JP2004241347A - Circular accelerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that incidence efficiency is reduced when a low energy beam emitted from an ion source is transported to a beam incident port of a circular accelerator through a beam transport system because the beam is influenced by a leaking magnetic field and deflected since the beam transport system passes between electromagnets constituting the circular accelerator, to prevent the beam from being influenced by the leaking magnetic field by deflecting and injecting the beam in a direction perpendicular to the circular accelerator. <P>SOLUTION: In this circular accelerator, a charged beam is circulated and accelerated, and the beam transport system is provided in a plane vertical to a circulating beam orbital plane of the circular accelerator, and not influenced by the leaking magnetic field. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a particle accelerator for accelerating charged particles (charged beams) such as protons and electrons, and more particularly to a circular accelerator for repeatedly accelerating on a circular orbit.
[0002]
[Prior art]
As is well known, for example, a circular accelerator that circulates and accelerates a charged beam includes, for example, an FFAG (Fixed Field Alternating Gradient) accelerator, a synchrotron, and a cyclotron accelerator. The FFAG accelerates the deflection and convergence of the charged beam under a constant magnetic field. The beam to be accelerated can be made incident on the FFAG either outside or inside the FFAG, but is generally designed to enter from the inside. In this case, the internal space of the FFAG has a narrow space, and an ion source and each device constituting a beam transport system until a beam emitted from the ion source is incident on the FFAG often cannot be accommodated in the internal space. In such a case, it is disclosed that a conventional ion source is installed outside the FFAG to solve the problem of the space (for example, see Non-Patent Document 1).
[0003]
[Non-patent document 1]
DEVELOPMENT OF A FFAG PROTON SYNCHROTRON. Proceedings of EPAC2000, Vienna, Austria (P582 FIG. 1)
[0004]
[Problems to be solved by the invention]
However, in the arrangement shown in Non-Patent Document 1, the beam exiting the ion source passes between the deflection and converging electromagnets of the FFAG accelerator. (Incident trajectory) is deviated, and the incident efficiency to the FFAG is reduced.
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and reduces the beam incidence efficiency by providing a beam transport system capable of entering a beam emitted from an ion source while deflecting the beam from the vertical direction of the inner space of the circular accelerator. It is intended to provide a circular accelerator that does not cause it to run.
[0005]
[Means for Solving the Problems]
A circular accelerator having a plurality of magnetically separated electromagnets having a beam incident portion and orbiting the beam, wherein the beam incident portion has an ion source and a beam from the ion source. A beam transport system for transporting the beam to the entrance is provided, and the beam transport system is provided in a plane perpendicular to the orbital plane of the circular accelerator.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a circular accelerator 100 that accelerates, for example, protons having an energy of 100 KeV at the time of incidence to 5 MeV. FIG. 2 is a plan layout view thereof. The floor 20 in FIG. 1 is drawn to show the vertical direction of the device. Here, the circular accelerator 100 is an example of an FFAG accelerator. As means for accelerating the incident beam to high energy, there are a high frequency acceleration and an induction acceleration method. In the first embodiment, an example of the induction acceleration method will be described. The circular accelerator 100 shown in FIGS. 1 and 2 includes a plurality of magnetically separated deflection, focusing electromagnets 2, vacuum ducts 3, ion sources 10, incident deflection electromagnets 11, inflectors 1, betatron cores 4, and coil power supplies 5. , A coil 6.
[0007]
Next, the operation of the circular accelerator 100 having the above configuration will be described.
The beam generated by the ion source 10 is deflected by 180 ° by the incident deflection electromagnet 11 as shown in the beam trajectory 12 of FIG. 1 and guided by the inflector 1 to the orbiting beam trajectory in the vacuum duct 3.
Here, a portion from the ion source 10 to the inflector 1 is referred to as a beam incident portion 50, and a beam transport path from the beam exiting the beam outlet 10a of the ion source 10 to the beam entrance 1a of the inflector 1 is shown. , Beam transport system 60.
One of the features of the first embodiment is that the beam incidence unit 50 is provided in the vicinity of the circular accelerator 100 and the beam transport system 60 is located in a plane perpendicular to the orbiting beam orbit plane 100 a of the circular accelerator 100. And a deflection trajectory as shown in the beam trajectory 12. Details of the structure will be described later.
In the example shown in FIG. 2, a plurality of magnetically separated deflecting and converging electromagnets 2 are provided at eight locations on the orbit of the beam to be accelerated, and are arranged to deflect and converge the beam. The betatron core 4 is made of a ferromagnetic material, and is arranged so as to surround the vacuum duct 3 and the deflection converging electromagnet 2 over the orbit of the beam. When an alternating current is supplied from the coil power supply 5 to the coil 6, an electric field proportional to the time change of the magnetic field is induced around the betatron core 4 so as to surround the betatron core 4 according to Faraday's induction law. The electric field does not exist for the orbiting beam due to the presence of the conductive vacuum duct 3, but the electric field is concentrated there by providing the electrically insulated acceleration gap 7 as shown in FIG. The electric field accelerates the beam.
[0008]
The ion generator of the ion source 10 is electrically floated at 100 KV, and the beam generated here is a beam having an energy of 100 KeV. The energy beam of 100 KeV is deflected and affected by the leakage magnetic field from the focusing electromagnet 2 and the like. For example, if a magnetic field of 5 Gauss is present over 1 _m, it will be deflected 5.5 _mm . As shown in FIG. 1, the ion source 10 is disposed below the orbital beam orbital surface 100a of the circular accelerator 100 so that the circular accelerator 100 can be made compact.
As described above, the beam from the ion source 10 passes through the beam trajectory 12 of 180 ° deflection by the incident deflection electromagnet 11 of the beam transport system 60, and the inflector of the beam entrance 1a provided between the deflection and focusing electromagnets 2 Reach one. That is, the beam transport system 60 is formed by providing the incident deflection electromagnet 11 between the deflecting and converging electromagnets 2 at the center of the circular accelerator 100 and below the orbiting beam orbital surface 100a. More specifically, based on FIG. 1 and FIG. 2, the beam transport system 60 is provided in a plane perpendicular to the orbiting beam orbital plane 100a, and in the perpendicular plane, 11 has a 180 ° deflection trajectory. Further, the ion source 10 of the beam incident part 50 including the beam transport system 60 is provided near the circular accelerator 100.
[0009]
The incident deflection electromagnet 11 generates a magnetic field in the vertical direction in the drawing shown in FIG. 1, and has magnetic poles so as to sandwich the beam trajectory 12. Generally, an electromagnet provided with a coil is used, but a permanent magnet may be used. In the incident deflecting electromagnet 11, the beam is deflected by 180 °, is deflected in the horizontal direction (vertical direction in FIG. 1) by the inflector 1 at the beam entrance 1a of the circular accelerator 100, and is incident on the circular accelerator 100. The incident beam is accelerated and the orbital radius is increased with an increase in energy.
[0010]
Here, since the beam emitted from the beam outlet 10a of the ion source 10 spreads in the beam transport system 60, it is necessary to reduce the spread by providing some converging means and perform efficient beam incidence. The incident deflection electromagnet 11 has a converging force in the horizontal direction (vertical direction in the figure), but does not have a converging force in the vertical direction (horizontal direction in the figure), so some converging means is required. Therefore, the magnetic poles at the entrance and exit of the beam of the incident deflecting electromagnet 11 are inclined (normally, the magnetic pole face is perpendicular to the beam trajectory) to obtain a converging function. Depending on the direction of the inclination, the divergence in the horizontal direction and the convergence in the vertical direction or vice versa, but the direction in which the convergence force is obtained in the vertical direction. In this case, although the divergence occurs in the horizontal direction, the internal magnetic field itself has a convergence action in the horizontal direction, so that the convergence force is obtained as a whole. Betatron core 4 is provided inside circular accelerator 100, and there is also a leakage magnetic field therefrom. Therefore, the shorter the space between the ion source beam extraction port 10a and the beam entrance 1a and the incident deflection electromagnet 11, the less the influence of the leakage magnetic field. In the first embodiment, the coil end of the incident deflection electromagnet 11 is formed in a saddle shape, and the coil end length in the beam traveling direction is shortened to shorten the space. Further, a shield end plate may be provided on an end face of the saddle coil to shield the external leakage magnetic field and the leakage magnetic field of the incident deflection electromagnet 11 so as to reduce the influence on the beam incident on the circular accelerator 100.
[0011]
As described above, in the configuration according to the first embodiment, the beam transport system 60 of the beam entrance 50 extending from the ion source 10 to the beam entrance 1 a is located within a plane perpendicular to the orbiting beam orbit plane 100 a of the circular accelerator 100. And has a deflection trajectory in a vertical plane, and because most of the beam path through the beam transport system 60 is in the incident deflection electromagnet 11, an external magnetic field is shielded by the incident deflection electromagnet 11. And the effect on the beam can be extremely reduced.
As a result, beam transport close to the design plan becomes possible, and the beam incidence efficiency is not reduced. Further, a compact beam transport system 60 can be realized. The betatron core 4 may have a structure provided at two locations on the orbit as shown in FIG.
[0012]
Embodiment 2 FIG.
The beam incident part 50 according to the second embodiment will be described with reference to FIG. In the above-described first embodiment, an example is shown in which the ion source 10 of the incident unit 50 is arranged below the orbiting beam orbital surface 100a of the circular accelerator 100. However, as shown in FIG. It is provided on the upper side of the beam track surface 100a. In this case, restrictions on the arrangement of the ion source 10 are reduced, so that the degree of freedom in designing the ion source 10 is increased. In addition, the maintenance of the ion source 10 is facilitated and the circular accelerator 100 is easily assembled. Further, in the system in which the ion source 10 is arranged away from the main body of the circular accelerator 100 as shown in FIG. 5, the above advantage is further enhanced.
In this case, since the beam transport system 60 becomes longer, a device for converging the beam is required. The convergence device 13 includes various means such as a quadrupole electromagnet, a permanent magnet, and a solenoid coil. Note that at least one or more quadrupole electromagnets are provided, and preferably two pairs are used.
[0013]
Embodiment 3 FIG.
The beam incident part 50 according to the third embodiment will be described with reference to FIG. As shown in the figure, the beam transport system 60 according to the third embodiment has the beam focusing device 13 provided between the incident deflection electromagnet 11 and the beam entrance 1 a and between the ion source 10. When such a configuration is employed, the shape of the incident beam can be adjusted. That is, when the shape of the beam emitted from the ion source 10 is uncertain or the shape of the emitted beam changes in time series, for example, the convergence is controlled by a signal from a beam monitor (not shown) provided in the beam transport system 60. The device 13 is controlled to adjust the shape and position of the incident beam. Further, there is an effect that the parameters of incidence on the main body of the circular accelerator 100 can be optimized. Although the convergence device 13 is provided on the entrance and exit side of the incident deflection electromagnet 11, it may be provided on only one side.
[0014]
Embodiment 4 FIG.
The beam incident part 50 according to the fourth embodiment will be described with reference to FIG.
As shown in the figure, a beam transport system 60 according to the fourth embodiment has two incident deflection electromagnets 11a for deflecting a beam at 90 °, and a converging device 13 disposed between them.
The reason for employing such a configuration will be described below.
Since the output fluctuation of the high voltage power supply of 100 KV of the ion source 10 is finite, the output beam energy changes as a result. For example, if there is a ± 0.2% variation in the high voltage power supply, the beam will vary ± 0.4 _mm . To avoid this, two 90 ° incident deflection electromagnets 11a and two converging devices 13 are provided between them as described above. The magnetic field strength of each of the incident deflection electromagnets 11a is reduced by the parameters of the convergence device 13 so that a change in the position of the beam having a different energy at the beam entrance 1a (displacement in a direction perpendicular to the orbiting beam orbital surface 100a) is substantially zero. It is possible. In the fourth embodiment, an example is shown in which two converging devices 13 are used. However, one converging device 13 may be used depending on how to select the end converging force of each of the incident deflection electromagnets 11a, and the number is limited. is not. This optimizes these parameters taking into account also the allowable beam size. Furthermore, as shown in FIG. 6 of the third embodiment, even in the fourth embodiment, if the focusing device 13 is also arranged between the incident deflection electromagnet 11a and the ion source 10 or the beam entrance 1a, a further optimum configuration can be obtained. Design becomes possible.
[0015]
Embodiment 5 FIG.
The beam incident part 50 according to the fifth embodiment will be described with reference to FIG. As shown in the figure, according to the fifth embodiment, the ion source 10 is installed so that the beam extraction port 10a of the ion source 10 is perpendicular to the orbiting beam orbit plane 100a, and the incident deflection electromagnet 11a Has a deflection angle of 90 °, and a convergence device 13 is provided between the ion source 10 and the incident deflection electromagnet 11a. With such a configuration, the beam incident portion 50 can be made compact, and the size of the incident deflection electromagnet 11a can be reduced, so that the cost can be reduced. The ion source 10 may be provided on the upper side of the orbiting beam orbital surface 100a.
[0016]
Embodiment 6 FIG.
As is well known, the incident deflection electromagnet 11 may adopt a method of giving a magnetic field gradient to obtain a converging force in the direction of the deflection magnetic field. Usually, a magnetic field gradient that weakens in the radial direction of the beam orbit is provided. In this case, end convergence is not required, and the shape of the electromagnet pole tip becomes simple.
As described above, according to the configuration of the sixth embodiment, the installation of the focusing device 13 is not always necessary, and the overall design of the incidence unit 50 is facilitated, and the cost is reduced. However, it goes without saying that more effective convergence becomes possible if the convergence device 13 is installed.
[0017]
Embodiment 7 FIG.
In the above-described embodiment, the description has been given of the method using the induction acceleration method as the acceleration means. However, the same effect can be obtained by the high-frequency acceleration method.
[0018]
【The invention's effect】
Since the present invention is a circular accelerator having the above-described configuration, it has the following effects.
A circular accelerator having a beam incident part and a plurality of magnetically separated electromagnets for orbiting a beam, wherein the beam incident part has an ion source and a beam from the ion source to a beam entrance of the circular accelerator. A beam transport system for transport is provided, and the beam transport system is provided in a plane perpendicular to the orbital beam orbit plane of the circular accelerator. Since it does not pass through the gap, it is not affected by the leakage magnetic field, and since the orbit in the incident deflection electromagnet of the beam transport system is almost the same, it is hardly affected by the leakage magnetic field of other components of the circular accelerator. As a result, there is an excellent effect that beam deflection in the beam transport system can be prevented, and a decrease in the efficiency of incidence on the circular accelerator can be avoided.
[Brief description of the drawings]
FIG. 1 is a sectional view of a circular accelerator according to Embodiment 1 of the present invention.
FIG. 2 is a plan layout view of the circular accelerator according to the first embodiment of the present invention.
FIG. 3 is a plan view of a circular accelerator showing another embodiment of the first embodiment of the present invention.
FIG. 4 is a diagram showing a beam incident part according to a second embodiment of the present invention.
FIG. 5 is a diagram showing a beam incident portion according to another embodiment of the second embodiment of the present invention.
FIG. 6 is a diagram showing a beam incident part according to a third embodiment of the present invention.
FIG. 7 is a diagram showing a beam incident part according to a fourth embodiment of the present invention.
FIG. 8 is a diagram showing a beam incident part according to a fifth embodiment of the present invention.
[Explanation of symbols]
1 inflector, 1a beam entrance, 2 deflection focusing electromagnet,
4 betatron core, 5 power supply, 6 coil, 10 ion source,
10a beam outlet, 11, 11a incident deflection electromagnet,
12 beam orbital, 50 beam entrance, 60 beam transport system,
100 circular accelerator, 100a orbital orbital plane.

Claims (20)

A circular accelerator having a plurality of magnetically separated electromagnets having a beam incident portion and orbitally accelerating the beam,
The beam incident portion is provided with an ion source and a beam transport system for transporting a beam from the ion source to a beam entrance of the circular accelerator, and the beam transport system is provided on a circular beam orbit plane of the circular accelerator. A circular accelerator, which is provided in a plane perpendicular to the circular accelerator. The circular accelerator according to claim 1, wherein the beam transport system has a deflection trajectory in a plane perpendicular to a circular beam trajectory plane of the circular accelerator. The circular accelerator according to claim 2, wherein the beam incident portion is provided at a central portion of the circular accelerator and close to the beam incident port. The circular accelerator according to claim 2, wherein the deflection trajectory is formed by an incident deflection electromagnet. The circular accelerator according to claim 4, wherein the incident deflection electromagnet has a deflection angle of 180 °. The circular accelerator according to claim 4, wherein the deflection trajectory is formed by two incident deflection electromagnets having a deflection angle of 90 °. The beam extraction port of the ion source is provided perpendicular to the orbital beam orbital plane, and the incident deflection electromagnet has a deflection angle of 90 °. Circular accelerator. The circular accelerator according to claim 4 or 7, wherein a pole tip surface of the incident deflection electromagnet facing a beam trajectory has an angle with respect to the beam incident surface. The circular accelerator according to claim 4, wherein a beam focusing device is provided in the beam transport system. The circular accelerator according to claim 9, wherein the beam focusing device is provided between the ion source and the incident deflection electromagnet. The circular accelerator according to claim 9, wherein the beam converging device is provided between the ion source and the incident deflection electromagnet and between the incident deflection electromagnet and the beam entrance. . The circular accelerator according to claim 6, wherein a beam focusing device is provided between the two incident deflection electromagnets. The circular accelerator according to any one of claims 9 to 12, wherein the beam focusing device comprises a quadrupole electromagnet. The circular accelerator according to any one of claims 9 to 12, wherein the beam convergence device is configured by a solenoid coil. The circular accelerator according to claim 9, wherein the beam focusing device includes a quadrupole electromagnet and a solenoid coil. 4. The circular accelerator according to claim 3, wherein the beam incident unit is provided below a circular beam trajectory plane of the circular accelerator. 5. 4. The circular accelerator according to claim 3, wherein the beam incident portion is provided above a circular beam orbit plane of the circular accelerator. 5. The circular accelerator according to claim 4, wherein the bending electromagnet has a saddle-shaped coil at an end, and an end plate is provided on an outer end surface of the saddle-shaped coil. The circular accelerator according to claim 1, further comprising a betatron having a betatron core, a coil provided in the core, and an AC power supply. 20. The circular accelerator according to claim 19, wherein the betatron core has a two-part structure so as to sandwich the incident bending electromagnet of the circular accelerator.

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