JP7249906B2 - Superconducting coil and superconducting magnet device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a superconducting coil in which a superconducting wire is wound around a magnetic core such as iron, and a superconducting magnet device including the same.

A superconducting magnet device is a device that generates a desired magnetic field by passing an electric current through a coil made of superconducting material cooled to an extremely low temperature. A superconducting material is a material whose electrical resistance becomes zero when the temperature drops below a certain level, and because it can carry a larger current than a conductive metal at normal room temperature, it can be used in equipment that requires a strong magnetic field, such as magnetic resonance. It is used in imaging devices and bending magnet devices for accelerators.

The temperature at which a superconducting material becomes superconducting is called the superconducting transition temperature. A superconducting coil maintained at a temperature lower than this superconducting transition temperature has zero electric resistance, but if it is subjected to a current with a large current density or placed in a strong magnetic field environment, the superconducting state cannot be maintained. Current density and magnetic field are factors that determine the superconducting state as well as temperature, and superconducting coils must be operated within a range in which the superconducting state determined by the three factors of temperature, current density, and magnetic field can be stably maintained.

In other words, even if the entire coil is wound with the same superconducting wire, if the temperature and magnetic field strength differ depending on the location, the performance of the superconducting wire in the most severe temperature and magnetic field environments may be exceeded. current cannot be conducted.

For example, some superconducting coils used in bending electromagnet devices have a racetrack shape consisting of straight portions and arc portions. This is because the bending magnet arrangement produces a uniform magnetic field along the long axis of the racetrack and a sharply changing magnetic field along the short axis. Generally, the purpose of using a superconducting coil in a bending magnet device is to generate a stronger magnetic field than a normal conducting coil or a permanent magnet in a narrow area. As well as shortening the minor axis dimension of the racetrack, the magnetic field must be produced in a smaller area.

When the entire racetrack-shaped superconducting coil is wound with the same superconducting wire, the magnetic field on the inner peripheral side of the racetrack-shaped circular arc portion becomes stronger. Therefore, even if the superconducting coil is cooled to a uniform temperature, the current amount of the superconducting magnet is determined by the tolerance of the superconducting wire on the inner peripheral side of the arc portion. If the short axis direction of the racetrack shape is shortened and the curvature of the arc portion is reduced, the magnetic field on the inner peripheral side of the coil arc portion becomes stronger than that in the straight portion, and the amount of current cannot be increased.

In Patent Document 1, in a racetrack-shaped coil having a straight part and a circular arc part and composed of a single-core superconductor material of an oxide superconductor, the cross-sectional area of the superconductor material at the part where the magnetic flux concentrates is An oxide superconductor coil is disclosed which is characterized by being made larger than other parts.

JP 2006-332577 A

According to the technique of Patent Document 1, in the racetrack-shaped superconducting coil, by increasing the cross-sectional area of the superconductor in the curvature portion where the magnetic flux concentrates, that is, the superconducting wire, the tolerance of the superconducting state is improved and a large current is generated. can be energized, it is possible to generate a strong magnetic field.
However, in order to change the cross-sectional area of the superconducting wire in the middle of the winding, it is necessary to connect wires with different cross-sections in the middle of the winding in the case of superconducting wires made by drawing niobium or titanium wires. be. The superconducting performance of the superconducting wire is likely to be degraded at the joints of the superconducting wires, and because the cross-sectional area of the coil increases, the arc of the racetrack-shaped superconducting coil becomes large, making it difficult to reduce the size while improving the magnetic field strength. becomes.

The present invention has been made in view of such circumstances, and in a superconducting magnet in which a racetrack-shaped superconducting coil is wound around the magnetic poles of a magnetic material such as iron, the performance of the superconducting wire is the same as that of the conventional superconducting magnet. Another object of the present invention is to provide a superconducting coil and a superconducting magnet device which are smaller and can generate a stronger magnetic field.

In order to solve the above-mentioned problems, the superconducting coil of the present invention includes a superconducting wire wound in a racetrack shape having a straight portion and an arc portion, and a spacer disposed between layers of the superconducting wire on the inner peripheral side of the arc portion. , and the arrangement interval of the spacers is made narrower toward the inner diameter side of the superconducting coil .

The superconducting magnet device of the present invention includes a pair of yokes arranged facing each other, magnetic poles projecting from each of the yokes, and a superconducting wire wound around the magnetic poles in a racetrack shape. and a superconducting coil, wherein the current density in the cross section of the superconducting coil is smaller on the inner peripheral side of the arc portion of the racetrack shape than the current density on the outer peripheral side of the arc portion.

The present invention provides a superconducting coil and a superconducting magnet device capable of generating a stronger magnetic field because it is possible to suppress an increase in the magnetic field strength in the arc portion of the racetrack-shaped superconducting coil without changing the size in the minor axis direction. can.

1 is a cross-sectional view of a superconducting coil of an embodiment in the direction of magnetic lines of force; FIG. It is the enlarged view which looked at 1/4 circumference|surroundings of the superconducting coil from the upper part explaining concentration of magnetic flux. FIG. 2 is an enlarged view of a quarter turn of a superconducting coil with and without a spacer, viewed from above; It is a figure which shows the structure of the circular-arc part cross section of a superconducting coil, magnetic flux density, and the relationship of a current density. It is a figure which shows the structure of the bending electromagnet of a bending electromagnet apparatus. It is a figure which shows the cross section of the up-down direction of a bending electromagnet apparatus. FIG. 4 is a diagram showing current directions and magnetic fluxes of a main coil and side coils of a bending electromagnet; 4 is a partially enlarged view of a main magnetic pole and side magnetic poles; FIG. FIG. 10 is a cross-sectional view of a superconducting coil having another configuration in the direction of magnetic lines of force; FIG. 4 is a cross-sectional view of a superconducting coil in which magnetic poles are inserted instead of spacers, taken in the direction of magnetic lines of force;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view of the superconducting coil 14 of the embodiment in the direction of the magnetic lines of force.
In the superconducting coil 14 of the embodiment, a superconducting wire 20 is wound around a magnetic pole 16 in a racetrack shape consisting of straight portions 14B and arc portions 14A, and a plurality of superconducting wires 20 are laminated. A spacer 17 is provided between the layers of the superconducting wire 20 on the inner peripheral side (on the magnetic pole 16 side) of the circular arc portion 14A.

As shown in FIG. 2, the inner peripheral portion 15 of the arc portion 14A in the racetrack-shaped superconducting coil 14 has a higher magnetic flux density than the straight portion 14B. Therefore, the magnetic field strength received by superconducting wire 20 is higher at inner peripheral portion 15 of the arc portion than at straight portion 14B, and the current value that can flow through superconducting wire 20 is limited.

Specifically, FIG. 2 is an enlarged view of a quarter turn of the racetrack-shaped superconducting coil 14 viewed from above. The magnetic flux 13 in the current direction of the superconducting coil 14 is shown. As is clear from FIG. 2, the density of the magnetic flux 13 decreases from the inner peripheral portion 15 of the arc portion 14A toward the outer peripheral direction. Furthermore, the density of the magnetic flux 13 is higher in the inner peripheral portion 15 of the arc portion 14A than in the straight portion 14B. That is, the inner peripheral portion 15 of the arc portion 14A has the highest concentration of magnetic flux in the superconducting coil 14 and the magnetic flux density is high.

Since the current value that can be passed through superconducting wire 20 is determined by the temperature and the magnetic field strength, if the temperature of superconducting coil 14 is uniform, the current value that can be passed through superconducting wire 20 is determined by the magnetic field strength.
Therefore, in the superconducting coil 14 of FIG. 2, it is possible to conduct current only up to a predetermined current value determined by the magnetic flux density of the inner peripheral portion 15 of the circular arc portion 14A.
Therefore, the magnetic field intensity of the straight portion 14B of the superconducting coil 14 is also limited by the magnetic flux density of the inner peripheral portion 15 of the arc portion 14A.

In the superconducting coil 14 of the embodiment, as shown in FIG. 1, the spacer 17 is arranged between the layers of the superconducting wire 20 on the inner peripheral side of the arc portion 14A to reduce the current density in the inner peripheral portion 15 of the arc portion 14A. and suppress concentration of the magnetic field strength (magnetic flux density) in the inner peripheral portion 15 of the arc portion 14A. As a result, the influence of the magnetic field intensity is reduced, so the current value that can be passed through the superconducting wire 20 of the superconducting coil 14 is increased, so that the superconducting coil 14 can generate a stronger magnetic field.
Here, the current density means the number of superconducting wires 20 per unit area in the cross section of the superconducting coil 14 .

Here, the spacer 17 will be explained.
The superconducting coil 14 is kept below the critical temperature at which the superconducting wire 20 becomes superconducting with a coolant such as liquid helium. In addition, the superconducting coil 14 is conductively cooled by a cryocooler to keep the superconducting wire 20 below the critical temperature at which the superconducting wire 20 becomes superconducting.
Therefore, the spacer 17 is made of a good thermal conductor such as metal, ceramics, or fiber-reinforced resin so that the superconducting coil 14 does not have a temperature distribution.

Also, the spacer 17 may be made of a ferromagnetic material such as iron, silicon steel, or permendur. According to this configuration, the current density in the inner peripheral portion 15 of the arc portion 14A is reduced, the magnetic flux passing through the spacer 17 is increased, and the magnetic flux passing through the superconducting wire 20 is reduced. That is, since the magnetic field intensity (magnetic flux density) in the inner peripheral portion 15 of the circular arc portion 14A is lower than in the case where the spacer 17 is made of a good thermal conductor, the current value that can be applied to the superconducting wire 20 of the superconducting coil 14 can be increased. 14 can generate a stronger magnetic field.

In FIG. 1, two spacers are installed on the inner peripheral side of one circular arc portion 14A, but one spacer or three or more spacers may be installed.

3A and 3B, how the spacer 17 reduces the magnetic flux density of the inner peripheral portion 15 of the arc portion 14A will be described in more detail.
FIG. 3A is an enlarged view of a 1/4 circumference of the racetrack-shaped superconducting coil 14 viewed from above. The dashed line indicates the coil arc portion in which the spacer 17 is not installed between the layers of the superconducting wire 20 of the arc portion (spacerless coil), and the solid line indicates the state in which the spacer 17 is installed on the inner peripheral side of the arc portion (with spacer). coil).

In FIG. 3A, the symbol "a" indicates the center of curvature of the arc portion in the longitudinal direction of the superconducting coil 14, the symbol "b" indicates the inner diameter position of the arc portion in the longitudinal direction, and the symbol "c" indicates the arc of the spacerless coil. , and symbol "d" indicates the outer diameter position of the spacer-equipped coil.

FIG. 3B is a diagram showing the relationship between the configuration of the arc section in the longitudinal direction of the superconducting coil 14, the magnetic flux density, and the current density.
In FIG. 3B, the horizontal direction of the paper is the radial direction of the arc part of the superconducting coil 14, the upper part shows the configuration of the arc part cross section, and the middle part shows the magnetic flux density of the arc part cross section of the coil without spacer (broken line) and the coil with spacer (solid line). B, the lower part shows the current density J of the cross section of the circular arc portion of the spacer-less coil (dashed line) and the spacer-attached coil (solid line).
Symbols "a", "b", "c", and "d" on the horizontal axis of FIG. 3B indicate the same positions as the positions of the spacers 17 described in FIG. 3A.

As shown in the graph of the magnetic flux density in the cross section of the circular arc in the middle of FIG. is getting bigger. Therefore, when the magnetic flux density B on the inner peripheral side of the coil exceeds a predetermined value, the current of the superconducting wire is limited, and the strength of the magnetic field generated by the superconducting coil 14 is limited.

Therefore, in the superconducting coil 14 of the embodiment, as shown in the diagram showing the configuration of the cross section of the arc portion in the upper row, on the inner peripheral side of the arc portion of the superconducting coil 14 in which the superconducting wire is laminated and wound, between the layers of the superconducting wire. A spacer 17 is arranged to reduce the current density in the arc section.
Specifically, on the inner peripheral side of the circular arc portion, the closer to the inner diameter position (marked “b”) of the superconducting coil 14 , the narrower the spacing of the spacers 17 (hatched portion).

Due to the arrangement of the spacers 17 described above, as shown in the lower graph of current density J in FIG. 3B,
The current density J of the spacer-equipped coil (solid line) decreases toward the inner diameter position (symbol “b”) in the arrangement range of the spacer 17 compared to the spacer-less coil (dashed line), which has a constant current density. do.

By changing the current density distribution due to the arrangement of the spacers 17, as shown in the graph of the magnetic flux density B of the arc section in the middle of FIG. ), the magnetic flux density B on the inner peripheral side of the arc is made smaller.
As a result, current limitation due to an increase in magnetic field intensity can be suppressed, so that the current value that can be passed through the superconducting wire 20 of the superconducting coil 14 can be increased, and the superconducting coil 14 can generate a stronger magnetic field.

Next, an example of a superconducting magnet device to which the superconducting coil 14 of the embodiment is applied will be described with reference to FIGS. 4 to 7. FIG.
The superconducting magnet device of the embodiment generates synchrotron radiation by applying periodic motion in a direction perpendicular to the beam traveling direction to a charged particle beam such as an electron beam or a proton beam emitted from an accelerator (not shown). It is a bending electromagnet device that

FIG. 4 is a diagram showing the configuration of the bending electromagnet 1 of the bending electromagnet device.
The superconducting coil 14 (not shown) of the bending magnet 1 is housed in a cryostat such as a vacuum vessel or a radiation shield and kept at a low temperature by a refrigerator or the like in order to maintain a superconducting state with zero electrical resistance.

The bending electromagnet 1 has a first magnetic pole 3, a second magnetic pole 4, and a third magnetic pole 5 arranged vertically facing each other along the straight portion of the beam duct 2, which is the trajectory of the charged particle beam. The magnetic poles of the first magnetic pole 3, the second magnetic pole 4 and the third magnetic pole 5 are made of a magnetic material such as iron, and are placed on a magnetic yoke 7 so as to face each other. The upper and lower yokes 7 are connected and supported by side yokes 10 made of magnetic or non-magnetic metal.

A closed magnetic circuit is formed by the opposing first magnetic poles 3, the opposing second magnetic poles 4, and the upper and lower yokes. Similarly, the opposing second magnetic pole 4, the opposing third magnetic pole 5, and the upper and lower yokes 7 form a closed magnetic circuit. Hereinafter, the second magnetic pole 4 will be referred to as the main magnetic pole, and the first magnetic pole 3, the third magnetic pole 5 and the side magnetic poles.

A superconducting coil 14 is wound around each of the first magnetic pole 3, the second magnetic pole 4, and the third magnetic pole 5, and the bending electromagnet device of the embodiment forms a three-pole superconducting magnet. . Hereinafter, the superconducting coil 14 around the main magnetic pole is called a main coil 8 and the superconducting coil 14 around the side magnetic poles is called a side coil 9 .

The six superconducting coils 14 that make up the main coil 8 and the side coils 9 each have a racetrack shape with two straight portions 14B perpendicular to the beam duct 2 and an arc portion 14A that connects the two straight portions 14B. (see FIG. 1).
A charged particle beam emitted from an accelerator advances through a beam duct 2 in order of a first magnetic pole 3 , a second magnetic pole 4 and a third magnetic pole 5 . A beam trajectory 6 in the beam duct 2 indicates the trajectory of the charged particle beam.

Next, referring to FIG. 5, the state of deflection of the charged particle beam by the superconducting magnet device of the embodiment will be described. FIG. 5 is a view showing a vertical cross section (a cross section perpendicular to the direction of the magnetic lines of force of the superconducting coil 14) of the bending electromagnet 1 of FIG. 5 indicate the same parts as those in FIG. 4, and detailed description thereof will be omitted.

When generating synchrotron radiation, the trajectory of the charged particle beam passing through the beam trajectory 6 is sharply bent to form a deflection trajectory 11 . At this time, synchrotron radiation is generated in the trajectory direction of the original charged particle beam.
Specifically, as shown in FIG. 5, the charged particle beam of the beam trajectory 6 incident on the bending electromagnet 1 is first deflected downward in the plane of the paper by the magnetic field generated by the first magnetic pole 3, that is, the side magnetic pole, and then The magnetic field generated by the second magnetic pole 4, ie, the main magnetic pole, deflects the magnetic field upward in the plane of the drawing. Further, the charged particle beam is deflected onto the beam trajectory 6 of the original charged particle beam by the third magnetic pole 5, that is, the side magnetic pole, and is restored.
When the charged particle beam passes through the magnetic field generated by the bending electromagnet 1 and is deflected to draw a deflection trajectory, synchrotron radiation is generated in the direction of the original trajectory.

In order to realize the deflection trajectory of the charged particle beam as described above, the magnetic fields between the main magnetic pole (second magnetic pole 4) and the side magnetic poles (first magnetic pole 3 and third magnetic pole 5) have opposite polarities. , and the integrated value of the magnetic field by the main magnetic pole and the integrated value of the magnetic field by the two side magnetic poles that the charged particles receive on the beam trajectory are made equal.

FIG. 6 is a diagram showing current directions 12 and magnetic fluxes 13 of the superconducting coils 14 in the main coil 8 and the side coils 9 of the bending electromagnet 1. As shown in FIG. Two closed magnets between the side pole (first pole 3) and the main pole (second pole 4) and between the main pole (second pole 4) and the side pole (third pole 5). Forming a circuit, the flux between the main poles is twice the flux between the side poles on one side. Therefore, the main coil 8 and the side coil 9 conduct current in different directions.
In the main coil 8 and the side coils 9 in FIG. 6, the symbols ◯ and  indicate the current flow from the front to the back, and the symbols ◯ and ● indicate the current flow from the back to the front.

FIG. 7 shows the distribution of the magnetic flux 13 in FIG. 6 by enlarging the main magnetic pole and the side magnetic pole. As shown in FIG. 7, in order to generate a strong magnetic flux density between the opposing main magnetic poles, a current 12 is applied in the same direction to the main coil 8 and the adjacent side coil 9 .

As shown in FIG. 6, in the case of the bending electromagnet 1 using one pair of main coils 8 and two pairs of side coils 9, the magnetic flux between the main magnetic poles is about twice that between the opposing side magnetic poles. is passing through. Therefore, the magnetic flux generated by the main coil 8 is greater than that of the side coil 9, and the magnetic field strength at the position where the superconducting wire 20 constituting the superconducting coil 14 is placed is near the center of the height of the main coil 8 on the main magnetic pole side. become the largest.

According to Ampere's law (2πrH=I, where H is the strength of the magnetic field, I is the current included in the integration path, and r is the radius of the integration path), the magnetic field is strongest near the surface of the superconducting coil 14 rather than at the center. It is clear that Similarly, the smaller the cross-sectional area of the superconducting coil 14, the stronger the magnetic field that the superconducting wire on the coil surface receives.

In the superconducting magnet apparatus of the embodiment, since the concentration of the magnetic flux density in the arc portion 14A of the racetrack-shaped superconducting coil 14 of the bending electromagnet 1 is reduced, the superconducting wire 20 can be formed without enlarging the minor axis direction of the superconducting coil 14. It is possible to increase the magnetic field intensity in the straight portion 14B by increasing the current value that can be applied to the straight portion 14B. As a result, the deflection magnetic field intensity of the charged particle beam can be increased without increasing the length of the straight portion of the beam duct 2 of the superconducting magnet device (the length of the superconducting magnet device).

Next, another structure of the racetrack-shaped superconducting coil 14 different from that of FIG. 1 will be described with reference to FIGS. 8 and 9. FIG.
FIG. 8 is a cross-sectional view of the superconducting coil 14 having another configuration in the direction of the magnetic lines of force.

The superconducting coil 14 in FIG. 8 includes the superconducting coil 14 described in FIG. 1, the coil portion in which the superconducting wire 20A is wound, and the superconducting wire 20B with the spacer 17 installed on the inner peripheral side of the arc portion 14A as a boundary. A wound coil portion and a coil portion wound with the superconducting wire 20C are provided in multiple. This reduces the current density in the arc portion 14A of each coil, and suppresses the concentration of the magnetic field strength (magnetic flux density) in the arc portion 14A.
This maximizes the current in each coil of superconducting wires 20A, 20B and 20C, allowing superconducting coil 14 to generate a stronger magnetic field.

Furthermore, each of the superconducting wires 20A, 20B and 20C may have different superconducting characteristics, such as using a superconducting wire that withstands a stronger magnetic field as the wire is wound on the inner circumference.
This makes it possible to generate a stronger magnetic field or realize a smaller superconducting magnet device.

In the superconducting coil 14 described with reference to FIGS. 1 and 8, an example in which two spacers 17 are arranged in each arc portion 14A has been described, but the number of spacers 17 is not limited to two. good. Also, the number may be three or more.
However, as explained with reference to FIG. 2, since the magnetic flux density increases toward the inner circumference of the arc portion 14A, the spacer 17 needs to be arranged on the inner circumference side of the arc portion of the superconducting coil 14. FIG.

The racetrack-shaped superconducting coil 14 of FIG. A magnetic body 18 forming a magnetic pole is formed in the yoke 7 in parallel with the magnetic pole 5 (see FIGS. 4 and 5). A gap was provided between the layers.

More specifically, since the magnetic material 18 constituting the magnetic poles has a small magnetic resistance and allows magnetic flux to pass through easily, the upper and lower yokes 7 and the side yokes 10 form a magnetic circuit. As a result, the magnetic flux density passing through the superconducting coil can be reduced, and the current limitation of the superconducting coil 14 can be suppressed, so that a superconducting magnet device with a stronger or smaller generated magnetic field can be formed.

As with the upper and lower superconducting coils 14 facing each other, the magnetic bodies 18 may be separated vertically and installed on the yoke 7. may be When connecting and integrating the upper and lower magnetic bodies 18 , the magnetic bodies 18 are formed in either the upper or lower yoke 7 .

In the superconducting magnet apparatus of the above embodiment, the bending electromagnet 1 in which the superconducting coils 14 of the embodiment are provided facing each other vertically has been described. can also be applied to
Moreover, the superconducting coil 14 of the embodiment can be applied not only to the two-pole bending electromagnet shown in FIG. 2 but also to a quadrupole electromagnet device.

Moreover, the present invention is not limited to the above-described embodiments, and includes various modifications. The above embodiments have been described in detail to facilitate understanding of the present invention, and are not necessarily limited to those having all the described configurations. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment.

REFERENCE SIGNS LIST 1 bending electromagnet 2 beam duct 3 first magnetic pole 4 second magnetic pole 5 third magnetic pole 6 beam trajectory 7 yoke 8 main coil (superconducting coil)
9 Side coil (superconducting coil)
REFERENCE SIGNS LIST 10 side yoke 13 magnetic flux 14 superconducting coil 15 inner periphery 16 magnetic pole 17 spacer 20 superconducting wire

Claims (7)

a superconducting wire wound in a racetrack shape having a straight portion and an arc portion;
a spacer disposed between layers of the superconducting wire on the inner peripheral side of the arc portion;
with
The arrangement interval of the spacers is narrowed toward the inner diameter side of the superconducting coil.
A superconducting coil characterized by: In the superconducting coil according to claim 1,
A superconducting coil, wherein the spacer is made of ceramics, fiber-reinforced resin, or a good thermal conductor of metal. In the superconducting coil according to claim 1,
A superconducting coil, wherein the spacer is made of a ferromagnetic material such as iron, a silicon steel plate, or permendur. In the superconducting coil according to any one of claims 1 to 3 ,
A superconducting coil, wherein the superconducting coil is divided by the spacer and wound with at least two different superconducting wires. a pair of yokes arranged facing each other;
magnetic poles projecting from each of the yokes;
a superconducting coil installed around the magnetic pole and wound with a superconducting wire in a racetrack shape;
with
A superconducting magnet device according to claim 1, wherein the superconducting coil has a cross-sectional current density smaller than that on the outer peripheral side of the arc portion on the inner circumference side of the racetrack-shaped arc portion. a pair of yokes arranged facing each other;
a first magnetic pole, a second magnetic pole, and a third magnetic pole projecting from each of the yokes;
a superconducting coil installed around the first magnetic pole, the second magnetic pole, and the third magnetic pole and having a superconducting wire wound in a racetrack shape;
with
The superconducting coil is characterized in that the magnetic poles of the magnetic material projecting from the yoke are inserted into the gaps between the winding layers of the superconducting wire of the respective superconducting coils on the inner circumference side of the circular arc portions at both ends of the racetrack shape. and a superconducting magnet device. A superconducting magnet device for deflecting a charged particle beam,
in each of the main magnetic field and the sub-magnetic field so that on the trajectory of the charged particle beam, a main magnetic field and two sub-magnetic fields with polarities opposite to that of the main magnetic field are formed before and after the main magnetic field. A superconducting magnet apparatus comprising the superconducting coil according to any one of claims 1 to 4 .

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