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WO2025187100A1 - Accélérateur de particules circulaire, système de thérapie par particules et procédé de fonctionnement d'accélérateur de particules circulaire - Google Patents

Accélérateur de particules circulaire, système de thérapie par particules et procédé de fonctionnement d'accélérateur de particules circulaire

Info

Publication number
WO2025187100A1
WO2025187100A1 PCT/JP2024/029911 JP2024029911W WO2025187100A1 WO 2025187100 A1 WO2025187100 A1 WO 2025187100A1 JP 2024029911 W JP2024029911 W JP 2024029911W WO 2025187100 A1 WO2025187100 A1 WO 2025187100A1
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WIPO (PCT)
Prior art keywords
magnetic field
circular accelerator
frequency
operating
relationship
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2024/029911
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English (en)
Japanese (ja)
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WO2025187100A8 (fr
Inventor
沙希子 足利
風太郎 えび名
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi High Tech Corp
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Hitachi High Tech Corp
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Publication of WO2025187100A1 publication Critical patent/WO2025187100A1/fr
Publication of WO2025187100A8 publication Critical patent/WO2025187100A8/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H13/00—Magnetic resonance accelerators; Cyclotrons
    • H05H13/04—Synchrotrons

Definitions

  • the present invention relates to a circular accelerator for accelerating heavy ions such as protons and carbon ions, a particle beam therapy system, and a method for operating a circular accelerator.
  • Patent Document 1 describes how, when a beam is extracted from an orbit, a means for changing the stable region boundary is operated at the timing of extraction, and the high-frequency signal generating section of the high-frequency generator is swept from frequency f1, which puts charged particles near the center of the orbiting beam into a resonant state, to frequency f2, which puts charged particles with nearly the maximum amplitude within the stable region boundary into a resonant state, and is controlled with an amplitude modulation waveform where f1 > f2.
  • Circular accelerators have traditionally been used for physics experiments and medical purposes, where a charged particle beam is accelerated in a circular path, extracted from the circular path, and transported via a beam transport system to irradiate the desired target.
  • the method used to extract (send) the beam from the circular accelerator is to apply a high-frequency electric field to the circulating beam, increasing the amplitude of the betatron oscillations and sending the beam outside the region where it stably passes through the circulating orbit.
  • Patent Document 1 describes a technology for an accelerator having a high-frequency generator for beam extraction, in which the betatron frequencies f1 and f2 of particles at the center of the beam and particles at the edge of the separatrix are given a function that increases the intensity of the RF frequency corresponding to the range f1 to f2 by as much as f1, thereby suppressing the decrease in particle density in the beam and reducing the cost of the main electromagnet power supply.
  • Beam extraction using radio frequency waves is achieved by applying radio frequency waves with an amplitude of several kV or more to an electrode (kicker) that generates an electric field component that kicks the beam horizontally. This means that the power consumption of the radio frequency generator and the power performance required of the device's power supply are high.
  • the region in which a beam orbits stably is determined by the magnitude of the quadrupole magnetic field near the beam orbit. Furthermore, the frequency of the radio-frequency electric field to be applied to the beam also depends on the magnitude of the quadrupole magnetic field in the orbit of each beam particle.
  • the RF frequency to be applied depends not only on the distance in phase space from the center of the beam, but also on the distance between the particle's passing position and the electromagnet.
  • An example of a situation where the quadrupole magnetic field distribution on the beam orbit is asymmetric horizontally from the direction of beam propagation is when a peeler magnetic field or the like is applied to extract the beam.
  • Patent Document 1 in an accelerator having a high-frequency generator for beam extraction, the betatron frequencies f1 and f2 of particles at the center of the beam and particles at the edge of the separatrix are given as a function that increases the intensity of the RF frequency corresponding to the range f1 to f2 by as much as f1.
  • the RF frequency to be applied for beam extraction cannot be determined solely from the betatron frequencies f1 and f2 of the particles at the center of the beam and the particles at the edge of the separatrix, and therefore a different method from that described in Patent Document 1 is required.
  • the present invention provides a circular accelerator, particle beam therapy system, and method of operating a circular accelerator that can extract a beam with less energy than conventional methods in a circular accelerator in which the quadrupole magnetic field distribution on the beam orbit is asymmetric horizontally when viewed from the direction of beam propagation.
  • the present invention includes multiple means for solving the above problems, but one example is a circular accelerator having electrodes that generate an electric field component that kicks the beam horizontally, and magnetic poles that generate a quadrupole magnetic field that is asymmetric when viewed from the direction of beam propagation, with the amplitude of betatron oscillation increased by the electrodes, and the strength of each frequency component of the electric field applied to the electrodes is controlled based on the relationship between the position where the beam particles pass under the magnetic field and the phase lead of the betatron oscillation per turn at the position of the electrodes.
  • FIG. 1 is a diagram showing an outline of the configuration of a particle beam therapy system according to an embodiment
  • FIG. 1 is a diagram showing a schematic external view of an accelerator according to an embodiment.
  • FIG. 2 is a diagram showing the cross-sectional configuration of the accelerator of the embodiment and the relationship between the devices involved in beam extraction.
  • FIG. 2 is a diagram showing a cross-sectional configuration of a radio-frequency kicker provided in the accelerator of the embodiment.
  • 4 is a diagram showing an example of the arrangement of magnetic pole pieces in the pole piece magnetic field region, viewed from the arrow A-A' in FIG. 3;
  • FIG. FIG. 6 is a diagram showing the distribution of the main magnetic field on the r axis in FIG. 5 .
  • FIG. 2 is a time chart illustrating a beam extraction procedure in the accelerator of the embodiment.
  • 1 is a diagram showing the behavior of beam particles in phase space at a high-frequency kicker point and resonance conditions in the accelerator of the embodiment;
  • 10A and 10B are diagrams for explaining a method for determining a high frequency wave to be input to a high frequency kicker in the accelerator of the embodiment.
  • 10 is a diagram showing an example of the relationship between the frequency fext required to generate resonance of betatron oscillation and the closest distance l between the center position of the peeler magnetic field region and the orbit of the beam particle.
  • FIG. 2 is a flowchart showing the procedure for controlling beam extraction in the accelerator of the embodiment.
  • FIG. 10 is a diagram showing the cross-sectional configuration of another form of accelerator of the embodiment and the relationship between the devices involved in beam extraction.
  • Figure 1 is a diagram showing the outline of the configuration of the particle beam therapy system of the embodiment.
  • the particle beam therapy system 1000 shown in Figure 1 includes an accelerator 1 that accelerates and extracts a beam, a beam transport device 2 that transports the beam extracted from the accelerator 1, an irradiation device 3, an overall control device 400 that controls the accelerator 1 and the beam transport device 2, an irradiation control device 50, a treatment plan database 60, a blocking device 350, and a treatment planning device 7.
  • the beam generated by the accelerator 1 is transported to the irradiation device 3 via the beam transport device 2.
  • the beam position is controlled by the magnetic field of a scanning electromagnet, and the beam is irradiated at a predetermined affected area of the patient 5 lying supine on the treatment table 4.
  • the irradiation device 3 has an internal dosimetry device 3a that measures the actual dose irradiated to the patient.
  • the treatment planning device 7 is a device that calculates and determines various control parameters related to the irradiation of the beam to the patient 5, and the created treatment plan is recorded in the treatment plan database 60.
  • the overall control device 400 controls each device based on the treatment plan obtained from the treatment plan database 60.
  • the overall control device 400 also determines the target energy to be accelerated based on the treatment plan and sends predetermined command values to each device.
  • the irradiation control device 50 is a control device for monitoring the irradiation dose and irradiation position, and when irradiation of a certain spot with the specified planned dose is completed, irradiation of the next spot is carried out. By repeating this process, it is possible to impart a dose distribution specified in the treatment plan previously prepared by the treatment planning device 7 to the appropriate position and depth.
  • the interruption device 350 is a shielding device that blocks the beam extracted from the accelerator 1 without transporting it to the subsequent stage (irradiation device 3), and is composed of a beam interruption electromagnet, an excitation power supply for the beam interruption electromagnet, and a beam dump that discards the beam components removed by the interruption electromagnet (all of which are omitted from the illustration).
  • the excitation power supply is connected to the interruption electromagnet, and the overall control device 400 is connected to the excitation power supply, and the discarding of the beam is controlled by controlling the excitation of the interruption electromagnet.
  • the accelerator 1 of this embodiment is a circular accelerator that has a time-constant magnetic field as the main magnetic field and accelerates protons circulating in the main magnetic field using a radio-frequency electric field. Its appearance is shown in Figure 2, and a cross-sectional diagram and the relationship between the equipment involved in beam extraction are shown in Figure 3.
  • the accelerator 1 has an outer shell formed by a main electromagnet 40 that can be separated vertically, and the beam acceleration region inside the main electromagnet 40 is evacuated.
  • an ion source 12 that generates a beam of ions to be injected into the main electromagnet 40, and an acceleration gap 11.
  • a high-frequency electric field is applied to the acceleration gap 11 by a high-frequency generator (both not shown).
  • the accelerator 1 has, as equipment for extracting the beam, an extraction control device 5000, a radio-frequency kicker 70, a high-energy beam transport system 47, and a peeler magnetic field region 44 and a regenerator magnetic field region 45 as magnetic field structures.
  • the accelerated beam is emitted from the beam extraction path entrance 82 to the outside of the acceleration region.
  • the high-energy beam transport system 47 for transporting the extracted beam from the inside of the main electromagnet 40 to the outside is arranged from the inside to the outside of the main electromagnet 40.
  • the extraction control device 5000 has a control computer 5001, a synthesizer 5002, a signal amplifier 5003, and a high-frequency kicker power supply 5004, and upon receiving a beam irradiation command from the overall control device 400, creates a high-frequency signal to be applied to the high-frequency kicker 70 and inputs it into the high-frequency kicker 70.
  • the radio-frequency kicker 70 is a device that applies a radio-frequency voltage to the circulating beam passing through it, and is an electrode that generates an electric field component that kicks the beam horizontally.
  • the control computer 5001 is a computer that calculates the relationship between the particle passage position and the phase advance of the betatron oscillation per turn at the position of the radio-frequency kicker 70. For example, the control computer 5001 calculates the frequency band and intensity of the radio-frequency voltage to be applied to the radio-frequency kicker 70 based on the results of measuring the magnetic field inside the accelerator 1, and controls the ON/OFF of the radio-frequency voltage applied to the radio-frequency kicker in accordance with the control signal from the overall control device 400.
  • control computer 5001 is not limited to a configuration that calculates the relationship between the particle passage position and the phase lead of the betatron oscillation per turn at the position of the high-frequency kicker 70, but can also be configured to receive input of the relationship between the particle passage position and the phase lead of the betatron oscillation per turn at the position of the high-frequency kicker 70 calculated by an external computing device.
  • the synthesizer 5002 is a device with electronic circuits that can freely modify and output the frequency and waveform of a signal, and synthesizes a high frequency wave in the corresponding frequency band based on the signal from the control computer 5001.
  • Signal amplifier 5003 is a signal amplifier that amplifies the signal created by synthesizer 5002 up to an amplitude of several kV.
  • the high-frequency kicker power supply 5004 is a power supply with a maximum output of several tens of kW, and supplies power to the signal amplifier 5003.
  • the main electromagnet 40 is internally formed with a peeler magnetic field region 44 and a regenerator magnetic field region 45, which are disturbance magnetic fields consisting of dipole and multipole magnetic fields.
  • the beam is extracted using a radio-frequency kicker 70, which generates an electric field component that kicks the beam horizontally, and the peeler magnetic field region 44 and regenerator magnetic field region 45, which are asymmetric quadrupole magnetic fields when viewed from the direction of beam propagation, with the amplitude of betatron oscillations increased by the radio-frequency kicker 70.
  • the beam of charged particles generated by the ion source 12 is injected into the beam acceleration region inside the main electromagnet 40.
  • the injected beam is accelerated by the radio-frequency electric field and orbits within the main magnetic field while gaining energy.
  • the radius of curvature of its orbit increases, and the beam traces a spiral trajectory from the center of the acceleration region outward.
  • the orbit that the beam follows from the start of acceleration until it reaches maximum energy is called the circular orbit.
  • the orbit through which the maximum energy beam passes is called the maximum energy beam orbit 80.
  • the surface on which the circular orbit describes a spiral is called the orbital plane or orbital surface.
  • the orbital plane is considered as a two-dimensional polar coordinate system with the center of the acceleration region as the origin, the axis extending radially outward from the center is called the r-axis.
  • betatron oscillation As the beam orbits, the charged particles vibrate in a direction perpendicular to the beam's orbit; this vibration is called betatron oscillation, and the frequency of this vibration is called the betatron frequency.
  • the frequency per orbit is called the tune, and the displacement of the beam on the r-axis outside the orbital plane per orbit is called the turn separation.
  • the betatron oscillation of an orbiting beam in the orbital plane and perpendicular to the beam's orbit is called horizontal betatron oscillation, and the tune is called horizontal tune. This betatron oscillation has the property that when an appropriate high-frequency voltage is applied, resonance occurs and the amplitude increases rapidly.
  • the main magnetic field is a magnetic field whose strength is constant in the circumferential direction, and forms a distribution in which the magnetic field on the orbit decreases as the beam energy increases, i.e., the magnetic field decreases on the outer radial side. Under such a magnetic field, betatron oscillation occurs stably in both the radial direction within the beam's orbital plane and in the direction perpendicular to the orbital plane.
  • the magnetic field is constant along the design orbit. As a result, the design orbit is circular, and the orbital radius and orbital time increase as the beam energy increases.
  • the main magnetic field distribution described above is formed by the main electromagnet 40 and the trim coils and pole pieces (not shown) installed inside the main electromagnet 40. These components that form the main magnetic field distribution are arranged symmetrically with respect to the orbital plane, so that on the orbital plane, the main magnetic field only has a magnetic field component in a direction perpendicular to the orbital plane.
  • the radio frequency acceleration voltage for accelerating the beam in the acceleration gap 11 is stopped, and the beam orbits on maximum energy beam orbit 80. Then, when the beam enters the radio frequency kicker 70, which is installed on maximum energy beam orbit 80 and applies radio frequency, radio frequency voltage is applied, and the betatron oscillation amplitude of the beam increases.
  • the beam with its betatron oscillation amplitude increased, eventually reaches the peeler magnetic field region 44 and regenerator magnetic field region 45, which are located a certain distance from the maximum energy beam orbit 80 on the outer periphery of the maximum energy beam orbit 80.
  • kicking refers to deflecting the beam by applying an electric or magnetic field to it.
  • the kick from the quadrupole magnetic field component of the peeler magnetic field region 44 further increases the betatron oscillation amplitude of the beam, and the turn separation increases.
  • the magnetic field of the regenerator magnetic field region 45 prevents the horizontal tune of the beam from changing suddenly, preventing the betatron oscillation from diverging in the vertical direction, which is 90 degrees perpendicular to the horizontal direction, and causing the beam to be lost before it is extracted.
  • the beam enters the septum coil 43, is kicked out of the orbital plane, passes through the high-energy beam transport system 47, and is extracted outside the accelerator 1.
  • the increase in turn separation due to the peeler magnetic field region 44 and regenerator magnetic field region 45 is much greater than the increase due to the high-frequency kicker 70.
  • beam emission can be resumed by restarting the application of high frequency to the high frequency kicker 70.
  • FIG 4 shows the cross-sectional configuration of the radio-frequency kicker 70.
  • the radio-frequency kicker 70 consists of a ground electrode 71 and a high-voltage electrode 72.
  • the two electrodes are installed facing each other, with the ground electrode 71 on the inner side and the high-voltage electrode 72 on the outer side, sandwiching the maximum energy beam trajectory 80.
  • the ground electrode 71 and high-voltage electrode 72 are shaped so that a high-frequency electric field acts in the orbital plane in a direction perpendicular to the orbit; in other words, the ground electrode 71 and high-voltage electrode 72 are shaped so that they are roughly parallel to the curve of the maximum energy beam orbit 80.
  • a metal protrusion 73 can be attached to the ground electrode 71 to increase the concentration of the high-frequency electric field generated between the ground electrode 71 and high-voltage electrode 72.
  • the high-voltage electrode 72, to which the high-frequency voltage is applied, is supported and insulated.
  • the beam In the cylindrical acceleration region, the beam describes an orbital plane near the center of the cylinder in the height direction.
  • Both the ground electrode 71 and the high-voltage electrode 72 have passage openings near the orbital plane through which the beam passes. Taking into account the beam's expansion due to betatron oscillation, these passage openings should be wide enough to prevent beam collisions.
  • the radio-frequency kicker 70 can be placed anywhere on the maximum energy beam orbit 80, but for example, it is placed near the septum coil 43 as shown in Figure 3.
  • the regenerator magnetic field region 44 and the regenerator magnetic field region 45 are regions where a multipole magnetic field acting on the beam exists.
  • This multipole magnetic field includes at least a quadrupole magnetic field component, but may also include a multipole magnetic field with more than four poles or a bipole magnetic field.
  • the magnetic field gradient is such that the main magnetic field weakens toward the radial outer periphery, whereas in the regenerator magnetic field region 45, the magnetic field gradient is such that the main magnetic field strengthens toward the radial outer periphery.
  • the peeler magnetic field region 44 can also be the region at the pole tip where the main magnetic field weakens.
  • peeler magnetic field regions 44 and regenerator magnetic field regions 45 are respectively positioned on the outer periphery of the maximum energy beam orbit 80, in azimuthal angular regions on either side of the beam extraction path entrance 82.
  • the peeler magnetic field region 44 and the regenerator magnetic field region 45 are positioned on the outer periphery of the maximum energy beam orbit 80, with a gap greater than the amplitude of the betatron oscillation before resonance. Furthermore, the peeler magnetic field region 44 is positioned upstream in the direction of beam progression, and the regenerator magnetic field region 45 is positioned downstream.
  • pole piece region 44 and the regenerator magnetic field region 45 multiple magnetic pole pieces or coils, or both, made of magnetic material, are fixed and arranged with non-magnetic material to form the desired multipole magnetic field.
  • a multipole magnetic field is formed using multiple pole pieces, and a dipole magnetic field is formed using coils.
  • the multiple pole pieces and coils can be positioned close to each other or at spatially separated locations.
  • pole pieces and coils correspond to the magnetic poles that generate the peeler magnetic field region 44 and the regenerator magnetic field region 45.
  • Figure 5 shows an example of the pole piece arrangement in the peeler magnetic field region 44, as seen from the arrows A-A' in Figure 1.
  • the pole pieces used include a magnetic field gradient shim 36 that generates a magnetic field gradient in the peeler magnetic field region 44, and a magnetic field correction shim 37 that cancels out the unnecessary magnetic field generated by the magnetic field gradient shim 36 on the inner side of the maximum energy beam orbit 80.
  • the regenerator magnetic field region 45 also uses magnetic field gradient shims that generate magnetic field gradients in the regenerator magnetic field region 45, and magnetic field correction shims that cancel out unnecessary magnetic fields generated by the magnetic field gradient shims on the inner side of the maximum energy beam orbit 80.
  • Figure 6 shows the distribution of the main magnetic field on the r-axis in Figure 5.
  • the magnetic field gradient ⁇ B/ ⁇ r drops slightly, allowing the beam to orbit stably.
  • the magnetic field gradient drops sharply, making the beam unstable and kicking it toward the outer periphery of the orbital plane.
  • the regenerator magnetic field region 45 in contrast to the peeler magnetic field region 44, the magnetic field gradient rises sharply, making the beam unstable and kicking it toward the inner periphery of the orbital plane.
  • Figure 7 is a diagram explaining the beam extraction procedure.
  • Figure 7 (a) is a graph showing the relationship between the acceleration voltage Vacc generated in the acceleration gap 11, the radio-frequency kicker voltage Vext applied to the radio-frequency kicker 70, and time T.
  • Figure 7 (b) is a graph showing the relationship between the current of the incoming beam, the current of the outgoing beam, and time T.
  • One acceleration cycle shown in Figure 7 (a) begins with the rise of the acceleration voltage Vacc (time T1). After that, when the acceleration voltage Vacc has risen sufficiently, a beam is injected from the ion source 12 (time T2). After the time t1 has elapsed since the beam was injected, high-frequency capture of the beam ends.
  • the captured beam i.e., the injected beam that is ready for acceleration, begins to accelerate using the acceleration voltage Vacc (time T3).
  • the acceleration radio frequency begins to be shut off (time T4), and after time t2 has passed, the acceleration radio frequency voltage Vacc is turned off.
  • the application of the radio frequency voltage Vext to the radio frequency kicker 70 begins (time T5). Note that the start of application of the radio frequency voltage Vext to the radio frequency kicker 70 (time T5) does not have to occur exactly at the same time as the acceleration radio frequency voltage Vacc is turned off.
  • the application of the high-frequency voltage Vext may begin immediately before, simultaneously with, or immediately after the acceleration high-frequency voltage is shut off (time T4), or immediately before or immediately after the acceleration high-frequency voltage Vacc is turned off.
  • the high-frequency voltage of the high-frequency kicker 70 rises quickly, with a response of a few microseconds, if the high-frequency kicker 70 is not a resonator structure and is designed so that the capacitance is an appropriate value.
  • betatron oscillation has the property that its amplitude increases resonantly when the product of either the tune or the decimal part of the tune and the orbital frequency of the beam is approximately the same as the frequency of the applied high-frequency voltage. How to select the high-frequency frequency required to generate this resonance will be described later.
  • a septum coil 43 is installed at the entrance 82 of the beam extraction path.
  • the beam is guided into the septum coil 43, where it is sufficiently deflected and guided to the high-energy beam transport system 47, where it is extracted.
  • the time until beam extraction can be shortened by applying as large a radio-frequency voltage as possible and quickly increasing the amplitude of the beam. Then, just before the beam reaches the peeler magnetic field region 44 or the regenerator magnetic field region 45 (time T6), the radio-frequency voltage is reduced, and the amount of beam traveling into the peeler magnetic field region 44 and the regenerator magnetic field region 45 can be adjusted, allowing for precise control of the beam extraction current.
  • the beam extraction current can also be changed by sweeping the frequency of the radio frequency applied to the radio frequency kicker 70 or by changing the phase of the radio frequency. This takes advantage of the property that the betatron frequencies of the charged particles contained in the beam vary over a certain distribution (tune spread).
  • the beam extraction current can be changed by matching it to a band in the distribution of the frequencies of the charged particles that cause resonance. Also, instead of lowering the radio frequency voltage Vacc, it can be cut off.
  • time T6 the application of the high-frequency voltage Vext to the high-frequency kicker 70 is stopped, thereby stopping the beam extraction (time T7).
  • Figure 8 explains in detail the behavior and resonance conditions in phase space of a beam particle undergoing betatron oscillation in the horizontal direction at the high-frequency kicker 70.
  • beam particle 500 is one of the constituent particles of a beam that orbits while oscillating betatronically near the maximum energy beam orbit 80.
  • Phase space 5500 is a two-dimensional space consisting of the horizontal displacement y of the beam particle as viewed from the beam center and the amount of change py in the beam orbit direction, with the beam center 501 corresponding to the origin.
  • Separatrix 502 is a region in phase space, representing the region in which the beam orbits stably. Inside separatrix 502, beam particles orbit stably, but outside separatrix 502, the beam diverges. The beam is extracted by bringing the beam particles inside separatrix 502 to the outside of separatrix 502. Beam particles 500 move inside separatrix 502.
  • phase angle ⁇ and phase radius J are parameters that represent the position of the beam particle 500 in phase space, and respectively represent the distance from the beam center and the angle between the line connecting the position of the beam particle 500 and the beam center and the positive direction of the r-axis.
  • the phase radius J is proportional to the amplitude of the particle's betatron oscillation. One period of betatron oscillation corresponds to the particle going around the phase space described above.
  • a radio-frequency voltage is applied to the radio-frequency kicker 70 at frequency fext.
  • fext is approximately equal to the product ⁇ r ⁇ frev of the decimal part ⁇ of the horizontal tune ⁇ of the beam particle 500 and the circular frequency frev of the maximum energy beam
  • the amplitude of the horizontal betatron oscillation increases resonantly.
  • the phase radius J of the beam particle 500 continues to increase with each circular revolution, and the beam eventually reaches the peeler magnetic field region 44.
  • the beam particle 500 As the beam particle 500 approaches the peeler magnetic field region 44, it is kicked toward the outer periphery, that is, in a direction where the displacement r from the beam center becomes larger, due to the effect of the magnetic field, and is emitted by entering the septum coil 43.
  • Figure 9 shows the frequency and amplitude of the high frequency voltage applied to the high frequency kicker 70.
  • the horizontal betatron tune ⁇ of a particle changes depending on the magnetic field gradient in the orbit through which the particle passes, so there is a tune spread of about 1/100 between particles in the beam. Therefore, the frequency fext of the radio frequency voltage applied to the radio frequency kicker 70 must be a band with a certain degree of width.
  • the extraction control device 5000 calculates the minimum and maximum values of the betatron tune ⁇ in the beam, ⁇ min and ⁇ max, as well as the high-frequency frequencies corresponding to each tune, based on the results of a simulation based on electromagnetic field analysis.
  • Nrf [(fmax - fmin) / ⁇ f] + 1 high-frequency rf1, rf2, ..., rfNrf is set at an appropriate frequency interval ⁇ f within the band from fmin to fmax, and a high-frequency waveform is created by inputting this into synthesizer 5002, which then inputs it into high-frequency kicker 70.
  • [(fmax - fmin) / ⁇ f] represents an integer not exceeding (fmax - fmin) / ⁇ f.
  • the frequency interval ⁇ f of the applied high frequency must be sufficiently small relative to the fluctuation in the high frequency resonance frequency that corresponds to the tuning fluctuation, and is on the order of several kHz to several tens of kHz.
  • the power Wrf supplied by the high frequency kicker power supply 5004 is expressed by the following equation (1):
  • V1, V2, ... are the amplitudes of the high-frequency waves rf1, rf2, ..., rfNrf.
  • R is the impedance of the high-frequency kicker 70.
  • Beam particle 500 receives a kick at time t expressed by the following equation (2) due to the electric field caused by the voltage of frequency f and amplitude V applied to the high-frequency kicker 70.
  • v is the velocity of the beam particle
  • ⁇ is the orbital radius of the maximum energy beam orbit 80
  • B is the average magnetic field on the beam particle orbit
  • L is the electrode length of the radio frequency kicker 70.
  • Figure 10 shows the relationship between the position and tune at the high-frequency kicker point of beam particles in accelerators that generally do not have a peeler magnetic field region or a regenerator magnetic field region, such as synchrotrons.
  • r represents the radial outer side of the beam orbit, and the beam center is the origin.
  • the magnitude of the magnetic field gradient on the orbit through which a particle passes is symmetrical about the r' axis in phase space, so the tune, or the phase advance angle ⁇ in phase space per orbit, depends primarily on the amplitude of the betatron oscillation. Therefore, as the amplitude of the particle's betatron oscillation increases, the betatron tune also changes, and the corresponding high-frequency frequency changes.
  • Figure 10(b) shows the relationship between the position of beam particles and tune near the peeler magnetic field region 44 in the accelerator 1 targeted by the present invention, where the quadrupole magnetic field distribution on the beam orbit is asymmetrical horizontally as viewed from the direction of beam travel.
  • r uses the same coordinates as r in Figure 5, with the beam center being the origin.
  • the accelerator 1 has a peeler magnetic field region 44, the magnitude of the magnetic field gradient on the orbit becomes asymmetric in phase space, and as the particle's orbit approaches the above-mentioned magnetic field region, it is kicked by the magnetic field of the magnetic field region, and the particle's tune, i.e., the phase lead angle ⁇ in phase space, increases or decreases.
  • the frequency fext band of the high-frequency voltage to be applied to the phase-leading high-frequency kicker 70 depends on the distance between the beam particles and the peeler magnetic field region 44, and even if the radius of the phase space is constant, the positional relationship between the beam particle trajectory and the peeler magnetic field region 44 fluctuates with each revolution due to betatron oscillation, causing the particle tune to fluctuate.
  • Figure 11 shows an example of the relationship between the frequency fext required to generate resonance in betatron oscillation, the center position of the peeler magnetic field region 44, and the closest distance l of the beam particle trajectory.
  • the origin is the center of the peeler magnetic field region 44.
  • the beam is preferably inserted into the beam extraction path when irradiating the target or discarding the remaining beam, but the strength of each frequency component of the electric field applied to the radio frequency kicker 70 is controlled based on the relationship between the position where the beam particles pass under the peeler magnetic field region 44 and the phase lead of the betatron oscillation per turn at the position of the radio frequency kicker 70.
  • the amount of kick received by the beam uniform by inputting an amount proportional to the reciprocal of the amount of change based on the relationship between the position where the beam particles pass under the peeler magnetic field region 44 and the phase advance of the betatron oscillation per turn at the position of the radio-frequency kicker 70.
  • the kick given to the beam is made uniform by controlling the amplitude of the radio frequency voltage of each frequency applied to the radio frequency kicker 70, taking into consideration the kick caused by the peeler magnetic field region 44. This makes it possible to give a consistent kick regardless of the position of the particle passing through in the beam, reducing the power required for beam extraction without over or undershooting the kick amount and allowing the use of an inexpensive radio frequency kicker power supply 5004.
  • the kick amount kick received by the beam particles is expressed as the differential dkick/df with respect to frequency f, provided that the number of applied frequencies Next is sufficiently large. This is expanded as shown in the following equation (3).
  • r is the closest distance between the center position of the peeler magnetic field region 44 and the trajectory of the beam particle.
  • dkick/dl Even if the positional relationship between the beam particle trajectory and the peeler magnetic field region 44 fluctuates with each revolution due to betatron oscillation, dkick/dl must be kept constant to ensure a uniform kick.
  • df(l)/dl is the first-order derivative of the frequency f required to generate resonance in betatron oscillation and the closest distance l between the center position of the peeler magnetic field region 44 and the beam particle trajectory.
  • Transforming equation (3) yields equation (4) below, and to keep the left-hand side a constant value, the single high-frequency kick dkick/df applied to the high-frequency kicker 70 can be made a quantity inversely proportional to df(l)/dl.
  • the amplitude of the high-frequency voltage of frequency fext applied to the high-frequency kicker 70 can be set to a x df(l)/dl.
  • a is a proportionality constant, and by controlling a, the amount of current in the emitted beam can be controlled.
  • Figure 12 shows the procedure for beam extraction control using the beam control method of the present invention.
  • Step S1 Before the accelerator 1 starts operating, preferably during the manufacture of the accelerator 1 or when the accelerator 1 is installed at the operating location, the extraction control device 5000 performs a numerical simulation of the beam particle trajectory by solving the equation of motion of the beam particle under an electromagnetic field based on the Runge-Kutta method, based on the magnetic field measurement results on the beam trajectory of the maximum energy of the accelerator 1.
  • the above numerical simulation is performed on n particles until the particles have completed one revolution within the accelerator, and the results of the simulation are used to calculate the orbit of the beam particles and the change in particle position in phase space before and after the beam particles have orbited within the accelerator, thereby calculating the closest distances r1, r2, ..., rn between the center position of the peeler magnetic field region 44 and the beam particle orbit, and the phase advances ⁇ 1, ⁇ 2, ..., ⁇ n in phase space generated by the particles orbiting within the accelerator.
  • the number of particles n calculated here can be around 10,000.
  • Step S2-1 The calculated data sets (l1, ⁇ 1), ..., (ln, ⁇ n) of the closest distance and phase lead between the center position of the peeler magnetic field region 44 and the beam particle trajectory are sorted in order from smallest to largest, and the difference between the preceding and following data is calculated.
  • the difference in phase lead is divided by the difference in the closest distance to calculate the value of df(l)/dl at the corresponding closest distance.
  • Step S2-2 The high-frequency frequency band to be applied to the high-frequency kicker 70 is determined from the maximum values ⁇ max and ⁇ min of the phase advance amounts ⁇ 1, ⁇ 2, ..., ⁇ n in the phase space of the simulation results. Frequencies are selected from the above-mentioned frequency band at frequency intervals ⁇ f according to the operating status of the accelerator 1, and the frequencies fext1, fext2, ... to be applied to the high-frequency kicker 70 are determined.
  • Step S3 The relative amplitudes Vref1, Vref2, ... of the respective high-frequency voltages are calculated by substituting the above-mentioned frequencies into the function V(f) that determines the amplitudes of the above-mentioned high-frequency voltages.
  • Information on the high-frequency frequencies fext1, fext2, ... and the relative amplitudes Vref1, Vref2, ... calculated as above is input to the synthesizer 5002.
  • Step S4 After the accelerator 1 starts operation, the extraction control device 5000 receives an instruction on the amount of extracted beam at the time of beam extraction from the overall control device 400. Based on this instruction, the control computer 5001 inputs a signal that scales the relative amplitudes Vref1, Vref2, ... by a factor of a to the signal amplifier 5003, and at the same time issues an instruction to the synthesizer 5002 to synthesize a high-frequency signal.
  • Step S5 Based on instructions from the control computer 5001, the synthesizer 5002 synthesizes high-frequency signals based on information on high-frequency frequencies fext1, fext2, . . . and relative amplitudes Vref1, Vref2, .
  • Step S6 Based on the scale signal from the control computer 5001, the high frequency signal is amplified by a factor a in the signal amplifier 5003, and the signal is applied to the high frequency kicker 70, starting beam extraction.
  • Step S7 After the beam is extracted, the dose measurement device 3a in the irradiation device 3 measures the irradiation dose, and based on the result, the overall control device 400 determines whether the beam is excessive or insufficient, and if so, again instructs the extraction control device 5000 to correct the extracted beam amount. If the overall control device 400 instructs the extraction control device 5000, step S4 and subsequent steps are executed again.
  • Steps S1, S2-1, and S2-2 may be executed on a computer separate from the control computer 5001 and input to the control computer 5001. Steps S2-1 and S2-2 may also be executed in parallel, or step S2-2 may be executed after step S2-1 is completed.
  • the relationship f(l) between the frequency f required to generate resonance of betatron oscillation and the closest distance l between the center position of the peeler magnetic field region 44 and the trajectory of the beam particle can be determined by providing position detectors 44A and 44B within the accelerator 1A, as in the accelerator 1A shown in Figure 13, and using these position detectors 44A and 44B to detect the passage position and passage time of the beam particle under the peeler magnetic field region 44 (used to determine the phase advance of betatron oscillation per turn at the position of the high-frequency kicker 70), and then determining this in the control computer 5001A within the extraction control device 5000A.
  • two detectors, 44A and 44B are provided in this embodiment, one or more detectors can be used.
  • the processing from step S4 onwards described above can be performed while performing the same processing as step S1.
  • step S4 the synthesis of the high-frequency signal by the synthesizer 5002 in step S4 may be performed before the accelerator 1 starts operating.
  • step S1 the processing of step S1 can be performed when reviewing the operation. This makes it possible to extract the beam with high accuracy over a long period of time.
  • the accelerator 1 of this embodiment described above has a radio-frequency kicker 70 that generates an electric field component that kicks the beam horizontally, and magnetic poles that generate a peeler magnetic field region 44, which is a quadrupole magnetic field that is asymmetrical when viewed from the direction of beam propagation, with the amplitude of betatron oscillation increased by the radio-frequency kicker 70.
  • the strength of each frequency component of the electric field applied to the radio-frequency kicker 70 is controlled based on the relationship between the position where the beam particles pass under the peeler magnetic field region 44 and the phase lead of the betatron oscillation per turn at the position of the radio-frequency kicker 70.
  • control computer 5001 that calculates the relationship between the particle passage position and the phase advance of the betatron oscillation per turn at the position of the high-frequency kicker 70, or receives input of this relationship from outside, making it possible to apply an electric field to the high-frequency kicker 70 at more appropriate timing.
  • the relationship can be determined in advance, enabling more accurate beam extraction.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)

Abstract

La présente invention comprend : un déflecteur hautes fréquences (70) qui génère un champ électrique ayant une composante qui dévie des faisceaux dans la direction horizontale ; et un pôle magnétique qui génère une région de champ magnétique d'atténuation (44) qui est un champ magnétique quadripolaire qui est latéralement asymétrique lorsqu'on l'observe depuis la direction de déplacement de faisceau dans laquelle l'amplitude des oscillations bêtatron est augmentée par le déflecteur hautes fréquences (70). L'intensité de chaque composante de fréquence d'un champ électrique appliqué au déflecteur hautes fréquences (70) est commandée à partir de la relation entre la position de passage de particules dans les faisceaux sous la région de champ magnétique d'atténuation (44) et l'avance de phase des oscillations bêtatron par tour à la position du déflecteur hautes fréquences (70).
PCT/JP2024/029911 2024-03-05 2024-08-22 Accélérateur de particules circulaire, système de thérapie par particules et procédé de fonctionnement d'accélérateur de particules circulaire Pending WO2025187100A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11176596A (ja) * 1997-12-08 1999-07-02 Mitsubishi Electric Corp 荷電粒子ビーム装置
JP2003282300A (ja) * 2002-03-26 2003-10-03 Hitachi Ltd 粒子線治療システム
US20160270204A1 (en) * 2012-07-27 2016-09-15 Massachusetts Institute Of Technology Phase-Lock Loop Synchronization Between Beam Orbit And RF Drive In Synchrocyclotrons
WO2021260988A1 (fr) * 2020-06-23 2021-12-30 国立研究開発法人量子科学技術研究開発機構 Accélérateur de particules et dispositif de thérapie à faisceau de particules
JP2022190590A (ja) * 2021-06-14 2022-12-26 株式会社日立製作所 粒子線加速器、および、粒子線治療システム

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11176596A (ja) * 1997-12-08 1999-07-02 Mitsubishi Electric Corp 荷電粒子ビーム装置
JP2003282300A (ja) * 2002-03-26 2003-10-03 Hitachi Ltd 粒子線治療システム
US20160270204A1 (en) * 2012-07-27 2016-09-15 Massachusetts Institute Of Technology Phase-Lock Loop Synchronization Between Beam Orbit And RF Drive In Synchrocyclotrons
WO2021260988A1 (fr) * 2020-06-23 2021-12-30 国立研究開発法人量子科学技術研究開発機構 Accélérateur de particules et dispositif de thérapie à faisceau de particules
JP2022190590A (ja) * 2021-06-14 2022-12-26 株式会社日立製作所 粒子線加速器、および、粒子線治療システム

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