JP2020191214A - Superconducting wire, method for manufacturing superconducting wire, superconducting magnet and magnetic resonance imaging apparatus - Google Patents

Abstract

To provide a super conducting wire having high local bending resistance, a method for manufacturing a superconducting wire, a superconducting magnet and a magnetic resonance imaging apparatus.SOLUTION: A superconducting wire 100 according to the present invention has: a superconducting filament 21; a metal sheath 22 coating the superconducting filament 21; a wire main portion 1 having a metal base material 23 coating the metal sheath 22; and a strain resistance reinforced- portion 2 which has, in an arbitrary portion including the wire main portion 1, an allowable tensile strain 0.01% higher than that of the other portion. The manufacturing method according to the present invention includes: a precursor manufacturing step S1 of manufacturing the precursor of the superconducting material 100; and a heat treatment step S2 of heat-treating the precursor thereby manufacturing the superconducting wire 100, wherein the heat treatment step S2 has a first heat treatment step of performing heat treatment thereby forming the wire main portion 1, and a second heat treatment step of performing heat treatment thereby forming the strain resistance-reinforced portion 2, wherein a heat treatment temperature in the second heat treatment step is higher than a heat treatment temperature in the first heat treatment step.SELECTED DRAWING: Figure 1

Description

The present invention relates to a superconducting wire, a method for manufacturing a superconducting wire, a superconducting magnet, and a magnetic resonance tomography apparatus.

When a strong and stable magnetic field is required in a magnetic resonance tomography apparatus (MRI apparatus) or the like, a desired magnetic field is obtained by energizing a superconducting coil with a current that is hardly attenuated. When an electromagnet is manufactured from a copper wire, the current density per cross-sectional area of the copper wire is about several A / mm ² , but in the case of a superconducting coil, a high current density of about several hundred A / mm ² can be obtained. it can. Therefore, the superconducting coil can generate a strong magnetic field with a coil having a small physique.

NbTi wire rods, which are low-temperature superconducting wire rods, are mainly used for conventional superconducting coils, but since the operating temperature is as low as about 4 Kelvin (K), cooling with liquid helium is mainly required. With the recent tightness of helium reception, superconducting wires that do not require liquid helium and can be used at high temperatures have been developed.

As superconducting wires that do not require liquid helium, Nb ₃ Sn superconducting wires, bismuth-based oxide superconducting wires, rare earth-based oxide superconducting wires, and MgB ₂ superconducting wires (simply called "MgB ₂ wires") may be used. ). Except for rare earth oxide superconducting wires, these production methods are generally roughly divided into two types. One is a method called a wind-and-react method, which is a method in which a precursor of a superconducting wire is wound into a coil and then heat-treated. The other is a method called the reactor-and-wind method, which is a method of winding a heat-treated superconducting wire into a coil.

The heat-treated superconducting wire has an allowable bending radius. If the superconducting wire is bent with a curvature smaller than the allowable bending radius, the superconducting characteristics will deteriorate. Therefore, the permissible bending radius is a constraint on the design and manufacture of superconducting coils using superconducting wires.

Here, MgB ₂ wire rod is shown as an example. For example, as described in Non-Patent Document 1, the allowable tensile strain when a tensile load or a bending load is applied to a heat-treated MgB ₂ wire rod at room temperature is about 0.2%. Therefore, when the heat-treated MgB ₂ wire is wound around to produce a superconducting coil, there is a concern that tension or bending of the wire may exceed the tensile strain allowed for the MgB ₂ wire and reduce its superconducting characteristics. .. As described in Non-Patent Document 1, the performance degradation due to bending of the MgB ₂ wire material is produced by strain applied to the MgB ₂ filaments are encapsulated in MgB ₂ wire material exceeds the allowable value. Strain applied to the MgB ₂ filaments due to bending of the MgB ₂ wire material, the distance from the bending neutral line of the filament, is generally proportional to the distance between the center of the filament and MgB ₂ wire material. Therefore, either in order to reduce the allowable bending radius places the MgB ₂ filaments only the center of the MgB ₂ wire material, but may be thinner overall MgB ₂ wire member, the area of the MgB ₂ filaments decreases in these solutions Therefore, the critical current value of the MgB ₂ wire rod is extremely lowered.

Hideki Tanaka et al., “Tensile and Bending Stress Tolerance on Round MgB2 Wire Made By In Situ PIT Process”, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 28, NO. 4, JUNE 2018.

Solenoid coil shapes are often used in superconducting coils and superconducting magnets, which are the main application devices for superconducting wires. In that case, the bending radius of the main winding portion forming the coil is approximately constant. On the other hand, for example, since the lead portion of the superconducting wire goes toward the connection to the electrode and other coils, it may be bent in a direction different from the winding direction of the main winding portion, or the bending radius of the main winding portion. It is necessary to bend with a tighter curvature than. If the outlets at both ends are bent with the same curvature as the main winding, the coil shape is limited, for example, the entire superconducting coil becomes large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a superconducting wire having high bending resistance locally, a method for manufacturing the superconducting wire, a superconducting magnet, and a magnetic resonance tomography apparatus. ..

The superconducting wire rod according to the present invention that solves the above problems includes a superconducting filament that conducts an electric current, a metal sheath that coats the superconducting filament, a wire rod main portion having a metal base material that coats the metal sheath, and the wire rod. It has a strain resistance strengthening portion in which the allowable tensile strain is 0.01% or more higher than that of other portions at any portion including the main portion.

According to the present invention, it is possible to provide a superconducting wire having high bending resistance locally, a method for producing a superconducting wire, a superconducting magnet, and a magnetic resonance tomography apparatus.
Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is a conceptual diagram explaining the overall structure of the superconducting wire rod which concerns on this embodiment. FIG. 2 is a cross-sectional view taken along the line IIa-IIa in FIG. It is an enlarged view of part IIb in FIG. 2A. It is a flowchart which shows an example of the preferable manufacturing method of the superconducting wire rod which concerns on this embodiment. It is a conceptual diagram explaining the state of heat-treating the superconducting wire material which concerns on this embodiment. It is a graph explaining an example of the transition of the heat treatment temperature of the first heat treatment step (upper graph) and the transition of the heat treatment temperature of the second heat treatment step (lower graph). It is a superconducting characteristic graph of a superconducting wire having a wire main part and a strain resistance strengthening part. It is a graph explaining another example of the temperature transition of the main part of the wire rod (upper graph) and the temperature transition of the strain resistance strengthening part (lower graph). It is a graph explaining another example of the temperature transition of the main part of the wire rod (upper graph) and the temperature transition of the strain resistance strengthening part (lower graph). It is a conceptual diagram explaining the state of manufacturing a superconducting wire after winding the precursor of the main part of a wire around a bobbin into a coil shape. It is a conceptual diagram explaining the mode of protecting the main winding part by using a heat removing device at the time of performing a 2nd heat treatment step. When it is predetermined to bend the superconducting wire in a specific direction at a specific position, the second heat treatment step is performed with the heat radiating member in thermal contact in the bending inner direction of the strain resistance strengthening portion. It is a schematic cross-sectional view explaining. It is schematic cross-sectional view explaining superconducting magnet using superconducting wire rod. It is schematic cross-sectional view explaining the magnetic resonance tomography apparatus using a superconducting magnet (that is, using a superconducting wire).

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Since the drawings referred to in the following description schematically show an embodiment, the scale, spacing, positional relationship, etc. of the members are exaggerated or deformed, or a part of the members is not shown. There may be. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various changes and modifications by those skilled in the art are possible within the scope of the technical ideas disclosed herein. Further, in all the drawings for explaining the present invention, those having the same function are designated by the same reference numerals, and the repeated description thereof may be omitted.
The "~" described in the present specification is used to mean that the numerical values described before and after it are used as the lower limit value and the upper limit value. In the numerical range described stepwise in the present specification, the lower limit value or the upper limit value described in one numerical range may be replaced with the lower limit value or the upper limit value described in another stepwise.

[Superconducting wire]
FIG. 1 is a conceptual diagram illustrating the overall configuration of the superconducting wire 100 according to the present embodiment. FIG. 2A is a cross-sectional view taken along the line IIa-IIa in FIG. Note that FIG. 2A shows the cross section of the superconducting wire 100 having a circular cross-sectional shape and eight superconducting filaments 21, but the cross-sectional shape and the number of superconducting filaments 21 are not limited to this. FIG. 2B is an enlarged view of part IIb in FIG. 2A.

As shown in FIG. 1, the superconducting wire rod 100 has a wire rod main portion 1 and a strain resistance strengthening portion 2. As shown in FIG. 2A, the superconducting wire 100 has a superconducting filament 21, a metal sheath 22, a metal base material 23, and a metal sheath outermost layer 24 throughout. The superconducting filament 21, the metal sheath 22, the metal base material 23, and the outermost layer 24 of the metal sheath can be formed of a known material used for a general superconducting wire. Regarding the superconducting wire 100, when it is difficult to distinguish the superconducting filament 21, the metal sheath 22, the metal base material 23, and the outermost layer 24 of the metal sheath at first glance, the cross section is etched under arbitrary conditions. The interface becomes clearly distinguishable.

Here, the superconducting filament 21 has a function of energizing an electric current. The superconducting filament 21 can be formed of Nb ₃ Sn, a bismuth-based oxide, a rare earth-based oxide, MgB _2, or the like, and is preferably formed of MgB ₂ . When the superconducting filament 21 is formed of MgB ₂ , a superconducting wire 100 that does not require liquid helium and can be used at a high temperature can be obtained at a relatively low cost.
The metal sheath 22 covers the superconducting filament 21. The metal sheath 22 can be formed of, for example, niobium, iron, stainless steel, or the like.
The metal base material 23 fills the space between the metal sheath 22 and the outermost layer 24 of the metal sheath and contributes to maintaining the strength of the superconducting wire 100. The metal base material 23 can be formed of, for example, copper, iron, stainless steel, or the like.
The outermost layer 24 of the metal sheath contributes to prevention of scratches on the wire and maintenance of strength. The outermost layer 24 of the metal sheath can be formed of, for example, copper, iron, stainless steel, a copper alloy, or the like.

Since the superconducting wire 100 has a length of several kilometers, it is generally heat-treated after being coiled around a bobbin B (see FIG. 9). That is, most of the wire rod main portion 1 corresponds to a coiled portion wound around the bobbin B. In the present specification, the coiled portion of the superconducting wire 100 may be referred to as the main winding portion 1a.

The strain resistance strengthening portion 2 can be provided at any position including the wire rod main portion 1, but as shown in FIG. 1, it is particularly preferable to provide the strain resistance strengthening portion 2 other than the main winding portion 1a. For example, the strain resistance strengthening portion 2 can be suitably provided at any portion as long as it extends from the main winding portion 1a. It is preferable that the strain resistance strengthening portion 2 is provided with a desired length toward the main winding portion 1a with the position 2b separated from the end face 2a by 20 cm or more as a base point. In other words, it is preferable that the strain resistance strengthening portion 2 is not provided in a range of less than 20 cm from the end face 2a. This is because the end portion of the strain resistance strengthening portion 2 is connected to other wire rods, terminals, etc., and therefore it is preferable to use the high superconducting characteristics of the main winding portion 1a as it is in consideration of connectivity. The strain resistance strengthening portion 2 can be provided at one or more locations in one wire rod.

The strain resistance strengthening portion 2 in the present embodiment has a allowable tensile strain higher than other portions by 0.01% or more at any portion including the wire rod main portion 1. That is, in the present embodiment, one superconducting wire 100 has at least one portion where the permissible tensile strain is locally higher than that of the main portion 1 of the wire by 0.01% or more. .. As a result, the superconducting wire 100 according to the present embodiment has high bending resistance locally. Therefore, in the present embodiment, the bending resistance of the strain resistance strengthening portion 2 is higher than that of the wire rod main portion 1, and the bending can be performed with a curvature (smaller curvature) than the bending radius of the main winding portion 1a. Therefore, the superconducting wire 100 can be bent at the strain resistance strengthening portion 2 with a bending radius smaller than that of the wire main portion 1, and for example, the degree of freedom in designing and manufacturing the superconducting coil 5 (see FIG. 9) is improved. To do. From this point of view, the allowable tensile strain of the strain resistance strengthening portion 2 is preferably higher than the allowable tensile strain of the wire rod main portion 1, and is not particularly limited, but is 0.02% or more and 0.03%. As mentioned above, it is preferably 0.04% or more, 0.05% or more, and the like. The higher the allowable tensile strain of the strain resistance strengthening portion 2 is higher than the allowable tensile strain of the wire rod main portion 1, the stricter the heat treatment conditions for obtaining the strain resistance strengthening portion 2, which may lead to deterioration of superconducting characteristics. is there. Therefore, the upper limit of the allowable tensile strain of the strain resistance strengthening portion 2 is preferably 0.3% higher than the allowable tensile strain of the wire rod main portion 1, and more preferably 0.2% higher. It is preferable that the upper limit is 0.1% higher.
The strain resistance strengthening portion 2 can be suitably formed by performing the heat treatment step S2 described in the manufacturing method described later.

The allowable tensile strain can be measured by any of the following methods (1) and (2).
(1) By applying a tensile load, it is possible to measure the critical tensile strain in which the superconducting characteristics do not deteriorate. Specifically, a plurality of short superconducting wires (several tens of millimeters to 100 millimeters in length, hereinafter referred to as "samples"), which are approximately linear, are prepared, and tensile strain of each size is applied to each sample. Normally, it is difficult to directly measure the tensile strain applied to the superconducting filament 21, but by attaching an extensometer or strain gauge to the sample surface and pulling it, the tensile strain of the superconducting filament 21 is measured as the tensile strain of the sample. can do. Then, the critical current of the sample is measured at an extremely low temperature to evaluate the critical current value and the n value, and the tensile strain limit value in which these performances are deteriorated is obtained.

(2) By applying a bending load, it is possible to measure the critical tensile strain and the critical compressive strain in which the superconducting characteristics do not deteriorate. Specifically, a plurality of short superconducting wires (several tens of millimeters to 100 millimeters in length, hereinafter referred to as "samples") having a substantially linear shape are prepared, and bending loads having different bending radii are applied to each sample. At this time, compressive strain is applied to the inside of the bending of the sample, and tensile strain is applied to the outside of the bending of the sample. The maximum tensile strain and maximum compressive strain applied to the superconducting filament 21 are determined by the longest distance from the bending center line (usually the thickness center in the bending radius direction of the sample) and the bending radius. That is, the maximum tensile strain is applied to the superconducting filament 21 in the most bending outer direction from the bending center line, and the maximum compressive distortion is applied to the superconducting filament 21 in the bending innermost direction from the bending center line. Then, the critical current of the sample is measured at an extremely low temperature to evaluate the critical current value and the n value, and the tensile strain limit value or the compression strain limit value whose performance is deteriorated is obtained.
Further, when a bending load is applied, it is also possible to observe the cross section of the sample whose characteristics have deteriorated due to the bending load and determine whether the deterioration is due to tensile strain or compressive strain. For example, in the case of deterioration due to tensile strain, rupture of the filament is observed in the superconducting filament 21 in the bending outer direction. Further, in the case of deterioration due to compression strain, buckling of the filament is observed in the superconducting filament 21 in the bending inner direction.

Here, a specific example in which one superconducting wire (MgB ₂ wire) is heat-treated at different heat treatment temperatures to improve strain resistance will be described.
[A] as shown in Non-Patent Document 1, the limit tensile strain of MgB ₂ wire material heat-treated at 600 ° C. was about 0.2%. The limit tensile strain was measured by both the methods (1) and (2) described above, and both were about 0.2%.
[B] On the other hand, the limit tensile strain at the portion where a part of the wire was heat-treated at 700 ° C. and 800 ° C. was about 0.3% and about 0.4%, respectively. That is, the limit tensile strain at the portion where a part of the wire is heat-treated at 700 ° C. and 800 ° C., respectively, is about 0.1% and 0.2% higher than that shown in Non-Patent Document 1. It was. These limit tensile strains were measured by the method (2) described above.
From the above [A] and [B], it was confirmed that the critical tensile strain was improved, that is, the allowable tensile strain was improved by raising the heat treatment temperature. Specifically, it was found that the critical tensile strain improves by about 0.05% as the heat treatment temperature increases by 50 ° C. (50K).

Further, when the superconducting filament 21 of the superconducting wire 100 is formed of MgB ₂ , the superconducting wire 100 is placed between the superconducting filament 21 and the metal sheath 22 other than MgB ₂ as shown in FIG. 2B. In many cases, an intermediate layer 25 having the above boron compound or magnesium compound is formed. For example, using the MgB ₂ superconducting filaments 21, when using the iron metal sheath 22, the intermediate layer 25 is formed mainly consisting of Fe ₂ B. Such an intermediate layer 25 grows by heat treatment at a high temperature or heat treatment at a long time. Therefore, as described above, when the strain resistance strengthening portion 2 is subjected to the second heat treatment temperature T2 (see FIGS. 5, 7, and 8), the extent to which the main portion 1 of the wire rod is affected by the preliminary trial production is performed. You can check. That is, by observing the cross section of the superconducting wire 100 after the heat treatment and tracing the thickness t ₂₅ of the intermediate layer 25 in the longitudinal direction of the wire, the portion affected by the second heat treatment temperature T2 can be confirmed.

Then, as shown in FIG. 2B, in the superconducting wire 100, the thickness t ₂₅ of the intermediate layer 25 in the strain resistance strengthening portion 2 is 1.2 times or more the thickness t ₂₅ of the intermediate layer 25 in the wire main portion 1. Is preferable. In such an aspect, the position of the strain resistance strengthening portion 2 can be easily confirmed. Further, the allowable tensile strain in the strain resistance strengthening portion 2 can be more reliably increased by 0.01% or more as compared with that in the wire rod main portion 1.

[Preferable manufacturing method of superconducting wire 100]
Next, a suitable manufacturing method of the superconducting wire 100 (hereinafter, may be simply referred to as “the present manufacturing method”) will be described. In the description of the present manufacturing method, the same components as those already described may be designated by the same reference numerals, and the description thereof may be omitted. Further, the present manufacturing method described below is merely an example for suitably manufacturing the above-mentioned superconducting wire 100, and is not limited to the following.

FIG. 3 is a flowchart showing an example of a suitable manufacturing method of the superconducting wire 100.
As shown in FIG. 3, this manufacturing method includes a precursor manufacturing step S1 and a heat treatment step S2, and these steps are performed in this order.

(Precursor preparation step S1)
In the precursor production step S1, the raw material of the superconducting filament 21 is coated with the metal sheath 22, and the metal sheath 22 is coated with the metal base material 23 to produce a precursor (not shown) of the superconducting wire 100. In the precursor manufacturing step S1, for example, a predetermined number of materials obtained by inserting the raw materials of the columnar superconducting filament 21 into the cylindrical metal sheath 22 are prepared, and these are placed around the columnar center material (not shown). It is preferably arranged at equal intervals. The central material is the metal base material 23. Then, while maintaining that state, they are inserted into the outermost layer 24 of the cylindrical metal sheath. Then, in this precursor manufacturing step S1, it is drawn by drawing or the like to prepare a precursor of the superconducting wire 100.

(Heat treatment step S2)
In the heat treatment step S2, the produced precursor is heat-treated to produce the superconducting wire 100. The heat treatment step S2 includes a first heat treatment step (not shown) for forming the wire rod main portion 1 by heat treatment and a second heat treatment step (not shown) for forming the strain resistance strengthening portion 2 by heat treatment. Have. In the present embodiment, the heat treatment temperature of the second heat treatment step is performed under conditions higher than the heat treatment temperature of the first heat treatment step. In this way, the allowable tensile strain of the strain resistance strengthening portion 2 can be made 0.01% or more higher than the allowable tensile strain of the wire rod main portion 1. The heat treatment temperature in the second heat treatment step is preferably 50 K or more higher than the heat treatment temperature in the first heat treatment step. By doing so, the allowable tensile strain of the strain resistance strengthening portion 2 can be more reliably increased by 0.01% or more, preferably 0.05% or more, than the allowable tensile strain of the wire rod main portion 1. it can. It is more preferable that the heat treatment temperature in the second heat treatment step is 100 K or more higher than the heat treatment temperature in the first heat treatment step. In this way, the allowable tensile strain of the strain resistance strengthening portion 2 can be made 0.1% or more higher than the allowable tensile strain of the wire rod main portion 1. The heat treatment temperature in the second heat treatment step can be made 0.2% higher than the allowable tensile strain of the wire rod main portion 1 by making it 200 K higher than the heat treatment temperature in the first heat treatment step.

The heat treatment step S2 can be performed as follows.
Note that FIG. 4 is a conceptual diagram illustrating a state in which the superconducting wire 100 is heat-treated. FIG. 5 is a graph illustrating an example of a transition of the heat treatment temperature in the first heat treatment step (upper graph) and a transition of the heat treatment temperature in the second heat treatment step (lower graph).

As shown in FIG. 4, the wire rod main portion 1 is coiled and heat-treated by the first heating device 3 at the first heat treatment temperature T1 (FIG. 5), and the strain resistance strengthening portion 2 is integrated without being separated from the wire rod main portion 1. As it is, it is heat-treated by the second heating device 4 at the second heat treatment temperature T2 (FIG. 5). Note that FIG. 4 shows a shape in which the strain resistance strengthening portion 2 is linearly extended away from the main winding portion 1a. For example, the strain resistance strengthening portion 2 is coiled from the coil-shaped main winding portion 1a. It is also possible to heat-treat the material away from the axial direction.

Then, in the heat treatment step S2, as shown in FIG. 5, the first heat treatment step and the second heat treatment step can be carried out at the same time. Assuming that the heat treatment temperature maintenance start time in the first heat treatment step and the second heat treatment step is t1 and the heat treatment temperature maintenance end time is t2, the wire main part 1 is the first over the heat treatment temperature maintenance start time t1 and the heat treatment temperature maintenance end time t2. The heat treatment temperature is maintained at T1. At the same time, the strain resistance strengthening portion 2 is maintained at the second heat treatment temperature T2 over the heat treatment temperature maintenance start time t1 to the heat treatment temperature maintenance end time t2. After reaching the heat treatment temperature maintenance end time t2, the wire rod main portion 1 and the strain resistance strengthening portion 2 are cooled toward room temperature T3. Here, the second heat treatment temperature T2 is higher than the first heat treatment temperature T1. The first heat treatment temperature T1 is a temperature sufficient to smooth the precursor of the superconducting wire 100 into a superconductor. Generally, since the superconducting filament 21 is covered with the metal sheath 22, the metal base material 23, the outermost layer 24 of the metal sheath, and the like, the metal sheath 22, the metal base material 23, and the like as the cooling toward room temperature T3 after the heat treatment occurs. And compression strain is applied by heat shrinkage of the outermost layer 24 of the metal sheath. Since the thermal expansion coefficient of the metal is about ^10-5 / ° C., for example, when the second heat treatment temperature T2 is 50 K higher than the first heat treatment temperature T1, the superconducting wire material heat-treated at the second heat treatment temperature T2. The superconducting filament 21 of 100 is subjected to a compressive strain up to about 0.05% higher than that of the superconducting filament 21 heat-treated at the first heat treatment temperature T1. As a result, when the heat treatment is performed with such a temperature difference, the allowable tensile strain is as high as 0.05% at the maximum. As these temperature differences increase, the allowable tensile strain also increases. For example, when the temperature difference is 100K, it can be increased by about 0.1%, and when the temperature difference is 200K, it can be increased by about 0.2%. The effect of improving the allowable tensile strain obtained by the second heat treatment step is 0.2% to 0.4%, which is the allowable tensile strain of the general superconducting wire 100 (that is, the allowable tensile strain 0.2 of the main part 1 of the wire). % To 0.4%), and it can be said that the improvement rate is remarkable from the viewpoint of improving the bending resistance of the superconducting wire 100.

FIG. 6 shows a superconducting characteristic graph of the superconducting wire 100 having the wire main part 1 and the strain resistance strengthening part 2. Generally, under the heat treatment conditions of the superconducting wire 100, the main part 1 of the wire is heat-treated under the condition where the critical current is the highest after considering the temperature and time. Therefore, the critical current characteristic 61 of the wire rod main portion 1 that has experienced the first heat treatment temperature T1 shown by the solid line in FIG. 6 is the criticality of the strain resistance strengthening portion 2 that has experienced the second heat treatment temperature T2 shown by the broken line in FIG. Compared with the current characteristic 62, the critical current value for the same empirical magnetic field is higher. Here, since the two are used in a single coil shape or an extension thereof without being separated, it is easy to distinguish between them by comparing the upper limits of the empirical magnetic fields in which the respective superconducting characteristics are equal to or higher than the critical current value Ic. Can be attached. Specifically, as shown in FIG. 6, the empirical magnetic field upper limit B1 of the wire rod main part 1 that experienced the first heat treatment temperature T1 and the empirical magnetic field upper limit B2 of the strain resistance strengthening part 2 that experienced the second heat treatment temperature T2. Has a relationship of B1> B2. Further, from this, it is preferable to use the strain resistance strengthening portion 2 having the strengthened bending resistance in a region where the magnetic field strength is lower than that of the wire rod main portion 1. In general, the magnetic field distribution of the solenoid coil-shaped superconducting coil 5 (see FIG. 9) can be easily calculated. The portion having the highest magnetic field strength is the innermost layer of the main winding portion 1a, and is a mouth portion separated from the main winding portion 1a (the portion including the end face 2a (for example, the portion from the end face 2a to the position 2b shown in FIG. 1). )) The magnetic field strength is relatively low. Therefore, the critical current characteristic 62 of the strain resistance strengthening portion 2 shown in FIG. 6 is compared with the magnetic field distribution of the wire main portion 1 and the superconducting magnet (not shown) in which it is combined, even if the magnetic field strength is low. The strain resistance strengthening portion 2 is located in a good place. In this way, even the strain resistance strengthening unit 2 having a relatively low critical current characteristic 62 can be used without any problem. Here, the superconducting wire 100 between the wire main portion 1 and the strain resistance strengthening portion 2 has a critical current characteristic intermediate between the two with a certain inclination (such a portion is referred to as an "inclined portion"). To be). Therefore, it is preferable to sufficiently compare the critical current characteristics of the inclined portion with the magnetic field strength and design the critical current characteristics to be higher than the energizing current value.

Further, in the heat treatment step S2, as shown in FIG. 7, after the precursor is subjected to the first heat treatment step, the second heat treatment step can be further performed on the predetermined portion. According to this aspect, the strain resistance strengthening portion 2 can be formed at an arbitrary position of the superconducting wire 100. Note that FIG. 7 is a graph illustrating another example of the temperature transition of the wire rod main portion 1 (upper graph) and the temperature transition of the strain resistance strengthening portion 2 (lower graph).

The aspect shown in FIG. 7 shows a heat treatment process when the heat treatment process for the strain resistance strengthening portion 2 is performed in two stages. As shown in the graph below FIG. 7, in this embodiment, the temperature of the strain resistance strengthening portion 2 experiences the first heat treatment temperature T1 over the heat treatment temperature maintenance start time t1 to the heat treatment temperature maintenance end time t2 together with the wire rod main portion 1. After that, the temperature is raised toward the second heat treatment temperature T2 at the heat treatment temperature maintenance end time t2 to the second heat treatment temperature maintenance start time t3. Then, the second heat treatment temperature T2 is maintained from the second heat treatment temperature maintenance start time t3 to the second heat treatment temperature maintenance end time t4. However, the maintenance time of the second heat treatment temperature T2 is preferably a short time such that the outermost layer 24 of the metal sheath and the metal base material 23 of the superconducting wire 100 reach the second heat treatment temperature T2. If the maintenance time of the second heat treatment temperature T2 becomes long, the superconducting characteristics of the superconducting filament 21 may deteriorate. During this period, as shown in the upper graph of FIG. 7, the wire rod main portion 1 is maintained at the first heat treatment temperature T1. After reaching the second heat treatment temperature maintenance end time t4, the wire rod main portion 1 and the strain resistance strengthening portion 2 are cooled toward room temperature T3. In this aspect, the strain resistance strengthening portion 2 is maintained at the first heat treatment temperature T1 for the heat treatment temperature maintenance start time t1 to the heat treatment temperature maintenance end time t2 to generate a superconductor. Therefore, as compared with the embodiment described with reference to FIG. 5, the critical current characteristic 62 of the strain resistance strengthening portion 2 is less likely to decrease, and performance relatively close to the critical current characteristic 61 of the wire rod main portion 1 can be obtained. Further, among the strain resistance strengthening portions 2, since the metal sheath outermost layer 24 and the metal base material 23 experience the second heat treatment temperature T2, the bending resistance becomes stronger than that of the wire rod main portion 1.

Further, the heat treatment step S2 includes a coil forming step (not shown) in which the wire rod main portion 1 is wound to form a coil between the first heat treatment step and the second heat treatment step. In this way, the strain resistance strengthening portion 2 can be formed at an arbitrary portion of the coiled superconducting wire 100. Here, FIG. 8 is a graph illustrating another example of the temperature transition of the wire rod main portion 1 (upper graph) and the temperature transition of the strain resistance strengthening portion 2 (lower graph). Further, FIG. 9 is a conceptual diagram illustrating a state in which the superconducting wire 100 is manufactured after winding the precursor around the bobbin B to form a coil.

The aspect shown in FIG. 8 shows a heat treatment process in which the strain resistance strengthening portion 2 is allowed to experience the second heat treatment temperature T2 after the superconducting wire 100 is wound in a substantially coil shape. As shown in FIG. 8, in this embodiment, first, the first heat treatment step is performed on the entire precursor of the superconducting wire 100 over the heat treatment temperature maintenance start time t1 to the heat treatment temperature maintenance end time t2, and the first heat treatment is performed. The temperature T1 is experienced to provide superconducting performance. Then, after cooling the superconducting wire 100 to near room temperature T3, the superconducting wire 100 is wound around the bobbin B to form a coil-shaped superconducting coil 5 (coil forming step). Then, as shown in the graph at the bottom of FIG. 8, a second heat treatment step is performed at an arbitrary portion of the superconducting wire 100 over a second heat treatment temperature maintenance start time t3 to a second heat treatment temperature maintenance end time t4. The strain resistance strengthening portion 2 is formed by experiencing the second heat treatment temperature T2. As shown in the upper graph of FIG. 8, the wire rod main part 1 is maintained at room temperature T3 while the strain resistance strengthening part 2 is allowed to experience the second heat treatment temperature T2.

As shown in FIG. 9, in this embodiment, a resin or the like that cannot withstand high-temperature heat treatment can be used for the insulating material or bobbin B forming the superconducting coil 5. In this case, when the strain resistance strengthening portion 2 is heat-treated, the superconducting coil 5 is maintained at room temperature T3 or a temperature close to room temperature T3. The strain resistance strengthening portion 2 extended from the superconducting coil 5 is heated to the second heat treatment temperature T2 by using the second heating device 4, and then cooled. When the heat treatment is performed only on the strain resistance strengthening portion 2 after being wound into the shape of the superconducting coil 5 as in this embodiment, it is not necessary to determine the portion where the bending resistance is to be strengthened before the coil is manufactured, and the portion is arbitrary. Bending resistance can be strengthened.

FIG. 10 is a conceptual diagram illustrating a state in which the main winding portion 1a is protected by using the heat removing device 6 when the second heat treatment step is performed.
Generally, the superconducting wire 100 contains a metal material such as oxygen-free copper that easily transfers heat. Therefore, during the heat treatment of the strain resistance strengthening portion 2, heat is transmitted to such a metal material and reaches the superconducting coil 5 (that is, particularly the main winding portion 1a of the wire rod main portion 1), and the temperature rises. It is possible. Therefore, as shown in FIG. 10, the strain resistance strengthening portion 2 transmits the wire rod main portion 1 to an arbitrary position between the strain resistance strengthening portion 2 and the wire rod main portion 1 (particularly, the main winding portion 1a). It is preferable to arrange the heat removing device 6 for removing heat and perform the heat treatment step S2 (that is, the first heat treatment step and the second heat treatment step) described above. As the heat removing device 6, for example, it is preferable to use a water-cooled device 6. In this way, the temperature of the wire rod main portion 1 can be maintained near room temperature by cooling the portion connected from the strain resistance strengthening portion 2 to the superconducting coil 5. Therefore, it is possible to prevent the superconducting characteristics of the superconducting filament 21 in the wire main portion 1 from deteriorating. Further, when the heat removing device 6 is used in this way, the distance from the wire rod main portion 1 to the strain resistance strengthening portion 2 can be shortened. In FIG. 10, a heat removing device (not shown) may be similarly provided at an arbitrary position between the other strain resistance strengthening portion 2c of the superconducting coil 5 and the wire rod main portion 1. Further, it is preferable to mark the superconducting wire 100 so that the position where the heat is removed by the heat removing device 6 can be known so that the position where the heat is removed by the heat removing device 6 can be known. In this way, workability when performing processing using the superconducting wire 100 is improved.

FIG. 11 shows a state in which the heat radiating member 19 is thermally contacted in the bending inner direction of the strain resistance strengthening portion 2 when the superconducting wire 100 is predetermined to be bent at a specific position in a specific direction. It is schematic cross-sectional view explaining the state of performing the 2nd heat treatment step.
As shown in FIG. 11, it is preferable to experience the second heat treatment temperature T2 (see, for example, FIG. 5) in a state where the heat radiating member 19 is in thermal contact with the bending inner direction 18 of the strain resistance strengthening portion 2. .. Examples of the heat radiating member 19 include, but are not limited to, a heat radiating plate and a metal block. As described above, in the present embodiment, the heat radiating member 19 is installed to maintain the temperature of the strain resistance strengthening portion 2 in the bending inner direction 18 so as to be lower than the second heat treatment temperature T2 in the bending outer direction 17. As a result, the critical current characteristic of the superconducting filament 21 located in the bending inner direction 18 of the strain resistance strengthening portion 2 becomes a characteristic close to the critical current characteristic 61 that has experienced the first heat treatment temperature T1. On the other hand, the outermost layer 24 of the metal sheath and the metal base material 23 located in the bending outer direction 17 of the strain resistance strengthening portion 2 experience a temperature close to the second heat treatment temperature T2, so that a corresponding compressive strain is generated. It is applied and the allowable tensile strain becomes high. That is, it is possible to exhibit high critical current characteristics while strengthening the bending resistance of the strain resistance strengthening portion 2.

[Superconducting magnet and magnetic resonance tomography]
As shown in FIGS. 12 and 13, the superconducting wire 100 according to the present embodiment described above can be suitably used for the superconducting magnet 200 and the magnetic resonance tomography apparatus (MRI apparatus) 300. FIG. 12 is a schematic cross-sectional view illustrating the superconducting magnet 200 using the superconducting wire 100. FIG. 13 is a schematic cross-sectional view illustrating the MRI apparatus 300 using the superconducting magnet 200 (that is, using the superconducting wire 100).

As shown in FIG. 12, the superconducting magnet 200 houses a cylindrical superconducting coil 5 using the superconducting wire 100, a permanent current switch 108 electrically connected to the superconducting coil 5, and these. It is configured to include a bottomed cylindrical refrigerating container 109 for cooling these with a refrigerant or a refrigerator. The permanent current flowing through the superconducting coil 5 and the permanent current switch 108 generates a static magnetic field with high time stability at the position of the measurement target 110 (see FIG. 13). The higher the static magnetic field strength, the higher the nuclear magnetic resonance frequency and the higher the nuclear magnetic resonance signal strength.

Further, as shown in FIG. 13, the MRI apparatus 300 includes a cylindrical gradient magnetic field coil 111 provided coaxially with the superconducting coil 5 inside the cylindrical superconducting magnet 200, and a gradient magnetic field coil 111. The gradient magnetic field amplifier 112, which is electrically connected to the cable, is provided. Further, the MRI apparatus 300 has an RF (Radio Frequency) antenna 113 inside the gradient magnetic field coil 111, and the RF antenna 113 is electrically connected to the RF transmitter / receiver 114. Then, the measurement target 110 described above is arranged inside the RF antenna 113.

In the MRI apparatus 300 having such a configuration, a current that changes with time as needed is supplied from the gradient magnetic field amplifier 112 to the gradient magnetic field coil 111, and a static magnetic field having a spatial distribution is generated at the position of the measurement target 110. To do. Further, the cross-sectional image diagnosis of the measurement target 110 can be performed by applying a magnetic field having a nuclear magnetic resonance frequency to the measurement target 110 using the RF antenna 113 and the RF transmitter / receiver 114 and measuring the reaction signal. A nuclear magnetic resonance (NMR) device can also be realized by using the same configuration as the MRI device 300. The configuration of the MRI apparatus 300 shown in FIG. 13 is an example, and the present invention is not limited to this.

The superconducting wire 100, the method for manufacturing the superconducting wire 100, the superconducting magnet 200, and the MRI apparatus 300 according to the present invention have been described in detail in accordance with the embodiments, but the gist of the present invention is not limited thereto. , Various variants are included. For example, the above-described embodiment has been described in detail in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to the one including all the described configurations. Further, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Further, it is possible to add / delete / replace a part of the configuration of each embodiment with another configuration.
Further, each of the above-mentioned configurations, functions, processing units, processing means, control means and the like may be realized by hardware by designing a part or all of them by, for example, an integrated circuit. Further, each of the above configurations, functions, and the like may be realized by software by the processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files that realize each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.
In addition, the control lines and information lines indicate those that are considered necessary for explanation, and do not necessarily indicate all the control lines and information lines in the product. In practice, it can be considered that almost all configurations are interconnected.

100 Superconducting wire 1 Wire main part 1a Main winding part 2 Strain resistance strengthening part 21 Superconducting filament 22 Metal sheath 23 Metal base material 24 Metal sheath outermost layer 25 Intermediate layer S1 Precursor manufacturing process S2 Heat treatment process

Claims (12)

A superconducting filament that carries an electric current, a metal sheath that coats the superconducting filament, and a main part of a wire rod having a metal base material that coats the metal sheath.
A strain resistance strengthening portion having a allowable tensile strain of 0.01% or more higher than other portions at any location including the main portion of the wire rod.
A superconducting wire rod characterized by having. In claim 1,
A superconducting wire rod characterized in that the superconducting filament is formed of MgB ₂ . In claim 2,
An intermediate layer having a boron compound or a magnesium compound other than MgB _{2 is provided} between the superconducting filament and the metal sheath.
A superconducting wire rod in which the thickness of the intermediate layer in the strain resistance strengthening portion is 1.2 times or more the thickness of the intermediate layer in the wire rod main portion. The main part of the wire rod having the superconducting filament, the metal sheath covering the superconducting filament, and the metal base material covering the metal sheath, and the allowable tensile strain of 0.01 than other parts at any part of the main part of the wire rod. It is a method for manufacturing a superconducting wire having a strain resistance strengthening portion having a high strain resistance of% or more.
A precursor manufacturing step of coating the raw material of the superconducting filament with the metal sheath and coating the metal sheath with the metal base material to prepare a precursor of the superconducting wire.
It has a heat treatment step of heat-treating the precursor to produce a superconducting wire.
The heat treatment step includes a first heat treatment step of performing heat treatment to form the main portion of the wire rod, and a second heat treatment step of performing heat treatment to form the strain resistance strengthening portion.
A method for producing a superconducting wire rod, characterized in that the heat treatment temperature of the second heat treatment step is higher than the heat treatment temperature of the first heat treatment step. In claim 4,
The heat treatment step is
A method for producing a superconducting wire rod, which comprises simultaneously performing the first heat treatment step and the second heat treatment step. In claim 4,
The heat treatment step is
A method for producing a superconducting wire rod, which comprises subjecting the precursor to the first heat treatment step and then further performing the second heat treatment step on a predetermined portion. In claim 4,
The heat treatment step is
A method for producing a superconducting wire rod, which comprises a coil forming step of winding the main portion of the wire rod into a coil shape between the first heat treatment step and the second heat treatment step. In claim 4,
The heat treatment step is performed by arranging a heat removing device for removing heat transferred from the strain resistance strengthening portion to the wire main portion at an arbitrary position between the strain resistance strengthening portion and the wire rod main portion. A method for manufacturing a superconducting wire rod, which is characterized by. In claim 4,
The second heat treatment step is a method for producing a superconducting wire rod, characterized in that the heat radiating member is thermally contacted in the bending inner direction of the strain resistance strengthening portion. In claim 4,
A method for producing a superconducting wire rod, characterized in that the heat treatment temperature of the second heat treatment step is 50 kelvin or more higher than the heat treatment temperature of the first heat treatment step. A superconducting magnet using the superconducting wire according to any one of claims 1 to 3. The magnetic resonance tomography apparatus using the superconducting wire according to any one of claims 1 to 3.

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