JPH04206507A - Nuclear magnetic resonance image diagnostic device (mri), superconducting coil and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce current attenuation rate, and to make it possible to generate a magnetic field which is stable for a long period of time by a method wherein the connection parts of a conducting wire are concentrated at the center part of a stabilizing material for connection by conducting plastic work on metal superconducting strands. CONSTITUTION:Twenty-four metal superconducting strands 33 are buried in stabilization copper on a cross section of Nb-Ti superconducting wires 31 and 32. The above- mentioned strands are dipped into nitric acid for the purpose of exposing the strands 33 on the terminal to be joined, the stabilized copper is removed, and after the strands have been exposed, they are rinsed. An Nb-Ti junction auxiliary member 34, which is same as the strands, is prepared in advance, and junction strands are enveloped. The stabilization copper on the auxiliary member 34 is removed using nitric acid in advance, and the strands are exposed. Then, oxygen free copper is inserted in the center part of the strands as a core material, a junction auxiliary strand 34 formed in advance covers the circumference of the strand group 33, which is inserted into the hollow part of the stabilized copper, placed in a mold and molded by applying pressure.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a superconducting magnetic field generator with a small current attenuation rate, and particularly to a superconducting magnetic field generator ( The present invention relates to MRI (hereinafter referred to as MRI), a coil suitable for use therein, a superconducting wire, a method for manufacturing the coil, and a method for connecting the superconducting wire.

The MRI of the present invention can be used in various fields of nuclear fusion devices.

[Conventional technology] Superconducting wires for connection are assembled by embedding a large number of superconducting wires in a stabilizing material such as copper (Cu) or aluminum (AQ) and drawing them to a desired outer diameter. Superconducting fine multi-wire is used.

Previously known connections such as soldering, brazing, pressure welding, and welding have been tried, but all of them have high electrical resistance at the connection and generate a lot of heat when energized. Therefore, there was a practical problem.

In order to improve the connection of superconducting fine multi-wires, as described in Japanese Patent Application Laid-Open No. 59-16207, exposed superconducting strands are stacked on top of each other and housed in a connection tube, and A method is adopted in which electrical continuity is established by pressing through a connecting tube.

This connection method involves removing the stabilizing material from the connecting portion of the superconducting wires to be connected, stacking the exposed superconducting filaments in a connecting pipe, and crimping them through the pipe. The superconductor filaments that have been stored are crimped and joined together.

However, with this connection method, the superconducting filaments that are to be connected to each other contact only the overlapping portions of their outer surfaces, making it difficult to ensure a high critical current value. Further, there was a problem in that the pressing was from one direction, and the superconductor filaments did not come into sufficient contact.

Furthermore, in order to improve the filling rate of superconducting filaments, a method for joining superconducting wires has been proposed in Japanese Patent Laid-Open No. 62-234880. This method is characterized by sandwiching the exposed multi-core of the superconducting wire for connection between each of the exposed core wires, covering the sandwiched parts together with a metal ring, and crimping and joining the metal rings. do. An example of this is to extend the tip of the filament of the connecting superconducting wire to the end of each stabilizing material of the superconducting wire, and position the end of the metal ring at the tip of the stretched filament. It is crimped. When there are very few superconducting wires (filaments) as in this example, applying superconducting filaments for connection is effective in improving the filling rate. However, the pressure for crimping was from one direction, and the adhesion between the superconducting filaments was still not sufficient. In addition, the thickness ratio of the filament and the stabilizing material in the cross section after crimping, the length of the stabilizing material, etc. have not been studied.
There was a problem that the connection resistance value varied, and there was a drawback that it was not a persistent current superconducting wire.

[Problems to be Solved by the Invention] The above-mentioned prior art does not consider the method of pressing the superconducting wire (filament) with a stabilizing material, nor the thickness ratio and length of the cross section of the joint. However, true superconducting strands could not be connected to each other, and there were problems with permanent electrical properties.

In other words, the main aim is to entangle superconducting strands, but a connection that prevents the proximity effect and shunt loss between superconducting strands has not yet been achieved.

An object of the present invention is to provide an MHI that can generate a magnetic field that is stable for a long period of time with an extremely low current attenuation rate, and also to provide a superconducting coil suitable for use in MRI and a method for manufacturing the same. be.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a coil configured by winding a superconducting wire configured by connecting the ends of a superconducting wire in which a plurality of superconducting wires are embedded in a stabilizing material;
In the device having a superconducting switch connected to both ends of the coil, and means for cooling the coil and the superconducting switch, a group of superconducting wires in the connecting portion is densely gathered and buried in a central portion of the stabilizing material. and the strands are in direct contact with each other, the stabilizing material is present in the center of the aggregate of the strands, and the stabilizing material and the strands are tightly joined. do.

Furthermore, in the present invention, the superconducting wire group and the other superconducting wire group are densely gathered and buried in the center part of the stabilizing material in the connection part, and the wires are in direct contact with each other, and the wire groups are Stabilizing materials are present in the center of the assembly, and the stabilizing materials and the wires are tightly joined to provide MRI.

Furthermore, according to the present invention, the connection portion has a connection resistance of 10-''Ω or less, and the critical current value of the superconducting wire is 8.
MRI with a critical current value of 0% or more can be provided.

The present invention is a coil unit formed by winding a superconducting wire in which a large number of superconducting wires are embedded in a stabilizing material, and connecting the superconducting wires to each other at the coil end to form a predetermined coil turn. In this method, the superconducting strands of the connection part are embedded in a stabilizing material, and are densely gathered in the center of the stabilizing material so that the strands are in direct contact with each other, and the aggregate of the strands is A low-resistance metal material is present in the center, and the stabilizing material, the metal material, and the wire are closely bonded to each other.

In this coil, a group of superconducting strands of the connection part and a group of superconducting wires for connection are embedded in the stabilizing material, and are densely gathered in the center of the stabilizing material so that the strands are in direct contact with each other. However, a low-resistance metal material exists in the center of the aggregate of strands,
The superconducting coil may be a superconducting coil in which the stabilizing material and the metal material are tightly joined to the wire. In this superconducting coil, the connecting portion has a connection resistance of 10-''Ω or less, and a critical current value of 80% or more of the critical current value of the superconducting wire.

In the present invention, the superconducting strands of the connection part are embedded in a stabilizing material, and are densely gathered in the center of the stabilizing material so that the strands are in direct contact with each other, and the strands of the strands are in direct contact with each other. A low-resistance metal material is present in the center of the aggregate, the stabilizing material, the metal material, and the wire are closely bonded to each other, and the connection portion has a connection resistance of 10-''''Ω or less. The present invention provides a superconducting wire having a critical current value that is 80% or more of the critical current value of the superconducting wire.

The present invention further provides the steps of: winding a superconducting wire to form a desired turn; exposing a group of superconducting strands at an end of the superconducting wire; and placing a core of a stabilizing material in the center of the strands. , inserting the superconducting strands together with the superconducting strands and the core material into the hollow part of the stabilizing material having a hollow part, and applying pressure from the outer periphery of the hollow stabilizing material to insert the exposed superconducting strands into the core material. The present invention provides a method for manufacturing a superconducting coil, in which a hollow stabilizing material and a core material are tightly joined to the superconducting wire by assembling them in a direction.

This manufacturing method includes a step of winding a superconducting wire in which a plurality of metal superconducting wires are embedded in a stabilizing material to form a coil, and a step of winding a superconducting wire in which a plurality of metal superconducting wires are embedded in a stabilizing material to form a coil, and A process of assembling the exposed superconducting strands to be connected to other wires and the connection auxiliary material with a core material made of a stabilizing material in the center, and the assembled superconducting strands and the ends of the superconducting wires. a process of inserting the superconducting wire into the hollow part of the hollow stabilizing material, applying pressure from the outside of the hollow stabilizing material to plastically process the collecting part, and collecting the superconducting wires in the central part of the hollow stabilizing material. , a method for manufacturing a coil of superconducting wire, including the steps of tightly joining the core material and the hollow stabilizing material to the superconducting wire, and bringing the superconducting wires into direct contact with each other.

In addition, the stabilizing core material can be used to connect the exposed strands at the connecting end of the superconducting wire with the metal superconducting strands exposed at the connecting end of the superconducting wire in which a plurality of metal superconducting strands are embedded in the stabilizing material. a process of assembling the superconducting strands around the strands, a process of inserting the assembled superconducting strands and the ends of the superconducting strands into the hollow part of the hollow stabilizing material, and plastic working the pushed-in gathering part to stabilize the superconducting strands in the hollow. Provided is a method for connecting superconducting wires, which includes the steps of: integrating the core material and the hollow stabilizing material into the central part of the superconducting wire, closely joining the core material and the hollow stabilizing material to the superconducting wire, and bringing the superconducting wires into direct contact with each other. .

The superconducting wire according to the present invention is a superconducting wire in which a plurality of metal superconducting strands are embedded in a stabilizing material and metal superconducting strands exposed at the ends of each unit superconducting wire are connected to each other. The superconducting strands of the connecting portion are assembled in the center of the cylindrical hollow stabilizing material for connection, and the stabilizing material for connection is, for example, metal-bonded with the superconducting wire and the superconducting strand to be connected.

The present inventor studied how to assemble superconducting strands in order to significantly reduce the connection resistance between the superconducting strands. For this reason, a connecting sleeve is made from a stabilizing material used in superconducting wires, a superconducting wire to be connected is inserted into the sleeve, and the stabilizing material sleeve is pressed. However, this method did not significantly improve the filling rate of the superconducting wire aggregate.

Here, the filling rate is the collection of superconducting strands or It is the ratio of the area (B) of the superconducting wire and the set of superconducting wires used as connection auxiliary material, and the area (B) is the area (A)
minus space or void. When this filling rate is 80% or more, the contact resistance between the superconducting strands becomes very small, and the connection resistance becomes small. In particular, when the filling rate is 90% or more, the connection resistance becomes extremely small.

If the filling rate does not improve even if you simply process the stabilizing material sleeve to gather the superconducting wires in the center, it may be because the stabilizing material is generally made of soft metal such as copper or aluminum. This is thought to be because the pressure of plastic working is not applied to aggregate the superconducting strands. Therefore, the present inventor placed a core material made of a low-resistance metal material, particularly a stabilizing material, in the center of the superconducting wire group so that the plastic working force sufficiently preceded the superconducting wire group. It was found that the filling factor of the superconducting strands was significantly increased, the contact between the superconducting strands was extremely good, and the superconducting strands and the stabilizing material were closely bonded.

When we measured the characteristics of a coil made using the superconducting wire with the joint obtained in this way, we found that the connection resistance of the connection was approximately 10-'''Ω or less, and in most cases to-'' Ω or less, and the critical current value of a superconducting wire having this connection portion is approximately 80% or more of the critical current value other than the connection portion. What is noteworthy is that the connection made by the connection method of the present invention has a significantly small variation in connection resistance;
When using the conventional method, the connection resistance was not constant, but this problem was completely resolved.

As a result of various studies on plastic working methods, it was found that isostatic pressing or a forming method using a mold with multiple pressing surfaces to assemble superconducting strands is extremely effective. According to this forming method, the more the superconducting wires are pressed, the more the superconducting wires gather toward the center of the stabilizer sleeve, improving the filling rate. It is also possible to control the filling rate. Adding vibrations such as ultrasonic waves when molding using a mold is effective in further increasing the filling rate.

Moreover, it is not possible to reduce the connection resistance and create a stable connection simply by connecting exposed superconducting strands. In other words, we focused on the fact that superconducting wires are protected by the surrounding stabilizing material to create a persistent current circuit, and it was necessary to clarify the relationship between the connecting parts and the stabilizing material. One of these is the need to find the ratio between the aggregated part of the superconducting strands to be connected and the safe running part around it. As a result of various studies, when the thickness in the cross section of the superconducting strand or the superconducting strand and other superconducting strands that are connection auxiliary materials is 1,
The cross-sectional thickness of the stabilizing material is preferably 7 or more, particularly 9 or more.

We also considered the length of the connection part. As a result, it was found that it is sufficient to wrap the superconducting wire with a stabilizing material having a length of 10 mm or more, particularly 15 mm or more, using the isotropic pressing method, although this is related to the quality of the connection of the superconducting wire. That is, in a typical example of the present invention, the superconducting strands are pressed by plastic working using isostatic pressure or by a device having multiple pressing surfaces, and the cross section of the stabilizing material around them is The connection is made so that the wall thickness l in the cross section of the superconducting wire including the auxiliary material to be connected is 7 or more, and the joining length is 15 nvn or more. Processing can be carried out at room temperature in the atmosphere, and cold metal joining can be performed by this method. After plastic working, it is preferable to further apply pressure or press to strengthen the contact between the superconducting strands.

Here, the unit superconducting wire may have a coil portion or may be simply linear. If wires are joined together, they become long electric wires.

The superconducting wires are gathered together at the center of the stabilizing material by plastic working, and the filling rate must be at least 80% or more, and the superconducting wires and surrounding stabilizing material must be separated after they are connected by plastic working. The wall thickness ratio in cross-sectional area should be lnea or more. Further, the cross-sectional area occupied by the core material is 1, assuming that the cross-sectional area of the superconducting strand or the superconducting strand and another superconducting strand that is a bonding auxiliary material (hereinafter, the latter is also simply referred to as a superconducting strand) is 1. The superconducting wire, the core material, and the stabilizing material are formed so that the cross-sectional thickness ratio is 1:0.3-5:7 or more, respectively. If the total cross-sectional area of the superconducting strands (in this case - does not include other superconducting strands that are bonding auxiliary materials) is 1 mm" or less, especially 0.5 in" or less, the filling of superconducting strands is necessary. Connection aids may be added to improve efficiency.

The material of the connection auxiliary material is the same wire material as the superconducting wire to be connected.
That is, Nb-Ti system, Nb, Sn system, etc., or stabilizing materials such as Cu, AQ, Ag, and Pb, Sn,
The use of a binder selected from Bi, In, etc. improves the filling rate. The shape can be selected from wire, powder, plating, thermal spraying, ion implantation, and vapor deposition.

Further, the stabilizing material for connection is selected from Cu, AQ, Au and Ag. Regarding the core material (:, u, AQ.

A single metal selected from Au and Ag, a composite metal thereof, a single metal selected from Pb, Sn, Bi, and In, or an alloy thereof is used.

As the plastic working method, connection is made using equipment selected from CIP (cold isostatic press), rolls, compressors, and the like. The device used is one equipped with a control mechanism for shaping the superconducting strands into a predetermined shape with a filling rate of 80% or more.

Application examples of MRI according to the present invention include nuclear fusion devices, nuclear magnetic resonance spectrometers (NMR), and the like.

NMR and M R' I are equipped with a shield, a liquid helium tank provided surrounding the shield, and a superconducting magnet disposed within the liquid helium tank, and the coil of the superconducting magnet is a superconducting magnet having the above-mentioned connection part. Consists of lines.

[Function] In the connection portion of the superconducting wire according to the present invention, the metal superconducting strands gather at the center of the connection stabilizing material by plastic working,
Since the filling rate of the wires is improved and they are closely connected, the proximity effect of the superconducting wires can be sufficiently obtained. A core material made of a low electrical resistance metal is inserted into the center of the exposed wire group, a wire group or a superconducting wire serving as a connection aid is placed on top of the core material, and then a cylindrical hollow is placed. By inserting the wire into the stabilizing material and applying isostatic pressure from the outer periphery, not only the filling rate of the wire group but also the ratio of the wire group to the surrounding stabilizing material is harmonized, and the proximity effect is also sufficiently obtained. A junction state with very low connection resistance loss can be easily achieved.

In order to sufficiently achieve the proximity effect, it is necessary to have tight adhesion between the wires. A strand of wire was inserted into the hollow part of the stabilizing material, and pressure was applied from the left and right sides using a split mold, etc., and the relationship between the pressure and the filling rate was investigated. When the connection resistance of the resulting joint was measured using the four-terminal method, it was found that a high critical current value could be obtained if the filling rate of the strands was 80% or more. If it is desired to obtain a more stable critical current value, it is preferable to set the filling rate to 90% or more.

Furthermore, in order to obtain a joint with low connection resistance loss, it is not possible to solve the problem by simply relying on the filling rate of the strands. The ratio of filling rate plus stabilizing material is important. The reason for this is that the ratio of the superconducting wire to the surrounding stabilizing material is important before connection. In the present invention, in order to approximate the superconducting wire before connection, we investigated the cross-sectional thickness ratio between the connected wire and the surrounding stabilizing material, and found that if the wire is 1, the stabilizing material should be 7 or more. , no decrease in critical current value was observed. The good range was 9-15. In addition, the cross-sectional area ratio of the core material is 0 to the cross-sectional area of the group of strands of 1.
．． 3-5, especially 0.5-1 is preferred.

In addition, there is a range in which a stable critical current can be maintained with respect to the length of the joint, and as a result of investigating the relationship between the joint length and the critical current value, it is related to the filling rate of the strands, but the filling rate is 80%.
If it is above, a joint length of 10 mm is good. An even better range is 20-25 m.

Further, a superconducting wire with a small critical current value has a small number of superconducting strands. If the number of strands is small, the filling rate between the strands will not improve. In order to ensure a filling rate of 80% or more, it is desirable that the cross-sectional area of all the connecting wires be 0.3 mm or more, especially 0.5 mm or more. It is preferable to add superconducting strands to improve the filling rate of the strands.

As for the materials for the bonding auxiliary material and the core material to improve the filling rate, as described above, metals with as high purity as possible are preferable, and it is even better if superconducting properties can be obtained in accordance with item 4.

Cu does not become superconducting.

'AQ, Au, Ag, etc. must have a high purity of at least 99.9%. 99.9% or more of other metals such as Pb and Sn are also applied.

It is desirable to use a cold isostatic pressure machine or a pressure device with double pressure surfaces as a device for joining. This is because the strands can be assembled and the strands and the stabilizer can be bonded together at the same time by applying pressure toward the center of the strands. Otherwise, it is formed into a predetermined shape by being sandwiched between rolls in the recess. It is also good to form the recessed metal into a cylindrical shape using a compressor.

〔Example〕

MRI, coil, and manufacturing method thereof according to the present invention will be described in detail below with reference to the drawings.

The basic structure of an MRI to which the present invention is applied and its circuit configuration are shown in FIGS. 1 and 2, respectively.

In FIG. 1, a plurality of superconducting coil units 1 are connected to adjacent coils at connecting portions 2 to form predetermined coil turns.

The coil is enclosed in a helium tank 3 and cooled to 4K. The helium tank 3 is surrounded by a heat insulating vacuum container 4, and a vacuum exhaust port 6 is attached to the heat insulating vacuum container 4. Injection pipe 10 for supplying liquid helium to helium tank 2, service port 1 for performing maintenance and inspection of the device
1. A power lead 9 is provided to connect to a power source.

FIG. 1 shows 1/2 of a cross section along the central axis of a cylindrical superconducting magnetic field generator.

Figure 2 shows the electric circuit of a superconducting coil, and the superconducting coil has coil units CIR, C2R, and C3R.

It is composed of connecting portions ① to O that connect the adjacent coil ends of OIL, C2L, and C3L, and a superconducting switch PC8.

The structure of these connections is shown in cross-sectional perspective views in FIGS. 3 and 4. In Figure 3, superconductivity @22,2
The end portion of the wire 2' was immersed in 60% HNO, and the stabilizing material 2o at that portion was removed to expose the superconducting wire I6. In the example shown in FIG. 3, there is an exposed superconducting wire 16 and a stabilizing material 18 inserted as a core material in the center of the superconducting wires 14 and 16 as a separately prepared connection auxiliary material.

The example shown in FIG. 4 includes only the superconducting wire 16 and is not combined with a stabilizing material for wire connection. That is, when the cross-sectional area of the superconducting strand group is 0.3 mm'' or more, particularly 0.5 m'' or more, connection can be made using only the superconducting strands.

The example shown in FIG. 5 is a quantification of the cross-sectional representation of the connection structure shown in FIG. 3, where l) is the core material and the wall thickness ratio is set to 1 as a reference.

ii) is a wire and 0.5 to 1.5.11) is a stabilizing material whose thickness ratio is 3 to 30. Also, ■) indicates the length of the connection part, and if it is set to 101 m1 to 30 mm, a connection with low resistance can be obtained.

FIG. 6 is a flowchart showing the connection method of the present invention.

In (a), the joint ends of superconducting wires 31 and 32 such as Nb-Ti metal superconducting wires are treated as described above to expose superconducting strands (filaments) 33, and pure copper is placed in the center of the assembly. plate (for example, 0.2I thickness 1.5mm x 25
mm length), and a separately prepared superconducting element wire 34 as a connection auxiliary material connected with a connecting wire (superconducting wire) 35 is placed over the gathering portion so as to surround it. As a result, the assembly shown in (C) is constructed. This assembly is covered with a copper sleeve and the assembly shown in (d) is assembled. Next, from the outer periphery of the copper sleeve, pressure is applied using a mold or the like to plastically process the superconducting strands 33, 3.
4 are assembled in the direction of the copper plate which is the core material, and as shown in (e), a copper sleeve is formed.

The superconducting wire, the superconducting wire for bonding assistance, and the core copper plate are brought into close contact with each other. In particular, the connection resistance can be significantly reduced by bringing the superconducting wires into direct and close contact with each other and by setting the filling rate to 80% or more.

Furthermore, in order to improve the bonding state, for example, if the obtained connection part is pressed from both the upper and lower directions and subjected to plastic working as shown in (f), the filling rate of the strands, the stabilizing material and the strands can be Adhesion can be further improved. After completing the joining work, cut off the connecting wire as necessary.

Observing the cross section of the central portion after bonding as described above, it can be seen that the superconducting strands and the superconducting strands for bonding alternately adhere to the outer periphery of the core material, increasing the filling rate.

The plastic working may be performed by isostatic pressure caulking or may be performed using a mold having a plurality of pressurizing surfaces.

When the bonding process is performed at room temperature, the strands are metallically bonded to each other, including the cleanliness of the strands before bonding, and as a result, there is a proximity effect to each other.

Figures 7 and 8 are cross-sectional views showing other embodiments, where Figure 7 (a) is a longitudinal cross-sectional view when superconducting wires are connected coaxially, and (b) is a plane perpendicular to the axis. FIG.

The manufacturing method for this joint is basically the same as the manufacturing method described above.

FIG. 8(a) is a sectional view in the longitudinal direction when a hollow copper pipe is inserted as a core material, and FIG. 8(b) is a sectional view in a plane perpendicular to the axis. In this case, either insert a stainless steel rod into the copper pipe, or use a copper rod to join them using the method described above, and then drill a hole in the center of the copper rod. In this way, the joint can be well cooled with liquid helium, so a joint with a large critical current value can be obtained.

<Example 1> The following embodiment will be explained using FIG.

Nb-Ti superconducting wire 31.32 has a diameter of 1. I chose Olm's. In one cross section, 24 metal superconducting strands 33 (75 μm in diameter) are embedded in the stabilizing steel. In order to expose the metal superconducting strands at the ends to be joined, they were immersed in nitric acid for about 30 minutes to remove the stabilizing copper and expose the metal superconducting strands, which were then washed with water.

On the other hand, the total bonding cross-sectional area of the superconducting wires is 0.2 mm.
”, so a bonding auxiliary material 34 made of the same Nb-Ti system as the superconducting strand was prepared in advance and wrapped around the bonding strand. The stabilizing copper of the bonding auxiliary material 34 was also removed in advance with nitric acid,
1060 exposed wires with a diameter of 35 μm (
A cross-sectional area of approximately 1.0 degrees 1) was used.

As shown in Figure 6(e), the thickness is 0.2 mm and the width is 1.5 mm.
.

Pure copper (oxygen-free steel) with a length of 25 mm was inserted into the center of the wire as a core material. Also, pre-made joining aids!
34 was placed around the wire group 33. Then Fig. 6(g)
As shown in Figure 2, it was inserted into a hollow part of stabilized copper with a diameter of 9.0 mm, an inner diameter of 2.2 ann, and a length of 25 m, placed in a mold, and molded by pressurizing with a compressor. Furthermore, plastic working was performed from the top and bottom of the stabilized copper sleeve to obtain a connection portion having a finished dimension of 7.2 to 6.8 na. The filling rate of the wires in the resulting connection was about 90%.

Further, the cross-sectional wall thickness ratio of the wire, core material, and stabilizing material in the central portion after joining is approximately 1:0.8:10. A cross-sectional view of the central portion after bonding is shown in FIG. 6(1).

<Example 2> The Nb-Ti based superconducting wires 31 and 32, the number of strands, etc. were made of the same materials as in Example 1, and the metal superconducting strands were exposed in the same manner. As in Example 1, an oxygen-free copper rod, diameter 1.0 + a + n, length 30 m is placed in the center of the wire group, and the joining auxiliary material is half of Example 1 because the core rod 11 is placed: diameter 3
The 530 wires (cross-sectional area: approximately 0.5 m') each having a diameter of 5 μm were used to wrap the strands arranged around the core rod. And cylindrical hollow stabilizing material/oxygen-free steel, outer diameter 9.0+a, inner diameter 2.2flI
! It was inserted into the hollow part of No. 11 as shown in FIG. 6(g).

Then, as in Example 1, pressure was applied in the direction of the center of the joint using a mold.
It was molded and further pressed in two directions, up and down, to obtain the connection part shown in FIG. 6(i). Finished dimensions are outer diameter 7.3~7. It was Omm. In this example, the cross-sectional area of the superconducting wires to be joined is 0.5. m', and it was thought that there was no need to use a joining auxiliary material, so only strands of wire were used.

The filling rate of the wires in the resulting connection was approximately 90%, which was sufficient for practical use.

Further, the ratio of the cross-sectional thicknesses of the wire, core material, and stabilizing material after bonding is approximately 1:0.5:12.

<Example 3> Nb-Ti superconductor #! 31 and 32 with a diameter of 1.7 m were selected. One cross section includes metal superconducting strands3. 1060 pieces with a diameter of 35 μm are embedded in the stabilized copper 4. In order to expose the metal superconducting strands at the joint portion, about 30 twn of the stabilized copper was removed with nitric acid and washed with water. Since the total cross-sectional area of this wire was 1.0+am'', no bonding aid was used. In order to further improve the critical current value, the diameter was 1.0 mm as in Example 2.

An oxygen-free steel rod with a length of 30 mm was inserted. It was inserted into the hollow part of the cylindrical hollow stabilizer made of oxygen-free steel and having an outer diameter of 9.0+NO+ and an inner diameter of 2.2mm. Thereafter, cold plastic working was performed using a mold. The finished outer diameter was 7.0 to 8.5 mm. The cross-sectional wall thickness ratio of the wire, core material, and stabilizing material thus joined was approximately 1:1:12.

<Comparative Example 1> The same superconducting wires 31 and 32 as in Example 1 were made by removing the stabilizing material at the joint portion to allow 25 mmjl of strands to protrude.

In this method, as shown in FIG. 6(b), the exposed superconducting strands 33 are stacked on top of each other and housed in a connecting copper sleeve, and are pressed from one direction through the connecting steel sleeve. The stored superconducting strands 33 are crimped and joined to each other. The filling rate of superconducting strands in the resulting connection was approximately 60%.

<Comparative Example 2> The same Nb-Ti based superconducting wires 31° 32 as in Example 1 with a diameter of 1.0 mm were selected, and other conditions were the same as in Example 1. The difference from Example 1 is the pressing method and the fact that a core material was not included, and crimping was performed from one direction using a compressor.

In other words, the cross-sectional view of the central part after bonding shows that the cross section of the bonded part obtained due to unidirectional pressure is rectangular, and the filling rate of the wires is about 70.
%Met.

Regarding the joined bodies joined and connected in the above examples and comparative examples, in liquid He without a magnetic field (OT) and in a magnetic field (1, OT)
The critical current value was measured when

The results are shown in FIG. For measurements, use a U-shaped holder.
The distance between the voltage terminals was measured at 15 mm. As can be seen from FIG. 9, the critical current values in the embodiments of the present invention are different, but this is due to differences in manufacturing methods and superconducting strands. There are also some variations within the same example, but this is due to measurements being made with various dimensions of the finished outer diameter of the stabilizing copper for connection. In any case, the critical current is higher than that of the comparative example, and the degree of variation is also small. These results show that the superconducting wire of the present invention is extremely superior.

We also created a persistent current circuit with a persistent current switch installed in the joint, and conducted an attenuation test on the connection.

The results are shown in FIG. As can be seen from Figure 10, examples 1, 2 and 3 show almost no current attenuation among the examples.
It is. Examples 1 to 3 demonstrate persistent current mode and therefore achieve the goal of the present invention.

The loop current ■ (shi) after a certain period of time in the persistent current circuit is determined by the following formula.

YuI(t)=I. e ′ where 1. is the initial loop current value (A), τ is the decay time constant of the circuit, and is the time. τ is determined by the following formula.

(Here, R is the circuit resistance and L is the inductance.) The decay time constant of persistent current circuit was measured experimentally.

The circuit used in the experiment is a well-known circuit consisting of a superconducting coil, a power source that supplies current to it, a persistent current switch connected in parallel to the power source and in series with the coil, and a power source and superconducting coil. It consists of a power switch that turns on and off. First, a current is passed from the power supply to the superconducting coil cooled to 4K, and when a superconducting state is formed, the persistent current switch is turned on and the power switch is turned off. At this stage 1
゜ and measure the decay time constant. L=0.5μH2τ
= 5 x 10' seconds, then R was 10-1 Ω. Also, L=108. If τ=101 seconds, R is 10−“
Ω, which was a very small value.

On the other hand, it can be seen that in Comparative Example 1, the attenuation was large and the connection was not good. In Comparative Example 2, the initial current was quite good, but the current value decreased slightly over time. This indicates that there is a slight resistance at the connection. It is clear that the superconducting wire of the present invention is also excellent in this joint damping test. Further, when the cross section of the joint was observed, it was found that the joint according to the present invention had a substantially elliptical shape, and the superconducting wire and the superconducting wire were brought close to each other through the cylindrical hollow stabilizing material for connection, and the metal bonding was good.

Various joining examples have been given above, and in all of them, the superconducting wire, the superconducting element wire, or the core material is metallurgically joined via the cylindrical hollow stabilizing material for connection, and a superconducting wire with extremely low connection resistance can be obtained. In the embodiment, an example using a 0.5T superconducting material has been described, but the present invention can also be applied to a superconducting wire with a high magnetic field, and a superconducting wire with extremely low connection resistance can be obtained.

As other cylindrical hollow stabilizing materials for connection, aluminum, ram, gold, silver, etc. can be used, and as the 8 rod, aluminum, gold, silver, or alloys thereof, Pb-3n
In, Bi, etc. can also be applied. Further, the present invention can be achieved as long as the device is a roll machine, a cold isostatic pressure machine, or the like that can apply pressure from the outer periphery of the cylindrical hollow stabilizing member for connection or from the other direction toward the center.

〔Effect of the invention〕

According to the superconducting magnetic field generating device according to the present invention, since the connection resistance of the connecting portion of the superconducting wire is very small and the critical current value is also large, it is possible to generate a magnetic field stably for a long time.

The present invention can be applied to various electromagnets, NMRl, nuclear fusion magnets, etc.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing the configuration of MRI according to the present invention;
Fig. 2 is a circuit diagram showing the structure of a superconducting coil, Figs. 3 and 4 are perspective views showing the structure of a superconducting wire connection part according to the present invention, and Fig. 5 shows a wall thickness ratio of a superconducting wire connection part. Perspective view,
FIG. 6 is a process diagram showing a method for connecting superconducting wires according to the present invention, FIGS. 7 and 8 are cross-sectional views of main parts showing different embodiments of the present invention, and FIG. 9 is a connection section according to the present invention and a comparison. FIG. 10 is a graph showing the critical current characteristics of the connection according to the present invention and the loop current attenuation characteristic of the connection according to the comparative example. 22.22', 31.32...Superconducting wire, 16°3
3... Metal superconducting wire, 20... Stabilizing material, 18.
・・Calculation of $7 8 Figure U (b) l Otsu (b) Kashizaki-”?A S Yun-°〉l-iE

Claims (13)

[Claims] 1. A coil configured by winding a superconducting wire formed by connecting the ends of a superconducting wire in which a plurality of superconducting wires are embedded in a stabilizing material, and a superconducting switch connected to both ends of the coil. , a nuclear magnetic resonance imaging apparatus having means for cooling the coil and the superconducting switch, wherein the group of superconducting wires of the connecting portion is buried in a dense group in the center of the stabilizing material, and there is no space between the wires. are in direct contact with each other, a stabilizing material is present in the center of an assembly of strands, and the stabilizing material and the strands are tightly joined. . 2. A coil formed by winding a superconducting wire formed by connecting the ends of a superconducting wire in which a plurality of superconducting wires are embedded in a stabilizing material, and a superconducting switch connected to both ends of the coil, In the nuclear magnetic resonance imaging apparatus having a means for cooling the coil and the superconducting wire switch, a group of superconducting wires and another group of superconducting wires are densely gathered and buried in a central portion of the stabilizing material at the connecting portion. The core is characterized in that the strands are in direct contact with each other, a stabilizing material is present in the center of the aggregate of the strands, and the stabilizing material and the strands are tightly joined. , magnetic resonance imaging equipment. 3. A coil configured by winding a superconducting wire formed by connecting the ends of a superconducting wire in which a plurality of superconducting wires are embedded in a stabilizing material, and a superconducting switch connected to both ends of the coil. , in a nuclear magnetic resonance imaging apparatus having a means for cooling the coil and a superconducting wire switch, the connecting portion has a connection resistance of 10^-^1^3 Ω or less, and 80% of the critical current of the superconducting wire. A nuclear magnetic resonance imaging diagnostic apparatus characterized by having a critical current value of or above. 4. Nuclear magnetic resonance imaging diagnosis in which superconducting wires are connected to each other at the coil end of a coil unit formed by winding a superconducting wire in which a large number of superconducting wires are embedded in a stabilizing material to form a predetermined coil turn. In the device, the superconducting strands of the connection part are buried in a stabilizing material, and are densely gathered in the center of the stabilizing material so that the strands are in direct contact with each other, and the strands are in direct contact with each other in the center of the assembly of strands. There is a low resistance metal material in the central part, and they are close to each other and the thickness ratio in the cross section is 0.5 to 1.5 if the low resistance metal material in the center is 1. A superconducting coil characterized in that the stabilizing material, the metal material, and the wire are closely joined so that the number of the materials is 3 to 10. 5. Nuclear magnetic resonance imaging diagnosis in which superconducting wires are connected to each other at the coil end of a coil unit formed by winding a superconducting wire in which multiple superconducting wires are embedded in a stabilizing material to form a predetermined coil turn. In the device, a group of superconducting strands of the connection portion and a group of superconducting wires for connection are embedded in the stabilizing material, and are densely gathered in the center of the stabilizing material so that the strands are in direct contact with each other, A low-resistance metal material exists in the center of a collection of strands, and they are close to each other, and the thickness ratio in cross-section is 0.5 when the low-resistance metal material in the center is 1. ˜1.5, and the stabilizing material, the metal material, and the strands are tightly bonded so that the stabilizing material has a weight of 3 to 10. 6. Nuclear magnetic resonance imaging diagnosis formed by winding a superconducting wire constructed by connecting the end of a superconducting wire in which many superconducting wires are embedded in a stabilizing material to the end of another superconducting wire. In the device, the superconducting coil is characterized in that the connecting portion has a connection resistance of 10^-^1^3 Ω or less and a critical current value of 80% or more of the critical current value of the superconducting wire. 7. In a nuclear magnetic resonance imaging diagnostic apparatus in which a plurality of superconducting strands are embedded in a stabilizing material, and the superconducting strands at the ends of the superconducting strands are connected to the strands at the ends of other superconducting wires, the superconducting strands at the connection part The groups are embedded in a stabilizing material, and are densely gathered in the central part of the stabilizing material so that the strands are in direct contact with each other, and a low-resistance metal material is placed in the center of the aggregate of the strands. exists, the stabilizing material, the metal material, and the wire are closely bonded to each other, the connection portion has a connection resistance of 10^-^1^3Ω or less, and the critical current value of the superconducting wire is 80 of
A superconducting wire characterized by having a critical current value of % or more. 8. Winding the superconducting wire to form a desired turn;
exposing a group of superconducting strands at an end of the superconducting wire;
arranging a core material of a stabilizing material in the center of the group of wires;
Inserting the superconducting wire group and the core material into a hollow part of a stabilizing material having a hollow part, and gathering the exposed superconducting wires in the direction of the core material by applying pressure from the outer periphery of the hollow stabilizing material. A method for manufacturing a superconducting coil, characterized in that the hollow stabilizing material and the core material are closely joined to the superconducting strands, and the strands are brought into close contact with each other. 9. A step of winding a superconducting wire in which a plurality of metal superconducting wires are embedded in a stabilizing material to form a coil, and winding the metal superconducting wire exposed at the connection end of the superconducting wire of the coil into another A step of assembling the exposed superconducting strands to be connected and the connection auxiliary material by placing a core material made of a stabilizing material in the center; A step of inserting the hollow stabilizing material into the hollow part, applying pressure from the outside of the hollow stabilizing material to plastically process the collecting part, and collecting the superconducting wires in the central part of the hollow stabilizing material. A method for manufacturing a coil of superconducting wire, comprising the steps of tightly joining a core material and the hollow stabilizing material to the superconducting wire, and bringing the superconducting wires into direct contact with each other. 10. A plurality of metal superconducting strands are embedded in a stabilizing material.The metal superconducting strands exposed at the connecting end of a superconducting wire are connected to the exposed strands at the connecting ends of other superconducting wires around the stabilizing core material. a step of inserting the assembled superconducting strands and the ends of the superconducting wires into the hollow part of the hollow stabilizing material, plastic working the inserted gathering part, and inserting the superconducting strands into the hollow stabilizing material. At the same time, the core material and the hollow stabilizing material are tightly joined to the superconducting strands, and the superconducting strands are brought into direct contact with each other. If the low resistance metal material is 1, its strand group is 0.
．． 5 to 1.5, and a stabilizing material of 3 to 10. 11. 11. The method for connecting superconducting wires according to claim 10, wherein the connection auxiliary material is selected from a superconducting wire made of the same material as the wire, a stabilizing material, and a binding material. 12. 11. The method for connecting superconducting wires according to claim 10, wherein the connection auxiliary material is a wire rod or powder. 13. In claim 10, the core material is Cu, Al, A.
A method for connecting superconducting wires made of u, Ag, or their alloy metals.