JPS6231800B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of operating a charged particle accelerator.

In general, charged particle accelerators, such as cyclotrons, operate by applying the output of a high-frequency oscillation circuit to the day electrode of the acceleration box to accelerate the ions emitted from the ion source, but multipactoring is often used when oscillation starts. (This is a discharge phenomenon peculiar to high frequencies that occurs in a vacuum. A discharge phenomenon that occurs when a high frequency wave is continuously applied to the day electrode, that is, when a continuous wave of high frequency is applied.) A high frequency voltage is generated in the day electrode and the resonator connected to it. Even if the voltage is applied, resonance may not occur and the high frequency voltage may not increase, and steady operation may not be possible. Therefore, in order to shift to steady operation, it is necessary to overcome the multipactoring phenomenon. Even if this multipactoring phenomenon can be overcome and steady operation can be achieved, if a spark discharge occurs inside the acceleration box, the output of the high frequency oscillation circuit (continuous high frequency wave) will temporarily decrease and operation will become impossible. Then, when the spark discharge etc. subside, it is necessary to overcome the multipactoring phenomenon again. Furthermore, when a multipactoring phenomenon occurs, the plate loss of the final stage electron tube of the high frequency oscillation circuit increases, potentially rendering the final stage electron tube unusable, so it is necessary to protect the final stage electron tube. Thus, when operating a charged particle accelerator, it is necessary to overcome the multipactoring phenomenon and to protect the final stage electron tube.

Conventionally, in order to overcome the multipactoring phenomenon, the oscillation frequency of the high frequency oscillation circuit was detuned from the natural frequency of the resonator, and the rise of the high frequency voltage in the resonator was increased to make it easier to overcome the multipactoring phenomenon. Although there are methods to overcome the multipactoring phenomenon, such methods require complicated operation and are not easy to operate. In addition, in order to protect the final stage electron tube, when the plate loss of the final stage electron tube increases, a short circuit is formed on the plate power supply side using an ignatron or thyratron, etc. A so-called crowbar device is used to short the plate power supply side of the final stage electron tube. However, the crowbar device is very expensive and has the disadvantage that it cannot be implemented at low cost.

SUMMARY OF THE INVENTION Therefore, the present invention has been made to provide a method of operating a charged particle accelerator that can quickly overcome the multipactoring phenomenon, protect the final stage electron tube, and be easy and inexpensive to operate.

A method of implementing the present invention will be explained in detail below with reference to the drawings. In this implementation method, as shown in the first diagram, the output of a high-frequency oscillation circuit 1 consisting of a main oscillator 1a and amplifiers 1b to 1d in the first stage, drive stage, and final stage for amplifying its oscillation output is applied to the D-electrode 2 in the acceleration box. In addition, in the method of accelerating the ions emitted from the ion source, the voltage of the D electrode 2 is detected by the voltage detector 3, and this detected voltage E _d is added to the sample hold circuit 4 to obtain a level proportional to the detected voltage. Sample and hold the voltage and output it. The sample hold voltage E _h and the set voltage E _s are applied to a comparator 5 for comparison, and the output E _c of the comparator 5 and the continuous wave operation command E _w are applied to a switching circuit 6 . The continuous wave operation command _Ew can be obtained, for example, by operating a switch. When the detection voltage E _d is small and the sample-and-hold voltage E _h is smaller than the set voltage E _s , the output E _c of the comparator 5 is added to the pulse modulator 7 via the switching circuit 6 so that the pulse modulator 7 can continue to operate. For example, if m = 1, n = 10, the time width t ₁ (second
(see figure). In the method of the present invention, the time width of duty m/n means the time width of m/n per unit time, and the time width _t1 of duty 1/10 is 1/n per unit time.
10, that is, if the unit time is 1 second, it is a time width of 1/10 second. Note that S _y is a synchronization signal for operating the pulse modulator 7 and the sample hold circuit 4 in synchronization. Pulse modulator 7 with duty 1/
By operating with a time width t ₁ of 10, the high frequency oscillation circuit 1 is pulse-operated as shown in the second diagram with a modulation pulse P _{1 of} a time width t 1 with a duty of 1/10. That is, the main oscillator 1a is operated only while the modulation pulse _P1 is applied, and the duty is 1/10.
An oscillating voltage (intermittent wave) _On with a time width _t1 is outputted, amplified by amplifiers 1b to 1d, and applied to the D electrode 2. Immediately after turning on the power switch and starting oscillation, the detection voltage E _d is small and the sample and hold voltage E _h is smaller than the set voltage E _s , so the high frequency oscillation circuit 1 is operated in pulses. This pulse operation overcomes the multipactoring phenomenon. That is, the multipactoring phenomenon is likely to occur when a high frequency continuous wave is applied, especially during the electrically unstable period at the start of oscillation, so at this time the high frequency intermittent wave O _n
The multipactoring phenomenon is overcome by adding . The time width t ₁ with duty 1/10 is an intermittent wave O that can overcome the multipactoring phenomenon and continue operation.
Of course, the time width is selected so that _n can be obtained. During the above pulse operation, the final stage amplifier 1d
The electron tube can reduce the plate loss of the final stage electron tube to 1/10 of the normal one by using the amplified intermittent wave _On , and can protect the final stage electron tube of the high frequency oscillation circuit 1.

When the multipactoring phenomenon is overcome, the high frequency voltage of the D-electrode 2 and the resonator increases, the detection voltage E _d increases, and the sample-and-hold voltage E _h becomes larger than the set voltage E _s . In such a case, the switching circuit 6 is switched and the continuous wave operation command E _w is applied to the pulse modulator 7 through the switching circuit 6, the pulse modulator 7 is made inoperable, and the modulated pulse is transmitted to the second pulse.
As shown in the figure, the high frequency oscillation circuit 1 is operated as a continuous wave. That is, the main oscillator 1a is caused to oscillate continuously, and a high frequency continuous wave O _c is output from it.
The signal is amplified by amplifiers 1b to 1d and applied to the D electrode 2. If the multipactoring phenomenon does not occur again, the operation will continue with the continuous wave O _c as shown in Figure 2 a.

After switching to continuous wave operation, the detection voltage E _d decreases due to the multipactoring phenomenon again.
When the sample hold voltage E _h becomes smaller than the set voltage E _s , the switching circuit 6 is switched and the voltage shown in FIG.
As shown, immediately shift to the above-mentioned pulse operation,
When the sample hold voltage E _h increases, the operation immediately shifts to continuous wave operation. In this way, the high frequency voltage of the D electrode 2 and the resonator is detected, this detected voltage E _d changes depending on the load condition, and the sample hold voltage E _h compared to this detected voltage E _d is compared to the set voltage E _s . Pulse operation is automatically switched to continuous wave operation depending on whether the wave is small or large.

In addition, when performing continuous wave operation (steady operation using continuous wave O _c ) to overcome the multipactoring phenomenon, spark discharge may occur in the acceleration box, and the degree of vacuum may decrease and claw discharge may occur, causing high frequency Even when no voltage is generated, the sample-and-hold voltage E _h is smaller than the set voltage E _s , so it automatically shifts to pulse operation with a time width t ₁ of duty 1/10, and when the above spark discharge etc. subsides. As the high frequency voltage increases,
The sample hold voltage E _h becomes larger than the set voltage E _s and the operation automatically shifts to continuous wave operation.

In addition, in the method of the present invention, when pulse operation and continuous wave operation are repeated, the number of repetitions is counted, and when a predetermined number of times is reached, the operation cancellation signal S is sent from the operation cancellation circuit 9 to the operation command circuit 8. Then, the operation command circuit 8 is made inoperative, the continuous wave operation command E _w is eliminated, and the output E _c of the comparator 5 is applied to the pulse modulator 7 through the switching circuit 6, and thereafter pulse operation is started (see Fig. 2 c). When the detection voltage E _d and therefore the sample hold voltage E _h continue to be larger than the set voltage E _s for a predetermined period of time, the continuous wave operation command E _w is issued again from the operation command circuit 8. You can also do this.

In addition, it is preferable to operate the ion acceleration performance by applying a high-frequency continuous wave O _c to the day electrode 2, but it is acceptable to perform pulse operation similar to continuous wave operation because the acceleration performance does not deteriorate that much. do not have. That is, in FIG. 1, the operation command circuit 8 is controlled by a pulse operation command E _p of a duty 8/10 and a time width t ₈ with a duty l/n (l and n are integers, and l is a value close to n, and l<n). When the sample and hold voltage E _h is smaller than the set voltage E _s ,
The high frequency oscillation circuit 1 is operated in pulses in the same manner as above,
When the sample and hold voltage E _h is larger than the set voltage E _s , the pulse modulator 7 is operated with a duty of 8/10 and a time width t ₈ to output a modulated pulse P ₈
The high frequency oscillation circuit 1 is operated in pulses. In this case, the steady operation is a pulse operation with a time width of 8/10 duty.

Note that the configuration of each part 1, 3 to 9 in the present invention can be achieved by conventional technology, and the configuration is not the gist of the invention, so a detailed explanation thereof is omitted.

As described above, according to the present invention, the day voltage is detected, the sample-and-hold voltage E _h proportional to the detected voltage E _d and the set voltage E _s are compared by the comparator 5, and the output E _c of the comparator 5 is compared with the set voltage E s. A continuous wave operation command E _w or a pulse operation command E _p with a time width of duty l/n is applied to the switching circuit 6, and when the sample and hold voltage E _h is smaller, the pulse modulator 7 is activated by the output E _c of the comparator 5. It is operated with a time width of duty m/n that allows continuous operation, and the high frequency oscillation circuit 1 is operated in pulses with the modulation pulse outputted from this, and when the sample hold voltage E _h is larger, pulse modulation is performed by the continuous wave operation command E _w . Either the high-frequency oscillation circuit 1 is operated in continuous wave mode with the modulator 7 inactive, or the pulse modulator 7 is activated by a pulse operation command E _p with a time width of duty l/n.
This method operates the high-frequency oscillation circuit 1 with a time width of duty l/n, and uses the modulated pulses outputted from it to drive the high-frequency oscillation circuit 1 in a manner close to continuous wave operation. When the sample-and-hold voltage E _h becomes smaller due to a drop in the high-frequency voltage due to glow discharge, etc., the system immediately shifts to pulse operation with a time width of duty m/n that allows operation to continue, ensuring that the multipactoring phenomenon is quickly eliminated. In addition to being able to overcome the
The plate loss of the final stage electron tube can be reduced to m/n, and the final stage electron tube can be protected. Moreover, since the output of the main oscillator 1a is usually about several tens of W or less, it is relatively easy to operate the main oscillator 1a in pulses, and an expensive crowbar device is not required, so it can be implemented at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an apparatus for carrying out the method of the present invention, and FIG. 2 is a time chart for explaining the same. 1... High frequency oscillation circuit, 2... Day electrode, 3
... Voltage detector, E _d ... Detection voltage, 4 ... Sample and hold circuit, E _h ... Sample and hold voltage, E _s ... Setting voltage, 5 ... Comparator, E _c ... Output of comparator 5 , 6...Switching circuit, 7...Pulse modulator, 8...Operation command circuit, _Ew ...Continuous wave operation command, _Ep ...Pulse operation command, 9...Operation cancellation circuit, S...Operation cancellation signal.

Claims (1)

[Claims] 1. In a method of accelerating ions emitted from an ion source by applying the output of a high-frequency oscillation circuit to a DE electrode in an acceleration box, the voltage of the DE electrode is detected by a voltage detector; The detected voltage is applied to a sample-and-hold circuit to sample and hold the voltage at a level proportional to the detected voltage and output, and this sample-and-hold voltage and the set voltage are applied to a comparator and compared, and the output of this comparator and the continuous wave When the sample and hold voltage is smaller, the output of the comparator is added to the pulse modulator by the switching operation of the switching circuit, and the duty m/n (m, n is an integer and m≪n)
The high frequency oscillator is operated with a time width of 1. A method for operating a charged particle accelerator, comprising: deactivating a high-frequency oscillation circuit, thereby causing a high-frequency oscillation circuit to perform continuous wave operation. 2 In a method of accelerating ions emitted from an ion source by applying the output of a high-frequency oscillation circuit to the DE electrode in the acceleration box, the voltage of the DE electrode is detected by a voltage detector, and this detected voltage is applied to the sample and hold circuit. In addition to this, sample and hold the voltage at a level proportional to the detected voltage and output it, add this sample and hold voltage to the set voltage and compare it to a comparator, and calculate the output of this comparator and the duty l/n (l, n is an integer, l is a value close to n, and a pulse operation command with a time width of l < n is applied to the switching circuit, and when the sample and hold voltage is smaller, the output of the comparator is pulse modulated by the switching operation of the switching circuit. In addition to the pulse modulator, the pulse modulator is operated with a time width of duty m/n (m, n are integers, m≪n) that is smaller than the above duty l/n and can continue operation, and the modulated pulses output from this are used to generate a high-frequency oscillator. When the sample and hold voltage is larger, the pulse operation command is applied to the pulse modulator by the switching operation of the switching circuit with a time width of duty l/n, and the pulse modulator is activated with a time width of duty l/n. 1. A method for operating a charged particle accelerator, characterized in that the high-frequency oscillator is operated in pulses with a duty cycle of l/n.