Accelerator, particle beam therapy system and control method

Abstract

To provide an accelerator capable of taking out charged particle beams with precision having desired energy.SOLUTION: An acceleration voltage measurement circuit 10 outputs acceleration voltage signals Vacc as measurement signals of a measured high-frequency voltage for acceleration excited in an acceleration cavity 9. A low-power high-frequency control system 25 inputs RF power for constant frequency control, which is included in a range of a resonant frequency of the acceleration cavity 9, to the acceleration cavity 9 as high-frequency power. The low-power high-frequency control system 25 is configured so as to, when a phase difference between the acceleration voltage signal Vacc and the high-frequency power for control is within a specified value, input High-frequency power for acceleration synchronized with the acceleration frequency, which is the frequency of the acceleration voltage signal Vacc to the acceleration cavity 9 as high-frequency power by feedback control, and after that, when the acceleration frequency reaches an output frequency Fext, stop input of the high-frequency power for acceleration to the acceleration cavity 9.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to an accelerator, a particle beam therapy system, and a control method. [Background technology]

[0002] As an accelerator for accelerating and extracting a charged particle beam, a circular accelerator that accelerates the charged particle beam by applying an accelerating electric field whose frequency is modulated over time in a main magnetic field whose strength is constant over time has attracted attention. This type of circular accelerator can generate the main magnetic field using a superconducting coil, which is advantageous for miniaturization and cost reduction, and is particularly applied to particle beam therapy systems.

[0003] In a circular accelerator, a tuning cavity may be used as an accelerating cavity that excites an accelerating high-frequency electric field to accelerate a charged particle beam. In this case, the capacitance or inductance of the accelerating cavity is changed over time to modulate the resonant frequency of the accelerating cavity over time. At this time, the high-frequency power input to the accelerating cavity needs to be tuned to the accelerating cavity (having a frequency that is approximately the same as the resonant frequency of the accelerating cavity). One technique for modulating the resonant frequency of the accelerating cavity is to install a rotating capacitor having a pair of opposing rotor-stator electrodes in the accelerating cavity as a modulator that modulates the accelerating cavity (see Patent Document 1).

[0004] Examples of circular accelerators include a synchrocyclotron and the eccentric orbit accelerator described in Patent Document 1. In a synchrocyclotron, the extraction energy, which is the energy of the extracted charged particle beam, is fixed, so the high frequency power input to the accelerating cavity is cut off a certain time after the beam is injected. On the other hand, in the central orbit accelerator described in Patent Document 2, the extraction energy is variable, so the high frequency power input to the accelerating cavity needs to be cut off at an appropriate timing according to the extraction energy. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2010 / 0045213 [Patent Document 2] JP 2019-133745 A Summary of the Invention [Problem to be solved by the invention]

[0006] In an accelerator that uses a tuned cavity as the accelerating cavity, the RF power input to the accelerating cavity needs to be tuned to the accelerating cavity. However, errors occur in the modulation pattern of the accelerating cavity depending on the manufacturing tolerance and control variation of the modulator, as well as the temperature of the accelerating cavity.

[0007] In the technology described in Patent Document 2, a programmed frequency pattern signal is input to the accelerating cavity via a radio frequency power amplifier as the radio frequency power for acceleration, so it is strongly affected by errors in the modulation pattern, causing errors in the energy of the charged particle beam. In addition, since the method described in Patent Document 1 is for synchrocyclotrons, when it is applied to an eccentric orbit accelerator in particular, it is not possible to cut off the radio frequency power for acceleration at an appropriate timing according to the desired extraction energy.

[0008] An object of the present invention is to provide an accelerator, a particle beam therapy system, and a control method that are capable of extracting a charged particle beam having a desired energy with high precision. [Means for solving the problem]

[0009] An accelerator according to one aspect of the present disclosure is an accelerator that accelerates a charged particle beam while circulating it with a time-constant main magnetic field and acceleration radio frequency voltage, and includes an acceleration cavity that excites the acceleration radio frequency voltage corresponding to a time-varying resonance frequency using input radio frequency power, a measurement unit that outputs a measurement signal measuring the acceleration radio frequency voltage, and a control unit that inputs, as the radio frequency power, control radio frequency power having a constant frequency included in the range of the resonance frequency to the acceleration cavity, and when a phase difference between the measurement signal and the control radio frequency power falls within a predetermined value, inputs, as the radio frequency power, acceleration radio frequency power synchronized with an acceleration frequency that is the frequency of the measurement signal by feedback control to the acceleration cavity, and when the acceleration frequency reaches a required value, stops inputting the acceleration radio frequency power to the acceleration cavity. Effect of the Invention

[0010] According to the present invention, it is possible to extract a charged particle beam having a desired energy with high precision. [Brief description of the drawings]

[0011] [Figure 1] 1 is a perspective view illustrating an example of the appearance of a circular accelerator according to an embodiment of the present disclosure. [Diagram 2] 1 is a cross-sectional view showing an example of the cross-sectional configuration of a circular accelerator according to an embodiment of the present disclosure. [Diagram 3] 1 is a longitudinal sectional view showing an example of the longitudinal sectional configuration of a circular accelerator according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a diagram showing an example of orbits of a charged particle beam according to energy. [Diagram 5] FIG. 2 is a diagram illustrating an example of the configuration of a low-power high-frequency control system. [Figure 6] 10 is a timing chart for explaining an example of a control sequence of a low power high frequency control system. [Figure 7] 1 is a diagram illustrating an example of the configuration of a particle beam therapy system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. EXAMPLES

[0013] 1 to 3 are diagrams showing an example of a circular accelerator according to an embodiment of the present disclosure. The accelerator 100 shown in FIGS. 1 to 3 is a circular accelerator that accelerates a charged particle beam (hereinafter, sometimes simply referred to as a beam) while circulating it by applying an accelerating high frequency voltage that has been frequency modulated in a main magnetic field whose intensity is constant over time. In this embodiment, the accelerator 100 accelerates a proton beam using protons as charged particles to any energy between 70 MeV and 235 MeV and emits it. However, the charged particle beam may be a heavy particle beam using helium and carbon, and the extraction energy, which is the energy of the beam to be emitted, is not limited to the range between 70 MeV and 235 MeV. In addition, the accelerator 100 is suitable for a particle beam therapy system (see FIG. 7), but is not limited to that application.

[0014] FIG. 1 is a perspective view showing the appearance of accelerator 100, FIG. 2 is a cross-sectional view showing the configuration of a cross section of accelerator 100 cut along a vertical central plane, and FIG. 3 is a vertical cross-sectional view showing the configuration of a cross section of accelerator 100 cut along line b-b' in FIG. 2.

[0015] The accelerator 100 has a main electromagnet 40 that can be divided into an upper part and a lower part with a central plane D in between, and an acceleration region 101, which is a substantially cylindrical space for accelerating a beam, is formed inside the main electromagnet 40. The acceleration region 101 is formed substantially symmetrically above and below the central plane D, and is evacuated.

[0016] The main electromagnet 40 has a yoke 41, a main coil 42, and a main magnetic pole 43. The yoke 41 forms the outer shell of the main electromagnet 40, and defines an acceleration region 101 inside. The main coils 42 are annular superconducting coils, and are disposed above and below the central plane D. Each of the main coils 42 is disposed along the inner wall of the yoke 41. A cryostat 50, which is a cooling mechanism for cooling the main coil 42 to a certain temperature (the temperature at which the main coil 42 exhibits complete diamagnetism) or lower, is disposed around the main coil 42. The main magnetic poles 43 are disposed on the inner periphery side of the main coil 42, above and below the central plane D.

[0017] When a current is supplied to the main coil 42, a time-constant magnetic field called the main magnetic field is excited in the acceleration region 101 by the main magnetic pole 43, and the beam revolves on the orbital plane of the acceleration region 101 due to the influence of the main magnetic field. At this time, the beam revolves in a different orbit for each energy. Hereinafter, each orbit for each energy in which the beam revolves is called an orbit. In this embodiment, the main electromagnet 40 is formed so that the center of the orbit of the beam is eccentric (displaced from the physical center of the acceleration region 101) (see FIG. 4). In other words, the accelerator 100 of this embodiment is an eccentric orbit type accelerator. Also, FIG. 2 shows a maximum energy orbit 61 in which the beam with the maximum energy revolves, and a minimum extraction energy orbit 62 with an energy of 70 Mev, among the orbits.

[0018] An ion source 51 is installed above the main electromagnet 40 to generate a beam to be injected into the acceleration region 101 inside the main electromagnet 40. The ion source 51 is, for example, an ECR (Electron Cyclotron Resonance) ion source. The ion source 51 is connected to an ion injection unit 53 in the acceleration region 101 via a low-energy beam transport system 52. As a result, the beam generated by the ion source 51 is injected into the acceleration region 101 from the ion injection unit 53 via the low-energy beam transport system 52. In this embodiment, the ion injection unit 53 is disposed on the side of the beam ejection path entrance 82, which is an entrance of a magnetic channel 81 for extracting the beam to the outside, rather than the physical center O of the acceleration region 101 on the center line A passing through the center of the accelerator 100. The ion source 51 may be disposed inside the acceleration region 101. In this case, a PIG (Penning Ionization Gauge) type ion source or the like is suitable as the ion source 51.

[0019] 1 and 2, the yoke 41 is provided with a plurality of through holes. For example, the yoke 41 is provided with a beam through hole 71, a coil through hole 72, a vacuum through hole 73, and a high-frequency system through hole 74 on the central plane D of the main electromagnet 40.

[0020] The beam through-hole 71 is a through-hole for ejecting a beam, and is provided with a high-energy beam transport system 80 for extracting and ejecting the beam from inside the yoke 41 to the outside. The high-energy beam transport system 80 is connected to a magnetic channel 81. The coil through-hole 72 is a through-hole for ejecting various coils (such as the main coil 42) provided inside the yoke 41 to the outside. The vacuum through-hole 73 is a through-hole for drawing a vacuum in the acceleration region 101. The radio frequency system through-hole 74 is a through-hole for inserting the acceleration cavity 9.

[0021] The accelerating cavity 9 is a member that excites an accelerating radio frequency voltage for accelerating the beam injected from the ion injection part 53 into the acceleration region 101. In this embodiment, the accelerating cavity 9 is a λ / 2 resonant cavity, and has a dee electrode 12, a dummy dee electrode 13, an inner conductor 14, an outer conductor 15, and a rotating capacitor 30.

[0022] The dee electrode 12 is a hollow electrode through which the beam passes, and has a generally sector-shaped shape with a predetermined spread angle, with a vertex at a point near the ion injection section 53. The inner conductor 14 is a conductor connected to the dee electrode 12 and extending from the dee electrode 12 to the outside of the main electromagnet 40. The outer conductor 15 is a conductor that surrounds the dee electrode 12 and the inner conductor 14. The dummy dee electrode 13 is an electrode at earth potential, and is connected to the outer conductor 15. The dummy dee electrode 13 is disposed opposite the dee electrode 12, and an acceleration gap 11 in which an accelerating high-frequency voltage is excited is formed between the dee electrode 12 and the dummy dee electrode 13.

[0023] The rotating capacitor 30 is a modulator for modulating the resonance frequency of the acceleration cavity 9. Specifically, the rotating capacitor 30 changes the capacitance according to the rotation angle of a rotating electrode (not shown) rotated by a motor 31, thereby changing the resonance frequency of the acceleration cavity 9 over time. The acceleration cavity 9 excites an acceleration high-frequency voltage corresponding to the time-varying resonance frequency to the acceleration gap 11. The rotating capacitor 30 or the motor 31 is provided with a detection unit (not shown) that detects the rotation angle of the rotating electrode and outputs it as an angle signal. The acceleration gap 11 is formed according to the orbital shape of the beam. In this embodiment, the number of harmonics is 1, that is, the orbital frequency at which the beam orbits and the acceleration frequency, which is the frequency of the acceleration high-frequency voltage (more specifically, the frequency of the acceleration electric field due to the acceleration high-frequency voltage), are approximately the same.

[0024] In addition, the accelerating cavity 9 is connected to a low-power high-frequency control system 25 via an input coupler 20, and a high-frequency power amplifier 7 and an input high-frequency measurement circuit 8 are provided between the input coupler 20 and the low-power high-frequency control system 25.

[0025] The low-power radio-frequency control system 25 outputs low-power radio-frequency power. The radio-frequency power amplifier 7 amplifies the radio-frequency power output from the low-power radio-frequency control system 25 and inputs it to the accelerating cavity 9 via the input coupler 20. The input coupler 20 is a device for inputting radio-frequency power to the accelerating cavity, and is connected to the inner conductor 14 of the accelerating cavity 9 by electrostatic or magnetic coupling. The accelerating cavity 9 excites an accelerating radio-frequency voltage in the accelerating gap 11 by the radio-frequency power input via the input coupler 20, and generates an accelerating electric field that accelerates the beam by the accelerating radio-frequency voltage. The input radio-frequency measurement circuit 8 measures the radio-frequency power input to the accelerating cavity 9, as described later.

[0026] In the accelerator 100 described above, the beam of charged particles generated in the ion source 51 is injected from the ion injection section 53 through the low-energy beam transport system 52 into the acceleration region 101 formed inside the main electromagnet 40. The injected beam is accelerated by the accelerating electric field excited in the accelerating cavity 9, and travels around in the main magnetic field while increasing in energy. As the energy of the beam increases, the radius of curvature of the beam's orbit increases, so the beam describes a spiral orbit.

[0027] In this embodiment, the orbit of the beam for each energy level is an eccentric orbit. The main magnetic field that realizes the eccentric orbit will be described below.

[0028] The main magnetic field may be a magnetic field whose strength is constant in the circumferential direction of the orbit, or may be an AVF (Azimuthal Varying Field) type magnetic field whose strength varies in the circumferential direction. In either case, the main magnetic field is an anisochronous magnetic field and is generated so as to satisfy the beam stability condition. The beam stability condition is that the value of n expressed by the following formula (1) is greater than 0 and less than 1.

number

[0029] When the beam stabilization condition is satisfied, a beam that is slightly displaced from the orbit in the radial direction receives a restoring force from the main magnetic field in a direction that returns the beam to the orbit, and a beam that is displaced in a direction perpendicular to the orbital plane receives a restoring force from the main magnetic field in a direction that returns the beam to the orbital plane. In other words, the beam stably orbits and accelerates while oscillating betatronically near the orbit. In addition, for beams of all energies, the betatron frequency (horizontal tune) ν r becomes a value close to 1. The main magnetic field is formed by the main pole 43 and the trim coil and pole piece (neither of which are shown) installed on the surface of the main pole 43, and these components are arranged symmetrically above and below the orbital plane. Therefore, on the orbital plane, the main magnetic field only has a component in a direction perpendicular to the orbital plane.

[0030] Fig. 4 is a diagram showing orbits of beams circulating in the main magnetic field according to their energies. In Fig. 4, the vertical axis is the axis pointing from the beam extraction path entrance 82 to the inner conductor 14 of the acceleration cavity 9, and the origin 0 is the position of the ion injection part 53. Fig. 4 also shows an orbit 200 of a beam with a maximum energy of 235 MeV located at the outermost position, and 50 types of orbits with the magnetic rigidity of the beam differing from that orbit by 0.04 Tm each.

[0031] 4, in the eccentric orbit accelerator 100, when the beam energy is low, the orbit 200 approximates a concentric orbit centered near the ion injection unit 53, similar to a cyclotron accelerator. However, when the beam energy is high, the orbits 200 do not become concentric, but converge on the side of the beam extraction path entrance 82 and become discrete on the side of the inner conductor 14. Hereinafter, the region where the orbits 200 are converged may be called a converged region, and the region where the orbits 200 are discrete may be called a discrete region.

[0032] 4, an iso-orbital phase line 201 connecting the same orbital phases of each orbit 200 is shown for every orbital phase π / 20 from the convergence region 203. The acceleration gap 11 formed between the Dee electrode 12 and the dummy Dee electrode 13 is installed along one of the iso-orbital phase lines 201 (for example, the iso-orbital phase line 201 that rotates ±90 degrees from the convergence point where the orbits 200 are closest to each other). More specifically, the Dee electrode 12 has a hollow sector-like shape with a tip near the center of the orbit 200 and a radius that follows the iso-orbital phase line 201.

[0033] Returning to the explanation of Figures 1 to 3, a radio frequency kicker 90, a peeler magnetic field region 91 which is a disturbance magnetic field consisting of a dipole magnetic field or a multipole magnetic field, and a regenerator magnetic field region 92 are formed inside the main electromagnet 40 in order to extract the circulating beam to the outside. The radio frequency kicker 90 is placed in a beam concentration region, and the peeler magnetic field region 91 and the regenerator magnetic field region 92 are placed on the outer periphery side of the maximum energy orbit 61.

[0034] The RF kicker 90 applies an RF voltage to the beam for extraction to extract the beam to the outside. The frequency of the RF voltage for extraction is set to a horizontal tune value v r The extraction radio frequency voltage may be a radio frequency voltage with a finite frequency band including frequency components substantially equal to the product.

[0035] The amplitude of the horizontal betatron oscillation of the beam continues to increase resonantly due to the extraction radio frequency voltage from the radio frequency kicker 90, and the beam reaches the peeler magnetic field region 91 and the regenerator magnetic field region 92. The beam is kicked out of the maximum energy trajectory 61 by the occurrence of secondary resonance in the peeler magnetic field region 91 and the regenerator magnetic field region 92, and reaches the entrance 82 of the beam extraction path. The beam is then guided into the magnetic channel 81, and is sufficiently deflected to be extracted to the outside of the accelerator 100 through the high energy beam transport system 80.

[0036] In this manner, in the present embodiment, since the beam is extracted from near the focusing region, it is possible to reduce the amount of kick required to extract the beam, and it is possible to easily extract a beam having the desired extraction energy.

[0037] Fig. 5 is a diagram showing a configuration example of a low-power high-frequency control system 25. The low-power high-frequency control system 25 shown in Fig. 5 is a control unit for controlling the accelerating cavity 9, and includes an oscillator 1, a changeover switch 2, a TDC (Time to Digital Converter) 3, a digital loop filter 4, a DCO (Digital Controlled Oscillator) 5, an RF (Radio Frequency) switch 6, a voltage amplitude comparator 16, a frequency comparator 17, and a controller 18. The low-power high-frequency control system 25 is connected to the accelerating cavity 9 via a high-frequency power amplifier 7 and an input high-frequency measurement circuit 8, and is further connected to an accelerating voltage measurement circuit 10 and a higher-level control system 19. At least a part of the functions of the higher-level control system 19 described below may be provided in the low-power high-frequency control system 25 (particularly the controller 18).

[0038] The oscillator 1 generates a frequency signal for controlling the start timing of inputting (starting up) high-frequency power for acceleration to the acceleration cavity 9. The frequency signal has a frequency f pre is included in the frequency modulation range, which is the range of the resonant frequency of the accelerating cavity 9. In this embodiment, the frequency f pre is the upper limit frequency of the frequency modulation range f maxA predetermined frequency f is a rotation frequency that is lower than the predetermined frequency f and corresponds to the incident energy, which is the energy of the beam injected into the acceleration region 101. inj The oscillator 1 is preferably one capable of generating a frequency signal whose frequency is constant over time with high accuracy, such as a crystal oscillator.

[0039] The changeover switch 2 is a switching unit that switches ON / OFF of feedback control by a PLL (phase locked loop) circuit, which will be described later.

[0040] The TDC 3, the digital loop filter 4, and the DCO 5 receive the output signal of the oscillator 1, or the output signal of the oscillator 1 and the acceleration voltage signal V acc The signal obtained by adding and is used as a reference signal, and the input current signal I out The PLL circuit has an input signal of 100 kHz. After the changeover switch 2 is turned on, the PLL circuit adjusts the phase of the input signal so that the phase difference between the input signal and the reference signal becomes zero, and outputs the input signal with the frequency of the input signal matched to the frequency of the reference signal. In the example of FIG. 5, the PLL circuit is an all-digital PLL circuit in which all circuits (TDC 3, digital loop filter 4, and DCO 5) are composed of digital circuits. However, the PLL circuit may be a PLL circuit in which analog circuits are used in some circuits, or a PLL circuit in which all circuits are composed of analog circuits. In addition, the PLL circuit may use a method in which the input signal and the reference signal are converted into IQ signals, respectively, and then the phase difference between the two signals is detected, and the output is controlled by an IQ modulator (not shown) so that the phase difference becomes zero by proportional-integral control.

[0041] The RF switch 6 switches between inputting and stopping the high frequency power, which is the output signal of the PLL circuit, to the accelerating cavity 9 .

[0042] The high frequency power amplifier 7 amplifies the high frequency power output from the low power high frequency control system 25 and inputs it as input high frequency power to the accelerating cavity 9. The high frequency power amplifier 7 is, for example, a semiconductor amplifier.

[0043] The input RF measurement circuit 8 between the RF power amplifier 7 and the accelerating cavity 9 uses a directional coupler to measure the input RF power, which is a traveling wave component toward the accelerating cavity 9, and outputs an input current signal I out 5 is an input measurement unit that outputs a signal as an input high frequency measurement circuit 8. The signal output from the input high frequency measurement circuit 8 may be an input voltage signal instead of an input current signal. Also, in Fig. 5, the input coupler 20 shown in Figs. 1 and 2 is omitted.

[0044] The acceleration voltage measurement circuit 10 measures the acceleration high-frequency voltage applied to the acceleration gap 11, and outputs a measurement signal indicating the measurement value as an acceleration voltage signal V acc For example, the acceleration voltage measurement circuit 10 processes a signal obtained from a pickup unit 21 near the acceleration gap 11 to output an acceleration voltage signal V acc The output is as follows:

[0045] The voltage amplitude comparator 16 detects the acceleration voltage signal V acc The amplitude of the accelerating voltage and the threshold value V thrd The acceleration voltage is compared with the threshold value V thrd When it reaches this value, an RFON command signal instructing the input of high frequency power for acceleration is output to the controller 18. When the above-mentioned IQ modulator is used, the voltage amplitude comparator 16 can be omitted.

[0046] The frequency comparator 17 detects the acceleration voltage signal V acc The acceleration frequency is the frequency of the acceleration and the output frequency F ext The acceleration frequency is compared with the output frequency F ext When the output frequency F reaches the predetermined frequency, the RFOFF command signal is output to the controller 18 to instruct the stopping of the high frequency power for acceleration. ext is the value of the acceleration frequency corresponding to the rotation frequency at which a beam having a desired extraction energy travels around the circular orbit.

[0047] The controller 18 controls the changeover switch 2 and the RF switch 6 to control the start and stop of the input of high-frequency power for acceleration to the accelerating cavity 9 .

[0048] In order to realize the above control, the controller 18 holds a look-up table showing the correspondence between the beam energy and the circulating frequency. When the controller 18 receives a beam request signal requesting preparation for beam extraction from the upper control system 19, the controller 18 controls the output frequency F according to the desired extraction energy in response to the beam request signal. ext is set in the frequency comparator 17. The beam request signal includes information indicating a desired extraction energy.

[0049] Then, the controller 18 turns the changeover switch 2 to the OFF state, turns the RF switch 6 to the ON state, and inputs a signal that is phase-synchronized with the output signal of the oscillator 1 to the accelerating cavity 9 as a control radio frequency power. After that, when the RFON signal becomes High, the controller 18 turns the changeover switch 2 to the ON state, and inputs the input current signal I out The acceleration voltage signal V from the acceleration voltage measurement circuit 10 is generated by using a PLL circuit. acc A signal phase-synchronized with this is input as acceleration radio frequency power to the accelerating cavity 9. This maintains a state in which acceleration radio frequency power having substantially the same frequency as the resonant frequency of the accelerating cavity 9 is input to the accelerating cavity 9, making it possible to continue accelerating the beam.

[0050] 5 is merely an example and is not limited to the configuration shown in the figure. For example, the input measurement signal from the input high frequency measurement circuit 8 is not limited to a current signal but may be a voltage signal. Also, the measurement signal from the acceleration voltage measurement circuit 10 is not limited to a voltage signal but may be a current signal. Also, a circuit for suppressing a phase shift in the output signal of the changeover switch 2 caused by switching the nodes of the changeover switch 2 may be provided between the changeover switch 2 and the TDC 3 of the PLL circuit.

[0051] 6 is a timing chart for explaining the control sequence of the low-power high-frequency control system 25. FIG. 6(a) shows the resonant frequency f cav(solid line) and the frequency f of the input high frequency power, which is the output signal of the high frequency power amplifier 7. out FIG. 6(b) shows the control signals used in the low-power high-frequency control system 25. FIG. 6(c) shows the acceleration voltage signal V acc and the high frequency voltage V applied to the high frequency kicker 90 ext Figure 6(d) shows the time variation of the current of the incoming beam and the outgoing beam.

[0052] The resonant frequency of the accelerating cavity 9 is f cav changes with the same frequency modulation pattern for each acceleration period shown in Fig. 6 as the rotating capacitor 30 rotates. In this embodiment, each control signal shown in Fig. 6(b) is activated at a high level and then reset to a low level after a certain period of time.

[0053] First, the controller 18 starts the following process when it receives a beam request signal from the upper control system 19 (time T0). At this time, the RF switch 6 and the changeover switch 2 are both in the OFF state.

[0054] The controller 18 monitors the angle signal of the rotating capacitor 30, and after the rotation angle of the rotating capacitor 30 reaches a predetermined angle (time T1), a certain time elapses and the resonant frequency f cav Near the time when the resonant frequency f starts to decrease monotonically with respect to the time axis, an ON signal is sent to the RF switch 6 to switch the RF switch 6 to the ON state (time T2). The predetermined angle is an angle that is set only once during one acceleration period, and is, for example, an angle equal to the resonant frequency f cav is preset to the angle at which the timing at which the

[0055] Immediately after the RF switch 6 is turned on, the resonant frequency f cav is the frequency of the output signal of the PLL circuit (output signal of DCO5) out (=f pre ), they are not in tune. Then, the resonant frequency f cavdecreases with the rotation of the rotating capacitor 30, and the frequency f out (=f pre ), and the phase difference between the input signal of the TDC3 and the reference signal approaches zero. Then, the frequency f out is the frequency f of the output signal of oscillator 1. pre is locked to the frequency f pre Approximately the same frequency as f out The control RF power having the above-mentioned structure is outputted as input RF power to an accelerating cavity 9 via a RF power amplifier 7.

[0056] In addition, the resonant frequency f cav and the frequency of the input high frequency power, f out While the difference between the resonant frequency f and the resonant frequency f of the accelerating cavity 9 is large (between times T2 and T3), the input high frequency power has a large component reflected by the accelerating cavity 9 and a small component input to the accelerating cavity 9. cav and the frequency of the input high frequency power, f out When the difference between the accelerating voltage V and the accelerating voltage V becomes small (approaching time T3), the reflected component of the input high frequency power is rapidly reduced, and the input high frequency power is input to the accelerating cavity 9. As a result, an accelerating high frequency voltage is applied to the accelerating gap 11, and the accelerating voltage signal V acc The voltage amplitude of increases.

[0057] After that, at time T3, the accelerating voltage signal V acc The amplitude of V thrd When the voltage amplitude comparator 16 reaches the reference signal V 1 , the voltage amplitude comparator 16 outputs an RFON command signal to the controller 18. When the controller 18 receives the RFON command signal, the controller 18 transmits a switching signal to the changeover switch 2 to turn the changeover switch 2 ON, and applies the acceleration voltage signal V 1 to the reference signal of the PLL circuit (reference signal of the TDC 3). acc (time T3). In this embodiment, the acceleration voltage signal V acc The amplitude of V thrd The acceleration voltage signal V acc This corresponds to the phase difference between the accelerating voltage signal V and the high frequency power for control falling within a predetermined value. accand the control high frequency power falling within a predetermined value, the voltage amplitude comparator 16 can be omitted as described above.

[0058] This allows the frequency of the output signal of the PLL circuit to be out is the resonant frequency f of the accelerating cavity 9 cav The acceleration voltage signal V is approximately the same as acc The time-varying resonance frequency f cav The accelerating RF power, which changes in accordance with the change in the ion beam, is input to the accelerating cavity 9 via the RF power amplifier 7 as an input RF power.

[0059] Thereafter, the controller 18 injects the beam from the ion source 51 into the acceleration region 101 in the main electromagnet 40 (time T4). Note that the controller 18 controls the ion source 51 via the host control system 19, for example, to inject the beam.

[0060] Time T4 is a time when a certain time has elapsed since time T3. Also, at time T4, the acceleration voltage signal V acc The frequency of the given frequency f inj The time may be the same as the given frequency f inj is an orbital frequency corresponding to the incident energy, which is the energy of the beam injected into the acceleration region 101. In this case, for example, a frequency comparator (not shown) is used to detect the acceleration voltage signal V acc The frequency of the given frequency f inj When the frequency comparator is set to output a signal when the frequency of the beam coincides with the frequency of the beam, the beam is injected into the acceleration region 101 when the controller 18 receives the signal. acc An AGC (Automatic Gain Controller, not shown) that controls the amplitude of the high frequency power may be provided after the DCO 5 so that the amplitude of the high frequency power reaches a set value before time T4.

[0061] And the acceleration voltage signal V acc The frequency of the output frequency f extWhen the frequency reaches , an RFOFF command signal is output from frequency comparator 17 to controller 18. When controller 18 receives the RFOFF command signal, it sends an OFF signal to RF switch 6 to switch RF switch 6 to the OFF state and stops the input of acceleration high frequency power to accelerating cavity 9 (time T5). This stops the acceleration of the beam, and the beam continues to revolve in an orbit according to the energy.

[0062] Furthermore, the upper control system 19 drives the high frequency kicker 90 to generate the high frequency voltage V ext is applied to the beam. As a result, the beam reaches the peeler magnetic field region 91 and the regenerator magnetic field region 92, and is further kicked out of the maximum energy orbit 61 by the peeler magnetic field region 91 and the regenerator magnetic field region 92, and reaches the entrance 82 of the beam extraction path. Thereafter, the beam is extracted to the outside of the accelerator 100 through the magnetic channel 81 and the high energy beam transport system 80 (time T6). After the controller 18 sends an acceleration end signal to the upper control system 19, the upper control system 19 drives and stops the high frequency kicker 90 after determining various conditions.

[0063] Then, the high-frequency voltage for extraction V ext When the excitation is stopped, the extraction of the beam is stopped (time T7). Note that the beam continues to be extracted as long as orbiting charges, which are charged particles circulating as a beam within the acceleration region 101, remain. The beam is also extracted when the host control system 19 controls the extraction radio frequency voltage V ext The laser can be emitted continuously or intermittently by adjusting the application time of the high-frequency voltage V ext If the beam cannot be detected by a beam dose monitor (not shown) arranged outside the accelerator even if the beam continues to be applied, the upper control system 19 may determine that the circulating charge has disappeared.

[0064] Then, when the beam is to be emitted again, the upper control system 19 transmits a beam request signal to the controller 18 again (time T0′).

[0065] Fig. 7 is a diagram showing an example of the configuration of a particle therapy system including the accelerator 100 described in Fig. 1 to Fig. 6. In Fig. 7, the particle therapy system 500 includes the accelerator 100, a treatment table 501, a beam transport device 502, an irradiation device 503, and an upper control system 19.

[0066] The treatment table 501 is a table on which a patient 600, who is an irradiation target to be irradiated with the beam, is placed. The beam transport device 502 is connected to the high-energy beam transport system 80 of the accelerator 100, and transports the beam extracted from the accelerator 100 to the irradiation device 503.

[0067] The irradiation device 503 irradiates the beam transported from the beam transport device 502 to the affected area of ​​the patient 600 on the treatment table 501. At this time, the irradiation device 503 irradiates the beam to each of a plurality of irradiation spots obtained by dividing the affected area of ​​the patient 600, measures the irradiation dose for each irradiation spot, and notifies the host control system 19. The host control system 19 calculates the required dose for each irradiation spot, transmits a beam request signal to the controller 18, and also controls the extraction radio frequency voltage V ext is controlled so that the required dose of the beam is irradiated to the affected area.

[0068] As described above, according to this embodiment, the acceleration voltage measurement circuit 10 outputs the acceleration voltage signal V acc The low-power high-frequency control system 25 inputs, as high-frequency power, a control high-frequency power having a constant frequency included in the range of the resonance frequency of the accelerating cavity 9 to the accelerating cavity 9. The low-power high-frequency control system 25 outputs an acceleration voltage signal V acc When the phase difference between the accelerating voltage signal V and the control high frequency power falls within a predetermined value, the high frequency power is fed back by feedback control. acc The high frequency power for acceleration synchronized with the acceleration frequency, which is the frequency of the output frequency F ext, the input of the acceleration high frequency power to the accelerating cavity 9 is stopped. Therefore, the input and stop of the acceleration high frequency power can be appropriately performed according to the actual resonance pattern of the accelerating cavity 9, and the beam can be appropriately accelerated to the desired energy. As a result, it is possible to extract a beam having the desired energy with high precision.

[0069] In addition, in this embodiment, the center of the orbit around which the beam revolves is shifted from the center of the acceleration region 101. This makes it possible to reduce the amount of kick required to extract the beam, and to easily extract a beam with the desired energy.

[0070] In this embodiment, the acceleration voltage is set to a threshold value V thrd The beam is injected into the acceleration region 101 a certain time after the acceleration voltage value reaches a threshold value V thrd When the frequency reaches a predetermined frequency after reaching the predetermined frequency, the beam is injected into the acceleration region 101. This makes it possible to inject the beam at an appropriate timing, and to extract a beam having a desired energy with high precision.

[0071] In this embodiment, the low-power high-frequency control system 25 uses a PLL circuit to convert an input measurement signal obtained by measuring the high-frequency power input to the accelerating cavity 9 into an acceleration voltage signal V acc By synchronizing the phase with the PLL circuit, high frequency power for acceleration is generated. In particular, the PLL circuit is entirely digital and uses IQ modulation. This makes it easy to input and stop high frequency power for acceleration.

[0072] In addition, in this embodiment, since the input and stop of the acceleration radio frequency power is controlled in accordance with the actual resonance pattern of the accelerating cavity 9, it is possible to appropriately accelerate the beam to the desired energy even if the acceleration radio frequency power is amplified using a semiconductor amplifier which takes a certain amount of time to start up.

[0073] The above-described embodiments of the present disclosure are illustrative examples of the present disclosure, and are not intended to limit the scope of the present disclosure to only these embodiments. A person skilled in the art can implement the present disclosure in various other forms without departing from the scope of the present disclosure. [Explanation of symbols]

[0074] 1: Oscillator 2: Changeover switch 3: TDC 4: Digital loop filter 5: DCO 6: RF switch 7: High frequency power amplifier 8: Input high frequency measurement circuit 9: Acceleration cavity 10: Acceleration voltage measurement circuit 11: Acceleration gap 12: Dee electrode 13: Dummy dee electrode 14: Inner conductor 15: Outer conductor 16: Voltage amplitude comparator 17: Frequency comparator 18: Controller 19: Upper control system 20: Input coupler 21: Pickup section 25: Low power high frequency control system 30: Rotating capacitor 31: Motor 40: Main electromagnet 41: Yoke 42: Main coil 43: Main magnetic pole 50: Cryostat 51: Ion source 52: Low energy beam transport system 53: Ion injection section 80: High energy beam transport system 81: Magnetic channel 82: Beam extraction path entrance 90: High frequency kicker 91: Peer magnetic field region 92: Regenerator magnetic field region 100: Accelerator 101: Acceleration region 500: Particle beam therapy system 501: Treatment table 502: Beam transport device 503: Irradiation device

Claims

1. An accelerator that accelerates a charged particle beam while rotating it using a time-constant main magnetic field and an accelerating high-frequency voltage, an accelerating cavity for exciting the accelerating high frequency voltage according to a time-varying resonant frequency by using an input high frequency power; a measurement unit that outputs a measurement signal obtained by measuring the accelerating high frequency voltage; a control unit that inputs, as the high frequency power, control high frequency power having a constant frequency included in the range of the resonant frequency to the acceleration cavity, and when a phase difference between the measurement signal and the control high frequency power falls within a predetermined value, inputs, as the high frequency power, acceleration high frequency power synchronized with an acceleration frequency which is the frequency of the measurement signal by feedback control to the acceleration cavity, and when the acceleration frequency reaches a required value, stops input of the acceleration high frequency power to the acceleration cavity.

2. The accelerator according to claim 1 , wherein the center of an orbit around which the charged particle beam revolves is offset from the center of an acceleration region in which the main magnetic field is excited.

3. 2. The accelerator according to claim 1, wherein the charged particle beam is injected into an acceleration region in which the main magnetic field is excited a fixed time after the phase difference becomes within a predetermined value.

4. 2. The accelerator according to claim 1, wherein when the frequency reaches a predetermined frequency after the phase difference falls within the predetermined value, the charged particle beam is injected into an acceleration region in which the main magnetic field is excited.

5. 2 . The accelerator according to claim 1 , wherein the control unit generates the accelerating high frequency power by using a phase locked loop to phase-synchronize an input measurement signal obtained by measuring the high frequency power with the measurement signal.

6. The accelerator of claim 5 , wherein the phase locked loop uses IQ modulation.

7. 7. The accelerator according to claim 6, wherein all of the circuits in the phase locked loop are digital circuits.

8. The accelerator according to claim 1 , further comprising a semiconductor amplifier for amplifying the high frequency power.

9. The accelerator of claim 1; and an irradiation device that irradiates an irradiation target with the charged particle beam extracted from the accelerator.

10. A method for controlling an accelerator having an accelerating cavity that excites an accelerating high-frequency voltage corresponding to a time-varying resonant frequency using input high-frequency power, and that accelerates a charged particle beam while circulating it using a time-constant main magnetic field and the accelerating high-frequency voltage, comprising the steps of: outputting a measurement signal obtained by measuring the accelerating high frequency voltage; inputting, as the high frequency power, a control high frequency power having a constant frequency included in the range of the resonant frequency into the accelerating cavity; when the phase difference between the measurement signal and the control high frequency power falls within a predetermined value, an acceleration high frequency power synchronized with an acceleration frequency, which is the frequency of the measurement signal, is input to the acceleration cavity as the high frequency power by feedback control; A control method comprising: stopping input of the acceleration high frequency power to the acceleration cavity when the acceleration frequency reaches a required value.

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