JPH0982519A - Solenoid coil for superconducting magnet, and oxide superconducting multicore wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a solenoid coil applicable to the superconducting magnet used in a high-resolution NMR analyzer, etc., by an oxide superconducting wire, and to provide the usable oxide superconducting wire as the raw material of such solenoid coil. SOLUTION: An oxide superconducting multicore wire with many buried Bi based 2212 type oxide superconducting filaments 1 in a silver or silver alloy sheath material 2, the thicknesses of whose filaments 1 are all made not larger than 50μm. By such a multicore wire, an applicable solenoid coil to the superconducting magnet used in a high-resolution NMR analyzer, etc., can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a strong magnetic field generated by an oxide superconductor to produce a solenoid coil useful as a material for a superconducting magnet used in a high resolution NMR analyzer and the like, and a solenoid coil for producing the solenoid coil. The present invention relates to a useful oxide superconducting multifilamentary wire.

[0002]

2. Description of the Related Art The superconducting phenomenon allows a large current to flow with zero resistance, and the use of this phenomenon is spreading to various fields such as high-current power transmission and strong magnetic field generators. For example, a superconducting magnet used in a high-resolution NMR analyzer or the like achieves a strong magnetic field by energizing a coil with a large current and a permanent current operation using zero resistance, and can be realized only by a superconducting phenomenon. This is a typical example of applied technology. In particular, the superconducting magnet used in a high-resolution NMR analyzer (hereinafter sometimes referred to as "NMR magnet") has a higher resolution as the generated magnetic field is higher, so that a higher magnetic field tends to be required in recent years. .

At present, what is generally used as a material for an NMR magnet is a metallic superconducting wire such as NbTi wire or Nb ₃ Sn wire. Since the critical magnetic field (highest magnetic field capable of maintaining superconducting properties) of these wires is about 11T and 23T, respectively, the medium / low magnetic field magnets are made of NbTi wire, and the high magnetic field magnets are made of NbTi wire as the outer layer magnet. Then, it is general that the inner layer magnets are made of Nb ₃ Sn wires and are combined with each other.

On the other hand, as a technique for achieving a higher magnetic field of the NMR magnet, the outer and middle layer magnets are each made of Nb.
It has been proposed that the wire is made of Ti wire or Nb ₃ Sn wire and the inner layer magnet is made of oxide superconducting wire. As a research aiming at this direction, Sato et al.
It has been reported that T could be generated (International Workshop on superconductivity, 199
5, June 18-21, Hawaii, P234). However, the inner layer coil in this technique is a so-called pancake coil in which a tape-shaped oxide superconducting wire material is wound into a pancake shape using a sheath material and is laminated.

By the way, the oxide superconductor has a superconducting transition temperature (hereinafter referred to as Tc) as compared with a conventional metal-based superconductor.
Further, since it has a characteristic that the above-mentioned critical magnetic field (hereinafter referred to as Hc ₂ ) is high, it is expected to be applied to various fields. For example, Bi-based oxides include a low Tc phase having a Tc of about 80K and a high Tc phase having a Tc of about 110K, and the molar ratio of Bi, Sr, Ca, and Cu is approximately 2: 2 :.
In the case of 1: 2 (Bi system 2212 type), it becomes a low Tc phase, and in the case of about 2: 2: 2: 3 (Bi system 22223).
It has been known that a high Tc phase is obtained in the mold, in which a part of Bi is replaced by Pb).
It is regarded as a promising substance showing a c-value.

To apply such an oxide superconductor to a superconducting magnet, an oxide superconducting wire made into a tape-like wire using a sheath material is produced as a pancake coil as described above. This is because the oxide superconductor has a large anisotropy and the critical current density (hereinafter referred to as Jc) of the wire cannot be increased unless the crystal grains are oriented. It is increasing the degree. Further, the coil made of the tape-shaped wire inevitably has a pancake coil form. Under such circumstances, a high-performance solenoid coil (coil wound in a cylindrical shape) has not been realized in the oxide superconducting wire.

[0007]

The characteristics required for the NMR magnet are not only that a high magnetic field is generated, but also that high magnetic field stability and magnetic field homogeneity are required. Among these characteristics, regarding the magnetic field stability, in the case of pancake coils, it is necessary to connect the pancakes of each stage with superconducting connection in multiple places, so the connection part is only the permanent current switch part. It can be easily predicted that the magnetic field stability is inferior to that of.

On the other hand, although the magnetic field homogeneity has not been studied so far at all, the present inventors have conducted simulation calculation to determine whether the required magnetic field homogeneity can be secured in the pancake coil. First, as shown in FIG. 1, inner diameter: 75 mmφ, outer diameter: 130 mmφ, 1
Double-layer pancake thickness: 18.4 mm, insulation layer thickness between each stage: 1.2 mm, 27-stage coil (total length: 49
6 mm), the magnetic field homogeneity was evaluated according to a conventional method (for example, “Superconductivity Engineering” (sha) edited by The Institute of Electrical Engineers, 1990).
2nd edition, pp.147-151). The results are shown in Table 1 below.
It is understood that the Z ² term shifts by 13 ppm only by shifting in the axial direction (0 μm).

[0009]

[Table 1]

Converting from the above results, in consideration of the correction of the shim coil, in order to achieve the magnetic field homogeneity necessary for the NMR magnet of 0.01 ppm in the 20 mmφ class,
It is necessary to make the assembly accuracy within 10 μm. However, since the numerical value within 10 μm exceeds the assembly accuracy of the pancake coil, it is practically impossible to manufacture a superconducting magnet with high uniformity using the pancake coil.

From the above results, it is impossible to think of a superconducting magnet for use in a high-resolution NMR apparatus or the like using an oxide superconducting wire except for a solenoid coil. I tried to design.

The present inventors first assumed a solenoid coil of the same size as the pancake coil shown in FIG. Then, assuming that the wire rod space factor of the coil winding portion is 0.7 and the cross-sectional area ratio of the oxide superconductor to the total cross-sectional area of the wire rod is 0.4, it is necessary to generate 2.5T in 21T. Jc of the oxide superconductor part is 2.5 × 10 ⁴ A
/ Cm ² . The condition of generating 2.5T in 21T is based on the assumption of a 1 GHz class NMR analyzer.

The above Jc value, that is, 2.5 × 10 ⁴ A / m
² is the highest level value currently known as a round / rectangular oxide superconducting wire applicable as a solenoid coil. However, in the NMR magnet, if the operating current (hereinafter referred to as Iop) is set near the critical current (hereinafter referred to as Ic) of the oxide superconducting wire itself (Iop≈Ic), the required magnetic field stability Is not secured at all and will be attenuated immediately. According to a study made by the present inventors, in order to secure good magnetic field stability, the ratio of Iop to Ic is less than 0.4 (Iop / I
It was necessary that c <0.4). After all, in order to operate stably as a superconducting magnet that generates 2.5T in 21T, the value of Jc is 6.
It is necessary to be larger than 3 × 10 ⁴ A / cm ² .
However, this value of Jc is more than double the value of the highest level currently known as a round / rectangular oxide superconducting wire applicable as a solenoid coil. That is, the conventional oxide superconducting wire cannot realize a solenoid coil for an NMR magnet that satisfies the above characteristics.

The present invention has been made under these circumstances, and an object thereof is to realize a solenoid coil applicable to a superconducting magnet used in a high-resolution NMR analyzer or the like by using an oxide superconducting wire, and An object is to provide an oxide superconducting wire which is useful as a material for the above solenoid coil.

[0015]

Means for Solving the Problems The present inventors have proposed a solenoid coil applicable to a superconducting magnet used in a high-resolution NMR analyzer, etc., by significantly improving the superconducting properties of an oxide superconducting multicore wire. We succeeded in producing it with oxide superconducting wire.

The oxide superconducting multifilamentary wire used in the solenoid coil is specifically an oxide superconducting multifilament in which a large number of Bi-based 2212 type oxide superconducting filaments are embedded in a sheath material made of silver or a silver alloy. A core wire material having a filament thickness of 50 μm or less.

That is, a solenoid coil applicable to an NMR magnet can be realized by producing the above oxide superconducting multifilamentary wire into a solenoid coil shape.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The operation of the present invention will be described along with the background of the completion of the present invention. In producing an oxide superconducting wire coil using a Bi-based 2212 type oxide superconductor, the following method is generally used. First, raw material powders made of BiO ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO, etc. are weighed, pulverized and mixed, and heat-treated for calcination. Next, silver or silver alloy pipe (sheath material)
Are filled in, and this is extruded and drawn and rolled to obtain a wire rod. The surface of this wire is subjected to insulation treatment, then shaped into a coil, and further heat-treated to crystallize the oxide in the sheath material.

According to the above manufacturing process, the present inventors have made a silver alloy sheath Bi system 22 having a cross section of 0.5 mm × 2.0 mm.
A 12-type oxide superconducting single-core wire was produced, and using this, outer diameter: 71 mmφ, inner diameter: 35 mmφ, length: 150 mm
And the solenoid coil. This is heat-treated in the heat-treatment pattern shown in FIG.
Excitation tests were conducted under an external magnetic field of. as a result,
A magnetic field of 1.6 T could be generated. When Jc at this time was calculated, it was a high level of 2.1 × 10 ⁴ A / cm ² , which was achieved only by carrying out the heat treatment pattern shown in FIG.

The inventors of the present invention have been researching the optimum heat treatment conditions for producing an oxide superconducting wire for some time, and as a part of the research, the partial melting temperature curve in the temperature-oxygen partial pressure phase diagram was determined. Based on this, a method for controlling the oxygen partial pressure in the processing atmosphere has already been proposed (Japanese Patent Application No. 6-83477). The heat treatment pattern shown in FIG. 2 is an example of a heat treatment pattern based on this method. This heat treatment pattern has an oxygen partial pressure (Po ₂ ) of 2.4 ba.
r (O ₂ = 20%, N ₂ = 80%, total pressure = 6.0 ba
r).

By performing the heat treatment in the heat treatment pattern as described above, it was possible to raise the Jc of the oxide superconducting wire to the maximum level.
The value of (2.1 × 10 ⁴ A / cm ² ) is N as described above.
It is only about 1/3 of the Jc value required for the MR magnet.

Therefore, the present inventors have conducted studies to further increase the Jc of the oxide superconducting wire. First, a part of the solenoid coil obtained as described above was cut off and the cross section of the wire rod was observed. The result is schematically shown in FIG. In FIG. 3, 1 is an oxide superconducting conductor portion embedded in a sheath material, 2 is a sheath material made of silver or silver alloy,
In the oxide superconducting conductor portion, 3 and 4 respectively indicate a portion in which crystal grains are highly oriented and a portion in which crystal grains have a random orientation. As shown in FIG. 3, the oxide superconducting conductor portion 1 is well oriented along the interface near the interface with the silver sheath material 2 (highly oriented portion 3), but in the central portion, the crystal grains are randomly oriented. It turned out to be taking (Part 4). It was considered that the presence of the portion 4 having such random orientation was the cause of lowering the Jc of the entire oxide superconducting wire. It was also found that the thickness of the highly oriented portion 3 was about 20 μm or more even if it was thick from the interface.

The orientation state as described above is considerably different from that of the Bi-based 2223 type oxide superconductor wire rod, which has been enthusiastically attempted to be multicore. This Bi type 2223
In the case of a type oxide superconducting wire, high orientation is obtained by pressing the wire in one direction.
The Jc of the 223 type oxide superconducting wire is overwhelmingly higher for the single-core tape wire, and then for the multi-core tape wire, this Jc is about 1/4 of the case of the single-core wire, the multi-core flat angle. -In the actual situation, for round wire rods, Jc of about 1/10 that of single-core tape wire rods can be achieved. Bi system 222 like this
Observation of the cross section of the 3 type oxide superconducting wire shows no significant difference in the degree of orientation at the interface between the oxide superconducting filament and the sheath material.

On the other hand, in the Bi-based 2212 type oxide superconducting wire, the thickness of the highly oriented portion 3 is affected by the heat treatment conditions. Therefore, if the present inventors define the thickness of the oxide superconductor filament according to the thickness of the highly oriented portion 3 which is expected to be generated by the heat treatment conditions, the portion 4 having the random orientation becomes large. Therefore, it was thought that good Jc could be obtained.
As a result of further study based on these findings, the above-described object was successfully achieved by making the Bi-based 2212 type oxide superconducting wire multicore and setting the thickness of the embedded oxide superconducting filament to 50 μm or less. To find out that
The present invention has been completed.

FIG. 4 is a schematic view showing a cross section of the wire of the present invention, and 2 in the figure has the same meaning as in FIG. In the present invention, the oxide superconducting conductor portion 1 (hereinafter referred to as “oxide superconducting filament”) in the Bi-based 2212 type oxide superconducting wire.
The thickness d of (referred to as) is 50 μm or less. In this way, any part of the oxide superconducting filament 1 is 25 μm or less from the interface with the sheath material 2, and a high degree of orientation can be realized in the entire cross section of the filament 1. Moreover, by manufacturing a solenoid coil using such an oxide superconducting wire, a solenoid coil useful as a material for a superconducting magnet used in a high-resolution NMR analyzer or the like was obtained.

The heat treatment pattern for producing the wire of the present invention is not particularly limited, and the heat treatment pattern may be set according to the thickness d of the highly oriented portion 3 to be produced. It is preferable to carry out the heat treatment pattern shown in FIG. 1 because the thickness d of the highly oriented portion 3 can be made as thick as possible.

Further, the wire of the present invention needs to have a multi-core structure, for the reason that the oxide superconducting filaments 1 are dispersed as much as possible and the thickness d of each filament is made small. Further, the cross-sectional shape of the wire of the present invention is not particularly limited, and any shape such as a round shape or a rectangular shape can be adopted as long as it can be formed into a solenoid coil shape.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification of the design of the present invention can be made without departing from the spirit of the preceding and the following. It is included in the technical scope.

[0029]

Example: Bi was prepared according to the above procedure except that the number of cores was changed.
A 2212 type oxide multifilamentary wire was prepared. At this time, extrusion wire drawing was repeated twice to obtain a 49-core multicore wire.
After applying insulation treatment to the surface of this wire, outer diameter: 74 mm
A solaid coil of φ, inner diameter: 35 mmφ, length: 150 mm was used, and heat treatment was performed according to the heat treatment pattern shown in FIG.

Regarding the obtained solenoid coil, 18
When an excitation test was conducted under the external magnetic field of T, 5
When T occurred, no metastasis was observed yet. at this point
Excitation was interrupted, but this may cause wire breakage due to electromagnetic force.
Because of that. Cut out a part of this coil and measure Jc
When determined, 19.8 × 10 in 4.2K, 20T ^Four 
A / cm² And almost reported on single core tape wire so far
The value obtained was comparable to the highest value. With this wire
Due to the multi-core structure, the silver ratio (silver sheath material / oxide superconducting film
(Lament area ratio) is 2.7 to 7.0 in case of single core
It was getting bigger, but this value is still 2.
A 1 GHz-class NMR analyzer that generates 5T was assumed.
Then, Iop / Ic = 0.28, which is the required value 0.4.
It will be possible to lower it with a margin. Also, this carp
When measuring the magnetic field homogeneity of the
Very high magnetic field homogeneity of 0.005ppm
Has been achieved.

[0031]

EFFECTS OF THE INVENTION The present invention is constructed as described above, and a Bi-based 2212 type oxide superconducting multifilamentary wire having a high Jc was obtained. Moreover, by using this multi-core wire,
A solenoid coil applicable to a superconducting magnet used in a high-resolution NMR apparatus or the like can be realized.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of the shape of a pancake coil.

FIG. 2 is a schematic view showing a cross section of a Bi-based 2212 type oxide superconducting single core wire.

FIG. 3 is a graph showing an example of a heat treatment pattern.

FIG. 4 is a schematic view showing a cross section of a Bi-based 2212 type oxide superconducting multifilamentary wire according to the present invention.

[Explanation of symbols]

1 oxide superconducting conductor part (oxide superconducting filament) 2 sheath material 3 highly oriented part 4 random orientation part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Ozaki 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Kobe Steel Works, Ltd. Kobe Research Institute

Claims (3)

[Claims] 1. A solenoid coil for a superconducting magnet, which is manufactured using an oxide superconducting multifilamentary wire. 2. An oxide superconducting multifilamentary wire in which a large number of Bi-based 2212 type oxide superconducting filaments are embedded in a sheath material made of silver or a silver alloy, wherein the filament thickness is 50 μm or less. An oxide superconducting multifilamentary wire characterized by being present. 3. A solenoid coil for a superconducting magnet, wherein the oxide superconducting multifilamentary wire according to claim 1 is the oxide superconducting multifilamentary wire according to claim 2.