Accelerator system, particle beam treatment system, control method of accelerator system, and control method of particle beam treatment system

Abstract

Provided is an accelerator system capable of easily suppressing a reduction in the number of accelerated (outgoing) particles in a charged particle beam. An accelerator (1) comprises an acceleration cavity (11) that, using an inputted high-frequency voltage, excites an acceleration high-frequency voltage that is in accordance with a resonance frequency. The accelerator accelerates an injected charged particle beam by means of a high-frequency voltage for acceleration and emits the particle beam. A high-frequency control device (3) inputs, to the acceleration cavity (11), a control-use high-frequency voltage which has a prescribed lock frequency, and when a resonance determination value reaches a threshold, starts feedback control to modulate the frequency of the high-frequency voltage for control so as to track changes in the resonance frequency.

Description

Accelerator system, particle beam therapy system, accelerator system control method, and particle beam therapy system control method

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

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

[0003] The accelerating RF voltage modulates the resonant frequency of the accelerating cavity using a modulator connected to the accelerating cavity that excites the accelerating RF voltage. The modulator temporally modulates the resonant frequency of the accelerating cavity by temporally changing the capacitance or inductance of the accelerating cavity. In this case, the RF power input to the accelerating cavity to excite the accelerating RF voltage needs to be adjusted to approximately the same frequency as the resonant frequency of the accelerating cavity.

[0004] Patent document 1 discloses a technology that uses a rotating capacitor as a modulator, which changes the capacitance by rotating one of a pair of opposing electrodes to change the area where the pair of electrodes overlap over time.

[0005] Furthermore, Patent Document 2 discloses a technique for adjusting the frequency of a control radio frequency power input to an accelerating cavity to the resonant frequency of the accelerating cavity. In this technique, the phase of the accelerating radio frequency voltage is detected, and when the phase difference between the phase of the accelerating radio frequency voltage and the phase of the control radio frequency power becomes less than a threshold, feedback control of the frequency of the control radio frequency power is initiated. This technique applies the principle that when a resonator such as an accelerating cavity is in a resonant state, the phase difference between the phase of the radio frequency voltage input to the resonator and the radio frequency voltage excited in the resonator becomes zero.

[0006] US Patent Application Publication No. 2010 / 0045213 JP 2023-87587 A

[0007] The technology described in Patent Document 2 requires the detection of the acceleration RF voltage, which requires a voltage detection means to be installed within the accelerating cavity, and the acceleration RF voltage to be detected by a measuring instrument outside the accelerator connected to the detection means via a cable such as a coaxial cable. Therefore, the detected acceleration RF voltage suffers a phase delay corresponding to the cable length. Similarly, a phase delay also occurs when detecting the control RF voltage. This poses a problem: the phase difference between the acceleration RF voltage and the control RF power does not necessarily become zero at the resonance point. Therefore, the technology described in Patent Document 2 may deviate from the ideal timing for starting feedback control, potentially resulting in a decrease in the number of particles accelerated (extracted) from the charged particle beam.

[0008] To solve the above problem, it is possible to use cables for measuring the accelerating RF voltage and the controlling RF power with the same length, calculate the phase delay in advance, and apply an offset corresponding to the phase delay to the detection results. However, this method requires complex hardware adjustments and complex control. Furthermore, in an accelerating cavity whose resonant frequency changes over time, the impedance matching point of the input controlling RF power is a single point within a certain modulation width, and perfect matching cannot be achieved for all modulation widths, making adjustment difficult.

[0009] Therefore, with the technique of Patent Document 2, it is not easy to suppress a decrease in the number of particles to be accelerated (extracted) from the charged particle beam.

[0010] An object of the present disclosure is to provide an accelerator system, a particle beam therapy system, a control method for an accelerator system, and a control method for a particle beam therapy system that can easily suppress a decrease in the number of particles accelerated (extracted) from a charged particle beam.

[0011] An accelerator system according to one aspect of the present disclosure includes an accelerator having an accelerating cavity that uses an input control radio-frequency voltage to excite an accelerating radio-frequency voltage corresponding to a resonance frequency, and that accelerates an incident charged particle beam with the accelerating radio-frequency voltage and extracts it; a response signal detection unit that detects a response signal of a radio-frequency monitor of the accelerating cavity; and a radio-frequency control device that inputs the control radio-frequency voltage having a predetermined lock frequency to the accelerating cavity, and when a resonance determination value obtained from the accelerating cavity input signal and the detected response signal reaches a threshold, starts feedback control to modulate the frequency of the control radio-frequency voltage so as to follow the resonance frequency that changes over time.

[0012] According to the present invention, it is possible to easily suppress a decrease in the number of particles to be accelerated (extracted) from a charged particle beam.

[0013] 1 is a diagram schematically illustrating a configuration of an accelerator system according to an embodiment of the present disclosure; FIG. 2 is a diagram illustrating an example of a hardware configuration of a radio frequency control device; FIG. 3 is a diagram illustrating an example of a memory map; FIG. 4 is a diagram illustrating an example of a configuration of a rotating capacitor; FIG. 5 is a diagram illustrating an example of a rotor electrode and a stator electrode; FIG. 6 is a diagram illustrating an example of a relationship between a rotor electrode, a stator electrode, and an angle detector; FIG. 7 is a diagram for explaining a method of generating a rotor origin signal taking into account a positional deviation; FIG. 8 is a diagram illustrating an example of a configuration of a counter circuit that outputs a rotor origin signal; FIG. 9 is a diagram illustrating a control timing chart of a radio frequency control device; FIG. 10 is a diagram illustrating an example of a configuration related to radio frequency signal processing of a radio frequency voltage control unit; FIG. 11 is a diagram illustrating another example of a configuration related to radio frequency signal processing of a radio frequency voltage control unit; and FIG.

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0015] 1 is a diagram schematically illustrating the configuration of an accelerator system according to an embodiment of the present disclosure. The accelerator system 100 shown in FIG. 1 includes an accelerator 1, a rotating condenser control device 2, a radio frequency control device 3, an amplifier 4, a directional coupler 5, and a host control device 6.

[0016] The accelerator 1 is a circular accelerator that accelerates and extracts an injected charged particle beam while causing it to circulate. The accelerator 1 includes an accelerating cavity 11, an accelerating voltage monitor 12, a rotating capacitor 13, and an angle detector 14.

[0017] The accelerating cavity 11 is a device for exciting an acceleration voltage (accelerating radio frequency voltage) for accelerating a charged particle beam. Specifically, the accelerating cavity 11 has acceleration electrodes (not shown) therein, and excites an acceleration voltage between the acceleration electrodes by a high-level radio frequency voltage, which is a control radio frequency voltage, input from outside. The acceleration voltage monitor 12 is a voltage detection unit that detects the acceleration voltage excited between the acceleration electrodes and outputs the detected voltage to the outside of the accelerating cavity as an acceleration voltage monitor signal.

[0018] The rotating capacitor 13 is connected to the accelerating cavity 11 and is a modulator that changes the resonant frequency of the accelerating cavity 11 over time. Specifically, the rotating capacitor 13 has one or more opposing electrode pairs (not shown in FIG. 1 ), and modulates the resonant frequency of the accelerating cavity 11 by rotating one of the electrode pairs to change the overlapping area of ​​the electrode pair and thereby changing the capacitance. The fixed electrode of the electrode pair is called a stator electrode, and the rotatable electrode facing the stator electrode is called a rotor electrode. The rotating capacitor 13 also includes a motor 15 that rotates the rotor electrode.

[0019] The angle detector 14 is an angle detection unit that detects the rotation angle of the rotary capacitor 13 and outputs an angle detection signal indicating the rotation angle. In this embodiment, the angle detector 14 is a rotary encoder that outputs a pulse signal corresponding to a change in the rotation angle as the angle detection signal.

[0020] The rotating capacitor control device 2 controls the motor 15 of the rotating capacitor 13. For example, the rotating capacitor control device 2 controls the start and stop of rotation of the motor 15, the rotation speed, and the like.

[0021] The radio frequency control device 3 outputs a low-level radio frequency voltage corresponding to the high-level radio frequency voltage to be supplied to the accelerating cavity 11, and controls the frequency, amplitude, etc. of the high-level radio frequency voltage to be supplied to the accelerating cavity 11. Specifically, the radio frequency control device 3 includes a digital oscillator (not shown in FIG. 1 ) that outputs a low-level radio frequency voltage, and controls the frequency of the digital oscillator to follow changes in the resonant frequency of the accelerating cavity 11 based on the frequency of the accelerating voltage indicated by an accelerating voltage monitor signal from the accelerating voltage monitor 12, while controlling the amplitude so that a desired accelerating voltage is generated at the accelerating electrode.

[0022] The amplifier 4 amplifies the low-level radio-frequency voltage output from the radio-frequency control device 3 to convert it into a high-level radio-frequency voltage, which is then supplied to the accelerating cavity 11 of the accelerator 1 via the directional coupler 5. In this embodiment, the accelerating cavity 11 is a cavity resonator with a Q factor of approximately 1000 to 3000. In this case, if the frequency of the high-level radio-frequency voltage amplified by the amplifier 4 matches the resonant frequency of the accelerating cavity 11, the reflected amplitude of the radio-frequency voltage from the accelerating cavity 11 is minimized, and a radio-frequency voltage is generated at the accelerating electrode. However, if the frequency of the high-level radio-frequency voltage and the resonant frequency of the accelerating cavity 11 differ by more than a certain amount, the high-level radio-frequency voltage supplied to the accelerating cavity 11 is reflected, and no radio-frequency voltage is generated at the accelerating electrode. The directional coupler 5 functions as a component detector that detects the traveling wave component of the high-level radio-frequency voltage supplied to the accelerating cavity 11 and the reflected wave component of the radio-frequency voltage reflected from the accelerating cavity 11, and outputs a traveling wave monitor signal and a reflected wave monitor signal indicating these components.

[0023] Specifically, the radio frequency control device 3 controls the frequency of the high-level radio frequency voltage supplied to the accelerating cavity 11 based on an acceleration voltage monitor signal from the acceleration voltage monitor 12 and a traveling wave monitor signal and a reflected wave monitor signal from the directional coupler 5. Furthermore, the radio frequency control device 3 calculates a rotor origin signal of the rotor electrode of a rotating capacitor 13 (described later) based on an angle detection signal from the angle detector 14, and outputs the signal to the higher-level control device 6.

[0024] The host controller 6 outputs various signals to the radio frequency controller 3 to control the entire accelerator system 100. For example, the host controller 6 outputs various setting information to the radio frequency controller 3. The setting information includes an amplitude target value which is a target value for the amplitude of the acceleration voltage, injection frequency data which indicates an injection frequency which is the frequency of the acceleration voltage when injecting the charged particle beam, extraction frequency data which indicates an extraction frequency which is the frequency of the acceleration voltage when extracting the charged particle beam, and various control parameters such as a feedback control gain which will be described later. The host controller 6 also outputs a master trigger signal which indicates the start of control of the accelerator 1 and an energy change signal which changes the energy of the charged particle beam output from the accelerator 1.

[0025] Fig. 2 is a diagram showing an example of the hardware configuration of the radio frequency control device 3. The radio frequency control device 3 shown in Fig. 2 has an external interface unit 31, an operation control unit 32, a memory 33, a control register 34, a radio frequency voltage control unit 35, a radio frequency interface unit 36, and an external device control timing signal output unit 37. The external interface unit 31, the operation control unit 32, and the memory 33 are connected to each other so as to be able to communicate with each other via an external interface bus 38, and the operation control unit 32, the memory 33, and the control register 34 are connected to each other so as to be able to communicate with each other via an internal interface bus 39.

[0026] The external interface unit 31 inputs and outputs various signals to and from the outside. For example, the external interface unit 31 receives angle detection signals (specifically, angle detection signals of phases A, B, and Z) from the angle detector 14, and a master trigger signal and an energy change signal from the upper control device 6. The external interface unit 31 also outputs a rotor origin signal to the upper control device 6. The external interface unit 31 also has a communication interface for inputting and outputting setting information (incident frequency data, emission frequency data, and control parameters). Of the angle detection signals, the phase A and phase B signals are output multiple times at equal intervals during one rotation of the rotating capacitor 13, with their phases shifted by 90°. The phase Z angle detection signal is output once per rotation of the rotating capacitor 13.

[0027] The operation control unit 32 is configured with, for example, a CPU (Central Processing Unit) and manages operation control that controls the operation of the accelerator system 100. The memory 33 stores setting information input to the external interface unit 31.

[0028] The control register 34 stores control parameters used by the radio frequency voltage control unit 35. The control parameters include a lock frequency, an input frequency, an output frequency, a lock determination value, a tracking determination value, a frequency P gain, a frequency I gain, a frequency D gain, a standby amplitude value, an amplitude target value, an amplitude P gain, and an amplitude I gain.

[0029] The lock frequency is the initial value of the frequency of the low-level radio-frequency voltage output from the digital oscillator (see FIGS. 10 and 11 ) of the radio-frequency control device 3. The output frequency is the frequency of the low-level radio-frequency voltage output from the digital oscillator. The lock determination value is a threshold value for determining whether frequency locking has occurred, in which the resonant frequency of the accelerating cavity 11 matches the frequency of the high-level radio-frequency voltage. The tracking determination value is a threshold value for determining whether frequency tracking control, which causes the frequency of the low-level radio-frequency voltage output from the digital oscillator to track the resonant frequency of the accelerating cavity 11, is being performed normally. The frequency P gain, frequency I gain, and frequency D gain are each gain of PID (Proportional-Integral-Differential) feedback control for achieving frequency tracking control.

[0030] The standby amplitude value is the initial value of the amplitude of the low-level high-frequency voltage output from the digital oscillator. The amplitude target value is a value used to control the amplitude of the low-level high-frequency voltage output from the digital oscillator and indicates the target value of the acceleration voltage. The amplitude P gain and amplitude I gain are each gain of PI (Proportional-Integral) feedback control that realizes amplitude feedback control to maintain the amplitude of the acceleration voltage at the amplitude target value. Note that the control parameters are not limited to these values ​​and may include other parameters such as an offset expiration value and an operation cycle expiration value, which will be described later.

[0031] The high frequency voltage control unit 35 is configured with a high speed digital signal processing circuit such as an FPGA (Field Programmable Gate Array), and controls the output of the high frequency voltage using the control parameters stored in the control register 34 .

[0032] The high frequency interface unit 36 ​​inputs and outputs signals related to the high frequency voltage, etc. Specifically, the high frequency interface unit 36 ​​receives an acceleration voltage monitor signal, a traveling wave monitor signal, and a reflected wave monitor signal, and outputs a low-level high frequency voltage.

[0033] The external device control timing signal output unit 37 outputs an external device control timing signal for controlling an external device. The external device control timing signal includes an incident frequency arrival signal indicating that the frequency of the low-level high-frequency signal has reached the incident frequency, and an output frequency arrival signal indicating that the frequency of the low-level high-frequency signal has reached the output frequency.

[0034] In this embodiment, the high-frequency control device 3 has a configuration in which the hardware for operation control and the hardware for output control of the high-frequency voltage are separated, making it possible to suppress delays in the output control of the high-frequency voltage. Note that the output frequency is set in the control register 34 so that the output frequency set in the digital oscillator when the high-frequency voltage control unit 35 is performing frequency tracking control can be accessed from the operation control unit 32 and the high-frequency voltage control unit 35.

[0035] 3 is a diagram showing an example of a memory map of the memory 33. As shown in FIG. 3, the memory 33 stores incident frequency data 331, output frequency data 332, reference frequency data 333, and amplitude target value data 334.

[0036] The injection frequency data 331 indicates an injection frequency that defines the timing at which a charged particle beam is injected into the accelerator 1 (the timing at which an injection frequency arrival signal is output) for each ion species, which is the type of charged particle that constitutes the charged particle beam. The injection frequency corresponding to the ion species is written in the control register 34 described above. The charged particle is, for example, a proton or various atomic nuclei (helium, carbon, etc.). Note that if the charged particle is limited to one type, only one injection frequency is required.

[0037] The extraction frequency data 332 indicates the extraction frequency that defines the timing at which the charged particle beam is extracted from the accelerator 1 (the timing at which the extraction frequency arrival signal is output), for each beam energy that is the energy of the charged particle beam extracted from the accelerator 1. In this embodiment, the beam energy is switched every time an energy change signal is input. Therefore, in the extraction frequency data 332, the extraction frequencies are set in an order that corresponds to the beam energy switching order, and every time an energy change signal is input, the addresses in the memory where the extraction frequencies are stored are updated, and the extraction frequencies stored at the updated addresses are set in the control register 34.

[0038] The amplitude target value data 334 indicates an amplitude target value for each frequency correspondence value indicating the resonant frequency of the acceleration cavity 11. The frequency correspondence value may be, for example, the rotation angle of the rotating capacitor 13 or the output frequency, which is the frequency of the low-level high-frequency voltage. The amplitude target value set in the control register 34 is updated in accordance with the angle detection signal (more specifically, the rotor clock signal based on the angle detection signal) output in accordance with the rotation of the rotating capacitor 13, or is updated in accordance with the output frequency, which is the frequency of the low-level high-frequency voltage.

[0039] The rotor clock signal is a signal that is output multiple times per rotation period of the rotating capacitor 13. When the amplitude target value set in the control register 34 is updated based on the angle detection signal, the same number of amplitude target values ​​as the number of rotor clock signals per rotation period of the rotating capacitor 13 are set in the amplitude target value data 334. On the other hand, when the amplitude target value is updated according to the output frequency, reference frequency data 333, in which a reference frequency that is a reference value for the output frequency is set, is prepared in advance. A plurality of amplitude target values ​​that correspond one-to-one to each reference frequency are set in the amplitude target value data 334. Then, each time the output frequency matches a reference frequency, the amplitude target value corresponding to the reference frequency is stored in the control register 34. Note that when the output frequency has a value between adjacent reference frequencies, the amplitude target value corresponding to the output frequency may be determined by linearly correcting each of the reference frequencies and the amplitude target values ​​corresponding to those reference frequencies.

[0040] FIG. 4 is a diagram showing the configuration of the rotating capacitor 13 in more detail. As shown in FIG. 4, the rotating capacitor 13 has a rotor electrode 131 and a stator electrode 132 that are arranged to face each other. There may be one or more pairs of rotor electrodes 131 and stator electrodes 132. In this embodiment, there are multiple pairs of rotor electrodes 131 and stator electrodes 132. In this case, management is performed so that the same radio-frequency voltage is supplied to the accelerating cavity 11 for each pair of rotor electrodes 131 and stator electrodes 132. In the example shown in FIG. 4, the stator electrode 132 is fixed to an outer conductor 142 that surrounds an inner conductor 141 that is connected to the accelerating electrode in the accelerating cavity 11, but it may also be fixed to the inner conductor 141.

[0041] The rotor electrode 131 is connected to the motor 15 and rotated by the motor 15. An angle detector 14 connected to the motor 15 outputs an angle detection signal indicating the rotation angle of the motor to the high frequency control device 3 in response to the rotation of the motor 15. The motor 15 rotates in response to a rotation control command from the rotating capacitor control device 2.

[0042] Fig. 5 is a view of a pair of rotor electrodes 131 and stator electrodes 132 viewed along the rotation axis of the rotor electrode 131. As shown in Fig. 5, as the rotor electrode 131 rotates, the area S of the overlapping portion 133 where the rotor electrode 131 and the stator electrode 132 overlap changes. As a result, the capacitance Crot of the rotating capacitor 13 shown in Equation 1 changes over time. where ε ０ is the dielectric constant in a vacuum, and d is the distance between the rotor electrode 131 and the stator electrode 132. In this embodiment, the rotating capacitor 13 is placed in a space that has been evacuated, and the space between the rotor electrode 131 and the stator electrode 132 is in a vacuum state.

[0043] As the capacitance Crot of the rotating capacitor 13 changes over time, the capacitance C of the accelerating cavity 11 to which the rotating capacitor is connected in parallel also changes over time, and the resonant frequency f of the accelerating cavity 11 shown in Equation 2 changes. ｒｅｓ also varies with time, i.e., is time modulated. Here, π is the ratio of the circumference of a circle to its diameter, and L is the inductance of the acceleration cavity 11.

[0044] FIG. 6 is a diagram showing the relationship between the rotor electrode 131, the stator electrode 132, and the angle detector 14 in the plane of rotation of the rotating capacitor 13.

[0045] In order to perform frequency tracking control to make the frequency of the low-level radio-frequency voltage follow the resonant frequency of the accelerating cavity 11, it is necessary to detect the resonant frequency of the accelerating cavity 11. However, since the resonant frequency of the accelerating cavity 11 cannot be directly observed, in this embodiment, the operation control unit 32 of the radio-frequency control device 3 determines the rotation angle of the rotating capacitor 13 based on the angle detection signal from the angle detector 14, thereby detecting the position of the rotor electrode 131 relative to the stator electrode 132 (more specifically, the position of the end of the rotor electrode 131), and the resonant frequency of the accelerating cavity 11 is estimated based on that position.

[0046] In this case, a rotor origin signal is required to indicate that the rotor end position, which is the position of the end of the rotor electrode 131, coincides with the rotor origin position at which the resonant frequency of the acceleration cavity 11 becomes a predetermined value. If the rotor origin position coincides with the angle detection position, which is the position of the end of the rotor electrode 131 when the Z-phase angle detection signal is output from the angle detector 14 for each rotation of the rotary capacitor 13, the Z-phase angle detection signal can be used as the rotor origin signal. However, it is difficult to mechanically perfectly match the rotor origin position and the angle detection position, and a positional deviation θ occurs between these positions. In this embodiment, the predetermined value of the resonant frequency is the maximum value of the resonant frequency. The positional deviation θ is expressed in terms of the rotation angle.

[0047] The accelerator 1 must be controlled taking into consideration the above-mentioned positional deviation θ. In particular, in order to shorten the time it takes for the high-frequency voltage supplied to the accelerating cavity 11 to be totally reflected, it is important to start the output control of the high-frequency voltage from a position where the rotor end is close to the rotor origin position, and therefore it is important to take the positional deviation θ into consideration.

[0048] FIG. 7 is a diagram for explaining a method for generating a rotor origin signal taking into consideration the positional deviation θ, and shows timing charts of various signals.

[0049] (1) Resonance Frequency As shown in FIG. 7, the resonance frequency of the rotating capacitor 13 changes periodically in an S-shape.

[0050] (2) Operation Cycle In this embodiment, there are multiple pairs of rotor electrodes 131 and stator electrodes 132 of the rotating capacitor 13. Therefore, the capacitance of the rotating capacitor 13 changes multiple cycles per rotation of the rotating capacitor 13. This allows the accelerator 1 to operate multiple times per rotation of the rotating capacitor 13. In other words, multiple operation cycles of the accelerator 1 are included within the output cycle of the Z-phase angle detection signal from the angle detector 14. Therefore, a rotor origin signal corresponding to each operation cycle is required.

[0051] (3) Acceleration Control Section The beam energy of the charged particle beam extracted from the accelerator 1 is determined by the extraction frequency indicated by the extraction frequency data from the host control device 6, that is, the frequency of the acceleration voltage when the acceleration of the charged particle beam is stopped. Therefore, the acceleration control section, which is the period during which the charged particle beam is accelerated in the accelerator 1, is set to be shorter than the operation cycle determined by the positional relationship between the rotor electrode 131 and the stator electrode 132. Specifically, the acceleration control section varies depending on the beam energy of the charged particle beam extracted from the accelerator 1, but is set to be shorter than the operation cycle even in the longest case. Furthermore, in this embodiment, the acceleration control section is a section in which the resonant frequency changes approximately linearly within the operation cycle.

[0052] (4) Rotor Rotation Signal X The rotor rotation signal X indicating the rotation angle of the rotor electrode 131 is generated by the operation control unit 32 based on the A-phase and B-phase angle detection signals output from the angle detector 14. The A-phase and B-phase angle detection signals are each output multiple times at equal intervals during one rotation of the motor 15, and are signals with a 90° phase difference between the output signals. Specifically, the operation control unit 32 generates the rotor rotation signal X by further multiplying the result of the exclusive OR of the A-phase and B-phase angle detection signals (X = A XOR B). This allows the rotor rotation signal X to detect angles more precisely than the angle detection signal. Note that if the angle detection signal can be output with sufficiently fine accuracy, the angle detection signal itself may be used as the rotor rotation signal X.

[0053] (5) Rotor Origin Signal In this embodiment, as described above, the rotor origin position is the rotor end position where the resonance frequency of the acceleration cavity 11 reaches its maximum value (peak), and therefore the positional deviation θ can be expressed as a count value obtained by counting the rotor rotation signal X from the time when the Z-phase angle detection signal is input until the resonance frequency of the acceleration cavity 11 reaches its maximum value. Taking advantage of this, in this embodiment, the operation control unit 32 includes two counter circuits, an offset counter and an operation cycle counter, as means for generating the rotor origin signal.

[0054] The offset counter comprises means for starting counting in response to input of the Z-phase angle detection signal, and means for outputting a rotor origin signal and outputting a count start command for the operation cycle counter when the count value reaches a predetermined offset expiration value. The operation cycle counter comprises means for starting counting using a rotor rotation signal based on the angle detection signal as a rotor clock signal in response to the counter start command output from the offset counter, and means for outputting a rotor origin signal and resetting the count value when the count value reaches an operation cycle expiration value corresponding to the operation cycle. A more detailed description of the counter circuit will be given later using Figure 8.

[0055] When a charged particle beam is extracted from the accelerator 1 and used in a beam utilization system, depending on the utilization conditions specified in the beam utilization system, the extraction time of the beam may become longer than the operation cycle of the accelerator 1. For this reason, in this embodiment, a master trigger signal indicating the start of operation of the accelerator system 100 is output in synchronization with the output of the rotor origin signal, and while a beam extraction command instructing extraction of the charged particle beam from the accelerator 1 is being output, the output of the rotor origin signal is ignored, thereby realizing operation control including extraction of the charged particle beam from the accelerator 1.

[0056] 8 is a diagram showing an example of the configuration of a counter circuit that outputs a rotor origin signal. The counter circuit 40 shown in FIG. 8 includes a waveform shaping circuit 41, a rotor rotation signal generating circuit 42, an offset counter 43, and an operation cycle counter 44.

[0057] The angle detection signals (A-phase, B-phase, and Z-phase) are input to the waveform shaping circuit 41 from the angle detector 14 of the accelerator 1. The waveform shaping circuit 41 performs waveform shaping processing to shape the waveform of the input angle detection signals, and outputs the angle detection signals that have been subjected to the waveform shaping processing. The waveform shaping processing includes, for example, processing to remove noise on the transmission line from the angle detection signals, processing to convert the signal level, and the like.

[0058] The A-phase and B-phase angle detection signals are input to the rotor rotation signal generation circuit 42 from the waveform shaping circuit 41. The rotor rotation signal generation circuit 42 further multiplies the result of an exclusive OR operation of the A-phase and B-phase angle detection signals to generate and output a rotor rotation signal X. The rotor rotation signal X is input to the count signal input terminals (IN) of the offset counter 43 and the operation cycle counter 44, and is also used for control within the high-frequency control device 3.

[0059] The offset counter 43 counts the rotor rotation signal X corresponding to the positional deviation θ between the rotor origin position and the angle detection position. In the offset counter 43, the rotor rotation signal X is input to a count signal input terminal (IN), the Z-phase angle detection signal is input to a count start input terminal (START), and the offset expiration value is input from the control register 34 of the high-frequency control device 3 to a comparison signal input terminal (COMP).

[0060] When the Z-phase angle detection signal is input, the offset counter 43 starts counting the rotor rotation signal X. The offset counter 43 also successively compares the counted count value with an offset expiration value, and when the count value reaches the offset expiration value, stops counting the rotor rotation signal X and outputs an offset counter expiration signal from the output terminal (OUT). The offset counter expiration signal is input to the reset terminal (RESET) of the offset counter 43. When the offset counter expiration signal is input, the offset counter 43 initializes the count value and waits for the input of the next Z-phase angle detection signal.

[0061] The operation cycle counter 44 is a counter that counts the rotor rotation signal X for the operation cycle of the accelerator 1. In the operation cycle counter 44, the rotor rotation signal X is input to a count signal input terminal (IN), an offset counter expiration signal is input from the offset counter 43 to a count start input terminal (START), and an operation cycle expiration value is input from the control register 34 of the high frequency control device 3 to a comparison signal input terminal (COMP).

[0062] When the offset counter expiration signal is input, the operation cycle counter 44 starts counting the rotor rotation signal X. The operation cycle counter 44 also successively compares the counted count value with the operation cycle expiration value, and when the count value reaches the operation cycle expiration value, outputs a rotor origin signal from the output terminal (OUT). The rotor origin signal is input to the reset terminal (RESET) of the operation cycle counter 44. When the rotor origin signal is input, the operation cycle counter 44 initializes the count value and continues counting the rotor rotation signal X.

[0063] The rotor origin signal output from the operation cycle counter 44 is also output to the host controller 6. Based on the rotor origin signal and a beam request signal (not shown) from the beam utilization system, the host controller 6 generates and outputs a master trigger signal that serves as an operation control start signal for devices such as electromagnet power supplies that constitute the accelerator 1. Based on the master trigger signal from the host controller 6, the radio frequency controller 3 starts output control of radio frequency voltage to the acceleration cavity 11.

[0064] The offset expiration value is determined by measuring the resonance frequency corresponding to the rotation angle with a network analyzer while the angle detection signals (A-phase, B-phase, and Z-phase) output from the angle detector 14 of the rotating capacitor 13 are input to the offset counter 43 and the operation cycle counter 44. Specifically, after the Z-phase angle detection signal is received from the angle detector 14 while the rotating capacitor 13 is rotating, the rotation angle at which the resonance frequency of the accelerating cavity 11 is maximized is searched for, and the count value of the offset counter 43 at the rotation angle at which the resonance frequency is maximized is set to the offset expiration value. The operation cycle expiration value is also determined by dividing the total number of rotor rotation signals X output during one rotation of the rotating capacitor 13 by the number of rotor electrodes 131 of the rotating capacitor 13.

[0065] FIG. 9 is a diagram showing a control timing chart of the high frequency control device 3.

[0066] As shown in FIG. 9, the resonant frequency of the accelerating cavity 11 changes in an S-shape as indicated by the broken line in response to the rotation of the rotating capacitor 13 .

[0067] The radio frequency control device 3 controls the frequency of the radio frequency voltage so as to follow the change in the resonant frequency of the accelerating cavity 11, thereby accelerating the charged particle beam to a desired energy.

[0068] Specifically, the high frequency control device 3 starts the operation control of the accelerator 1 based on a master trigger signal input from the upper control device 6 .

[0069] In the operation control, first, the radio frequency control device 3 updates its control parameters and waits until a frequency search timing signal (frequency search) is input. When the frequency search timing signal is input, frequency search control for searching for the resonance frequency of the accelerator 1 is started.

[0070] In the frequency search control, the high frequency control device 3 first starts outputting a low level high frequency voltage. The frequency of the low level high frequency voltage is set to a preset lock frequency (F ｌｏｃｋ ), and the amplitude value is maintained at the standby amplitude value. The low-level radio frequency voltage is amplified by the amplifier 4 and supplied to the accelerating cavity 11 via the directional coupler 5 as a high-level radio frequency voltage. In this embodiment, the lock frequency is set to the incident frequency (F ｉｎｊ ) is higher than

[0071] If the resonant frequency of the accelerating cavity 11 and the lock frequency, which is the frequency of the high-level radio frequency voltage, deviate by more than a certain amount, no radio frequency voltage is generated in the accelerating cavity 11, and therefore the output level of the acceleration voltage monitor signal remains at 0. As the resonant frequency of the accelerating cavity 11 approaches the lock frequency, the output of the acceleration voltage monitor signal gradually increases, and when the resonant frequency of the accelerating cavity 11 coincides with the lock frequency, the value of the acceleration voltage monitor signal reaches a maximum. For this reason, in this embodiment, the radio frequency voltage control unit 35 determines whether the amplitude of the acceleration voltage indicated by the acceleration voltage monitor signal exceeds a threshold voltage amplitude value (V ｌｏｃｋ ) is reached, it is determined that frequency lock has occurred. In this case, the acceleration voltage monitor signal is a response signal of the high frequency monitor of the acceleration cavity 11, and the acceleration voltage monitor 12 functions as a response signal detector that detects the response signal. The amplitude of the acceleration voltage is the resonance determination value.

[0072] As a result, in a control method in which the frequency of the control high-frequency voltage of the high-frequency voltage control unit 35 is feedback-controlled so as to reduce to zero the phase difference obtained by comparing the phase of the acceleration voltage monitor signal of the acceleration voltage monitor 12 with the phase of the traveling wave of the directional coupler 5, it is possible to determine that the frequency has been locked without taking into account the phase delay due to the cables from the acceleration voltage monitor 12 and the directional coupler 5 to the high-frequency voltage control unit 35.

[0073] The method for determining frequency lock is not limited to the above example. For example, it may be performed as follows. Specifically, the radio frequency voltage control unit 35 first calculates a voltage standing wave ratio (VSWR) representing the ratio between the traveling wave monitor signal and the reflected wave monitor signal from the directional coupler 5 during frequency search control. If the resonant frequency of the accelerating cavity 11 and the lock frequency are far apart, the radio frequency voltage supplied to the accelerating cavity 11 is totally reflected back to the amplifier 4, and the voltage standing wave ratio becomes infinity. The voltage standing wave ratio decreases as the resonant frequency of the accelerating cavity 11 approaches the lock frequency, and is minimum when these frequencies coincide. The radio frequency voltage control unit 35 calculates a threshold standing wave ratio (VSWR) representing the ratio of the traveling wave monitor signal and the reflected wave monitor signal from the directional coupler 5 during frequency search control. ｌｏｃｋ ) is reached, it is determined that frequency lock has occurred. In this case, the reflected wave monitor signal is a response signal from the high frequency monitor of the accelerating cavity 11, and the directional coupler 5 functions as a response signal detector that detects the response signal. The voltage standing wave ratio is the resonance determination value.

[0074] Even in this case, in a control method in which the frequency of the control high-frequency voltage of the high-frequency voltage control unit 35 is feedback-controlled so as to reduce to zero the phase difference obtained by comparing the phase of the acceleration voltage monitor signal of the acceleration voltage monitor 12 with the phase of the traveling wave of the directional coupler 5, it is possible to determine that the frequency has been locked without taking into account the phase delay due to the cables from the acceleration voltage monitor 12 and the directional coupler 5 to the high-frequency voltage control unit 35.

[0075] If there is a large difference between the resonant frequency of the accelerating cavity 11 and the lock frequency of the radio frequency voltage, the high-level radio frequency voltage supplied to the accelerating cavity 11 will be entirely reflected by the amplifier 4. In order to suppress the influence of this reflected high-level radio frequency voltage on the amplifier 4, a frequency search signal is input at a timing when the difference between the resonant frequency of the accelerating cavity 11 and the lock frequency becomes small.

[0076] When the frequency is locked, the radio frequency voltage control unit 35 outputs an acceleration start signal and starts frequency tracking control, which is control for making the frequency of the radio frequency voltage follow the resonance frequency of the accelerating cavity 11 .

[0077] In this embodiment, as described above, the lock frequency is higher than the incident frequency. Therefore, frequency tracking control can be started before the resonant frequency of the accelerating cavity 11 reaches the incident frequency. This allows a certain amount of waiting time to be ensured between the start of frequency tracking control and the time when the resonant frequency of the accelerating cavity 11 reaches the acceleration control interval. If this waiting time is set sufficiently longer than the response time between the start of frequency tracking control and the time when the frequency of the low-level radio-frequency voltage actually changes to follow the resonant frequency of the accelerating cavity 11, the frequency of the low-level radio-frequency voltage can be made to follow the resonant frequency of the accelerating cavity 11 from the beginning of the acceleration control interval.

[0078] In frequency tracking control, the radio frequency voltage control unit 35 sequentially compares the frequency of the low-level radio frequency voltage to determine whether it matches the injection frequency and the extraction frequency. When the frequency of the low-level radio frequency voltage matches the injection frequency, the radio frequency voltage control unit 35 outputs a beam injection signal (injection frequency arrival signal shown in FIG. 2 ) to an injection device (not shown) that injects a charged particle beam into the accelerator 1. The injection device may be, for example, a voltage power supply for an extraction electrode of an ion source. In this embodiment, the injection frequency is set so that the beam injection signal is output when the acceleration voltage monitor signal is stable. However, the output timing of the beam injection signal may be any timing as long as the frequency of the low-level radio frequency voltage reaches the lock frequency. Similarly, when the frequency of the low-level radio frequency voltage matches the extraction frequency, the radio frequency voltage control unit 35 outputs an acceleration end signal to the host control device 6 to instruct the end of acceleration of the charged particle beam, and the control transitions to beam extraction control, in which the charged particle beam is extracted from the accelerator 1.

[0079] FIG. 10 is a diagram showing an example of the configuration of the high frequency voltage control unit 35 for high frequency signal processing.

[0080] The high frequency voltage control unit 35 shown in FIG. 10 includes an ADC (Analog-to-Digital Converter) 101, an IQ conversion circuit 102, a polar coordinate conversion circuit 103, a frequency feedback calculation circuit 104, a digital oscillator 105, an amplitude feedback calculation circuit 106, an IQ conversion circuit 107, an IQ modulation circuit 108, a DAC (Digital-to-Analog Converter) 109, an LPF (Low Pass Filter) 110, an F / B operation switching circuit 111, an RF output control circuit 112, a tracking determination circuit 113, an incident frequency determination circuit 114, and an emission frequency determination circuit 115.

[0081] 10, characters in rounded squares (such as amplitude target values) indicate data stored in the control register 34. Arrows pointing towards data in the control register 34 indicate writing of data to the control register 34, and arrows pointing out from data in the control register 34 indicate reading of data from the control register 34. Characters in circles (FS, L, S, and E) indicate flag registers. Arrows pointing towards flag registers indicate writing of data, and arrows pointing out from flag registers indicate reading of data. Characters in diamonds (N) indicate an output signal from the digital oscillator 105. Initial values ​​are set in the control register 34 and the flag register in response to the input of a master trigger signal, and these values ​​are updated as appropriate as the operation sequence progresses.

[0082] The ADC 101 converts the acceleration voltage monitor signal from the acceleration voltage monitor 12 and the traveling wave monitor signal and reflected wave monitor signal from the directional coupler 5 into digital signals. The IQ conversion circuit 102 converts each digital signal converted by the ADC 101 into an IQ signal. The polar coordinate conversion circuit 103 converts the IQ signal converted by the IQ conversion circuit 102 into a polar coordinate signal including an amplitude signal AMP indicating the amplitude and a phase signal ψ indicating the phase. The output signal of the digital oscillator 105 is used as a reference signal required for detection processing in the IQ conversion circuit 102.

[0083] The frequency feedback calculation circuit 104 performs frequency tracking control to cause the frequency of the low-level radio frequency voltage output from the radio frequency voltage control unit 35 to follow the resonant frequency of the accelerating cavity 11. Since frequency tracking control is realized by feedback control, it is also called frequency feedback control. The frequency feedback calculation circuit 104 generates a frequency signal indicating the resonant frequency of the accelerating cavity 11 based on, for example, the signals converted into polar coordinate signals by the IQ conversion circuit 102 (more specifically, the phase difference between the acceleration voltage monitor signal and the traveling wave monitor signal). The frequency feedback calculation circuit 104 writes the value of the frequency signal into the control register 34 as an output frequency and outputs the frequency signal to the digital oscillator 105 to perform frequency tracking control.

[0084] The digital oscillator 105 outputs a low-level, high-frequency voltage having a frequency (output frequency) indicated by the frequency signal from the frequency feedback calculation circuit 104. In this embodiment, the digital oscillator 105 is an NCO (Numerically Controlled Oscillator).

[0085] The amplitude feedback calculation circuit 106 compares the amplitude target value, which is the target value of the amplitude of the acceleration voltage, with the amplitude value of the acceleration voltage monitor, and corrects the amplitude of the low-level radio frequency voltage through amplitude feedback control. The IQ conversion circuit 107 converts the signal from the amplitude feedback calculation circuit 106 into an IQ signal and outputs it as radio frequency voltage amplitude data indicating the amplitude value of the low-level radio frequency voltage.

[0086] The IQ modulation circuit 108 modulates the amplitude of the low-level high-frequency voltage output from the digital oscillator 105 with the high-frequency voltage amplitude data output from the IQ conversion circuit 107 .

[0087] The DAC 109 converts the low-level high-frequency voltage modulated by the IQ modulation circuit 108 into an analog signal. The LPF 110 smoothes the low-level high-frequency voltage of the analog signal output from the DAC 109 and outputs it to the amplifier 4.

[0088] The F / B operation switching circuit 111 switches the operation between the frequency feedback calculation circuit 104 and the amplitude feedback calculation circuit 106. The RF output control circuit 112 switches the output of the low-level high-frequency voltage on and off.

[0089] The tracking judgment circuit 113 compares the phase difference between the traveling wave monitor signal and the acceleration voltage monitor signal with a tracking judgment value, and judges whether the frequency tracking control is operating properly by successively determining whether the phase difference is equal to or less than the tracking judgment value. If the frequency tracking control is not operating normally (if the phase difference between the traveling wave monitor signal and the acceleration voltage monitor signal exceeds the tracking judgment value), the tracking judgment circuit 113 stops outputting the low-level high-frequency voltage.

[0090] The incident frequency determination circuit 114 compares the output frequency, which is the frequency of the low-level high-frequency voltage, with the incident frequency, and if the output frequency matches the incident frequency, it outputs an incident frequency arrival signal and injects a charged particle beam into the accelerator 1.

[0091] The extraction frequency determination circuit 115 compares the output frequency of the low-level high-frequency voltage with the extraction frequency, and if the output frequency matches the extraction frequency, outputs an extraction frequency arrival signal and extracts the charged particle beam from the accelerator 1.

[0092] The control of the frequency and amplitude of the low-level high-frequency voltage by the high-frequency voltage control unit 35 will be described in more detail below.

[0093] (1) Master Trigger Input When a master trigger signal is input, the high frequency control device 3 sets predetermined initial values ​​in the control register 34 and flag register. Thereafter, the high frequency control device 3 waits until a frequency search timing signal is input.

[0094] Since the rotating capacitor 13 is controlled to rotate at a uniform speed, the time from the input of the master trigger signal until the resonant frequency of the accelerating cavity 11 reaches the lock frequency is generally reproducible. For this reason, instead of inputting the frequency search timing signal from outside the radio frequency control device 3 (for example, from the upper control device 6), the frequency search timing signal may be input by expiration processing of a timer function that starts upon input of the master trigger signal inside the radio frequency control device 3.

[0095] (2) Frequency Search Control When a frequency search timing signal is input, the high frequency voltage control unit 35 writes the frequency search timing signal to the frequency search flag register (FS) and inputs it from the frequency search flag register to the F / B operation switching circuit 111 and the RF output control circuit 112.

[0096] When the frequency search timing signal is input, the F / B operation switching circuit 111 switches the switch FBSW2 in the frequency feedback calculation circuit 104 to the lock frequency side to set the frequency of the low-level high-frequency voltage to the lock frequency. The F / B operation switching circuit 111 also opens the switch FBSW3 in the amplitude feedback calculation circuit 106 to disable amplitude feedback control, and further switches the switch FBSW4 in the amplitude feedback calculation circuit 106 to the standby amplitude value side to set the value of the high-frequency voltage amplitude data to the standby amplitude value.

[0097] On the other hand, when the frequency search timing signal is input, the RF output control circuit 112 closes the switch RFSW provided between the IQ modulation circuit 108 and the DAC 109, and outputs a low-level high-frequency voltage from the high-frequency control device 3, with the frequency set to the lock frequency and the amplitude set to the standby amplitude value.

[0098] The low-level radio-frequency voltage output from the radio-frequency control device 3 is amplified by the amplifier 4 to a high-level radio-frequency voltage and supplied to the accelerating cavity 11 via the directional coupler 5. If the high-level radio-frequency voltage supplied to the accelerating cavity 11 deviates from the resonant frequency of the accelerating cavity 11 by more than a certain degree, no acceleration voltage, which is a radio-frequency voltage, is generated between the accelerating electrodes of the accelerating cavity 11. As the rotating capacitor 13 rotates, the resonant frequency of the accelerating cavity 11 gradually approaches the frequency of the high-level radio-frequency voltage, and an acceleration voltage is generated between the accelerating electrodes. This acceleration voltage is detected by the acceleration voltage monitor 12, and the acceleration voltage monitor 12 outputs an acceleration voltage monitor signal indicating the detected acceleration voltage.

[0099] In the radio frequency voltage control unit 35 shown in FIG. 10, the acceleration voltage monitor signal and the traveling wave monitor signal and reflected wave monitor signal from the directional coupler 5 are converted into digital signals by the ADC 101 so that they can be easily processed by the digital signal processing circuit, and then converted into phase data Φ and amplitude data amp by the polar coordinate conversion circuit 103, respectively.

[0100] The frequency feedback calculation circuit 104 determines whether the frequency is locked, i.e., whether the resonant frequency of the accelerating cavity 11 and the frequency of the high-level radio frequency voltage match, based on the acceleration voltage monitor signal from the acceleration voltage monitor 12. In this embodiment, the frequency lock determination is performed by a frequency lock determination circuit 201 in the frequency feedback calculation circuit 104. The frequency lock determination circuit 201 compares the value of the acceleration voltage monitor signal with a lock determination value stored in the control register 34, and determines that the frequency is locked when the value of the acceleration voltage monitor signal is equal to or greater than the lock determination value. The frequency lock determination circuit 201 writes a frequency lock determination signal indicating that the frequency is locked into a frequency lock flag register (L), and starts acceleration control for accelerating and extracting the charged particle beam by the accelerator 1.

[0101] (3) Start of acceleration control When the frequency lock determination signal is output, the radio frequency control device 3 performs frequency tracking control to make the frequency of the low-level radio frequency voltage follow the resonant frequency of the accelerating cavity 11, and also starts AVC (Automatic Voltage Control) to set the voltage amplitude value generated in the accelerating electrode to a desired amplitude value.

[0102] In this embodiment, frequency tracking control is performed by a PID control unit 202 in the frequency feedback calculation circuit 104, which performs PID feedback control based on the phase difference between the phase of the traveling wave monitor signal of the directional coupler 5 and the phase of the acceleration voltage monitor. Also, AVC is performed by a PI control unit 301 in the amplitude feedback calculation circuit 106, which performs PI feedback control based on the deviation of the detection signal of the acceleration voltage monitor from the amplitude target value, which is the target value of the acceleration voltage. The operations of these two feedback calculation circuits will be described in more detail below.

[0103] When a frequency lock determination signal is written to the frequency lock flag register (L), the F / B operation switching circuit 111 closes the switch FBSW1 in the frequency feedback calculation circuit 104 and switches the switch FBSW2 to the feedback loop side to enable feedback control. The F / B operation switching circuit 111 also closes the switch FBSW3 in the amplitude feedback calculation circuit 106 and switches the switch FBSW4 to the feedback loop side. By switching these switches FBSW1 to FBSW4, frequency feedback control and amplitude feedback control become enabled.

[0104] In the amplitude feedback control, the amplitude feedback calculation circuit 106 uses the amplitude target value data 334 in the memory 33 to update the amplitude target value stored in the control register 34 in accordance with the rotor rotation signal, thereby controlling the amplitude of the low-level high-frequency voltage in synchronization with changes in the frequency of the low-level high-frequency voltage.

[0105] Furthermore, when a frequency lock determination signal is written to the frequency lock flag register (L), the initial phase difference sample and hold circuit (S / H) 203, tracking determination circuit 113, incident frequency determination circuit 114, and output frequency determination circuit 115 in the frequency feedback calculation circuit 104 start operating. The operation of these four circuits will be described below.

[0106] (A) Initial Phase Difference Sample-and-Hold Circuit 203 The initial phase difference sample-and-hold circuit 203 is an initial phase storage unit that samples and holds, as an initial phase difference, the phase difference between the phase of the traveling wave monitor signal of the directional coupler 5 when the frequency is locked and the phase of the acceleration voltage monitor signal from the acceleration voltage monitor 12. By using the phase difference when the frequency is locked as the initial phase difference, it becomes easier to understand changes in the phase difference during frequency tracking control, and the tracking judgment value set in the tracking judgment circuit 113 can be managed at a constant value regardless of the operation cycle. Furthermore, monitoring the deviation from the initial phase difference makes it easier to adjust the control parameters of the frequency feedback calculation circuit 104 when adjusting the accelerator 1.

[0107] (B) Tracking Determination Circuit 113 The tracking determination circuit 113 determines whether frequency tracking control is being performed normally in order to stably accelerate the charged particle beam. If the phase difference between the acceleration voltage monitor signal and the traveling wave monitor signal exceeds a predetermined tracking determination value, the tracking determination circuit 113 determines that frequency tracking control is not being performed normally and outputs a tracking abnormality signal. The tracking abnormality signal is stored in a tracking abnormality flag register (E) and input from the tracking abnormality flag register (E) to the RF output control circuit 112. When the tracking abnormality signal is input, the RF output control circuit 112 opens the switch RFSW and stops outputting the low-level radio frequency voltage.

[0108] (C) Incident Frequency Determination Circuit 114 The incident frequency determination circuit 114 successively compares the output frequency written in the control register 34, i.e., the resonance frequency of the accelerating cavity 11, with the extraction frequency written in the control register 34, and when the output frequency matches the incident frequency, outputs an incident frequency arrival signal from the output terminal DO. Based on this incident frequency arrival signal, a charged particle beam is injected from the injection device into the accelerator 1.

[0109] (D) Extraction Frequency Determination Circuit 115 The extraction frequency determination circuit 115 successively compares the output frequency written in the control register 34, i.e., the resonance frequency of the accelerating cavity 11, with the extraction frequency written in the control register 34, and when the output frequency matches the extraction frequency, outputs an extraction frequency arrival signal from the output terminal DO. Based on this extraction frequency arrival signal, a beam extraction radio frequency voltage for extracting the charged particle beam from the accelerator 1 is supplied to an extraction electrode (not shown) in the accelerator 1, and the charged particle beam circulating within the accelerator 1 is extracted to the outside of the accelerator 1.

[0110] The output frequency arrival signal is also stored in the output frequency determination register (S). The RF output control circuit 112 opens the switch RFSW at the timing when the output frequency arrival signal is stored in the output frequency determination register (S) to stop the output of the low-level radio frequency voltage. At the timing when the output frequency arrival signal is stored, the frequency tracking control by the frequency feedback calculation circuit 104 and the amplitude feedback control by the amplitude feedback calculation circuit 106 are stopped, and the radio frequency control device 3 waits for the input of the next master trigger signal.

[0111] The radio frequency voltage control unit 35 may be configured entirely or partially as a digital circuit. If the initial phase difference sample-and-hold circuit 203 is a digital circuit, the initial phase difference sample-and-hold circuit 203 may set the initial phase difference (the phase difference between the phase of the traveling wave monitor signal from the directional coupler 5 and the phase of the acceleration voltage monitor signal from the acceleration voltage monitor 12) to zero when the radio frequency voltage control unit 35 locks the frequency, i.e., when frequency tracking control begins. In this case, it is not necessary to precisely match the length of the cable from the acceleration voltage monitor 12 to the radio frequency voltage control unit 35 with the length of the cable from the directional coupler 5 to the radio frequency voltage control unit 35, thereby simplifying hardware adjustment. The difference in the lengths of the cables may be, for example, within approximately one-quarter of the wavelength of the radio frequency voltage. Furthermore, the method for setting the initial phase difference to zero is not particularly limited, and examples thereof include digital processing using orthogonal transformation.

[0112] Fig. 11 is a diagram showing another example of the configuration related to radio frequency signal processing of the radio frequency voltage control unit 35. The radio frequency voltage control unit 35 shown in Fig. 11 differs from the radio frequency voltage control unit 35 shown in Fig. 10 in that the frequency lock determination circuit 201 uses the output result of the VSWR calculation circuit 204 to determine whether the frequency is locked, instead of using the value of the acceleration voltage monitor signal.

[0113] The VSWR calculation circuit 204 calculates a voltage standing wave ratio VSWR, which indicates the ratio between the forward wave monitor signal and the reflected wave monitor signal from the directional coupler 5 during frequency search control. Specifically, the voltage standing wave ratio VSWR can be calculated from the value of the forward wave component (detected voltage) and the value of the reflected wave component (detected voltage) of the directional coupler, as shown in Equation 3 and Equation 4. where Γ is the voltage reflection coefficient and Z ０ denotes the characteristic impedance of the transmission line, Z denotes the impedance of the load, and V ＦＷＤ indicates the detected voltage of the traveling wave component (output voltage of the traveling wave monitor signal), and V ＲＥＦ indicates the detected voltage of the reflected wave component (output voltage of the reflected wave monitor signal).

[0114] The frequency lock determination circuit 201 determines that the frequency is locked when the voltage standing wave ratio calculated by the VSWR calculation circuit 204 reaches a predetermined value (VSWRlock).

[0115] Fig. 12 is a diagram showing an example of the configuration of a particle therapy system including the accelerator system 100 described in Fig. 1 to Fig. 11. In Fig. 12, the particle therapy system 500 includes an accelerator 1 including the accelerator system 100, a beam transport device 502 that transports a charged particle beam supplied from the accelerator 1 to an irradiation device 504, a rotating gantry device 503 that enables the charged particle beam to be irradiated from any angle on the patient, an irradiation device 504 that forms an irradiation field by adjusting the charged particle beam transported by the beam transport device 502 and the rotating gantry device 503 to the shape of the affected area of ​​the patient 600, a treatment table 505 that positions and fixes the patient 600 in the irradiation field, and a host control device 6 that controls these devices in an integrated manner.

[0116] The irradiation device 504 controls the irradiation field of the charged particle beam according to the shape of the affected area of ​​the patient 600. Specifically, the irradiation device 504 manages and controls the irradiation dose by dividing the shape of the affected area into dose division regions, which are multiple irradiation positions called spots, and applying a desired dose to each spot. The depth direction (range) of the spot position from the body surface is controlled by the energy of the charged particle beam supplied from the accelerator 1, and the irradiation position is controlled by a scanning electromagnet (not shown) in the irradiation device 504. The irradiation dose and beam position are measured by a dose monitor 506 and a spot position monitor 507 installed on the irradiation path of the irradiation device 504, and the upper control device 6 monitors and controls the irradiation dose and spot position of the charged particle beam. The upper control device 6 pre-stores irradiation dose values ​​(target values) that are targets for the irradiation dose of the charged particle beam for each spot position.

[0117] In the particle beam therapy system 500, the energy of the charged particle beam supplied from the accelerator 1 is set according to the range of the spot position. The accelerator system 100 sets an extraction energy determination value based on the input of the extraction energy of the charged particle beam from the host controller 6. After treatment begins, the accelerator 1 injects a charged particle beam from the ion source, and the accelerator system 100 accelerates the charged particle beam to a desired energy. When the energy of the charged particle beam reaches the extraction energy, an acceleration end signal is output to the host controller 6. After extraction from the accelerator 1, the accelerated charged particle beam is supplied to the irradiation device 504 via the beam transport device 502 and the rotating gantry device 503. When the irradiation device 504 starts irradiating the spot position with the charged particle beam, the host controller 6 begins monitoring and controlling the irradiation dose and irradiation position using the dose monitor 506 and the spot position monitor 507. Based on the irradiation dose data measured by the dose monitor 506, when the irradiation dose at a certain spot position reaches a target value, the host controller 6 changes the spot position to be irradiated with the charged particle beam to the next spot position, thereby irradiating each spot position with the charged particle beam in sequence. In this embodiment, the host controller 6 changes the beam irradiation position using the scanning magnet and irradiates the charged particle beam again. However, instead of controlling the scanning magnet, the irradiation position may be changed by moving the treatment table 505. After repeating this irradiation control and completing irradiation of all spot positions within the range, the host controller 6 outputs an energy change command to the accelerator system 100. Based on this energy change command, the accelerator system 100 updates the extraction frequency data and then starts accelerating the charged particle beam. By repeating this series of controls, the affected area of ​​the patient 600 can be irradiated with the desired dose.

[0118] As described above, according to this embodiment, the accelerator 1 includes the accelerating cavity 11 that uses an input radio-frequency voltage to excite an accelerating radio-frequency voltage corresponding to the resonance frequency, and the rotating capacitor 13, which is a modulator that temporally varies the resonance frequency. The accelerator 1 accelerates the incident charged particle beam to the extraction energy level using the accelerating radio-frequency voltage. The radio-frequency control device 3 inputs a control radio-frequency voltage having a predetermined lock frequency to the accelerating cavity 11. When the resonance determination value reaches a threshold, the accelerator 13 starts feedback control to modulate the frequency of the control radio-frequency voltage so that it follows the change in the resonance frequency. Therefore, the feedback control can be started at an appropriate timing without considering the phase delay of the accelerating radio-frequency voltage or the control radio-frequency voltage, and therefore, it is possible to easily suppress a decrease in the number of particles accelerated (extracted) in the charged particle beam.

[0119] In this embodiment, the resonance determination value is a voltage standing wave ratio, which is the ratio between the forward component and the reflected component of the amplitude of the acceleration high-frequency voltage or the control high-frequency voltage. In this case, it is possible to appropriately grasp the difference between the lock frequency and the resonance frequency, and therefore it is possible to start feedback control at a more appropriate timing.

[0120] Furthermore, in this embodiment, the initial phase difference sample-and-hold circuit 203 stores the phase difference between the control high-frequency voltage and the response signal as zero when feedback control begins. In this case, changes in the phase difference during frequency tracking control become easier to understand, and the tracking determination value set in the tracking determination circuit 113 can be managed at a constant value regardless of the operation cycle. Furthermore, monitoring the deviation from the initial phase difference makes it easier to adjust the control parameters of the frequency feedback calculation circuit 104 when adjusting the accelerator 1.

[0121] In this embodiment, the lock frequency is constant, which makes it easier to determine the timing for starting feedback control.

[0122] 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 these embodiments. Those skilled in the art can implement the present disclosure in various other forms without departing from the scope of the present disclosure. Furthermore, the components described in the present embodiment can be selected arbitrarily, and the disclosure including the selected configurations is also included in the present disclosure. Furthermore, the configurations described in the claims can be combined in combinations other than those explicitly stated in the claims.

[0123] For example, although the accelerator 1 to be controlled in the present disclosure is described as a circular accelerator that accelerates an injected charged particle beam while causing it to circulate, the accelerator 1 may also be a linear accelerator.

[0124] 1: Accelerator 2: Rotating condenser control device 3: High-frequency control device 4: Amplifier 5: Directional coupler 6: Host control device 11: Accelerating cavity 12: Accelerating voltage monitor 13: Rotating condenser 14: Angle detector 15: Motor 19: Host control system 31: External interface unit 32: Operation control unit 33: Memory 34: Control register 35: High-frequency voltage control unit 36: High-frequency interface unit 37: External device control timing signal output unit 38: External interface bus 39: Internal interface bus 40: Counter circuit 41: Waveform shaping circuit 42: Rotor rotation signal generation circuit 43: Offset counter 44: Operation cycle counter 100: Accelerator system 102: IQ conversion circuit 103: Polar coordinate conversion circuit 104: Frequency feedback calculation circuit 105: Digital oscillator 106: Amplitude feedback calculation circuit 107: IQ conversion circuit 108: IQ modulation circuit 110: LPF 111: B operation switching circuit 112: RF output control circuit 113: Tracking determination circuit 114: Incident frequency determination circuit 115: Extraction frequency determination circuit 131: Rotor electrode 132: Stator electrode 133: Superimposing unit 201: Frequency lock determination circuit 202: PID control unit 203: Initial phase difference sample hold circuit 204: VSWR calculation circuit 301: PI control unit 500: Particle beam therapy system 502: Beam transport device 503: Rotating gantry device 504: Irradiation device 505: Treatment table 600: Patient

Claims

1. An accelerator system comprising: an accelerator cavity that uses an input control radio-frequency voltage to excite an acceleration radio-frequency voltage according to a resonance frequency, and that accelerates an incident charged particle beam with the acceleration radio-frequency voltage and extracts it; a response signal detection unit that detects a response signal from a radio-frequency monitor of the acceleration cavity; and a radio-frequency control device that inputs the control radio-frequency voltage having a predetermined lock frequency to the acceleration cavity, and when a resonance judgment value based on the detected response signal reaches a threshold, starts feedback control to modulate the frequency of the control radio-frequency voltage so as to follow the resonance frequency that changes over time.

2. The accelerator system according to claim 1, wherein the response signal detection unit is a voltage detection unit that detects the acceleration high-frequency voltage as the response signal, and the resonance judgment value is the amplitude of the acceleration high-frequency voltage detected by the voltage detection unit.

3. The accelerator system according to claim 1, wherein the response signal detection unit is a component detection unit that detects a traveling wave component of the control high-frequency voltage directed toward the accelerating cavity as the response signal, and also detects a reflected wave component reflected by the accelerating cavity, and the resonance judgment value is a voltage standing wave ratio, which is the ratio between the traveling wave component and the reflected wave component.

4. An accelerator system according to any one of claims 1 to 3, wherein the high frequency control device further has an initial phase storage unit that stores the phase difference between the control high frequency voltage and the response signal as zero when the feedback control starts.

5. The accelerator system according to claim 4, wherein the initial phase storage unit is configured with a digital circuit and stores the phase difference as zero by digital processing using an orthogonal transformation at the start of the feedback control.

6. An accelerator system according to any one of claims 1 to 5, wherein the lock frequency is constant.

7. A particle beam therapy system comprising: an accelerator system according to any one of claims 1 to 6; and an irradiation device that irradiates a patient with a charged particle beam extracted from the accelerator system.

8. A particle beam therapy system according to claim 7, further comprising: a dose monitor that measures the irradiation dose of the charged particle beam; and a host control device that controls the charged particle beam to be irradiated in sequence to a plurality of irradiation positions within the patient, wherein the host control device changes the irradiation position to which the charged particle beam is irradiated when the irradiation dose irradiated to any of the irradiation positions reaches a target value.

9. A particle beam therapy system as described in claim 8, wherein the high frequency control device changes the energy of the charged particle beam extracted from the accelerator when an energy change command is input, and the upper control device outputs the energy change command to the high frequency control device when irradiation of the charged particle beam having a predetermined energy is completed.

10. A control method for an accelerator having an accelerating cavity that excites an accelerating radio-frequency voltage according to a resonance frequency using an input control radio-frequency voltage, and that accelerates and extracts an injected charged particle beam using the accelerating radio-frequency voltage, comprising the steps of: detecting a response signal from a radio-frequency monitor of the accelerating cavity; inputting the control radio-frequency voltage having a predetermined lock frequency to the accelerating cavity; and, when a resonance judgment value based on the detected response signal reaches a threshold, starting feedback control to modulate the frequency of the control radio-frequency voltage so as to follow the resonance frequency that changes over time.

11. The control method according to claim 10, wherein the response signal detection comprises detecting the accelerating high frequency voltage as the response signal, and the resonance determination value is the amplitude of the detected accelerating high frequency voltage.

12. A control method as described in claim 10, wherein in detecting the response signal, a traveling wave component of the control high frequency voltage directed toward the accelerating cavity is detected, and a reflected wave component reflected by the accelerating cavity is detected as the response signal, and the resonance judgment value is a voltage standing wave ratio, which is the ratio between the traveling wave component and the reflected wave component.

13. A control method according to any one of claims 10 to 12, wherein the phase difference between the control high frequency voltage and the response signal is stored as zero at the start of the feedback control.

14. The control method according to claim 13, wherein the storage of the phase difference uses a digital circuit to store the phase difference as zero through digital processing using an orthogonal transformation at the start of the feedback control.

15. A control method according to any one of claims 10 to 13, wherein the lock frequency is constant.

16. A method for controlling a particle beam therapy system comprising: an accelerator having an acceleration cavity that uses an input control radio-frequency voltage to excite an acceleration radio-frequency voltage according to a resonance frequency, and that accelerates and extracts an injected charged particle beam by the acceleration radio-frequency voltage; and an irradiation device that irradiates a patient with the charged particle beam extracted from the accelerator, the method comprising: detecting a response signal of a radio-frequency monitor of the acceleration cavity; inputting the control radio-frequency voltage having a predetermined lock frequency into the acceleration cavity; and, when a resonance judgment value based on the detected response signal reaches a threshold, starting feedback control to modulate the frequency of the control radio-frequency voltage so as to follow the time-varying resonance frequency; measuring an irradiation dose of the charged particle beam; and controlling the charged particle beam to be irradiated sequentially to a plurality of irradiation positions in the patient; and, in the control, changing the irradiation position to which the charged particle beam is irradiated when the irradiation dose irradiated to any of the irradiation positions reaches a target value.

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