in a permanent current switch element, a magnetic field generator, etc., it is a stable and highly reliable permanent current switch. An element can be obtained, and a superconducting device that is electromagnetically stable and highly reliable can be obtained.

In manufacturing the permanent current switch element, the heater wire is wound around the coil winding frame, the superconducting wire is wound around the heater wire, and the heater and the superconducting wire are impregnated and cured with a resin. In the case of a compound wire, it is advisable to wind the superconducting wire, heat-treat it, and then impregnate it.

[0042]

As described above, according to the present invention, since a metal coating having a small electric resistivity is provided on the outer periphery of the linear base material to form a low resistance base material, the electromagnetic property of the wire material is reduced. It is possible to increase the resistance value in the longitudinal direction of the wire when the superconducting state is broken, since the low resistance base material is discontinuous in the longitudinal direction as well as being excellent in mechanical stability. Therefore, it is possible to obtain a superconducting wire used for this kind of permanent current switch which is electromagnetically stable and highly reliable.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of a superconducting wire according to the present invention.

FIG. 2 is a partially cutaway perspective view showing another embodiment of the superconducting wire of the present invention.

FIG. 3 is a block diagram for explaining a manufacturing process of the superconducting wire of the present invention.

FIG. 4 is a block diagram for explaining a manufacturing process of the superconducting wire of the present invention.

FIG. 5 is a block diagram for explaining a manufacturing process of the superconducting wire of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between a magnetic field and a critical current / stabilized current.

FIG. 7 is a partially cutaway perspective view showing another embodiment of the superconducting wire of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Superconducting filament, 2 ... High resistance base material, 3 ... Low resistance base material, 4 ... Diffusion barrier, 5 ... Insulation, 11 ... Superconducting filament, 22 ... High resistance base material.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Naoki Maki 7-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (12)

[Claims] 1. A superconducting wire formed by embedding a superconducting filament in a linear base material having a high electrical resistivity, wherein a metal coating having a low electrical resistivity is provided on the outer periphery of the linear base material. A superconducting wire rod, wherein the metallic coating is formed discontinuously in the longitudinal direction of the linear base material. 2. A superconducting wire formed by embedding a superconducting filament in a linear base material having a large electric resistivity, wherein the electric resistance is smaller than that of the linear base material on the outer periphery of the linear base material. A metal coating is provided in contact with the outer peripheral surface of the linear base material, the metal coating is discontinuous in the longitudinal direction of the linear base material, and an insulating coating is provided on the outer peripheral surface. A superconducting wire that is characterized. 3. The high resistance base material is a Cu-Ni based alloy, and the superconducting filament is Nb-T.
The superconducting wire according to claim 1 or 2, wherein the superconducting wire is an alloy-based superconductor based on i, and the low-resistance metal coating is Cu. 4. A superconducting wire in which a superconducting filament is embedded in a linear base material having a large electric resistance and a diffusion barrier is provided on the outer periphery of the linear base material, wherein the outer periphery of the diffusion barrier is in contact with the diffusion barrier. A superconducting wire rod, characterized in that a metal coating having a small electric resistivity is provided, the metal coating is formed discontinuously in the longitudinal direction of the linear base material, and an insulating coating is provided on the outer periphery thereof. . 5. The high resistance base material is made of an alloy having Cu—Sn as a base, the superconducting filament is a compound superconductor having NbSn as a base, and the diffusion barrier is Ta.
The superconducting wire according to claim 4, wherein the superconducting wire is Nb or an alloy containing them as a base, and the low resistance metal coating is Cu. 6. A compound superconductor in which the high resistance base material is made of Cu—Ni or an alloy having Nb as a base, and the superconducting filament is a compound superconductor having NbAl as a base, and the diffusion barrier is Ta, Nb or those. The superconducting wire according to claim 4, wherein the superconducting wire is an alloy serving as a base, and the low resistance metal coating is Cu. 7. A superconducting filament is embedded in a high resistance base material having an electric resistivity of 10 μΩcm or more, and a low resistance base material having an electric resistivity of 0.1 μΩcm or less is coated on the outer periphery of the high resistance base material. A superconducting wire, characterized in that the electric resistance of the wire in a normal conducting state is formed so that the average value in the longitudinal direction of the wire is 1 μΩcm or more. 8. A superconducting filament is embedded in a high resistance base material having an electric resistivity of 10 μΩcm or more, and a low resistance base material having an electric resistivity of 0.1 μΩcm or less is coated on the outer periphery of the high resistance base material. In the superconducting wire, the electrical resistivity of the wire in the normal conducting state is formed so that the average value in the longitudinal direction of the wire is 1 μΩcm or more, and an insulating coating is formed on the outer periphery of the wire. Superconducting wire that does. 9. When forming a metallic coating having a small electric resistivity in the longitudinal direction of the linear base material discontinuously on the outer periphery of the linear base material having a large electric resistivity in which a superconducting filament is embedded, After making a composite of low-resistance metal on the outer periphery of the high-resistance base material and thinning it, the low-resistance metal layer was dissolved and removed so as to be discontinuous in the longitudinal direction of the wire. A method for producing a characteristic superconducting wire. 10. When forming a metallic coating having a small electric resistivity in the longitudinal direction of the linear base material discontinuously on the outer periphery of the linear base material having a large electric resistivity in which the superconducting filaments are embedded, It is characterized in that a composite body in which a superconductor is embedded in a resistance base material is formed, thinned, and then coated so that a low resistance metal layer is discontinuously formed in the longitudinal direction of the wire material. Manufacturing method of superconducting wire. 11. A permanent wire obtained by winding a heater wire and the superconducting wire according to claim 1, 2, 3, 4, 5, 6 or 7 around a coil winding frame, and impregnating and hardening a resin in the heater wire and the superconducting wire. Current switch element. 12. A superconducting device comprising the permanent current switch element according to claim 11.