Accelerator electromagnet, accelerator, and particle beam therapy system

Abstract

To provide an accelerator electromagnet that can reduce the deviation between the trajectory of a high-energy charged particle and the trajectory of a low-energy charged particle compared to the conventional art, and an accelerator and a particle beam therapy system including the same.SOLUTION: An accelerator electromagnet includes a return yoke 42 and a pair of magnetic poles 41 fixed to the return yoke 42, and a return yoke hole 43 is formed in the return yoke 42 in a region that intersects with the emission trajectory of a charged particle beam, and the return yoke hole 43 is configured such that its shape differs depending on the energy of the passing charged particle beam, thereby adjusting the magnetic field distribution therein.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an accelerator electromagnet, an accelerator, and a particle beam therapy system. [Background technology]

[0002] Patent Document 1 describes an example of a small accelerator capable of extracting a beam of variable energy and a particle beam therapy system equipped with the accelerator, which includes an acceleration radio frequency application device capable of frequency modulation and applying an acceleration radio frequency to accelerate the beam, a radio frequency kicker that applies an extraction radio frequency to extract the beam and has a different frequency from the acceleration radio frequency, a peeler magnetic field region and a regenerator magnetic field region that form a disturbance magnetic field region consisting of a higher-order magnetic field including magnetic field components with two or more poles and including at least a quadrupole magnetic field component, and a septum electromagnet having a magnetic shim, an inner septum coil conductor, an outer septum coil conductor, a coil conductor connection portion, and a coil outlet portion.

[0003] Patent Document 2 describes a synchrocyclotron in which a correction coil is provided to move low-energy charged particles closer to a high-energy charged particle orbit, so that particles of different energies are placed on extraction orbits at approximately the same position. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-38797 A [Patent Document 2] JP 2021-141062 A Summary of the Invention [Problem to be solved by the invention]

[0005] An accelerator is a device that accelerates charged particles, such as electrons, protons, and ions, to high speeds.

[0006] Accelerators are used in nuclear and particle physics experiments, radioactive nuclide production, particle beam therapy, etc. Among these, circular accelerators are generally used in particle beam therapy devices.

[0007] Circular accelerators are broadly divided into two types. One is the synchrotron, which accelerates charged particles while keeping the orbit radius constant by adjusting the magnetic field and the frequency of the electric field that accelerates the particles. The other is the cyclotron, which accelerates charged particles while increasing the orbit radius with fixed magnetic and electric fields. One type of cyclotron is the synchrocyclotron, which adjusts the frequency of the electric field to synchronize with the acceleration of the charged particles.

[0008] While synchrotrons can extract charged particles with variable energies, cyclotrons generally extract charged particles with a single energy. Cyclotrons can be made smaller than synchrotrons, but after extracting charged particles with a single energy, it was common to install a device called a degrater, which changes the energy by colliding the charged particles, resulting in a problem of reduced beam utilization efficiency.

[0009] In response to this, Patent Documents 1 and 2 disclose an idea of ​​extracting variable energy particles using an accelerator that generates a fixed magnetic field, such as a cyclotron.

[0010] In a cyclotron-type circular accelerator, the orbital radii of the high-energy charged particles and the low-energy charged particles are different in a fixed magnetic field, so the horizontal deviation between the orbits of the high-energy charged particles and the low-energy charged particles increases as the charged particles move downstream. All energetic charged particles leaving the accelerator are transported to the target through a transport magnet.

[0011] The transport electromagnet must be large enough to allow all the charged particles coming out of the accelerator to pass through the magnetic field it generates. On the other hand, it is desirable to place the transport electromagnet close to the accelerator's main electromagnet to minimize the energy loss of the charged particles.

[0012] In order to prevent interference between the transport electromagnets and the main electromagnets, it is necessary to make the transport electromagnets as small as possible. To achieve this, it is important to minimize the deviation between the orbits of the high-energy charged particles and the low-energy charged particles.

[0013] The present invention provides an accelerator electromagnet that can reduce the deviation between the trajectory of a high-energy charged particle and the trajectory of a low-energy charged particle compared to the conventional art, and an accelerator and a particle beam therapy system including the same. [Means for solving the problem]

[0014] The present invention includes multiple means for solving the above problems. One example is an electromagnet for an accelerator that generates charged particle beams of different energies, the electromagnet having a return yoke and a pair of magnetic poles fixed to the return yoke, the return yoke having a hole formed in a region that intersects with the emission trajectory of the charged particle beam, and the hole is configured to have a different shape depending on the energy of the charged particle beam passing through it, thereby adjusting the magnetic field distribution therein. Effect of the Invention

[0015] According to the present invention, the deviation between the trajectory of a high-energy charged particle and the trajectory of a low-energy charged particle can be reduced compared to the conventional art. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0016] [Figure 1] 1 is a bird's-eye view of an accelerator according to embodiment 1. FIG. [Diagram 2] 1 is a diagram showing a cross section of an accelerator according to a first embodiment. [Diagram 3] 2 is a diagram showing a cross section of an exit port of the accelerator according to the first embodiment. FIG. [Figure 4] FIG. 11 is a diagram showing a cross section of an exit port of an accelerator according to a second embodiment. [Diagram 5] FIG. 11 is a diagram showing a cross section of an exit port of an accelerator according to a third embodiment. [Figure 6] FIG. 11 is a diagram showing a schematic configuration of a particle beam therapy system according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, embodiments of the accelerator electromagnet, accelerator, and particle beam therapy system of the present invention will be described with reference to the drawings. In the drawings used in this specification, the same or similar reference numerals are used for the same or corresponding components, and repeated explanations of these components may be omitted.

[0018] In addition, the following are merely examples of implementation, and are not intended to limit the content of the invention to the specific embodiments described below. The invention itself can be implemented in various forms in accordance with the content described in the claims.

[0019] For example, in the following embodiments, an eccentric orbit accelerator in which the orbits of beams with different energies are offset from the center of the accelerator to one side in the radial direction will be described as an example of the accelerator; however, the present invention can also be applied to other types of accelerators, such as a synchrocyclotron in which the orbits of beams with different energies coincide with the center of the accelerator.

[0020] <Embodiment 1> A first embodiment of an accelerator electromagnet and an accelerator of the present invention will be described with reference to FIGS. 1 to 3. FIG.

[0021] First, the overall configuration of an accelerator 100 equipped with an accelerator electromagnet 10 will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a bird's-eye view of the accelerator according to the first embodiment, and Fig. 2 is a cross-sectional view of the accelerator according to the embodiment.

[0022] The accelerator 100 shown in Fig. 1 and Fig. 2 is an accelerator that generates charged particle beams with different energies, characterized by an eccentric charged particle orbit. The accelerator 100 includes the injector 1 and the injected charged particle introduction hole 2, the main electromagnet coil 3, the main electromagnet core 4, the vacuum vessel 5, the radio frequency acceleration cavity 6, the extraction radio frequency application device 71, the upstream side multipole magnetic field generating member 72, the downstream side multipole magnetic field generating member 73, the bulkhead 81 and the antiseptum 82 that constitute the extraction channel, the transport electromagnet core 91, and the transport electromagnet coil 92, all of which are shown in Fig. 1. Among these, the accelerator electromagnet 10 includes the return yoke 42 and a pair of magnetic poles 41 fixed to the return yoke 42.

[0023] The space in which the charged particles move is entirely covered by a vacuum vessel 5 , which is connected to the outside of the accelerator 100 via a vacuum port 51 , a current extraction port 52 and an extraction port 53 .

[0024] The injector 1 supplies charged particles to an incident charged particle introduction hole 2, and the charged particles are injected into the accelerator from the incident charged particle introduction hole 2. The positively charged particles move in a counterclockwise circular orbit due to the magnetic field (directed toward the depth of the page) generated inside the main electromagnet coil 3 and the magnetic pole 41 of the main electromagnet iron core 4, and are accelerated by the accelerating electric field generated between the high-voltage electrode 61 and the ground electrode 62 by the high-frequency acceleration cavity 6, increasing their energy with each revolution.

[0025] When the charged particles reach the desired energy, they are deflected from their eccentric orbit and placed on an ejection orbit by the electric field generated by the extraction high-frequency application device 71 and the multipole magnetic fields generated by the upstream multipole magnetic field generating member 72 and the downstream multipole magnetic field generating member 73.

[0026] The charged particles on the extraction trajectory are guided to the return yoke hole 43 formed in the return yoke 42 by the magnetic field generated between the partition wall 81 and the antiseptum 82. This return yoke hole 43 is a hole provided in a region of the return yoke 42 that intersects with the extraction trajectory of the charged particle beam.

[0027] The charged particles on the emission orbit reach the vicinity of the return yoke hole 43 in a counterclockwise direction due to the magnetic field in the vicinity of the magnetic pole 41, and within the return yoke hole 43, they describe a clockwise orbit due to the magnetic field opposite to the main magnetic field.

[0028] The charged particles leaving the return yoke hole 43 pass through a transport electromagnet 9 consisting of a transport electromagnet core 91 and a transport electromagnet coil 92 .

[0029] Since the magnetic field inside the return yoke hole 43 can be adjusted by the shape of the return yoke hole 43, the following measures are taken to solve the above problems.

[0030] When the magnetic field strength felt by the charged particles is the same, the radius of the orbit of the low-energy charged particle is smaller than that of the high-energy charged particle, so the deviation between the low-energy charged particle orbit and the high-energy charged particle orbit becomes large until the low-energy charged particle reaches the return yoke hole 43. On the other hand, the deviation between the low-energy charged particle orbit and the high-energy charged particle orbit becomes small after entering the return yoke hole 43. It is desirable to make this deviation as small as possible in order to improve the installation ease of the transport electromagnet 9 and to prevent it from becoming too large.

[0031] For this purpose, the return yoke hole 43 is configured so that its shape varies depending on the energy of the passing charged particle beam, thereby adjusting the magnetic field distribution therein. For example, the return yoke hole 43 is configured so that the magnetic field in the region through which the low-energy charged particle beam passes is stronger than the magnetic field in the region through which the high-energy charged particle beam passes.

[0032] 3 shows an AA' cross section of the return yoke hole 43 in the embodiment of the present invention. On the A side there is a low energy charged particle orbit, and on the A' side there is a high energy charged particle orbit.

[0033] For example, on the low-energy charged particle orbit side inside the return yoke hole 43, the vertical gap (perpendicular to the A-A' direction) of the return yoke hole 43 is narrowed to increase the magnetic field in order to significantly bend the low-energy charged particles toward the high-energy charged particle orbit side as shown in Fig. 3. On the other hand, on the high-energy charged particle orbit side inside the return yoke hole 43, the vertical gap of the return yoke hole 43 is made wider than that on the low-energy side so that the degree of bending of the high-energy charged particles is smaller than that of the low-energy charged particles.

[0034] In this way, the return yoke hole 43 has a narrower vertical gap on the low energy side than on the high energy side.

[0035] Moreover, the wall shape of the return yoke hole 43 in the circumferential direction of the accelerator is inclined, connecting the end of the return yoke hole 43 on the low energy side and the end of the return yoke hole 43 on the high energy side with a straight line.

[0036] The vertically inclined shape of the return yoke hole 43 is symmetrical.

[0037] There is no particular limitation on the wall shape of this return yoke hole 43 in the transport direction of the charged particles, and it can be the same shape as the shape shown in Fig. 3 in all directions, both upstream and downstream in the transport direction. It is also possible to have a different shape on the upstream and / or downstream sides in the transport direction. When changing the wall shape on the upstream and / or downstream sides in the transport direction, it is up to the design whether to narrow the gap on the low energy side of the return yoke hole 43 to strengthen the magnetic field, or to widen the gap to weaken the magnetic field, and this can be changed as appropriate.

[0038] Next, the effects of this embodiment will be described.

[0039] The electromagnet 10 for an accelerator according to the first embodiment of the present invention described above is an electromagnet for an accelerator 100 that generates charged particle beams with different energies, and the electromagnet has a return yoke 42 and a pair of magnetic poles 41 fixed to the return yoke 42, and the return yoke 42 has a return yoke hole 43 formed in a region that intersects with the emission trajectory of the charged particle beam, and the return yoke hole 43 is configured to have a different shape depending on the energy of the passing charged particle beam, thereby adjusting the magnetic field distribution therein. For example, the magnetic field in the return yoke hole 43 is stronger in a region where a charged particle beam on the low energy side passes than in a region where a charged particle beam on the high energy side passes.

[0040] This enhances the bending effect of the low-energy charged particles, and the deviation between the low-energy charged particle trajectory and the high-energy charged particle trajectory can be suppressed to be smaller than in the past. Therefore, it is possible to reduce the deviation between the trajectory of the high-energy charged particle and the trajectory of the low-energy charged particle compared to the past. Therefore, it is possible to realize a main electromagnet return yoke hole shape that enables the emission of variable energy charged particles without equipment interference, and to avoid an increase in the size of the transport electromagnet 9 on the downstream side.

[0041] In addition, since the vertical gap on the low energy side of the return yoke hole 43 is narrower than the vertical gap on the high energy side, it is possible to achieve magnetic field strength adjustment with a simple shape, which makes it easier to improve the installation ease of the transport electromagnet 9 and to prevent it from becoming too large.

[0042] Furthermore, the wall shape of the return yoke hole 43 is inclined, connecting the low energy side and the high energy side with a straight line, so that in the accelerator 100 in which the energy of the extracted beam changes continuously, the magnetic field strength within the return yoke hole 43 can also be changed continuously, thereby realizing a more appropriate magnetic field design.

[0043] <Embodiment 2> An accelerator electromagnet and an accelerator according to a second embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a diagram showing a cross section of the extraction port of the accelerator according to the second embodiment.

[0044] In the accelerator electromagnet 10A of this embodiment shown in Fig. 4, the wall shape of the return yoke hole 43A provided in the return yoke 42 is such that the low energy side and the high energy side are connected in a stepped manner, and the end of the return yoke hole 43 on the A side is connected to the end of the return yoke hole 43 on the A' side in a stepped manner. There is no particular limit to the number of steps, and it can be two or more.

[0045] The other configurations and operations are substantially the same as those of the accelerator electromagnet and accelerator of the first embodiment described above, and the details are omitted.

[0046] The accelerator electromagnet and accelerator according to the second embodiment of the present invention also provide substantially the same effects as those of the accelerator electromagnet and accelerator according to the first embodiment described above.

[0047] In addition, the wall shape of the return yoke hole 43A is such that the low energy side and the high energy side are connected in a step-like manner, which is an effective structure when a stronger magnetic field needs to be generated on the energy charged particle orbit side, and similarly to embodiment 1, it is possible to improve the installation ease of the transport electromagnet 9 and prevent it from becoming too large.

[0048] <Embodiment 3> An accelerator electromagnet and an accelerator according to a third embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a diagram showing a cross section of the extraction port of the accelerator according to the third embodiment.

[0049] The accelerator electromagnet 10B of this embodiment shown in FIG. 5 has a return yoke hole 43B formed therein that is larger in diameter than the return yoke hole 43 provided in the return yoke 42 of the accelerator electromagnet 10 of embodiment 1, and a mechanism is provided inside the hole to enable attachment and / or removal of one or more horizontal iron plates 44 and / or vertical iron plates 45.

[0050] The details of the mechanism for enabling the attachment and / or removal of the horizontal iron plate 44 and the vertical iron plate 45 are not particularly limited, and can take various forms, such as attachment and removal using bolts or a sliding type.

[0051] In addition, if the actual magnetic field becomes uniformly larger than the design magnetic field, for example, the magnetic field can be reduced by adding horizontal iron plates 44 to reduce the area through which the magnetic flux passes. Also, if the actual magnetic field is stronger in the upper half and weaker in the lower half, the magnetic field can be compensated by reducing the upper side of vertical iron plates 45 and adding the lower side to adjust the vertical gap.

[0052] The other configurations and operations are substantially the same as those of the accelerator electromagnet and accelerator of the first embodiment described above, and the details are omitted.

[0053] The accelerator electromagnet and accelerator according to the third embodiment of the present invention also provide substantially the same effects as those of the accelerator electromagnet and accelerator according to the first embodiment described above.

[0054] In addition, the return yoke hole 43B allows one or more horizontal iron plates 44 and vertical iron plates 45 to be attached and / or removed from its inside, which makes it possible to compensate for magnetic field deviations due to assembly errors in the electromagnets and surrounding magnetic materials, making it easier to adjust the magnetic field to a specified level.

[0055] In addition, the shape of the inner circumference of the return yoke hole 43B when installing and / or removing one or more horizontal iron plates 44 and vertical iron plates 45 does not have to be linear as shown in FIG. 5, and may be stepped as in embodiment 2 shown in FIG. 4.

[0056] <Embodiment 4> Next, a fourth embodiment of the present invention in which the accelerator 100 of the present embodiment is applied to a particle beam therapy system for use in particle beam therapy or the like will be described with reference to Fig. 6. Fig. 6 is a diagram showing a schematic configuration of the particle beam therapy system according to the fourth embodiment.

[0057] A particle beam therapy system 300 shown in FIG. 6 includes an accelerator 100, an extraction port 53, a rotating gantry 190, an irradiation device 192, a treatment table 201, and a control device 191.

[0058] The ion beam of a specific energy extracted from the accelerator 100 is transported to the irradiation device 192 by the extraction port 53 and the rotating gantry 190. The transported ion beam of a specific energy is shaped in the irradiation device 192 so as to match the shape of the affected area, and a predetermined amount of ion beam is irradiated to the affected area target of the patient 200 lying on the treatment table 201.

[0059] The operations of the accelerator 100 , the exit port 53 , the rotating gantry 190 , the irradiation device 192 , and the treatment table 201 are controlled by a control device 191 .

[0060] The control device 191 is composed of a computer, etc. The computers that compose these devices are equipped with a CPU, memory, interface, etc., and control of the operation of each device and various arithmetic processing, which will be described later, are executed based on various programs. These programs are stored in internal recording media, external recording media, and data servers in each component, and are read and executed by the CPU.

[0061] The operation control processes may be integrated into one program, or may be divided into multiple programs, or may be a combination of these. Also, some or all of the programs may be realized by dedicated hardware, or may be modularized. Furthermore, various programs may be installed into each device from a program distribution server, an internal storage medium, or an external storage medium.

[0062] The accelerator electromagnet provided in the accelerator 100 does not have to be the accelerator electromagnet 10 of embodiment 1, but can be either the accelerator electromagnet 10A shown in embodiment 2 or the accelerator electromagnet 10B shown in embodiment 3, and is not particularly limited.

[0063] Moreover, it is possible to provide a plurality of irradiation devices 192. Furthermore, the irradiation device 192 may be fixed without rotating. Furthermore, the irradiation method used by the irradiation device 192 is not particularly limited, and may be either a scanning method that scans a beam or a wobbler method that uses a scatterer.

[0064] <Other> The present invention is not limited to the above-described embodiment, but includes various modified examples. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to the embodiment having all of the described configurations.

[0065] It is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment.It is also possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0066] The embodiment of the present invention may be in the following form.

[0067] (1) An electromagnet for an accelerator that generates charged particle beams of different energies, the electromagnet having a return yoke and a pair of magnetic poles fixed to the return yoke, the return yoke having a hole formed in a region that intersects with the extraction trajectory of the charged particle beam, the hole being configured so that its shape differs depending on the energy of the charged particle beam passing through it, thereby adjusting the magnetic field distribution inside the hole.

[0068] (2) In the accelerator electromagnet described in (1), the magnetic field inside the hole is stronger in the region on the low energy side through which the charged particle beam passes than in the region on the high energy side through which the charged particle beam passes.

[0069] (3) In the accelerator electromagnet described in (1), the hole has a narrower vertical gap on the low energy side than a narrower vertical gap on the high energy side.

[0070] (4) In the accelerator electromagnet described in (3), the wall shape of the hole is an inclined type connecting the low energy side and the high energy side by a straight line.

[0071] (5) In the accelerator electromagnet described in (3), the hole has a wall shape in which the low energy side and the high energy side are connected in a step shape.

[0072] (6) In the accelerator electromagnet according to any one of (3) to (5), the hole is capable of mounting and / or removing one or more iron plates inside thereof.

[0073] (7) An accelerator comprising an accelerator electromagnet according to any one of (1) to (6).

[0074] (8) A particle beam therapy system comprising the accelerator described in (7). [Explanation of symbols]

[0075] 1...Injector 2...Injection hole for charged particles 3...Main electromagnet coil 4...Main electromagnet core 5...Vacuum container 6...High frequency acceleration cavity 9…Transportation electromagnet 10,10A,10B…Accelerator electromagnet 41...Magnetic pole 42…Return yoke 43, 43A, 43B...Return yoke hole (hole) 44…Horizontal iron plate (iron plate) 45…Vertical iron plate (iron plate) 51…Vacuum port 52…Current extraction port 53…Exit port 61...High voltage electrode 62...Ground electrode 71...High frequency emission device 72...Upstream multipole magnetic field generating member 73...Downstream multipole magnetic field generating member 81...Bulkhead 82...Anti-septum 91...Transportation electromagnet core 92...Transportation electromagnetic coil 100...Accelerator 190…Rotating gantry 191...Control device 192…Irradiation device 200...patient 201…Treatment table 300…Particle beam therapy system

Claims

1. An electromagnet for an accelerator that generates charged particle beams with different energies, wherein the electromagnet has a return yoke and a pair of magnetic poles fixed to the return yoke, the return yoke has a hole formed in a region intersecting the emission orbit of the charged particle beam, the hole is configured such that the shape of the hole varies according to the energy of the passing charged particle beam, thereby adjusting the magnetic field distribution inside the hole An electromagnet for an accelerator.

2. The electromagnet for an accelerator according to Claim 1, wherein the magnetic field inside the hole is stronger than the magnetic field in the region where the charged particle beam on the low energy side passes compared to the magnetic field in the region where the charged particle beam on the high energy side passes An electromagnet for an accelerator.

3. The electromagnet for an accelerator according to Claim 2, wherein the vertical gap on the low energy side of the hole is narrower than the vertical gap on the high energy side An electromagnet for an accelerator.

4. The electromagnet for an accelerator according to Claim 3, wherein the shape of the wall surface of the hole is an inclined type that connects the low energy side and the high energy side with a straight line An electromagnet for an accelerator.

5. The electromagnet for an accelerator according to Claim 3, wherein the shape of the wall surface of the hole is such that the low energy side and the high energy side are connected in a stepped manner An electromagnet for an accelerator.

6. The electromagnet for an accelerator according to Claim 3, wherein one or more iron plates can be attached and / or removed inside the hole An electromagnet for an accelerator.

7. An accelerator comprising the electromagnet for an accelerator according to any one of Claims 1 to 6.

8. In the accelerator according to Claim 7, a main magnetic field coil and main magnetic field poles that generate a magnetic field on the circulating orbit of the charged particle beam, and a high-frequency accelerating cavity that generates an accelerating electric field for accelerating the charged particle beam An accelerator.

9. A particle beam therapy system comprising the accelerator according to Claim 7.

10. A particle beam therapy system comprising the accelerator according to Claim 8.

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