JP4697128B2 - Superconducting coil - Google Patents

Description

  The present invention relates to a superconducting coil, and more particularly to a single pancake type superconducting coil formed by winding a thin film superconducting wire having a multilayer structure.

Conventionally, a thin film superconducting wire having a multilayer structure is provided in Japanese Patent Application Laid-Open No. 2003-323822 and the like.
There is provided a single pancake type superconducting coil in which the thin film superconducting wire is overlapped with an insulating tape such as a prepreg tape and wound around a winding frame in a spiral shape. An inner electrode is attached to the tip of the circumferential turn, and an outer electrode is attached to the tip of the outermost turn.

  The thin film superconducting wire having a multilayer structure is formed by laminating a substrate layer made of metal, an intermediate layer made of ceramics, a superconducting layer, and a stabilizing layer made of silver, and both the front and back surfaces are different layers on the superconducting layer side and the substrate side. Therefore, when the thin film superconducting wire is continuously wound, the inner peripheral surface of the innermost turn and the outer peripheral surface of the outermost turn become different layers.

  In the single pancake type coil, as shown in FIG. 5, the inner electrode 13 is fixed to the central winding frame 12, so the inner electrode 13 is the inner peripheral surface side of the tip of the innermost turn of the thin film superconducting wire 11. And the inner peripheral surface side is the superconducting layer side S. In that case, the outer peripheral surface at the tip of the outermost turn is the substrate side B. Since the electrode needs to be attached to the superconducting layer side S, as shown in FIG. 5, the outer electrode 14 is necessarily attached to the inner peripheral surface side of the tip of the outermost turn.

JP 2003-323822 A

  However, as shown in FIG. 5, when the outer electrode 14 is attached to the inner peripheral side of the outermost turn of the thin film superconducting wire 11, the thickness of the thin film superconducting wire 11 (usually 0.2 mm or less) and the thickness of the outer electrode 14 (usually normal). 2 mm or more), a gap is generated between the outer electrode 14 and the thin film superconducting wire 11, and in particular, the thin film superconducting wire 11 is bent at the corners of the outer electrode 14, which may cause distortion.

  In this type of single pancake type superconducting coil, a so-called impregnated coil in which a thin film superconducting wire is formed on a winding frame by being overlapped with an insulating tape such as a prepreg tape and then solidified by heat treatment. Since the gap is eliminated by interposing an insulating material between the turns, the stability is extremely excellent. However, in the case of the impregnated coil, since it is formed into a strong structure with no gap between the coil turns that are solidified integrally with the insulating sheet, if the distortion occurs partially, there is a risk of affecting the whole. There is.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a superconducting coil that significantly reduces the strain generated in the vicinity of the electrode mounting portion of the thin film superconducting wire and does not decrease the critical current value over a long period of time. .

In order to solve the above problems, the present invention provides a single pancake type superconducting coil formed by winding a thin film superconducting wire having a multilayer structure in which one side is a superconducting layer side and the other side is a substrate side.
An inner electrode on the inner peripheral surface of the innermost turn of the innermost turn of the thin film superconducting wire, an outer electrode attached to the outer peripheral surface of the outermost turn,
At least one or an odd number of positions between the inner electrode mounting position and the outer electrode mounting position, a switching joint that reverses the stacking order from the inner peripheral surface side to the outer peripheral surface side is provided,
A superconducting coil is provided in which the electrode mounting surface side is the superconducting layer side at the mounting position of the inner electrode and the outer electrode.

  According to the present invention, the inner circumferential surface side and the outer circumferential surface side are switched and joined at least at one place or odd places, so that the stacking order of the thin film superconducting wires is reversed at the switching joint, and the innermost circumference. The outer electrode can be attached to the outer peripheral surface of the tip of the outermost turn while the inner electrode is attached to the inner peripheral surface of the tip of the turn. That is, since the outer electrode can be arranged outside the superconducting coil, no gap is generated inside the superconducting coil even if the electrode is thick, and the thin-film superconducting wire is not distorted. As a result, a decrease in the critical current value can be suppressed and a more stable superconducting coil can be obtained.

Furthermore, according to the present invention, a long thin film superconducting wire can be joined and lengthened. Therefore, the end material of a thin film superconducting wire can be used effectively, and a thin film superconducting wire manufactured by a batch process can be used.
Usually, the production of thin film superconducting wire is performed in a continuous process, but since the production process includes vacuum processes such as vapor deposition and sputtering, the vacuum state is more stable and better performance is produced by a batch process. A thin film superconducting wire can be manufactured.

If the switching junction is at least one or an odd number, the outer electrode is attached to the inner peripheral surface of the outermost turn if the number is an even number, and the superconducting coil similar to the conventional one having no switching junction is used. This is because of the configuration.
From the viewpoint of obtaining a more stable superconducting coil that does not lower the critical resistance value, the number of switching junctions is preferably as small as possible, and more preferably three or less. Most preferably, it is one location.

In the present invention, the attachment surface of the inner electrode and the outer electrode is on the superconducting layer side.
This is because the distance from the electrode to the superconducting layer can be shortened and the resistance can be further reduced when the electrode mounting surface is on the substrate side rather than the substrate side.

In the switching joining portion, it is preferable that the superconducting layers of the two thin film superconducting wires are joined by soldering, ultrasonic welding, resistance welding, or a conductive adhesive.
By joining the superconducting layer sides of the thin film superconducting wire to each other, the distance between the superconducting layers of the two thin film superconducting wires can be brought close to each other and electrically joined, so that no extra resistance is generated.
In addition, the joining method is not limited as long as two thin film superconducting wires are electrically joined. However, the joining method is preferable in terms of obtaining high electrical conductivity and sufficient joining strength. Sonic welding and resistance welding are more preferable.

  The length of the switching joint is preferably 5 mm or more and 30 mm or less. This is because if the length of the switching joint portion is less than 5 mm, it may not be possible to electrically and safely join, and if it exceeds 30 mm, the thickness increases and the maximum bending diameter increases.

  The thin film superconducting wire has a substrate layer made of metal, an intermediate layer made of ceramics, a superconducting layer, and a stabilization layer made of silver, and the entire circumference is coated with copper, and the superconductivity is passed through the silver stabilization layer. The side on which the layer is located is preferably the superconducting layer side.

The substrate is preferably a metal, more preferably a substrate containing crystals having crystal orientation on at least the surface, and an oriented metal substrate is most preferably used. However, the present invention is not limited to this, and a single crystal plate other than metal can also be used.
Specifically, a nickel alloy such as nickel or Hastelloy (registered trademark), stainless steel, or a laminate of copper (alloy), aluminum (alloy), and nickel (alloy) bonded together is used as the metal. Can do. Among these, nickel and Hastelloy (registered trademark) are particularly preferably used.
The substrate is preferably in the form of a tape, and since it is necessary to impart strength to the wire, the thickness is preferably about 80 to 100 μm.

The intermediate layer is used to alleviate the mismatch of the crystal lattice between the substrate and the superconducting layer, or to avoid deterioration of the performance of the superconducting layer due to mutual diffusion between the substrate and the superconducting layer in heating or the like when forming the superconducting layer. It is formed on a metal substrate. Therefore, having a crystal structure close to the crystal of the superconducting layer, preferably has a thermal expansion coefficient close to the thermal expansion coefficient of the superconducting layer, for example, YSZ (yttrium stabilized _zirconia), SrTiO 3, MgO, etc. CeO ₂ ceramics It is preferable to form with a system material.
The intermediate layer may be formed by any film forming method such as sputtering, vacuum deposition, laser deposition, or chemical vapor deposition (CVD). Among these, it is preferable to use a pulsed laser deposition method (PLD method) that has a high film formation rate and is excellent in mass production.
The thickness of the intermediate layer is generally about several μm.

  The superconducting layer is not particularly limited as long as it exhibits superconducting properties, and an oxide superconductor is preferable. For example, a rare earth element-containing perovskite oxide superconductor, Bi-Sr-Ca-Cu-O-based oxide superconductor, or Tl-Ba-Ca-Cu-O-based oxide superconductor is used.

Examples of the oxide superconductor containing a rare earth element and having a perovskite structure include a REM ₂ CuO _7-X- based oxide. Here, RE is at least one element selected from rare earth elements such as Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb, and M is selected from Ba, Sr, and Ca. At least one element selected, X is a number of 1 or less.
Of REM ₂ CuO _7-X , a part of Cu can be substituted with Ti, V, Cr, Mn, Fe, Co, Ni, and Zn.
Specific examples _include YBa 2 _{CuO 7-X.}

In addition, the oxide superconductor of Bi-Sr-Ca-Cu- O _system, include oxide represented by _{Bi 2 Sr 2 Ca 2 Cu 3} O X and _{Bi 2 (Sr, Ca) 3} Cu 2 O X It is. Among these, a part of Bi can be replaced with Pb. Typically, (Bi, Pb) ₂ Ca ₂ Sr ₂ Cu ₃ O _X , (Bi, Pb) ₂ Ca ₂ Sr ₃ Cu ₄ O _{X, and the} like can be given. Tl-Ba-Ca-Cu- O based oxide _{superconductor, Tl 2 Ba 2 Ca 2 Cu} 3 O X and _{Tl 2 (Ba, Ca) 3} Cu 2 O X, Tl 1 Ba 2 Ca 2 Cu 3 O X , Oxides represented by Tl ₁ Ba ₂ Ca ₃ Cu ₄ O _{X, and the} like.
Among these oxide superconductors, oxide superconductors containing a rare earth element and having a perovskite structure are preferably used. Of these, holmium-based and yttrium-based oxide superconductors are particularly preferable, and holmium-based is most preferable.

  The superconducting layer is formed by using various thin film forming methods such as sputtering, which is physical vapor deposition, reactive vapor deposition, laser vapor deposition, chemical vapor deposition, CVD, and metal organic chemical vapor deposition (MOCVD). It can be formed on an intermediate layer. Among them, it is preferable to use a PLD method that can form a uniform film at a high film forming speed continuously for a long time. In order to perform laser deposition by the PLD method, a sintered body of a superconductor material is used as a target, and this target is irradiated with an excimer laser in a vacuum to form a plasma, and a superconducting layer is formed on a substrate with an intermediate layer facing the target. Deposit.

The stabilizing layer is made of a material that does not react with the superconducting layer or has little reaction. In particular, a metal material having a thermal expansion coefficient close to or larger than that of the oxide superconductor is preferably used. For example, gold, silver, platinum, or an alloy thereof can be used. In particular, silver is preferable in terms of economy.
The thickness of the stabilization layer is about 1 μm to several tens of μm.
Any of the various film forming methods described above may be used as a method of forming the stabilization layer. The gold or silver stabilization layer can be formed at a very high deposition rate by laser vapor deposition. In particular, high productivity is achieved by enabling the apparatus for forming the oxide superconducting layer and the apparatus for forming the stabilizing layer to be operated continuously.

Furthermore, it is preferable that the thin film superconducting wire is covered with a metal film on the entire circumference so that the substrate and the superconducting layer are electrically connected. The metal film is preferably formed of gold, platinum, silver, copper or the like, and particularly preferably copper.
Thus, the function of the stabilization layer can be imparted also to the substrate side by establishing conduction between the substrate and the superconducting layer.
The metal film is preferably formed by electroless plating on a thin film superconducting wire.
The thickness of the metal film is about 1 μm to several tens of μm.

  As described above, the thin film superconducting wire has a multilayer structure. In particular, an intermediate layer formed of a ceramic material is strong against compression but weak against tension. For this reason, it is preferable that the intermediate layer is positioned on the inner peripheral side and the superconducting layer side is wound on the inner peripheral side.

The position of the switching joint is preferably within 100 mm from the outer electrode or in the outermost turn.
By positioning the switching joint in the outermost peripheral turn, there is no joint between the coil turns, and a dense impregnated coil structure can be maintained.
Furthermore, when the position of the switching junction is within 100 mm and is closer to the outer electrode, the superconducting layer side that is the inner peripheral side can be increased, and the thin-film superconducting wire can be made less susceptible to distortion.

Further, it is preferable that the inner electrode and the outer electrode are made of copper and attached to the thin film superconducting wire by soldering, ultrasonic welding, resistance welding or conductive adhesive.
The inner electrode and the outer electrode are preferably gold, platinum, silver, copper, or an alloy containing at least one of these, and particularly preferably made of copper.
The joining method may be that the electrode and the thin film superconducting wire are electrically joined, but the joining method is preferable in that high conductivity and sufficient joining strength can be obtained, and in particular, soldering, ultrasonic welding, resistance welding. Is more preferable.

As described above, according to the present invention, the outer electrode can be attached to the outer peripheral surface side of the outermost peripheral turn of the thin film superconducting wire while the electrode attachment surfaces of the inner electrode and the outer electrode are the same surface of the thin film superconducting wire. Therefore, it is possible to reduce the occurrence of distortion at the electrode mounting portion of the thin film superconducting wire, and to obtain a superconducting coil in which the critical current value does not decrease over a long period of time.
Furthermore, since it is possible to lengthen by joining short thin film superconducting wires, the end materials of thin film superconducting wires can be used effectively, and superconducting coils using high performance thin film superconducting wires manufactured by a batch process are used. be able to.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 show a first embodiment of the present invention.
The superconducting coil 10 is a single pancake type coil formed by winding a thin film superconducting wire 11 having a multilayer structure around a winding frame 12 together with an insulating tape (not shown) such as a prepreg tape, and heat-treating it so as to be integrally formed. It is.

  The thin film superconducting wire 11 has a thickness t1 of 100 to 150 μm and a width w1 of 10 to 12 mm. The inner electrode 13 is attached and electrically connected to the inner peripheral surface of the tip of the innermost turn of the thin film superconducting wire 11, and the inner electrode 13 is fixed to an attachment portion provided on the winding frame 12. On the other hand, the outer electrode 14 is attached to the outer peripheral surface of the outermost turn of the thin film superconducting wire 11 for electrical connection.

As shown in FIG. 2, the multi-layered thin film superconducting wire 11 is formed by sequentially laminating a substrate 50, an intermediate layer 60, a superconducting layer 70, and a stabilizing layer 80, and covering the entire periphery with a metal protective film 90 made of copper. Yes.
The thin film superconducting wire 11 is formed of a thin film superconducting wire 11-1 and a thin film superconducting wire 11-2 that are joined so that the stacking order is reversed at the position of the outermost turn of the single pancake.

  That is, the thin film superconducting wire 11-1 is cut at the position of the outermost turn, the thin film superconducting wire 11-2 and the superconducting layer side S are joined by the solder 16, and the switching joint 15 is provided. In the present embodiment, the position of the switching joint 15 is 50 mm from the tip of the outermost peripheral turn T2, and the length L of the switching joint 15 is 25 mm.

  Thereby, it is set as the one thin film superconducting wire 11 continuous in the said switching junction 15, and the inner peripheral side of the thin film superconducting wire 11-1 is made into the superconducting layer side S which located the superconducting layer 70 through the stabilization layer 80. The outer peripheral side is the substrate side B. On the other hand, the outer peripheral side of the thin film superconducting wire 11-2 is the superconducting layer side S where the superconducting layer 70 is located via the stabilization layer 80, and the inner peripheral side is the substrate side B.

  As shown in FIG. 3, the inner electrode 13 is attached to the tip of the superconducting layer side S which is the inner peripheral side of the thin film superconducting wire 11-1, and the superconducting layer side S which is the outer peripheral side of the thin film superconducting wire 11-2. The outer electrode 14 is attached to the tip of the.

The thin film superconducting wire 11-1 has a superconducting layer side S as an inner peripheral surface and is wound around the winding frame 12 in a spiral shape, and the inner electrode 13 is positioned on the inner peripheral surface of the innermost turn T1. It is fixed to the mounting part.
When the thin film superconducting wire 11-1 is wound and reaches a position where the outermost turn T2 is reached, the thin film superconducting wire 11-2 having the outer peripheral side as the superconducting layer side S is wound, and the outer electrode is placed on the outer peripheral surface of the tip. 14 is located.
From the tip of the outermost turn of the thin film superconducting wire 11, only the insulating tape is wound a plurality of times to form a protective layer (not shown).

  The inner electrode 13 and the outer electrode 14 are each made of a copper electrode, and are attached to the thin film superconducting wire 11 by soldering. The thickness t2 of the inner electrode 13 and the outer electrode 14 is 2 to 3 mm, the width w2 is 20 to 30 mm, and the length L2 (the length corresponding to the length direction of the thin film superconducting wire 11) is 20 mm.

  The laminated structure of the thin film superconducting wire 11 will be described in detail. The substrate 50 is made of Hastelloy (registered trademark) tape, the intermediate layer 60 is made of YSZ (yttrium stabilized zirconia), and the superconducting layer 70 is a holmium oxide superconductor. The stabilization layer 80 is made of silver, and the intermediate layer 60, the superconducting layer 70, and the stabilization layer 80 are sequentially formed on the surface of the substrate 50 by laser vapor deposition or the like, and the entire periphery of the laminate is electrolessly plated. Is covered with a metal protective film 90 made of copper.

  The intermediate layer 60 has a thickness of several μm, the superconducting layer 70 has a thickness of about 1 μm to several tens of μm, the stabilization layer 80 has a thickness of about 1 μm to several tens of μm, and the metal film 90 has a thickness of about 1 μm to several tens of μm. The total thickness (t1) of the wire 11 is 100 to 150 μm. Therefore, the distance to the superconducting layer 70 is different between the front surface and the back surface of the thin film superconducting wire 11, and the surface resistance between the front surface and the back surface side is different.

In the superconducting coil 10 having the above configuration, the inner electrode 13 attached to the inner peripheral surface of the innermost turn T1 of the thin film superconducting wire 11 is attached to the superconducting layer side S and attached to the outer peripheral surface of the outermost turn T2. The outer electrode 14 is attached to the superconducting layer side S.
As described above, since both the mounting surfaces of the inner electrode 13 and the outer electrode 14 are the superconducting layer side S, the same electrical connection is made to the electrical connection portion between the thin film superconducting wire 11 of the inner electrode 13 and the outer electrode 14. Connection characteristics can be imparted and, since the inner electrode 13 and the outer electrode 14 are connected to the superconducting layer side S, no extra resistance is generated and high conductivity can be maintained.
In particular, since the outer electrode 14 is attached to the outer peripheral side of the tip of the outermost peripheral turn T2, it is possible to prevent the thin film superconducting wire 11-2 from being distorted and to reduce the critical current value for a long period of time. can do.

  In the first embodiment, the switching joint 15 is provided in the outermost turn T2, but it may be provided in an intermediate turn between the outermost turn T2 and the innermost turn T1. The superconducting layer side S is used for both the inner peripheral surface of the innermost turn T1 at the mounting position of the inner electrode 13 and the outer peripheral surface of the outermost turn T2 at the mounting position of the outer electrode 14. Can do.

FIG. 4 shows a superconducting coil 20 according to the second embodiment.
The difference from the first embodiment is that the switching joint 15 is provided in one place in the first embodiment, but in the second embodiment, three switching joints 15A, 15B and 15C are provided, and the switching joint 15 is provided. It is the point which joins in part 15A-15C and attachment to the thin film superconducting wire 11 of the inner electrode 13 and the outer electrode 14 by the welding by resistance welding or ultrasonic welding.
That is, the inner layer thin film superconducting wire 11-1 and the first intermediate layer thin film superconducting wire 11-2 are joined at the switching junction 15A, and the first intermediate layer thin film superconducting wire 11-2 and the second intermediate layer The thin film superconducting wire 11-3 and the switching junction 15B are joined, and the thin film superconducting wire 11-3 of the second intermediate layer and the thin film superconducting wire 11-4 of the outer peripheral layer are joined by the switching junction 15C.

As described above, when switching is performed at three places, both the inner peripheral surface of the tip end of the innermost turn T1 and the outer peripheral surface of the tip end of the outermost turn T2 can be stacked in the same stacking order to be the superconducting layer side S.
Therefore, when the inner electrode 13 is attached to the inner peripheral surface of the tip end of the innermost turn T1 and the outer electrode 14 is attached to the outer peripheral surface of the tip end of the outermost turn T2, the electrode mounting surface side becomes the superconducting layer side S.
Moreover, since the three switching joints 15A to 15C are joined by welding, the switching joints do not become thicker than soldering.

Thus, in the second embodiment, the inner and outer electrodes 13 and 14 can be attached to the superconducting layer side S as in the first embodiment, and in the second embodiment, a short thin film superconducting wire is joined. The length can be increased. Therefore, a thin film superconducting wire with high performance manufactured by a batch process can be used.
For example, a 4 m long thin film superconducting wire can be switched and joined at three locations to connect them together to form a superconducting coil wound with a 16 m long thin film superconducting wire.
Since other configurations and operational effects are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  The present invention is not limited to the first and second embodiments, but includes modifications within the scope equivalent to the scope of claims.

(A) of the superconducting coil of 1st Embodiment of this invention is a schematic perspective view, (B) is the principal part enlarged view of the electrode attachment part periphery of (A). It is a cross-sectional schematic diagram of a thin film superconducting wire. (A) of the superconducting coil of 1st Embodiment is a plane schematic diagram, (B) is the principal part enlarged view of the electrode attachment part periphery of the outer electrode of (A). It is a plane schematic diagram of the superconducting coil of the second embodiment. (A) of the conventional superconducting coil is a schematic plan view, and (B) is an enlarged view of the main part around the electrode mounting portion of the outer electrode of (A).

Explanation of symbols

10, 20 Superconducting coil 11 (11-1, 11-2, 11-3, 11-4) Thin film superconducting wire 12 Winding frame 13 Inner electrode 14 Outer electrode 15 Switching junction S Superconducting layer side B Substrate side

Claims (5)

In a single pancake type superconducting coil formed by winding a thin film superconducting wire having a multilayer structure in which one side is a superconducting layer side and the other side is a substrate side,
An inner electrode on the inner peripheral surface of the innermost turn of the innermost turn of the thin film superconducting wire, an outer electrode attached to the outer peripheral surface of the outermost turn,
At least one or an odd number of positions between the inner electrode mounting position and the outer electrode mounting position, a switching joint that reverses the stacking order from the inner peripheral surface side to the outer peripheral surface side is provided,
A superconducting coil characterized in that an electrode mounting surface side is the superconducting layer side at a mounting position of an inner electrode and an outer electrode.   The superconducting coil according to claim 1, wherein the superconducting layer side of the thin film superconducting wire is joined by soldering, ultrasonic welding, resistance welding, or a conductive adhesive at the switching joint.   The superconducting coil according to claim 1 or 2, wherein a length of the switching joint is 5 mm or more and 30 mm or less.   4. The superconducting coil according to claim 1, wherein the position of the switching joint is located within 100 mm from the outer electrode or in an outermost turn. 5. The thin film superconducting wire has a substrate layer made of metal, an intermediate layer made of ceramics, a superconducting layer, and a stabilization layer made of silver, and the entire circumference is coated with copper, and the superconductivity is passed through the silver stabilization layer. The side on which the layer is located is the superconducting layer side,
The superconducting device according to any one of claims 1 to 4, wherein the inner electrode and the outer electrode are made of copper and are attached to the thin film superconducting wire by soldering, ultrasonic welding, resistance welding, or a conductive adhesive. coil.

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