JPS6029200B2 - linear electron accelerator - Google Patents

Description

[Detailed Description of the Invention] This invention detects the radiation output of a linear electron accelerator, normalizes it, holds the maximum value, and then holds the normalized output at this maximum value. The present invention relates to a linear electron accelerator that stabilizes the energy of an accelerated electron beam.

A conventional device of this type is shown in FIG.

In FIG. 1, 1 is an electron gun that generates an electron beam; 2 is an electron gun that generates an electron beam;
is an acceleration tube for accelerating the electron beam generated by the electron gun 1, and 3 is a deflection electromagnet for deflecting the accelerated electron beam; the deflection electromagnet 3 may not be provided in a device that makes the electron beam travel straight. 4 is a radiation generation mechanism for generating radiation such as X-rays or electron beams.
il) and which can generate both X-rays and electron beams has a switching mechanism for both.

5 is a flattening filter for flattening the X-ray distribution, which is removed in the case of electron beams.

A is radiation generated by the radiation generating mechanism 4, 6 is a detector for monitoring the intensity of this radiation A, 7a, 7
Detectors b are used to monitor the intensity distribution of radiation, and one or more pairs of detectors are installed in different areas irradiated with radiation. 8 is an amplifier that amplifies the radiation intensity signal detected by the detector 6, 9 is an output setting mechanism that arbitrarily sets the radiation intensity, and 1 is the output of the amplifier 8 and the output setting mechanism 9.
An output stabilization circuit compares the output with the output of the output setting mechanism 9 and stabilizes the radiation output by controlling the radiation output to the output determined by the output setting mechanism 9. 11 is a pulse repetition frequency and pulse width determined by the output of the output stabilization circuit 10. or a pulse generator in which parameters determining radiation intensity, such as both, are controlled;
2 is a pulse modulator that generates a high voltage modulation pulse according to the output pulse of the pulse generator 11; 13 is a pulse transformer that boosts the output of the pulse modulator 12; 14 is supplied with the output of the pulse transformer 13; A klystron or magnetron is usually used.

Further, 15a and 15b are amplifiers for amplifying the outputs of the accelerators 7a and 7b, respectively, and 16 is both amplifiers 15a and 15b.
A differential amplifier 17 detects the difference between the outputs of the differential amplifier 1.
The output of the controller 6 is used to flatten the radiation intensity distribution, and the output of the controller 6 controls the microwave frequency of the microwave generator 14.

Next, the operation will be explained.

The electron beam generated by the electron gun 1 enters the acceleration tube 2, and the electron beam is accelerated by microwave power supplied to the acceleration tube 2 from the microwave generator 14.

The accelerated electron beam is deflected by a deflection electromagnet, but in an apparatus that does not require deflection of the electron beam, the deflection electromagnet 3 is not installed, and the trajectory of the electron beam is a straight line. The radiation generating mechanism 4 is installed on the electron beam orbit, and radiation A is generated by the electron beam. Radiation generation mechanism 4
If it is a heavy metal target, radiation A is an X-ray,
If it is made into a scattering film, the radiation A becomes an electron beam. In the case of X-rays, since the X-ray intensity is directional,
The flattening filter 5 flattens the X-ray intensity distribution within the maximum X-ray irradiation field specific to the apparatus, but in the case of electron beams, the flattening filter 5 is unnecessary and is therefore removed. Radiation A
The intensity of the signal is monitored by a detector 6, and the signal is amplified by an amplifier 8.

On the other hand, the radiation intensity distribution is monitored by detectors 7a and 7b, and the signals thereof are simultaneously amplified by amplifiers 15a and 15b. The detectors 7a and 7b may be a pair as shown in the figure, but
Depending on the device, several more pairs may be provided. If the radiation intensity distribution becomes uneven, the detectors 15a, 15
A difference occurs in the output of b, but it does not occur if it is flat.

In the case of a device with a bending electromagnet 3, the cause of the difference may be a change in the accelerated electron beam energy, a change in the acceleration conditions such as a change in the electron beam trajectory, or a change in the magnetic field of the electromagnet. may vary. Since the magnetic field of the electromagnet is usually stabilized by itself, it is often caused by fluctuations in acceleration conditions, and for this reason, a control mechanism is provided to eliminate the difference in the outputs of the detectors 15a and 15b.

In this example, it is assumed that a difference occurs between the detectors 15a and 15b due to fluctuations in the electron beam energy, and a case is shown in which the microwave frequency is controlled assuming that the electron beam energy is mainly caused by fluctuations in the microwave frequency. The difference between the outputs of the detectors 15a and 15b is detected by the differential amplifier 16, and based on this difference, the controller 17 controls the microwave frequency of the microwave generator 14 to return to flat radiation. However, since the electron beam energy varies depending on the microwave power, the electron beam current incident on the accelerating tube, the applied voltage of the electron beam, etc., there are devices in which the control unit 17 selects and controls these items. Alternatively, assuming that the flatness of the radiation intensity distribution is lost due to fluctuations in the trajectory of the electron beam,
For example, a steering coil may be used at the exit of the accelerating tube 2 to control the electron beam trajectory. As described above, a control mechanism is provided to make the intensity distribution of the radiation A uniform, but in addition to this, a control mechanism is provided separately to stabilize the radiation intensity.

The radiation intensity can be determined arbitrarily within the specifications specific to the device. This setting mechanism is the output setting mechanism 9, which compares the output of the amplifier 8 with the output of the output setting mechanism 9, and adds the variation from the predetermined setting intensity to the output of the output setting mechanism 9 to set the output. Stabilize. The output stabilizing circuit 10 has this function, and since the output is set by the device by the pulse repetition frequency or pulse width, the pulse repetition frequency or pulse width of the pulse generator 11 is adjusted accordingly. The pulse width or both are controlled to obtain a predetermined output. Based on the output of the pulse generator 11, the pulse modulator 12 generates a high voltage pulse, which is further boosted by the pulse transformer 13, and the necessary high voltage is applied to the electron gun 1 and the microwave generator 14, respectively. When controlling the pulse width, for example, a triode electron gun may be used to control the pulse width of the electron beam incident on the acceleration tube. The conventional device is configured as described above, and includes a control mechanism such as the output stabilization circuit 10 for stabilizing the radiation intensity, and a control mechanism such as the control section 17 for stabilizing the electron beam energy. Since each was provided separately, there was a drawback that the control mechanism was complicated.

Furthermore, radiation output is strongly dependent on electron beam energy, especially in the case of X-rays, so although separate control mechanisms are provided for each, they interfere with each other and do not operate independently, making it difficult to obtain a stable operating point. There were disadvantages such as difficulty in This invention was made to eliminate the drawbacks of the conventional ones as described above, and the radiation intensity obtained by a predetermined electron beam energy and electron beam current is determined by the optimum state according to the parameters of the apparatus set to obtain the radiation intensity. When the radiation output setting mechanism is set arbitrarily, the output per pulse is maximum and the flatness is good, and the parameters of the device are controlled so as to obtain this maximum value. , once the maximum value has been determined, this maximum value is memorized and controlled to always obtain this maximum value, thereby achieving stable radiation output and a flat radiation intensity distribution with a simple configuration. The purpose is to provide an accelerator. An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, the symbols used in FIG. 1 indicate the same parts as in FIG. 1, and here the output of the output setting mechanism 9 is directly input to the pulse generator 11.

18 is a signal conversion circuit that converts the pulse repetition frequency signal of the pulse generator 11 into a signal proportional to the set output of the output setting mechanism 9; 19 is the output of the signal conversion circuit 18 that converts the radiation intensity of the output of the amplifier 8; This is a normalization circuit that calculates the output radiation intensity per unit pulse by dividing by .

Here, the setting output of the output setting mechanism 9 may be directly input as one input of the normalization circuit 19. This is a differentiation circuit that differentiates the output of the two-way normalization circuit 19, and generates a differential value at an appropriate period based on the timing pulse of the timing circuit 21.

22 is an amplifier for the output of the differentiation circuit 20; 23 is a peak hold circuit that holds the maximum value of the output of the normalization circuit 19;
4 is a differential amplifier having two inputs, the output of the peak hold circuit 23 and the output of the normalization circuit 19; 25 is the differential amplifier 2;
The control gate mechanism operates when the output of the amplifier 22 exceeds a certain value, and generates a control signal so that the output of the amplifier 22 increases the radiation output.

26 is a control mechanism that controls the microwave frequency.

In the above, the circuit portion surrounded by the one-dot chain line constitutes an electron beam energy control circuit 32 that controls the microwave frequency, which is a parameter that determines the electron beam energy, by the output of the peak hold circuit 23 and the output of the normalization circuit 19. FIG. 3 shows a detailed circuit diagram of the peak hold circuit 23.

27 and 28 are amplifiers with high input impedance, D is a low leakage current diode connected between both amplifiers 27 and 28, and C is a low leakage current peak hold connected between the cathode of this diode D and the ground. It is a capacitor for When the voltage at the output of amplifier 27 becomes higher than the voltage charged in capacitor C, diode D becomes conductive;
Capacitor C is charged to a new high voltage and held. SW and R are switches and resistors for discharging the charge of capacitor C when irradiation is finished. Next, the operation will be explained.

An electron beam generated from an electron gun 1 is accelerated by an accelerating tube 2, and when a deflection electromagnet 3 is provided, the electron beam is deflected and enters a radiation generation mechanism 4, where radiation A is generated.

The intensity of this radiation A is determined by the output setting mechanism 9,
Normally, the pulse repetition frequency and pulse width are set arbitrarily. The pulse generator 11 and pulse modulator 12 operate according to the output of the output setting mechanism 9, and high voltage pulses from the pulse transformer 13 are applied to the microwave generator 14 and the electron gun 1. Although the radiation intensity varies depending on the electron beam energy and electron beam current, in the embodiment shown in FIG. 2, the microwave frequency is controlled as a parameter for determining the electron beam energy.

That is, the radiation intensity detected by the detector 6 is amplified by the amplifier 8, while the pulse repetition frequency signal of the pulse generator 11 is converted by the signal conversion circuit 18 into a signal proportional to the set output of the output setting mechanism 9. Then, the output of the amplifier 8 is divided by a normalization circuit 19 using a signal proportional to the set output of the output setting mechanism 9, thereby performing so-called normalization. Therefore, the output of this normalization circuit 19 has a value that is not related to the set output. As a result, the output of the normalization circuit 19 fluctuates because the electron beam acceleration is no longer in the optimum state. In the case of optimal acceleration, the output of the normalization circuit 19 is maximum, so the peak hold circuit 23 stores the normalized output in the optimal state. The differential amplifier 24 detects the difference between the peak hold value of the peak hold circuit 23 and the output of the normalization circuit 19, and since the output is an amount that indicates the variation in the acceleration state from the optimum acceleration state, this is determined. When the set value is exceeded, the control gate mechanism 25 is activated and a control signal is applied to the control mechanism 26. Since this control is performed to increase the normalized output, the output of the normalizing circuit 19 is first differentiated by the differentiating circuit 20.

Differential operation is performed periodically by timing pulses from a timing circuit 21, and the differential value is amplified by an amplifier 22. When the output of the differential amplifier 24 increases and the gate of the control gate mechanism 25 is opened, the differential value is converted into a control signal, but when the differential value is negative, the control gate mechanism 25 is far from the optimal state. An internal flip-flop inverts and generates a control signal that reverses the direction of control by control mechanism 26. When the differential value is positive, it is close to the optimal state, so the built-in flip-flop does not invert,
A control signal is generated that leaves the direction of control by the control mechanism 26 unchanged. Then, the absolute value of the control signal is determined by the differential amplifier 2.
4, and the microwave frequency is controlled by the control mechanism 26 by the absolute value of the control signal in the positive and negative directions of the control signal. When the optimum acceleration state is reached as a result of the control, the normalized output returns to the maximum value again, so the output of the differential amplifier 24 becomes a sufficiently small value, and the gate of the control gate mechanism 25 is closed to maintain the optimum acceleration state. . In this way, in the linear electron accelerator of this embodiment, the radiation output is normalized by dividing it by the set output in the normalization circuit, the maximum value of this normalized output is held in the peak hold circuit, and the peak value held is By controlling the microwave frequency according to the difference from the normalized radiation output, the electron beam energy can always be kept in an optimal state, and stable operation can always be performed.

FIG. 4 shows another embodiment of the control gate mechanism. In the figure, 29 is an absolute value circuit that takes the absolute value of the output of the amplifier 22;
30 is an analog addition circuit that performs analog addition of the output of the absolute value circuit 29 and the output of the differential amplifier 24; 31 is the amplifier 2;
Control mechanism 2 determines whether the output of 2 is positive or negative, and controls the control mechanism 2 according to the result.
This is a positive/negative discrimination circuit that controls the direction of control by 6. The absolute value of the output of the differentiating circuit 20 amplified by the amplifier 22 is taken by the absolute value circuit 29, and added in analog form to the output of the differential amplifier 24.

Further, the differential value of the output of the amplifier 22 is determined by a positive/negative determining circuit 31, and when the differential value is negative, it is far from the optimal state, so the built-in flip-flop is inverted and the control mechanism 26
When it is positive, the direction of control by the control mechanism 26 is reversed, and since it is close to the optimum state, the built-in flip-flop is not reversed, the direction of control by the control mechanism 26 is left unchanged, and the control mechanism 2
6, control is performed in the direction of the control by the output of the adder circuit 30. Note that in the embodiment described above, the output stabilizing circuit 10 for stabilizing the radiation output intensity is not provided;
By maintaining the electron beam energy in an optimal state with the electron beam energy control circuit, the radiation output can be sufficiently stabilized within the specification range.

However, an output stabilizing circuit 10 as shown in FIG. 1 may be provided, and in this case, unlike the conventional case shown in FIG. 1, the electron beam energy stabilizing circuit controls the normalized output, so the output It is possible to stably control radiation output without causing mutual interference with the stabilizing circuit. Furthermore, although the above embodiment describes the case where the microwave frequency is controlled, the high voltage output of the pulse modulator, the microwave power supplied to the accelerating tube, the electron beam current incident on the accelerating tube, etc. also determine the electron beam energy. These are the parameters that control the control, and the same control can be achieved by controlling these parameters.

Further, in the above embodiment, the case of a linear electron accelerator has been explained, but in a radiation generating apparatus such as a betatron, for example, the accelerated electron beam can be adjusted by dividing the radiation output by the output of the output setting mechanism or the output stabilizing circuit.
A mechanism can be provided to maintain the optimal state of energy.

As described above, according to the linear electron accelerator of the present invention,
By keeping the normalized value of the radiation output at the maximum value, the acceleration state of the device is controlled to be kept in the optimal state, so the electron beam energy is stabilized and fluctuations in the radiation output caused by this can be suppressed. , the control circuit of the device becomes simpler.

Furthermore, the stability of radiation output and electron beam energy is improved, and mutual interference due to the provision of a plurality of control mechanisms is eliminated, so that the control mechanisms always operate stably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional linear electron accelerator, FIG. 2 is a block diagram of a linear electron accelerator according to an embodiment of the present invention, and FIG. 3 is a circuit diagram of the peak hold circuit of FIG. FIG. 4 is a block diagram of another embodiment of the control gate mechanism of the present invention. 1...Electron gun, 2...Acceleration tube, 4...Radiation generation mechanism, 6...Detector, 9...Radiation output setting mechanism, 19... ...Normalization circuit, 20
... Differential circuit, 23 ... Peak hold circuit, 24 ... Differential amplifier, 25 ... Control gate mechanism, 26 ... Control mechanism, 31.・・・・・・
・Electron beam energy control circuit. In the figures, the same reference numerals indicate the same or equivalent parts. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. An electron gun that generates an electron beam, an acceleration tube that accelerates the electron beam, a radiation generation mechanism that generates radiation using the electron beam accelerated by the acceleration tube, and a radiation generation mechanism that generates radiation using the electron beam accelerated by the acceleration tube. a detector for detecting the intensity of radiation generated by the mechanism; a radiation output setting mechanism for arbitrarily setting the radiation output; and dividing the output of the detector by a signal proportional to the set output of the output setting mechanism. A normalization circuit that performs normalization, a peak hold circuit that holds the maximum value of the output of this normalization circuit, and an electron beam energy that is determined according to the difference between the output of this peak hold circuit and the output of the normalization circuit. A linear electron accelerator comprising: an electron beam energy control circuit that controls parameters. 2. The electron beam energy control circuit includes a differentiation circuit that differentiates the output of the normalization circuit, a differential amplifier that takes the difference between the output of the peak hold circuit and the output of the normalization circuit, and a differential amplifier that takes the difference between the output of the peak hold circuit and the output of the normalization circuit. A patent characterized in that it includes a control gate mechanism that generates a control signal based on an output and an output of the differentiating circuit, and a control mechanism that changes a parameter that determines the electron beam energy based on the control signal of the control gate mechanism. A linear electron accelerator according to claim 1.