JP7664874B2 - Superconducting layer connection structure, superconducting wire, superconducting coil, superconducting device, and superconducting layer connection method - Google Patents

Description

Embodiments of the present invention relate to a superconducting layer connection structure, a superconducting wire, a superconducting coil, a superconducting device, and a method for connecting a superconducting layer.

For example, in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) devices, superconducting coils are used to generate strong magnetic fields. Superconducting coils are formed by winding superconducting wire around a reel.

To make superconducting wire longer, for example, multiple superconducting wires are connected. For example, the ends of two superconducting wires are connected using a connection structure. The connection structure that connects the superconducting wires is required to have low electrical resistance and high mechanical strength.

Patent No. 5828299 Patent No. 6675590 Patent No. 6178779

The problem that this invention aims to solve is to provide a connection structure for superconducting layers that can achieve low electrical resistance and high mechanical strength.

The connection structure of the superconducting layer of the embodiment includes a first superconducting layer, a second superconducting layer, and a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including crystal grains containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), and a region that is present in a portion other than the crystal grains and has a carbon atom concentration higher than the carbon atom concentration of the crystal grains, the distribution of the major axes of the crystal grains including a bimodal distribution, the bimodal distribution having a first distribution including a first peak and a second distribution including a second peak, the first major axis corresponding to the first peak being larger than the second major axis corresponding to the second peak.

FIG. 2 is a schematic cross-sectional view of a connection structure of superconducting layers according to the first embodiment. FIG. 4 is an enlarged schematic cross-sectional view of a portion of the connection layer according to the first embodiment. FIG. 4 is a diagram illustrating the definition of the major axis and minor axis of a crystal grain according to the first embodiment. 5 is a diagram showing the major axis distribution of crystal particles contained in the connection layer according to the first embodiment. FIG. FIG. 4 is a process flow diagram of an example of a method for connecting superconducting layers according to the first embodiment. FIG. 13 is an enlarged schematic cross-sectional view of a portion of a connection layer according to a modified example of the first embodiment. FIG. 5 is a schematic cross-sectional view of a superconducting wire according to a second embodiment. FIG. 11 is a schematic cross-sectional view of a first modified example of the superconducting wire of the second embodiment. FIG. 11 is a schematic cross-sectional view of a second modified example of the superconducting wire of the second embodiment. FIG. 13 is a schematic cross-sectional view of a third modified example of the superconducting wire of the second embodiment. FIG. 13 is a schematic cross-sectional view of a fourth modified example of the superconducting wire of the second embodiment. FIG. 13 is a schematic perspective view of a superconducting coil according to a third embodiment. FIG. 11 is a schematic cross-sectional view of a superconducting coil according to a third embodiment. FIG. 13 is a block diagram of a superconducting device according to a fourth embodiment.

Below, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same reference numerals will be used to designate identical or similar components, and descriptions of components that have already been described may be omitted as appropriate.

In this specification, the long axis of a particle is the maximum length between any two points on the periphery of the particle. The short axis of a particle is the length of a line segment that passes through the midpoint of the line segment corresponding to the long axis, is perpendicular to the line segment, and has the periphery of the particle as both ends. The long axis and short axis of a particle can be determined, for example, by image analysis of a cross-sectional image taken with a scanning electron microscope (SEM). In this specification, the line segment corresponding to the long axis is referred to as the long axis. The line segment corresponding to the short axis is referred to as the short axis.

The detection of elements contained in particles and the measurement of the atomic concentration of elements can be performed, for example, using energy dispersive X-ray spectroscopy (EDX) or wavelength dispersive X-ray analysis (WDX). Furthermore, the identification of substances contained in particles can be performed, for example, using powder X-ray diffraction.

(First embodiment)
The connection structure of the superconducting layer of the first embodiment includes a first superconducting layer, a second superconducting layer, and a connection layer provided between the first and second superconducting layers, the connection layer including crystal grains containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), and an area having a carbon atom concentration higher than the carbon atom concentration of the crystal grains, the distribution of the major axis of the crystal grains including a bimodal distribution. The bimodal distribution has a first distribution including a first peak and a second distribution including a second peak, and the first major axis corresponding to the first peak is larger than the second major axis corresponding to the second peak.

Figure 1 is a schematic cross-sectional view of a connection structure of superconducting layers of the first embodiment. The connection structure 100 of the first embodiment is a structure that physically and electrically connects two superconducting layers. The connection structure 100 is used, for example, to connect two superconducting wires and extend the length of the superconducting wires.

The connection structure 100 includes a first superconducting member 10, a second superconducting member 20, and a connection layer 30. The connection structure 100 is a structure in which the first superconducting member 10 and the second superconducting member 20 are connected by the connection layer 30. The connection layer 30 is provided between the first superconducting member 10 and the second superconducting member 20.

The first superconducting member 10 comprises a first substrate 12, a first intermediate layer 14, and a first superconducting layer 16. The second superconducting member 20 comprises a second substrate 22, a second intermediate layer 24, and a second superconducting layer 26.

The first substrate 12 is, for example, a metal. The first substrate 12 is, for example, a nickel alloy or a copper alloy. The first substrate 12 is, for example, a nickel-tungsten alloy.

The first superconducting layer 16 is, for example, an oxide superconducting layer. The first superconducting layer 16 includes, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first superconducting layer 16 includes, for example, at least one rare earth element (RE) selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

The first superconducting layer 16 has a _chemical composition expressed, for example, as (RE) _{Ba2Cu3Oδ ( RE} is a rare earth element, 6≦δ≦7). The first superconducting layer 16 has a chemical composition expressed, for example, as _GdBa2Cu3Oδ (6 _≦ δ≦7), _YBa2Cu3Oδ ( ₆ ≦δ≦7), or _EuBa2Cu3Oδ ( _{6 ≦} δ _≦ 7).

The first superconducting layer 16 includes, for example, a single crystal having a perovskite structure.

The first superconducting layer 16 is formed on the first intermediate layer 14, for example, by using a metal organic decomposition method (MOD method), a pulsed laser deposition method (PLD method), or a metal organic chemical vapor deposition method (MOCVD method).

The first intermediate layer 14 is provided between the first substrate 12 and the first superconducting layer 16. The first intermediate layer 14 is in contact with the first superconducting layer 16, for example. The first intermediate layer 14 has the function of improving the crystal orientation of the first superconducting layer 16 formed on the first intermediate layer 14.

The first intermediate layer 14 includes, for example, a rare earth oxide. The first intermediate layer 14 has, for example, a laminated structure of a plurality of films. The first intermediate layer 14 has, for example, a structure in which yttrium oxide (Y ₂ O ₃ ), yttria-stabilized zirconia (YSZ), and cerium oxide (CeO ₂ ) are laminated from the first substrate 12 side.

The second substrate 22 is, for example, a metal. The second substrate 22 is, for example, a nickel alloy or a copper alloy. The second substrate 22 is, for example, a nickel-tungsten alloy.

The second superconducting layer 26 is, for example, an oxide superconducting layer. The second superconducting layer 26 includes, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first superconducting layer 16 includes, for example, at least one rare earth element (RE) selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

The second superconducting layer 26 has a _chemical composition expressed, for example, as (RE) _{Ba2Cu3Oδ ( RE} is a rare earth element, 6≦δ≦7). The second superconducting layer ₂₆ has a chemical composition expressed, for example, as _GdBa2Cu3Oδ (6 _≦ δ≦7), _YBa2Cu3Oδ ( ₆ ≦δ≦7), or _EuBa2Cu3Oδ ( _{6 ≦} δ≦7).

The second superconducting layer 26 includes, for example, a single crystal having a perovskite structure.

The second superconducting layer 26 is formed on the second intermediate layer 24, for example, using the MOD method, the PLD method, or the MOCVD method.

The second intermediate layer 24 is provided between the second substrate 22 and the second superconducting layer 26. The second intermediate layer 24 is in contact with the second superconducting layer 26, for example. The second intermediate layer 24 has the function of improving the crystal orientation of the second superconducting layer 26 formed on the second intermediate layer 24.

The second intermediate layer 24 includes, for example, a rare earth oxide. The second intermediate layer 24 has, for example, a laminated structure of a plurality of films. The second intermediate layer 24 has, for example, a structure in which yttrium oxide (Y ₂ O ₃ ), yttria-stabilized zirconia (YSZ), and cerium oxide (CeO ₂ ) are laminated from the second substrate 22 side.

The connection layer 30 is provided between the first superconducting layer 16 and the second superconducting layer 26. The connection layer 30 contacts the first superconducting layer 16. The connection layer 30 contacts the second superconducting layer 26.

The connection layer 30 is an oxide superconducting layer. The connection layer 30 includes a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 includes at least one rare earth element (RE) selected from the group consisting of, for example, yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

Figure 2 is an enlarged schematic cross-sectional view of a portion of the connection layer of the first embodiment.

The connection layer 30 includes first crystal particles 31, second crystal particles 32, carbon-containing particles 33, and voids 34. The connection layer 30 is formed by sintering the first crystal particles 31, the second crystal particles 32, and the carbon-containing particles 33.

The first crystal particle 31 and the second crystal particle 32 are examples of crystal particles. The carbon-containing particle 33 is an example of a region having a carbon atom concentration higher than the carbon atom concentration of the crystal particles.

The connection layer 30 is, for example, porous. For example, voids 34 exist between the particles contained in the connection layer 30. The connection layer 30 does not necessarily need to have voids 34.

The first crystal particles 31 contain a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first crystal particles 31 are rare earth oxides. The first crystal particles 31 are, for example, single crystals or polycrystals having a perovskite structure.

The first crystal grains 31 have a chemical composition expressed, for example, as (RE) _{Ba2Cu3Oδ ( RE} is _a rare earth element, 6≦δ≦7). The first crystal grains 31 have a chemical composition expressed, for example, as _GdBa2Cu3Oδ (6 _≦ δ≦7), _YBa2Cu3Oδ ( _{6 ≦} δ≦7), or _EuBa2Cu3Oδ ( _{6 ≦} δ≦7).

The first crystal grain 31 is a superconductor.

The first crystal particle 31 has, for example, a plate-like or flat shape. A flat shape means that the aspect ratio of the particle is 2 or more. The aspect ratio of a particle is the ratio of the long axis to the short axis of the particle (long axis/short axis).

The median aspect ratio of the first crystal particles 31 is, for example, 2 or more.

Figure 3 is a diagram showing the definition of the major axis and minor axis of the crystal particle in the first embodiment. Figure 3 shows the first crystal particle 31 as an example.

The long axis of a particle is the maximum length between any two points on the periphery of the particle. The short axis of a particle is the length of a line segment that passes through the midpoint of the line segment corresponding to the long axis, is perpendicular to the line segment, and has the periphery of the particle as both ends.

For example, the long axis of the first crystal particle 31 shown in FIG. 3 is the length of line segment L1. The short axis of the first crystal particle 31 shown in FIG. 3 is the length of line segment S1. Line segment S1 passes through midpoint M1 of line segment L1. The aspect ratio of the first crystal particle 31 shown in FIG. 3 is L1/S1.

The median long diameter of the first crystal grains 31 is, for example, 100 nm or more and 10 μm or less. The median long diameter of the first crystal grains 31 is, for example, greater than the thickness (t in FIG. 2 ) of the connection layer 30 in the direction from the first superconducting layer 16 to the second superconducting layer 26.

The long axis direction of the first crystal grains 31 is inclined, for example, with respect to the interface between the first superconducting layer 16 and the connection layer 30. The angle of the long axis direction of the first crystal grains 31 with respect to the interface between the first superconducting layer 16 and the connection layer 30 is a first inclination angle. The first inclination angle is, for example, 15 degrees or more and 90 degrees or less.

The second crystal particles 32 contain a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The second crystal particles 32 are rare earth oxides. The second crystal particles 32 are, for example, single crystals or polycrystals having a perovskite structure. The second crystal particles 32 have a chemical composition represented, for example, by (RE)Ba ₂ Cu ₃ O _δ (RE is a rare earth element, 6≦δ≦7).

The second crystal particles 32 contain a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The second crystal particles 32 are rare earth oxides. The second crystal particles 32 are, for example, single crystals or polycrystals having a perovskite structure. The second crystal particles 32 have a chemical composition represented, for example, by (RE)Ba ₂ Cu ₃ O _δ (RE is a rare earth element, 6≦δ≦7).

The second crystal particles 32 are, for example, superconductors.

The second crystal particles 32 contain, for example, the same rare earth element as the first crystal particles 31. The chemical composition of the second crystal particles 32 is, for example, the same as the chemical composition of the first crystal particles 31.

The second crystal particles 32 may, for example, contain a different rare earth element than the first crystal particles 31. The chemical composition of the second crystal particles 32 may, for example, be different from the chemical composition of the first crystal particles 31.

The second crystal particles 32 are, for example, spherical or amorphous. The median aspect ratio of the second crystal particles 32 is, for example, smaller than the median aspect ratio of the first crystal particles 31. The median aspect ratio of the second crystal particles 32 is, for example, less than 2.

The median long diameter of the second crystal grains 32 is smaller than the median long diameter of the first crystal grains 31. The median long diameter of the second crystal grains 32 is, for example, 10 nm or more and less than 1 μm. The median long diameter of the second crystal grains 32 is, for example, smaller than the thickness (t in FIG. 2) of the connection layer 30 in the direction from the first superconducting layer 16 to the second superconducting layer 26.

The median long diameter of the first crystal particles 31 is, for example, 10 times or more and 1000 times or less than the median long diameter of the second crystal particles 32.

Figure 4 is a diagram showing the major axis distribution of the crystal particles contained in the connection layer of the first embodiment. Figure 4 shows the major axis distribution of the first crystal particles 31 and the second crystal particles 32 contained in the connection layer 30.

As shown in FIG. 4, the major axis distribution of the crystal particles contained in the connection layer 30 includes a bimodal distribution. The bimodal distribution has a first distribution including a first peak (Pk1 in FIG. 4) and a second distribution including a second peak (Pk2 in FIG. 4).

The major axis distribution of the crystal particles contained in the connection layer 30 may be a multimodal distribution with three or more peaks.

The crystal particles contained in the first distribution are the first crystal particles 31. The crystal particles contained in the second distribution are the second crystal particles 32.

The major axis corresponding to the first peak Pk1 is the first major axis (d1 in FIG. 4). The major axis corresponding to the second peak Pk2 is the second major axis (d2 in FIG. 4).

The first major diameter d1 is larger than the second major diameter d2. The first major diameter d1 is, for example, 10 times or more and 1000 times or less than the second major diameter d2.

The first major diameter d1 is, for example, 100 nm or more and 10 μm or less. The second major diameter d2 is, for example, 10 nm or more and less than 1 μm.

The first major axis d1 is, for example, larger than the thickness (t in FIG. 2) of the connection layer 30 in the direction from the first superconducting layer 16 to the second superconducting layer 26. The second major axis d2 is, for example, smaller than the thickness (t in FIG. 2) of the connection layer 30 in the direction from the first superconducting layer 16 to the second superconducting layer 26.

The carbon-containing particles 33 contain carbon (C). The atomic concentration of the carbon-containing particles 33 is higher than the atomic concentration of the first crystal particles 31. The atomic concentration of the carbon-containing particles 33 is higher than the atomic concentration of the second crystal particles 32.

The atomic concentration of the carbon-containing particles 33 is, for example, 10 times or more than the atomic concentration of the first crystal particles 31. The atomic concentration of the carbon-containing particles 33 is, for example, 10 times or more than the atomic concentration of the second crystal particles 32.

The carbon-containing particles 33 include, for example, barium (Ba), carbon (C), and oxygen (O). The carbon-containing particles 33 are, for example, barium carbonate. The carbon-containing particles 33 have, for example, a chemical composition expressed as Ba ₂ CO ₃ .

The carbon-containing particles 33 are, for example, spherical or amorphous. The aspect ratio of the carbon-containing particles 33 is, for example, smaller than the aspect ratio of the first crystal particles 31. The aspect ratio of the carbon-containing particles 33 is, for example, less than 2.

The median major axis of the carbon-containing particles 33 is, for example, smaller than the median major axis of the first crystal particles 31. The median major axis of the carbon-containing particles 33 is, for example, smaller than the first major axis d1.

The median major axis of the carbon-containing particles 33 is, for example, smaller than the median major axis of the second crystal particles 32. The median major axis of the carbon-containing particles 33 is, for example, smaller than the second major axis d2.

The median major axis of the carbon-containing particles 33 is, for example, 10 nm or more and less than 1 μm.

The number of carbon-containing particles 33 in the connection layer 30 is, for example, less than the number of second crystal particles 32 in the connection layer 30. The number of carbon-containing particles 33 in the connection layer 30 is, for example, less than one-tenth the number of second crystal particles 32 in the connection layer 30.

The method for connecting the superconducting layers of the first embodiment includes preparing a first superconducting layer and a second superconducting layer, preparing an oxide superconductor containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), pulverizing the oxide superconductor to prepare first crystal particles, preparing an organometallic salt solution in which a powder of an organic acid salt of the rare earth element (RE), a powder of an organic acid salt of barium (Ba), and a powder of an organic acid salt of copper (Cu) are dissolved, preparing a slurry in which the first crystal particles are mixed into the organometallic salt solution, applying the slurry onto the first superconducting layer, and performing a heat treatment with the slurry sandwiched between the first superconducting layer and the second superconducting layer.

Below, an example of a method for connecting the superconducting layers in the first embodiment is described.

Figure 5 is a process flow diagram of an example of a method for connecting superconducting layers in the first embodiment. As shown in Figure 5, the example of the method for connecting superconducting layers in the first embodiment includes a conductive layer preparation step S01, an oxide superconductor preparation step S02, a first crystal particle preparation step S03, an organometallic solution preparation step S04, a slurry preparation step S05, a slurry application step S06, and a heat treatment step S07.

First, the first superconducting layer 16 and the second superconducting layer 26 are prepared (S01). The first superconducting layer 16 and the second superconducting layer 26 are formed, for example, by the MOD method, the PLD method, or the MOCVD method.

Next, an oxide superconductor containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O) is formed (S02). The oxide superconductor is formed, for example, by a solid-state reaction method. The oxide superconductor is produced, for example, by mixing and compressing rare earth element (RE) oxide powder, barium (Ba) carbonate powder, and copper (Cu) oxide powder to produce a green compact, and then sintering the green compact.

In forming the oxide superconductor, for example, powders of Gd ₂ O ₃ , BaCO _{3 ,} and CuO are mixed and compressed to produce a green compact, which is then sintered to form an oxide superconductor having a composition of, for example, GdBa ₂ Cu ₃ O _δ (6≦δ≦7).

Next, the oxide superconductor is crushed to produce first crystal particles 31 (S03). The first crystal particles 31 contain rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O). For example, particles of a desired size and shape are selected as the first crystal particles 31 from the particles produced by crushing.

For example, the first crystal particles 31 are fabricated so that the first crystal particles 31 have a plate-like or flat shape. For example, the first crystal particles 31 are fabricated so that the median aspect ratio of the first crystal particles 31 is 2 or more.

Next, the connection layer 30 is formed using the MOD method.

An organic metal salt solution is prepared by dissolving a powder of an organic acid salt of a rare earth element (RE), a powder of an organic acid salt of barium (Ba), and a powder of an organic acid salt of copper (Cu) (S04). For example, the organic metal salt solution is prepared using a powder of Gd( _OCOCH3 ) ₂ , a powder of Ba( _OCOCH3 ) ₂ , and a powder of Cu( _OCOCH3 ) ₂ .

Next, the first crystal particles 31 are mixed into the prepared organometallic salt solution to prepare a slurry (S05).

Next, the prepared slurry is applied onto the first superconducting layer 16 (S06).

Next, heat treatment is performed with the slurry sandwiched between the first superconducting layer 16 and the second superconducting layer 26 (S07). The heat treatment is performed, for example, while the first superconducting layer 16 and the second superconducting layer 26 are pressurized in a direction from the first superconducting layer 16 to the second superconducting layer 26.

The heat treatment is performed, for example, in an atmosphere containing oxygen. The heat treatment is performed, for example, at a temperature of 800° C. or less. The connection layer 30 is formed by the heat treatment.

The slurry is fired to form second crystal particles 32. The second crystal particles 32 contain rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O).

The median major axis of the second crystal particles 32 is smaller than the median major axis of the first crystal particles 31. The median aspect ratio of the second crystal particles 32 is smaller than the median aspect ratio of the first crystal particles 31, for example.

Carbon-containing particles 33 are formed by firing the slurry. The carbon-containing particles 33 contain, for example, barium (Ba), carbon (C), and oxygen (O). The median long diameter of the carbon-containing particles 33 is, for example, smaller than the median long diameter of the first crystal particles 31. The median long diameter of the carbon-containing particles 33 is, for example, smaller than the median long diameter of the second crystal particles 32.

By the above method, the first superconducting layer 16 and the second superconducting layer 26 are connected. By the above method, the superconducting layer connection structure 100 of the first embodiment is formed.

In addition, oxide superconductors can also be formed using, for example, the MOD method, the PLD method, or the MOCVD method instead of the solid-state reaction method.

Next, the action and effect of the superconducting layer connection structure and superconducting layer connection method of the first embodiment will be described.

For example, in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) devices, superconducting coils are used to generate strong magnetic fields. Superconducting coils are formed by winding superconducting wire around a reel.

To make superconducting wire longer, for example, multiple superconducting wires are connected. For example, the ends of two superconducting wires are connected using a connection structure. The connection structure that connects the superconducting wires is required to have low electrical resistance and high mechanical strength.

In the first embodiment of the superconducting layer connection method, the connection layer 30 that connects the first superconducting layer 16 and the second superconducting layer 26 includes first crystal particles 31 with a large major axis, second crystal particles 32 with a small major axis, and carbon-containing particles 33. By including the first crystal particles 31, the second crystal particles 32, and the carbon-containing particles 33 in the connection layer 30, a superconducting layer connection structure 100 with low electrical resistance and high mechanical strength can be realized. This will be described in detail below.

The superconducting layer connection structure 100 of the first embodiment has first crystal grains 31 with a large major axis, which reduces the electrical resistance of the connection layer 30. The first crystal grains 31 with a large major axis reduce the crystal grain interfaces in the connection layer 30. Therefore, the interface resistance of the crystal grain interfaces is prevented from increasing the electrical resistance of the connection layer 30.

In addition, in the superconducting layer connection structure 100 of the first embodiment, the second crystal grains 32 with a smaller major axis fill the spaces between the first crystal grains 31 with a larger major axis. The second crystal grains 32 bond the first crystal grains 31 and the second crystal grains 32 together, improving the mechanical strength of the connection layer 30.

When the carbon atom concentration in the crystal grains of the oxide superconductor increases, the conductivity of the crystal grains decreases. The carbon atom concentration of the first crystal grains 31 is lower than the carbon atom concentration of the carbon-containing grains 33. The carbon atom concentration of the second crystal grains 32 is also lower than the carbon atom concentration of the carbon-containing grains 33.

By lowering the carbon atom concentration of the first crystal particles 31 and the second crystal particles 32, the electrical resistance of the connection layer 30 can be reduced. In particular, by lowering the carbon atom concentration of the first crystal particles 31, which contributes greatly to reducing the electrical resistance of the connection layer 30, the electrical resistance of the connection layer 30 can be reduced.

As described above, the superconducting layer connection structure 100 of the first embodiment can achieve low electrical resistance and high mechanical strength.

From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the carbon atom concentration of the carbon-containing particles 33 is 10 times or more the carbon atom concentration of the first crystal particles 31. From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the carbon atom concentration of the carbon-containing particles 33 is 10 times or more the carbon atom concentration of the second crystal particles 32.

In other words, from the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the carbon-containing particles 33 of the first crystal particles 31 have a carbon atom concentration of 1/10 or less than that of the carbon-containing particles 33. From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the carbon-containing particles 33 of the second crystal particles 32 have a carbon atom concentration of 1/10 or less than that of the carbon-containing particles 33.

From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the number of carbon-containing particles 33 in the connection layer 30 is smaller than the number of second crystal particles 32 in the connection layer 30. It is more preferable that the number of carbon-containing particles 33 in the connection layer 30 is one-tenth or less of the number of second crystal particles 32 in the connection layer 30.

From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the median long diameter of the carbon-containing particles 33 is smaller than the median long diameter of the first crystal particles 31. Also, from the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the median long diameter of the carbon-containing particles 33 is smaller than the median long diameter of the second crystal particles 32.

The carbon-containing particles 33 do not have superconducting properties and have low electrical conductivity. Therefore, by reducing the number of carbon-containing particles 33, the increase in electrical resistance of the connection layer 30 can be suppressed. In addition, by reducing the major axis of the carbon-containing particles 33, the increase in electrical resistance of the connection layer 30 can be suppressed.

From the viewpoint of reducing the electrical resistance of the connection layer 30, the median major axis of the first crystal particles 31 is preferably 100 nm or more, more preferably 1 μm or more, and even more preferably 3 μm or more. From the viewpoint of reducing the electrical resistance of the connection layer 30, the first major axis d1 is preferably 100 nm or more, more preferably 1 μm or more, and even more preferably 3 μm or more.

From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the median major axis of the first crystal grains 31 is greater than the thickness (t in FIG. 2) of the connection layer 30 in the direction from the first superconducting layer 16 to the second superconducting layer 26. From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the first major axis d1 is greater than the thickness (t in FIG. 2) of the connection layer 30 in the direction from the first superconducting layer 16 to the second superconducting layer 26.

From the viewpoint of reducing the electrical resistance of the connection layer 30, it is preferable that the median aspect ratio of the first crystal particles 31 is larger than the median aspect ratio of the second crystal particles 32. It is preferable that the median aspect ratio of the second crystal particles 32 is smaller than the median aspect ratio of the first crystal particles 31.

From the viewpoint of reducing the electrical resistance of the connection layer 30, the median aspect ratio of the first crystal particles 31 is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more.

From the viewpoint of reducing the electrical resistance of the connection layer 30, the median aspect ratio of the second crystal particles 32 is preferably less than 2, and more preferably less than 1.5.

From the viewpoint of reducing the electrical resistance of the connection layer 30, the median of the first inclination angle of the long axis direction of the first crystal grains 31 with respect to the interface between the first superconducting layer 16 and the connection layer 30 is preferably 15 degrees or more, more preferably 20 degrees or more, and even more preferably 30 degrees or more.

From the viewpoint of increasing the mechanical strength of the connection layer 30, the median major axis of the second crystal particles 32 is preferably less than 1 μm, more preferably 500 nm or less, and even more preferably less than 200 nm. From the viewpoint of increasing the mechanical strength of the connection layer 30, the second major axis d2 is preferably less than 1 μm, more preferably 500 nm or less, and even more preferably less than 200 nm.

From the viewpoint of increasing the mechanical strength of the connection layer 30, it is preferable that the median major axis of the first crystal particles 31 is 10 times or more the major axis of the second crystal particles 32. From the viewpoint of increasing the mechanical strength of the connection layer 30, it is preferable that the first major axis d1 is 10 times or more the second major axis d2.

From the viewpoint of increasing the mechanical strength of the connection layer 30, it is preferable that the chemical composition of the first crystal particles 31 and the chemical composition of the second crystal particles 32 are the same.

In the method for connecting superconducting layers of the first embodiment, the first crystal particles 31 and the second crystal particles 32 are formed in independent manufacturing steps. The first crystal particles 31 are formed by crushing a prefabricated oxide superconductor. Meanwhile, the second crystal particles 32 are formed by the MOD method. Therefore, it is easy to optimize the characteristics of the first crystal particles 31 and the second crystal particles 32 to achieve low electrical resistance and high mechanical strength of the connection layer 30.

The characteristics that are particularly required for the first crystal particles 31, from the viewpoint of reducing the electrical resistance of the connection layer 30, are, for example, high crystallinity, a large particle long diameter, a high aspect ratio, and a low carbon atom concentration. By selecting optimal manufacturing conditions, it is possible to obtain high crystallinity and a low carbon atom concentration for the prefabricated oxide superconductor. Furthermore, by selecting optimal grinding conditions and particle selection conditions when crushing the oxide superconductor to produce the first crystal particles 31, it is possible to produce first crystal particles 31 with a large particle long diameter and a high aspect ratio.

The characteristics that are particularly required for the second crystal particles 32 are that the long diameter of the particles is small and that the particles have a high degree of sinterability with each other, from the viewpoint of improving the mechanical strength of the connection layer 30. In addition, from the viewpoint of not deteriorating the superconducting properties of the first superconducting layer 16 and the second superconducting layer 26, the second crystal particles 32 are required to be formed at low temperatures. By using the MOD method, it is possible to form second crystal particles 32 that have a small long diameter and a high degree of sinterability with each other at low temperatures.

In addition, by using the MOD method, the number of carbon-containing particles 33 in the connection layer 30 and the major axis of the carbon-containing particles 33 can be reduced. Therefore, the electrical resistance of the connection layer 30 is reduced.

As described above, the superconducting layer connection method of the first embodiment makes it possible to manufacture a superconducting layer connection structure with low electrical resistance and high mechanical strength.

The prefabricated oxide superconductor is preferably formed using a solid-state reaction method. The prefabricated oxide superconductor is preferably produced by mixing rare earth element (RE) oxide powder, barium (Ba) carbonate powder, and copper (Cu) oxide powder, compressing them to produce a green compact, and sintering the green compact. The above method makes it possible to produce an oxide superconductor with high crystallinity and a low carbon atom concentration.

The heat treatment to form the second crystal particles 32 is preferably carried out in an atmosphere containing oxygen in order to achieve high sinterability.

The heat treatment to form the second crystal grains 32 is preferably performed at a temperature of 800°C or less, and more preferably 700°C or less. By performing the heat treatment at a low temperature, deterioration of the superconducting properties of the first superconducting layer 16 and the second superconducting layer 26 can be suppressed.

From the viewpoint of increasing the mechanical strength of the connection layer 30, it is preferable that the median long diameter of the second crystal particles 32 is smaller than the median long diameter of the first crystal particles 31. Also, from the viewpoint of increasing the mechanical strength of the connection layer 30, it is preferable that the median aspect ratio of the second crystal particles 32 is smaller than the median aspect ratio of the first crystal particles 31.

(Modification)
6 is an enlarged schematic cross-sectional view of a portion of a connection layer of a modified example of the first embodiment. The connection layer 30 of the modified example differs from the connection layer 30 of the first embodiment in that it includes a carbon-containing portion 35 instead of the carbon-containing particles 33.

The first crystal particle 31 and the second crystal particle 32 are examples of crystal particles. The carbon-containing portion 35 is an example of a region having a carbon atom concentration higher than the carbon atom concentration of the crystal particles.

The carbon-containing portion 35 contains carbon (C). The atomic concentration of the carbon-containing portion 35 is higher than the atomic concentration of the first crystal grain 31. The atomic concentration of the carbon-containing portion 35 is higher than the atomic concentration of the second crystal grain 32.

The atomic concentration of the carbon-containing portion 35 is, for example, 10 times or more than the atomic concentration of the first crystal grain 31. The atomic concentration of the carbon-containing portion 35 is, for example, 10 times or more than the atomic concentration of the second crystal grain 32.

The carbon-containing portion 35 includes, for example, barium (Ba), carbon (C), and oxygen (O). The carbon-containing portion 35 is, for example, barium carbonate. The carbon-containing portion 35 has, for example, a chemical composition expressed _{as Ba2CO3} .

The carbon-containing portion 35 has an irregular shape.

As described above, the connection structure and modified examples of the superconducting layer of the first embodiment can achieve low electrical resistance and high mechanical strength.

Second Embodiment
The superconducting wire of the second embodiment includes a first superconducting wire including a first superconducting layer, a second superconducting wire including a second superconducting layer, a third superconducting layer having a first surface and a second surface facing the first surface, and a connection layer provided between the first superconducting layer and the third superconducting layer and between the second superconducting layer and the third superconducting layer, the connection layer including crystal grains including rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), and a region having a carbon atom concentration higher than the carbon atom concentration of the crystal grains, the distribution of the major axis of the crystal grains including a bimodal distribution. The first superconducting layer and the second superconducting layer are located on the first surface side of the third superconducting layer. The bimodal distribution has a first distribution including a first peak and a second distribution including a second peak, and the first major axis corresponding to the first peak is larger than the second major axis corresponding to the second peak. The superconducting wire of the second embodiment uses the connection structure of the superconducting layer of the first embodiment as a structure for connecting the first superconducting wire and the second superconducting wire. Hereinafter, some of the contents that overlap with the first embodiment will be omitted.

Figure 7 is a schematic cross-sectional view of a superconducting wire of the second embodiment. The superconducting wire 400 of the second embodiment includes a first superconducting wire 401, a second superconducting wire 402, and a connecting member 403. The superconducting wire 400 of the second embodiment is elongated by connecting the first superconducting wire 401 and the second superconducting wire 402 using the connecting member 403.

The first superconducting wire 401 comprises a first substrate 12, a first intermediate layer 14, a first superconducting layer 16, and a first protective layer 18. The second superconducting wire 402 comprises a second substrate 22, a second intermediate layer 24, a second superconducting layer 26, and a second protective layer 28. The connecting member 403 comprises a third substrate 42, a third intermediate layer 44, and a third superconducting layer 46.

The first superconducting wire 401, the second superconducting wire 402, and the connecting member 403 have a structure similar to that of the first superconducting member 10 and the second superconducting member 20 of the first embodiment.

The connection layer 30 is provided between the first superconducting layer 16 and the third superconducting layer 46. The connection layer 30 contacts the first superconducting layer 16. The connection layer 30 contacts the third superconducting layer 46.

The connection layer 30 is provided between the second superconducting layer 26 and the third superconducting layer 46. The connection layer 30 contacts the second superconducting layer 26. The connection layer 30 contacts the third superconducting layer 46.

The connection layer 30 between the first superconducting layer 16 and the third superconducting layer 46 and the connection layer 30 between the second superconducting layer 26 and the third superconducting layer 46 are continuous.

The connection layer 30 does not exist, for example, between the first superconducting layer 16 and the second superconducting layer 26. Between the first superconducting layer 16 and the second superconducting layer 26, for example, there is an air gap.

The connection layer 30 is an oxide superconducting layer. The connection layer 30 includes a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 includes, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 includes, for example, at least one rare earth element (RE) selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

The connection layer 30 of the second embodiment has a configuration similar to that of the connection layer 30 of the first embodiment shown in FIG. 2.

In the second embodiment of the superconducting wire 400, for example, a current flows from the first superconducting wire 401 through the connection layer 30, the connection member 403, and the connection layer 30 to the second superconducting wire 402.

The first superconducting wire 401 and the connection member 403 are connected using the connection layer 30, so that the connection structure connecting the first superconducting wire 401 and the connection member 403 has low electrical resistance and high mechanical strength. The second superconducting wire 402 and the connection member 403 are connected using the connection layer 30, so that the connection structure connecting the second superconducting wire 402 and the connection member 403 has low electrical resistance and high mechanical strength.

Therefore, the connection structure connecting the first superconducting wire 401 and the second superconducting wire 402 has low electrical resistance and high mechanical strength. Therefore, the superconducting wire 400 has low electrical resistance and high mechanical strength.

It is also possible to connect three or more superconducting wires to form an even longer superconducting wire.

(First Modification)
8 is a schematic cross-sectional view of a first modified example of the superconducting wire of the second embodiment. The superconducting wire 410 of the first modified example of the second embodiment differs from the superconducting wire 400 of the second embodiment in that the superconducting wire 410 includes a reinforcing member 60.

The reinforcing material 60 is provided between the first superconducting wire 401 and the second superconducting wire 402. The reinforcing material 60 is provided, for example, between the first superconducting layer 16 and the second superconducting layer 26.

The reinforcing material 60 contacts, for example, the first superconducting wire 401 and the second superconducting wire 402. The reinforcing material 60 contacts, for example, the connection layer 30.

The inclusion of the reinforcing material 60 improves the mechanical strength of the superconducting wire 410.

The reinforcing material 60 is, for example, a metal or a resin. The reinforcing material 60 is, for example, a solder. The reinforcing material 60 is, for example, a solder containing silver (Ag) and indium (In).

(Second Modification)
9 is a schematic cross-sectional view of a second modified example of the superconducting wire of the second embodiment. A superconducting wire 420 of the second modified example of the second embodiment differs from the superconducting wire 400 of the second embodiment in that the connection layer 30 includes a first region 30a and a second region 30b that are spaced apart from each other.

The connection layer 30 includes a first region 30a and a second region 30b. The first region 30a and the second region 30b are spaced apart.

The first region 30a is provided between the first superconducting layer 16 and the third superconducting layer 46. The first region 30a contacts the first superconducting layer 16. The first region 30a contacts the third superconducting layer 46.

The second region 30b is provided between the second superconducting layer 26 and the third superconducting layer 46. The second region 30b contacts the second superconducting layer 26. The second region 30b contacts the third superconducting layer 46.

(Third Modification)
10 is a schematic cross-sectional view of a third modified example of the superconducting wire of the second embodiment. A superconducting wire 430 of the third modified example of the second embodiment differs from the superconducting wire 420 of the second modified example of the second embodiment in that a part of a surface of the first superconducting layer 16 facing the third superconducting layer 46 is exposed, and a part of a surface of the second superconducting layer 26 facing the third superconducting layer 46 is exposed.

There is an area where the connection layer 30 is not present near the end of the upper surface of the first superconducting layer 16 on the side of the second superconducting layer 26. Also, there is an area where the connection layer 30 is not present near the end of the upper surface of the second superconducting layer 26 on the side of the first superconducting layer 16.

(Fourth Modification)
11 is a schematic cross-sectional view of a fourth modified example of the superconducting wire of the second embodiment. The superconducting wire 440 of the fourth modified example of the second embodiment differs from the superconducting wire 430 of the third modified example of the second embodiment in that the superconducting wire 440 includes a reinforcing material 60.

The reinforcing material 60 is provided between the first superconducting wire 401 and the second superconducting wire 402. The reinforcing material 60 is provided, for example, between the first superconducting layer 16 and the second superconducting layer 26. The reinforcing material 60 is provided, for example, between the first superconducting layer 16 and the third superconducting layer 46. The reinforcing material 60 is provided, for example, between the second superconducting layer 26 and the third superconducting layer 46. The reinforcing material 60 is provided, for example, between the first region 30a and the second region 30b.

The inclusion of the reinforcing material 60 improves the mechanical strength of the superconducting wire 440.

The reinforcing material 60 is, for example, a metal or a resin. The reinforcing material 60 is, for example, a solder. The reinforcing material 60 is, for example, a solder containing silver (Ag) and indium (In).

As described above, according to the second embodiment and the modified example, a superconducting wire having low electrical resistance and high mechanical strength can be realized by connecting two superconducting wires to a long length.

Third Embodiment
The superconducting coil of the third embodiment includes the superconducting wire of the second embodiment. In the following, some of the contents that overlap with the second embodiment may be omitted.

Figure 12 is a schematic perspective view of a superconducting coil of the third embodiment. Figure 13 is a schematic cross-sectional view of a superconducting coil of the third embodiment.

The superconducting coil 700 of the third embodiment is used as a coil for generating a magnetic field in superconducting equipment such as NMR, MRI, heavy particle beam therapy equipment, or superconducting magnetic levitation railway vehicles.

The superconducting coil 700 includes a winding frame 110, a first insulating plate 111a, a second insulating plate 111b, and a winding section 112. The winding section 112 includes a superconducting wire 120 and an inter-wire layer 130.

Figure 13 shows the state after removing the first insulating plate 111a and the second insulating plate 111b.

The reel 110 is made of, for example, fiber-reinforced plastic. The superconducting wire 120 is, for example, tape-shaped. As shown in FIG. 13, the superconducting wire 120 is wound around the reel 110 in a concentric, so-called pancake shape around the winding center C.

The inter-wire layer 130 has the function of fixing the superconducting wire 120. The inter-wire layer 130 has the function of preventing the superconducting wire 120 from being damaged by vibration during use of the superconducting device or by friction between the wires.

The first insulating plate 111a and the second insulating plate 111b are formed of, for example, fiber-reinforced plastic. The first insulating plate 111a and the second insulating plate 111b have the function of insulating the winding portion 112 from the outside. The winding portion 112 is located between the first insulating plate 111a and the second insulating plate 111b.

The superconducting wire 120 is the superconducting wire of the second embodiment.

As described above, according to the third embodiment, a superconducting coil with improved characteristics can be realized by using superconducting wire with low electrical resistance and high mechanical strength.

(Fourth embodiment)
The superconducting device of the fourth embodiment is a superconducting device including the superconducting coil of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

Figure 14 is a block diagram of a superconducting device according to a fourth embodiment. The superconducting device according to the fourth embodiment is a heavy particle beam therapy device 800. The heavy particle beam therapy device 800 is an example of a superconducting device.

The heavy ion beam therapy device 800 includes an injection system 50, a synchrotron accelerator 52, a beam transport system 54, an irradiation system 56, and a control system 58.

The injection system 50 has a function of, for example, generating carbon ions to be used in treatment and performing preliminary acceleration for injection into the synchrotron accelerator 52. The injection system 50 has, for example, an ion generation source and a linear accelerator.

The synchrotron accelerator 52 has the function of accelerating the carbon ion beam injected from the injection system 50 to an energy level suitable for treatment. The superconducting coil 700 of the third embodiment is used in the synchrotron accelerator 52.

The beam transport system 54 has the function of transporting the carbon ion beam injected from the synchrotron accelerator 52 to the irradiation system 56. The beam transport system 54 has, for example, a bending electromagnet.

The irradiation system 56 has a function of irradiating the carbon ion beam injected from the beam transport system 54 to the patient who is the irradiation target. The irradiation system 56 has, for example, a rotating gantry that enables the carbon ion beam to be irradiated from any direction. The superconducting coil 700 of the third embodiment is used for the rotating gantry.

The control system 58 controls the injection system 50, the synchrotron accelerator 52, the beam transport system 54, and the irradiation system 56. The control system 58 is, for example, a computer.

The fourth embodiment of the heavy particle beam therapy device 800 uses the superconducting coil 700 of the third embodiment in the synchrotron accelerator 52 and the rotating gantry. Therefore, a heavy particle beam therapy device 800 with excellent characteristics is realized.

In the fourth embodiment, a heavy particle beam therapy device 800 has been described as an example of a superconducting device, but the superconducting device may also be a nuclear magnetic resonance device (NMR), a magnetic resonance imaging device (MRI), or a superconducting magnetic levitation railway vehicle.

Example 1
Two oxide superconducting wires with a length of 10.5 cm were prepared, each wire having an intermediate layer and _{a GdBa2Cu3O7 -δ} layer (oxide superconducting layer) formed on a Hastelloy substrate and covered with a protective layer of silver and copper. A portion 1.0 cm from one end was wet etched using a mixed solution of nitric acid, ammonia, and hydrogen peroxide to expose the oxide superconducting layer.

Powders of Gd ₂ O ₃ , BaCO ₃ and CuO were prepared, appropriately weighed, thoroughly mixed, and the mixed powder was compressed to produce a green compact. The obtained green compact was sintered at 930°C to produce an oxide superconductor with a GdBa ₂ Cu ₃ O _7-δ composition. The obtained oxide superconductor was pulverized by beating in a mortar, and particles of an appropriate diameter were selected using a sieve or the like to produce a superconductor powder with a high aspect ratio, with a median major axis of 5 μm or more and a median minor axis of 2 μm or less.

The two types of superconductor powders thus obtained were mixed with an organometallic salt solution in which Gd(OCOCH ₃ ) ₂ , Ba(OCOCH ₃ ) ₂ , and Cu(OCOCH ₃ ) ₂ were dissolved, in a weight ratio of 1:2, to prepare a slurry.

The obtained slurry was applied to the exposed oxide superconducting layer of one of the above superconducting wires. The part of the superconducting wire to which the slurry was applied was then placed face-to-face with the part of the other superconducting wire where the superconducting layer was exposed.

The overlapping wires were clamped from above and below with a jig and pressure was applied.

While still clamped in the jig, the wire was heated to 780°C in an air atmosphere to carry out the first heat treatment. It was then cooled to near room temperature, oxygen gas was introduced into the furnace, and the wire was heated to 500°C in an oxygen atmosphere to carry out the second heat treatment, forming a connection structure for the superconducting wire.

After connecting the superconducting wire, terminals were attached to both ends and the temperature dependence of electrical resistance was measured. A clear superconducting transition was confirmed at around 93 K with a transition width of approximately 1 K. The critical current value after the superconducting transition for this connection structure is set as a reference value of 1.0, and the relative critical current values are shown in the following examples and comparative examples.

When the cross section of the connection part was observed by SEM and SEM-EDX, the first crystal particles of GdBa ₂ Cu ₃ O _7-δ composition, which were plate-like or flat and had almost no carbon (C) observed, and the second crystal particles of GdBa ₂ Cu ₃ O _7-δ composition, which had an irregular shape and a low aspect ratio, were confirmed. The average major axis of the first crystal particles was about 5 μm, the minor axis was 2 μm, and the particle size (second particle size) of the second crystal particles was about 90 nm in both major and minor axes, which was a bimodal distribution. Furthermore, around the second particles, carbon-containing particles 33 of an irregular shape smaller than the second particles were confirmed, and carbon (C) was observed from these particles at an intensity 10 times or more that of the first crystal particles.

(Comparative Example 1)
Two oxide superconducting wires with a length of 10.5 cm were prepared, each wire having an intermediate layer and _{a GdBa2Cu3O7 -δ} layer (oxide superconducting layer) formed on a Hastelloy substrate and covered with a protective layer of silver and copper. A portion 1.0 cm from one end was wet etched using a mixed solution of nitric acid, ammonia, and hydrogen peroxide to expose the oxide superconducting layer.

Powders of Gd ₂ O ₃ , BaCO ₃ and CuO were prepared, appropriately weighed, thoroughly mixed, and the mixed powder was compressed to produce a green compact. The obtained green compact was sintered at 930°C to produce an oxide superconductor with a GdBa ₂ Cu ₃ O _7-δ composition. The obtained oxide superconductor was pulverized by beating in a mortar, and particles of an appropriate diameter were selected using a sieve or the like to produce a superconductor powder with a high aspect ratio, with a median major axis of 5 μm or more and a median minor axis of 2 μm or less.

The obtained superconductor powder, _{Gd2O3 powder} having a particle size of about 50 nm, _BaCO3 powder having a particle size of about 70 nm, and CuO powder having a particle size of about 30 nm were mixed in a mortar. Water and sodium alginate were added to the obtained mixed powder to make a slurry.

After applying the slurry to the exposed oxide superconducting layer of one of the superconducting wires, the part of the superconducting wire to which the slurry was applied was placed face-to-face with the part of the other superconducting wire with its exposed superconducting layer.

The overlapping wires were clamped from above and below with a jig and pressure was applied.

While still clamped in the jig, the wire was heated to 780°C in an air atmosphere to carry out the first heat treatment. It was then cooled to near room temperature, oxygen gas was introduced into the furnace, and the wire was heated to 500°C in an oxygen atmosphere to carry out the second heat treatment, forming a connection structure for the superconducting wire.

After connecting the superconducting wire, terminals were attached to both ends and the temperature dependence of electrical resistance was measured. A clear superconducting transition was confirmed near 93 K with a transition width of approximately 1 K. The critical current value after the superconducting transition was 0.8.

When the cross section of the connection was observed with SEM and SEM-EDX, plate-like or flat first crystal particles and irregularly shaped second crystal particles with a low aspect ratio were observed. Carbon (C) was detected on the surface of the second crystal particles. In addition, clumps of irregularly shaped carbon-containing particles 33 measuring approximately 100 nm to 2 μm were observed, which were larger than those in Example 1.

Example 2
Three oxide superconducting wires were prepared, each of which had an intermediate layer and a GdBa ₂ Cu ₃ O _7-δ layer (oxide superconducting layer) formed on a Hastelloy substrate and was covered with a protective layer of silver and copper. One of the wires was 2.2 cm long, and the remaining two were 10 cm long. The 2.2 cm wire was wet etched between both ends, and the two 10 cm wires were wet etched 1.0 cm from one end using a mixed solution of nitric acid, ammonia, and hydrogen peroxide to expose the oxide superconducting layer.

Powders of Gd ₂ O ₃ , BaCO ₃ and CuO were prepared, appropriately weighed, thoroughly mixed, and the mixed powder was compressed to produce a green compact. The obtained green compact was sintered at 930°C to produce an oxide superconductor with a GdBa ₂ Cu ₃ O _7-δ composition. The obtained oxide superconductor was pulverized by beating in a mortar, and particles of an appropriate diameter were selected using a sieve or the like to produce a superconductor powder with a high aspect ratio, with a median major axis of 5 μm or more and a median minor axis of 2 μm or less.

The smaller particles obtained during sorting were further pulverized in a ball mill for more than three hours to produce superconductor powder with a median particle size of 3 μm or more and a low aspect ratio of less than 2.

The two types of superconductor powders thus obtained were mixed with an organometallic salt solution in which Gd(OCOCH ₃ ) ₂ , Ba(OCOCH ₃ ) ₂ , and Cu(OCOCH ₃ ) ₂ were dissolved, in a weight ratio of 1:1:4, to prepare a slurry.

The obtained slurry was applied to the exposed oxide superconducting layer of the 2.2 cm superconducting wire. Then, the portion of the 2.2 cm superconducting wire to which the slurry was applied was placed face-to-face with the portion of the 10 cm superconducting wire with the exposed superconducting layer, resulting in the structure shown in FIG. 7.

The overlapping wires were clamped from above and below with a jig and pressure was applied.

While still clamped in the jig, the wire was heated to 780°C in an air atmosphere to carry out the first heat treatment. It was then cooled to near room temperature, oxygen gas was introduced into the furnace, and the wire was heated to 500°C in an oxygen atmosphere to carry out the second heat treatment, forming a connection structure for the superconducting wire.

After connecting the superconducting wire, terminals were attached to both ends and the temperature dependence of electrical resistance was measured. A clear superconducting transition was confirmed near 93 K with a transition width of approximately 1 K. In addition, the critical current value after the superconducting transition was 1.0.

(Variation 1)
After forming a connection structure according to the procedure of Example 2, solder containing silver and indium was placed on the surfaces of the 10 cm superconducting wires of the connection structure facing each other, and the solder was melted and bonded by heating at 200°C to form a reinforcing material.

After connecting the superconducting wire, terminals were attached to both ends and the temperature dependence of electrical resistance was measured. A clear superconducting transition was confirmed near 93 K with a transition width of approximately 1 K. In addition, the critical current value after the superconducting transition was 1.0.

(Variation 2)
The superconducting wire and slurry were prepared according to the procedure of Example 2, the slurry was applied to the exposed superconducting layers of two 10 cm superconducting wires, and the 2.2 cm superconducting wire and the portions of the two 10 cm superconducting wires to which the slurry had been applied were placed face to face and overlapped.

The wire was clamped from above and below with a jig, and the same heat treatment as in Example 2 was carried out while applying pressure to form a connection structure for the superconducting wire, and measurements were then carried out.

A clear superconducting transition was confirmed at around 93 K, with a transition width of approximately 1 K. In addition, the critical current value after the superconducting transition was 1.0.

(Variation 3)
A superconducting wire and a slurry were prepared according to the procedure of Example 2, and the slurry was applied to a range of 0.9 cm from each end of the exposed oxide superconducting layer of a 2.2 cm superconducting wire. The portion of the 2.2 cm superconducting wire to which the slurry was applied was then placed face-to-face with the portion of the 10 cm superconducting wire where the superconducting layer was exposed, to obtain the structure shown in Figure 10.

The wire was clamped from above and below with a jig, and the same heat treatment as in Example 2 was carried out while applying pressure to form a connection structure for the superconducting wire, and measurements were then carried out.

A clear superconducting transition was confirmed at around 93 K, with a transition width of approximately 1 K. In addition, the critical current value after the superconducting transition was 1.0.

(Variation 4)
After forming a connection structure according to the procedure of variant example 3, solder containing silver and indium was placed on the opposing surfaces of the 10 cm superconducting wires of the connection structure, and the solder was melted and bonded by heating at 200°C to form a reinforcing material.

After connecting the superconducting wire, terminals were attached to both ends and the temperature dependence of electrical resistance was measured. A clear superconducting transition was confirmed near 93 K with a transition width of approximately 1 K. In addition, the critical current value after the superconducting transition was 1.0.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. For example, components of one embodiment may be replaced or changed with components of another embodiment. These embodiments and their modifications are included within the scope and gist of the invention, and are included in the scope of the invention and its equivalents as set forth in the claims.

16 First superconducting layer 26 Second superconducting layer 30 Connection layer 31 First crystal grain 32 Second crystal grain 33 Carbon-containing particle 35 Carbon-containing portion 46 Third superconducting layer 100 Connection structure 400 Superconducting wire of second embodiment 401 First superconducting wire 402 Second superconducting wire 700 Superconducting coil 800 Heavy particle beam therapy device Pk1 First peak Pk2 Second peak d1 First major axis d2 Second major axis

Claims (20)

A first superconducting layer;
A second superconducting layer; and
a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including crystal grains containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), and a region that is present in a portion other than the crystal grains and has a carbon atom concentration higher than the carbon atom concentration of the crystal grains, the distribution of the major axes of the crystal grains including a bimodal distribution;
Equipped with
the bimodal distribution has a first distribution including a first peak and a second distribution including a second peak;
A connection structure of superconducting layers, wherein a first major axis corresponding to the first peak is larger than a second major axis corresponding to the second peak. The superconducting layer connection structure according to claim 1, wherein the carbon atom concentration in the region is 10 times or more the carbon atom concentration in the crystal grains. The connection structure of the superconducting layer according to claim 1 or claim 2, wherein the region contains particles containing barium (Ba), carbon (C), and oxygen (O). The superconducting layer connection structure according to claim 3, wherein the median major axis of the particles is smaller than the first major axis. The superconducting layer connection structure according to claim 3 or claim 4, wherein the median major axis of the particles is smaller than the second major axis. The superconducting layer connection structure according to any one of claims 1 to 5, wherein the median aspect ratio of the crystal grains having a major axis corresponding to the first distribution is greater than the median aspect ratio of the crystal grains having a major axis corresponding to the second distribution. The connection structure of the superconducting layer according to any one of claims 1 to 6, wherein the crystal grains having a major axis corresponding to the first distribution include crystal grains having a plate-like or flat shape. the first major axis is larger than a thickness of the connection layer in a direction from the first superconducting layer to the second superconducting layer,
The connection structure of superconducting layers according to claim 1 , wherein the second major axis is smaller than the thickness. a first superconducting wire including a first superconducting layer;
a second superconducting wire including a second superconducting layer;
a third superconducting layer having a first surface and a second surface opposite to the first surface;
a connection layer provided between the first superconducting layer and the third superconducting layer and between the second superconducting layer and the third superconducting layer, the connection layer including crystal grains containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), and a region that is present in a portion other than the crystal grains and has a carbon atom concentration higher than the carbon atom concentration of the crystal grains, the distribution of the major axes of the crystal grains including a bimodal distribution;
Equipped with
the first superconducting layer and the second superconducting layer are located on a side of the third superconducting layer facing the first surface;
the bimodal distribution has a first distribution including a first peak and a second distribution including a second peak;
A superconducting wire, wherein a first major axis corresponding to the first peak is larger than a second major axis corresponding to the second peak. The superconducting wire according to claim 9, wherein the carbon atom concentration in the region is 10 times or more the carbon atom concentration in the crystal grains. The superconducting wire according to claim 9 or 10, wherein the region contains particles containing barium (Ba), carbon (C), and oxygen (O). The superconducting wire according to claim 11, wherein the median major axis of the particles is smaller than the first major axis. The superconducting wire according to claim 11 or 12, wherein the median major axis of the particles is smaller than the second major axis. A superconducting coil comprising the superconducting wire according to any one of claims 9 to 13. A superconducting device comprising the superconducting coil according to claim 14. providing a first superconducting layer and a second superconducting layer;
An oxide superconductor containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) is prepared;
pulverizing the oxide superconductor to produce first crystal particles;
A solution of organic metal salts is prepared by dissolving a powder of an organic acid salt of a rare earth element (RE), a powder of an organic acid salt of barium (Ba), and a powder of an organic acid salt of copper (Cu);
preparing a slurry by mixing the first crystal particles with the organometallic salt solution;
applying the slurry onto the first superconducting layer;
A method for connecting superconducting layers, comprising: performing a heat treatment with the slurry sandwiched between the first superconducting layer and the second superconducting layer. The method for connecting superconducting layers according to claim 16, wherein the oxide superconductor is produced by mixing and compressing rare earth element (RE) oxide powder, barium (Ba) carbonate powder, and copper (Cu) oxide powder to produce a green compact, and then sintering the green compact. The method for connecting superconducting layers according to claim 16 or 17, wherein the heat treatment is carried out at a temperature of 800°C or less in an oxygen-containing atmosphere. The method for connecting superconducting layers according to any one of claims 16 to 18, wherein the median aspect ratio of the first crystal grains is 2 or more. forming second crystal particles containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) by the heat treatment;
the median value of the major axis of the second crystal grains is smaller than the median value of the major axis of the first crystal grains;
20. The method for connecting superconducting layers according to claim 16, wherein a median aspect ratio of the second crystal grains is smaller than a median aspect ratio of the first crystal grains.

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