JP2007158265A - Superconducting coil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconducting coil capable of suppressing a generation of quenching by applying a required load or less to a drum portion of spool to which the superconducting wire is wound when non-energizing, and by preventing a superconducting wire from moving outward in radial direction when energizing. <P>SOLUTION: The superconducting coil comprises: a formal flow layer portion which generates a magnetic field of specific direction, and receives electromagnetic force outward in a radial direction of the superconducting coil by the magnetic field simultaneously; and an opposite flow layer portion receiving the electromagnetic force inward in the direction of the superconducting coil by the magnetic field of the specific direction in such a way that current flows in a circumferential direction opposite to this formal flow layer portion. The superconducting coil is constituted by arranging the opposite flow layer portion at an outer diameter side of the formal flow layer portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a superconducting coil excited at an extremely low temperature.

  Conventionally, superconducting coils are used in superconducting magnets that use cryogenic refrigerants such as liquid helium. As this superconducting coil, a coil formed by winding a superconducting wire around a winding frame is generally known. In this type of superconducting coil, for example, a superconducting wire is wound around a cylindrical winding frame like a solenoid in the axial direction, folded back at the axial end of the winding frame, and overlapped from the outer diameter side to the already wound superconducting wire. Thus, it can be formed by further winding in the axial direction and repeating this, thereby providing a configuration in which a plurality of layers of the superconducting wire are arranged in the radial direction of the winding frame.

  When an electric current is passed through the superconducting wire of the superconducting coil, an axial magnetic field is generated at the central portion thereof. At this time, an electromagnetic force (Lorentz) is applied to the superconducting wire due to the interaction between the magnetic field and the energizing current. Force) acts. When a so-called wire motion occurs in which the superconducting wire is displaced from the initial winding state due to this electromagnetic force, the temperature of a part of the superconducting wire may exceed the critical temperature due to the frictional heat, and electric resistance may be generated. . When a normal conducting part having electrical resistance is generated in this way, self-heating is induced by current flowing through the part, and eventually a so-called quench phenomenon occurs in which the entire superconducting coil is shifted to the normal conducting state. become. In addition, when the superconducting wire is distorted due to the electromagnetic force, the characteristics of the superconducting wire may be affected.

In view of this, for example, Patent Document 1 below discloses that a bind wire formed of a member having a thermal contraction rate larger than that of the superconducting wire is wound around the outer periphery of the superconducting coil. When the superconducting coil disclosed in Patent Document 1 is cooled with liquid helium or the like, the thermal contraction rate differs between the superconducting wire and the binding wire, so the binding wire is more radially inward than the superconducting wire. Since it contracts greatly, the superconducting wire is strongly suppressed inward in the radial direction. Therefore, even when this superconducting coil is energized and excited, the movement of the superconducting wire displaced outward in the radial direction is suppressed by this bind wire.
JP-A-4-134808

  However, in the above-described conventional method, since an inward force in the radial direction always acts on the superconducting wire before the superconducting coil is energized and excited, the winding is performed to resist the inward force in the radial direction. It is necessary to increase the radial rigidity of the frame. That is, for example, it is necessary to increase the thickness of the body portion in the radial direction so that the body portion of the winding frame around which the superconducting wire is wound is not deformed by receiving the inward force in the radial direction. It was. Further, in the state before excitation, a strong force is always applied inward in the radial direction to the superconducting wire wound around the winding frame, which may affect the characteristics of the superconducting wire.

  The present invention has been made in view of the above-described problems, and suppresses the movement of the superconducting wire that is displaced radially outward without applying an unnecessary load to the body of the winding frame around which the superconducting wire is wound. It is an object to provide a superconducting coil that can be used.

  In order to solve the above-described problems, a superconducting coil according to the present invention includes a winding frame having a cylindrical outer peripheral surface, and a plurality of superconducting wire rods formed by winding a superconducting wire in a solenoid shape on the outer peripheral surface of the winding frame. A superconducting coil that generates a magnetic field in a specific direction along the axial direction of the winding frame when a current flows through the superconducting wire. The coil portion is composed of one or a plurality of the coil layers, and a current flows through the superconducting wire forming the coil layer, thereby generating a magnetic field in the specific direction and the radial direction of the superconducting coil by the magnetic field. It consists of a forward flow layer that receives an electromagnetic force outward and one or more coil layers. The superconducting wire that forms this coil layer is electrically charged in the opposite direction to the forward flow layer. And a backflow layer that receives an electromagnetic force inward in the radial direction of the superconducting coil by the current and the magnetic field in the specific direction, and the backflow on the outer diameter side of the forward flow layer It is characterized in that the layer portion is arranged.

  According to this configuration, since the backflow layer portion is provided on the outer diameter side of the forward flow layer portion, the backflow layer portion can suppress the forward flow layer portion from being displaced radially outward. . That is, when a current flows in the positive flow layer portion and a magnetic field in a specific direction is generated, the positive flow layer portion is directed radially outward due to the interaction between the magnetic field in the specific direction and the current flowing in the positive flow layer portion. Although the electromagnetic force is received, in the backflow layer portion, the current flowing in the forward flow layer portion and the current in the reverse direction of the circumferential direction flow. Therefore, due to the interaction between the magnetic field in the specific direction and the current flowing in the backflow layer portion, The backflow layer receives electromagnetic force inward in the radial direction. Therefore, the outward displacement in the radial direction of the normal flow layer portion due to the action of the electromagnetic force is suppressed by a force that attempts to displace the reverse flow layer portion in the radial direction.

  Also, when the superconducting coil is not energized, a magnetic field is not generated, and electromagnetic force does not act on the forward flow layer or the reverse flow layer, so a radially inward force is applied to the body of the reel. There is no effect. Therefore, unlike the conventional method of suppressing the radial outward displacement of the coil portion with the bind wire, a strong radial inward force does not act on the body portion of the winding frame in a non-use state. There is no need to increase the thickness of the body in the radial direction.

  In addition, although the magnetic field of the direction which cancels the magnetic field of the said specific direction is formed by electricity supply of a reverse flow layer part, the ratio of a normal flow layer part and a reverse flow layer part is made so that the magnetic field of the said specific direction has sufficient strength. If set, a radially inward force can be generated in the backflow layer.

  Specifically, it is preferable that the number of coil layers forming the backflow layer portion disposed in the coil portion is less than 30% of the total number of coil layers forming the coil portion.

  Further, as a specific aspect of the superconducting coil of the present invention, the winding direction of the superconducting wire in the forward flow layer is configured to be opposite to the winding direction of the superconducting wire in the backflow layer. And at least one set of the adjacent current flow layer portion and the reverse flow layer portion formed of one continuous superconducting wire, and a current flowing in the forward flow layer portion and a current flowing in the reverse flow layer portion are Those configured to flow in opposite directions in the circumferential direction are preferable.

  According to this configuration, the normal flow layer portion and the reverse flow layer portion which are adjacent to each other are formed using one superconducting wire, so that the circuit configuration is facilitated and the configuration of the superconducting coil can be simplified. Moreover, since there is no connection part between both layers, connection reliability is also improved.

  Moreover, as another aspect, the superconducting wire in the forward flow layer portion and the superconducting wire in the reverse flow layer portion are wound in the same direction in the circumferential direction, respectively, and the adjacent forward flow layer portion and the reverse flow layer are wound. The current flowing in the forward flow layer portion and the current flowing in the reverse flow layer portion are mutually connected by connecting currents from the terminal ends or the start ends not connected to each other. You may comprise so that it may flow in the circumferential direction reverse direction.

  According to this configuration, current can be supplied from one power source to the forward flow layer portion and the reverse flow layer portion, so that the circuit configuration is facilitated and the configuration of the superconducting coil can be simplified.

  Furthermore, as another aspect, power supplies for supplying current to the forward flow layer portion and the reverse flow layer portion are separately provided, and the current flowing in the forward flow layer portion and the current flowing in the reverse flow layer portion are circumferentially connected to each other. The power source may be connected to the forward flow layer portion and the reverse flow layer portion so as to flow in the opposite direction.

  Further, the position of the backflow layer portion can be set as appropriate, but it is preferable that the backflow layer portion be disposed on the outer diameter side of the intermediate position in the radial direction of the coil portion.

  According to this configuration, since the backflow layer is disposed away from the central axis of the coil portion in the radial direction, a magnetic field in a direction opposite to the specific direction generated by current flowing through the backflow layer is The influence on the magnetic field can be weakened.

  On the other hand, it is preferable that the innermost layer of the coil portion is the positive flow layer portion.

  According to this configuration, the tangential layer portion is disposed at a position closest to the central axis of the winding frame, so that a magnetic field in a specific direction can be generated more strongly.

  Moreover, it is preferable that the outermost layer of the said coil part is the said backflow layer part.

  According to this configuration, since the superconducting wire is prevented from being displaced radially outward by the backflow layer located in the outermost layer, the entire coil portion is prevented from being displaced radially outward (inflated). can do.

  Moreover, the said coil part is good also as a structure which has a some backflow layer part and the normal flow layer part is arrange | positioned between each backflow layer part.

  According to this configuration, the backflow layer portions are dispersedly arranged, and these backflow layer portions can suppress displacement of the normal flow layer portion to the outer diameter side at each position. The forward flow layer portion can be more effectively pressed down than when a single reverse flow layer portion having the same thickness as the total thickness of the layer portions is provided.

  According to the superconducting coil of the present invention, a radially inward force is not generated in the state before energizing the superconducting coil, and a radially inward force is generated during energization so that the superconducting wire is directed radially outward. Displacement can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, FIG. 1 is a schematic cross-sectional view showing the superconducting coil of the present invention, and FIG. 2 is an enlarged schematic cross-sectional view of the right portion of FIG.

  As shown in FIG. 1, the superconducting coil 1 includes a winding frame 2 around which the superconducting wire 3 is wound, and a coil portion 4 formed by winding the superconducting wire 3 around the winding frame 2.

  The winding frame 2 has a cylindrical body portion 2a and a flange portion 2b extending in the radial direction from both axial end portions of the body portion 2a. A cylindrical outer peripheral surface 2c is formed on the body portion 2a on the outer side in the radial direction, and the superconducting wire 3 is wound on the cylindrical outer peripheral surface 2c.

  The coil portion 4 is formed by a coil layer 4a formed by winding the superconducting wire 3 in a solenoid shape from one end to the other end of the body portion 2a of the winding frame 2, and is formed by the coil layer 4a. The normal flow layer portion 5 and the reverse flow layer portion 6 are alternately stacked in this order from the inner diameter side of the coil portion 4. In the example shown in FIG. 2, the forward flow layer portion 5 and the reverse flow layer portion 6 are arranged in two places.

  In the example shown in FIG. 2, the normal flow layer portion 5 is wound counterclockwise (counterclockwise) when the superconducting wire 3 is viewed from the axial end (referred to as the upper end) on the upper side of the coil portion 4 in the drawing. The coil layer 4a is formed by laminating eight layers of the coil layer 4a in the radial direction, and a current flows through the superconducting wire 3 constituting the coil layer 4a to generate a magnetic field in a specific direction. . Therefore, the positive flow layer portion 5 receives a radially outward electromagnetic force by the magnetic field in the specific direction when the superconducting coil 1 is energized.

  The backflow layer 6 is formed by laminating two layers of the coil layer 4a wound counterclockwise (counterclockwise) in the radial direction when the superconducting wire 3 is viewed from the upper end of the coil 4. It has been done. The superconducting wire 3 constituting the coil layer 4a generates a magnetic field in the direction opposite to the specific direction by flowing a current in the direction opposite to the circumferential direction of the forward flow layer portion 5, but the forward flow layer portion. Since the magnetic field generated by 5 is set to be strong, the superconducting coil 1 as a whole forms a magnetic field in the specific direction. Therefore, the backflow layer 6 receives a radially inward electromagnetic force by the magnetic field in the specific direction.

  Here, the formation method of such a coil part 4 is demonstrated. First, the forward flow layer portion 5 located on the innermost diameter side is formed. That is, the first coil located on the innermost diameter side of the forward flow layer portion 5 by winding the superconducting wire 3 counterclockwise from the upper end side of the body portion 2a of the winding frame 2 onto the cylindrical outer peripheral surface 2c. Layer 4a is formed. Then, it is folded back at the axial end portion (lower end portion) of the body portion 2a, and further wound in the axial direction so as to overlap the already wound first coil layer 4a from the outer diameter side. The coil layer 4a is formed. By repeating this winding operation eight times to form the eighth coil layer 4a, the forward flow layer portion 5 is formed.

  Next, the backflow layer 6 is formed on the outer diameter side of the already formed normal flow layer 5. A through-hole (not shown) that penetrates in the thickness direction of the collar portion 2 b is formed in the collar portion 2 b of the winding frame 2, and the eighth coil of the forward flow layer portion 5 extends from the through-hole. The end portion of the layer 4a is once taken out to the outside (axially outside the winding frame 2) and returned to the inside in the axial direction from another through hole, and this time the superconducting wire 3 is wound clockwise as viewed from the upper end. That is, the first coil layer 4a located on the inner diameter side of the backflow layer 6 is formed by winding the superconducting wire 3 clockwise on the eighth coil layer 4a. In this way, the winding direction of the superconducting wire 3 is reversed by positioning a part of the superconducting wire 3 outside the winding frame 2 through the through-hole of the collar portion 2b. Therefore, the normal flow layer portion 5 and the reverse flow layer portion 6 are formed by one superconducting wire 3 without being cut. Then, after the first coil layer 4a of the backflow layer portion 6 is formed, similarly, the backflow layer portion 6 is formed by forming the second coil layer 4a on the first coil layer 4a. Is formed.

  Further, similarly, after the end portion of the backflow layer portion 6 is once taken out from the through-hole of the collar portion 2b, it is returned to the inside through another through-hole, and the outer diameter side than the backflow layer portion 6. The positive flow layer portion 5 is formed. In this way, when the coil layer 4a having a different winding direction is formed, the terminal portion of the coil layer 4a that has already been wound around the winding frame 2 is moved outward in the axial direction through the through hole of the collar portion 2b. Reverse the winding direction via By repeating this operation, as shown in FIG. 2, the coil part 4 provided with two each of the normal flow layer part 5 and the reverse flow layer part 6 is formed. That is, the coil part 4 in this embodiment is formed with one continuous superconducting wire 3.

  When the superconducting coil 1 in this embodiment having the coil part 4 formed in this way is energized, a current flows through the superconducting wire 3 forming the coil part 4. For example, when a current is passed from the start end side of the forward flow layer portion 5 located on the innermost diameter side, a current flows in the winding direction of each coil layer 4a, and the forward flow layer portion 5 is counterclockwise when viewed from the upper end portion. Around, a current flows clockwise through the backflow layer 6. That is, in FIG. 2, current flows in the direction flowing through from the front side of the paper surface to the back side (X is indicated by a symbol surrounded by a circle) in the forward flow layer portion 5, and the direction flowing from the back side of the paper surface to the front side (black circle). Current flows in the circle). When a current flows through each coil layer 4a, a magnetic field is generated in the superconducting coil 1 in FIG. 2 that is axially upward (in the direction of the arrow 7a in FIG. 2) along the central axis of the winding frame 2.

  That is, the forward flow layer portion 5 generates an upward magnetic field in the axial direction and the reverse flow layer portion 6 generates a downward magnetic field in the axial direction. However, the forward flow layer portion 5 is located on the inner diameter side of the reel 2. In addition, since the coil layer 4 a is formed more than the backflow layer portion 6, the magnetic field generated from the forward flow layer portion 5 is generated relatively stronger than the magnetic field generated in the backflow layer portion 6. Therefore, the magnetic field generated by the backflow layer 6 is canceled out by the magnetic field generated by the forward flow layer 5, and an axially upward magnetic field (a magnetic field in a specific direction) is formed as the entire superconducting coil 1.

  Then, the axially upward magnetic field (magnetic field in a specific direction) generated by the forward flow layer 5 receives the electromagnetic force in the radially outward direction, and the reverse flow layer 6 becomes inward in the radial direction. Receives electromagnetic force. That is, as shown in FIG. 2, the forward flow layer portions 5 positioned on the inner diameter side and the outer diameter side of the winding frame 2 receive electromagnetic force in the direction indicated by the arrow 7b (radially outward) by the magnetic field in a specific direction. Therefore, these positive flow layer portions 5 tend to be displaced radially outward by the electromagnetic force. On the other hand, as shown in FIG. 2, the backflow layer 6 receives an electromagnetic force in the direction indicated by the arrow 7 c (radially inward) by a magnetic field in a specific direction, and therefore tends to be displaced inward in the radial direction. The force to move outward in the radial direction of the reverse flow layer portion 6 cancels out the force to move outward in the radial direction of the forward flow layer portion 5, and the outward movement of the forward flow layer portion 5 in the radial direction It is suppressed.

  Thus, in the superconducting coil 1 of the present invention, when a current flows through each coil layer 4a, the positive current layer portion 5 is deformed so as to expand outward in the radial direction by the magnetic field formed by the positive current layer portion 5. However, since the backflow layer portion 6 tends to shrink inward in the radial direction, the displacement of the forward flow layer portion 5 in the radially outward direction is suppressed. Since the radially inward force of the backflow layer portion 6 is offset by the radially outward force of the forward flow layer portion 5, the forward force is applied to the body portion 2a of the winding frame 2 without applying a load more than necessary. The movement of the fluidized bed portion 5 can be suppressed. In addition, a magnetic field is not formed in a state before energization, and no radial inward force is generated by the backflow layer 6, so that no radial inward force acts on the body 2 a of the reel 2. . Therefore, as in the conventional method, the superconductivity is compared with the case where the coil portion 4 is prevented from bulging radially outward by applying a radially inward force to the coil portion 4 with a binding wire or the like before energization. The occurrence of the quenching phenomenon can be suppressed without applying an unnecessary load on the body 2a of the winding frame 2 around which the wire 3 is wound inward in the radial direction.

  In addition, since an excessive force is not applied to the body portion 2a of the reel 2, if the strength of the magnetic field formed in a specific direction is the same, the reel 2 can be compared with a conventional method using a bind line or the like. What formed the thickness of the trunk | drum 2a thinly in the radial direction can be used.

  Although the number of turns of the superconducting wire 3 is increased, it is not necessary to make the body portion 2a of the winding frame 2 heavy as described above, and the use of a conventional resin binder or the like is unnecessary or can be reduced. In general, a compact structure can be maintained.

  Moreover, although the said embodiment demonstrated the case where the normal flow layer part 5 and the reverse flow layer part 6 were formed with one superconducting wire 3, the normal flow layer part 5 and the reverse flow layer part 6 were each made into separate superconductivity. It is good also as a structure which forms with the wire rod 3 and each connects.

  Moreover, although the said embodiment demonstrated the case where the normal flow layer part 5 and the reverse flow layer part 6 were mutually reverse in the circumferential direction about the winding direction, they were mutually wound in the same direction in the circumferential direction. Also good. In the example shown in FIG. 3, the normal flow layer portion 5 located on the inner diameter side and the reverse flow layer portion 6 disposed on the outer diameter side are wound in the same direction in the circumferential direction. Specifically, the superconducting wire 3 is wound counterclockwise from the upper end of the body portion 2 a of the winding frame 2 to form the normal flow layer portion 5, and the superconducting wire is formed on the outer peripheral surface of the positive flow layer portion 5. 3 is wound counterclockwise to form the backflow layer 6. Then, the end of the forward flow layer portion 5 and the end of the reverse flow layer portion 6 are connected by a connection line 9b, and the start end of the forward flow layer portion 5 and the start end of the reverse flow layer portion 6 are connected to the power source 8 by a connection line 9a. To do. With such a connection configuration, the direction of the current flowing in the forward flow layer portion 5 and the direction of the current flowing in the reverse flow layer portion 6 are reversed in the circumferential direction by a simple circuit configuration using a single power source. can do. In the example of FIG. 3, the case where the ends of the normal flow layer portion 5 and the reverse flow layer portion 6 are connected to each other and current is supplied from the start ends of the normal flow layer portion 5 and the reverse flow layer portion is shown. The starting ends of the layer portion 5 and the backflow layer portion may be connected to each other, and current may be supplied from the end of the forward flow layer portion 5 and the backflow layer portion 6.

  In the above embodiment, an example using a single power source has been described. However, the forward flow layer portion 5 and the reverse flow layer portion 6 are configured to flow currents in opposite directions in the circumferential direction using different power sources. Also good. For example, in the example shown in FIG. 4, the normal flow layer portion 5 located on the inner diameter side and the reverse flow layer portion 6 disposed on the outer diameter side are wound in the same direction in the circumferential direction, and are separated from each other. There is a power supply. Specifically, the superconducting wire 3 is wound counterclockwise from the upper end of the body portion 2 a of the winding frame 2 to form a normal flow layer portion, and the superconducting wire 3 is formed on the outer peripheral surface of the positive flow layer portion 5. Is wound counterclockwise to form the backflow layer 6. Then, the start end of the positive flow layer portion 5 is connected to the positive electrode of the power source 8a, and the end of the positive flow layer portion 5 is connected to the negative electrode of the power source 8a through the connection line 9a. Further, the starting end of the backflow layer 6 is connected to the negative electrode of the power supply 8b, and the end of the backflow layer 6 is connected to the positive electrode of the power supply 8b through the connection line 9b. With such a circuit configuration, the direction of the current flowing in the forward flow layer portion 5 and the direction of the current flowing in the reverse flow layer portion 6 can be reversed in the circumferential direction. In addition, in the example of FIG. 4, although the winding direction of the normal flow layer part 5 and the backflow layer part 6 is made into the same direction, it may be wound so that it may become a mutually reverse direction. However, it is necessary to adjust the connection form with the power supply connected to each layer so that the currents in the circumferential direction reverse to each other flow in the forward flow layer portion 5 and the reverse flow layer portion 6.

  Moreover, in the said embodiment, although the backflow layer part 6 arrange | positioned inside the radial direction intermediate position of the coil part 4 is included, all the backflow layer parts 6 arrange | positioned are the radial direction intermediate | middle of the coil part 4. It is good also as a structure arrange | positioned on the outer diameter side rather than a position. In this case, the influence of the magnetic field generated by the backflow layer 6 on the magnetic field in a specific direction generated by the forward flow layer 5 can be reduced.

  Moreover, in the said embodiment, although the example which arrange | positions two each of the normal flow layer part 5 and the reverse flow layer part 6 in this order was demonstrated, as shown in FIG. It is good also as a structure which provides one each and makes the outermost layer of the coil part 4 into the backflow layer part 6. FIG. In this case, since the backflow layer 6 is formed at a position radially outward from the central axis of the winding frame 2, the magnetic field generated by the backflow layer 6 is changed to the magnetic field generated by the forward flow layer 5. Since the backflow layer portion 6 is provided in the outermost layer, the entire coil portion 4 can be prevented from bulging outward in the radial direction only by the backflow layer portion 6.

  In addition, the number of coil layers 4a forming the backflow layer portion 6 arranged in the coil portion 4 is preferably smaller than the total number of coil layers forming the coil portion 4, and the ratio is the total number of coil layers. Less than 30%, more preferably less than 25%. In this case, the superconducting coil 1 that generates a strong magnetic field in a specific direction with less influence on the magnetic field generated by the positive current layer 5 can be obtained.

  Note that the wire type of the superconducting wire 3 that forms the forward flow layer portion 5 and the reverse flow layer portion 6 may be the same or different. Moreover, when the several normal flow layer part 5 or the backflow layer part 6 is provided, the wire material type | molds of the normal flow layer parts 5 or the reverse flow layer parts 6 may each be changed.

It is a schematic sectional drawing which shows the superconducting coil of this invention. It is sectional drawing to which the principal part of the superconducting coil in one Embodiment of this invention was expanded. It is sectional drawing to which the principal part of the superconducting coil in other embodiment was expanded. It is sectional drawing to which the principal part of the superconducting coil in other embodiment was expanded. It is sectional drawing to which the principal part of the superconducting coil in other embodiment was expanded.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Superconducting coil 2 Winding frame 2a Body part 3 Superconducting wire 4 Coil part 4a Coil layer 5 Forward flow layer part 6 Backflow layer part

Claims (9)

A winding frame having a cylindrical outer peripheral surface;
A coil part formed in a state where a plurality of coil layers made of the superconducting wire are laminated in a radial direction by winding the superconducting wire in a solenoid shape on the outer peripheral surface of the winding frame;
In a superconducting coil that generates a magnetic field in a specific direction along the axial direction of the winding frame by causing a current to flow through the superconducting wire,
The coil portion is
A current flows through the superconducting wire that forms one or a plurality of the coil layers, thereby generating a magnetic field in the specific direction and receiving an electromagnetic force radially outward of the superconducting coil by the magnetic field. A positive flow layer,
A current flows in the circumferential direction opposite to the forward flow layer portion through the superconducting wire that forms one or a plurality of the coil layers, and the diameter of the superconducting coil is determined by the current and the magnetic field in the specific direction. A backflow layer receiving electromagnetic force inwardly in the direction,
Have
The superconducting coil, wherein the backflow layer is disposed on the outer diameter side of the forward flow layer.   The winding direction of the superconducting wire in the normal flow layer portion is configured to be opposite to the winding direction of the superconducting wire in the reverse flow layer portion, respectively in the circumferential direction, and at least one set of the positive flow layer portions adjacent to each other. The backflow layer is formed of a single continuous superconducting wire, and the current flowing in the forward flow layer and the current flowing in the backflow layer are configured to flow in opposite directions in the circumferential direction. The superconducting coil according to claim 1, wherein the coil is a superconducting coil.   The superconducting wire in the forward flow layer portion and the superconducting wire in the reverse flow layer portion are wound in the same direction in the circumferential direction, respectively, and the adjacent ends of the forward flow layer portion and the reverse flow layer portion, or Since the ends are connected and current is supplied from the ends or the start ends that are not connected to each other, the current flowing in the forward flow layer portion and the current flowing in the reverse flow layer portion flow in opposite directions in the circumferential direction. The superconducting coil according to claim 1, wherein the superconducting coil is configured as follows.   Power supplies for supplying current to the forward flow layer portion and the reverse flow layer portion are separately provided, so that the current flowing in the forward flow layer portion and the current flowing in the reverse flow layer portion flow in opposite directions in the circumferential direction. The superconducting coil according to claim 1, wherein the power source is connected to the forward flow layer portion and the reverse flow layer portion.   5. The superconducting coil according to claim 1, wherein the backflow layer portion is disposed on an outer diameter side of a radial intermediate position of the coil portion.   The superconducting coil according to any one of claims 1 to 5, wherein the innermost layer of the coil portion is the positive flow layer portion.   The superconducting coil according to any one of claims 1 to 6, wherein the outermost layer of the coil portion is the backflow layer portion.   The superconducting coil according to any one of claims 1 to 7, wherein the coil portion has a plurality of backflow layer portions, and a forward flow layer portion is disposed between the backflow layer portions. .   The number of coil layers forming the backflow layer portion disposed in the coil portion is less than 30% of the total number of coil layers forming the coil portion. Superconducting coil.

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