Accelerators and particle beam therapy devices

Abstract

The present invention provides an accelerator capable of improving ion beam extraction efficiency. The disturbed magnetic field region located on the outer periphery of the main magnetic field region (30) of the accelerator has: a stripping region (31) in which the magnetic field strength decreases as it moves outward; a regeneration region (32) in which the magnetic field strength increases as it moves outward; and a generally flat region (33) in which the magnetic field strength is greater than that of the stripping region (31) and less than that of the regeneration region (32).

Description

Technical Field

[0001] This disclosure relates to accelerators and particle beam therapy devices. Background Technology

[0002] Particle beam therapy is a type of radiation therapy that uses ion beams, such as protons or carbon beams, to destroy the cells within a tumor. A particle beam therapy system comprises an ion source that generates ions, an accelerator that accelerates the ions generated by the ion source to form an ion beam, a beam delivery system that transports the ion beam from the accelerator to the treatment room, a rotating gantry that changes the direction of the ion beam delivered by the beam delivery system onto the tumor, an irradiation system that irradiates the tumor with the ion beam from the rotating gantry, and a control system that controls the above components.

[0003] As accelerators, particle beam therapy systems utilize circular accelerators such as synchrotrons, cyclotrons, or synchro-cyclotrons. In recent years, to achieve miniaturization of particle beam therapy systems, the miniaturization of circular accelerators has been developed. A powerful approach to miniaturizing circular accelerators is to increase the strength of the main magnetic field surrounding the ion beam within the circular accelerator; a powerful approach to increasing the strength of the main magnetic field is to apply a superconducting magnet to the main electromagnet that generates the main magnetic field. From the viewpoint of applying superconducting magnets, cyclotrons and synchro-cyclotrons using a static main magnetic field are advantageous compared to synchrotrons that dynamically adjust the magnitude of the main magnetic field. Non-Patent Document 1 discloses a synchro-cyclotron accelerator using a superconducting magnet as the main electromagnet.

[0004] In circular accelerators such as cyclotrons and synchrotrons, where the main magnetic field is static, the energy of the ion beam extracted to the outside is generally fixed. The energy of the ion beam irradiating the tumor is adjusted by attenuating the ion beam outside the circular accelerator through a scatterer called a degrading agent.

[0005] In contrast, Patent Document 1 discloses a circular accelerator that uses a static main magnetic field and makes the energy of the extracted ion beam variable, thereby eliminating the need for external attenuation of the ion beam.

[0006] In the circular accelerator described in Patent Document 1, after an ion beam circulating within the circular accelerator is accelerated to a desired energy, a high-frequency electric field is applied to the ion beam in a direction approximately perpendicular to the direction of the ion beam's propagation and the direction of the magnetic pole gap of the main magnetic field (hereinafter referred to as the vertical direction). Regarding the ion beam to which the high-frequency electric field is applied, the horizontal amplitude of the electron-induced accelerated vibration, which vibrates around a central orbit, gradually increases as it passes through magnetic field regions called stripping magnetic field and regeneration magnetic field, used to generate resonance of the electron-induced accelerated vibration formed around the central orbit. Regarding the ion beam passing through the stripping magnetic field and regeneration magnetic field, the horizontal amplitude of the electron-induced accelerated vibration increases sharply, it is injected into the extraction diaphragm magnetic field, and extracted to the outside of the accelerator.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2019-133745

[0010] Non-patent literature

[0011] Non-patent document 1: XiaoYu Wu, "Conceptual Design and Orbit Dynamics in a250MeV Superconducting Synchrocyclotron", Ph.D.Thesis, submitted to Michigan State University Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Regarding the ion beam generated by stripping and regenerating the magnetic field, the horizontal amplitude increases sharply due to resonance, and the vertical amplitude also increases. If the vertical amplitude of the ion beam increases, the extraction efficiency of the ion beam decreases. Therefore, in the technology described in Patent Document 1, there is room for improvement in the extraction efficiency of the ion beam.

[0014] The purpose of this disclosure is to provide an accelerator and a particle beam therapy device that can improve the efficiency of ion beam extraction.

[0015] Solution for solving the problem

[0016] One aspect of this disclosure is an accelerator that uses a main magnetic field and a high-frequency electric field for acceleration to accelerate an ion beam while it is orbiting. It comprises: a main magnetic field generating device having multiple magnetic poles arranged opposite each other, which generates the main magnetic field in the space between the magnetic poles; an emission channel that extracts the ion beam; a displacement section that displaces the ion beam orbiting the main magnetic field region to the outside of the main magnetic field region; and a disrupting magnetic field region located on the outer periphery of the main magnetic field region, which generates a magnetic field that disrupts the ion beam displaced to the outside and guides it to the emission channel. The disrupting magnetic field region comprises: a first region where the magnetic field strength decreases as it moves outward; a second region where the magnetic field strength increases as it moves outward; and a third region where the magnetic field strength is greater than that of the first region and less than that of the second region.

[0017] The effects of the invention are as follows.

[0018] According to the present invention, the ion beam extraction efficiency can be improved. Attached Figure Description

[0019] Figure 1 This is a structural diagram of a particle beam therapy system according to an embodiment of this disclosure.

[0020] Figure 2 It is a three-dimensional diagram of the main magnetic field magnet that generates the main magnetic field.

[0021] Figure 3 It is a longitudinal cross-sectional view of the main magnetic field magnet along the vertical plane.

[0022] Figure 4 It is a cross-sectional view of the main magnetic field magnet along the middle plane.

[0023] Figure 5 It is a diagram showing the magnetic field distribution along the center line of the main magnetic field.

[0024] Figure 6 This is a diagram used to illustrate the orbit of the ion beam.

[0025] Figure 7 It is a schematic diagram showing the magnetic field distribution on the middle plane of the main magnetic field.

[0026] Figure 8 It is a diagram showing the radial distribution of the magnetic field on the middle plane at the periphery of the magnetic pole.

[0027] Figure 9 This is a diagram used to illustrate a comparative example.

[0028] Figure 10 This is a cross-sectional view of the main magnetic field magnet in another vertical plane.

[0029] In the picture:

[0030] 1—Main magnetic field magnet, 4—Upper yoke, 5—Lower yoke, 6—Coil, 7—Vacuum container, 8—Upper magnetic pole, 9—Lower magnetic pole, 20—Acceleration space, 30—Main magnetic field region, 31—Stripping region, 32—Regeneration region, 33—Generally flat region, 40—High-frequency thruster, 1001—Particle beam therapy system, 1002—Ion beam generating device, 1003—Ion source, 1004—Accelerator, 1005—Beam delivery system, 1006—Rotating gantry, 1007—Irradiation device, 1008—Treatment planning device, 1009—Control system, 1019—Emission channel, 1019a—Opening, 1037—High-frequency acceleration cavity. Detailed Implementation

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0032] Example 1

[0033] Figure 1 This is a diagram showing the overall structure of a particle beam therapy system according to an embodiment of the present disclosure. Figure 1 The particle beam therapy system 1001 shown is a system that irradiates a subject with an ion beam formed by accelerating ions using an accelerator 1004 described below. In this embodiment, the accelerator 1004 accelerates an ion beam using hydrogen ions, i.e., protons, as the ion beam to any energy within a predetermined range and emits it. In this embodiment, the predetermined range is from 70 MeV to 235 MeV. However, the ion beam may also be a heavy particle ion beam using helium, carbon, etc., and the emission energy of the emitted ion beam is not limited to the range of 70 MeV to 235 MeV.

[0034] Figure 1 The particle beam therapy system 1001 shown is installed on the floor of a building (not shown). The particle beam therapy system 1001 includes an ion beam generating device 1002, a beam delivery system 1005, a rotating gantry 1006, an irradiation device 1007, a treatment planning device 1008, and a control system 1009. The ion beam generating device 1002 includes an ion source 1003 and an accelerator 1004.

[0035] Ion source 1003 is an ion introduction device that supplies ions to accelerator 1004. Accelerator 1004 accelerates the ions supplied from ion source 1003 to form an ion beam and emits the ion beam. Accelerator 1004 is connected to a high-frequency power supply 1036, a coil excitation power supply 1057, and an emission channel power supply 1082, which serve as power supplies for driving accelerator 1004. In addition, accelerator 1004 is connected to an ion beam current measuring device 1098 for measuring the current of the ion beam. Ion beam current measuring device 1098 includes a moving device 1017 and a position detector 1039. Furthermore, accelerator 1004 will be described in more detail below.

[0036] The beam delivery system 1005 is a delivery system that delivers the ion beam emitted from the accelerator 1004 to the irradiation device 1007, and has an ion beam path 1048 through which the ion beam passes. The ion beam path 1048 is connected to the emission channel 1019 in the accelerator 1004 for emitting the ion beam and the irradiation device 1007. Furthermore, in the ion beam path 1048, electromagnets for delivering the ion beam are arranged from the accelerator 1004 toward the irradiation device 1007 in the following order: a plurality of quadrupole electromagnets 1046, a deflecting electromagnet 1041, a plurality of quadrupole electromagnets 1047, a deflecting electromagnet 1042, a quadrupole electromagnet 1049, a quadrupole electromagnet 1050, a deflecting electromagnet 1043, and a deflecting electromagnet 1044.

[0037] The rotating gantry 1006 is configured to rotate about a rotation axis 1045, and is a rotating device that causes the irradiation apparatus 1007 to rotate around the rotation axis 1045. A portion of the ion beam path 1048 is provided on the rotating gantry 1006. In addition, deflecting electromagnets 1042, 1049, 1050, 1043, and 1044, which are used to transport the ion beam, are provided on the rotating gantry 1006.

[0038] The irradiation device 1007 is mounted on the rotating gantry 1006 and connected to the ion beam path 1048 downstream of the deflection electromagnet 1044.

[0039] The irradiation device 1007 includes scanning electromagnets 1051 and 1052, a beam position monitor 1053, and a dose monitor 1054. The scanning electromagnets 1051 and 1052, the beam position monitor 1053, and the dose monitor 1054 are disposed within a housing (not shown) of the irradiation device 1007. Furthermore, the scanning electromagnets 1051 and 1052, the beam position monitor 1053, and the dose monitor 1054 are arranged along the central axis of the irradiation device 1007, i.e., the beam axis of the ion beam.

[0040] Scanning electromagnets 1051 and 1052 constitute a scanning system that deflects the ion beam and scans it in approximately orthogonal directions within a plane substantially perpendicular to the central axis of the irradiation device 1007. A beam position monitor 1053 and a dose monitor 1054 are disposed downstream of the scanning electromagnets 1051 and 1052. The beam position monitor 1053 measures the position of the ion beam. The dose monitor 1054 measures the dose of the ion beam.

[0041] Downstream of the irradiation device 1007, a treatment table 1055 is arranged opposite to the irradiation device 1007 for the patient 2001, who is the subject, to lie on.

[0042] The treatment planning device 1008 generates an ion beam irradiation plan for the patient 2001 and notifies the control system 1009 of this plan. The irradiation plan includes, for example, the irradiation area, irradiation energy, irradiation angle, and number of irradiations.

[0043] The control system 1009 is a control unit that controls the ion beam generating device 1002, the beam delivery system 1005, the rotating gantry 1006, and the irradiation device 1007 to irradiate the patient 2001 with an ion beam according to the treatment plan notified by the treatment planning device 1008.

[0044] The control system 1009 includes a central control device 1066, an accelerator / conveying system control device 1069, a scanning control device 1070, a rotation control device 1071, and a database 1072.

[0045] The central control unit 1066 controls the ion beam generating device 1002, the beam delivery system 1005, the rotating gantry 1006, and the irradiation device 1007 via the accelerator / delivery system control unit 1069, the scanning control unit 1070, and the rotation control unit 1071 according to the treatment plan notified from the treatment planning unit 1008, and irradiates the patient 2001 with the ion beam.

[0046] Accelerator / delivery system control device 1069 controls ion beam generating device 1002 and beam delivery system 1005. Scan control device 1070 controls irradiation device 1007. Specifically, scan control device 1070 controls scanning electromagnets 1051 and 1052 to scan the ion beam based on measurement results from beam position monitor 1053 and dose monitor 1054. Rotation control device 1071 controls rotating gantry 1006. Database 1072 stores treatment plans notified from treatment planning device 1008. Furthermore, database 1072 can also store various information used by central control device 1066.

[0047] In addition, the central control unit 1066 has a CPU (Central Processing Unit) 1067 as a central arithmetic unit and a memory 1068 connected to the CPU 1067. Furthermore, the database 1072, the accelerator / transport system control unit 1069, the scanning control unit 1070, and the rotation control unit 1071 are connected to the CPU 1067 within the central control unit 1066.

[0048] According to the treatment plan stored in the database 1072, the CPU 1067 reads the program for controlling each device constituting the particle beam therapy system 1001, executes the read program, and thus performs control processing to control each device within the particle beam therapy system 1001. Specifically, the CPU 1067 outputs instructions to each device via the accelerator / delivery system control device 1069, the scan control device 1070, and the rotation control device 1071, thereby controlling each device to irradiate the patient 2001 with an ion beam according to the treatment plan. The memory 1068 stores various data used as the working area of ​​the program and used and generated in the processing of the CPU 1067.

[0049] Furthermore, the program executed by CPU 1067 can be a single program or multiple programs. Part or all of the processing performed by the program can also be implemented by dedicated hardware. The program can be installed from database 1072 to central control device 1066, or it can be installed to central control device 1066 from a program distribution server (not shown) or external storage medium. Furthermore, the devices within control system 1009 can be configured by connecting two or more devices via wired or wireless connections.

[0050] <Accelerator 1004>

[0051] Next, use Figures 1-4 The accelerator 1004 of the ion beam generating device 1002 will be described in more detail. Figure 2 This is a 3D diagram of Accelerator 1004. Figure 3 This is a longitudinal sectional view of accelerator 1004 along vertical plane 3. Figure 4 This is a cross-sectional view of the accelerator 1004 along the intermediate plane 2.

[0052] (Main magnetic field magnet 1)

[0053] like Figures 2-4 As shown, accelerator 1004 has a main magnetic field magnet 1. The main magnetic field magnet 1 is a main magnetic field generating device that generates the main magnetic field used to surround the ion beam, such as... Figure 2 As shown, the main magnetic field magnet 1 has an upper yoke 4 and a lower yoke 5 that are roughly disk-shaped when viewed from the vertical direction.

[0054] The upper yoke 4 and the lower yoke 5 have a shape that is approximately symmetrical about each other with respect to the intermediate plane 2. The intermediate plane 2 passes approximately through the center of the main magnetic field magnet 1 in the vertical direction and roughly coincides with the orbital plane drawn by the ion beam accelerated in the accelerator 1004.

[0055] Furthermore, the upper yoke 4 and the lower yoke 5 are approximately perpendicular to the intermediate plane 2, and have a roughly symmetrical shape relative to the plane passing approximately through the center of the main magnetic field magnet 1 at the intermediate plane 2, i.e., the vertical plane 3. In addition, Figure 2 In the diagram, the intersection of the middle plane 2 with respect to the main magnetic field magnet 1 is shown by a single-dotted line, and the intersection of the vertical plane 3 with respect to the main magnetic field magnet 1 is shown by a dashed line.

[0056] like Figure 3 As shown, within the space enclosed by the upper side yoke 4 and the lower side yoke 5, two coils 6 are arranged approximately symmetrically with respect to the central plane 2. The coils 6 are superconducting coils, for example, constructed from superconducting wires using superconductors such as niobium-titanium. The coils 6 are housed inside a cryostat (not shown), which serves as a cooling mechanism for the coils 6, and are cooled by this cryostat to a temperature below a certain point (the temperature at which the coils 6 are completely diamagnetic). Furthermore, the coils 6 are... Figure 1 The coil lead wire 1022 shown is led out to the outside of the main magnetic field magnet 1 and connected to the coil excitation power supply 1057. The coil excitation power supply 1057 is the power supply that supplies power to the coil 6 and is controlled by the accelerator / transport system control device 1069.

[0057] Furthermore, a vacuum container 7 is positioned inside the space enclosed by the upper yoke 4 and the lower yoke 5, closer to the coil 6. The vacuum container 7 is a container used to maintain an internal vacuum state, and is made, for example, of stainless steel. The upper magnetic pole 8 and the lower magnetic pole 9 are arranged symmetrically inside the vacuum container 7, separated by the intermediate plane 2, and are respectively connected to the upper yoke 4 and the lower yoke 5. The upper yoke 4, the lower yoke 5, the upper magnetic pole 8, and the lower magnetic pole 9 are formed, for example, of pure iron or low-carbon steel with reduced impurity concentration.

[0058] The main magnetic field magnet 1 with the above structure forms a main magnetic field that applies a vertical magnetic field to the acceleration space 20 inside the intermediate plane 2. The main magnetic field is generally uniform within the intermediate plane 2, but has a slightly non-uniform intensity distribution.

[0059] The strength of the main magnetic field is designed such that ions supplied from the ion source 1003 are stably orbited as an ion beam within the acceleration space 20 due to the principle of weak convergence. The principle of weak convergence is illustrated by the following: the main magnetic field monotonically decreases as it approaches the outer periphery, and the ions are stably orbited as an ion beam when its gradient is contained between a predetermined upper and lower limit value.

[0060] Figure 5 This is a diagram showing the intensity distribution along the center line of the main magnetic field. The center line is the intersection of the intermediate plane 2 and the vertical plane 3. In this embodiment, the direction along this intersection line is defined as the Y-axis direction, and the direction perpendicular to the Y-axis direction on the intermediate plane 2 is defined as the X-axis direction.

[0061] like Figure 5 As shown, the strength of the main magnetic field is at a predetermined position O1, which is offset along the Y-axis from the center O2 of the upper magnetic pole 8 and the lower magnetic pole 9, which is the center plane 2. It gradually decreases as it approaches the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9. Furthermore, hereafter, position O1 is sometimes referred to as the center of the main magnetic field distribution.

[0062] (Ion source 1003)

[0063] exist Figure 2 In this example, the ion source 1003 is positioned above the main magnetic field magnet 1. Through-holes 17 are provided on the upper yoke 4 and the upper magnetic pole 8 for guiding ions from the ion source 1003 to position O1 in the acceleration space 20. The central axis (ion injection axis) 12 of the through-hole 24 is substantially perpendicular to the intermediate plane 2 and leads to position O1. The ion source 1003 is positioned above the through-hole 17, through which ions are introduced to position O1 in the acceleration space 20. Alternatively, the ion source 1003 can also be positioned inside the main magnetic field magnet 1. In this case, the through-hole 17 is not required.

[0064] (Ejection Channel 1019)

[0065] And, as Figures 2-4As shown, the accelerator 1004 has an emission channel 1019 for extracting an ion beam and ejecting it into the beam delivery system 1005. In this embodiment, the emission channel 1019 has a structure with an electromagnet (not shown), disposed outside the acceleration space 20, more specifically on the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9, closer to the center O1 of the main magnetic field distribution on the Y-axis. The emission channel 1019 has an opening 1019a near the Y-axis, from which an ion beam of desired energy is obtained and extracted to the outside of the accelerator 1004 via through holes 18 provided on the upper side yoke 4 and the lower side yoke 5. The through holes 18 are provided with the front end of the beam delivery system 1005, through which the extracted ion beam is guided to the irradiation device 1007.

[0066] The power supply line that supplies power to the electromagnet in the emission channel 1019 is led out from the through hole 15 located in the upper yoke 4 and the lower yoke 5 to the outside of the accelerator 1004, and connects with... Figure 1 The ejection channel shown is connected to a power supply 1082. The power supply 1082 for the ejection channel is a power source capable of supplying power to the output channel and is controlled by the accelerator / delivery system control device 1069. Alternatively, the ejection channel 1019 may not have an electromagnet and may be composed only of a magnetic material. In this case, a power supply for the ejection channel 1019 is not required.

[0067] (High-frequency accelerating cavity 1037)

[0068] Additionally, the accelerator 1004 includes a high-frequency accelerating cavity 1037, which serves as a component for accelerating ions injected into the accelerating space 20 to form an ion beam. The high-frequency accelerating cavity 1037 includes a pair of D-shaped electrodes 1037a disposed across the intermediate plane 2. The D-shaped electrodes 1037a have a fan-shaped shape when viewed from the vertical direction. The D-shaped electrodes 1037a are configured such that the apex (center) of the fan is located near the center O1 of the main magnetic field distribution, covering a portion of the trajectory of the ion beam, including the magnetic pole center O2.

[0069] A ground electrode (not shown) is arranged facing the end face of the D-shaped electrode 1037a in the radial direction, and an acceleration electric field is formed between the end face of the D-shaped electrode 1037a in the radial direction and the ground electrode as an acceleration high-frequency electric field for accelerating the ion beam.

[0070] The D-shaped electrode 1037a is formed as a fan shape with position O1 as the vertex, thereby enabling the forward direction of the surrounding ion beam to be parallel to the accelerating electric field. That is, the accelerating electric field can be applied at the position where the axis parallel to the X-axis intersects the center of each surrounding orbit of the ion beam.

[0071] The high-frequency accelerating cavity 1037, located between the upper side yoke 4 and the lower side yoke 5, is led out to the outside of the main magnetic field magnet 1 through a through-hole 16 arranged along the Y-axis, where it is connected to the waveguide 1010. A high-frequency power supply 1036 is connected to the waveguide 1010. The high-frequency power supply 1036 supplies power to the high-frequency accelerating cavity 1037 through the waveguide 1010 and is controlled by the accelerator / delivery system control device 1069. Using the power supplied from the high-frequency power supply 1036, a high-frequency electric field is excited between the D-shaped electrode 1037a and the ground electrode as an accelerating electric field.

[0072] As explained below, the orbital radius of the orbit of the ion beam circulating within the acceleration space 20 gradually increases as the ion beam accelerates. To properly accelerate the ion beam, the accelerating electric field needs to be tuned to the ion beam; therefore, the resonant frequency of the high-frequency accelerating cavity 1037 needs to be modulated according to the energy of the ion beam. For example, the resonant frequency can be modulated by adjusting the inductance or capacitance of the high-frequency accelerating cavity 1037. Known methods can be used to adjust the inductance or capacitance of the high-frequency accelerating cavity 1037. For example, in the case of adjusting the capacitance, the resonant frequency can be modulated by controlling the capacitance of a variable capacitor connected to the high-frequency accelerating cavity 1037.

[0073] (The density of the orbital space)

[0074] Figure 6 This is a diagram used to illustrate the orbital paths of ion beams circulating within the acceleration space 20, showing the orbital paths 125 of ion beams with different energies.

[0075] Ions introduced from ion source 1003 into acceleration space 20 are formed into an ion beam by the high-frequency electric field that serves as the accelerating electric field, and circulate within acceleration space 20. For example... Figure 5 As shown, the main magnetic field of the acceleration space 20 is maximum at position O1, which is offset from the center of the magnetic poles O2, and gradually decreases as it approaches the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9. In this case, the lower-energy ion beam orbits along an orbit centered at position O1. As the ion beam is accelerated by the high-frequency electric field, the orbital radius increases, and the center of the orbit gradually approaches position O2, which is the central axis 13 of the upper magnetic pole 8 and the lower magnetic pole 9. Figure 4 The orbit 127 of the ion beam with maximum energy shown is roughly shaped along the outer periphery of the upper magnetic pole 8 and the lower magnetic pole 9, with its center roughly coinciding with position O2.

[0076] Therefore, as Figure 6As shown, the orbital path 125 of the ion beam is close between position O1 and position Y1 at the end of the acceleration space 20 in the Y-axis direction, and sparse between position O1 and position Y2 at the end of the Y-axis direction on the opposite side of position O2, which is separated from the center of the upper magnetic pole 8 and the lower magnetic pole 9.

[0077] For example, such as Figure 4 As shown, in the orbital orbit 125, the center of the orbital orbit 127 of the maximum energy beam, which corresponds to the maximum energy (235 MeV) of the extractable ion beam, is approximately aligned with the magnetic pole center O2. Furthermore, the center O3 of the orbital orbit 126 of the minimum energy beam, which corresponds to the lowest energy of the extractable ion beam, lies on the line segment connecting the magnetic pole center O2 to the center O1 of the main magnetic field distribution.

[0078] (Ion beam extraction)

[0079] Accelerator 1004 has a high-frequency thruster 40, a stripping region 31, a regeneration region 32 and a generally flat region 33 as a mechanism for guiding an ion beam that orbits within the acceleration space 20 to the ejection channel 1019, and extracting an ion beam with a predetermined range of energy by utilizing the density of the orbital track 125.

[0080] The high-frequency thruster 40 is a displacement section that displaces the ion beam surrounding the main magnetic field region of the excitation main magnetic field in the acceleration space 20 outward. The high-frequency thruster 40, for example, increases the amplitude of the electron-induced acceleration oscillation of the ion beam by applying a horizontal high-frequency electric field to it. As a result, the ion beam is displaced through the stripping region 31, the regeneration region 32, and the generally flat region 33. The stripping region 31, the regeneration region 32, and the generally flat region 33 constitute a disturbed magnetic field region that excites a magnetic field that disturbs the ion beam displaced by the high-frequency thruster 40 and guides it to the emission channel 1019.

[0081] Figure 7 This is a diagram illustrating the configuration of the stripping region 31, the regeneration region 32, and the generally flat region 33, showing the magnetic field distribution on the intermediate plane 2 around which the ion beam is surrounded.

[0082] exist Figure 7 The main magnetic field region 30 shown has formed Figure 5 The magnetic field distribution is shown. A stripping region 31, a regeneration region 32, and a generally flat region 33 are formed at the periphery of the magnetic poles outside the main magnetic field region 30. The stripping region 31 and the regeneration region 32 are located outside the tightly packed region surrounding the ion beam orbit 125 of the main magnetic field region 30.

[0083] Figure 8This is a diagram showing the radial distribution of the magnetic field in the stripping region 31, the regeneration region 32, and the generally flat region 33. The magnetic field distribution in the stripping region 31 is similar to... Figure 7 The magnetic field distribution along line AA' corresponds to the magnetic field distribution in regeneration region 32. Figure 7 The magnetic field distribution along the BB' line corresponds to the magnetic field distribution in the roughly flat region 33. Figure 7 The magnetic field distribution along the CC' line corresponds to this.

[0084] The magnetic fields at the innermost positions (positions A, B, and C) of the peeling region 31, the regeneration region 32, and the generally flat region 33 are essentially the same. The peeling region 31 is the first region where the magnetic field strength decreases significantly as it moves outward (from A to A'). The regeneration region 32 is the second region where the magnetic field strength increases significantly as it moves outward (from B to B'). The generally flat region 33 is the third region where the magnetic field is approximately constant. In this embodiment, the magnetic field of the generally flat region 33 decreases slightly more gently as it moves outward (from C to C') than the magnetic field of the peeling region 31. Therefore, at the outer periphery of each region, the magnetic field of the peeling region 31 is the smallest, the magnetic field of the regeneration region 32 is the largest, and the magnetic field of the flat region 33 is between the magnetic fields of the peeling region 31 and the regeneration region 32.

[0085] The following describes the operation of extracting an ion beam with the desired energy from accelerator 1004.

[0086] Accelerator / delivery system control device 1069, according to instructions from central control device 1066, causes ion source 1003 to generate ions and guides these ions through through-hole 17 to position O1 of acceleration space 20 within main magnetic field magnet 1. Accelerator / delivery system control device 1069 uses high-frequency acceleration cavity 1037 to generate an accelerating electric field in acceleration space 20, accelerating the ions to form an ion beam. The formed ion beam increases its energy while undergoing circling motion.

[0087] If the ion beam reaches the desired energy, the accelerator / delivery system control device 1069 cuts off the power supply to the high-frequency acceleration cavity 1037 and activates the high-frequency thruster 40. This applies a high-frequency electric field to the ion beam, overlapping with the main magnetic field. As a result, the ion beam's orbital path 125 is displaced radially (in the direction approaching position Y1). For example, as... Figure 7 As shown, when the ion beam is the lowest energy beam, the orbital 126 is displaced radially as orbital 126′, and when the ion beam is the highest energy beam, the orbital 127 is displaced radially as orbital 127′.

[0088] As a result, the ion beam passes through the stripping region 31 and the regeneration region 32. This generates a horizontally oriented electron-induced accelerated vibration called a 2 / 2 resonance, causing the ion beam to diverge radially and reach the opening 1019a of the emission channel 1019. The ion beam is completely detached from the orbit by the emission channel 1019 and is thus extracted to the outside of the accelerator 1004 through the through-hole 18.

[0089] Figure 9 This diagram is used as a comparative example to illustrate the ion beam extraction method described in Non-Patent Document 1, i.e., the existing method.

[0090] In existing methods, only the ion beam with the highest energy is extracted. Therefore, the orbit 128 of the ion beam surrounding the main magnetic field region 30A is formed in a concentric circle. The ion beam is accelerated and its orbit expands, thereby passing through the stripping region 31A and the regeneration region 32A. At this time, since only the ion beam with the highest energy needs to be extracted, the stripping region 31A is formed throughout the entire periphery of the magnetic poles except for the regeneration region 32A. That is, the magnetic field gradient of the stripping region 31A and the magnetic field gradient of the regeneration region 32A are designed only considering the ion beam with the highest energy.

[0091] In contrast, in this embodiment, the energy of the extracted ion beam is variable. Therefore, not only the maximum energy beam, but also the region traversed by the lowest energy beam needs to form a stripping region 31 and a regeneration region 32.

[0092] To properly induce resonance from electronically induced accelerated vibrations, the product of the magnitude of the magnetic field gradient and the length of the region containing the magnetic field gradient is important. For example... Figure 7 As shown, the lower the energy of the ion beam, the shorter the length of the ion beam passing through the stripping region 31 and the regeneration region 32. Therefore, in order to induce resonance in the low-energy ion beam, it is preferable to increase the magnetic field gradient to compensate for the short passage length through the stripping region 31 and the regeneration region 32.

[0093] An ion beam with energy greater than that of the lowest-energy beam passes through the stripping region 31 and the regeneration region 32 in the same manner as the lowest-energy beam. Therefore, if a region with a gradient magnetic field distribution, such as the stripping region 31A of the comparative example, is formed, the product of the magnitude of the magnetic field gradient and the length of the region with the magnetic field gradient becomes too large, thereby making the ion beam unstable relative to the horizontal and vertical directions.

[0094] Therefore, in this embodiment, the stripping region 31 is limited to a narrower range, and the periphery of the magnetic pole, excluding the stripping region 31 and the regeneration region 32, becomes... Figure 8The generally flat region 33 shown has a substantially constant magnetic field. Furthermore, since the magnetic field naturally decreases at the periphery of the magnetic poles, and the ion beam is stabilized by the principle of weak convergence, the magnetic field of the generally flat region 33 has a slightly reduced gradient in this embodiment.

[0095] In addition, in this embodiment, in order to make the magnetic field gradient of the stripping region 31 larger than that of the comparative example, such as Figure 3 As shown, the gap L between the upper magnetic pole 8 and the lower magnetic pole 9 at position 41, which sandwiches the stripping region 31, is significantly wider than the gap gaps at positions sandwiching the regeneration region 32 and the generally flat region 33. Furthermore, Figure 10 This is a longitudinal cross-sectional view of the accelerator 1004 along a vertical plane passing through the regeneration region 32, showing the gap interval M at position 42 sandwiching the regeneration region 32 and the gap interval N at position 43 sandwiching the generally flat region 33. Figure 10 As shown, the gap N is wider than the gap M.

[0096] Furthermore, in this embodiment, taking advantage of the relatively large gap L at the position 41 sandwiching the peeling region 31, an opening 1019a is provided at the position of the peeling region 31 as the entrance to the ejection channel 1019. However, it is also possible not to provide an opening 1019a at the position of the peeling region 31.

[0097] As described above, according to this embodiment, the disturbing magnetic field region located on the outer periphery of the main magnetic field region 30 of the accelerator 1004 includes a stripping region 31 where the magnetic field strength decreases towards the outside, a regeneration region 32 where the magnetic field strength increases towards the outside, and a generally flat region 33 where the magnetic field strength is greater than that of the stripping region 31 and less than that of the regeneration region 32. Therefore, the distance the ion beam travels through the stripping region 31 and the regeneration region 32, which are the resonant regions of the electron-induced accelerated vibrations that generate the ion beam, can be shortened, thereby suppressing the increase in the vertical amplitude of the ion beam and improving the ion beam extraction efficiency.

[0098] Furthermore, in this embodiment, the strength of the magnetic field in the generally flat region 33 decreases more gradually towards the outside than in the stripping region 31. In this case, due to the principle of weak convergence, the ion beam can stably pass through both the stripping region 31 and the regeneration region 32.

[0099] Furthermore, in this embodiment, the ion source 1003 introduces ions to a predetermined position O1 near the emission channel side of the magnetic pole center O2 in the main magnetic field region 30. The stripping region 31 and the regeneration region 32 are located at the position O1 where the ion source 1003 introduces ions, near the emission channel 1019 side. In this case, since a tight surrounding orbit can be formed on the emission channel 1019 side, the amount of collision required for beam extraction can be reduced, and a beam with the desired energy can be easily extracted.

[0100] Furthermore, in this embodiment, since the generally flat region 33 is larger than the combined area of ​​the stripping region 31 and the regeneration region 32, the distance the ion beam travels through the stripping region 31 and the regeneration region 32 is shorter.

[0101] Furthermore, in this embodiment, the opening 1019a, which serves as the entrance to the emission channel 1019, is located in the stripping region 31. In this case, compared to the case where the opening 1019a of the emission channel 1019 is located outside the stripping region 31, the number of turns the extracted ion beam makes before reaching the opening 1019a can be reduced by one or two. This suppresses the diffusion of the ion beam in both the vertical and horizontal directions, thereby improving the quality of the extracted ion beam.

[0102] Furthermore, in this embodiment, the main magnetic field magnet 1 generates the main magnetic field in a manner that deflects the orbit around which the ion beam is surrounded and accelerates the ion beam. Therefore, the amount of collision required for beam extraction can be reduced, and a beam with the desired energy can be easily extracted.

[0103] The embodiments described above are illustrative of the present disclosure and are not intended to limit the scope of the disclosure to the above embodiments. Those skilled in the art can implement the present disclosure in various other ways without departing from its scope.

Claims

1. An accelerator that uses a main magnetic field and a high-frequency electric field for acceleration to accelerate an ion beam while it is circling around it, characterized in that, have: The main magnetic field generating device has multiple magnetic poles arranged opposite each other, which generate the main magnetic field in the space between the magnetic poles. The emission channel extracts the aforementioned ion beam; A displacement section that displaces the ion beam surrounding the main magnetic field region where the main magnetic field is excited to the outside of the main magnetic field region; and A disruptive magnetic field region, located on the outer periphery of the main magnetic field region, generates a magnetic field that disrupts the ion beam displaced to the outer side and guides it to the emission channel. The aforementioned disturbed magnetic field regions have the following characteristics: The first region where the strength of the magnetic field decreases as it moves outwards; The second region where the strength of the magnetic field increases outwards; and In a third region, at a distance equidistant from the center of the aforementioned magnetic poles, the magnetic field strength is greater than that of the first region but less than that of the second region. In the third region mentioned above, the strength of the magnetic field decreases more gradually towards the outside compared to the first region. The spacing between the first portion of the first region and the magnetic poles is wider than the spacing between the second portion of the second region and the magnetic poles. The spacing between the third portion of the aforementioned magnetic poles, which sandwiches the third region, is narrower than the spacing between the first portion and wider than the spacing between the second portion. The entrance for the ion beam to enter the aforementioned emission channel is located in the aforementioned first region.

2. The accelerator according to claim 1, characterized in that, It also includes an ion-importing device that introduces ions forming the ion beam into a predetermined position in the main magnetic field region that is closer to the emission channel side than the center of the magnetic pole. The first region and the second region are located closer to the ejection channel than the predetermined position.

3. The accelerator according to claim 1, characterized in that, The third region mentioned above is larger than the combined area of ​​the first region and the second region mentioned above.

4. The accelerator according to claim 1, characterized in that, The aforementioned main magnetic field generating device generates the aforementioned main magnetic field by decentering the orbit around which the aforementioned ion beam is surrounded and by accelerating the ion beam.

5. A particle beam therapy device, characterized in that, have: The accelerator as claimed in claim 1; and An irradiation device for irradiating the ion beam extracted from the aforementioned accelerator.

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