JP5542703B2 - Charged particle beam irradiation system and operation method of circular accelerator - Google Patents

Description

  The present invention relates to a charged particle beam irradiation system that takes out charged particles accelerated by a circular accelerator as a charged particle beam and irradiates an irradiation target.

  A charged particle is accelerated by a circular accelerator such as a synchrotron, and the charged particle accelerated to high energy is taken out from its orbit, and a beam-shaped charged particle (also called a charged particle beam or particle beam) is used as a beam transport system. It is used for medical experiments such as physical experiments for transporting and irradiating desired objects and cancer treatment. The synchrotron is a vacuum duct that circulates a charged particle beam for a long period of time, a circular orbit and an electromagnet group that generates a converging magnetic field for controlling the charged particle beam size, and a high-frequency voltage (acceleration voltage) synchronized with the circulatory period. A high-frequency accelerator for accelerating the beam, an incident device for introducing charged particles into the vacuum duct, and an extraction device for extracting charged particles out of the circular accelerator. Among the above-described components, the high-frequency accelerator includes a high-frequency source that generates an acceleration voltage, a high-frequency source controller that controls the high-frequency source, a high-frequency acceleration cavity (also referred to as an acceleration cavity) that applies the acceleration voltage, and a circular beam. A beam monitor for detecting the trajectory and intensity of the beam, a voltage pickup for detecting a high-frequency voltage generated in the acceleration cavity, and the like.

The operation of a circular accelerator consists of incident, acceleration, and emission. A high-frequency accelerator is a mass of beams on a stable acceleration region by applying an acceleration voltage to an incident beam with a uniform distribution in time.
Bunch). In acceleration, the frequency of the acceleration voltage applied to the acceleration cavity is increased. Synchrotrons, which are a type of circular accelerator (in addition to synchrotrons whose circular radii are constant, there are cyclotrons whose circular radii increase with acceleration), in order to make the circular radii constant, high-frequency acceleration The apparatus controls the acceleration voltage frequency in accordance with the strength of the deflection magnetic field generated by the deflection electromagnet. The beam accelerated to the maximum energy is finally taken out of the circular accelerator from the extraction device.

Conventionally, when a beam is extracted from a circular accelerator, its output beam intensity (the amount of charged particles emitted per unit time, also referred to as emission current) is changed by using an RF knockout electrode which is one of the emission devices. A high frequency voltage is applied to the laser beam to emit light (for example, Patent Document 1)
). The relationship of the emitted beam intensity with respect to the applied high-frequency voltage is obtained in advance by experiments or the like, and the control data is stored in advance in a control computer or the like as pattern data. Since the emission is performed using the resonance phenomenon of charged particles, the adjustment parameter of the emission beam intensity is required to have a very high accuracy of 0.1% level.

  On the other hand, a technique for optimizing the waveform of a high-frequency acceleration voltage in order to maximize the amount of charged particles that can be accelerated by the synchrotron, that is, the acceleration current is known (for example, Patent Document 2).

JP 2007-260193 A JP 2002-75698 A

The charged particle beam irradiation system using the circular accelerator as described above has the following problems. The particle beam (charged particle beam) is taken out by the method of resonance emission when the charged particle is emitted, but the control parameter needs to be adjusted with high accuracy of 0.1% level. When it is necessary to change the emission current, a long adjustment time is required.
An object of the present invention is to solve the above problems and to provide a charged particle beam irradiation system capable of stably changing the emission current of a particle beam necessary for scanning irradiation or the like with a simple control device.

A charged particle beam irradiation system according to the present invention includes a deflection electromagnet that forms a charged particle beam by rotating charged particles along a circular orbit, a high-frequency acceleration cavity for accelerating the charged particles, and a high-frequency wave in the high-frequency acceleration cavity. A circular shape including a high-frequency source for injecting a beam, a focusing electromagnet for converging a charged particle beam, a hexapole electromagnet for exciting resonance in a circular orbit, and an extraction device for extracting charged particles from the circular orbit Accelerator, beam transport system for transporting charged particle beam emitted from circular orbit, beam irradiation system for irradiating target object with charged particle beam transported by this beam transport system, and charged particle beam for irradiating target object In a charged particle beam irradiation system including a beam irradiation control device for controlling the frequency, a high frequency source control for controlling a high frequency generated by the high frequency source is provided. Equipped with a device, the high-frequency source controller is sent from the beam irradiation controller, based on the signal of the beam intensity of the charged particle beam beam irradiation system requires at least starting acceleration from the time of incidence of the charged particles During the period up to an initial predetermined time, at least one of the frequency, amplitude and phase of the high frequency generated by the high frequency source is shifted from the optimum value of acceleration of the charged particles .

  According to the present invention, a charged particle beam irradiation system can be obtained in which the emission current of a particle beam can be changed stably with a simple control method and control device, and the particle beam intensity required for an object can be stably obtained.

It is a block diagram which shows schematic structure of the charged particle beam irradiation system by Embodiment 1 of this invention. It is a typical diagram explaining operation | movement of the charged particle beam irradiation system by Embodiment 1 of this invention. It is another schematic diagram explaining operation | movement of the charged particle beam irradiation system by Embodiment 1 of this invention. It is a diagram which shows an example of the acceleration pattern of the charged particle beam irradiation system by Embodiment 1 of this invention. It is a diagram which shows an example of the relationship between the acceleration current of the charged particle beam irradiation system by Embodiment 1 of this invention, and an emitted current. It is a diagram which shows an example of the relationship between the acceleration current of a conventional charged particle beam irradiation system, and an emitted current. It is a schematic diagram when irradiating a patient's affected part with a particle beam. It is a typical diagram explaining operation | movement of the charged particle beam irradiation system by Embodiment 2 of this invention. It is another schematic diagram explaining operation | movement of the charged particle beam irradiation system by Embodiment 2 of this invention. It is a block diagram which shows schematic structure of the charged particle beam irradiation system by Embodiment 3 of this invention. It is a diagram which shows an example of operation | movement of the charged particle beam irradiation system by Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a schematic configuration of a charged particle beam irradiation system according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a circular accelerator which is a synchrotron, and is composed of the following components. That is, the circular accelerator 1 includes a front accelerator 2, a vacuum duct 3 for circulating a charged particle beam for a long time, an incident device 4 for causing charged particles from the front accelerator 2 to enter the vacuum duct 3, and a charged particle being a vacuum duct. Deflection electromagnets 5a, 5b, 5c, 5d (collectively referred to as deflection electromagnets 5) for deflecting the trajectory of the charged particles so as to form a charged particle beam by circling along the circular trajectory in 3; Converging electromagnets 6a, 6b, 6c, 6d that converge so that the charged particle beam formed above does not diverge (these are collectively referred to as converging electromagnet 6), and a high-frequency voltage synchronized with circulating charged particles is applied. The high-frequency accelerating cavity 7 to be accelerated, the emission device 8 for taking out the charged particle beam in the circular accelerator out of the circular accelerator 1, and the resonance of the circular orbit of the charged particle beam A hexapole electromagnet 9 for raising and emitting charged particles from the emission device 8, a high frequency source 10 for supplying a high frequency voltage to the high frequency acceleration cavity 7, a high frequency control device 11 for controlling the high frequency source 10, and a generated magnetic field Circular accelerator control for controlling the entire circular accelerator 1 by controlling other components such as the deflection electromagnet control device 12, the high frequency control device 11, the deflection electromagnet control device 12 and the converging electromagnet 6 for controlling the excitation current of the deflection electromagnet for control. It is comprised by the apparatus 13 grade | etc.,. In the present invention, the high frequency source control device 11 includes a high frequency voltage waveform control unit 110 that controls a waveform that is one of the parameters of the high frequency voltage generated by the high frequency source 10 therein.

  Reference numeral 20 denotes a beam transport system that transports the charged particle beam emitted from the emission device 8, and reference numeral 30 denotes a beam irradiation system that irradiates the irradiation target with the charged particle beam transported by the beam transport system 20. Reference numeral 40 denotes a beam irradiation control device that controls a beam to be irradiated, and controls the beam irradiation system 30 and the circular accelerator control device 13. When the charged particle beam irradiation target is, for example, a cancer tissue, that is, when the charged particle beam irradiation system is a particle beam therapy system using a charged particle beam, the beam irradiation control device 40 includes a treatment planning device, and a treatment plan Accordingly, information such as beam energy, beam intensity, and beam ON / OFF timing required for irradiation is sent to the beam irradiation system 30 and the circular accelerator control device 13, and charged particles required by the beam irradiation system 30 from the circular accelerator 1. The beam is emitted.

  As described above, the charged particles incident on the vacuum duct 3 by the incident device 4 from the pre-accelerator 2 are deflected by the deflecting electromagnet 5 to circulate the orbit. Meanwhile, the charged particles are accelerated by being given energy from the high frequency when passing through the high frequency acceleration cavity 7. In order to accelerate, it is necessary to apply a high frequency acceleration voltage in synchronization with the circulation cycle of the charged particles that circulate. In addition, if the magnetic field generated by the deflecting electromagnet 5 is the same, the deflection angle of the charged particle decreases as the charged particle is accelerated. Therefore, the magnetic field generated by the deflecting electromagnet 5 is increased according to the acceleration of the charged particle. And control to form a charged particle beam. At this time, since the divergence state of the charged particle beam also changes, the magnetic field of the focusing electromagnet 6 is also changed so that the charged particle beam does not diverge. In this way, by controlling the frequency and voltage of the high-frequency source 10 and the exciting current of the deflection electromagnet 5, the charged particles are controlled to circulate so as to match the passage formed by the vacuum duct 3 to form a charged particle beam. , Charged particles are accelerated by gaining energy from high frequency.

  Note that the converging electromagnet 6 is not necessarily required for the circular accelerator. Since the converging electromagnet can be made to function by adjusting the edge angle of the end of the deflection electromagnet, there is a circular accelerator that does not include the converging electromagnet.

  As described above, the excitation current of the deflecting electromagnet 5 increases at the time of acceleration from a constant excitation current. However, when the charged particles reach a predetermined energy, the excitation current of the deflection electromagnet 5 is made constant again for resonance excitation. Charged particles are emitted by controlling the parameters of the hexapole electromagnet 9 and the emission device 8, that is, the emission parameters. After the exit of the charged particles, the exciting current of the deflection electromagnet 5 is lowered. By repeating this, incidence, acceleration, and emission are performed using a circular accelerator.

  The charged particles that circulate in the high-frequency acceleration cavity 7 are accelerated when the phase of the high-frequency acceleration voltage applied when the charged particles pass through the high-frequency acceleration cavity 7 is in the accelerating phase. That is, charged particles passing through in synchronization with the high-frequency acceleration voltage are accelerated. FIGS. 2A and 2B are schematic diagrams showing the time waveform of the acceleration voltage applied to the high-frequency acceleration cavity and the beam current that can be accelerated. The waveform shown in FIG. 2A is a voltage waveform created by controlling the high frequency source 10 by the high frequency source control device 11 and applied to the high frequency acceleration cavity 7. The dotted line is a sine wave and the solid line is a non-sine wave. FIG. 2B shows a beam current (acceleration current) that can be accelerated by the circular accelerator. The dotted line is when a sine wave is applied, and the solid line is when a non-sine wave is applied. When a non-sine wave is applied, the time width of the charged particle beam can be made longer than when a sine wave is applied. That is, when a non-sine wave is applied, more charged particles can be accelerated than when a sine wave is applied, and the acceleration current can be increased.

  The high-frequency voltage waveform is created as follows. A non-sinusoidal wave can be created by adding harmonics to the fundamental wave. In FIG. 2, the dotted line is an example of the waveform of only the fundamental wave, and the solid line is an example of the waveform when a triple harmonic is applied. Here, when the acceleration voltage ratio between the fundamental wave and the triple harmonic is up to 1: 0.5, the acceleration current increases as the triple harmonic increases. FIG. 3 shows a schematic diagram of the relationship between the ratio of the third harmonic to the fundamental harmonic and the magnitude of the acceleration current. From this figure, it can be seen that the acceleration current can be adjusted by adjusting the amplitude intensity of the triple harmonic. When accelerating with a high-frequency accelerating voltage obtained by adding the third harmonic to the fundamental wave, an emission current substantially proportional to the acceleration current can be realized by emitting with the same emission parameters as when accelerating with only the fundamental wave.

At the time of acceleration, the frequency of the fundamental wave is gradually increased from 1 MHz to 10 MHz, for example, according to the acceleration. It is necessary to change the 3rd harmonic from 3 MHz to 30 MHz following the change in the frequency of the fundamental wave. If the third harmonic is generated based on the fundamental wave, it is possible to easily generate the third harmonic that follows the change in the frequency of the fundamental wave. In addition, the effect of space charge (the effect of repulsion between charged particles and charged particles) is large at low energy and small at high energy, so triple harmonics up to a certain acceleration energy (for example, about 20 MeV for protons). The same effect is obtained by exciting only the fundamental wave thereafter.

  In the above, an example in which a non-sinusoidal wave is created by adding a third harmonic to the fundamental wave has been described, but a non-sinusoidal wave can also be created by adding a second harmonic to the fundamental wave. Since the waveform of the high frequency voltage can be changed by changing the amplitude of the second harmonic applied to the fundamental wave, the emission current can be controlled by the amplitude of the second harmonic. Moreover, the waveform of the high-frequency voltage can be changed by adding more than four times higher harmonics to the fundamental wave and changing the amplitude of the added harmonics. Furthermore, the harmonics of a plurality of different multiples such as the second harmonic and the third harmonic are added. The waveform of the high frequency voltage can also be changed by adding a wave and changing the amplitude of the added harmonic. Thus, by adding a harmonic more than twice to the fundamental wave and changing the amplitude of the added harmonic, the waveform of the high frequency voltage can be changed, and the acceleration current can be changed.

  In this way, the acceleration current can be changed by changing the waveform of the high-frequency voltage generated by the high-frequency source 10, and the emission current can be changed while the emission parameter remains fixed. Therefore, the beam can be controlled by controlling the waveform of the high-frequency voltage. Control for obtaining the beam intensity required by the irradiation system 30 can be performed.

4A and 4B show an example of the relationship between the acceleration pattern (accelerated charged particle energy) of the circular accelerator and the emission current. The charged particles are accelerated to the required energy in the period A, and then circulate around the circular orbit of the circular accelerator at the energy, that is, at the speed. The emission parameters are set so that the charged particles that circulate with the constant energy are emitted from the emission device 8 during the period B, and are taken out as an emission current. In the present invention, the acceleration current value is changed by changing the waveform of the high-frequency voltage for each acceleration, and the beam is extracted with the same emission parameters. In the example of FIG. 4B, the beam is emitted four times with one acceleration. However, depending on the request from the beam irradiation system 30, the beam may be emitted once continuously.

FIGS. 5A and 5B show the relationship between the acceleration current and the emission current of the circular accelerator 1 in the charged particle beam irradiation system of the present invention. In the first acceleration, for example, the ratio of the third harmonic to the fundamental wave is set to 0.5, a large current is accelerated, and a large current beam is emitted. In the second acceleration, for example, when the ratio of the third harmonic to the fundamental wave is set to 0.25, the acceleration current is made smaller than that in the first acceleration, and the beam is extracted with the same extraction parameters as in the first acceleration. The current to be performed is smaller than the first current. In this way, the emission current can be controlled by changing the waveform of the high frequency voltage generated by the high frequency source 10 by changing the ratio of the third harmonic without changing the emission parameter.

  6A and 6B show the relationship between the acceleration current and the emission current of a conventional circular accelerator. The acceleration current is constant, and the emission current intensity is changed by changing the emission parameter. That is, the number of charged particles orbiting the circular orbit of the circular accelerator 1 after accelerating to a predetermined energy is the same every time, and the emission parameter is changed so that the number of emitted particles per time changes, and the value of the emission current is changed. . In contrast, in the present invention, as described above, the number of charged particles that circulate around the circular orbit of the circular accelerator 1 is changed by changing the waveform of the high-frequency acceleration voltage, and the emission current is changed without changing the emission parameter. The value of was changed.

  Here, an example in which a charged particle beam (particle beam) is used in a particle beam therapy system will be described. FIG. 7 shows a schematic diagram when the particle beam is taken out from the circular accelerator and irradiated to the affected part of the patient in the irradiation chamber. When the affected part is irradiated with the particle beam, the distance in the depth direction where the particle beam stops depends on the energy of the particle beam. Further, the energy density, that is, the dose given to the path through which the irradiated particle beam passes until it stops at the affected area has a maximum value at the stop position of the particle beam.

  For this reason, in the scanning irradiation method, which is a method of irradiating a shape according to the affected part while scanning a thin particle beam having a diameter of less than 10 mm, the depth direction of the affected part is divided from several layers to several tens of layers (a in FIG. , B, c, and d), and each layer is scanned with a fine particle beam and irradiated. Adjustment in the depth direction is performed by changing the energy of the particle beam. Since the dose to be irradiated varies depending on the position even within one layer, it is necessary to control the dose to be a predetermined dose by controlling the time to irradiate each spot. In addition, each layer may have a different slice cross-sectional size, and there are the following problems when managing the dose with one outgoing beam intensity. When irradiation is performed with a low emission beam intensity, irradiation time is required when irradiating the entire affected area. When irradiation is performed at a high exit beam height, it is necessary to scan the beam very quickly or turn it on / off when the slice cross section is small, and it is difficult to perform irradiation with sufficiently high accuracy. Therefore, high-precision and short-time irradiation can be realized by irradiating the beam with several kinds of outgoing beam intensities according to the area of the slice cross section.

Therefore, the beam irradiation control device 40 generates parameters for the next slice plane so as to perform irradiation in accordance with the shape of the affected part, and sends the parameters to the circular accelerator control device 13. The circular accelerator control device 13 determines the necessary acceleration current and performs high frequency. The high-frequency voltage waveform control unit 110 of the high-frequency source control device 11 generates a high-frequency voltage waveform for obtaining the acceleration current and sends the voltage waveform to the high-frequency source 10. To control the acceleration current.
By comprising in this way, the emission current of a particle beam can be changed stably with a simple control method and control equipment.

Embodiment 2. FIG.
In the first embodiment, the high-frequency voltage waveform is created by adjusting the amplitude of the triple harmonic. However, even if the amplitude is constant and the phase between the triple harmonic and the fundamental wave is adjusted, the high-frequency voltage waveform is generated. The waveform can be changed. Specifically, the phase between the triple harmonic and the fundamental wave is adjusted to the phase where the acceleration current is maximized (optimal phase), and the acceleration current is decreased by shifting the triple harmonic from the optimal phase. Is possible. The emission is performed with the same emission parameters as in the case of only the fundamental wave, and an emission current roughly proportional to the acceleration current can be realized.

  FIG. 8 and FIG. 9 show the high frequency voltage waveform when the phase of the third harmonic is shifted from the optimum phase, and the acceleration current when accelerating with the waveform. The waveform shown by the solid line in FIG. 8A is a waveform when the phase of the third harmonic is shifted by 15 degrees from the waveform of the solid line shown in FIG. The solid line in FIG. 8B represents the acceleration current at that time, and the dotted line represents the acceleration current when accelerating with a sine wave (only the fundamental wave). Compared to FIG. 2B, the phase width (corresponding to the time width) of the acceleration current indicated by the solid line is narrow, and it can be seen that the acceleration current is decreased by shifting the phase of the third harmonic. . Further, FIGS. 9A and 9B show the acceleration voltage waveform and the acceleration current at that time when the phase of the third harmonic is further shifted by 15 degrees, that is, by 30 degrees from the waveform of FIG. Is. The time width of the acceleration current shown by the solid line is further narrower than the time width shown in FIG. 8B, and the acceleration current further decreases. Thus, the acceleration current can be changed by changing the phase of the third harmonic. Further, when the waveform of the high-frequency voltage is changed by changing the phase of the third harmonic, the acceleration current can be reduced rather than accelerating with a sine wave. By changing the amplitude of the third harmonic in addition to the phase, the range of change in the acceleration current can be further expanded.

As described in Embodiment 1, a non-sinusoidal wave can also be created by adding a second harmonic to the fundamental wave. Since the waveform of the high frequency voltage can be changed by changing the phase of the second harmonic applied to the fundamental wave, the emission current can be controlled by the phase of the second harmonic. Moreover, the waveform of the high frequency voltage can be changed by adding more than 4 times higher harmonics to the fundamental wave and changing the phase of the added harmonics. Furthermore, the harmonics of multiple different multiples such as the 2nd harmonic and the 3rd harmonic are added. The waveform of the high frequency voltage can also be changed by adding a wave and changing the phase of the added harmonic. In this way, the waveform of the high frequency voltage can be changed and the acceleration current can be changed by adding a harmonic more than twice to the fundamental wave and changing the phase of the added harmonic. Further, by changing the amplitude of the harmonic in addition to the phase, the range of change in the acceleration current can be further expanded.
As described above, according to the second embodiment, the emission current of the particle beam can be changed stably with a simple control method and control device.

Embodiment 3 FIG.
FIG. 10 is a block diagram showing a schematic configuration of a charged particle beam irradiation system according to the third embodiment of the present invention. 10, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. In FIG. 10, the part different from FIG. 1 is a fundamental wave that sets a deviation amount of at least one parameter among a high frequency, amplitude, and phase in the high frequency source controller 11 instead of the high frequency voltage waveform controller 110. The parameter deviation amount setting unit 111 is provided. In the first and second embodiments, the fundamental wave and the harmonic are used in creating the high-frequency voltage pattern. However, the maximum acceleration current is set to at least one of the frequency, amplitude, and phase using only the fundamental wave. The acceleration current can also be controlled by shifting from the optimum value obtained.

In conventional circular accelerators, the frequency, amplitude, and phase of the high-frequency voltage are optimized and changed to accelerate charged particles to obtain as much acceleration current as possible, and the emission current is controlled by changing the emission parameters. It was. In the third embodiment of the present invention, when the emission current required by the circular accelerator control device 13 is the maximum, the frequency, amplitude, and phase of the high-frequency voltage are optimized and changed for acceleration of charged particles, as in the prior art. When the emission current required by the circular accelerator control device 13 is smaller than the maximum value, the acceleration current is set to the maximum value by shifting at least one parameter of the frequency, amplitude, and phase of the high-frequency voltage from the optimum value for acceleration of the charged particles. Lower from. In the fundamental wave parameter deviation amount setting unit 111, the emission current required by the circular accelerator control device 13 based on the signal of the beam intensity of the charged particle beam required by the beam irradiation system 30 sent from the beam irradiation control device 40. Corresponding to the above, the amount by which at least one parameter of the frequency, amplitude, and phase of the high-frequency voltage is shifted from the optimum value, that is, the amount of deviation is determined and set. In this way, the emission current is controlled by at least one parameter among the frequency, amplitude, and phase of the high-frequency voltage. Thus, a control method for obtaining the required emission current by shifting the parameter of the high-frequency voltage from the optimum acceleration value has not been conceived in the past.

  FIG. 11 shows the controllability when the emission current is controlled by shifting the frequency of the fundamental wave from the optimum value. FIG. 11 shows the result of beam analysis regarding which stage of incidence, acceleration, and emission can be controlled to control the emission current. In FIG. 11A, the horizontal axis represents time, and the vertical axis represents the deflection magnetic field. The change in the deflection magnetic field shown in FIG. 11A is a change in the magnetic field necessary for accelerating the incident charged particles. In FIG. 11A, the charged particles are incident until about 0.4 seconds. This is a necessary magnetic field that does not change and shows that the magnetic field is increased in response to the acceleration in order to start the acceleration thereafter. FIG. 11B shows the time dependency of the controllability when the frequency is shifted among the parameters of the high-frequency voltage with respect to the change in the deflection magnetic field. The vertical axis in FIG. 11 (b) shows the fluctuation rate (controllability) of the emission current in percent. Controllability represents the degree to which the output current can be controlled by shifting the fundamental frequency from the optimum value for acceleration of charged particles, and how much the output current varies from the maximum output current obtained by acceleration. It can be (decreased) expressed as a percentage.

  FIG. 11B shows the analysis result when the synchrotron frequency after the start of acceleration is 320 Hz. In this case, about 0.1 second after the start of acceleration from the time of incidence, that is, the synchrotron after the start of acceleration. Controllability of about 25% can be obtained up to about 30 times the time of one cycle of vibration, but thereafter the controllability decreases. Thus, high controllability can be obtained from the time of incidence to the beginning of acceleration. This period is a period in which the charged particles occupy all the acceleration phases and transition to a state in which they circulate within the stable acceleration phase (separatory), and the acceleration current value is increased by changing the minute fundamental wave. It is because it can influence. As described above, high controllability can be obtained within a predetermined time from the time of incidence to the beginning of acceleration, preferably within 50 times the time of one cycle of the synchrotron oscillation at the time of acceleration after the start of acceleration. In FIG. 11B, the result of shifting the frequency of the high-frequency fundamental wave is shown. However, when the emission current is controlled by shifting the amplitude or phase, as in the case of frequency transition, Therefore, high controllability can be obtained within a predetermined time from the beginning of acceleration. After this period, it is difficult to change the output current unless the amplitude, frequency, and phase are significantly changed, control becomes difficult, and control responsiveness deteriorates. From this, it can be seen that it is effective to control from the time of incidence to the beginning of acceleration.

  As described above, according to the third embodiment, the emission current of the particle beam can be changed stably with a simple control method and control device.

1: Circular accelerator 2: Pre-stage accelerator 3: Vacuum duct 4: Incident device 5, 5a, 5b, 5c, 5d: Bending electromagnet 6, 6a, 6b, 6c, 6d: Converging electromagnet 7: High-frequency acceleration cavity 8: Ejecting device 9: Resonant excitation hexapole magnet 10: High frequency source 11: High frequency source control device 12: Deflection magnet control device 13: Circular accelerator control device 20: Beam transport system 30: Beam irradiation system 40: Beam irradiation control device 110: High frequency voltage Waveform control unit 111: Fundamental parameter deviation amount setting unit

Claims (4)

A deflecting electromagnet that circulates incident charged particles along a circular orbit to form a charged particle beam, a high-frequency acceleration cavity for accelerating the charged particles, a high-frequency source that causes a high-frequency to enter the high-frequency acceleration cavity, A circular accelerator comprising: a converging electromagnet for converging the charged particle beam; a hexapole electromagnet for exciting resonance in the orbit; and an extraction device for extracting the charged particles from the orbit;
A beam transport system for transporting the charged particle beam emitted from the orbit,
A beam irradiation system for irradiating an object with the charged particle beam transported by the beam transport system;
In a charged particle beam irradiation system comprising a beam irradiation control device for controlling the charged particle beam irradiated to an object,
A high-frequency source control device that controls a high-frequency generated by the high-frequency source, and the high-frequency source control device sends a beam intensity of the charged particle beam required by the beam irradiation system sent from the beam irradiation control device; Based on the signal, at least one of the frequency, amplitude, and phase of the high frequency generated by the high frequency source from the time when the charged particle is incident to a predetermined time at the beginning of acceleration is determined as an optimum value for acceleration of the charged particle. A charged particle beam irradiation system characterized by being shifted from 2. The charged particle beam irradiation system according to claim 1 , wherein the predetermined time at the beginning of acceleration is a time within 50 times the time of one cycle of synchrotron oscillation at the start of acceleration after the start of acceleration. . The incident charged particles are deflected by a deflecting electromagnet and circulated along a circular orbit to form a charged particle beam. The charged particles are accelerated by a high frequency voltage applied to a high frequency accelerating cavity, and the charged particle beam is accelerated by a focusing electromagnet. In the operation method of the circular accelerator, the resonance is excited in the orbit by the hexapole electromagnet and the charged particles are taken out from the orbit by the emission device.
At least one of the frequency, amplitude, and phase of the high-frequency voltage applied to the high-frequency acceleration cavity is shifted from the optimum acceleration value of the charged particles for at least a predetermined time from the time when the charged particles are incident to the beginning of acceleration. And changing the emission current of the charged particle beam extracted from the orbit. The acceleration start initial predetermined time after the start of acceleration, the method of operating a circular accelerator according to claim 3, characterized in that the 50-fold within hours of time of one cycle of the synchrotron oscillation of the acceleration at the start .

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