JP4939567B2 - Circular accelerator - Google Patents

Description

  The present invention relates to a circular accelerator that accelerates a charged particle beam by generating a non-sinusoidal high-frequency voltage in a high-frequency accelerator. In this specification, the charged particle means an ion.

  There is a circular accelerator such as a synchrotron as an apparatus for accelerating a charged particle beam to high energy. The synchrotron generates an incident device that introduces a charged particle beam, a vacuum duct in which the incident charged particle beam circulates, and a deflection magnetic field and a converging magnetic field that control the orbit of the charged particle beam and the charged particle beam size. Deflecting electromagnet, high-frequency accelerator (acceleration voltage) that generates a high-frequency voltage (acceleration voltage) synchronized with the circulation cycle and accelerates the charged particle beam, and emission that emits the accelerated charged particle beam outside the synchrotron It consists of devices.

  In the synchrotron, in order to make the orbit of the charged particle beam constant, it is necessary to control the acceleration voltage and the frequency of the high-frequency voltage applied to the high-frequency accelerator according to the strength of the deflection magnetic field by the deflection electromagnet. By the way, the upper limit of the acceleration current value of the synchrotron is determined by the beam becoming unstable due to the Coulomb repulsion (space charge effect) force between charged particles. As a method for suppressing the beam loss due to the space charge effect, a method has been proposed in which a high frequency (fundamental wave) of the fundamental frequency and its integer harmonic are used in combination with the acceleration voltage (Patent Document 1). By adding harmonics, the stable acceleration region can be expanded and the space charge effect can be mitigated. In order to accelerate stably, it is required that the relationship between the phase and amplitude between the fundamental wave component and the harmonic component is always stably set to a predetermined relationship, so that complicated electronic circuits and complicated control are required. This is necessary, and it is necessary to feedback control the positional deviation of the orbiting charged particle beam.

  FIG. 7 is a diagram conceptually illustrating the configuration of a conventional circular accelerator. The characteristic is that the B clock signal from the B clock signal generator 34 and the beam position monitor signal (beam position information) from the beam position monitor 24 are used, and feedback control is performed on the output voltage of the high-frequency acceleration power source 20 to perform beam The position is held within a predetermined design value range. Here, the B clock signal is a clock signal generated each time the magnetic field intensity of the deflection electromagnet 13 increases or decreases by a predetermined value or more by measurement of the B monitor 33. Assume that this B clock signal is generated. Further, the beam position information is sent to the FB control circuit 36 by the beam position monitor 24. Considering that a non-sinusoidal voltage is input to the high-frequency accelerator 15 now, a plurality of FB control circuits 36 for fundamental waves and harmonics are required. In this example, the third harmonic is taken into consideration.

  The FB control circuit 36 grasps the beam position error from the beam position information, and calculates the FB amount of the frequency and phase for each fundamental wave and harmonic as feedback information necessary to eliminate the error. This FB amount is input to the high-frequency waveform correction circuit 37. This high-frequency waveform correction circuit 37 is also required for each fundamental wave and each harmonic component. From the high-frequency waveform correction circuit 37, the corrected waveform information of each component is output to the harmonic acceleration voltage waveform generation circuit 32. The harmonic acceleration voltage waveform generation circuit 32 receives the waveform information and generates a non-sinusoidal wave. When this waveform is input to the high-frequency acceleration power source 20, the high-frequency acceleration power source 20 generates the calculated non-sinusoidal acceleration voltage. Output time-varying waveform. An acceleration voltage is output from the high-frequency acceleration power supply 20 in synchronization with the B clock.

  In normal operation except for the FB system, when the emission energy E based on the emission E set value 30 is input to the control device 35, the control device 35 generates the electromagnetic coil current from the deflection electromagnet power source 22 at a predetermined rate of time change. While gradually increasing, voltage waveform information set in advance is input to the high-frequency acceleration voltage waveform generation circuit 32. With this information, the high frequency acceleration voltage waveform generation circuit 32 generates a voltage waveform. The previous FB system corrects this amount. In the conventional circular accelerator, the time clock signal is not used, and the coil current of the deflecting electromagnet 13, in other words, the time change of the magnetic field strength and the time change of the high frequency acceleration voltage of the high frequency accelerator 15 are not synchronized. It is a point to say. For this reason, an FB system is required, and an error in the beam position is used as a basic amount for calculating the FB amount. For this reason, particularly when a non-sinusoidal voltage is used as the acceleration voltage, complicated control including FB control is required for each harmonic in addition to the fundamental wave, which complicates the entire system.

JP 2002-75698 A

Thus, when a non-sinusoidal waveform voltage is applied to a high-frequency accelerator with a circular accelerator, the relationship between the phase and amplitude between the fundamental wave component and the harmonic component that form the non-sinusoidal waveform is always a predetermined value. In addition, for the reason described above, there has been a problem that a complicated electronic circuit and complicated control are necessary because the positional deviation of the orbiting charged particle beam needs to be feedback-controlled. .
The present invention has been made to solve the above problems, and an object thereof is to provide a circular accelerator that accelerates a charged particle beam by generating a non-sinusoidal acceleration voltage with a simple configuration and control. And

A circular accelerator according to the present invention controls an incident device for introducing a charged particle beam, a vacuum duct around which the incident charged particle beam circulates, a circular orbit of the charged particle beam, and the charged particle beam size. A deflection electromagnet that generates a deflection magnetic field and a converging magnetic field, an electromagnet power source for energizing a coil constituting the deflection electromagnet, a high frequency acceleration power source that outputs a high frequency voltage, and a high frequency voltage output from the high frequency acceleration power source are input. In a circular accelerator comprising a high-frequency accelerator that accelerates the charged particle beam that circulates by the input high-frequency voltage, and an emission device that emits the charged particle beam accelerated by the high-frequency accelerator,
The electromagnet power source is between time change waveform I (t) data of a current value supplied to the coil and time change waveform B (t) data of a deflection magnetic field strength B generated by the deflection electromagnet correspondingly. Corresponding to the I (t) / B (t) correlation data obtained in advance, and in synchronization with the clock signal, a time change waveform I (t) of the current corresponding to the I (t) data is output, The high-frequency acceleration power source is a non-sinusoidal wave necessary for acceleration corresponding to energy determined by time-varying waveform E (t) data of energy E that can maintain the charged particle beam in a predetermined orbit with respect to the B (t) data. A voltage time-varying waveform V (t) is output in synchronization with the clock signal.

According to the circular accelerator of the present invention, from the correlation data between the coil current I (t) obtained in advance and the deflection magnetic field intensity B (t) generated by the deflection electromagnet, the orbital energy of the charged particles corresponding to B (t). E (t) is determined, a time-varying waveform V (t) of acceleration voltage necessary for acceleration to E (t) is calculated, and I (t) and V (t) are set to the same time clock signal. By inputting them to the deflecting electromagnet and the high-frequency accelerator in synchronization, the feedback control for the displacement of the charged particle beam becomes unnecessary, and the high-frequency acceleration voltage waveform can be given as a function of time. A waveform can be easily generated with a simple high-frequency voltage waveform generation circuit such as a signal generator, and the time-varying waveform of the acceleration voltage can be easily generated by inputting the waveform to a high-frequency acceleration power supply.

It is a block diagram which shows the circular accelerator which is Embodiment 1 of this invention. It is a figure which shows the relationship between the electric current sent through the coil of a deflection | deviation electromagnet, and magnetic field intensity. It is a wave form diagram which shows the time change waveform of the acceleration voltage generated in a high frequency accelerator and the beam current which can be accelerated. 6 is an explanatory diagram showing a method for applying a coil current applied to the deflection electromagnet in Embodiment 1. FIG. FIG. 2 is a diagram for explaining a configuration of a circular accelerator in the first embodiment. It is a wave form diagram which shows the ON / OFF relationship of the magnetic field which generate | occur | produces with the electric current sent through the coil of a bending electromagnet, and B clock (deflection magnetic field clock) control. It is a figure explaining the structure of the conventional circular accelerator.

Embodiment 1 FIG.
1 is a block diagram showing a circular accelerator according to Embodiment 1 of the present invention. In the figure, a circular accelerator is charged after a charged particle beam is incident from an injector 12 via a beam transport system 11 from a pre-accelerator 19 and the incident charged particle beam is accelerated while circling around an equilibrium orbit 14. A particle beam is supplied from an extraction device 17 to an irradiation chamber (not shown) via an extraction beam transport system 18. Although only the beam trajectory is illustrated in the figure, a pipe-shaped vacuum duct is actually arranged around the beam trajectory.

  The circular accelerator according to the first embodiment includes an incident device 12 that receives a charged particle beam transported from a previous accelerator 19, a high-frequency accelerator (for example, an acceleration cavity) 15 that applies energy to the charged particle beam and accelerates it, and a circular orbit. The deflection electromagnet 13 that generates a deflecting magnetic field and a converging magnetic field for bending the beam trajectory and controlling the charged particle beam size, the hexapole electromagnet 16 for exciting resonance at the time of emission, and the charging with increased betatron oscillation amplitude. An emission device 17 for emitting the particle beam to the emission beam transport system 18 and a beam position monitor 24 for measuring the beam position are provided. The convergent magnetic field is generated at both ends of the deflecting electromagnet 13 by adopting an edge focus type deflecting electromagnet to control the charged particle beam size.

  A high-frequency voltage waveform generation device (for example, a digital signal generator) 21 that creates a time-varying waveform of a high-frequency voltage and a time-varying waveform of the created high-frequency voltage are input to a high-frequency acceleration power source to generate a voltage output having the same waveform A high-frequency acceleration power supply 20 applied to the high-frequency acceleration device 15. In addition, an electromagnet power source 22 that energizes the coil of the deflection electromagnet 13 and a coil current waveform generator 23 that creates a time-varying waveform of the current applied to the electromagnet power source 22 are provided. The electromagnet power source 22 and the coil current waveform generation device 23 may be configured integrally.

  FIG. 2 is a diagram showing the relationship between the current flowing through the coil of the deflection electromagnet 13 and the magnetic field strength created by the deflection electromagnet 13. The horizontal axis is time, the coil current is made constant at the time of incidence, is increased with acceleration at the time of acceleration, is made constant again when a predetermined energy is reached, and the coil current is lowered after the emission of charged particles is completed. By repeating this, incidence, acceleration, and emission using a circular accelerator can be performed. The current and the magnetic field intensity are not completely linear, and have a time-varying waveform in which the magnetic field is delayed from the coil current due to the influence of eddy currents.

  FIG. 3 is a waveform diagram showing time-varying waveforms of the acceleration voltage generated in the high-frequency accelerator and the beam current that can be accelerated. Although only a little less than two cycles are shown in the figure, this time-varying waveform is actually continuous. The waveform shown in FIG. 3A is obtained by inputting a voltage waveform created by using the high-frequency voltage waveform generator 21 to the high-frequency acceleration power source, and applying the output from the high-frequency acceleration power source 20 to the high-frequency accelerator 15. An acceleration voltage waveform generated in the acceleration device 15 is shown. A dotted line indicates a time when a sine wave is applied to the high-frequency accelerator 15, and a solid line indicates a time when a non-sine wave is applied to the high-frequency accelerator 15.

  The waveform in FIG. 3B shows a time-varying waveform of the beam current accelerated by the circular accelerator. The dotted line is when a sine wave is applied, and the solid line is when a non-sine wave is applied. When a non-sinusoidal wave is applied, the time width of the charged particle beam can be increased, that is, the distribution length of the charged particles in the circumferential direction can be increased. Can be suppressed, and a large current can be accelerated. This relationship is the same in the conventional high-frequency accelerator. The point of the first embodiment is that a non-sinusoidal acceleration voltage is obtained as a function of time in consideration of the time dependency of the magnetic field strength of the deflection electromagnet, and is applied to the high-frequency accelerator 15 to provide feedback with a simple circuit and control It is intended to provide a circular accelerator that can be operated stably without control.

  FIG. 4 is an explanatory diagram showing a method of applying a coil current applied to the deflection electromagnet in the first embodiment. The coil current waveform generator 23 creates a relationship I (t) between the time t and the coil current I, sends the time-varying waveform to the electromagnet power supply 22, and flows the current generated by the electromagnet power supply 22 through the coil of the deflection electromagnet 13. . Then, a magnetic field is excited in the deflection electromagnet 13 and a deflection magnetic field 25 is generated. The deflection magnetic field B is also a function B (t) of the time t, but is not proportional to the coil current I as described above. Therefore, an approach based on the relationship between the two has not been made.

  In a circular accelerator, the momentum related to the energy of the charged particle beam is proportional to the product of the deflection magnetic field and the deflection radius. Since the deflection radius is constant in the synchrotron, it is necessary to increase the deflection magnetic field with increasing energy. That is, the coil current of the deflection electromagnet is increased with increasing energy. The synchrotron used in the particle beam therapy system performs control that raises the maximum energy in several hundreds of milliseconds, so coil excitation is controlled accordingly. The frequency applied to the high-frequency accelerator 15 changes to the orbital frequency or an integer multiple thereof because the orbital frequency changes when the energy is different. The acceleration voltage waveform is also used to control how the incident charged particle beam is bunched (bundled in the circumferential direction), and is not directly related to the deflection electromagnet waveform.

In order to perform predetermined acceleration, it is necessary to perform control in the following flow.
The coil current value of the deflecting electromagnet is given as a function of time. If the coil current of the deflection electromagnet is determined, the deflection magnetic field is determined as a function of time. Once the deflection magnetic field is determined, the energy of the charged particle beam that can maintain the trajectory according to the deflection radius of the deflection electromagnet is determined as a function of time. Once the energy of the charged particle beam is determined, the high-frequency voltage, frequency, and phase, which are necessary conditions for acceleration corresponding to the energy, can be calculated. The voltage is changed with energy because the voltage needs to be controlled in order to stabilize the charged particles in the process of bunching during acceleration. Changing the frequency together with energy depends on the energy, and the time that the charged particle beam makes one round of the ring changes, so it is necessary to change the frequency according to the energy in order to accelerate the charged particle beam at a predetermined phase. Because there is. The reason for changing the phase with energy is that it is necessary to make the phase optimal for acceleration.

  FIG. 5 is a diagram illustrating the configuration of the circular accelerator according to the first embodiment. The high-frequency voltage waveform generation device 21 creates a time-varying waveform of the acceleration voltage (high-frequency voltage) generated by the high-frequency acceleration device 15. FIG. 5 shows an example in which a non-sinusoidal acceleration voltage waveform is generated in consideration of, for example, the fundamental wave to the third harmonic. That is, for the waveform generation, the fundamental frequency f1 (t), voltage Vm1 (t), phase φ1 (t), second harmonic frequency f2 (t), voltage Vm2 (t), phase φ2 (t) The third harmonic wave frequency f3 (t), voltage Vm3 (t), and phase φ3 (t) components are sent to the high-frequency voltage waveform generator 21 and the combined waveform information of the fundamental wave, the second harmonic wave, and the third harmonic wave. Is input as V (t) waveform information.

  In the first embodiment, each device is configured such that a correspondence relationship is established including the time axis between the output I (t) of the electromagnet power supply 22 and the output V (t) of the high frequency acceleration power supply 20. This correspondence is called correlation here. First of all, it is necessary to obtain I (t) / B (t) correlation data. This data is obtained by correlating the deflection magnetic field strength B (t) generated in the deflection electromagnet 13 with respect to the time-varying waveform I (t) data of the current applied to the deflection electromagnet coil, and can be obtained by actual measurement and calculation. It is assumed that this data has been obtained in advance.

  In the coil current waveform generator 23, I (t) data from the I (t) / B (t) correlation data 27 is input, and an I (t) waveform that is a time-varying waveform corresponding to this I (t) data. Is generated and output. The emission energy E based on the emission E setting value 30 is input, and I (t) necessary for this is obtained. If E is determined, the corresponding B for keeping the trajectory constant is determined, and the maximum value of I (t) is determined from this.

  The electromagnet power source 22 receives the I (t) waveform and outputs a current time change waveform I (t). This output is energized to the coil of the deflection electromagnet 13 and the deflection electromagnet 13 generates a deflection magnetic field B (t). The electromagnet power source 22 is output in synchronization with the time clock signal (t clock signal) from the t clock signal generator 31.

  The B (t) / E (t) correlation data calculation device 28 is used to keep the orbit constant with respect to the magnetic field strength of the B (t) data from the I (t) / B (t) correlation data 27. This is a device for calculating the energy E (t) of a charged particle beam. The energy value obtained here is called E (t) data.

  In the V (t) calculating device 29, a time-varying waveform V (t) of acceleration voltage, which is a condition necessary for acceleration corresponding to the energy, is obtained for E (t), and a fundamental wave constituting this is obtained. Calculate the voltage, frequency, and phase of each harmonic component as a function of time. This is collectively synthesized and called V (t) waveform information. Since a non-sinusoidal wave is adopted as V (t), not only the fundamental wave but also a harmonic component exists. The I (t) / B (t) correlation data 27, the B (t) / E (t) correlation data calculation device 28, and the V (t) calculation device 29 constitute a time-dependent waveform information generation unit for high frequency voltage. To do.

  The high-frequency voltage waveform generation device 21 receives the V (t) waveform information and outputs a V (t) waveform. A digital signal generator is an example, and a digital synthesizer (arbitrary waveform device) is used. Yes. By using a digital synthesizer, the phase adjustment of each harmonic becomes simple. The output energy E is inputted and V (t) necessary for this is obtained. The V (t) waveform is not necessarily the same as V (t) obtained as a necessary condition for acceleration of E (t) and its maximum value.

  The high-frequency acceleration power supply 20 receives the V (t) waveform and outputs the finally required acceleration voltage waveform V (t). This output is input to the high frequency accelerator 15, whereby an acceleration electric field of the charged particle beam is formed in the high frequency accelerator 15. The high-frequency acceleration power supply 20 is output in synchronization with the time clock signal (t clock signal) from the t clock signal generator 31. Therefore, B (t) and V (t) are in a synchronized state via the t clock signal. Therefore, unlike the conventional circular accelerator using the B clock signal, the feedback control of the beam position is unnecessary, and the circular accelerator has a simple configuration and can be operated with simple control.

  In the first embodiment, I (t) / B (t) correlation data is derived by measurement or calculation based on the fact that the deflection magnetic field is determined as a function of time if the coil current of the deflection electromagnet is determined. The time clock signal is used to synchronize between the electromagnet power source and the acceleration power source. Therefore, predetermined acceleration can be performed without feedback control.

  In the conventional example, it was thought that the relationship between the coil current value of the deflection electromagnet and the deflection magnetic field could not be obtained with sufficient accuracy. Therefore, the deflection magnetic field strength was measured, and when the predetermined value was increased or decreased, feedback control was performed. That is, the operation was performed by synchronizing the electromagnet power source and the acceleration power source with the B clock signal. However, when accelerating a charged particle beam with a non-sinusoidal wave, it is necessary to precisely match the phase of the fundamental wave and the harmonics, and in the case of up to the third harmonic, about 2 to 3 degrees. It is necessary to adjust with accuracy. Therefore, in the conventional example, the entire system is a very complicated control circuit. In the conventional example, the fundamental wave, the second harmonic, and the third harmonic are used as separate control circuits. This is because the fundamental wave and harmonic signal transmission characteristics are different, so even if a predetermined waveform is generated by the waveform generator, the phase of the fundamental wave and the harmonic wave will shift while transmitting the cable, and the acceleration voltage of the high frequency accelerator will be This is because a control circuit for correcting the difference from the predetermined one is necessary.

The features of the first embodiment will be described in comparison with the conventional example.
(A) In the first embodiment, feedback control for the positional deviation of the charged particle beam is not necessary.
It becomes unnecessary to detect a deviation (positional deviation) of the beam trajectory from the central orbit with a beam position monitor and feed back the signal to the acceleration frequency of the high-frequency voltage to be input to the high-frequency accelerator.
In the conventional example, the frequency (f1, f2, f3) of the high-frequency acceleration voltage is adjusted in order to reduce the positional deviation (ΔR) from the central orbit of the beam orbit of the charged particle beam measured by the beam position monitor 24. Without feedback control, the beam could not be accelerated stably. That is, in the conventional example, the variable is B (deflection magnetic field). When the deflection magnetic field increment reaches a certain value, one B clock is output, and the acceleration voltage, frequency, phase, and amplitude change to a certain value. On the other hand, in the first embodiment, the variable is time. A waveform with a variable time can be created in advance by a digital synthesizer. However, when B is a variable, it is difficult to create a waveform in advance, resulting in a complicated control circuit as in the conventional example.

  In the conventional example, taking into account that the deflection magnetic field changes slightly after the coil current, a B clock is output every time the deflection magnetic field changes to a certain value, and ΔR is positive (that is, centered each time the B clock is output). When the orbit is shifted outside the orbit), the acceleration phase is changed to reduce the acceleration voltage, and when ΔR becomes negative (ie when the orbit is shifted inward from the center orbit), the acceleration phase is changed. Increase the acceleration voltage to adjust the beam trajectory. It is necessary for the beam to circulate in a vacuum duct or a region where a predetermined magnetic field is generated (effective magnetic field region). This is because the region is within a certain range from the central trajectory, and the beam will not circulate stably if the region is deviated.

  In the first embodiment, it is possible to perform an operation based on a high-frequency acceleration voltage waveform generated and generated first without performing feedback control. In order to realize this, the relationship between the coil current of the deflection electromagnet and the deflection magnetic field is measured or calculated in detail, B (t) is calculated in advance based on the data, and the high-frequency acceleration voltage waveform is calculated based on the data. Generate. If the time dependency of the magnetic field is known, the time dependency of energy can be calculated, and the specification of the acceleration voltage applied to the high-frequency accelerator can be determined. Conventionally, feedback control is required because the time dependence of the magnetic field was not known.

(B) In the first embodiment, a high-frequency acceleration voltage waveform is given as a function of time.
In the conventional example, since the relationship between the coil current and the B magnetic field has not been grasped, the high frequency acceleration voltage waveform, that is, the frequency, the maximum amplitude of the acceleration voltage, and the phase are changed according to the B clock signal of the deflection magnetic field. Control is implemented. That is, the frequency of the high-frequency acceleration voltage, the maximum amplitude of the acceleration voltage, and the phase are determined according to the intensity change of B. Note that the B clock is a clock that is output every magnetic field change ΔB of the deflection magnetic field, and is a clock that is output at a constant period if there is a constant magnetic field increase / decrease.
On the other hand, in the first embodiment, if the time dependency of the magnetic field is known, the time dependency of energy can be calculated, and the specification of the acceleration voltage applied to the high-frequency accelerator can be determined. Conventionally, feedback control is required because the time dependence of the magnetic field was not known.

In the first embodiment, a high-frequency acceleration voltage waveform that takes time as a function (considering up to the third harmonic,
First, the fundamental wave of the high-frequency acceleration voltage and the frequency, acceleration voltage, and phase of each harmonic are generated, and operation is performed with the acceleration voltage having a non-sinusoidal waveform that is a function of time formed by combining these. In order to realize a non-sinusoidal waveform that is a function of this time, the relationship between the coil current of the deflection electromagnet and the deflection magnetic field is measured or calculated in detail, and B (t) is determined in advance based on the data. Based on B, the frequency, acceleration voltage, and phase of the high-frequency acceleration voltage are determined.
More specifically, the process for determining the frequency f, acceleration voltage V, and phase φ of the high-frequency acceleration voltage from B is as follows.
(1) Measure or calculate the relationship between the coil current of the deflection electromagnet and the deflection magnetic field.
(2) When the coil current I (t) is determined, the deflection magnetic field B (t) is determined from (1).
(3) When the deflection magnetic field B is determined, the energy E of the charged particles that go around a fixed orbit under the deflection magnetic field condition is determined, and the velocity v of the charged particles is determined from E. When v is determined, the time t0 for the charged particle to make one round is determined, and its reciprocal is f. Therefore, f (t) is determined.
(4) As for the acceleration voltage V, V (E) for each energy is determined by acceleration simulation in which charged particles are bunched and stably accelerated. Therefore, V (t) is determined.
(5) As with V, φ (E) for each energy is determined by acceleration simulation in which charged particles are bunched and accelerated stably as in the case of V. Therefore, φ (t) is determined.

Since the acceleration voltage waveform including harmonics can be grasped as a function of time by the procedure described above, the coil current waveform also grasped as a function of time is input to the deflection electromagnet, and the time-dependent waveform of the acceleration voltage is obtained. In the first embodiment, the following effects can be obtained by applying the high frequency accelerator.
(1) It is not necessary to detect a deviation (positional deviation) of the beam trajectory from the central trajectory with a beam position monitor, and to feed back the signal to the acceleration frequency of the high-frequency voltage input to the high-frequency accelerator, which is a simple circuit. Can be controlled.
(2) Since the high-frequency acceleration voltage waveform is a function of time, a time-varying waveform of the acceleration voltage including the frequency and phase can be easily created with a digital signal generator (for example, a digital synthesizer).
(3) The space charge effect can be reduced by applying a non-sinusoidal waveform with a simple circuit without complicated control and feedback control.

Embodiment 2. FIG.
In the first embodiment, the non-sinusoidal acceleration voltage waveform is generated in the high-frequency accelerator 15 in consideration of the third harmonic, but the same control is possible even when the sinusoidal acceleration voltage does not consider the harmonic. is there.
Therefore, in the second embodiment,
(1) Since there is no feedback control for ΔR, it can be controlled with a simple circuit.
(2) Since the high frequency acceleration voltage waveform is a function of time, the waveform can be easily created with a digital signal generator.

Embodiment 3 FIG.
FIG. 6 is a waveform diagram showing the temporal change of the deflection magnetic field intensity generated by the current flowing through the coil of the deflection electromagnet, that is, the on / off relationship between B (t) and B clock (deflection magnetic field clock) control. The charged particle beam becomes unstable due to the effect of space charge mainly at low energy. When the energy is low, control by time (ie, control by t clock) is performed as in the first embodiment, and acceleration is in progress. It may be switched to B clock control (control by a deflection magnetic field clock) of the conventional example at a certain timing TB1. T1 indicates the start of t clock control, TB2 indicates the timing of switching from B clock control to t clock control, and T4 indicates the end of t clock control. TB2 to T4 may be performed by B clock control. This on / off switching can be performed in an operation control device that controls the operation of a circular accelerator, for example, which is not shown. The B clock control is a control for outputting a clock every time the magnetic field change amount of the deflection electromagnet reaches a certain value and generating a voltage waveform or a current waveform corresponding to the clock. On the other hand, the t clock control is a control that outputs a clock at regular intervals and generates a voltage waveform and a current waveform according to the clock, and the t clock control is performed on a daily basis. Clock control is unique to charged particle accelerators.

  If the time waveform of the magnetic field and the time waveform of the accelerating voltage are all determined, they can only be emitted at the same timing. It is said that the time waveform is determined in advance because acceleration, the beam turning time for the exit after the acceleration, and the like are operated with a predetermined time change pattern. When applied to a particle beam therapy system, for example, it is necessary to irradiate a charged particle beam at an arbitrary timing in accordance with the movement of the affected part, and control is difficult with a predetermined time waveform. That is, it is necessary to maintain the state for emission in a flexible manner each time. In order to meet such a demand, as in the third embodiment, when switching to the B clock control (control by the deflection magnetic field clock) of the conventional example at a certain timing during acceleration, any timing according to the movement of the affected area is selected. Can be irradiated with a charged particle beam.

  In the beam emission, resonance emission is performed. There are various methods of emitting the resonance, but the time during which the emission is performed differs depending on the shape of the affected part. Therefore, it is difficult to operate with a predetermined time waveform pattern, and it is necessary to change for each patient. The control of this part is a part that can be realized by a conventional particle beam therapy system, and it is desirable to carry out by the same control system as the conventional system in order to increase the reliability of the system. Therefore, it is desirable to switch from the control in Embodiment 1 to the control in the conventional example at a certain timing. The deceleration process may be controlled by B clock control or t clock control.

According to the invention relating to the third embodiment, the following effects can be obtained.
(1) Since there is no feedback control for ΔR, it can be controlled with a simple circuit.
(2) Since the high frequency acceleration voltage waveform is a function of time, the waveform can be easily created with a digital signal generator.
(3) At the time of extraction, it is necessary to frequently turn on / off the charged particle beam or change the extraction time by scanning irradiation, respiratory synchronization, or the like. At the time of emission, the conventional control method is used, and time control is performed only during the initial stage of acceleration or during the acceleration from the incident, thereby making it easy to change from the conventional circular accelerator.

DESCRIPTION OF SYMBOLS 11 Beam transport system 12 Injector 13 Deflection magnet 14 Equilibrium orbit 15 High frequency accelerator 16 Hexapole magnet 17 Output device 18 Beam transport system for output 19 Pre-accelerator 20 High frequency acceleration power source 21 High frequency voltage waveform generator 22 Electromagnetic power source 23 Coil current waveform Generation device 24 Beam position monitor 27 I (t) / B (t) correlation data 28 B (t) / E (t) correlation data calculation device 29 V (t) calculation device 30 Output E set value 31 t Clock signal generation device

Claims (4)

An incident device for introducing a charged particle beam; a vacuum duct in which the charged particle beam circulates; a deflecting electromagnet for generating a circular orbit of the charged particle beam, a deflection magnetic field for controlling the charged particle beam size, and a convergence magnetic field; An electromagnet power source for energizing a coil constituting the deflection electromagnet, a high-frequency acceleration power source for outputting a high-frequency voltage, and a high-frequency voltage output from the high-frequency acceleration power source. A circular accelerator comprising: a high-frequency accelerator that accelerates the charged particle beam; and an emission device that emits the charged particle beam accelerated by the high-frequency accelerator.
The electromagnet power source is between time change waveform I (t) data of a current value supplied to the coil and time change waveform B (t) data of a deflection magnetic field strength B generated by the deflection electromagnet correspondingly. Corresponding to the I (t) / B (t) correlation data obtained in advance, and in synchronization with the clock signal, a time change waveform I (t) of the current corresponding to the I (t) data is output, The high-frequency acceleration power source is a non-sinusoidal voltage necessary for acceleration corresponding to the energy determined by the time-varying waveform E (t) data of the energy E that can maintain the charged particle beam in a predetermined orbit with respect to the B (t) data. The time-varying waveform V (t) is output in synchronization with the clock signal. A coil current waveform generation device; a B (t) / E (t) correlation data calculation device; a V (t) calculation device; and a high-frequency voltage waveform generation device.
The coil current waveform generation device generates an I (t) waveform that is a time-varying waveform when the I (t) data is input, and outputs the I (t) waveform to the electromagnet power source. The electromagnet power source outputs a current time-varying waveform I (t) based on the I (t) waveform,
The B (t) / E (t) correlation data calculation device receives the B (t) data, and energy E that can maintain a charged particle beam in a predetermined orbit with respect to the input B (t) data. (T) The data is calculated and output to the V (t) calculating device.
The V (t) calculating device receives the E (t) data, and the fundamental wave component and the fundamental wave constituting the non-sinusoidal voltage V (t) necessary for acceleration from the inputted E (t) data. Is calculated as V (t) waveform information, and is output to the high-frequency voltage waveform generation device.
The high frequency voltage waveform generator receives the V (t) waveform information, generates the non-sinusoidal voltage V (t) waveform from the input V (t) waveform information, and outputs the non-sinusoidal voltage V (t) waveform to the high frequency acceleration power source The high-frequency accelerating power source receives the V (t) waveform and outputs a time-varying waveform V (t) of the non-sinusoidal voltage based on the input V (t) waveform. The circular accelerator according to claim 1, wherein there is a circular accelerator.   The circular accelerator according to claim 2, wherein the high-frequency voltage waveform generator is a digital synthesizer.   The circular accelerator further includes an operation control device, and the operation control device controls an operation from when the charged particle is substantially incident by the incident device to before the extraction is started by the extraction device. The circular accelerator of any one of Claims 1-3.

Images