JP2005116372A - Deflection electromagnet and charged particle accelerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a compact deflection electromagnet which has a focusing capacity to satisfy the circuiting condition of an accelerator in a deflection electromagnet used in an accelerating device in which the circumference orbit of charged particles spreads in a radial direction by acceleration. <P>SOLUTION: In order to adjust the focusing capacity by an edge focus according to the incident location of the charged particles to the deflection electromagnet 1, a leakage magnetic field adjusting means 13a is provided which adjusts a leakage magnetic field distribution shape along the travelling orbit of the charged particles from the deflection electromagnet 1 in the vicinity of the incident or outgoing orbit face of the charged particles by depending on the incident or outgoing location of the charged particles of the deflection electromagnet 1, by adjusting a magnetic field leakage factor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a deflection electromagnet that is one of components of a charged particle acceleration device that accelerates charged particles, and a charged particle acceleration device that uses this deflection electromagnet.

  In recent years, the development of charged particle accelerators called FFAG (Fixed Field Alternating Gradient) accelerators has been highlighted. This acceleration device is provided with acceleration means for accelerating charged particles, and a plurality of deflecting electromagnets for deflecting charged particles incident on the acceleration device by their magnetic fields are arranged in a circumferential direction, so that the overall shape is substantially circular. It is configured. The charged particles circulate in the accelerator while increasing energy by acceleration by the acceleration means. Since the circular orbit extends in the radial direction of the acceleration device with acceleration, the position of the incident point of the charged particles on the deflection electromagnet moves outward in the radial direction of the acceleration device with acceleration. Along with this, the exit point position of the charged particles from the deflection electromagnet also moves as the incident point position moves. The deflection electromagnet used in this acceleration device has a constant magnetic field strength and does not change in time, and the magnetic field strength increases as the orbit expands. As a result, the acceleration device can be miniaturized.

  In such an accelerating device, it is important how to apply a converging force that satisfies an orbital condition for causing the charged particles to circulate stably. In the conventional synchrotron accelerator that keeps the orbit constant by changing the magnetic field with time, the magnetic field of the deflecting electromagnet magnetic field and the quadrupole electromagnet having a converging force arranged between the deflecting electromagnets can be changed with time. By doing so, it was easy to obtain a converging force that satisfies the circulation condition. However, in the acceleration device in which the charged particle orbit increases in the radial direction with acceleration, the charged particle orbit expands in the radial direction, so it is adopted in the normal synchrotron accelerator with constant orbit. Therefore, it is not easy to realize a means having a converging force that satisfies the rotation condition for the entire orbit extending in the radial direction.

  The “convergence force that satisfies the circulation condition” means a convergence force that is necessary to prevent the tune, which is an operation parameter of the accelerator, from being applied to the resonance line. When charged particles orbit around the accelerator, the orbiting charged particles orbit around the orbit called the equilibrium orbit corresponding to the energy at that time (referred to as betatron oscillation). Tune is the number of vibrations per round, and the vibration components are divided into X and Y directions that are orthogonal to each other on a plane perpendicular to the running direction, generally the horizontal and vertical directions. Called horizontal direction.) Tune, Y direction (hereinafter referred to as vertical direction) tune.

  Since the betatron oscillation depends on the convergence force, the tuning depends on the convergence force and the circumference of the equilibrium orbit. The circumference depends on the charged particle energy in the accelerator and the magnetic field strength of the deflecting electromagnet, and the convergence force is determined by the operating conditions of the electromagnet installed in the accelerator. Therefore, it can be said that tune is an operating parameter of the accelerator. “Resonance” means when the accelerator becomes unstable in a set of horizontal and vertical tunes. Usually, this “set” is on a plane with the horizontal and vertical tunes as coordinate axes. Is called a “resonance line” because it forms a straight line. In general, there are a plurality of straight lines. The term “unstable” as used herein refers to a phenomenon in which the amplitude of betatron oscillation of charged particles that circulate in the acceleration device becomes larger than an allowable value. In the acceleration device, a vacuum vessel is introduced to circulate charged particles in a vacuum environment, and the charged particles circulate in the vacuum vessel. When the tune is applied to the resonance line, even a slight disturbance increases the amplitude of the betatron oscillation, and as a result, the charged particles collide with the inner wall of the vacuum vessel, and the charged particles disappear and can circulate. Disappear. Therefore, in order to circulate the charged particles stably, it is necessary to determine the operating conditions so that the tune does not reach any resonance line in the acceleration process. For this reason, the “convergence force that satisfies the circulation condition” means “the convergence force that is required to prevent the tune that is the operating parameter of the accelerator from being applied to the resonance line”. .

  In the following, only the convergence force in the vertical direction is treated as the convergence force. In order to prevent the resonance line from being applied, it is necessary to prevent the resonance line from being applied as a set of horizontal and vertical tunes, but in the FFAG accelerator, the change in the horizontal tune is small and there is no need to worry about it. This is because the discussion in this paper on the convergence force in the vertical direction can be applied to accelerators other than FFAG accelerators that must take into account changes in the horizontal tune. For these reasons, unless otherwise specified, “convergence force” refers to “vertical convergence force”, and “tune” refers to “vertical direction tune”.

  As described above, in the FFAG accelerator, the orbit is widened in the radial direction, and it is difficult to realize the convergence force as described above with the quadrupole electromagnet. Therefore, it is considered to obtain a predetermined convergence force by using the convergence action of the deflection electromagnet. This is a so-called edge focus method (see Non-Patent Document 1). When a normal sector-type deflection electromagnet is incorporated in an acceleration device, the vertical focusing force due to the edge focus increases depending on the radial direction of the acceleration device. Therefore, the tune increases rapidly as the orbit of charged particles increases due to the increase in acceleration energy. This is because an increase in the circumference of the orbit and a decrease in the period of betatron oscillation due to an increase in the convergence force occur simultaneously. Thus, when the change of tune is remarkable, it will be applied to one of the resonance lines, and the charged particles cannot go around. Therefore, the convergence force by the normal edge focus cannot be a “convergence force that satisfies the circulation condition”.

  Therefore, as a measure for imparting a “convergence force that satisfies the orbital condition”, a deflection electromagnet having a configuration in which deflection electromagnets having opposite polarities are installed on both sides of a normal sector-type deflection electromagnet has been proposed (non-patent document). Reference 2). The horizontal focusing force is changed to the vertical focusing force by inverting the sign of the deflection radius by providing the deflecting electromagnets on both sides and providing the edge focusing function on both sides. The "convergence power that satisfies the circuit condition" is realized.

"High Energy Accelerator Seminar OHO'87" Text, 1987.8, I-p6 `` DEVELOPMENT OF A FFAG PROTON SYNCHROTRON '', Proceedings of EPAC 2000, Vienna, Austria, p.582, Fig.1

  However, when the acceleration device is configured by using a pair of deflection electromagnets configured by arranging the opposite polarity deflection electromagnets on both sides of the original deflection electromagnet, the desired convergence force can be obtained. Has the disadvantage of becoming larger. For example, the deflection angle of the original deflection electromagnet is θ1, and the deflection angle of the reverse polarity deflection electromagnet is θ2. Then, the deflection angle θt as a whole of the set of deflection electromagnets is equal to θ1−θ2 * 2, which is smaller by θ2 * 2 than in the case where there is no reverse polarity deflection electromagnet. In order to make the charged particles circulate, a plurality of deflecting electromagnets must be arranged so that the total deflection angle of the deflecting electromagnets is equal to 2π. Since a combination of electromagnets is required, and a space for a deflecting electromagnet having a reverse polarity is required, the size of the entire acceleration device is increased. Thus, from the viewpoint of miniaturization of the acceleration device, there has been a demand for a compact deflection electromagnet having a converging force that satisfies the rotating condition of charged particles in the acceleration device.

  The deflection electromagnet of the present invention is a deflection electromagnet in which charged particle incident positions are distributed in a direction substantially orthogonal to the deflection magnetic field and the trajectory on which the charged particle is incident. Leakage magnetic field adjustment means for adjusting the leakage magnetic field distribution from the deflection magnetic field in the orbital direction near each orbit to a different distribution shape depending on the incident or exiting position by adjusting the leakage rate of the magnetic field. It is provided.

  The deflecting electromagnet of the present invention can obtain a converging force satisfying the rotating condition of charged particles with a compact shape by the above configuration.

Embodiment 1
A deflection electromagnet according to a first exemplary embodiment of the present invention is shown in FIGS. In the following description, the two magnetic poles of the deflecting electromagnet are arranged in the vertical vertical direction and the charged particles circulate between them. In addition, here, the magnetic pole of this deflecting electromagnet is a shape formed of a part of a shape obtained by planarly projecting a helical shape on each of incident and outgoing sides of charged particles in a plan view (hereinafter abbreviated as a helical shape). )).
FIG. 1 is a bird's-eye view showing the upper half of the deflection electromagnet 1 according to the present invention. Since the deflection electromagnet 1 has a vertically symmetrical shape with respect to the charged particle deflection track surface 14 (see FIG. 3), only the upper half is shown. FIG. 2 is a plan view of the bending electromagnet 1, and FIG. 3 is a side view from the AA 'direction of FIG. BB ′, CC ′, and DD ′ in FIG. 2 correspond to differences in the charged particle incident position or outgoing position of the deflection electromagnet 1, respectively. 1 to 3, a deflection electromagnet 1 includes an iron core 10, coils 12a and 12b (12b is omitted in FIGS. 1 and 2) wound around the iron core 10 to form a magnetic pole, and the wound coil. The magnetic poles 11a and 11b formed by 12a and 12b (not shown in FIGS. 1 and 2) and the outer surfaces of the coils 12a and 12b on the side where charged particles enter or exit the deflecting electromagnet 1 are covered. The magnetic pole plates 13a and 13b (13b are omitted in FIGS. 1 and 2) and the magnetic pole plates 13a and 13b made of a magnetic material, which are changed in accordance with the position where the light enters or exits the deflection electromagnet 1, and the iron core 10 And support members 18a and 18b made of a magnetic material for magnetically coupling and fixing to the substrate (18b is omitted in FIG. 1 and 18a and 18b are also omitted in FIG. 2). As shown at both ends of FIG. 3, the iron core 10 also serves as a return yoke for the magnetic flux. Similarly, FIG. 3 shows a charged particle deflection track surface 14 when the deflection electromagnet 1 is incorporated in an acceleration device. The charged particle deflection orbit surface 14 coincides with the orbital surface of the charged particles in the deflection electromagnet portion. A charged particle corresponding to specific energy passing through the deflection electromagnet is exemplified as number 15.

  Next, the magnetic pole plates 13a and 13b will be described in a little more detail. In the magnetic pole plates 13 a and 13 b, the distance between the deflection track surface and the surface of the magnetic pole plate facing the deflection track surface is set depending on the position where it enters or exits the deflection electromagnet 1. (A), (b), and (c) of FIG. 4 show this, and show cross-sectional views along BB ′, CC ′, and DD ′ of FIG. 2, respectively. . In FIG. 4A, the pole plates 13a and 13b almost completely cover the sides of the coils 12a and 12b except for the height necessary for charged particles to pass through the deflecting electromagnet. In FIG. 4 (b), in addition to the height necessary for the passage of the charged particles, the magnetic pole plates 13a and 13b expose approximately half of the side surfaces of the coils 12a and 12b, and the remaining half of the coil side surfaces. Covering. In FIG. 4 (c), the magnetic pole plates 13a and 13b expose almost the entire side surfaces of the coils 12a and 12b in addition to the height necessary for the passage of the charged particles. This can also be read from the shapes of the magnetic pole plate 13a in FIG. 1 and the magnetic pole plates 13a and 13b in FIG.

  Next, the operation of the bending electromagnet according to the present invention will be described. As shown in FIG. 1, the magnetic pole plate 13a made of the above-mentioned magnetic material is attached to the iron core 10 via the support member 18a on the side surface of the coil 12a, thereby reducing the leakage rate of the magnetic field by the coil 12a and the side surface of the coil 12a. It can be reduced according to the area covered by the magnetic pole plate 13a. Here, as the area of the magnetic pole plate 13a covering the coil 12a is reduced from the BB ′ position to the DD ′ position of the deflection electromagnet 1, the leakage magnetic field is small in the vicinity of BB ′. The leakage magnetic field increases as it approaches DD ′. The same applies to the magnetic pole plate 13b arranged symmetrically with the magnetic pole plate 13a across the deflection track surface 14 shown in FIG. Therefore, due to the effects of both, the distribution shape of the leakage magnetic field along the circular orbit in the vicinity of the circular orbit of the charged particle greatly changes depending on the position where it enters or exits the deflection electromagnet 1.

  The shapes of the magnetic pole plates 13a and 13b are preliminarily determined by calculation of charged particle beam dynamics and magnetic field analysis of the deflection electromagnet 1 in the acceleration device on the assumption that the acceleration device using the deflection electromagnet 1 is determined in advance. Can be sought. From the calculation of the charged particle beam dynamics, a necessary convergence force condition is obtained, and the leakage magnetic field distribution of the deflecting electromagnet for obtaining this convergence force is obtained. Next, the shape of the magnetic pole plate 13 can be obtained by performing a three-dimensional magnetic field analysis calculation in order to realize this necessary leakage magnetic field distribution. In the side view of FIG. 3, the distance between the deflection track surface 14 and the surface of the magnetic pole plate 13 facing the deflection track surface 14 is drawn so as to change linearly with the incident or exit position of the charged particles. However, it does not always change linearly. As described above, it is obtained by calculation. The magnetic pole plates 13a and 13b are also installed on the incident side and the outgoing side of the deflection electromagnet 1, respectively, but the shapes of the incident side and the outgoing side are not necessarily the same. There is no shape restriction as long as the leakage rate changes in accordance with the incident and exiting positions of charged particles and the combination allows obtaining a predetermined convergence force by the above calculation.

  Next, the operation and effect of this bending electromagnet 1 when such a bending electromagnet 1 is installed in an acceleration device will be described. FIG. 6 is a conceptual diagram of the FFAG acceleration device 2 configured by incorporating a plurality of bending electromagnets 1. The FFAG acceleration device 2 includes a deflection electromagnet 1 (six in this example), an incident means 3 used for making charged particles incident, and an acceleration means 4 for accelerating the incident charged particles. The charged particles are generated by charged particle generating means (not shown), and the generated charged particles are incident on the incident means 3 by charged particle transport means (not shown). The incident charged particles enter the charged particle orbit 5 via the incident means 3 and circulate in the acceleration device 2 along the orbit 5. The circulating charged particles are accelerated by the acceleration means 4 on the way, and the energy increases. Then, when charged particles pass through the deflection electromagnet 1, the deflection radius when receiving the deflection by the deflection electromagnet 1 is increased, and the outer orbit is circulated. In this way, the charged orbit that goes around the acceleration device 2 increases in the orbit every time it passes through the acceleration means 4, and the orbit increases up to the orbit 6. Therefore, as the charged particles accelerate, the trajectory passing through the deflecting electromagnet 1 moves outward in the radial direction of the acceleration device.

  As described above in “Background Art”, the convergence force due to edge focus of a normal sector-type deflecting electromagnet increases as the circular orbit expands. This is because the leakage magnetic field distribution shape does not depend on the positions of incident and outgoing charged particles. As described above, the magnetic field leakage rate is changed in accordance with the position of incident and exiting charged particles, and the leakage rate is reduced on the inner side in the radial direction of the accelerator, so that the charged particles enter or exit the deflecting electromagnet 1 near the orbit. The distribution of the leakage magnetic field along the trajectory of the accelerator can be made a distribution shape depending on the radial position of the accelerator, thereby increasing the convergence force on the radially inner side of the accelerator compared to the case without the magnetic pole plate 13a. be able to. Since the tune increases as the convergence force increases, the tune when the charged particles orbit around the inside of the accelerating device in the radial direction increases as compared with the case without the magnetic pole plate. Therefore, by adopting the bending electromagnet 1 according to the present invention in the acceleration device 2, it becomes possible to reduce the change in the tune due to the acceleration energy.

  FIG. 7A and FIG. 7B are diagrams showing the effect of the present invention by simulation calculation. FIG. 7A shows the dependence of the tune on the charged particle energy when the magnetic pole plates 13a and 13b are removed from the deflection electromagnet 1 shown in FIGS. 1 to 3 and used in the acceleration device shown in FIG. FIG. 7B shows the dependence of the tune on the charged particle energy when the magnetic pole plates 13a and 13b are attached thereto. Since charged particle energy increases with acceleration, both FIGS. 7 (a) and 7 (b) show tune changes during acceleration. When the magnetic pole plates 13a and 13b are not attached, the change in the tune is large, and the change is particularly remarkable in the early stage of acceleration. However, when the magnetic pole plates 13a and 13b are attached, the change in the tune is small as a whole including the initial stage of acceleration. It has become. Therefore, the tune is not applied to the resonance line, and stable acceleration is possible.

  As described above, in the present invention, a magnetic pole plate is installed in the deflection electromagnet, and the magnetic field leakage rate is changed depending on the position where the charged particles are incident or emitted, so that the charged particles depend on the position where the charged particles are incident or emitted. The leakage magnetic field distribution shape along the orbit around the orbit changes. Thereby, when this deflection electromagnet is incorporated in an acceleration device, it becomes possible to apply a convergence force that satisfies the circumstance of charged particles with a simple structure. Accordingly, it is possible to reduce the size of the acceleration device using the deflection electromagnet.

  FIG. 4A shows the trim coil 16a attached to the magnetic pole 11a. As described in “Background Art”, this trim coil is installed in order to increase the magnetic field strength of the deflecting electromagnet 1 as it approaches the outside in the radial direction of the accelerator. It is similarly attached to the magnetic pole 11b, but the reference numerals are omitted. The same applies to FIGS. 4B and 4C. FIG. 5 schematically shows an installation state of the trim coil 16a, taking a rectangular magnetic pole shape as an example in the plan view. The trim coil 16a is installed on the inner side of the coil 12a, but the coils 12a and 12b are omitted so that the installation status can be understood. Since the magnetic field strength is distributed by the trim coil, the leakage magnetic field distribution is also non-uniform. However, when the leakage magnetic field distribution along the trajectory of the charged particles is seen, it is similar at any incident and outgoing position, and its shape does not change. Therefore, it can be said that the presence or absence of the trim coil does not affect the effect of the present invention.

  In addition to the trim coil, there is a method of giving a magnetic field gradient. In this method, the interval between the magnetic poles is changed depending on the charged particle entrance / exit position to the deflection electromagnet. The present invention can be similarly applied to such a bending electromagnet. For example, taking FIG. 2 as an example, a magnetic field gradient similar to that when the trim coil is arranged can be obtained by increasing the magnetic pole spacing of the BB ′ portion and decreasing the magnetic pole spacing of the DD ′ portion. . However, in this configuration, the leakage magnetic field becomes large at the portion where the interval between the magnetic poles is large, that is, the B-B 'portion, and the leakage magnetic field tends to be reversed. When such a deflecting electromagnet is used for the acceleration device as shown in FIG. 6, it is impossible to provide a convergence force that satisfies the rotation condition as it is, but the magnetic pole plate can compensate for the reverse state of the magnetic field leakage rate. For example, there is room for a bending electromagnet that can provide a converging force that satisfies the circuit condition.

  In the above description, the spiral magnetic pole is taken as an example. However, the effects described so far are established regardless of the shape of the deflection electromagnet magnetic pole. Details of this will be described in the fifth embodiment. Here, the reason why the spiral-shaped deflecting electromagnet is taken as an example is that it is realistic to combine the present invention and the spiral shape in the FFAG accelerator which is a powerful application destination of the present invention. This point will also be described in Embodiment 5. In the above description, the deflecting surface of the deflecting electromagnet has been described as being a horizontal plane. However, the present invention is not limited to this, and the deflecting electromagnet can be installed in any direction, and similar effects can be achieved.

Embodiment 2
The magnetic pole plate 13a of the deflection electromagnet 1 according to Embodiment 2 of the present invention is a position adjustment type magnetic pole plate provided with a position adjustment unit that makes the distance between the magnetic pole plate 13a and the charged particle orbiting surface 14 variable.
Specific examples are shown in FIGS. FIG. 8 shows a magnetic pole plate 13a according to an embodiment of the present invention. As shown in FIG. 8, there are a plurality of position adjusting portions 17a in the longitudinal direction of the magnetic pole plate 13a corresponding to the incident or outgoing position of the charged particles of the deflection electromagnet 1. Is provided. The position adjusting unit 17a includes, for example, a position adjusting hole 19a opened in the magnetic pole plate 13a, and a position adjusting fastener 20a such as a screw for fixing the magnetic pole plate 13a to the support plate 18a through the position adjusting hole 19a. The position adjusting unit 17a moves the magnetic pole plate 13a in the direction indicated by the white arrow in FIG. 8 and fixes it to the support plate 18a. Can be changed. FIG. 9 is a cross-sectional view taken along line EE ′ shown in FIG. FIG. 10 shows another example of the position adjusting type magnetic pole plate 13a. Here, the support plate 18 a that supports the magnetic pole plate 13 a is eliminated, and the magnetic pole plate 13 a is directly attached to the iron core 10. Alternatively, the magnetic pole plate 13a and the support plate 18a may be integrated, and the position adjusting unit 17a may be installed on the support plate 18a and fixed to the iron core 10 via this.

  Thus, by making the distance of the magnetic pole plate from the deflection track surface variable, it is possible to easily adjust the distribution of the leakage magnetic field of the deflection electromagnet. Therefore, the converging force in the radial direction by the deflecting electromagnet can be easily adjusted even after the deflection electromagnet is manufactured, and a deflecting electromagnet having a converging force satisfying the rotation condition can be obtained with higher accuracy. By using a deflecting electromagnet capable of adjusting the leakage magnetic field distribution shape in the acceleration device, the tune change during the acceleration process can be easily reduced for the same reason as described in the first embodiment. Therefore, the tune of the accelerator is not applied to the resonance line, and more stable acceleration is possible.

  In FIG. 10, the pole plate distance from the deflection track surface is made variable by moving the pole plate up and down as a whole. However, as shown in FIG. The distance between the magnetic pole plate and the magnetic pole plate may be variable. In FIG. 11, in addition to the same position adjustment unit 17a as shown in FIG. 8, a rotation position adjustment unit 21a made to be rotatable around the position adjustment fastener 20a of the position adjustment unit 17a is provided. . This rotation is allowed within the rotation angle range of the rotation position adjusting hole 22a. Further, the pole plate can be adjusted up and down within the range of the position adjustment hole 19a with respect to the position adjustment fastener 20a, and after the vertical adjustment, the position adjustment fastener 20a is rotated and fixed. It can also be made. In this way, the pole plate distance from the deflection track surface can be made variable.

Embodiment 3
FIG. 12 shows a magnetic pole plate 13a of the bending electromagnet 1 according to Embodiment 3 of the present invention. In the magnetic pole plate 13a of this embodiment, the magnetic pole plate is divided into a plurality of pieces in the longitudinal direction so that the magnetic pole plate distance from the deflection track surface 14 can be adjusted for each divided magnetic pole plate. The magnetic pole plate 13a includes at least one position adjusting portion 17a for each divided magnetic pole plate. The method for supporting the magnetic pole plate 13a to the deflection electromagnet 1 is the same as the method described in the second embodiment.

  As with the case of the first embodiment, the design of the divided magnetic pole plate (the number of divided pieces and the distance from the deflection surface) is the same as in the first embodiment, so that the necessary leakage magnetic field distribution can be obtained in the vicinity of the orbit. It is determined based on dynamic calculation and three-dimensional magnetic field analysis calculation. The shape of the divided magnetic pole plate may be rectangular as shown in FIG. 12, or the magnetic pole plate shown in FIG. 8 may be simply divided in the longitudinal direction, and can be freely determined. . As described above, by adjusting the magnetic pole plate distance from the deflection track surface for each divided magnetic pole plate, it is possible to easily and accurately adjust the distribution of the leakage magnetic field of the deflection electromagnet. Therefore, it is possible to easily and accurately adjust the dependence of the convergence force by the deflecting electromagnet on the acceleration device radial direction even after the deflection electromagnet is manufactured, and to obtain a deflecting electromagnet having a convergence force that satisfies the rotation condition with higher accuracy. I can do it. In addition to the effects described in the first and second embodiments, by using a deflecting electromagnet capable of fine adjustment of the leakage magnetic field distribution in this way, the tune change during the acceleration process can be made easier and smaller. Therefore, the tune of the accelerator is not applied to the resonance line, and more stable acceleration is possible.

Embodiment 4
FIG. 13 shows a bending electromagnet 1 according to Embodiment 4 of the present invention. The present embodiment is an invention relating to a deflection electromagnet having a leakage magnetic field adjusting means other than a magnetic pole plate. In FIG. 13, the coils 12a and 12b are omitted so that the installation condition of the trim coil can be easily seen. The magnetic pole shape is also shown as a rectangle and simplified. In the deflection electromagnet 1 of FIG. 13, when the deflection electromagnet 1 is installed in the acceleration device 2, the distance between the magnetic poles 11a and 11b is made narrower as it approaches the radially inner side of the acceleration device. If the gap between the magnetic poles is small, the magnetic field leakage rate will be small. Therefore, by expanding the gap between the magnetic poles along the radial direction, the area covering the coil side surface with the magnetic pole plate will be reduced along the radial outside. Similar effects can be obtained. However, if this is done, the magnetic field becomes stronger as it approaches the inner side in the radial direction, and the radial dependence of the deflection magnetic field strength distribution required by the FFAG accelerator 2 is reversed. In the present invention, in order to correct this, trim coils 21a and 21b are provided to compensate for the magnetic field strength distribution. A specific compensation method using a trim coil is to generate a strong magnetic field in the opposite direction to the magnetic pole when the deflection radius is small and to compensate the magnetic field strength distribution, and to generate a strong magnetic field in the same direction as the magnetic pole when the deflection radius is large. And a method for compensating the magnetic field strength distribution. FIG. 13 shows the former example. The degree of compensation can be changed according to the application by changing the installation mode of the trim coil and the energization amount to the trim coil.

  As described in the first embodiment, the magnetic pole spacing is determined from the beam dynamics calculation to determine the leakage magnetic field distribution shape required to obtain the convergence force satisfying the circular condition. The distance between the magnetic poles necessary for the realization is obtained by three-dimensional magnetic field analysis calculation.

  Thus, there is a leakage magnetic field adjusting means other than the magnetic pole plate. Whatever method is used, the leakage magnetic field adjusting means is added to the deflection electromagnet, and the leakage magnetic field adjustment means changes the leakage magnetic field distribution shape along the circular orbit near the deflection surface from the deflection electromagnet according to the radial direction. Thus, adjusting the dependence of the converging force in the vertical direction of the deflection electromagnet on the acceleration device radial direction has never been achieved, and the effects as described in the first to fourth embodiments can be achieved. It is a useful invention.

Embodiment 5
In the present embodiment, any one of the leakage magnetic field adjusting means described in the first to fourth embodiments is combined with a deflection electromagnet having a helical magnetic pole. First, the necessity of the spiral magnetic pole will be described. In the FFAG accelerator 2, the magnetic field strength is increased in the radial direction of the deflecting electromagnet 1, but due to this magnetic field gradient, a diverging force acts on the charged particles in the vertical direction, which hinders stable circulation of the charged particles. In order to obtain a converging force for suppressing the diverging force, a deflection electromagnet 1 having a helical magnetic pole is employed. By making the magnetic pole in a spiral shape, the incident angle of the charged particles to the deflection electromagnet and the emission angle φ of the charged particles from the deflection electromagnet (φ is the line perpendicular to the traveling direction of the equilibrium orbit and the magnetic pole surface of the deflection electromagnet Can be made larger than that of a normal sector-type deflection electromagnet, and the same angle can be set for incident and outgoing from any orbit. Since the vertical focusing force due to edge focus is proportional to tanφ, such a helical deflecting electromagnet, when compared to a normal sector-shaped deflecting electromagnet, has a vertical focusing force with respect to charged particles. It is possible to increase the size uniformly without depending on the position of the orbit. Therefore, it can be said that the spiral magnetic pole is an effective choice for suppressing the radial size of the accelerator. However, as described above, since it is unavoidable that there is a conflict with the resonance line due to the tune change during the acceleration process, one of the leakage magnetic field adjusting means described in the first to fourth embodiments is selected. In combination with a deflection electromagnet having the above-mentioned helical magnetic pole, it is possible to reduce the tune change during the acceleration process and realize a compact deflection electromagnet in the circumferential direction compared to conventional deflection electromagnets. I can do it. By adopting this deflection electromagnet in the acceleration device, the acceleration device can also be made compact. Note that the leakage magnetic field distribution shape is affected by the magnetic pole shape, so the magnetic pole shape influences the shape design of the magnetic pole plate. However, the significance and effects of the present invention described so far are shapes other than the helical shape. This is true regardless of the magnetic pole shape.

  Further, although the FFAG accelerator as shown in FIG. 6 has been described as an example of the accelerator using the deflection electromagnet according to the present invention, it is not necessarily limited to the FFAG accelerator. In the acceleration process of charged particles, the change in the tune is reduced by changing the vertical convergence force depending on the radial direction of the deflecting electromagnet for an acceleration device in which the change in the vertical tune is large. It can be used in common if it is used.

The bird's-eye view of the upper half of the bending electromagnet according to Embodiment 1 of the present invention FIG. 2 is a plan view of a bending electromagnet according to Embodiment 1 of the present invention. Side view of the bending electromagnet according to Embodiment 1 of the present invention. (A) BB ′ sectional view of the deflection electromagnet according to Embodiment 1 of the present invention (b) CC ′ sectional view of the deflection electromagnet according to Embodiment 1 of the present invention (c) Implementation of the present invention DD 'sectional drawing of the bending electromagnet which concerns on form 1 The perspective view (conceptual figure) which shows the trim coil laying state of the bending electromagnet which concerns on Embodiment 1 of this invention Schematic diagram of FFAG accelerator using deflection electromagnet according to Embodiment 1 of the present invention (A) Change due to acceleration energy of vertical tune (without pole plate) (b) Change due to acceleration energy of vertical tune (with pole plate) Side view of the bending electromagnet according to Embodiment 2 of the present invention Sectional drawing 1 of the bending electromagnet which concerns on Embodiment 2 of this invention Sectional drawing 2 of the bending electromagnet based on Embodiment 2 of this invention The side view by the other example of the bending electromagnet based on Embodiment 2 of this invention Side view of a bending electromagnet according to Embodiment 3 of the present invention Perspective view (conceptual diagram) of a bending electromagnet according to Embodiment 4 of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 The deflection electromagnet which concerns on this invention, 2 The circular acceleration apparatus incorporating the deflection electromagnet which concerns on this invention, 3 Charged particle injection means, 4 Acceleration means, 5 Charged particle circular orbit in the early stage of acceleration, 6 Charged particle circular orbit in the final stage of acceleration, 10 iron core, 11a, 11b magnetic pole, 12a, 12b coil, 13a, 13b magnetic pole plate, 14 charged particle orbiting surface, 15 charged particle, 16a trim coil, 17a position adjusting portion, 18a support material, 19a position adjusting hole, 20a position Fastening for adjustment, 21a Rotation position adjustment part, 22a Rotation position adjustment hole, 23a Rotation position adjustment fastener

Claims (7)

In a deflecting electromagnet in which charged particle incident positions are distributed in a direction substantially perpendicular to the deflection magnetic field and the trajectory on which the charged particle is incident, the charged particles entering and exiting the deflecting electromagnet in the vicinity of each trajectory. A deflecting electromagnet provided with a leakage magnetic field adjusting means for adjusting a leakage magnetic field distribution from a deflection magnetic field in an orbital direction to a different distribution shape depending on the incident or exiting position by adjusting a leakage rate of the magnetic field. The leakage magnetic field adjusting means arranges a magnetic pole plate made of a magnetic material on the outermost surface of the coil on the side where charged particles enter or exit the deflecting electromagnet via an iron core constituting the deflecting electromagnet. An air gap distance between the surface of the magnetic pole plate facing the deflection trajectory surface of the charged particle by the electromagnet and the deflection trajectory surface is set depending on the incident or exit position of the deflection electromagnet. The deflection electromagnet according to claim 1. 3. The deflecting electromagnet according to claim 2, wherein the magnetic pole plate includes a position adjusting unit, and the air gap distance is made variable by the position adjusting unit. The magnetic pole plate is composed of a divided magnetic pole plate that is divided into a plurality of parts corresponding to positions where charged particles enter or exit the deflection electromagnet, and each of the divided magnetic pole plates is provided with a position adjusting unit. The deflection electromagnet according to claim 3. The leakage magnetic field adjusting means has a configuration in which the interval between the deflecting electromagnet magnetic poles is changed depending on the position where the charged particle enters or exits the deflecting electromagnet, and the magnetic field strength depends on the position where the incident or exiting is present. The bending electromagnet according to claim 1, further comprising a trim coil for adjusting the distribution. The projected shape of the deflecting electromagnet magnetic pole on the charged particle deflection orbital surface is a part of a shape formed by planarly projecting a helical shape on each of incident and outgoing charged particle sides. The deflection electromagnet according to any one of 1 to 5. A charged particle acceleration apparatus comprising two or more deflection electromagnets according to claim 1.

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