Accelerator, particle beam therapy system, and control method

Abstract

The present invention provides an accelerator capable of extracting a charged particle beam having a desired energy with high accuracy. An acceleration voltage measurement circuit (10) outputs an acceleration voltage signal (V acc ) as a measurement signal obtained by measuring an acceleration high-frequency voltage excited by an acceleration cavity (9). A low-power high-frequency control system (25) inputs, to the acceleration cavity (9), as a high-frequency power, a control high-frequency power of a certain frequency included in a range of a resonance frequency of the acceleration cavity (9). The low-power high-frequency control system (25) inputs, as the high-frequency power, to the acceleration cavity (9), an acceleration high-frequency power synchronized with an acceleration frequency that is a frequency of the acceleration voltage signal (V acc ) by feedback control, in a case where a phase difference between the acceleration voltage signal (V acc ) and the control high-frequency power is within a predetermined value, and then stops inputting the acceleration high-frequency power to the acceleration cavity (9) in a case where the acceleration frequency reaches an output frequency (F ext ).

Description

Technical Field

[0001] This disclosure relates to accelerators, particle beam therapy systems, and control methods. Background Technology

[0002] As an accelerator for accelerating and ejecting charged particle beams, attention has been paid to circular accelerators that accelerate charged particle beams by applying a time-modulated accelerating electric field within a main magnetic field of constant intensity over time. Such circular accelerators can use superconducting coils to generate the main magnetic field, thus facilitating miniaturization and cost reduction, and are particularly suitable for applications such as particle beam therapy systems.

[0003] In circular accelerators, tuned cavities are sometimes used as accelerating cavities for the high-frequency electric field used to excite acceleration in order to accelerate charged particle beams. In this case, the resonant frequency of the accelerating cavity is modulated in time by changing the capacitance or inductance of the accelerating cavity. At this time, the high-frequency power input to the accelerating cavity needs to be tuned to the accelerating cavity (having a frequency approximately the same as the resonant frequency of the accelerating cavity). As a technique for modulating the resonant frequency of the accelerating cavity, there is a technique in which a rotating capacitor having opposing rotor-stator electrode pairs is provided in the accelerating cavity as a modulator for modulating the accelerating cavity (see Patent Document 1).

[0004] Furthermore, examples of circular accelerators include synchrotron accelerators and the eccentric orbit accelerator described in Patent Document 1. In a synchrotron accelerator, since the energy of the emitted charged particle beam, i.e., the emission energy, is fixed, the high-frequency power input to the accelerating cavity is cut off after a certain period of time following beam incidence. On the other hand, in the eccentric orbit accelerator described in Patent Document 2, since the emission energy is variable, it is necessary to cut off the high-frequency power input to the accelerating cavity at an appropriate timing corresponding to the emission energy.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: U.S. Patent Application Publication No. 2010 / 0045213

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-133745 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In accelerators that use tuned cavities as accelerating cavities, it is necessary to tune the high-frequency power input to the accelerating cavity with the accelerating cavity. However, in the modulation mode of the accelerating cavity, errors arise corresponding to the manufacturing tolerances and control deviations of the modulator, as well as the temperature of the accelerating cavity.

[0011] In the technology described in Patent Document 2, the programmed frequency pattern signal is input into the accelerating cavity as high-frequency power for acceleration via a high-frequency power amplifier. Therefore, it is strongly affected by the error 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 geared towards synchrotron accelerators, it is particularly difficult to cut off the high-frequency power for acceleration at an appropriate timing corresponding to the desired output energy, especially when it is intended for application in eccentric orbital accelerators.

[0012] The purpose of this invention is to provide an accelerator, a particle beam therapy system, and a control method capable of extracting charged particle beams with desired energy with high precision.

[0013] Methods for solving problems

[0014] One aspect of the accelerator disclosed herein accelerates a beam of charged particles while it orbits the particle using a time-constant main magnetic field and a high-frequency voltage for acceleration. The accelerator comprises: an acceleration cavity that uses input high-frequency power to excite the high-frequency voltage for acceleration, which corresponds to a time-varying resonant frequency; a measurement unit that outputs a measurement signal obtained by measuring the high-frequency voltage for acceleration; and a control unit that inputs high-frequency power for control at a certain frequency encompassing the range of the resonant frequency into the acceleration cavity as the high-frequency power. When the phase difference between the measurement signal and the high-frequency power for control is within a predetermined value, the control unit, through feedback control, inputs high-frequency power for acceleration synchronized with the acceleration frequency, which is the frequency of the measurement signal, into the acceleration cavity as the high-frequency power. When the acceleration frequency reaches a required value, the input of the high-frequency power for acceleration into the acceleration cavity is stopped.

[0015] Invention Effects

[0016] According to the present invention, it is possible to extract a beam of charged particles with the desired energy with high precision. Attached Figure Description

[0017] Figure 1 This is a perspective view showing an example of the appearance of a circular accelerator according to an embodiment of the present disclosure.

[0018] Figure 2 This is a cross-sectional view showing a structural example of a circular accelerator according to an embodiment of the present disclosure.

[0019] Figure 3 This is a longitudinal sectional view showing a structural example of a circular accelerator according to an embodiment of the present disclosure.

[0020] Figure 4 This is a diagram illustrating an example of the orbital paths of a beam of charged particles at various energies.

[0021] Figure 5 This is a diagram illustrating an example of the structure of a low-power, high-frequency control system.

[0022] Figure 6 This is a timing diagram used to illustrate the control sequence of a low-power, high-frequency control system.

[0023] Figure 7 This is a diagram illustrating a structural example of a particle beam therapy system according to an embodiment of the present disclosure. Detailed Implementation

[0024] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0025] [Example 1]

[0026] Figures 1-3 This is a diagram illustrating an example of a circular accelerator according to an embodiment of the present disclosure. Figures 1-3 The accelerator 100 shown is a circular accelerator that accelerates a charged particle beam (hereinafter sometimes simply referred to as a beam) while it orbits within a main magnetic field of constant intensity over time by applying a frequency-modulated high-frequency voltage for acceleration. In this embodiment, the accelerator 100 uses a proton beam, which is used as the charged particle, as the beam and accelerates it to an arbitrary energy of 70 MeV to 235 MeV before ejecting it. The charged particle beam can also be a heavy particle beam using helium or carbon, and the energy of the emitted beam, i.e., the emission energy, is not limited to the range of 70 MeV to 235 MeV. Furthermore, the accelerator 100 is suitable for particle beam therapy systems (see [reference]). Figure 7 However, it is not limited to this purpose.

[0027] Figure 1 This is a three-dimensional view showing the appearance of accelerator 100. Figure 2 This is a cross-sectional view showing the structure after the accelerator 100 is cut along the longitudinal center plane. Figure 3 This means that the accelerator 100 will be along Figure 2 A longitudinal sectional view of the structure after the longitudinal section is cut off by line b-b'.

[0028] The accelerator 100 has a main electromagnet 40 that can be divided into an upper and a lower part across a central plane D. Inside the main electromagnet 40, a roughly cylindrical space, namely an acceleration region 101, is formed to accelerate the beam. The acceleration region 101 is formed to be roughly symmetrical vertically across the central plane D and is evacuated.

[0029] The main electromagnet 40 has a yoke 41, a main coil 42, and main magnetic poles 43. The yoke 41 forms the outer shell of the main electromagnet 40, and forms an acceleration region 101 inside. The main coils 42 are annular superconducting coils, respectively arranged in the vertical direction with a central plane D between them. The main coils 42 are arranged along the inner wall of the yoke 41. A cooling mechanism, namely a cryostat 50, is provided around the main coils 42 to cool them to a certain temperature (the temperature at which the main coils 42 are completely diamagnetic) or below. The main magnetic poles 43 are arranged in the vertical direction with a central plane D between them on the inner circumference of the main coils 42.

[0030] When current is supplied to the main coil 42, a time-constant magnetic field, known as the main magnetic field, is excited in the acceleration region 101 through the main magnetic pole 43. Due to the influence of this main magnetic field, the beam orbits on the track plane of the acceleration region 101. At this time, the beam orbits on different tracks according to its energy. Hereinafter, each track of the beam orbiting according to its energy will be referred to as the orbital track. In this embodiment, the main electromagnet 40 is formed such that the center of the orbital track of the beam is off-center (offset from the physical center of the acceleration region 101) (see reference). Figure 4 That is, the accelerator 100 in this embodiment is an eccentric orbital accelerator. Furthermore, in Figure 2 The diagram shows the maximum energy orbit 61, around which the beam with the highest energy in the orbit is orbited, and the minimum output energy orbit 62, with an energy of 70 MeV.

[0031] Additionally, an ion source 51 is provided on the upper part of the main electromagnet 40. This ion source 51 generates a beam that is directed into the acceleration region 101 located 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 the ion incident section 53 within the acceleration region 101 via a low-energy beam delivery system 52. Thus, the beam generated by the ion source 51 is directed from the ion incident section 53 into the acceleration region 101 via the low-energy beam delivery system 52. In this embodiment, the ion incident section 53 is positioned on the beam exit path inlet 82 side, relative to the physical center O of the acceleration region 101, on the centerline A passing through the center of the accelerator 100. The beam exit path inlet 82 is the entrance port of the magnetic channel 81 for extracting the beam to the outside. Alternatively, the ion source 51 may also be located inside the acceleration region 101. In this case, a PIG (Penning Ionization Gauge) type ion source is preferred as the ion source 51.

[0032] In addition, such as Figure 1 and Figure 2As shown, the yoke 41 has multiple through-holes. For example, the yoke 41 has 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 center plane D of the main electromagnet 40.

[0033] The beam penetration 71 is a penetration for beam emission, and a high-energy beam delivery system 80 is provided for extracting the beam from the inside of the magnetic yoke 41 to the outside for beam emission. The high-energy beam delivery system 80 is connected to the magnetic channel 81. The coil penetration 72 is a penetration for leading out various coils (main coil 42, etc.) located inside the magnetic yoke 41. The vacuum evacuation penetration 73 is a penetration for evacuating the acceleration region 101. The high-frequency system penetration 74 is a penetration for inserting into the acceleration cavity 9.

[0034] The acceleration cavity 9 is a component used to excite a high-frequency voltage for acceleration, which is used to accelerate the beam incident from the ion incident section 53 into the acceleration region 101. In this embodiment, the acceleration cavity 9 is a λ / 2 resonant cavity, having a D-shaped electrode 12, a virtual D-shaped electrode 13, an inner conductor 14, an outer conductor 15, and a rotating capacitor 30.

[0035] The D-shaped electrode 12 is a hollow electrode through which the beam passes, having a generally fan-shaped shape with a point near the ion incident section 53 as its vertex and a predetermined expansion angle. The inner conductor 14 is a conductor connected to the D-shaped electrode 12 and extending from the D-shaped electrode 12 to the outside of the main electromagnet 40. The outer conductor 15 is a conductor that encloses the D-shaped electrode 12 and the inner conductor 14. The virtual D-shaped electrode 13 is an electrode with a ground potential and is connected to the outer conductor 15. The virtual D-shaped electrode 13 is positioned opposite the D-shaped electrode 12, and an acceleration gap 11 for exciting a high-frequency voltage is formed between the D-shaped electrode 12 and the virtual D-shaped electrode 13.

[0036] The rotating capacitor 30 is a modulator used to modulate the resonant frequency of the accelerating cavity 9. Specifically, the rotating capacitor 30 changes its electrostatic capacitance in accordance with the rotation angle of the rotating electrode (not shown) rotated by the motor 31, thereby causing the resonant frequency of the accelerating cavity 9 to change over time. The accelerating cavity 9 is excited with a high-frequency voltage for acceleration corresponding to this time-varying resonant frequency at the acceleration gap 11. A detection unit (not shown) is provided in the rotating capacitor 30 or the motor 31 to detect the rotation angle of the rotating electrode and output it as an angle signal. In addition, the acceleration gap 11 is formed according to the trajectory shape of the beam. Furthermore, in this embodiment, the harmonic number is 1, that is, the surrounding frequency of the beam is approximately the same as the frequency of the high-frequency voltage for acceleration (more specifically, the frequency of the accelerating electric field based on the high-frequency voltage for acceleration), i.e., the acceleration frequency.

[0037] In addition, the acceleration cavity 9 is connected to the low-power high-frequency control system 25 via the input coupler 20. 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.

[0038] The low-power high-frequency control system 25 outputs low-power high-frequency power. The high-frequency power amplifier 7 amplifies the high-frequency power output from the low-power high-frequency control system 25 and inputs it to the acceleration cavity 9 via the input coupler 20. The input coupler 20 is a device for inputting high-frequency power into the acceleration cavity and is connected to the inner conductor 14 of the acceleration cavity 9 via electrostatic or magnetic coupling. The acceleration cavity 9, through the high-frequency power input via the input coupler 20, excites an acceleration high-frequency voltage in the acceleration gap 11, which generates an accelerating electric field that accelerates the beam. As described later, the input high-frequency measurement circuit 8 measures the high-frequency power input to the acceleration cavity 9.

[0039] In the accelerator 100 described above, a beam of charged particles generated by the ion source 51 is incident from the ion incident section 53 into the acceleration region 101 formed inside the main electromagnet 40 via the low-energy beam delivery system 52. The incident beam is accelerated by the accelerating electric field excited by the acceleration cavity 9, and orbits in the main magnetic field while increasing its energy. As the energy of the beam increases, the radius of curvature of the beam's trajectory increases, thus the beam traces a helical trajectory.

[0040] Furthermore, in this embodiment, the trajectory of the energy beam, i.e., the orbital path, becomes an eccentric orbit. The main magnetic field that realizes the eccentric orbit will be explained below.

[0041] The main magnetic field can be a magnetic field with a constant circumferential strength relative to the orbit, or it can be an AVF (Azimuthal Varying Field) type magnetic field with a circumferentially varying strength. In either case, the main magnetic field is a non-isochronous magnetic field, generated in a manner that satisfies the beam stability condition. The beam stability condition is expressed by the following equation (1), where the value of n is greater than 0 and less than 1.

[0042] [Number 1]

[0043]

[0044] Here, ρ is the deflection radius around the orbit, B is the strength of the main magnetic field, and δB / δr is the magnetic field gradient in the radial direction. Furthermore, the r-axis is the axis pointing outwards in the radial direction when the orbital plane is represented by a two-dimensional polar coordinate system with the center of the acceleration region 101 as the origin.

[0045] Under the condition of beam stabilization, a beam that is slightly deflected radially from the orbit experiences a restoring force from the main magnetic field in the direction that returns the beam to the orbit, and a beam that is deflected in the direction vertical relative to the orbital plane experiences a restoring force from the main magnetic field in the direction that returns to the orbital plane. That is, the beam stably orbits and accelerates while undergoing electron cyclotron acceleration oscillations near the orbital plane. Furthermore, in the beam of all energy, the electron cyclotron acceleration oscillation number (horizontal harmonics) in the direction parallel to the orbital plane and orthogonal to the orbital plane is v. r It becomes a value close to 1. Furthermore, the main magnetic field is formed by the main magnetic pole 43 and fine-tuning coils and pole pieces (not shown) disposed on the surface of the main magnetic pole 43; these structural elements are configured symmetrically with respect to the track plane. Therefore, the main magnetic field on the track plane only has a component in the direction perpendicular to the track plane.

[0046] Figure 4 This represents the orbital path of each energy level of the beam circulating within the main magnetic field. Figure 4 In this configuration, the vertical axis is set as the axis extending from the beam exit path inlet 82 toward the inner conductor 14 of the acceleration cavity 9, and the origin 0 is set as the position of the ion incident section 53. Additionally, in Figure 4 In the example, as orbital orbit 200, an orbital orbit with a maximum energy of 235 MeV is shown on the outermost orbital orbit, and 50 orbital orbits with the magnetic stiffness of the beam differing by 0.04 Tm each time starting from this orbital orbit.

[0047] like Figure 4 As shown, in the eccentric orbit type accelerator 100, when the beam energy is low, similar to cyclotron type accelerators, the orbital 200 approximates a concentric orbit centered near the ion incident section 53. However, when the beam energy is high, the orbital 200s do not become concentric orbits, but rather become orbits that converge at the beam exit path inlet 82 and disperse at the inner conductor 14. Hereinafter, the region where the orbital 200s converge is sometimes referred to as the convergence region, and the region where the orbital 200s disperse is referred to as the dispersion region.

[0048] In addition, Figure 4 In the diagram, every π / 20 of the converging region represents an equal-circling phase line 201 connecting the same circling phase of each of the circling orbits 200. The acceleration gap 11 formed between the D-shaped electrode 12 and the virtual D-shaped electrode 13 is positioned along any one of the equal-circling phase lines 201 (e.g., an equal-circling phase line 201 encircling ±90 degrees when viewed from the converging point where the circling orbits 200 are closest to each other). More specifically, the D-shaped electrode 12 is made into a hollow fan-shaped structure with its leading edge near the center of the circling orbit 200 and its radius along the equal-circling phase line 201.

[0049] return Figures 1-3 The following description is provided. Inside the main electromagnet 40, in order to extract the surrounding beam to the outside, a high-frequency impactor 90, an interference magnetic field consisting of a two-pole magnetic field or a multi-pole magnetic field (i.e., a stripping magnetic field region 91), and a regenerating magnetic field region 92 are formed. The high-frequency impactor 90 is located in the beam convergence region, and the stripping magnetic field region 91 and the regenerating magnetic field region 92 are located on the outer periphery relative to the maximum energy track 61.

[0050] The high-frequency impactor 90 applies a high-frequency voltage for extracting the beam to the outside. The frequency of the high-frequency voltage for extraction is set to approximately equal to the horizontal harmonic v of the beam with the desired output energy. r The fractional part of the output voltage is the product of the orbital frequency of the beam with the desired output energy. Alternatively, the high-frequency voltage used for extraction can also be a high-frequency voltage with a finite bandwidth containing approximately the same frequency components as the product.

[0051] Through the high-frequency voltage from the high-frequency impactor 90, the amplitude of the horizontal electron cyclotron acceleration vibration of the beam continuously increases resonantly, and the beam reaches the stripping magnetic field region 91 and the regeneration magnetic field region 92. The beam undergoes two resonances in the stripping magnetic field region 91 and the regeneration magnetic field region 92, thereby jumping to the outside of the maximum energy trajectory 61 and reaching the beam exit path inlet 82. Afterwards, the beam is guided into the magnetic channel 81, subjected to sufficient deflection, and exits the accelerator 100 through the high-energy beam delivery system 80.

[0052] Thus, in this embodiment, since the beam is extracted from near the convergence area, the jump required to extract the beam can be reduced, and a beam with the desired emission energy can be easily extracted.

[0053] Figure 5 This illustrates the structure of a low-power high-frequency control system 25. Figure 5The low-power high-frequency control system 25 shown is a control unit for controlling the acceleration cavity 9, and includes an oscillator 1, a switching 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. Furthermore, the low-power high-frequency control system 25 is connected to the acceleration cavity 9 via a high-frequency power amplifier 7 and an input high-frequency measurement circuit 8, and is also connected to the acceleration voltage measurement circuit 10 and the upper-level control system 19. In addition, at least some of the functions of the upper-level control system 19 described below may be incorporated into the low-power high-frequency control system 25 (particularly the controller 18).

[0054] Oscillator 1 generates a frequency signal that controls the timing of the start of input (start-up) of high-frequency power for acceleration into acceleration cavity 9. The frequency f of the frequency signal... pre This is included within the frequency modulation range that is the resonant frequency range of the accelerating cavity 9. In this embodiment, the frequency f of the frequency signal is... pre Set as the upper limit frequency f of the frequency modulation range max Lower than the following predetermined frequency f inj Large values, where the predetermined frequency f inj It is the orbital frequency corresponding to the energy of the beam incident on the acceleration region 101, i.e., the incident energy. Preferably, the oscillator 1 is capable of generating a frequency signal with high time-constant frequency, such as a crystal oscillator.

[0055] The switching switch 2 is a switching unit that switches the connection / disconnection of the feedback control of the PLL (phase locked loop) circuit described later.

[0056] TDC3, digital loop filter 4, and DCO5 constitute a PLL circuit. This PLL circuit combines the output signal of oscillator 1, or the output signal of oscillator 1 with the accelerating voltage signal V. acc The summed signals are used as a reference signal and input to the output signal of the high-frequency measurement circuit 8, i.e., the input current signal I. out As the input signal, after 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, thereby ensuring that the frequency of the input signal is consistent with the frequency of the reference signal when output. Figure 5In the example, the PLL circuit is a fully digital PLL circuit where all circuits (TDC3, digital loop filter 4, and DCO5) are composed of digital circuits. However, a PLL circuit can be a PLL circuit that uses analog circuits in some parts, or a PLL circuit where all circuits are composed of analog circuits. Additionally, a PLL circuit can be used as follows: after converting the input signal and reference signal into IQ signals respectively, the phase difference between the two signals is detected, and the output is controlled by an IQ modulator (not shown) to make the phase difference zero through proportional-integral control.

[0057] RF switch 6 switches the high-frequency power, which serves as the output signal of the PLL circuit, to the input and stop of the acceleration cavity 9.

[0058] 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 high-frequency power into the acceleration cavity 9. The high-frequency power amplifier 7 is, for example, a semiconductor amplifier.

[0059] The input high-frequency measurement circuit 8, located between the high-frequency power amplifier 7 and the accelerating cavity 9, uses a directional coupler to measure the input high-frequency power as a traveling wave component toward the accelerating cavity 9, and as an input current signal I. out The input measurement unit outputs the signal. Furthermore, the signal output by the high-frequency measurement circuit 8 may not be an input current signal, but rather an input voltage signal. Additionally, in Figure 5 In the middle, the following was omitted. Figure 1 and Figure 2 The input coupler 20 is shown.

[0060] The acceleration voltage measurement circuit 10 measures the high-frequency acceleration voltage applied to the acceleration gap 11 and uses the measurement signal representing this value as the acceleration voltage signal V. acc The measurement unit that outputs the signal. For example, the acceleration voltage measurement circuit 10 processes the signal obtained from the pickup unit 21 near the acceleration gap 11 and outputs it as the acceleration voltage signal V. acc Output.

[0061] Voltage amplitude comparator 16 will accelerate the voltage signal V acc The amplitude, i.e., the accelerating voltage value and the threshold V thrd The comparison is performed when the acceleration voltage value reaches the threshold V. thrd At that time, an RF turn-on command signal is output to the controller 18 to indicate the input of high-frequency power for acceleration. Furthermore, when using the aforementioned IQ modulator, the voltage amplitude comparator 16 can be omitted.

[0062] Frequency comparator 17 will serve as the accelerating voltage signal V acc The acceleration frequency and the output frequency F, which is the required value.ext Comparison, when the acceleration frequency reaches the output frequency F ext At that time, an RF disconnect command signal is output to controller 18 to indicate the cessation of high-frequency power used for acceleration. Output frequency F ext It is the value of the acceleration frequency corresponding to the orbital frequency of the beam with the desired output energy orbiting in the orbital orbit.

[0063] The controller 18 controls the start and stop of the input of high-frequency power for acceleration to the acceleration cavity 9 by controlling the switching switch 2 and the RF switch 6.

[0064] To achieve the above control, the controller 18 maintains a lookup table representing the correspondence between the beam energy and the orbital frequency. When it receives a beam request signal from the host control system 19 requesting beam launch preparation, the controller 18 sets the output frequency F of the frequency comparator 17 to correspond to the desired launch energy based on the beam request signal. ext In addition, the beam request signal contains information indicating the desired output energy.

[0065] Then, controller 18 disconnects switch 2 and connects RF switch 6, inputting a signal synchronized with the output signal of oscillator 1 as a high-frequency power input for control to acceleration cavity 9. Afterwards, when the RF connection signal becomes high, controller 18 connects switch 2, using a PLL circuit to input the input current signal I from input high-frequency measurement circuit 8. out Becomes the acceleration voltage signal V from the acceleration voltage measurement circuit 10 acc A phase-synchronized signal is input to the acceleration cavity 9 as high-frequency power for acceleration. This maintains a state where high-frequency power with a frequency approximately the same as the resonant frequency of the acceleration cavity 9 is supplied to the acceleration cavity 9, thereby enabling continuous acceleration of the beam.

[0066] also, Figure 5 The low-power high-frequency control system 25 shown is only one example and is not limited to the illustrated structure. For example, the input measurement signal obtained by the input high-frequency measurement circuit 8 is not limited to a current signal, but can also be a voltage signal. Furthermore, the measurement signal obtained by the accelerating voltage measurement circuit 10 is not limited to a voltage signal, but can also be a current signal. Additionally, a circuit can be provided between the switching switch 2 and the TDC3 of the PLL circuit to suppress the phase shift of the output signal of the switching switch 2 caused by the switching of nodes by the switching switch 2.

[0067] Figure 6 This is a timing diagram used to illustrate the control timing of the low-power high-frequency control system 25. Figure 6 In the figure, (a) represents the resonant frequency f of the accelerating cavity 9. cav(Solid line) and the frequency f of the input high-frequency power as the output signal of the high-frequency power amplifier 7. out (Dashed line) indicates the change over time. Figure 6 (b) in the text represents the control signals used in the low-power high-frequency control system 25. Figure 6 (c) in the figure represents the acceleration voltage signal V obtained by the acceleration voltage measurement circuit 10. acc and the high-frequency voltage V applied to the high-frequency impactor 90 for extraction ext Changes over time. Figure 6 In the equation (d), the time variation of the current in the incident beam and the current in the outgoing beam is represented.

[0068] Furthermore, the resonant frequency f of the accelerating cavity 9 cav As the rotating capacitor 30 rotates, in Figure 6 Each acceleration cycle shown varies with the same frequency modulation pattern. Furthermore, in this embodiment, Figure 6 The control signals shown in (b) are activated at a high level and then reset to a low level after a certain period of time.

[0069] First, when controller 18 receives a beam request signal from the host control system 19 (at time T0), it begins the following processing. At this time, both RF switch 6 and switch 2 are in the off state.

[0070] Controller 18 monitors the angle signal of rotating capacitor 30. After the rotation angle of rotating capacitor 30 reaches a predetermined angle (time T1), and after a certain period of time, the resonant frequency f is reached. cav Near the point where the time axis changes monotonically with respect to the time axis, an on signal is sent to RF switch 6, switching RF switch 6 to the on state (time T2). The predetermined angle is an angle that is set only once in one acceleration cycle, for example, preset to the resonant frequency f. cav Increased timing angle.

[0071] Immediately after RF switch 6 is turned on, the resonant frequency f cav The frequency f of the output signal of the PLL circuit (the output signal of DCO5) out (=f) pre High, they are not in a tuned state. Afterwards, the resonant frequency f... cav As the rotating capacitor 30 rotates, the frequency f of the output signal of the PLL circuit decreases. out (=f) pre The phase difference between the input signal of TDC3 and the reference signal is close to zero. Furthermore, the frequency f of the output signal of the PLL circuit (the output signal of DCO5) is equal to that of the reference signal. out The frequency f of the output signal of oscillator 1 is locked. pre, will have frequency f pre Approximately the same frequency f out The control uses high-frequency power as input. The high-frequency power is output to the acceleration cavity 9 via the high-frequency power amplifier 7.

[0072] Additionally, at the resonant frequency f of the accelerating cavity 9 cav With the frequency f of the input high-frequency power out During the period of large difference (between time T2 and T3), the component of the input high-frequency power reflected by the accelerating cavity 9 is large, while the component input to the accelerating cavity 9 is small. Afterwards, when the resonant frequency f of the accelerating cavity 9... cav With the frequency f of the input high-frequency power out When the difference in voltage decreases (approaching time T3), the reflected component of the input high-frequency power decreases sharply, and the input high-frequency power is input to the acceleration cavity 9. Consequently, an acceleration high-frequency voltage is applied to the acceleration gap 11, and the acceleration voltage signal V... acc The voltage amplitude increases.

[0073] Subsequently, at time T3, the accelerating voltage signal V... acc The amplitude reached the threshold V thrd At that time, the voltage amplitude comparator 16 outputs an RF turn-on command signal to the controller 18. Upon receiving the RF turn-on command signal, the controller 18 sends a switching signal to the switch 2, turning the switch 2 into the on state, and applying an accelerating voltage signal V to the reference signal of the PLL circuit (the reference signal of TDC3). acc (Time T3). Furthermore, in this embodiment, the accelerating voltage signal V... acc The amplitude reaches the threshold V thrd Corresponding to the accelerating voltage signal V acc The phase difference between the high-frequency power used for control is within a predetermined value. Furthermore, when an IQ modulator is used in the PLL circuit, the accelerating voltage signal V can be detected using the PLL circuit. acc Since the phase difference with the high-frequency power used for control is within a predetermined value, the voltage amplitude comparator 16 can be omitted as described above.

[0074] Therefore, the frequency f of the output signal of the PLL circuit out Locked to the resonant frequency f with the accelerating cavity 9 cav Roughly the same accelerating voltage signal V acc The acceleration frequency will be the resonant frequency f that varies with time. cav The acceleration of the change is achieved by using high-frequency power as input. The high-frequency power is input to the acceleration cavity 9 via high-frequency power amplifier 7.

[0075] Subsequently, the controller 18 directs the beam from the ion source 51 into the acceleration region 101 within the main electromagnet 40 (time T4). Furthermore, the controller 18 may, for example, control the ion source 51 to direct the beam via a host control system 19.

[0076] Time T4 is the moment after a certain period of time has elapsed from time T3. Alternatively, time T4 could also be the accelerating voltage signal V. acc The frequency and the predetermined frequency f inj Consistent moments. Predetermined frequency f inj This is the orbital frequency corresponding to the energy of the beam incident on the acceleration region 101, i.e., the incident energy. In this case, for example, a frequency comparator (not shown) is used, set to the acceleration voltage signal V. acc The frequency and the predetermined frequency f inj When the frequency comparator outputs a signal, the controller 18, upon receiving this signal, directs the beam into the acceleration region 101. Additionally, an AGC (Automatic Gain Controller, not shown) can be configured after the DCO5 to control the amplitude of the high-frequency power, enabling... Figure 6 As shown in (c), the accelerating voltage signal V acc The amplitude becomes the set value before time T4.

[0077] Then, when the accelerating voltage signal V acc The frequency reaches the output frequency f ext At that time, the frequency comparator 17 outputs an RF disconnect command signal to the controller 18. Upon receiving the RF disconnect command signal, the controller 18 sends a disconnect signal to the RF switch 6, switching the RF switch 6 to the disconnected state and stopping the input of high-frequency power to the acceleration cavity 9 (time T5). Thus, the acceleration of the beam stops, and the beam continues to orbit in the orbit corresponding to the energy.

[0078] Furthermore, the upper control system 19 drives the high-frequency impactor 90 to apply a high-frequency voltage V for beam extraction. ext Thus, the beam reaches the stripping magnetic field region 91 and the regeneration magnetic field region 92, and then jumps outward from the maximum energy trajectory 61 through the stripping magnetic field region 91 and the regeneration magnetic field region 92 to reach the beam exit path entrance 82. Afterward, the beam exits to the outside of the accelerator 100 through the magnetic channel 81 and the high-energy beam delivery system 80 (time T6). Furthermore, after the controller 18 sends an acceleration termination signal to the upper control system 19, the upper control system 19 drives and stops the high-frequency impactor 90 based on various condition determinations.

[0079] Afterwards, when the extraction was stopped using high-frequency voltage V extAt time T7, beam emission ceases. However, during the period when charged particles, i.e., the orbiting charges, remain within the acceleration region 101 as part of the beam, beam emission continues. Furthermore, the high-frequency voltage V used for extraction is adjusted by the upper control system 19. ext The application time determines whether the beam is emitted continuously or intermittently. Even with continuous application, a high-frequency voltage V is used for extraction. ext If the beam cannot be detected by the beam quantity monitor (not shown) located outside the accelerator, the upper control system 19 can determine that there is no surrounding charge.

[0080] Then, when the beam is fired again, the upper control system 19 sends the beam request signal to the controller 18 again (at time T0').

[0081] Figure 7 Indicates having the ability to Figures 1-6 The structure of the particle beam therapy system of the accelerator 100 described herein is an example. Figure 7 In the particle beam therapy system 500, there is an accelerator 100, a treatment table 501, a beam delivery device 502, an irradiation device 503, and a host control system 19.

[0082] Treatment table 501 is used to place patient 600, who is the subject of the irradiation beam. Beam delivery device 502 is connected to high-energy beam delivery system 80 of accelerator 100 and delivers the beam emitted from accelerator 100 to irradiation device 503.

[0083] The irradiation device 503 targets the affected area of ​​the patient 600 on the treatment table 501 and irradiates it with a beam delivered from the beam delivery device 502. At this time, the irradiation device 503 irradiates multiple irradiation points after the affected area of ​​the patient 600 is segmented, measures the radiation dose for each irradiation point, and notifies the upper control system 19. The upper control system 19 calculates the requested radiation dose for each irradiation point, sends a beam request signal to the controller 18, and controls the extraction of high-frequency voltage V. ext This allows the required amount of radiation to be directed onto the affected area.

[0084] As described above, according to this embodiment, the acceleration voltage measurement circuit 10 outputs an acceleration voltage signal V. acc The measurement signal is obtained by measuring the high-frequency voltage used for acceleration excited by the acceleration cavity 9. The low-power high-frequency control system 25 inputs a control high-frequency power of a certain frequency contained within the resonant frequency range of the acceleration cavity 9 as high-frequency power into the acceleration cavity 9. acc When the phase difference between the high-frequency power used for control is within a predetermined value, the acceleration voltage signal V is input to the acceleration cavity 9 via feedback control. accThe acceleration frequency, i.e., the acceleration frequency synchronization, uses high-frequency power as the acceleration power, and then, when the acceleration frequency reaches the output frequency F... ext In this case, the input of high-frequency power for acceleration to the acceleration cavity 9 is stopped. Therefore, the input and stopping of high-frequency power for acceleration can be appropriately controlled according to the actual resonance mode of the acceleration cavity 9, thus enabling the beam to be appropriately accelerated to the desired energy. Therefore, the beam with the desired energy can be extracted with high precision.

[0085] Furthermore, in this embodiment, the center of the orbit around the beam is offset from the center of the acceleration region 101. Therefore, the jump required for beam extraction can be reduced, and a beam with the desired energy can be easily extracted.

[0086] Furthermore, in this embodiment, when the acceleration voltage value reaches the threshold V... thrd After a certain period of time, the beam is directed into the acceleration region 101. Alternatively, the beam is directed when the acceleration voltage reaches the threshold V. thrd Then, when the frequency reaches the predetermined frequency, the beam is incident on the acceleration region 101. Therefore, by incidenting the beam at the appropriate timing, a beam with the desired energy can be extracted with high precision.

[0087] In addition, in this embodiment, the low-power high-frequency control system 25 uses a PLL circuit to make the input measurement signal obtained by measuring the high-frequency power input to the acceleration cavity 9 and the acceleration voltage signal V acc This achieves phase synchronization, thereby generating high-frequency power for acceleration. In particular, the entire PLL circuit is constructed of digital circuitry, using IQ modulation. Therefore, the input and stop of the high-frequency power for acceleration can be easily performed.

[0088] Furthermore, in this embodiment, the input and stop of the high-frequency power for acceleration are controlled according to the actual resonance mode of the acceleration cavity 9. Therefore, even if a semiconductor amplifier that takes a certain amount of time to start is used to amplify the high-frequency power for acceleration, the beam can be appropriately accelerated to the desired energy.

[0089] The embodiments described above are illustrative examples of this disclosure and are not intended to limit the scope of this disclosure to these embodiments. Those skilled in the art can implement this disclosure in various other ways without departing from its scope.

[0090] Explanation of reference numerals in the attached figures

[0091] 1: Oscillator

[0092] 2: Switch

[0093] 3: TDC

[0094] 4: Digital Loop Filter

[0095] 5: DCO

[0096] 6: RF switch

[0097] 7: High-frequency power amplifier

[0098] 8: Input high-frequency measurement circuit

[0099] 9: Accelerating the cavity

[0100] 10: Accelerated voltage measurement circuit

[0101] 11: Acceleration Interval

[0102] 12: D-shaped electrode

[0103] 13: Virtual D-shaped electrode

[0104] 14: Inner conductor

[0105] 15: External conductor

[0106] 16: Voltage Amplitude Comparator

[0107] 17: Frequency comparator

[0108] 18: Controller

[0109] 19: Upper Control System

[0110] 20: Input Coupler

[0111] 21: Pick-up Department

[0112] 25: Low-power high-frequency control system

[0113] 30: Rotating capacitor

[0114] 31: Electric motor

[0115] 40: Main electromagnet

[0116] 41: Magnetic yoke

[0117] 42: Main coil

[0118] 43: Main magnetic pole

[0119] 50: Low-temperature thermostat

[0120] 51: Ion source

[0121] 52: Low-energy beam delivery system

[0122] 53: Ion injection section

[0123] 80: High-energy beam delivery system

[0124] 81: Magnetic Channel

[0125] 82: Beam exit path entrance

[0126] 90: High-frequency impactor

[0127] 91: Stripping the magnetic field region

[0128] 92: Regenerated Magnetic Field Region

[0129] 100: Accelerator

[0130] 101: Acceleration Zone

[0131] 200: Orbital

[0132] 201: Iso-circular phase line

[0133] 500: Particle Beam Therapy System

[0134] 501: Treatment Table

[0135] 502: Beam delivery device

[0136] 503: Irradiation device.

Claims

1. An accelerator that accelerates a beam of charged particles while it orbits, using a time-constant main magnetic field and a high-frequency voltage for acceleration, characterized in that, The accelerator has: An acceleration cavity that uses the input high-frequency power to excite the acceleration high-frequency voltage corresponding to a time-varying resonant frequency; The measurement unit outputs a measurement signal obtained by measuring the high-frequency voltage used for acceleration; as well as The control unit inputs high-frequency power for control, which has a certain frequency within the range of the resonant frequency, into the acceleration cavity. When the phase difference between the measurement signal and the high-frequency power for control is within a predetermined value, it inputs high-frequency power for acceleration, which is synchronized with the acceleration frequency of the measurement signal, into the acceleration cavity via feedback control. When the acceleration frequency reaches a required value, it stops inputting the high-frequency power for acceleration into the acceleration cavity.

2. The accelerator according to claim 1, characterized in that, The center of the orbit around which the charged particle beam is encircled is offset from the center of the acceleration region that excites the main magnetic field.

3. The accelerator according to claim 1, characterized in that, After a certain period of time following the phase difference becoming within a predetermined value, the charged particle beam is incident on the acceleration region that excites the main magnetic field.

4. The accelerator according to claim 1, characterized in that, When the frequency becomes a predetermined frequency after the phase difference becomes within the predetermined value, the charged particle beam is incident on the acceleration region that excites the main magnetic field.

5. The accelerator according to claim 1, characterized in that, The control unit generates the acceleration high-frequency power by using a phase synchronization circuit to synchronize the input measurement signal obtained from measuring the high-frequency power with the measurement signal.

6. The accelerator according to claim 5, characterized in that, The phase synchronization circuit uses IQ modulation.

7. The accelerator according to claim 6, characterized in that, The entire phase synchronization circuit is composed of digital circuits.

8. The accelerator according to claim 1, characterized in that, The accelerator also has a semiconductor amplifier that amplifies the high-frequency power.

9. A particle beam therapy system, characterized in that, have: The accelerator as claimed in claim 1; and An irradiation device that irradiates a target with a beam of charged particles extracted from the accelerator.

10. A method for controlling an accelerator, the accelerator having an accelerating cavity that is excited by an input high-frequency electrical current and an accelerating high-frequency voltage corresponding to a time-varying resonant frequency, wherein a charged particle beam is accelerated while orbiting by a time-constant main magnetic field and the accelerating high-frequency voltage, characterized in that, Output the measurement signal obtained by measuring the high-frequency voltage used for acceleration; The high-frequency power is input into the acceleration cavity as the high-frequency power input to a certain frequency range that is included in the resonant frequency range. When the phase difference between the measured signal and the control high-frequency power is within a predetermined value, feedback control is used to input acceleration high-frequency power synchronized with the acceleration frequency, which is the frequency of the measured signal, into the acceleration cavity as the high-frequency power. Once the required acceleration frequency is reached, the input of the high-frequency power for acceleration to the acceleration cavity is stopped.

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