JP4296001B2 - Circular accelerator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a particle beam accelerator that accelerates charged particles (charged beams) such as protons and electrons, and more particularly to a circular accelerator that repeatedly accelerates on a circular orbit.
[0002]
[Prior art]
As is well known, circular accelerators that accelerate by rotating a charged beam include, for example, FFAG (Fixed Field Alternating Gradient) accelerators, synchrotrons, and cyclotron accelerators. The FFAG accelerates the charged beam with a constant deflection magnetic field. The beam to be accelerated can be incident on the FFAG either outside or inside the FFAG, but is generally designed to be incident from the inside. In this case, the internal space of the FFAG is narrow, and the devices constituting the beam transport system until the ion source and the beam emitted from the ion source enter the FFAG often do not fit in the internal space. In such a case, it has been shown 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 Fig1)
[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 focusing electromagnets of the FFAG accelerator, so that the beam trajectory receives the deflection and divergent forces due to the leakage magnetic field of the electromagnet. There is a problem in that the incidence efficiency to the FFAG is reduced due to the deviation of the (incidence trajectory).
The present invention has been made to solve the above-mentioned problems. By providing a beam transport system that can be incident while deflecting the beam emitted from the ion source from the vertical direction of the inner space of the circular accelerator, the beam incident efficiency is lowered. It is an object of the present invention to provide a circular accelerator that is not allowed to occur.
[0005]
[Means for Solving the Problems]
A circular accelerator having a plurality of magnetically separated electromagnets having a beam incident part and accelerating the beam, wherein the beam incident part receives an ion source and a beam from the ion source. There is a beam transport system that transports to the entrance,
The beam incident part is provided in the central part of the circular accelerator and close to the beam incident port,
The beam transport system is formed by an incident deflection electromagnet having a deflection angle of 180 ° so as to have a deflection trajectory in a plane perpendicular to the circular beam trajectory plane of the circular accelerator .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of a circular accelerator 100 that, for example, accelerates protons with an energy of 100 KeV upon 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 equipment. Here, the circular accelerator 100 is an example of an FFAG accelerator. In addition, 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 is shown. A circular accelerator 100 shown in FIGS. 1 and 2 includes a plurality of magnetically separated deflection, focusing electromagnet 2, vacuum duct 3, ion source 10, incident deflection electromagnet 11, inflector 1, betatron core 4, and coil power source 5. The coil 6 is configured.
[0007]
Next, the operation of the circular accelerator 100 having the above configuration will be described.
The beam produced 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 circular beam trajectory in the vacuum duct 3.
Here, the beam from the ion source 10 to the inflector 1 is referred to as a beam incident part 50, and the beam transport path from the beam exiting the beam extraction port 10a of the ion source 10 to the beam entrance 1a of the inflector 1 is shown. This is referred to as a beam transport system 60.
One of the features of the first embodiment is that the beam incident portion 50 is provided close to the circular accelerator 100 and the beam transport system 60 is in a plane perpendicular to the circular beam trajectory surface 100 a of the circular accelerator 100. In addition, as shown in the beam trajectory 12, a deflection trajectory is provided. 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 positions on the orbit of the accelerating beam and arranged so as to deflect and converge the beam. The betatron core 4 is made of a ferromagnetic material, and is disposed so as to surround the vacuum duct 3 and the deflection converging electromagnet 2 across the beam orbit. 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 from the Faraday induction law. The electric field does not exist because there is a conductive vacuum duct 3 for the circulating beam, but the electric field is concentrated there by providing an electrically insulated acceleration gap 7 as shown in FIG. The beam is accelerated by the electric field.
[0008]
The ion generating part of the ion source 10 is electrically floated at 100 KV, and the beam produced here is a beam having an energy of 100 KeV. This 100 KeV energy beam has a problem of deflection and the influence of a leakage magnetic field from the focusing electromagnet 2 and the like. For example, if a 5 Gauss magnetic field is present over 1 _m, it will be deflected by 5.5 _mm . As shown in FIG. 1, the ion source 10 is disposed on the lower side of the circular beam orbital surface 100a of the circular accelerator 100, and the circular accelerator 100 is 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 1 a provided between the deflection and focusing electromagnet 2. Reach 1 That is, the beam transport system 60 is formed by providing the incident deflection electromagnet 11 between the deflection and focusing electromagnets 2 at the center of the circular accelerator 100 and the lower side of the orbiting beam trajectory surface 100a. 1 and FIG. 2, the beam transport system 60 is provided in a plane perpendicular to the orbiting beam trajectory surface 100a, and the incident deflection electromagnet 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 close to the circular accelerator 100.
[0009]
The incident deflection electromagnet 11 generates a magnetic field in the vertical direction of the diagram shown in FIG. 1 and is provided with magnetic poles so as to sandwich the beam trajectory 12. In general, an electromagnet having a coil is used, but a permanent magnet may be used. In the incident deflection electromagnet 11, the beam is deflected by 180 °, deflected in the horizontal direction (vertical direction in FIG. 1) by the inflector 1 of the beam entrance 1 a of the circular accelerator 100, and is incident on the circular accelerator 100. The incident beam is accelerated and the orbit radius is increased as the energy increases.
[0010]
Here, since the beam emitted from the beam extraction port 10a of the ion source 10 spreads within the beam transport system 60, it is necessary to provide some convergence means to reduce the spread and to perform efficient beam incidence. The incident deflection electromagnet 11 has a convergence force in the horizontal direction (vertical direction in the figure), but does not have a convergence force in the vertical direction (horizontal direction in the figure), so that a convergence means is required. Therefore, the beam entrance and exit magnetic poles of the incident deflection electromagnet 11 are inclined (usually, the pole end face and the beam trajectory are perpendicular) to obtain a convergence function. Depending on the direction of the inclination, the divergence in the horizontal direction, 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, the horizontal direction is divergent, but the internal magnetic field itself has a converging action in the horizontal direction, so that the whole becomes a converging force. The betatron core 4 is provided inside the circular accelerator 100, and there is also a leakage magnetic field therefrom. Therefore, the ion source beam extraction port 10a and the space between the beam incident port 1a and the incident deflection electromagnet 11 are less susceptible to the leakage magnetic field as much as possible. In the first embodiment, the coil end portion of the incident deflection electromagnet 11 is formed into a bowl 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 the end face of the saddle coil to shield the external leakage magnetic field and the leakage magnetic field of the incident deflection electromagnet 11 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 from the ion source 10 to the beam entrance 1 a is in a plane perpendicular to the circular beam trajectory plane 100 a of the circular accelerator 100. In addition, since the deflecting trajectory is in a vertical plane and most of the beam path passing through the beam transport system 60 is in the incident deflecting electromagnet 11, the external magnetic field is shielded by the incident deflecting electromagnet 11. The influence on the beam can be extremely reduced.
As a result, beam transportation close to the design plan is possible, and the beam incidence efficiency is not lowered. In addition, a compact beam transport system 60 can be realized. It should be noted that the betatron core 4 may have a structure in which two places are provided on the orbit as shown in FIG.
[0012]
Embodiment 2. FIG.
The beam incident part 50 of Embodiment 2 is demonstrated based on FIG. In the above-described first embodiment, the example in which the ion source 10 of the incident unit 50 is disposed on the lower side of the circular beam trajectory surface 100a of the circular accelerator 100 has been described. However, as illustrated in FIG. It is provided on the upper side of the beam track surface 100a. In this case, there are effects that restrictions on the arrangement of the ion source 10 are reduced, the degree of freedom in designing the ion source is increased, maintenance of the ion source 10 is facilitated, and the circular accelerator 100 is easily assembled. Further, as shown in FIG. 5, in the system in which the ion source 10 is arranged away from the main body of the circular accelerator 100, the advantage is further increased.
In this case, since the beam transport system 60 becomes long, an apparatus 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, which are appropriately selected and used. It should be noted that at least one quadrupole electromagnet is provided, and preferably a pair of two.
[0013]
Embodiment 3 FIG.
The beam incident part 50 of Embodiment 3 is demonstrated based on FIG. As shown in the figure, in the beam transport system 60 according to the third embodiment, the beam converging device 13 is provided between the incident deflection electromagnet 11 and the beam entrance 1a, and between the ion source 10. When such a configuration is adopted, the shape of the incident beam can be adjusted. That is, when the shape of the emitted beam from the ion source 10 is uncertain or the time-series shape change of the emitted beam, for example, the convergence is performed by a signal from a beam monitor (not shown) provided in the beam transport system 60. The device 13 is controlled to adjust the incident beam shape and position. Furthermore, there is also an effect that the parameters of incidence on the main body of the circular accelerator 100 can be optimized. In addition, although the example which provides the convergence apparatus 13 in the entrance / exit side of the incident deflection electromagnet 11 was shown, it is good also as only one side.
[0014]
Embodiment 4 FIG.
The beam incident part 50 of Embodiment 4 is demonstrated based on FIG.
As shown in the figure, the beam transport system 60 according to the fourth embodiment is provided with two incident deflecting electromagnets 11a for performing 90 ° beam deflection, and the focusing device 13 is disposed between them.
The reason for adopting such a configuration will be described below.
Since the output fluctuation of the 100 KV high-voltage power source 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 change by ± 0.4 _mm . In order to avoid this, as described above, two 90 ° incident deflecting electromagnets 11a and two converging devices 13 are provided between them. The magnetic field intensity of each of the incident deflection electromagnets 11a is made substantially zero by changing the position of the beams having different energies at the beam entrance 1a (shifting in the vertical direction with respect to the orbiting beam trajectory plane 100a) according to the parameters of the focusing device 13. It is possible. In the fourth embodiment, an example is shown in which two converging devices 13 are used. However, there may be a case where one converging device 13 may be used depending on how the end converging force of each incident deflection electromagnet 11a is selected. is not. This optimizes these parameters taking into account the allowable beam size. Furthermore, as shown in FIG. 6 of the third embodiment, even in this fourth embodiment, if the focusing device 13 is arranged between the incident deflection electromagnet 11a and the ion source 10 or the beam entrance 1a, it is further optimal. Design becomes possible.
[0015]
Embodiment 5 FIG.
The beam incident part 50 of Embodiment 5 is demonstrated based on 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 trajectory surface 100a, and the incident deflection electromagnet 11a. Has a deflection angle of 90 °, and a focusing 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 incident deflection electromagnet 11a can be reduced in size and the cost can be reduced. The ion source 10 may be provided on the upper side of the orbiting beam raceway surface 100a.
[0016]
Embodiment 6 FIG.
As is well known, the incident deflection electromagnet 11 may have a magnetic field gradient to obtain a convergence force in the direction of the deflection magnetic field. Normally, a magnetic field gradient that weakens in the radial direction of the beam trajectory is applied. In this case, end convergence is not necessary, and the shape of the end portion of the electromagnet magnetic pole becomes simple.
As described above, according to the configuration of the sixth embodiment, it is not always necessary to install the converging device 13, the entire design of the incident portion 50 is facilitated, and the cost can be reduced. However, it goes without saying that more effective convergence can be achieved by installing the convergence device 13.
[0017]
Embodiment 7 FIG.
In the above embodiment, the method using the induction acceleration method as the accelerating means has been described. However, the same effect can be obtained even with the high frequency acceleration method.
[0018]
【The invention's effect】
Since the present invention is a circular accelerator configured as described above, the following effects can be obtained.
A circular accelerator having a plurality of magnetically separated electromagnets that have a beam entrance and circulate and accelerate the beam. The beam entrance includes an ion source and a beam from the ion source to the beam entrance of the circular accelerator. There is a beam transport system to transport,
The beam entrance is provided in the center of the circular accelerator and close to the beam entrance, and the beam transport system has a deflection trajectory in a plane perpendicular to the circular beam trajectory plane of the circular accelerator. Since it is formed by an incident deflecting electromagnet having a deflection angle of 180 ° , the beam transport system does not pass between the deflection converging electromagnets of the circular accelerator, so that it is not affected by the leakage magnetic field, and further the incident deflection of the beam transport system. Since most of the trajectories are in the electromagnet, they are hardly affected by the leakage magnetic field of other components of the circular accelerator. As a result, it is possible to prevent beam deflection in the beam transport system and to achieve an excellent effect of avoiding a reduction in incident efficiency to the circular accelerator.
[Brief description of the drawings]
FIG. 1 is a sectional view of a circular accelerator according to a first embodiment 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 layout view of a circular accelerator showing another aspect 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 part according to another aspect 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 deflecting and focusing electromagnet,
4 betatron core, 5 power supply, 6 coils, 10 ion source,
10a Beam outlet, 11, 11a Incident deflection electromagnet,
12 beam trajectory, 50 beam entrance, 60 beam transport system,
100 circular accelerator, 100a orbit beam trajectory plane.

Claims (13)

A circular accelerator having a plurality of magnetically separated electromagnets having a beam entrance and accelerating the beam;
The beam incident part is provided with an ion source and a beam transport system for transporting the beam from the ion source to the beam entrance of the circular accelerator,
The beam incident part is provided in the central part of the circular accelerator and close to the beam incident port,
A circular accelerator characterized in that the beam transport system is formed by an incident deflecting electromagnet having a deflection angle of 180 ° so as to have a deflection trajectory in a plane perpendicular to the circular beam trajectory plane of the circular accelerator. The circular accelerator according to claim 1, wherein the deflection trajectory is formed by two incident deflection electromagnets having a deflection angle of 90 °. 3. The circular accelerator according to claim 1, wherein a magnetic pole end surface facing the beam trajectory of the incident deflection electromagnet has an angle with respect to the beam incident surface. 4. The circular accelerator according to claim 1, wherein a beam focusing device is provided in the beam transport system. The circular accelerator according to claim 4, wherein the beam focusing device is provided between the ion source and the incident deflection electromagnet. 5. The circular accelerator according to claim 4, wherein the beam focusing device is provided between the ion source and the incident deflection electromagnet, and between the incident deflection electromagnet and the beam entrance. 6. . The circular accelerator according to claim 2, wherein a beam focusing device is provided between the two incident deflection electromagnets. The circular accelerator according to any one of claims 4 and 7, wherein the beam converging device comprises a quadrupole electromagnet. The circular accelerator according to claim 4, wherein the beam converging device is configured by a solenoid coil. The circular accelerator according to claim 4, wherein the beam converging device includes a quadrupole electromagnet and a solenoid coil. 2. The circular accelerator according to claim 1, wherein the incident deflection 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 including a betatron core, a coil provided in the core, and an AC power source. The circular accelerator according to claim 12, wherein the betatron core has a two-part structure so as to sandwich an incident deflection electromagnet of the circular accelerator.

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