JP6214196B2 - Oxide superconducting coil and superconducting equipment provided with the same - Google Patents

Description

  The present invention relates to an oxide superconducting coil and a superconducting device including the same.

Superconducting devices such as cables, coils, motors, and magnets that use oxide superconductors as low-loss conductive materials have been developed. As a superconductor used in these superconducting devices, for example, Bi-based superconducting wires _{(Bi 2 Sr 2 CaCu 2 O} 8 + δ: Bi2212, Bi 2 Sr 2 Ca 2 Cu 3 O 10 + δ: Bi2223) or RE-123-based superconducting wires ( REBa ₂ Cu ₃ O _7-x : RE is a rare earth element including Y and Gd).
In general, as shown in FIG. 10, the RE-123-based oxide superconducting wire C is formed on a tape-like metal substrate 100 through an underlayer 101 such as a diffusion prevention layer and an intermediate layer 102 with good crystal orientation. After the superconducting layer 103 is formed, a first metal stabilizing layer 104 made of Ag is formed so as to cover the surface of the oxide superconducting layer 103. In addition, an oxide superconducting wire is configured by laminating a second metal stabilization layer (not shown) made of Cu depending on the application, and subjecting the outer periphery to insulation treatment as necessary. The metal stabilization layer is provided as a current path when the oxide superconducting wire is dislocated from the superconducting state to the normal conducting state for some reason.

In addition, an oxide superconducting coil obtained by winding this oxide superconducting wire in a plurality of layers on the outer periphery of a winding drum is known. The model structure of this oxide superconducting coil is shown in FIG. Regarding the oxide superconducting coil 105 shown in FIG. 11A, it is known that a magnetic field in a different direction acts on the oxide superconducting wire depending on the portion of the coil.
Magnetic field distribution in the case of analyzing the cross section (the hatched area S in FIG. 11A) of the upper side of the oxide superconducting coil 105 of the cylindrical model in the standing state shown in FIG. Is shown in FIG. In the region S of the partial cross section of the oxide superconducting coil 105, the direction and magnitude of the magnetic field acts as shown by the arrow in FIG. In FIG. 11B, the arrow indicates the direction and magnitude (strength) of the magnetic field as a vector.
As shown in FIG. 11B, in the superconducting coil 105, the magnetic field component in the X direction (radial direction) increases as it approaches the upper end of the coil, and the Y direction (the standing state of the superconducting coil 105 increases as it approaches the center of the coil. It can be seen that the magnetic field component in the height direction increases.

Further, the tape-shaped oxide superconducting wire has a magnetic field direction dependency, and as shown in FIG. 10, it is more perpendicular to the oxide superconducting wire C (in the direction of arrow F1 ) than in the direction of the magnetic field (arrow F2). Direction) or a certain magnetic field acting from any arbitrary direction (arrow F3 direction), the critical current decreases. For this reason, the operating current of the oxide superconducting coil depends on the oxide superconducting wire C to be used, which direction of the magnetic field reduces the critical current, and at which position in the superconducting coil the critical current decreases most. It is necessary to grasp and limit. In general, when using a superconducting coil to which an oxide superconducting wire, which is a high-temperature superconducting wire, is used, the operating current is often limited in consideration of the characteristics of the upper portion of the superconducting coil and the portion near the vertical direction in the superconducting coil.

Conventionally, when a superconducting coil is manufactured, a superconducting thin wire is manufactured by dividing a tape-shaped oxide superconducting wire into three or more narrow widths, and a thin oxide superconducting coil is manufactured using this superconducting thin wire. A technique for manufacturing an oxide superconducting coil by stacking a plurality of layers is known. When a tape-shaped oxide superconducting wire is divided into three or more narrow superconducting wires, a superconducting thin wire obtained by cutting from both ends in the width direction or from the center in the width direction of the tape-shaped oxide superconducting wire It is known that the critical current values of are different.
Then, in view of the state of the magnetic field at each position described above, a superconducting coil made of a superconducting thin wire having a high critical current is arranged on the end side in the stacking direction, and a superconducting coil made of a superconducting thin wire having a low critical current is arranged on the center side in the laminating direction A laminated superconducting coil having the above structure is known (see Patent Document 1).
In addition, when a high temperature superconducting coil is applied, the operating current is often limited in a portion close to the vertical direction at the upper and lower portions of the coil. On the other hand, there is known a method of controlling the direction of the magnetic field by arranging another coil at the upper part or the lower part of the coil so that the direction of the magnetic field at both ends of the coil is close to the horizontal direction with respect to the wire. Patent Document 1).

JP2011-258696A

Masafumi Kobetsu, et al. “Performance improvement of superconducting coil by utilizing multi-core tape wire” The 80th Spring 2009 Low Temperature Engineering and Superconductivity Society 3D-a01 Coil Application (3) P209

Since the laminated superconducting coil described in Patent Document 1 has a structure in which the superconducting wire is narrowed and thinned, the width of the superconducting wire becomes narrow, and there is a problem that restrictions are likely to occur in designing the superconducting coil.
In addition, as described in Non-Patent Document 1, a coil structure has been proposed in which a subcoil is additionally arranged on the outer peripheral portion of the upper end portion and the lower end portion of the superconducting coil to control the magnetic field. However, in the structure in which the subcoil is arranged on the outer periphery of the coil, there is a problem that the outer diameter of the coil at the subcoil installation position becomes large.

  The present invention has been made in view of the above circumstances, and can suppress deterioration of superconducting characteristics due to the angular dependence of the magnetic field acting on the coil, and suppress a decrease in operating current in the magnetic field of the coil without changing the outer dimensions of the coil. An object of the present invention is to provide a superconducting coil that can be used and a superconducting device including the same.

The oxide superconducting coil of the present invention is an oxide superconducting coil in which an oxide superconducting wire having an intermediate layer and an oxide superconducting layer is wound on a tape-shaped substrate so as to form a plurality of layers on the outer periphery of the winding drum. The oxide superconducting wire formed on the oxide superconducting wire wound on the other end of the winding drum. It is characterized by being thicker than the formed oxide superconducting layer.
The present invention is an oxide superconducting coil in which an oxide superconducting wire provided with an intermediate layer and an oxide superconducting layer on a tape-like substrate is wound so as to form a plurality of layers on the outer periphery of a winding drum. In the oxide superconducting wire wound so as to form a plurality of layers on the outer side of the cylinder, the thickness of the oxide superconducting layer of the oxide superconducting wire on the inner peripheral side close to the outer peripheral surface of the winding cylinder is outside the winding cylinder. The thickness of the oxide superconducting wire in the other part of the oxide superconducting wire wound so as to form a plurality of layers is greater than the thickness of the oxide superconducting layer.

In the tape-shaped oxide superconducting wire having a structure having an intermediate layer and an oxide superconducting layer on the base material, according to the present inventors' research, the thicker the oxide superconducting layer, the more the critical current tends to increase. I know. It can be understood that this tendency is the same in an environment where a strong magnetic field such as 0.5 T or more acts in a temperature range where the superconducting layer can be maintained in a superconducting state.
For this reason, in a coil structure in which a plurality of layers of tape-shaped oxide superconducting wires are wound around a winding drum, the thickness of the oxide superconducting layer of the oxide superconducting wire wound on the lengthwise end side of the winding drum is If it is made thicker than the oxide superconducting layer in other parts, even if the influence of a magnetic field acts on the thick oxide superconducting layer to reduce its critical current, the structure of the thin oxide superconducting layer is better. Since the critical current can be increased, a decrease in operating current as a superconducting coil can be suppressed. For this reason, it is possible to provide an oxide superconducting coil capable of maintaining the operating current at a high level, considering the magnetic field angle dependency acting on the oxide superconducting wire.
In addition, even in oxide superconducting wires wound in multiple layers on the outside of the winding drum, by making the superconducting layer of the oxide superconducting wire on the inner peripheral side thicker than other parts, a thin oxide superconducting wire Since the critical current can be increased as compared with the structure in which the layer is provided, it is possible to suppress a decrease in the operating current as the superconducting coil.

  In the oxide superconducting coil of the present invention, the oxide superconducting wire wound around the inside and outside of the coil body among the oxide superconducting wires wound around the outer periphery of the winding drum to constitute the annular coil body. A structure in which the thickness of the formed oxide superconducting layer is thicker than the thickness of the oxide superconducting layer formed on the oxide superconducting wire wound inside the coil body between the inside and the outside But it ’s okay.

  When the oxide superconducting coil is cooled to be in a superconducting state, different thermal stress acts on the oxide superconducting wire wound around the outer side of the winding drum at each position. The thermal stress acts on the oxide superconducting layer of the middle oxide superconducting wire located between the inner side and the outer side outside the winding drum as a larger peeling force. For this reason, if the oxide superconducting layer formed on the oxide superconducting wire wound inside the outer side of the winding drum is made thinner than the oxide superconducting layer in other parts, A structure that does not easily peel off due to thermal stress can be obtained. For this reason, it is possible to provide a superconducting coil in which the critical current does not easily decrease even when thermal stress acts during cooling.

  In the oxide superconducting coil of the present invention, with respect to the coil width along the radial direction of the coil body formed by the oxide superconducting wire wound outwardly of the winding drum, the coil width is determined based on the innermost circumferential position. The thickness of the oxide superconducting layer formed on the oxide superconducting wire wound in the region of 8% to 75% is formed in the oxide superconducting wire wound in the other region. It is characterized by being made thinner than the thickness of the oxide superconducting layer.

  When the oxide superconducting coil is cooled to be in the superconducting state, the oxide superconducting wire wound around the outer side of the winding drum is subjected to different thermal stresses at each position. Many thermal stresses are concentrated in the region of 8% or more and 75% or less of the coil width starting from the position. For this reason, if the thickness of the oxide superconducting layer of the oxide superconducting wire provided in this region is made thinner than that of the oxide superconducting layer in other regions, the structure is difficult to peel off due to thermal stress during cooling. Can do. For this reason, it is possible to provide a superconducting coil in which the critical current does not easily decrease even when thermal stress acts during cooling.

A superconducting device according to the present invention includes the oxide superconducting coil according to any one of the preceding items.
If it is a superconducting apparatus provided with the above-mentioned oxide superconducting coil, it has a feature that it can be used by setting the operating current higher than that of a superconducting apparatus provided with a superconducting coil having a general structure.

  According to the present invention, since the oxide superconducting layer at a position susceptible to the influence of the magnetic field at the time of energization is thickened, the critical current reduction can be suppressed even under the influence of the magnetic field. A superconducting coil and a superconducting device capable of setting a high operating current can be provided.

FIG. 1A is a schematic diagram of the oxide superconducting coil according to the first embodiment of the present invention, FIG. 1B is a diagram showing a stacked state of pancake coils constituting the oxide superconducting coil, and FIG. ) Is a perspective view showing an example of a pancake coil constituting the oxide superconducting coil. FIG. 2 is a partial cross-sectional view showing an example of an oxide superconducting wire for constituting the oxide superconducting coil. FIG. 3 is a graph showing an example of the magnetic field angle dependency of the tape-shaped oxide superconducting wire. FIG. 4 is a graph showing a ratio of the axial radial critical current (Ic) of the innermost layer in the coil radial direction to the minimum value Ic_min. FIG. 5 is a graph showing an example of the calculation result of the coil average critical current (Ic) ratio in the coil radial direction. 6 is an enlarged view of calculation of a coil average critical current (Ic) ratio shown in FIG. FIG. 7 is a diagram showing an example of a thermal stress distribution analysis result from the inner part to the outer part of the coil body in the pancake coil constituting the oxide superconducting coil. FIG. 8A is a view showing an example of a stud pin used when a peeling test by the stud pull method is performed, and FIG. 8B shows a correlation between the oxide superconducting layer thickness and the 50% peeling stress by the cumulative hazard method. Graph showing. FIG. 9 is a graph showing the correlation between the oxide superconducting layer thickness and the critical current in a self magnetic field and in a 3T external magnetic field. FIG. 10 is a partial sectional view showing an example structure of a tape-shaped oxide superconducting wire. FIG. 11A is a perspective view showing an example structure of a conventional oxide superconducting coil, and FIG. 11B is a vector diagram showing a magnetic field distribution at each cross-sectional position in the oxide superconducting coil.

Hereinafter, a first embodiment of a connection structure of oxide superconducting wires according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments described below. In addition, the drawings used in the following description may show the main parts in an enlarged manner for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of the respective components are the same as the actual ones. Not always.
FIG. 1A shows an oxide superconducting coil A according to the first embodiment. This superconducting coil A is composed of a tape-shaped oxide superconducting wire 1 described below in a bobbin (winding frame) 3 in multiple layers. Thus, the coil is wound.

The oxide superconducting wire 1 applied to the superconducting coil A has an intermediate layer 5, an oxide superconducting layer 6, a protective layer 7, above one surface (surface) of the tape-like substrate 2 as shown in FIG. The metal stabilizing layer 8 is laminated to form a tape-shaped superconducting laminate 9, and the insulating layer 10 is covered with an adhesive layer 10 a so as to cover the outer periphery of the superconducting laminate 9.
The superconducting coil A of this embodiment is configured by stacking a plurality (six in this embodiment) of thin pancake coils 4 each having a number of turns of the oxide superconducting wire 1 wound around a thin winding drum. And the saddle plate 3B is attached to both ends in the length direction of the winding drum 3A constituted by stacking six thin winding drums, and the bobbin 3 is formed by the winding drum 3A constituted by stacking and the two saddle plates 3B. It is configured.

  In the example of FIG. 1A, the structure described above is simplified and shown as a state where six pancake coils 4 are stacked, and a plurality of tape-shaped oxide superconducting wires wound around each pancake coil 4 1 is shown in a simplified form as a thin plate as viewed in cross section. Accordingly, in FIG. 1A, the thin plate-like oxide superconducting wire 1 is shown to be wound 11 turns on the outside of the winding drum 3A, but in accordance with the performance required for an actual superconducting coil. It is wound from several tens of turns to several hundreds of turns. Since six pancake coils 4 are stacked and then fixed with resin impregnation, an impregnated resin layer 11 such as an epoxy resin layer is surrounded around each oxide superconducting wire 1 in FIG. Simplified display as covered structure.

Below, each element which comprises the oxide superconducting wire 1 is demonstrated.
In the oxide superconducting wire 1, the base material 2 is preferably in the form of a tape, a sheet or a thin plate in order to obtain a long superconducting wire having flexibility. The material used for the substrate 2 is preferably a material having a relatively high mechanical strength, heat resistance, and a metal that can be easily processed into a wire, such as stainless steel and hastelloy. Examples thereof include various heat-resistant metal materials such as nickel alloys, or materials obtained by arranging ceramics on these various metal materials. Among these, a commercially available product is preferably Hastelloy (trade name, manufactured by Haynes, USA), which is known as a kind of Ni alloy. This kind of Hastelloy includes Hastelloy B, C, G, N, W, etc., which have different amounts of components such as molybdenum, chromium, iron, cobalt, etc., and any kind can be used here. Moreover, what is necessary is just to adjust the thickness of the base material 2 suitably according to the objective, and is 10-500 micrometers normally, Preferably it is 20-200 micrometers. Moreover, as the base material 2, an oriented Ni—W alloy tape base material in which a texture is introduced into a nickel alloy can also be applied.

As the intermediate layer 5, a structure in which an underlayer 5 </ b> A composed of a diffusion prevention layer or a bed layer, an alignment layer 5 </ b> B, and a cap layer 5 </ b> C are stacked in this order can be applied as an example.
When the base material 2 or another layer receives a thermal history as a result of heat treatment when forming another layer on the upper surface side of this layer, a part of the constituent elements of the base material 2 diffuses. And it has a function which suppresses mixing in the oxide superconducting layer 6 side as an impurity. A specific example of the diffusion preventing layer is not particularly limited as long as it can exhibit the above functions, but Al ₂ O ₃ , Si ₃ N ₄ , or GZO (Gd _A single layer structure or a multilayer structure composed of ₂ Zr ₂ O ₇ ) or the like is desirable.

The bed layer is used to suppress the reaction of constituent elements at the interface between the base material 2 and the oxide superconducting layer 6 and to improve the orientation of the layer provided above this layer. The specific structure of the bed layer is not particularly limited as long as it can exhibit the above functions, but Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , Dy ₂ O ₃ , Er ₂ O, which have high heat resistance. ₃ , a single layer structure or a multilayer structure composed of rare earth oxides such as Eu ₂ O ₃ and Ho ₂ O ₃ is desirable. Both the diffusion preventing layer and the bed layer may be provided, or only one of them may be provided, and may be omitted depending on the constituent material of the alignment layer.

The alignment layer 5 </ b> B has a function of controlling the crystal orientation of the cap layer 5 </ b> C and the oxide superconducting layer 6 formed thereon, and a function of suppressing the constituent elements of the base material 2 from diffusing into the oxide superconducting layer 6. And a function to alleviate a difference in physical characteristics such as a coefficient of thermal expansion and a lattice constant between the base material 2 and the oxide superconducting layer 6. The constituent material of the alignment layer 5B is not particularly limited as long as it can exhibit the above functions. When a metal oxide such as Gd ₂ Zr ₂ O ₇ , MgO, or ZrO ₂ —Y ₂ O ₃ (YSZ) is used, a crystal is formed in an ion beam assisted deposition method (hereinafter sometimes referred to as IBAD method). A layer with high orientation can be obtained, and the crystal orientation of the cap layer 5C and the oxide superconducting layer 6 can be made better, which is particularly preferable.

The cap layer 5C controls the crystal orientation of the oxide superconducting layer 6 to be equal to or higher than that of the oriented layer, and diffuses the elements constituting the oxide superconducting layer 6 toward the intermediate layer 5 or the oxide superconducting layer 6. It has the function etc. which suppress reaction of the gas used at the time of lamination | stacking, and the intermediate | middle layer 5. The material of the cap layer is not particularly limited as long as it can express the above _{functions, CeO 2, Y 2 O 3} , Al 2 O 3, Gd 2 O 3, ZrO 2, Ho 2 O 3, Nd 2 Metal oxides such as O ₃ , YSZ, and LMnO ₃ are preferable from the viewpoint of lattice matching with the oxide superconducting layer 6. Among them, CeO ₂ or LMnO ₃ is particularly preferable because of the matching with the oxide superconducting layer 6. Here, when CeO ₂ is used for the cap layer, the cap layer may include a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.

The oxide superconducting layer 6 has a function of flowing current when in the superconducting state. The material used for the oxide superconducting layer 6 can be widely applied to an oxide superconductor having a generally known composition, such as a copper oxide superconductor such as a Y-based superconductor. It is done. The composition of the Y-based superconductor is, for example, REBa ₂ Cu ₃ O _7-x (RE is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, And one or more rare earth elements among Tm, Yb, and Lu. _X represents oxygen deficiency. Specifically, Y123 (YBa ₂ Cu ₃ O _7-x ), Gd123 ( _{GdBa 2 Cu 3 O 7-x} ) and the like. Although the base material of this oxide superconductor is an insulator, it becomes an oxide superconductor with a well-crystallized structure by incorporating oxygen by oxygen annealing, and has the property of exhibiting superconducting properties. In order for the oxide superconducting layer 6 to exhibit such an excellent crystal orientation, it is formed on the cap layer having the above-described good crystal orientation.
The oxide superconducting layer 6 having such excellent crystal orientation exhibits excellent critical current characteristics when the oxide superconducting wire 1 is cooled below the critical temperature and energized.

  The protective layer 7 becomes a current path that bypasses an overcurrent generated by some accident when the oxide superconducting wire 1 is energized, and in order to facilitate the incorporation of oxygen into the oxide superconducting layer 6, it transmits oxygen during heating. Has a function to facilitate. For this reason, it is preferable that the protective layer 7 is formed from a material mainly composed of Ag, such as Ag or an Ag alloy. The material for forming the protective layer 7 may be a mixture or alloy containing a noble metal such as Au or Pt, or a plurality of these may be used.

  In the present embodiment, a metal stabilizing layer 8 is provided on the protective layer 7. The use of the metal stabilization layer 8 varies depending on the use of the oxide superconducting wire 1. For example, when used for a superconducting cable, a superconducting motor, or the like, it is used as a main part of a bypass that commutates an overcurrent generated when quenching occurs due to some accident and the oxide superconducting 6 transitions to a normal conducting state. At this time, the material used for the metal stabilization layer 8 is made of a relatively inexpensive material such as copper, a Cu-Zn alloy (brass), a copper alloy such as a Cu-Ni alloy, aluminum, an aluminum alloy, and stainless steel. It is preferable to use copper, and it is preferable to use copper because it has high conductivity and is inexpensive. Further, when the oxide superconducting wire 1 is used for a superconducting fault current limiter, the stabilization layer is used to instantaneously suppress an overcurrent generated when a quench occurs and the state transitions to a normal conducting state. In the case of this application, examples of the material used for the metal stabilization layer 8 include high-resistance metals such as Ni-based alloys such as Ni-Cr.

  The metal stabilizing layer 8 is mainly composed of a metal tape bonding structure or a plating layer. When the metal stabilization layer 8 has a metal tape bonding structure, a conductive bonding material such as solder is provided on the inner surface side of the metal stabilization layer 8. In the structure shown in FIG. 2, the display of the conductive bonding material is omitted, but examples of tin alloys such as solder constituting the conductive bonding material include Sn, Sn—Ag alloy, Sn—Bi alloy, and Sn—Cu. Lead-free solder, Pb—Sn alloy solder, eutectic solder, low-temperature solder, etc. made of an alloy containing Sn as a main component, such as a Sn-based alloy or Sn—Zn-based alloy. It can also be used in combination of more than one species.

  Next, in the oxide superconducting coil A of the present embodiment, among the oxide superconducting wire 1 wound around the outer side of the winding drum 3A, both ends of the winding drum 3A in the length direction, that is, the flange plate 3B. The thickness of the oxide superconducting layer 6 formed on the pancake coil 4 disposed at the closest position is thicker than the thickness of the oxide superconducting layer 6 formed on the pancake coil 4 at other positions. Is formed. For ease of explanation, of the six pancake coils 4 stacked as shown in FIG. 1 (a), the two upper and lower pancake coils 4 closest to the slat 3B are connected to the pancake coil 4A. And the other pancake coils 4 may be distinguished and described as pancake coils 4B.

The oxide superconducting layer 6 formed on the oxide superconducting wire 1 can be formed to an arbitrary thickness within the range of 0.8 μm to 6 μm. Even within this range, for example, it is preferable to select a range of 1 μm to 4 μm.
Since the oxide superconducting layer 6 can be formed by a film deposition method such as a laser vapor deposition method, a sputtering method, a vacuum vapor deposition method, a chemical vapor deposition method (CVD method), or a coating pyrolysis method (MOD method), The thickness of the film can be freely set by changing various conditions such as the film formation time, the transport speed of the base material, the distance between the target and the base material, and the temperature condition.

Therefore, as an example, when the thickness of the oxide superconducting layer 6 provided on the oxide superconducting wire constituting the pancake coil 4B is 1 μm, the oxide superconducting wire constituting the pancake coil 4A is provided on the oxide superconducting wire. The thickness of the oxide superconducting layer 6 can be 1.7 μm. In addition, when the thickness of the oxide superconducting layer 6 provided on the oxide superconducting wire constituting the pancake coil 4B is set to 1 to 2 μm, the oxide superconducting wire constituting the pancake coil 4A is provided on the oxide superconducting wire. The thickness of the oxide superconducting layer 6 provided on the oxide superconducting wire constituting the pancake coil 4A constitutes the pancake coil 4B, such as a configuration in which the thickness of the oxide superconducting layer 6 is 3 to 4 μm. It is formed thicker than the oxide superconducting layer 6 provided on the oxide superconducting wire.
The oxide superconducting layer 6 provided on the oxide superconducting wire constituting the pancake coil 4A is formed thicker than the others when the superconducting coil A shown in FIG. This is because the influence of the magnetic field is the largest on the oxide superconducting layer 6 of the oxide superconducting wire 1 located at both ends in the length direction of the electrode, and the critical current of the oxide superconducting layer 6 at that position is reduced. Therefore, the oxide superconducting layer 6 provided on the oxide superconducting wire constituting the pancake coil 4A located on both ends of the winding drum 3A is provided on the oxide superconducting wire constituting the other pancake coil 4B. It is formed thicker than the oxide superconducting layer 6.
At present, the inventor's research shows that the oxide superconducting layer has a thickness in the range of 0.5 μm to 6 μm, and the thickness of the oxide superconducting layer is increased under the condition that a magnetic field of 0.5 T or more acts. It has been found that the critical current tends to increase.
For this reason, it is preferable to employ the above-described structure in the oxide superconducting coil A shown in FIG.

Next, in any one pancake coil 4 of the oxide superconducting coil A shown in FIG. 1 (a), the oxide superconducting wire 1 extends from the inner side to the outer side on the outer side (outer peripheral side) of the winding drum 3A. However, the thickness of the oxide superconducting layer 6 wound inside from the inside is thinner than the thickness of the oxide superconducting layer 6 wound inside, and It is preferable that the thickness is smaller than the thickness of the oxide superconducting layer 6 wound from the side to the outside.
As an example, in the pancake coil 4, an oxide superconducting wire having a thick superconducting layer is wound inside the coil, and the oxide superconducting wire having a thin oxide superconducting layer is connected to the oxide superconducting wire. It is possible to adopt a structure in which an oxide superconducting wire having a thick oxide superconducting layer is connected to this superconducting wire and wound outside the coil.
As an example, in the cross section of the region where the oxide superconducting wire 1 is wound, with respect to the radial distance from the innermost peripheral position (winding start side position) to the outermost peripheral position (winding end side position), A thick oxide superconducting layer 6 is provided in a range up to less than 8%, and a thin oxide superconducting layer 6 is provided in a range up to 8% or more (about 10 MPa or more as a peeling stress) and less than 75%. It is preferable that a thick oxide superconducting layer 6 is provided in a range of up to 100%. In the region of 8% or more and 75% or less, the peeling stress increases to about 10 MPa or more. Therefore, it is preferable to use an oxide superconducting wire provided with a thin oxide superconducting layer 6.

  In the oxide superconducting coil A shown in FIG. 1A, when the internal thermal stress is analyzed in a coil structure in which one pancake coil 4 is impregnated with epoxy resin, the oxide superconducting coil A manufactured at room temperature is operated. Therefore, since it is cooled to a temperature of 77K or less, thermal stress acts on the inside as it cools. Assuming that a large number of layers of the oxide superconducting wire 1 are wound around the outer circumference of the winding drum 3A for one pancake coil 4, the thermal stress varies depending on the position. . Regarding the action of the thermal stress, when described in the above range, the range of 20 to 55% is the largest from the innermost peripheral position to the outermost peripheral position, and the range of 13 to 20% and the range of 55 to 62% are the second. The range of 10-13% and the range of 62-70% are the third largest. Hereinafter, in order of 8 to 10% range, 70 to 75% range, 4 to 8% range, and 75 to 82% range, the size decreases gradually toward the innermost and outermost sides. Become. When thermal stress acts as described above, peeling stress acts on the oxide superconducting layer 6.

  When the oxide superconducting wire 1 is cooled below the critical temperature, the oxide superconducting wire 1 of each pancake coil 4 is individually separated from the inner region and the outer region in the radial direction of the pancake coil 4 due to thermal stress during cooling. Also, a greater stress acts on the middle region. For example, along the cross section of the pancake coil 4 (cross section along the radius of the pancake coil 4), a stress acting in the tensile direction acts on the oxide superconducting wire 1. Even if such stress acts, in the oxide superconducting coil A of the present embodiment, the oxide superconducting layer 6 in the region where the stress of the pancake coil 4 acts largely is made thin. There is little possibility that peeling occurs in the superconducting layer 6. This is because the thin oxide superconducting layer 6 is stronger in peeling force than the thick oxide superconducting layer 6.

  For this reason, the oxide superconducting wire 1 in the position as described above can be used for the action of thermal stress by selectively using the thick oxide superconducting layer 6 and the thin oxide superconducting layer 6 as described above. Even if it receives, it can be set as the pancake coil 4 with which a critical current cannot fall easily. In addition, providing such a pancake coil 4 in the oxide superconducting coil A has an effect of providing the superconducting coil A with improved operating current.

  By the way, the thickness of the oxide superconducting layer 6 formed on the oxide superconducting wire 1 is in the range of 0.8 to 6 μm, and it is assumed that the thickness is properly used in this range. Since the dimensional influence on the outer shape of the coil 4 is about several hundreds μm, the outer size of the pancake coil 4 does not greatly differ, and no dimensional problem occurs.

  The oxide superconducting coil A shown in FIG. 1 can be used for a purpose by generating a magnetic field by cooling the whole to a critical temperature or lower (for example, 77 K or lower) and energizing the oxide superconducting wire 1.

In addition, a magnetic field can be generated when the oxide superconducting wire 1 of the superconducting coil A is energized. However, when a self-magnetic field acts on the oxide superconducting layer 6 of the pancake coil 4, However, since the oxide superconducting wire 1 having the thick oxide superconducting layer 6 is disposed on the inner peripheral side, the superconducting coil A has a large critical current as a coil and is resistant to the above-described thermal stress. Can be provided.
The present invention can be applied to various superconducting devices such as a superconducting magnet and a superconducting motor provided with the superconducting coil A.

Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
A plurality of tape-shaped substrates having a width of 5 mm, a thickness of 100 μm, and a length of 170 m made of Hastelloy (trade name Hastelloy C-276, manufactured by Haynes, USA) were prepared, and the surface was polished.
Next, a diffusion prevention layer, a bed layer, an alignment layer, and a cap layer were laminated in this order on one surface of a plurality of substrates under the following formation conditions. When each film is formed, a feed reel and a take-up reel that transport the tape-shaped substrate are provided inside the film forming apparatus, and the film is sequentially formed on the substrate while moving the substrate at a predetermined speed. Went.
First, a 100 nm-thick diffusion prevention layer made of Al ₂ O ₃ is formed on a tape-like substrate by ion beam sputtering, and then Y ₂ is formed on the diffusion prevention layer by ion beam sputtering. A bed layer made of O ₃ and having a thickness of 20 nm was formed. Next, an alignment layer having a thickness of 10 nm made of MgO was formed on the bed layer by IBAD.

After forming the alignment layer, a 400 nm thick cap layer made of CeO ₂ is formed by the PLD method, and a 1.7 μm thick oxide superconducting layer having a composition of YBa ₂ Cu ₃ O _7-x is formed. A protective layer of 2 μm thick Ag was formed by sputtering to obtain a laminate. This laminated body was subjected to oxygen annealing treatment at 500 ° C. for 10 hours in an oxygen atmosphere, and then a 300 μm-thick copper metal stabilization tape was bonded to the protective layer with an Sn solder layer and bonded to form a tape-shaped oxide superconductor. A laminate was obtained. A polyimide resin tape was wound around the outer periphery of the oxide superconducting laminate to form an insulating layer, thereby obtaining an oxide superconducting wire.
This oxide superconducting wire is wound 100 turns around a cylindrical winding cylinder made of GFRP (fiber reinforced plastic) having an inner diameter of 60 mm, an outer diameter of 132 mm, and a height of 10.5 mm, and a pan having a coil inner diameter of 60 mm and a coil outer diameter of 132 mm. A cake coil was prepared.
In addition, the pancake coal of the same size manufactured with the thickness of the oxide superconducting layer being 1 μm in the oxide superconducting wire having the same structure was produced.
Table 1 below shows the performance of a superconducting coil constructed by using these two types of pancake coils to create a superconducting coil having a six-layer structure and impregnating with an epoxy resin.

As shown in Table 1, design example 1 has 1 oxide superconducting layer of superconducting wire wound around the first (bottom) to sixth (top) pancake coil among six layers. A thick oxide superconducting layer of 0.7 μm, and the oxide superconducting layer of the oxide superconducting wire wound around the second to fifth pancake coils is a thin (1 μm thick) oxide superconducting layer.
The comparative example shown in Table 1 is a superconducting coil having a structure in which six layers of pancake coils formed by using only an oxide superconducting wire provided with an oxide superconducting layer having a thickness of 1 μm are stacked.
Compared with the superconducting coil of the comparative example, the superconducting coil of design example 1 has a larger coil critical current and coil center magnetic field.
Although not described in Table 1, all of the oxide superconducting wires wound around the first to sixth pancake coils are made of an oxide superconducting layer having a thickness of 1.7 μm. The critical current of the superconducting coil manufactured as follows is 220A. From this comparison, the oxide superconducting layer provided in the other part of the oxide superconducting layer provided in the lowermost and uppermost pancake coils, that is, the coil on the axial end side of the winding drum. It can be seen that by using a material thicker than the layer, an excellent coil critical current can be obtained without using a thick oxide superconducting layer for the entire coil.

FIG. 3 shows the critical current (Ic :) when a magnetic field of 0.5 T is applied from various angles (θ) to the cross section of the oxide superconducting wire having the oxide superconducting layer having a thickness of 1.7 μm manufactured previously. A: 77K) is shown.
As shown in FIG. 3, the oxide superconducting wire has an angle dependency of the critical current (Ic) depending on the direction of the magnetic field. In consideration of this angle dependency, the maximum performance of the superconducting coil is obtained. Desired structural design needs to be done.

FIG. 4 shows a pancake coil having an inner diameter of 60 mm and an outer diameter of 132 mm using an oxide superconducting wire having the same structure as the above-described oxide superconducting wire except for a structure in which the bonded copper thickness is 100 μm and the width is 5 mm. The superconducting coil which laminated | stacked six layers of pancake coils is shown the calculation result of the ratio (coil axial direction) of the superconducting coil Ic in 50K.
In the angle dependence of the critical current shown in FIG. 3, the lowest value is obtained in the vicinity of 40 ° at the angle θ of FIG. The value of the ratio of Ic-min (Ic / Ic-min) to the value of the critical current (Ic) obtained at the coil axial position is the value shown in FIG.
The coil axial direction distribution in the innermost layer of the superconducting coil of this example is as shown in FIG. Since a portion having a particularly low critical current (Ic) is generated at the end portion (upper side in FIG. 4) of the superconducting coil, a more effective superconducting coil can be produced by disposing a thick oxide superconducting layer near the end portion in the axial direction. It is considered possible. Specifically, it is desirable to dispose an oxide superconducting wire having an oxide superconducting layer that is 18% or more thicker than the other parts on the uppermost layer of the superconducting coil (the upper end of the superconducting coil). Thus, the critical current of the entire superconducting coil can be improved by 18% without changing the coil size, which is considered to be an effective means.

5 and 6 show the correlation between the critical current (Ic) distribution of the superconducting coil and the critical current (Ic) ratio in the radial direction.
The base material thickness is 100 μm, the bonded copper thickness is 300 μm, the width is 10 mm, and the other structure is the same structure as the oxide superconducting wire of the previous embodiment, and has two layers with an inner diameter of 260 mm, an outer diameter of 535 mm, and a coil height of 20.6 mm. A coil Ic (77K) at each point was calculated from each magnetic field distribution of the pancake coil (a structure in which two layers of pancake coils were laminated), and an average Ic in the width direction of one layer (single pancake) coil was calculated. FIG. 5 shows the relationship between the ratio of the average coil Ic in the width direction and the minimum Ic of the entire coil (corresponding to Ic-min in the previous example). Moreover, the expansion of the area | region of radial direction 130mm-160mm of the horizontal axis of FIG. 5 is shown in FIG.
5 and FIG. 6, Ic / minimum Ic when Iop (energization current) = 162 A is shown.

From the results shown in FIG. 6, an oxide superconducting wire having an oxide superconducting layer with a film thickness that improves Ic by 12.5% or more is formed inside the superconducting coil (a region of 130 to 157.5 mm, which will be described later. It can be expected that Ic as a superconducting coil can be improved by 12.5% or more by applying to the portion having a low thermal stress shown in the result of No. 7.
Further, an oxide provided with an oxide superconducting layer having a thickness that improves Ic by 4.5% or more on the inner side of the superconducting coil (region of 130 to 141 mm: a portion having a lower thermal stress shown in the result of FIG. 7 described later). By using a superconducting wire, it can be expected that Ic as a superconducting coil can be improved by 4.5% or more.
As described above, the coil Ic is hardly affected by the thermal stress, and the coil dimensions are hardly changed (thickness to increase the superconducting layer × number of turns or less; for example, 2 μm thick, and in the case of 240 turns, the coil A superconducting coil can be provided in which the dimensions are accommodated by an increase of about 480 μm.

FIG. 7 is an explanatory view showing the result of analyzing the position where the thermal stress acts on the cross section of the pancake coil 4 in this cross section.
The stress distribution analysis in the pancake coil shown in FIG. 7 is a result of simulation based on the finite element method (ANSYS). Two-layer pancake coil in which two pancake coles having an inner diameter of 260 mm and an outer diameter of 530 mm are laminated using an oxide superconducting wire having a substrate thickness of 100 μm, a bonded copper metal stabilization layer thickness of 300 μm, and a width of 10 mm FIG. 7 shows the thermal stress distribution simulation result in the coil cross section when the superconducting coil impregnated with epoxy resin and cooled with the epoxy resin is cooled from room temperature to 77K.

From the simulation results shown in FIG. 7, it was found that different stresses act for each position from the inner side (the innermost circumferential position side) to the outer side (the outermost circumferential position side) of the superconducting coil.
When analyzing the stress at each winding position of the oxide superconducting wire along the radial direction from the innermost position to the outermost position, the length from the innermost position to the outermost position (winding the oxide superconducting wire Coil width of the coil main body portion) with the innermost peripheral position as a base point, the greatest stress acts on the region of 20% to 55%, and the region of 13% to less than 20% and more than 55% to 62% It can be seen that the second largest stress acts on the region of% or less, and the third largest stress acts on the region of 10% or more and less than 13% and the region exceeding 62% and 70% or less. The fourth stress acts on the region of 8% or more and less than 10% and the region of 70% or more and 75% or less, and the region of 4% or more and less than 8% and the region of 75% or more and 82% or less. It can be seen that the fifth stress acts on.
For example, as described with reference to FIG. 6, the region of 130 to 157.5 mm is the region of 8% or more and 20% or less shown in FIG. 7, and thus the superconductivity of the oxide superconducting wire in the region of 20% or more and 55% or less. It is preferable to use an oxide superconducting wire having an oxide superconducting layer that is thicker than Ic (e.g., 12.5% or more) with respect to the layer thickness.
Further, as described with reference to FIG. 6, the region of 130 to 141 mm is the region of 8% or less shown in FIG. 7, and therefore the thickness of the superconducting layer of the oxide superconducting wire in the region of 20% or more and 55% or less. On the other hand, it is preferable to use an oxide superconducting wire having an oxide superconducting layer that is thick only because of high Ic (eg, 4.5% or more).
5, 6, and 7, the 20% to 55% region and the 55% to 100% region in FIG. 7 use an oxide superconducting wire having an oxide superconducting layer of the same thickness, and 0 to 20%. It can be explained that the oxide superconducting wire provided with the oxide superconducting layer having a thicker film thickness can be used in the region of less than%. It can also be seen that the coil critical current Ic can be increased by 12.5% or more when an oxide superconducting layer having a large critical current Ic of 12.5% or more is used in the region of 0 to less than 20%. It can also be seen that the coil critical current Ic increases by 4.5% or more when an oxide superconducting layer having a large critical current Ic of 4.5% or more is used in the region of 0 to less than 8%.
That is, in the region where the critical current Ic is 12.5%, 4.5% or more, the critical current Ic is proportional to the film thickness of the oxide superconducting layer in the magnetic field. It will be 5% or more.

Next, the relationship between the peel strength and the layer thickness in the oxide superconducting layer of the oxide superconducting wire was investigated. The peel strength was measured by a stud pull method using a stud pin having the configuration shown in FIG. In the oxide superconducting wire manufactured in the above-described process, a wire 20 in which an oxide superconducting layer and a protective layer are formed on a base material is separately prepared. It was measured by a method in which a stud pin 23 having a diameter of 2.7 mm was adhered to the surface of the opposite protective layer with an epoxy resin 24 and the stud pin 23 was pulled out in the length direction.
In the peel test, 30 samples corresponding to each thickness were measured, Weibull analysis was performed by the cumulative hazard method, and 50% peel stress was calculated.
FIG. 8B shows a correlation between the layer thickness (μm) of the oxide superconducting layer and the peeling stress (MPa).

From the results shown in FIG. 8 (b), it was found that the peeling stress gradually decreases as the thickness of the oxide superconducting layer increases. From this result, it can be seen that a thin oxide superconducting layer having a thickness of 0.8 μm to 4 μm has a higher peel stress and a thicker one has a smaller peel stress. Therefore, when a peeling stress corresponding to the thermal stress acts on the oxide superconducting coil, a thin oxide superconducting layer is disposed in the oxide superconducting layer having a thickness of 0.8 μm to 4 μm at a position where a large peeling stress acts, It can be assumed that disposing a thick oxide superconducting layer at a position where a small peeling stress acts is effective against thermal stress.
From the above example, when the thin film is used in the region of 20 to 55% because the thermal stress is large, the film thickness is not particularly limited. An oxide superconducting layer provided in another region by selecting an oxide superconducting wire having an oxide superconducting layer with a thickness capable of exhibiting a critical current necessary for the target superconducting coil in a range of 0.8 to 4 μm. It is desirable to use a thinner oxide superconducting layer.

Next, the characteristics of the oxide superconducting wire in the magnetic field were investigated. Fig. 3 shows the result of measuring the critical current density (Jc) of the superconducting layer at 77K in a self-magnetic field generated by the superconducting wire to be measured and a 3T external magnetic field using a superconducting magnet capable of generating a 3T (Tesla) magnetic field. 9 shows. In addition, the critical current densities (Jc: 77K: MA / cm ² ) of the oxide superconducting layers (1.4 μm, 1.6 μm, 2.5 μm, 5.5 μm) having different thicknesses in an external magnetic field of 3T are set. It was measured. These results are shown together in FIG. FIG. 9 means that the critical current density Jc in a self magnetic field without an external magnetic field and the critical current density Jc in a 3T external magnetic field were measured by changing the film thickness of the oxide superconducting layer.

  From the results shown in FIG. 9, the critical current density tends to be lower when the oxide superconducting layer is thicker in the self magnetic field, but almost all the dependence on the thickness of the oxide superconducting layer is seen in the 3T magnetic field. Absent. FIG. 9 means that the critical current density does not decrease even when the oxide superconducting layer becomes thicker, and the critical current increases as the oxide superconducting layer becomes thicker.

  A ... Superconducting coil, 1 ... Oxide superconducting wire, 2 ... Base material, 3 ... Bobbin, 3A ... Winding drum, 3B ... Plate, 4, 4A, 4B ... Pancake coil, 5 ... Intermediate layer, 6 ... Oxide Superconducting layer, 7 ... protective layer (first metal stabilizing layer), 8 ... second metal stabilizing layer, 9 ... superconducting laminate, 10 ... coating layer, 11 ... impregnated resin layer.

Claims (5)

A pancake coil in which an oxide superconducting wire having an intermediate layer, an oxide superconducting layer, and a metal stabilizing layer in this order on a tape-like substrate is wound so as to form a plurality of layers on the outer periphery of the winding drum , An oxide superconducting coil having an annular coil body formed by providing one in the length direction of a winding drum, and formed on an oxide superconducting wire wound inside and outside the coil body the thickness of the superconducting layer, characterized in that it is thicker than the thickness of the coil body of the inner and outer oxide superconducting layer formed on the oxide superconducting wire is wound around the middle side between Oxide superconducting coil. A pancake coil in which an oxide superconducting wire having an intermediate layer, an oxide superconducting layer, and a metal stabilizing layer in this order on a tape-like substrate is wound so as to form a plurality of layers on the outer periphery of the winding drum , An oxide superconducting coil having an annular coil body formed by stacking two in the longitudinal direction of a winding drum, and formed on an oxide superconducting wire wound inside and outside the coil body the thickness of the superconducting layer, characterized in that it is thicker than the thickness of the coil body of the inner and outer oxide superconducting layer formed on the oxide superconducting wire is wound around the middle side between Oxide superconducting coil. With respect to the coil width along the radial direction of the coil main body formed by the oxide superconducting wire wound around the outer side of the winding drum, it is in a region of 8% or more and 75% or less of the coil width starting from the innermost peripheral position. The thickness of the oxide superconducting layer formed on the wound oxide superconducting wire is thinner than the thickness of the oxide superconducting layer formed on the oxide superconducting wire wound in the other region. The oxide superconducting coil according to claim 1 or 2 , wherein the oxide superconducting coil is formed. The oxide superconducting coil according to any one of claims 1 to 3, wherein a thickness of the oxide superconducting layer is in a range of 0.8 µm to 6 µm.   A superconducting device comprising the oxide superconducting coil according to any one of claims 1 to 4.

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