JPH1145800A - Electron beam accelerating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain energy variation during rise of a beam pulse, and establish good energy spectrum characteristic, by modulating amplitude during beam rise of an accelerating high-frequency source, and canceling a beam loading effect. SOLUTION: A signal generated by a stabilizing high-frequency oscillator 1 is amplified by a buffer amplifier 2, is divided equally by a 3dB devider 3, and enters into a first phase modulator 4 and a second phase modulator 5. The both phase modulators 4, 5 are controlled by a first phase modulating control signal 8 and a second phase modulating control signal 9 from a phase modulating control device 7. Signals from the phase modulators 4, 5 are vector- added by a combiner 6, and any amplitude and phase are modulated based on a standard phase 20. The added high-frequency signals are power-amplified by a driver amplifier 10 up to a degree where driving of a klystron amplifier 11 is allowed, is amplified to high peak power as accelerating high-frequency by the klystron amplifier 11, and supplied to an accelerating tube 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam accelerator which can be used for an electron linac device or the like in which acceleration energy fluctuations due to beam loading occur. The device of the present invention can also be used for a high-power proton linac device and an ion irradiation device. (Explanation of terms) (1) “Beam loading” refers to a phenomenon in which the acceleration beam energy is transferred to the electron beam by accelerating the electron beam with the acceleration tube, and the acceleration energy is reduced. The larger the current amount of the electron beam is, the larger the decrease amount of the acceleration energy is.

[0002] This phenomenon is similar to a phenomenon in which the terminal voltage of a battery drops due to the internal resistance of the battery when current is just applied to the battery. (2) The “crest portion of the acceleration phase” refers to the top of the acceleration electric field shown in FIG. The crest portion of the acceleration phase is a portion where electrons can be most effectively accelerated.

[0003] The interval between two adjacent crest portions must be equal to the interval between electronic bunches. (3) “Electron bunch” In the electron linac device, electrons need to be concentrated on the crest portion of the acceleration phase, and thus the electrons are divided into small chunks. Each of these masses is called an electronic bunch. (4) "Luminosity" In an electron linac device, an electron beam is accelerated as a bunch. The density of electrons in the electron bunch is called luminosity.

When the amount of current of the electron beam is constant, the smaller the electron bunch is compressed in both the radial direction and the traveling direction, the higher the luminosity is. (5) The “reference phase” is a phase of an accelerating high frequency such that an electron bunch is placed on the crest portion of the accelerating phase of the accelerating high frequency in the accelerating tube, and is uniquely determined by a pulsed electron source connected to the accelerating tube. (6) “High frequency” includes RF waves and microwaves.

[0005]

2. Description of the Related Art The prior art is shown in FIGS. FIG.
FIG. 7 is a diagram showing a configuration of a conventional device, FIG. 7 is a diagram showing an electron beam input timing of an accelerating RF source of the conventional device, and FIG.
FIG. 4 is a diagram showing an example of energy fluctuation of a conventional device.

[0006] As shown in FIG. 6, a conventional apparatus includes a stabilized high-frequency oscillator 1, a buffer amplifier 2, a driver amplifier 10, a klystron amplifier 11, and an accelerating tube 51.
And a pulsed electron source 54.

The output of the accelerating high frequency at the entrance of the accelerating tube 51 rises stepwise as shown in FIG. As for the acceleration energy of the conventional apparatus, as shown in FIG. 8, at the same time when the electron beam is turned on, electrons having much higher energy than in the steady state are output from the acceleration tube 51, and thereafter the acceleration energy is reduced to be in a steady state.

That is, in the conventional apparatus, after the accelerating radio frequency is supplied from the accelerating radio frequency source, after the filling time of the accelerating tube elapses (ie, after the accumulating of the accelerating high frequency energy inside the accelerating tube is completed), the electron beam is emitted. The acceleration is performed by inputting a pulse.In this case, at the time of the rising of the electron beam pulse, for about the filling time of the accelerating tube,
A beam having a higher acceleration energy than the steady state is output.

This is generated because the accelerating microwaves supplied to the accelerating tube and the accelerating high frequency accumulated in the accelerating tube contribute to the beam acceleration. It can be as high as 10%.

[0010]

The prior art has the following problems. (1) In order to reduce the phenomenon that a beam having a higher acceleration energy than the steady state is output during the filling time of the accelerator tube at the time of the rising of the electron beam pulse, the filling time of the accelerator tube elapses after the supply of the acceleration high frequency. Before this, measures such as inputting an electron beam are taken. However, at present, a sufficient effect of suppressing fluctuation of acceleration energy is not obtained, and an energy spectrum having a wide tail portion is present.

Particularly in the case of a high-power electronic linac device, this tail causes beam loss in the beam transport system, leading to thermal damage and activation of the beam line. (2) As another method for suppressing energy fluctuation, an energy width compression device (hereinafter, referred to as ECS; ECS: Ener) is used.
gy Compression System) may be used.

In this method, an energy analysis is performed by a deflection magnet or the like, so that an optical path difference is generated between electrons having a high energy component and electrons having a low energy component. In this method, a low-energy component is input to an acceleration tube for compressing an energy width in such a phase as to receive an accelerating electric field.

However, in order to obtain a sufficient energy width compression effect, the bunch width is considerably widened, and a reduction in luminosity poses a problem in applications such as collision experiments. (3) Further, four deflection magnets for ECS are required, and when the electron energy is high, the magnet becomes a large magnet, and the magnet power supply and the magnet increase the installation place and cost.

The present invention provides an apparatus capable of solving these problems (ie, an apparatus capable of suppressing energy fluctuation at the time of rising of a beam pulse and achieving good energy spectrum characteristics). Aim.

[0015]

[Means for Solving the Problems]

(First Means) An electron beam accelerator according to the present invention comprises a stabilized high-frequency oscillator 1 and a high-power pulse high-frequency source 1 for acceleration.
1 and an apparatus provided with the accelerating tube 21 in the above order,
(A) a high frequency dividing means 3 for dividing the high frequency generated by the stabilized high frequency oscillator 1, (B) a phase modulator (4, 5) for adjusting each phase of the divided high frequency,
(C) Means 6 for synthesizing each high frequency whose phase has been adjusted
(D) inputting a synthesized high frequency from the synthesizing means 6,
A high-power pulse high-frequency source 11 for outputting a high-frequency pulse for acceleration to the acceleration tube 21;
(F) The phase modulator (4, 5) instructs each of the phase modulators (4, 5) to perform a phase modulation instruction for each of the divided high-frequency waves. Means 7 for applying amplitude modulation to correct a change in acceleration energy due to a beam loading effect generated at a rising portion of an electron beam pulse. (Second Means) The electron beam accelerator according to the first aspect of the present invention is arranged so that the high-frequency pulse high-frequency power source for acceleration 11 in the first means does not change the phase of the high-frequency pulse for acceleration input to the acceleration tube (21). When the required amplitude modulation is given by correcting the phase variation of the high frequency for acceleration at the time of amplitude modulation, after the phase modulation is given to each of the two systems of the high frequency divided equally by the high frequency dividing means 3, the vector It is characterized in that arbitrary amplitude and phase modulation are performed by combining. (Third Means) In the electron beam accelerator according to the present invention, in the first means, each divided high-frequency wave is compensated for so as to compensate for the phase modulation generated in the high-power pulse high-frequency power source 11 in accordance with the output power. And phase modulation control means for instructing the above modulation.

That is, the apparatus of the present invention is characterized in that the amplitude at the rising edge of the pulse of the accelerating high-frequency source is modulated to cancel the beam loading effect, thereby suppressing the energy fluctuation at the rising edge of the beam pulse.

Therefore, even in an electron linac apparatus having a deep beam loading, it is possible to suppress the energy fluctuation at the time of rising of the beam pulse, and to secure a good energy spectrum characteristic.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
5 to FIG. 5 and FIGS. 9 to 12. FIG. 1 is a diagram showing the configuration and operating principle of the first embodiment, FIG. 2 is a diagram showing an example of amplitude modulation of an accelerating high-frequency source and the timing of electron beam input, and FIG. Diagram,
FIG. 4 is a diagram showing a simulation result of acceleration energy when the acceleration high-frequency source and the electron beam input shown in FIG. 2 are performed. FIG. 4 is a diagram showing a distribution of an electric field level in an acceleration tube in a steady state. FIG. 9 is a diagram showing a Y-type power divider used as a 3 dB divider, FIG. 9 is a diagram showing an electric field in an acceleration tube in a steady state in the absence of an electron beam, and FIG. 10 is a description of a crest portion and an electron bunch in an acceleration phase. FIG. 11, FIG.
FIG. 12 is a diagram showing a relationship between energy required for electron acceleration and electron velocity, and FIG. 12 is an explanatory diagram of an acceleration electric field based on an acceleration high frequency acting on an electron bunch in an acceleration tube.

The apparatus according to the present invention is shown in FIG. 2 in order to make the rising of the acceleration wave from the high-frequency pulse high-frequency source 11 for acceleration smoothly rise as shown by the line c in FIG. 3 and connect it to the line b without overshoot. As shown in the figure, the acceleration applied to the acceleration tube rises from low output to full output during the filling time of the acceleration tube at the rising part of the acceleration high frequency, and then maintains full output until the end of the electron beam pulse. An object of the present invention is to suppress fluctuation of acceleration energy by amplitude-modulating a high frequency.

In order to correct the beam loading effect and to prevent the fluctuation of the acceleration energy generated at the rising portion of the electron beam pulse, the electric field distribution in the accelerator tube at the time of the ON of the electron beam pulse has a steady state. It must be the same as the electric field distribution.

For this purpose, the accelerating high frequency generating means 31 shown in FIG.
(From the stabilized high-frequency oscillator 1 to the klystron amplifier 11
Up to), an accelerating high frequency satisfying the following condition is created and output to the accelerating tube 21. (Condition a) The interval (distance) between the crest portions of two adjacent acceleration phases of the acceleration high frequency (acceleration electric field) shown in FIG.
Distance (distance) of the electron bunch 29 from the pulsed electron source 24
(Condition b) The phase of the accelerating radio frequency (acceleration electric field) output to the accelerating tube 21 is set so as not to change with respect to the reference phase.

More specifically, since the phase of the klystron amplifier 11 changes according to the output level, the first phase modulator 4 and the second phase modulator 4 cancel the change in the phase so that the phase does not change at the inlet 22 of the acceleration tube. Phase modulation for correction is given by the phase modulator 5 so that the condition b is satisfied. (Condition c) At the time of turning on the electron beam, in order to achieve the electric field distribution in the tube shown in FIG. Change from output to full output. (Operation in Acceleration Tube) By outputting the acceleration high frequency (acceleration electric field) to the acceleration tube 21, the electron beam (electron bunch) from the pulsed electron source 24 in the acceleration tube is as follows. Operate.

Since the mass of an electron is much lighter than an electric charge, it is easily accelerated and immediately approaches the speed of light. Normally, electrons accelerated by the accelerating tube are accelerated to energy of 10 MeV or more by another means. At this point, the velocity of the electrons is as shown in FIG.
As shown in FIG. 1, it is about 99.9% of the speed of light.

According to the theory of special relativity, matter cannot exceed the speed of light and electrons gradually approach the speed of light with acceleration, but cannot exceed the speed of light and the mass of electrons increases with acceleration. The number of electrons of 10 MeV is about 20 times that of electrons at rest.

The electrons in the accelerating tube can only be accelerated to a small extent, and their mass increases with acceleration. At the same time, in the accelerating tube, the accelerating electric field advances at the speed of light due to the accelerating high frequency as shown in FIG.

The electron bunch 29 also travels in the accelerating tube at substantially the speed of light. If the top (crest portion) of the acceleration phase of the accelerating high frequency (acceleration electric field) just hits the electron bunch 29 (the acceleration in this case). The high frequency has a reference phase according to the condition b), and the electron bunch 29 always feels the maximum acceleration electric field and proceeds, and is accelerated most efficiently.

With the acceleration, the speed of the electrons hardly changes at the speed of light, and the mass increases more and more. The manner in which the electrons and the accelerating high frequency (acceleration electric field) are accelerated by accelerating at the same speed is similar to a state in which a carrot is hung from the nose of a horse and runs. (Electric Field Level Distribution in Accelerator Tube) FIG. 4 assumes that a traveling wave type regular CG accelerator tube has a damping constant of 0.57 Neper and 80 cavities (accelerator tube effective length of 2.8 m). The electric field level distribution in the acceleration tube in a steady state when the power of the acceleration high frequency at the entrance of the acceleration tube is 12 MW is shown.

FIG. 4A shows the electric field level near the entrance of the acceleration tube, and FIG. 4B shows the electric field level at the exit of the acceleration tube. In the steady state of the electron beam ON, the energy of the accelerating high frequency is consumed for accelerating the electron beam as it proceeds downstream, and the electric field level decreases as shown in FIG.

In a steady state in the absence of an electron beam, the electric field distribution in the traveling wave type regular CG tube is substantially constant (actually, as shown in FIG. 9, the shunt impedance of the cavity increases as it goes downstream). The electric field level increases slightly).

If amplitude acceleration is not applied at the rising portion of the acceleration high frequency and a step-like acceleration high frequency as in the conventional apparatus shown in FIG. 7 is input to the acceleration tube, the electric field level distribution in the acceleration tube at the time when the electron beam is turned on. Is in the state shown in FIG.

In order to achieve the electric field distribution in the tube shown in FIG. 4 at the time of turning on the electron beam, the acceleration high frequency is amplitude-modulated during a period corresponding to the filling time of the acceleration tube at the rising portion of the high frequency of the acceleration. It is necessary to change from output to full output.

In FIG. 2, "a" indicates the time when the electron beam is turned on.
The output pattern of the acceleration high frequency necessary to generate the electric field level distribution in the acceleration tube shown in FIG. 4 is obtained by numerical analysis.

The accelerating high frequency is initially 5 to full output.
%, And reaches a full output in 0.864 μsec corresponding to the filling time of the accelerator tube in the pattern shown in FIG.

Thereafter, the full output is continued until the end of the electron beam pulse, and is turned off at the end of the electron beam pulse. The electron beam pulse is turned on at the same time when the accelerating high frequency becomes full output.

FIG. 3 is a numerical simulation result of the acceleration energy in the case described above. Although the electron beam is actually turned on and accelerated after the time point a in FIG. 3, a large energy fluctuation after the electron beam is turned on as shown in FIG. It can be seen that a constant acceleration energy has been obtained from the rise time of. (Means for Generating Amplitude Modulation and Phase Modulation, and Means for Generating Accelerated High Frequency) FIG. 1 shows an embodiment of an apparatus including the means for generating amplitude modulation of accelerating high frequency as described above, and a principle diagram of amplitude modulation generation. Show.

2856 MH generated by stabilized oscillator 1
The signal of z is amplified by the buffer amplifier 2 and equally divided by the 3 dB divider 3 and enters the first phase modulator 4 and the second phase modulator 5, respectively.

As the 3 dB divider 3, a one-stage Y-type power divider composed of a microstrip line can be used. The phase modulators (4, 5) are controlled by a first phase modulation control signal 8 and a second phase modulation control signal 9 from a phase modulation controller 7.

The signals from the two phase modulators (4, 5) are vector-added by the combiner 6. FIGS. 1B and 1C show examples of the state of the vector addition. FIG. 1 (B)
Is an example of vector addition when the synthetic amplitude is zero.
The high frequency signal from the phase modulator 4 is -9 to -9 from the reference phase.
The second phase modulator 5 modulates by 0 degrees (13 in FIG. 1).
Is modulated by +90 degrees from the reference phase 20 (14 in FIG. 1), and the vectors of both signals are shifted from each other by 180 degrees, resulting in a composite amplitude of zero (1 in FIG. 1).
5).

The reference phase 20 is a phase of an accelerating high frequency such that an electron bunch is just placed on the crest portion of the accelerating phase of the accelerating high frequency in the accelerating tube, and is uniquely determined by the pulsed electron source 24 connected to the preceding stage of the present apparatus. .

FIG. 1C shows an example of vector addition when the combined amplitude and phase are not zero. The high-frequency signal from the first phase modulator 4 is modulated with a shift of −80 degrees from the reference phase 20 (17 in FIG. 1), and the high-frequency signal from the second phase modulator 5 is modulated with a shift of +70 degrees from the reference phase 20. (18 in FIG. 1), the result of addition of these vectors (19 in FIG. 1) is a combined result shifted by −5 degrees from the reference phase 20.

As described above, a required phase modulation is given to each of the two divided high-frequency signals, and by adding these vectors, modulation of an arbitrary amplitude and phase can be performed.

The combiner 6 can be easily realized by reversing the input port of the one-stage Y-type power distributor described above. The high-frequency signal vector-added by the combiner 6 is amplified by the driver amplifier 10 to a power of about several hundred watts capable of driving the klystron amplifier 11, and further amplified by the klystron amplifier 11 to a high peak power as an accelerating high-frequency signal.
1 is supplied.

What is required on the accelerating tube side is amplitude modulation of the accelerating high frequency. It is necessary that the phase remains unchanged as the reference phase. However, the klystron amplifier 11 changes its phase depending on the output level. And the first phase modulator 4 and the second phase modulator 5 apply phase modulation for correction so that there is no phase change at the entrance 22 of the acceleration tube.

The phase characteristics of the klystron amplifier 11 are determined by the design of the klystron, and are uniquely determined when the type of the ball is determined. The amplitude controlled by the phase modulation controller 7 in FIG.
Since the phase modulation changes depending on the parameters of the accelerator tube, the electron beam current, and the characteristics of the klystron, an appropriate program is selected by a control computer or the like according to the conditions to generate control signals (8 and 9 in FIG. 1).

[0045]

Since the present invention is configured as described above, it has the following effects. (1) Even in an electron linac apparatus with a deep beam loading, it is possible to suppress energy fluctuation at the time of rising of a beam pulse. (2) Therefore, good energy spectrum characteristics can be secured, and the energy spectrum can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration and an operation principle of a first embodiment.

FIG. 2 is a diagram showing an example of amplitude modulation of an accelerating high-frequency source and the timing of electron beam input.

FIG. 3 is a diagram showing a correction result of energy fluctuation.

FIG. 4 is a diagram showing a distribution of an electric field level in an acceleration tube in a steady state.

FIG. 5 is a diagram showing a structure of a Y-type power divider used as a 3 dB divider.

FIG. 6 is a diagram showing a configuration of a conventional device.

FIG. 7 is a diagram showing the timing of inputting an electron beam to an accelerating high-frequency source of a conventional device.

FIG. 8 is a diagram showing an example of energy fluctuation of a conventional device.

FIG. 9 is a diagram showing an electric field in an acceleration tube in a steady state when there is no electron beam.

FIG. 10 is an explanatory diagram of a crest portion and an electron bunch in an acceleration phase.

FIG. 11 is a diagram illustrating a relationship between energy required for accelerating electrons and electron velocity.

FIG. 12 is an explanatory diagram of an accelerating electric field based on an accelerating high frequency acting on an electron bunch in an accelerating tube.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Stabilized high frequency oscillator 2 ... Buffer amplifier 3 ... High frequency dividing means (3dB divider) 4 ... First phase modulator 5 ... Second phase modulator 6 ... Means for combining high frequency (combiner) 7 ... Phase modulation controller 8 ... First phase modulation control signal 9 ... Second phase modulation control signal 10 ... Driver amplifier 11 ... High-output pulse high-frequency source (klystron amplifier) 13 ... Output vector diagram of first phase modulator 14 ... Second phase modulator 15 ... Combined vector 17 ... Output vector diagram of the first phase modulator 18 ... Output vector diagram of the second phase modulator 19 ... Combined vector 20 ... Reference phase 21 ... Accelerator tube 22 ... Accelerator tube entrance 23 ... Acceleration Tube outlet 24 ... Pulse electron source 25 ... Excessive acceleration radio frequency 26 ... Acceleration radio frequency at the entrance of the acceleration tube 27 ... Electron beam 28 ... Acceleration electron beam 29 ... Child bunch 30 ... Crest portion of acceleration phase 31 ... Acceleration high frequency generating means 51 ... Acceleration tube 52 ... Acceleration tube entrance 53 ... Acceleration tube exit 54 ... Pulse electron source 55 ... Excessive acceleration high frequency 56 ... Acceleration high frequency at the acceleration tube entrance 57 ... Electron beam 58… Accelerated electron beam

Claims (3)

[Claims] 1. An apparatus comprising a stabilized high-frequency oscillator (1), a high-frequency pulse high-frequency source for acceleration (11) and an accelerating tube (21) in the stated order, wherein (A) the stabilized high-frequency oscillator (1) High-frequency dividing means (3) for dividing the generated high-frequency wave; (B) phase modulators (4, 5) for adjusting the respective phases of the divided high-frequency waves; and (C) phase-adjusted high-frequency waves. Means for synthesizing (6), and (D) inputting the synthesized high frequency from the synthesizing means (6), and
(1) a high-frequency pulse high-frequency source for acceleration that outputs a high-frequency pulse for acceleration in (1);
A pulsed electron source (24) for outputting an electron beam to 1),
(F) By giving a phase modulation instruction to each of the phase modulators (4, 5) for each divided high frequency, amplitude modulation is applied to the rising portion of the high frequency pulse for acceleration, and the rising portion of the electron beam pulse is generated. Means (7) for correcting fluctuations in acceleration energy due to a beam loading effect generated in the electron beam acceleration device. 2. A high-frequency pulse high-frequency source for acceleration (11) for correcting a phase change of a high-frequency wave for acceleration during amplitude modulation so that a phase of a high-frequency wave for acceleration inputted to an acceleration tube (21) does not change. When amplitude modulation is applied, after performing phase modulation on each of the two systems of high-frequency divided equally by the high-frequency dividing means (3), arbitrary amplitude and phase modulation is performed by vector synthesis. The electron beam accelerator according to claim 1, wherein: 3. A high-frequency pulse high-frequency power source for acceleration (11) having phase modulation control means for instructing modulation for each divided high-frequency wave so as to compensate for phase modulation generated in accordance with output power. The electron beam accelerator according to claim 1, wherein