JP3053175B2 - Charged particle beam emission method and emission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for emitting a charged particle beam, and more particularly to a charged particle beam emission method suitable for emitting a charged particle beam accelerated and accumulated from a circular accelerator and its emission. Related to the device.

[0002]

2. Description of the Related Art A charged particle beam in a circular accelerator such as a synchrotron orbits around a design orbit while performing betatron oscillation. In this case, there is a stability limit called separatrix, and a beam within the stability limit circulates stably, but a beam exceeding the stability limit has a property of diverging due to an increase in vibration amplitude. In the conventional beam extraction method, low-order resonance of betatron oscillation has been used. That is, using a four-pole magnet, the tune representing the betatron frequency per one revolution of the accelerator is made to approach an integer ± 1/2, and at the same time, the eight-pole magnet is excited (secondary resonance), and the tune is made an integer ± 1 / 3 and the 6-pole magnet was excited (third-order resonance). Especially in the process of extraction, Experimental Physics Course 2
8 "Accelerator": edited by Hiroo Kumagai, Kyoritsu Shuppan Co., Ltd., p. 5
As described in 25, the stability limit of the beam is gradually reduced by changing the tune by controlling the excitation amount of the quadrupole magnet, and the charged particles whose betatron oscillation amplitude exceeds the stability limit are sequentially emitted. Was.

[0003]

In the above-mentioned conventional beam emitting method, the beam orbital gradient at the emitting position changes with time, so that the beam emitting efficiency deteriorates. In order to prevent this, it is necessary to control the beam trajectory temporally,
There is a problem that control becomes complicated. Further, when changing the energy of the emitted beam, it is necessary to change the control method for each energy, and there is a problem that the control becomes more difficult.

An object of the present invention is to provide a charged particle beam emitting method and an emitting device capable of always emitting a beam with high efficiency even if the energy of the emitted beam changes.

[0005]

Means for Solving the Problems The feature of the present invention to achieve the above object, in the case of emitting a charged particle beam from the circular accelerator by applying a high-frequency electromagnetic field to the charged particle beam circulating, emitted from the circular accelerator An object of the present invention is to control the frequency of a high-frequency electromagnetic field in accordance with the circulating frequency of the charged particle beam and the tune .

[0006]

[0007]

[0008]

According to the above-mentioned feature of the present invention, the frequency of the high-frequency electromagnetic field used for emission is controlled in accordance with the circulating frequency of the charged particle beam that changes with the change in energy of the emitted charged particle beam and the tune. Therefore, the frequency of the high-frequency electromagnetic field is controlled according to the change in the energy of the emitted charged particle beam. Therefore, the energy of the charged particle beam emitted can you to emit efficiently charged particle beam vary.

[0010]

[0011] Hereinafter, an emission process of the preferred charged particle bi <br/> over beam described extraction of the charged particle beam at the stability limit constant with reference to FIG. The figure shows the phase space at the position of the emitter of the circular accelerator.The excitation current of the quadrupole magnet is kept constant, that is, the stability limit is kept constant, and a high-frequency electromagnetic field is applied to the charged particle beam to stabilize it. The betatron oscillation amplitude of the charged particles within the limit is gradually increased, and the charged particles exceeding the stability limit are emitted by resonance. The horizontal axis represents the position x of the charged particles of the beam, and the vertical axis represents the gradient dx / ds of the orbit.
(S is the distance in the circumferential direction). The dashed line is the stability limit, and the solid thick solid line within the dashed line indicates the trajectory of the beam circling stably. Charged particles exceeding the stability limit increase in vibration amplitude due to resonance and are emitted from between the emitter electrodes.However, by keeping the stability limit constant, the orbit gradient of the emitted charged particle beam becomes constant, A charged particle beam can be emitted with high efficiency.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a first embodiment in which the present invention is applied to a medical device. The medical device of this embodiment is
It is composed of a device installed in the accelerator room 20, a device installed in the irradiation room 9, and a device installed in the control room 21. In the accelerator room 20, the pre-accelerator 1 generates a charged particle beam, and the beam is incident on the synchrotron by the injector 2. The synchrotron has a orbit for orbiting the beam, and a deflecting magnet for deflecting the beam, a quadrupole magnet for converging or diverging the beam, an accelerating cavity for accelerating the beam, and emitting the beam in the orbit. And an electrode 7 for increasing the betatron oscillation amplitude of the beam. An electric field is generated by the accelerating cavity 5 in the beam traveling direction, and the beam is accelerated to a desired energy by the electric field. Then, a high-frequency electromagnetic field is applied to the beam by the electrode 7 to increase the amplitude of the betatron oscillation. And gradually irradiates the affected part of the patient 19 in the irradiation room 9. At the time of irradiation treatment of the patient 19, it is effective from the viewpoint of safety to perform irradiation treatment while observing the state of the patient 19 using a monitor camera or the like installed in the irradiation room 9.

Next, a method of emitting a beam by the apparatus shown in FIG. 1 will be described with reference to a flowchart shown in FIG. First, the energy, the energy width, the operating point (tune) of the accelerator, and the dose of the beam to be irradiated on the patient are input as data to the controller 10 (100, 100 in FIG. 2).
101, 102, 103). Here, the tune is the betatron frequency of the beam per one rotation of the synchrotron. Next, it is checked whether or not the input data is correct (104 in FIG. 2). If the input data is correct, the high-frequency signal generator 11 generates a high-frequency signal 15 having a frequency component necessary for emission based on the data. (10 in FIG. 2)
5). If the input data is incorrect, reenter the data. The high frequency signal 15 is adjusted to an amplitude to be applied to the electrode 7 by a gain controller 13 such as an amplifier (FIG. 2).
107), and is applied to the electrode 7 as the high frequency voltage 16 (108 in FIG. 2).

At the same time, the irradiation dose is measured by the radiation monitor 8 in the irradiation room 9 (110 in FIG. 2),
Compares the measured value 17 of the irradiation dose output from the radiation monitor 8 with the set value 14b of the irradiation dose output from the control device 10, and adjusts the gain controller 13 so that the measured value 17 becomes the set value 14b. To output the gain control signal 18 to control the amplitude of the high-frequency voltage 16 applied to the electrode 7 (111, 107, and 108 in FIG. 2). Finally, it is checked whether or not the beam irradiation on the patient 19 has been completed (109 in FIG. 2).
If the irradiation is not completed, the steps below the gain control 107 are repeated. By applying a high-frequency electromagnetic field to the circulating beam from the electrode 7 in this way, the amplitude of the betatron oscillation of the beam can be increased. The light can be emitted efficiently.

In the embodiment shown in FIG. 1, the electrode 7 is used as a means for applying a high-frequency electromagnetic field to the beam. Instead of the electrode 7, the same high-frequency voltage 16 as that of the accelerating cavity 5 is used. The same effect can be obtained by applying an electromagnet having a high-speed response instead of the electrode 7 or by flowing a high-frequency current having the high-frequency component to the electromagnet.

Next, the high-frequency signal generator 11 will be described in detail. First, a high-frequency signal used for emission will be described. FIG. 3 shows a frequency spectrum of an ideal high-frequency signal required for emission. The beam in the synchrotron circulates around the design orbit while oscillating betatron, and the tune representing the betatron frequency per lap of the accelerator has a width. Includes frequency bands. That is, assuming that the revolving frequency of the beam is frev and the fractional parts of the minimum and maximum values of the tune are ν _min and ν _max , the required center frequency f ₀ and frequency width Δf of the required high-frequency signal are given by the following equations.

[0017]

F ₀ = frev · (ν _max + ν _min ) / 2 (Equation 1)

[0018]

Δf = frev · (ν _max −ν _min ) (Equation 2) The circulating frequency frev can be expressed by the following equation using the energy E of the beam.

[0019]

Equation 3] _{frev = c {1- (m 0} · c 2 /E)2}0.5/L ... ( Equation 3) where, c is the speed of light, m ₀ is the rest mass of a charged particle, L is the beam Orbit length.

Therefore, given the energy E of the beam and the minimum and maximum values (ν _min , ν _max ) of the tune, the center frequency f ₀ and the frequency of the high-frequency signal required for emission can be calculated using equations (1) to (3). The width Δf can be obtained. Further, even when the beam energy E, the energy width ΔE, and the tune center value ν ₀ are given, the center frequency f ₀ and the frequency width Δf can be obtained using the following equation.

[0021]

F ₀ = ν ₀ · G (E) (Equation 4)

[0022]

Δf = ν ₀ · {G (E + ΔE / 2) −G (E−ΔE / 2)} (Equation 5) Here, G (E) is a function representing the right side of Equation 3.

Incidentally, when it is usually called a tune of an accelerator,
The tune center value ν ₀ is shown, and the tune center value ν ₀ , maximum value ν _max , and minimum value ν _min can be considered as design conditions determined at the time of designing the synchrotron. Therefore, in addition to the above-described embodiment, the beam energy E and the tune (center value ν ₀ , width Δν = ν _max −ν) are determined in advance.
_min ) is stored in the memory, only the energy E is input as data, the corresponding tune is read from the memory, and the center frequency f ₀ and the frequency width Δf of the high-frequency signal required for emission are obtained. Can also. Of course, it is also possible to use a measured value as a tune used for these calculations.

Further, since the frequency intensity (amplitude) V is determined by the required irradiation dose, the relationship between the amplitude V and the irradiation dose is determined experimentally or theoretically in advance, so that the high frequency necessary for emission from the irradiation dose is obtained. The amplitude V of the signal can be determined.

By applying the electromagnetic field having the high frequency component obtained in this way to the beam, all of the beams that have a distribution in energy using a minimum necessary high frequency electromagnetic field, that is, a beam having a distribution in tune, are formed. Since the vibration amplitude of the charged particles can be surely increased, a highly efficient beam can be emitted with a constant stability limit.

The effect of the present invention having the above-described features will be compared with a comparative example having no such features. For example, when a high-frequency signal (Δf ₁ ) having a frequency width smaller than Δf given by Expressions 2 and 4 is used, charged particles not included in the energy width ΔE ₁ corresponding to Δf ₁ cannot be reliably emitted. . When a high-frequency signal having a frequency width wider than Δf is used, all charged particles can be emitted, but more power is required for beam emission, and overall emission taking into account input power is also considered. Efficiency does not always increase.

Next, a first embodiment of the high-frequency signal generator 11 of FIG. 1 will be described with reference to FIG. In the present embodiment, the high-frequency signal generator 11 includes an arithmetic unit 61 and a D / A (digital / analog) converter 62. Arithmetic unit 61
Is the data 1 relating to the energy of the output beam output from the control device 10, the energy width, and the tune of the accelerator.
Based on 4a, the frequency characteristics (center frequency and frequency width) necessary for emission are obtained as described above, and a frequency spectrum is created in the frequency domain. At this time, the phase of each frequency component is made random. By converting the high frequency spectrum data in the frequency domain into the time domain using the inverse Fourier transform, the high frequency data 63 having the frequency characteristics shown in FIG. 3 is created. The D / A converter 62 converts the high-frequency data 63 into an analog signal, and generates a high-frequency signal 15.

Next, the high-frequency signal generator 1 will be described with reference to FIG.
A second embodiment of the present invention will be described. In the present embodiment, the high-frequency signal generator 11 includes a white noise source 31 and band-pass filters 32 to 35 in which frequency bands to be passed according to the energy of the output beam are separately set in advance. Among the data 14a output from the control device 10, according to data on the energy of the output beam,
By selecting a bandpass filter, a high-frequency signal 15 having the frequency spectrum shown in FIG. 3 is generated. In addition to this configuration, a similar result can be obtained by using a band-pass filter having a variable center frequency and pass frequency width.

Next, the high-frequency signal generator 1 will be described with reference to FIG.
A third embodiment will be described. In this embodiment, the high-frequency signal generator 11 includes a controller 46 and oscillators 41 to 4.
4 and an adder 45, and a plurality of oscillators 41 to 4
4 are added by an adder 45 to generate a high-frequency signal 15 having a required frequency spectrum. At this time, the controller 46 controls the data 1 output from the control device 10.
4a, the necessary oscillation frequency and phase control signals 47 to 50 according to the data relating to the energy of the output beam.
To each of the oscillators 41 to 44, and each oscillator outputs a required high-frequency signal based on the control signal. Thus, the high-frequency signal 15 having the frequency spectrum shown in FIG. 3 is generated.

Next, the high-frequency signal generator 1 will be described with reference to FIG.
A fourth embodiment will be described. In this embodiment, the high-frequency signal generator 11 includes a controller 51 and a frequency sweeper 5.
And 2. The controller 51 includes the control device 10
Generates a frequency sweep pattern set in advance for each energy in accordance with the data relating to the energy of the output beam in the data 14a output from the
2 performs a frequency sweep in a required frequency range based on this pattern. The sweep pattern is determined in advance by operating the synchrotron with no patient in the irradiation room and measuring the irradiation dose.

Next, a second embodiment in which the present invention is applied to a medical device will be described with reference to FIG. FIG. 8 shows the same synchrotron configuration as that of the embodiment shown in FIG. 1, and data relating to the energy of the output beam, the energy width, the tune of the accelerator, and the irradiation dose are input to the control device 10. The high-frequency signal generator 11 has a high-frequency signal 15 having a frequency characteristic necessary for extraction based on data 14a on the energy, energy width, and tune of the output beam.
Occurs. The gain controller 13 outputs the high-frequency signal 1
5 is adjusted to the size necessary for emission, and the high-frequency voltage 1
6 is applied to the electrode 7. At the same time, the current monitor 81 is installed on the beam line between the irradiation room 9 and the emission device 6, and the operation is performed without the patient 19 in the irradiation room 9.

The comparator 12 calculates a measured value 82 of the beam current measured by the current monitor 81 and a set value 14 of the beam current corresponding to the set value of the irradiation dose which is the output of the control device 10.
c to the gain controller 13 so that the measured value 82 becomes the set value 14c.
8 is output. The gain controller 13 controls the amplitude of the high frequency voltage 16 applied to the electrode 7 based on the gain control signal 18. In this way, in a state where the patient 19 is not in the irradiation room 9, the gain control signal 18 is taken into the control device 10 from the operation start to the end, and
The optimal operating conditions for irradiation are stored. Thereafter, the patient 19 is set in the irradiation room 9, and the operation is controlled by the control device 10 according to the operation condition data 84 stored in the control device 10.

Next, a third embodiment in which the present invention is applied to a medical device will be described with reference to FIG. FIG. 9 shows the same equipment configuration as that of the embodiment shown in FIG. 1, and the control device 10 sets the energy of the output beam based on the exciting current 91 of the deflecting magnet 3. Such control is possible because there is a correlation between the intensity of the deflecting magnetic field of the deflecting magnet 3 and the energy of the beam that can stably circulate on the orbit of the synchrotron. 1 is the same as the embodiment of FIG. 1 except that a high-frequency voltage 16 required for emission is generated based on the exciting current of the deflecting magnet 3 constituting the synchrotron, and the description is omitted here. In this embodiment, the energy of the emitted beam is set by the exciting current of the bending electromagnet 3, but it is also possible to set the energy of the emitted beam by the frequency of the acceleration cavity 5 or the like.

In the embodiments described above, a synchrotron for medical use has been described. However, the extraction method and apparatus of the present invention can be applied to all circular accelerators that emit a charged particle beam using a high-frequency electromagnetic field. .

[0035]

According to the present invention, the orbital frequency that changes with the change in the energy of the emitted charged particle beam , and
Since the frequency of the high-frequency electromagnetic field is controlled according to the tune , the charged particle beam can be emitted efficiently even if the energy of the emitted charged particle beam changes.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment in which the present invention is applied to a medical device.

FIG. 2 is a diagram showing a beam emitting method according to the present invention.

FIG. 3 is a diagram showing a frequency spectrum of a high-frequency signal required for emission.

FIG. 4 is a diagram showing a first embodiment of a high-frequency signal generator.

FIG. 5 is a diagram showing a second embodiment of the high-frequency signal generator.

FIG. 6 is a diagram showing a third embodiment of the high-frequency signal generator.

FIG. 7 is a diagram showing a fourth embodiment of the high-frequency signal generator.

FIG. 8 is a diagram showing a second embodiment in which the present invention is applied to a medical device.

FIG. 9 is a diagram showing a third embodiment in which the present invention is applied to a medical device.

FIG. 10 is a view for explaining beam emission at a constant stability limit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pre-accelerator, 2 ... Injector, 3 ... Deflection magnet, 4 ... Quadrupole magnet, 5 ... Acceleration cavity, 6 ... Ejector, 7 ... Electrode, 8 ... Radiation monitor, 9 ... Irradiation room, 10 ... Control device , 11: High frequency signal generator, 12: Comparator, 13: Gain controller, 15: High frequency signal, 16: High frequency voltage, 17: Measurement value of irradiation dose, 20: Accelerator room, 21: Control room, 31
... white noise source, 32 ... bandpass filter, 3
3 bandpass filter, 34 bandpass filter, 35 bandpass filter, 41 oscillator, 42
... Oscillator, 43 ... Oscillator, 44 ... Oscillator, 45 ... Adder, 46 ... Controller, 51 ... Controller, 52 ...
Frequency sweeper, 61: arithmetic unit, 62: D / A converter, 81: current monitor, 82: measured value of beam current.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichi Hirota 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Energy Research Laboratory, Hitachi, Ltd. (72) Inventor Masashi Nishi 7-2-2, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Energy Research Laboratory, Hitachi, Ltd. (56) References JP-A-7-14699 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05H 13/04 H05H 7/10

Claims (8)

(57) [Claims] 1. A charged particle beam extraction method for emitting a charged particle beam from the circular accelerator by applying a high-frequency electromagnetic field to the charged particle beam circulating, revolution frequency of the charged particle beam extracted from the circular accelerator And controlling the frequency of the high-frequency electromagnetic field according to the tune and the tune . 2. The frequency of the high-frequency electromagnetic field has a width, and the width of the frequency of the high-frequency electromagnetic field and the center frequency are
2. The charged particle beam emitting method according to claim 1, wherein control is performed in accordance with a circulating frequency and the tune. 3. A charged particle beam emitting method for emitting a charged particle beam from a circular accelerator by applying a high-frequency electromagnetic field generated by an electromagnetic field applying device to an orbiting charged particle beam based on an input high-frequency signal. A charged particle beam emitting method, wherein a frequency of the high frequency signal is controlled according to a circulating frequency and a tune of the charged particle beam emitted from the circular accelerator. 4. The frequency of the high-frequency signal has a width, and the frequency width and the center frequency of the high-frequency signal are defined by the frequency.
4. The charged particle beam emitting method according to claim 3, wherein control is performed in accordance with a turning frequency and the tune. 5. A charged particle beam emitting device comprising an electromagnetic field applying device for emitting a charged particle beam from a circular accelerator by applying a high frequency electromagnetic field to a circulating charged particle beam, wherein the charged particle beam is emitted from the circular accelerator. A charged particle beam emitting device, comprising: a control unit that controls the frequency of the high-frequency electromagnetic field according to the circulating frequency and the tune of the charged particle beam. 6. The frequency of the high-frequency electromagnetic field has a width, and the control means controls the frequency of the high-frequency electromagnetic field to be
The charged particle beam emitting device according to claim 5 , wherein a center frequency is controlled according to the circulating frequency and the tune. 7. An electromagnetic field applying apparatus for generating a high-frequency electromagnetic field based on an input high-frequency signal and applying the generated high-frequency electromagnetic field to a circulating charged particle beam to emit the charged particle beam from a circular accelerator. A charged particle beam extraction device, comprising: a control unit that controls a frequency of the high-frequency signal according to a circulating frequency and a tune of the charged particle beam emitted from the circular accelerator. Emission device. 8. The frequency of the high-frequency signal has a width, and the control means determines whether the frequency of the high-frequency signal is in the middle range.
The charged particle beam emitting device according to claim 7 , wherein a cardiac frequency is controlled according to the orbital frequency and the tune.