Circular particle accelerator, particle therapy system, and method for operating circular particle accelerator

Abstract

The present invention comprises: a high-frequency kicker (70) that generates an electric field having a component that kicks beams in the horizontal direction; and a magnetic pole that generates a peeler magnetic field region (44) that is a quadrupole magnetic field that is laterally asymmetric as viewed from the beam traveling direction in which the amplitude of the betatron oscillations is increased by the high-frequency kicker (70). The intensity of each frequency component of an electric field applied to the high-frequency kicker (70) is controlled from the relationship between the passage position of particles in the beams under the peeler magnetic field region (44) and the phase advance of the betatron oscillations per turn at the position of the high-frequency kicker (70).

Description

Circular accelerator, particle beam therapy system, and method of operating a circular accelerator

[0001] 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.

[0002] As an example of a technique for solving the problem that the stable region boundary of betatron oscillation fluctuates and is emitted due to ripples in the main electromagnet power supply, Patent Document 1 describes that 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 a frequency f1 that puts charged particles near the center of the orbiting beam into a resonant state to a frequency f2 that puts charged particles with almost the maximum amplitude within the stable region boundary into a resonant state, and is controlled with an amplitude modulation waveform such that f1 > f2.

[0003] Patent No. 4650382

[0004] Circular accelerators have been used for physics experiments and medical applications, in which a charged particle beam is accelerated circularly, extracted from the circular orbit, and transported by a beam transport system to irradiate a desired target.

[0005] In this case, the method of extracting the beam from the circular accelerator involves applying a high-frequency electric field to the circulating beam to increase the amplitude of the betatron oscillation, and then extracting the beam by moving it outside the region where it stably passes through the circulating orbit.

[0006] In order to increase the amplitude of the betatron oscillation of the beam by using a high frequency electric field, it is necessary to apply RF having a frequency corresponding to the oscillation velocity of the betatron oscillation.

[0007] Patent Document 1 describes a technology for suppressing a decrease in particle density in a beam and reducing the cost of the main electromagnet power supply in an accelerator having a high-frequency generator for beam extraction. This technology applies a function that increases the intensity of the RF frequency corresponding to the range of f1 to f2 by as much as f1, with respect to the betatron frequencies f1 and f2 of particles at the center of the beam and particles at the edge of the separatrix.

[0008] In order to reduce the operating and initial costs of accelerators, it is necessary to reduce the power consumption during operation of the high frequency device and to realize beam extraction using an inexpensive, low-power high frequency device power supply.

[0009] The beam extraction using radio frequency is performed 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 for the device's power supply are high.

[0010] The region in which the beam circulates stably in a circular accelerator is determined by the magnitude of the quadrupole magnetic field near the beam orbit, and the frequency of the radio frequency electric field applied to the beam also depends on the magnitude of the quadrupole magnetic field along the orbit of each beam particle.

[0011] When the quadrupole magnetic field distribution on the beam orbit is asymmetric in the horizontal direction as viewed from the beam direction, the RF frequency to be applied depends not only on the distance in phase space from the beam center but also on the distance between the particle passing position and the electromagnet. The case where the quadrupole magnetic field distribution on the beam orbit is asymmetric in the horizontal direction as viewed from the beam direction is when a peeler magnetic field or the like is applied to extract the beam.

[0012] If the frequency of the high frequency electric field to be applied to the beam is off or the intensity is insufficient, a part of the beam will not be extracted, or the extracted beam will have a disturbance in intensity that will be inconvenient for use.

[0013] In Patent Document 1, in an accelerator having a high frequency generator for beam extraction, the intensity of the RF frequency corresponding to the range of f1 to f2 is given by a function that increases as f1 increases, with respect to the betatron frequencies f1 and f2 of particles at the center of the beam and particles at the edge of the separatrix.

[0014] However, unlike the accelerator described in Patent Document 1, in the case of an accelerator in which the quadrupole magnetic field distribution on the beam orbit is asymmetric between the left and right in the horizontal direction as viewed from the direction of beam propagation, 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 method different from that described in Patent Document 1 is required.

[0015] The present invention provides a circular accelerator, a particle beam therapy system, and a 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 asymmetrical horizontally when viewed from the direction of beam propagation.

[0016] The present invention includes multiple means for solving the above-mentioned problems. One example is a circular accelerator having electrodes that generate an electric field with a 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 progression, 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 through which the beam particles pass under the magnetic field and the phase advance of the betatron oscillation per turn at the position of the electrodes.

[0017] According to the present invention, a beam can be extracted with less energy than in the past. Objects, configurations and effects other than those described above will become apparent from the following description of the embodiments.

[0018] 5 is a diagram showing an outline of the configuration of a particle beam therapy system of an embodiment. FIG. 6 is a diagram showing an outline of the external appearance of an accelerator of an embodiment. FIG. 7 is a diagram showing the cross-sectional configuration of an accelerator of an embodiment and the relationship between equipment involved in beam extraction. FIG. 8 is a diagram showing the cross-sectional configuration of a radio frequency kicker provided in an accelerator of an embodiment. FIG. 9 is a diagram showing an example of pole piece arrangement in a peeler magnetic field region as viewed from the arrows A-A' in FIG. 3. FIG. 10 is a diagram showing the distribution of the main magnetic field on the r-axis in FIG. 5. FIG. 11 is a time chart illustrating the beam extraction procedure in an accelerator of an embodiment. FIG. 12 is a diagram showing the behavior of beam particles in phase space at the radio frequency kicker point and resonance conditions in an accelerator of an embodiment. FIG. 13 is a diagram explaining a method for determining the radio frequency to be input to the radio frequency kicker in an accelerator of an embodiment. FIG. 14 is a diagram explaining fluctuations in betatron tune during the beam extraction process in an accelerator. FIG. 15 is a diagram showing an example of the relationship between the frequency fext required to generate resonance of betatron oscillations and the closest distance l of the orbit of a beam particle between the center position of the peeler magnetic field region and the beam particle. FIG. 16 is a flowchart illustrating the procedure for beam extraction control in an accelerator of an 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.

[0019] Embodiments of the circular accelerator, particle beam therapy system, and circular accelerator operating method of the present invention will be described with reference to Figures 1 to 13. In the drawings used in this specification, identical or corresponding components are designated by identical or similar reference numerals, and repeated description of these components may be omitted.

[0020] First, a particle therapy system according to a preferred embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram showing an outline of the configuration of the particle therapy system according to the embodiment.

[0021] The particle beam therapy system 1000 shown in FIG. 1 includes an accelerator 1 that accelerates a beam and extracts it to the outside, 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.

[0022] In the particle beam therapy system 1000, a beam generated in an accelerator 1 is transported to an irradiation device 3 via a beam transport device 2. In the irradiation device 3, the beam position is controlled by the magnetic field of a scanning electromagnet, and the beam is irradiated onto a predetermined affected area of ​​a patient 5 lying supine on a treatment couch 4. The irradiation device 3 has a dosimetry device 3a inside that measures the dose actually irradiated to the patient.

[0023] The treatment planning device 7 is a device that calculates and determines various control parameters related to the irradiation of the beam onto the patient 5 , and the created treatment plan is recorded in a treatment plan database 60 .

[0024] The overall control device 400 controls each device based on the treatment plan acquired 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 transmits predetermined command values ​​to each device.

[0025] While the patient 5 is being irradiated with the beam, the irradiation device 3 constantly measures the irradiated dose and outputs the measurement results to the irradiation controller 50. The irradiation controller 50 is a control device for monitoring the irradiation dose and irradiation position, and when irradiation of a certain spot with a predetermined planned dose is completed, irradiation of the next spot is started. By repeating this process, it is possible to impart a dose distribution specified in a treatment plan previously prepared by the treatment planning device 7 to an appropriate position and depth.

[0026] The blocking 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 blocking electromagnet, an excitation power supply for the beam blocking electromagnet, and a beam dump that discards the beam components removed by the blocking electromagnet (all of which are omitted for convenience of illustration). The excitation power supply is connected to the blocking electromagnet, and the overall control device 400 is connected to the excitation power supply, and the beam discard control is performed by controlling the excitation of the blocking electromagnet.

[0027] 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 its cross-sectional configuration and the relationship between the equipment involved in beam extraction are shown in Figure 3.

[0028] The accelerator 1 of this embodiment can be an accelerator such as a synchrocyclotron.

[0029] As shown in FIG. 2, the accelerator 1 has an outer shell formed by a main electromagnet 40 which can be separated in the vertical direction, and the beam acceleration region inside the main electromagnet 40 is evacuated.

[0030] An ion source 12 that generates a beam of ions to be incident on the main electromagnet 40 and an acceleration gap 11 are installed inside the main electromagnet 40. A radio frequency electric field is applied to the acceleration gap 11 by a radio frequency generator (both not shown).

[0031] 3, the accelerator 1 includes, as beam extraction equipment, 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 extracted from the acceleration region through a beam extraction path entrance 82. The high-energy beam transport system 47, which transports the extracted beam from inside the main electromagnet 40 to outside, is arranged from inside to outside the main electromagnet 40.

[0032] The extraction control device 5000 has a control computer 5001, a synthesizer 5002, a signal amplifier 5003, and a radio frequency kicker power supply 5004, and upon receiving a beam irradiation instruction from the overall control device 400, creates a radio frequency signal to be applied to the radio frequency kicker 70 and inputs it to the radio frequency kicker 70.

[0033] The radio frequency kicker 70 is a device that applies a radio frequency voltage to the circulating beam passing through the inside of itself, and is an electrode that generates an electric field component that kicks the beam in the horizontal direction.

[0034] The control computer 5001 is a computer that calculates the relationship between the passing position of the particle 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 to be applied to the radio-frequency kicker according to the control signal from the overall control device 400.

[0035] The control computer 5001 is not limited to a configuration that calculates the relationship between the particle passing 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 passing position and the phase lead of the betatron oscillation per turn at the position of the high-frequency kicker 70 calculated by an external arithmetic device.

[0036] The synthesizer 5002 is a device having an electronic circuit that freely changes the frequency and waveform of a signal and outputs it, and synthesizes a high frequency wave in a corresponding frequency band based on a signal from the control computer 5001.

[0037] The signal amplifier 5003 is a signal amplifier and has the function of amplifying the signal generated by the synthesizer 5002 up to an amplitude of several kV at maximum.

[0038] The high frequency kicker power supply 5004 is a power supply having a maximum output of several tens of kW, and supplies power to the signal amplifier 5003 .

[0039] A peeler magnetic field region 44 and a regenerator magnetic field region 45, which are disturbance magnetic fields consisting of a dipole magnetic field and a multipole magnetic field, are formed inside the main electromagnet 40. For beam extraction, a radio-frequency kicker 70 is used, which generates an electric field component that kicks the beam horizontally, and the peeler magnetic field region 44 and the regenerator magnetic field region 45 are quadrupole magnetic fields that are asymmetrical when viewed from the direction of beam propagation, with the amplitude of betatron oscillation increased by the radio-frequency kicker 70.

[0040] Here, the movement of the beam from when it is injected into the accelerator 1 until when it is extracted will be briefly described.

[0041] First, 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 moves around in the main magnetic field while increasing its energy. As the beam is accelerated, the radius of curvature of its orbit increases, and the beam traces a spiral orbit from the center of the acceleration region outward.

[0042] Here, within the beam acceleration region, the orbit that the beam follows from the start of acceleration until it reaches its maximum energy (e.g., 230 MeV) is called the circular orbit. Of the circular orbits, the orbit through which the maximum-energy beam passes is called the maximum-energy beam orbit 80. The plane on which the circular orbit describes a spiral is called the orbital plane or orbital surface. Furthermore, when 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.

[0043] During this orbit, the charged particles of the beam oscillate in a direction perpendicular to the beam's orbit. This oscillation is called betatron oscillation, and the frequency of this oscillation 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 the 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 radio-frequency voltage is applied, resonance occurs and the amplitude increases rapidly.

[0044] The main magnetic field is a magnetic field with constant strength 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 direction. Under such a magnetic field, betatron oscillations occur stably in both the radial direction within the orbital plane of the beam and in the direction perpendicular to the orbital plane. The magnetic field is constant along the designed orbit. As a result, the designed orbit becomes circular, and the orbital radius and orbital time increase as the beam energy increases.

[0045] In such a system, particles that deviate slightly from the design orbit in the radial direction are subjected to a restoring force that returns them to the design orbit, while particles that deviate perpendicular to the orbital plane are also subjected to a restoring force from the main magnetic field in a direction that returns them to the orbital plane. In other words, if the magnetic field is appropriately reduced relative to the beam energy, particles that deviate from the design orbit will always experience a restoring force in the direction that tries to return them to the design orbit, and will oscillate near the design orbit. This makes it possible to stably orbit and accelerate the beam. This oscillation centered on the design orbit is called betatron oscillation. For a full-energy beam, the betatron frequency (horizontal tune) ν, parallel to the orbital plane and perpendicular to the orbit, is set to a value close to 1.

[0046] 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 the main magnetic field, on the orbital plane, only has a magnetic field component in a direction perpendicular to the orbital plane.

[0047] When the beam is accelerated to maximum energy in this main magnetic field, the RF acceleration voltage for accelerating the beam in acceleration gap 11 is stopped, and the beam orbits on maximum energy beam orbit 80. Then, when the beam enters RF kicker 70, which is installed on maximum energy beam orbit 80 and applies RF, RF voltage is applied, and the betatron oscillation amplitude of the beam increases.

[0048] The beam with increased betatron oscillation amplitude eventually reaches the peeler magnetic field region 44 and regenerator magnetic field region 45 located at a certain distance from the maximum energy beam orbit 80 on the outer periphery of the maximum energy beam orbit 80.

[0049] The beam that reaches the peeler magnetic field region 44 is kicked toward the outer periphery of the orbital plane, and the beam that reaches the regenerator magnetic field region 45 is kicked toward the inner periphery of the orbital plane. Here, "kicking" means deflecting the beam by applying an electric or magnetic field to the beam.

[0050] The beam is kicked by the quadrupole magnetic field component of the peeler magnetic field region 44, further increasing the betatron oscillation amplitude and increasing the turn separation. At the same time, the magnetic field of the regenerator magnetic field region 45 prevents the horizontal tune of the beam from fluctuating suddenly, preventing the beam from being lost due to the betatron oscillation diverging in the vertical direction, which is 90 degrees perpendicular to the horizontal direction, before being extracted. When sufficient turn separation is obtained, the beam enters the septum coil 43, is kicked out of the orbital plane, passes through the high-energy beam transport line 47, and is extracted to the outside of the accelerator 1.

[0051] The increase in turn separation due to the peeler magnetic field region 44 and the regenerator magnetic field region 45 is much greater than the increase due to the high frequency kicker 70 .

[0052] Therefore, by adjusting the radio frequency voltage applied by the radio frequency kicker 70, it is possible to adjust the amount of the beam circulating on the maximum energy beam orbit 80 that reaches the peeler magnetic field region 44 and the regenerator magnetic field region 45.

[0053] On the other hand, by stopping the application of high frequency to the high frequency kicker 70 during the beam extraction, the beam will not reach the peeler magnetic field region 44 and the regenerator magnetic field region 45, and the beam extraction from the accelerator 1 can be interrupted.

[0054] Therefore, by restarting the application of high frequency to the high frequency kicker 70, the beam can be extracted again.

[0055] 4 shows a cross-sectional configuration of the radio frequency kicker 70. The radio frequency kicker 70 is composed of a ground electrode 71 and a high-voltage electrode 72. The two electrodes are arranged facing each other, with the ground electrode 71 on the inner periphery and the high-voltage electrode 72 on the outer periphery, sandwiching the maximum energy beam orbit 80 therebetween.

[0056] The ground electrode 71 and high-voltage electrode 72 are shaped so that a radio-frequency electric field acts in a direction perpendicular to the orbit within the orbit plane, i.e., the ground electrode 71 and high-voltage electrode 72 are shaped so that they are approximately parallel to the curve of the maximum energy beam orbit 80. A metallic protrusion 73 can be attached to the ground electrode 71 to enhance the concentration of the radio-frequency electric field generated between the ground electrode 71 and high-voltage electrode 72. The high-voltage electrode 72, to which a radio-frequency voltage is applied, is supported and insulated.

[0057] Within 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 may be located anywhere on the maximum energy beam orbit 80, but for example, it should be located near the septum coil 43 as shown in Figure 3.

[0058] The regenerator magnetic field region 45 and the regenerator magnetic field region 44 are regions where multipole magnetic fields acting on the beam exist. These multipole magnetic fields include at least a quadrupole magnetic field component, but may also include a multipole magnetic field with more than four poles or a dipole magnetic field.

[0059] In the peeler magnetic field region 44, the magnetic field gradient is in the direction of weakening the main magnetic field toward the outer periphery in the radial direction, whereas in the regenerator magnetic field region 45, the magnetic field gradient is in the direction of strengthening the main magnetic field toward the outer periphery in the radial direction. Note that the peeler magnetic field region 44 can also be the region at the tip of the magnetic pole where the main magnetic field is weakened.

[0060] These peeler magnetic field region 44 and regenerator magnetic field region 45 are respectively arranged 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 .

[0061] Moreover, to prevent the beam from traveling into the peeler magnetic field region 44 or the regenerator magnetic field region 45 before the betatron oscillation amplitude is increased by the high-frequency kicker 70, the peeler magnetic field region 44 and the regenerator magnetic field region 45 are arranged 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 arranged upstream of the beam traveling direction, and the regenerator magnetic field region 45 is arranged downstream.

[0062] A plurality of magnetic pole pieces and / or coils made of magnetic material are fixedly arranged by a non-magnetic material in the vicinity of the pole piece region 44 and the regenerator magnetic field region 45 to form the desired multipole magnetic field.

[0063] For example, a multipole magnetic field is formed by multiple pole pieces and a dipole magnetic field is formed by coils for each of the pole piece region 44 and the regenerator magnetic field region 45. The multiple pole pieces and coils can be positioned close to each other or spaced apart.

[0064] These pole pieces and coils correspond to the magnetic poles that generate the peeler magnetic field region 44 and the regenerator magnetic field region 45 .

[0065] 5 shows an example of the arrangement of magnetic pole pieces in the peeler magnetic field region 44, as viewed from the arrows A-A' in Fig. 1. The magnetic pole pieces used include magnetic field gradient shims 36 that generate a magnetic field gradient in the peeler magnetic field region 44, and magnetic field correction shims 37 that cancel out unnecessary magnetic fields generated by the magnetic field gradient shims 36 on the inner side of the maximum energy beam orbit 80.

[0066] Furthermore, although Figure 5 has been explained using the peeler magnetic field region 44 as an example, 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.

[0067] Figure 6 shows the distribution of the main magnetic field on the r-axis in Figure 5. Up to the maximum energy beam orbit 80, the magnetic field gradient ∂B / ∂r drops slightly, allowing the beam to orbit stably. However, in the peeler magnetic field region 44, the magnetic field gradient drops sharply, making the beam unstable and kicking it toward the outer periphery of the orbital plane. In addition, in the regenerator magnetic field region 45, the magnetic field gradient rises sharply, in contrast to the peeler magnetic field region 44, making the beam unstable and kicking it toward the inner periphery of the orbital plane.

[0068] 7A and 7B are diagrams illustrating the beam extraction procedure. Fig. 7A 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. Fig. 7B is a graph showing the relationship between the current of the incident beam, the current of the extracted beam, and time T.

[0069] 7A, one acceleration cycle 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 lapse of time t1 from the injection of the beam, the radio frequency capture of the beam ends.

[0070] The trapped beam, i.e., the beam that is ready for acceleration among the injected beams, begins to accelerate by the acceleration voltage Vacc (time T3). When the beam reaches the desired extraction energy, for example, the maximum energy of 230 MeV, the acceleration RF power is shut off (time T4), and after a time t2 has elapsed, the acceleration RF voltage Vacc is turned off. At the same time, the application of the RF voltage Vext to the RF kicker 70 begins (time T5). Note that the start of application of the RF voltage Vext to the RF kicker 70 (time T5) does not have to be exactly the same time as the acceleration RF voltage Vacc is turned off.

[0071] The application of the high frequency voltage Vext may start immediately before, simultaneously with, or immediately after the accelerating high frequency voltage is turned off (time T4), or may start immediately before or immediately after the accelerating high frequency voltage Vacc is turned off.

[0072] The high-frequency voltage of the high-frequency kicker 70 rises quickly, with a response of several microseconds, if the high-frequency kicker 70 is not a resonator structure and is designed so that the capacitance is an appropriate value. Here, 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. The method for selecting the high-frequency frequency required to generate this resonance will be described later.

[0073] The beam is kicked toward the outer periphery when it passes through the peeler magnetic field region 44, and is kicked toward the inner periphery when it passes through the regenerator magnetic field region 45. Because both the peeler magnetic field region 44 and the regenerator magnetic field region 45 have a magnetic field gradient in the radial direction, the amount of kick gradually increases as the beam makes multiple orbits, and the turn separation increases. In other words, the turn separation is increased by utilizing the resonance condition of betatron oscillation, 2νr=2.

[0074] A septum coil 43 is installed at the beam extraction path entrance 82. When a turn separation that greatly exceeds the thickness of a coil conductor (not shown) installed on the inner periphery of the septum coil 43 is obtained, the beam is guided into the septum coil 43, is sufficiently deflected, and is guided to the high-energy beam transport line 47 and extracted.

[0075] Immediately after the start of application of the radio frequency voltage to the radio frequency kicker 70 (time T5), the time until the beam is extracted can be shortened by applying as large a radio frequency voltage as possible and quickly increasing the amplitude of the beam. Then, immediately 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 to adjust the amount of the beam traveling into the peeler magnetic field region 44 and the regenerator magnetic field region 45, thereby enabling precise control of the beam extraction current.

[0076] Instead of lowering the radio frequency voltage Vext, 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 utilizes the property that the betatron frequencies of the charged particles contained in the beam vary over a certain distribution (tune spread). By changing the frequency of the radio frequency, the beam extraction current can be changed by adjusting it to a certain band in the distribution of the frequencies of the charged particles that cause resonance. Also, instead of lowering the radio frequency voltage Vacc, it may be cut off.

[0077] Then, after a time t4 has elapsed since the start of beam extraction (time T6), the application of the radio frequency voltage Vext to the radio frequency kicker 70 is stopped, thereby stopping the beam extraction (time T7). By adjusting this time t4, the beam extraction time can be controlled.

[0078] In particle beam therapy, it is necessary to irradiate the tumor to be irradiated with a beam without exceeding the allowable range of the irradiation dose predetermined in the treatment plan, etc. Therefore, when changing the irradiation layer, etc., after the beam extraction is stopped (time T8), it is possible to apply as large a radio frequency voltage as possible and irradiate the beam remaining in the accelerator 1 to the cutoff device 350 to prevent excessive dose irradiation. This is called beam discard operation, and continues until time t5 has passed, at which time the number of beam particles remaining in the accelerator 1 becomes almost zero. The beam control technology of the present invention can be applied not only during beam extraction but also during such beam discard operation.

[0079] Because the amount of beam charge extracted varies for each pulse due to factors such as the thermal stability of the ion source 12, and because temporal stability of the beam current is important for particle beam therapy, it is necessary to control the intensity of the beam extracted from the accelerator 1. Below, the behavior of the beam particles in phase space at the radio frequency kicker 70 and the resonance conditions will be described in detail with reference to FIG.

[0080] 8 explains 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. Also, 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 displacement y of the beam particle in the horizontal direction as viewed from the beam center and the amount of change py in the beam orbit direction, and the beam center 501 corresponds to the origin.

[0081] In the accelerator 1, a peeler magnetic field region 44 exists in the positive direction of displacement y as shown in Figure 8. The separatrix 502 is a region in phase space, representing the region where the beam circulates stably. Inside the separatrix 502, the beam particles circulate stably, but outside the separatrix 502, the beam diverges. The beam is extracted by bringing the beam particles inside the separatrix 502 to the outside of the separatrix 502. The beam particles 500 move inside the separatrix 502.

[0082] The phase angle θ and phase radius J are parameters that represent the position of the beam particle 500 in the 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 betatron oscillation of the particle. One period of the betatron oscillation corresponds to the particle going around once in the above-mentioned phase space.

[0083] After the beam reaches its maximum energy, if no radio frequency voltage is applied to the radio frequency kicker 70, the beam particle 500 orbits in the phase space 5500 with a constant phase radius J. The phase advance angle Δθ, which is the amount of change in the phase angle θ that occurs each time the beam orbits in the accelerator 1, is Δθ=2πν radians, where ν is the horizontal tune of the beam particle 500.

[0084] When extracting the beam, a radio-frequency voltage is applied to the radio-frequency kicker 70 at a frequency fext. At this time, when fext is approximately equal to the product Δνr × frev of the decimal part Δν of the horizontal tune v of the beam particle 500 and the circular frequency frev of the maximum-energy beam, the amplitude of the horizontal betatron oscillation increases resonantly. That is, 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. As the beam particle 500 approaches the peeler magnetic field region 44, it is kicked toward the outer periphery, i.e., in a direction where the displacement r from the beam center becomes larger, due to the effect of the magnetic field, and is then extracted by entering the septum coil 43.

[0085] 9, a method for determining the high frequency to be input to the high frequency kicker 70 will be described. FIG. 9 shows the frequency and amplitude of the high frequency voltage to be applied to the high frequency kicker 70.

[0086] In general, the horizontal betatron tune ν of a particle varies depending on the magnetic field gradient on the orbit through which the particle passes, so that the tune spread is 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 in a band with a certain degree of width.

[0087] The extraction control device 5000 calculates the minimum value vmin and maximum value vmax of the betatron tune v in the beam and the high frequency frequencies corresponding to each tune based on the results of a simulation based on electromagnetic field analysis.

[0088] When the high frequency frequencies corresponding to the minimum value vmin and maximum value vmax of the betatron tune v are fmax and fmin, as shown in Fig. 9, Nrf = [(fmax - fmin) / Δf] + 1 high frequency rf1, rf2, ..., rfNrf is set at an appropriate frequency interval Δf in the band from fmin to fmax, and a high frequency waveform is created by inputting this to synthesizer 5002, and then inputting it to high frequency kicker 70. Here, [(fmax - fmin) / Δf] represents an integer not exceeding (fmax - fmin) / Δf.

[0089] Generally, the tune of the beam particles fluctuates during the beam extraction process, so the frequency interval Δf of the applied high frequency must be sufficiently small relative to the fluctuation in the high frequency resonance frequency corresponding to the tune fluctuation, and is on the order of several kHz to several tens of kHz. At this time, the power Wrf supplied by the high frequency kicker power supply 5004 is expressed by the following equation (1):

[0090]

[0091] In the formula (1), V1, V2, ... are the amplitudes of the high frequency waves rf1, rf2, ..., rfNrf, and R is the impedance of the high frequency kicker 70.

[0092] The beam particle 500 receives a kick expressed by the following equation (2) at time t due to an electric field caused by a voltage of frequency f and amplitude V applied to the high frequency kicker 70.

[0093]

[0094] In equation (2), v is the velocity of the beam particle, ρ is the radius of the maximum energy beam orbit 80, B is the average magnetic field on the beam particle orbit, and L is the electrode length of the high frequency kicker 70.

[0095] Since high-power power supplies are expensive and from the viewpoint of reducing the operating costs of the accelerator 1, it is important to suppress the output of the radio-frequency kicker power supply 5004. However, in order to increase the betatron amplitude of the beam particle 500, it is necessary to provide a radio-frequency amplitude Vext of frequency fext corresponding to the horizontal tune ν with sufficient strength.

[0096] Next, we will explain the fluctuation of the betatron tune during the beam extraction process using Figure 10. Figure 10(a) shows the relationship between the tune and the position at the RF kicker point of the beam particle in an accelerator that does not generally have a peeler magnetic field region or a regenerator magnetic field region, such as a synchrotron. Here, r represents the radial outer side of the beam orbit, and the beam center is the origin.

[0097] In accelerators such as synchrotrons, 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, i.e., the phase advance angle Δθ in phase space per revolution, mainly depends on the amplitude of the betatron oscillation. Therefore, as the amplitude of the betatron oscillation of a particle increases, the betatron tune also changes, and the corresponding radio frequency changes.

[0098] Therefore, in order to move the beam particles outside the separatrix using a radio frequency electric field, as described in Patent Document 1, by applying a radio frequency voltage in the frequency band from fc to fo corresponding to the tunes νc and νo of the particles at the center of the beam and the edge of the separatrix, with amplitudes Vc and Vo of the radio frequency at frequencies fc and fo being Vc > Vo, particles closer to the beam center are more likely to be kicked, and the particles tend to gather near the separatrix, making it easier to control the beam extraction. This achieves the effects described in Patent Document 1, namely, reduced cost of the main electromagnet power supply and stabilization of the extracted beam.

[0099] 10(b) shows the relationship between the position of the beam particle and the tune in the vicinity of the peeler magnetic field region 44 in the accelerator 1 of the present invention, in which the quadrupole magnetic field distribution on the beam orbit is asymmetric between the left and right in the horizontal direction as viewed from the direction of beam propagation. r uses the same coordinates as r in FIG. 5, with the beam center being the origin.

[0100] Since 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 advance angle ν in phase space, increases or decreases.

[0101] Therefore, 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 particle 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's orbit and the peeler magnetic field region 44 fluctuates with each revolution due to betatron oscillation, so the particle tune fluctuates.

[0102] The principle of beam control of the present invention will be explained below. Figure 11 shows an example of the relationship between the frequency fext required to generate resonance of betatron oscillation, the center position of the peeler magnetic field region 44, and the closest distance l of the beam particle trajectory. Here, the origin is the center of the peeler magnetic field region 44.

[0103] In the present invention, the high frequency kicker 70 is preferably inserted into the beam extraction path when the beam is irradiated onto the irradiation target or when the remaining beam is discarded, and the strength of each frequency component of the electric field applied to the high 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 advance of the betatron oscillation per turn at the position of the high frequency kicker 70.

[0104] In this case, it is desirable to make 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 high-frequency kicker 70.

[0105] The frequency fext required to generate resonance changes rapidly as the beam particle passage position approaches the peeler magnetic field region 44. This is because the beam particle is kicked by the magnetic field in the vicinity of the peeler magnetic field region 44. Since the kick is much stronger than the kick caused by the electric field of the high-frequency kicker 70, the beam can be emitted even if the kick caused by the electric field of the high-frequency kicker 70 is weaker as the beam particle approaches the peeler magnetic field region 44.

[0106] In the present invention, 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 due to the peeler magnetic field region 44. This makes it possible to give a constant kick regardless of the position of the particle passing through in the beam, reducing the power required for beam extraction without excess or deficiency of the kick amount, and allowing the use of an inexpensive radio frequency kicker power supply 5004.

[0107] The principle of determining the amplitude of the radio frequency voltage to uniformly apply a kick to the beam is explained below. With respect to the amount of kick (kick) received by the beam particle, the kick due to a single radio frequency applied to the radio frequency kicker 70 is expressed as the derivative (dkick / df) with respect to the frequency (f) when the number (Next) of applied frequencies is sufficiently large. This is expanded as shown in the following equation (3).

[0108]

[0109] Here, in 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.

[0110] In order to make the kick received uniform even when the positional relationship between the beam particle trajectory and the peeler magnetic field region 44 fluctuates for each revolution due to betatron oscillation, dkick / dl must be kept constant. df(l) / dl is the first-order derivative of the relationship between 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 the following equation (4), and in order to make the left-hand side a constant value, the kick dkick / df from the single high frequency applied to the high frequency kicker 70 can be made a quantity inversely proportional to df(l) / dl.

[0111]

[0112] That is, the amplitude of the high frequency voltage of frequency fext applied to the high frequency kicker 70 can be set to a×df(l) / dl, where a is a proportionality constant, and the amount of current of the extracted beam can be controlled by controlling a.

[0113] FIG. 12 shows the procedure for controlling beam extraction using the beam control method of the present invention.

[0114] (Step S1) Before the accelerator 1 starts operating, preferably during its manufacture or installation 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 using the Runge-Kutta method based on the magnetic field measurement results on the beam trajectory of the maximum energy of the accelerator 1.

[0115] In this way, it is desirable to calculate 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 by calculating the magnetic field strength of the peeler magnetic field region 44 measured before the accelerator 1 is actually operated.

[0116] Specifically, the above numerical simulation is performed on n particles until the particles make one revolution inside the accelerator, and the orbits of the beam particles and the changes in particle positions in phase space before and after the beam particles make one revolution inside the accelerator are calculated from the simulation results, thereby calculating the closest distances r1, r2, ..., rn between the center position of the peeler magnetic field region 44 and the orbits of the beam particles, and the phase advances Δθ1, Δθ2, ..., Δθn in phase space generated by the particles making one revolution inside the accelerator. The number of particles n calculated here can be around 10,000.

[0117] (Step S2-1) The calculated data sets (l1, Δθ1), ..., (ln, Δθn) 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. By interpolating df(l) / dl at each closest distance l1, l2, ..., rn, a function V(f) is created that determines the amplitude of the high-frequency voltage of frequency fext to be applied to the high-frequency kicker 70.

[0118] (Step S2-2) The maximum values ​​Δθmax and Δθmin of the phase advances Δθ1, Δθ2, ..., Δθn in the phase space of the simulation results are used to determine the high-frequency frequency band to be applied to the high-frequency kicker 70. Frequencies are selected from the above-mentioned frequency band at frequency intervals Δf 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.

[0119] (Step S3) The above-mentioned frequencies are substituted into the function V(f) that determines the amplitude of the above-mentioned high-frequency voltages to calculate the relative amplitudes Vref1, Vref2, ... of the 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.

[0120] After this, the accelerator will start operating.

[0121] (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 simultaneously issues an instruction to the synthesizer 5002 to synthesize a high-frequency signal.

[0122] (Step S5) Based on instructions from the control computer 5001, the synthesizer 5002 synthesizes high-frequency signals based on information on the high-frequency frequencies fext1, fext2, . . . and the relative amplitudes Vref1, Vref2, .

[0123] (Step S6) Based on the scale signal from the control computer 5001, the high frequency signal is amplified by a times in the signal amplifier 5003, and the signal is applied to the high frequency kicker 70, starting beam extraction.

[0124] (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.

[0125] Steps S1, S2-1, and S2-2 may be executed by a computer separate from the control computer 5001 and input to the control computer 5001. Steps S2-1 and S2-2 may be executed in parallel, or step S2-2 may be executed after step S2-1 is completed.

[0126] 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 orbit of the beam particle can be determined by providing position detectors 44A and 44B in the accelerator 1A as shown in Fig. 13, and detecting the passage position and passage time of the beam particle under the peeler magnetic field region 44 (used to determine the phase advance of the betatron oscillation per turn at the position of the high-frequency kicker 70) using these position detectors 44A and 44B, and then determining the relationship in a control computer 5001A in the extraction control device 5000A. Note that although two detectors, 44A and 44B, are provided in this embodiment, the number of detectors can be one or more. In the case of the accelerator 1A shown in Fig. 13, the processing from step S4 onwards described above can be performed while performing the same processing as in step S1.

[0127] Furthermore, the synthesis of the high frequency signal by the synthesizer 5002 in step S4 may be performed before the accelerator 1 is put into operation.

[0128] Furthermore, the relationship between the beam particle passage position 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 can be modified over time. In this case, the process of step S1 can be executed when reviewing the operation. This allows for highly accurate beam extraction over a long period of time.

[0129] Next, the effects of this embodiment will be described.

[0130] The accelerator 1 of this embodiment described above has a radio-frequency kicker 70 that generates an electric field with a 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 and in which the amplitude of betatron oscillation is increased by the radio-frequency kicker 70.The intensity of each frequency component of the electric field applied to the radio-frequency kicker 70 is controlled based on the relationship between the passage position of the beam particles 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.

[0131] This allows the beam particles to be given just the right amount of kick due to the asymmetric magnetic and radio-frequency electric fields, making it possible to extract the entire beam even with lower radio-frequency power. This means that the cost and power consumption of the radio-frequency power supply used for beam extraction can be reduced compared to conventional methods, making it possible to realize an accelerator that can be operated with even less energy.

[0132] In addition, the control computer 5001 is provided to calculate the relationship between the particle passing position and the phase advance of the betatron oscillation per turn at the position of the high-frequency kicker 70, or to receive input of the relationship from outside, thereby making it possible to apply an electric field to the high-frequency kicker 70 at a more appropriate timing.

[0133] Furthermore, by calculating the relationship from the peeler magnetic field region 44 measured before the accelerator 1 is actually put into operation, the relationship can be determined in advance, thereby realizing more accurate beam extraction.

[0134] Furthermore, by inserting the beam into the beam emission path when irradiating the irradiation target or discarding the remaining beam, the beam can be emitted reliably.

[0135] Furthermore, based on the relationship, by inputting an amount proportional to the inverse of the amount of change and by equalizing the amount of kick received by the beam, it is possible to reliably extract the entire amount of the beam.

[0136] <Others> The present invention is not limited to the above-described embodiments, and various modifications and applications are possible. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations.

[0137] DESCRIPTION OF SYMBOLS 1, 1A...Accelerator 2...Beam transport device 3...Irradiation device 3a...Dosimetry device 4...Treatment couch 5...Patient 7...Treatment planning device 11...Acceleration gap 12...Ion source 36...Magnetic field gradient shim 37...Magnetic field correction shim 40...Main electromagnet 43...Septum coil 44...Pier magnetic field region 44A, 44B...Position detector 45...Regenerator magnetic field region 47...High energy beam transport system 50...Irradiation control device 60...Treatment plan database 70...Radio frequency kicker 71...Ground electrode 72...High voltage electrode 73...Protrusion 80...Maximum energy beam trajectory 82...Beam extraction path entrance 350...Shutter device 400...Overall control device 500...Beam particle 501...Beam center 502...Separatrix 1000...Particle beam therapy system 5000, 5000A...Extraction control device 5001, 5001A...Control computer (calculating device) 5002...Synthesizer 5003...Signal amplifier 5004...High frequency kicker power supply 5500...Phase space

Claims

1. A circular accelerator having electrodes that generate an electric field with a component that kicks the beam horizontally, and magnetic poles that generate a quadrupole magnetic field that is asymmetrical when viewed from the direction of beam progression, with the amplitude of betatron oscillation increased by the electrodes, and which controls the strength of each frequency component of the electric field applied to the electrodes based on the relationship between the position at which the beam particles pass under the magnetic field and the phase advance of the betatron oscillation per turn at the position of the electrodes.

2. A circular accelerator according to claim 1, comprising a calculation device that calculates the relationship between the particle passage position and the phase advance of betatron oscillation per turn at the electrode position, or that receives input of said relationship from an external source.

3. A circular accelerator according to claim 1 or 2, wherein the relationship is determined by calculation from a magnetic field measured before the circular accelerator is actually put into operation.

4. A circular accelerator according to any one of claims 1 to 3, wherein the beam is inserted into the beam extraction path when the beam is irradiated onto an irradiation target or when the remaining beam is discarded.

5. A circular accelerator according to any one of claims 1 to 4, wherein an amount proportional to the reciprocal of the amount of change based on said relationship is input.

6. A circular accelerator according to any one of claims 1 to 5, wherein the amount of kick received by the beam is made uniform.

7. A particle beam therapy system comprising: the circular accelerator according to any one of claims 1 to 6; and an irradiation device that emits the beam extracted from the circular accelerator.

8. A method for operating a circular accelerator having electrodes that generate an electric field with a 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 progression, with the amplitude of betatron oscillation increased by the electrodes, wherein the strength of each frequency component of the electric field applied to the electrodes is controlled based on the relationship between the position at which the beam particles pass under the magnetic field and the phase advance of the betatron oscillation per turn at the position of the electrodes.

9. A method for operating a circular accelerator according to claim 8, comprising calculating the relationship between the particle passing position and the phase advance of the betatron oscillation per turn at the electrode position.

10. A method for operating a circular accelerator according to claim 8 or 9, wherein the relationship is determined by calculation from a magnetic field measured before actual operation of the circular accelerator.

11. A method for operating a circular accelerator according to any one of claims 8 to 10, wherein the beam is inserted into the beam extraction path when irradiating an irradiation target or discarding the remaining beam.

12. A method for operating a circular accelerator according to any one of claims 8 to 11, wherein an amount proportional to the reciprocal of the amount of change is input based on the relationship.

13. A method for operating a circular accelerator according to any one of claims 8 to 12, wherein the amount of kick received by the beam is made uniform.

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