CN108493081B - Asymmetric pulse voltage modulation electron beam method based on beam instability suppression - Google Patents
Asymmetric pulse voltage modulation electron beam method based on beam instability suppression Download PDFInfo
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Abstract
The invention relates to an asymmetric pulse voltage modulation electron beam method based on beam current instability suppression, which comprises the following steps of ⑴ adjusting the direct current bias of a control electrode through a high-voltage pulse signal⑵ triggering logic drive circuit of high-voltage switch by trigger signal, determining frequency of high-voltage pulse signal and pulse width of high-voltage pulse according to the frequency and pulse width of trigger signal, ⑶ calculating frequency of high-voltage pulse signal according to ion beam convolution frequency, ⑷ setting modulation period T in an injection period, ⑸ setting frequency f of trigger signalePulse width Um, ⑹ setting DC bias amplitude + U and-U, ⑺ setting start time T of synchronous time sequence control command of each modulation periodsAnd a termination time Te⑻ setting modulation mode ⑼ triggering modulation system the invention has the advantages of flexible adjustment combination and easy implementation.
Description
Technical Field
The invention relates to a method for modulating an electron beam, in particular to a method for modulating an electron beam based on asymmetric pulse voltage for inhibiting beam instability.
Background
The improvement of the beam quality is an important task of the heavy ion storage ring, the direct current electron beam and the heavy ion beam are subjected to coulomb collision for a plurality of times through interaction between the direct current electron beam and the heavy ion beam, so that the quality of the heavy ion beam is effectively improved, and meanwhile, some heavy ion beam current instability phenomena caused by the action are observed in experiments, and the inhibition of the instability phenomena becomes necessary.
At present, a set of sine wave electron beam modulation systems is established, the system is composed as shown in fig. 1, a sine wave modulation signal is amplified, processed, photoelectrically converted and transmitted to a control electrode, when a gun area is in a proper direct current electric field state, a direct current electron beam is generated, the direct current electron beam generates static charges, and a capacitive detection element cannot sense the signal; the modulation principle is to modulate 3MHz @6V sinusoidal signals provided by an external signal source on an electron beam emission control electrode power supply, the modulation frequency is different from the cyclotron frequency of a heavy ion beam cluster so as to be beneficial to later-stage spectrum signal analysis, and a direct-current electron beam is modulated into a sinusoidal waveform to be sensed by a capacitive detector (see figure 2). At present, the speed, distribution and flow intensity of the electron beams are not changed when the modulation method is used, although the direct-current electron beam signals are modulated into sine-wave electron beam signals, the electron beams are still continuous, and the instability of the heavy ion beams cannot be inhibited by utilizing the electron beam research with the characteristics. Sine wave high voltage modulation of the gate bias voltage can be used to study suppression of beam instability, but the cost to achieve this modulation is very high and the efficiency is very low.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an asymmetric pulse voltage modulation electron beam method based on beam instability suppression, which has flexible adjustment combination and is easy to realize.
In order to solve the above problems, the method for modulating an electron beam based on an asymmetric pulse voltage for suppressing beam current instability of the present invention comprises the following steps:
⑴ the DC bias of the control electrode is modulated into pulse voltage by high voltage pulse signal, other basic DC parameters of the system are changed correspondingly according to the modulation requirement;
⑵ a logic driving circuit for triggering the high-voltage switch by a trigger signal, determining the frequency of the high-voltage pulse signal and the pulse width of the high-voltage pulse according to the frequency and the pulse width of the trigger signal;
when the frequency of the high-voltage pulse signal, the amplitude of the high-voltage pulse and the pulse width of the high-voltage pulse are changed, the high-voltage switch is synchronous with the trigger signal, and the high-voltage switch outputs the high-voltage pulse signal;
⑶ calculating the frequency of the high voltage pulse signal according to the cyclotron frequency of the ion beam;
⑷ setting a modulation period T within one injection period;
⑸ setting the frequency f of the trigger signalePulse width Um;
⑹ setting DC bias amplitude + U and-U;
⑺ sets the start time T of the synchronous timing control command for each modulation cyclesAnd a termination time Te；
⑻ setting a modulation mode;
⑼ trigger the modulation system.
Compared with the prior art, the invention has the following advantages:
1. the invention modulates direct current electron beams into pulse electron beams by high-voltage pulse signal modulation control electrode voltage, changes the shape distribution and the current intensity of the extracted electron beams, an electric field generated by space charge is transmitted to a heavy ion beam rail along the electron beams, the longitudinal electric field generates certain longitudinal kisk to the heavy ion beams, and the instability of the heavy ion beams is inhibited by the action of electron beam clusters generated by the change of the frequency, the amplitude and the pulse width of modulation signals on the heavy ion beams.
2. The invention utilizes the trigger signal to control the frequency and the pulse width of the high-voltage pulse, changes the preset asymmetric direct current bias amplitude value and changes the amplitude of the high-voltage pulse, and has the advantages of flexible combination and easy realization.
3. The invention can improve the performance of HIRFL-CSR, provide high-precision and high-resolution heavy ion beams for users, and lay a theoretical foundation for the comprehensive improvement of the next machine performance.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of a conventional sine wave modulated electron beam system.
Fig. 2 is a schematic diagram of a modulation waveform of a sine wave electron beam in the prior art.
FIG. 3 is a schematic diagram of a modulated pulse voltage waveform according to the present invention.
FIG. 4 is a time domain schematic of a pulsed electron bunch in accordance with the present invention.
FIG. 5 is a diagram illustrating the intensity of a pulsed electron beam according to the present invention.
Fig. 6 is a waveform diagram of a basic modulation mode pulse voltage according to the present invention.
FIG. 7 is a waveform diagram of a combined modulation mode pulse voltage according to the present invention.
Fig. 8 is a diagram of a narrow pulse modulation voltage waveform of the present invention.
FIG. 9 is a diagram of a broad pulse modulation voltage waveform of the present invention.
Detailed Description
The method for modulating the electron beam based on the asymmetric pulse voltage for inhibiting the beam instability comprises the following steps:
⑴ the DC bias of the control electrode is modulated into pulse voltage by high voltage pulse signal, and other basic DC parameters of the system are changed correspondingly according to the modulation requirement.
⑵ the logic driving circuit of the high-voltage switch is triggered by the trigger signal, and the frequency of the high-voltage pulse signal and the pulse width of the high-voltage pulse are determined according to the frequency and the pulse width of the trigger signal.
When the frequency of the high-voltage pulse signal, the amplitude of the high-voltage pulse and the pulse width of the high-voltage pulse are changed, the high-voltage switch is synchronous with the trigger signal, and the high-voltage switch outputs the high-voltage pulse signal.
Fig. 3 is a schematic diagram of a pulse voltage waveform. The waveforms of the pulse voltage shown in a and b in fig. 3 are waveforms under different trigger signals and different dc bias states, and in order to obtain a required effective high-voltage pulse signal, the trigger signal and the dc bias setting signal need to work synchronously, and when a predetermined signal triggers the high-voltage switch, an asymmetric high-voltage pulse signal can be obtained, and the high-voltage pulse waveform in fig. 3-a is a schematic diagram under different dc biases without changing the frequency and pulse width of the trigger signal. A sequence of trigger signals may generate a plurality of effective high voltage pulse modulated voltage waveforms, where p1-pn is the waveform of the positive biased high voltage pulse amplitude, n1-nn is the waveform of the negative biased high voltage pulse amplitude, and n1p1 is the first waveform of a sequence of high voltage pulses, where the negative dc bias is first ensured to effectively turn off the electron beam, and the minimum value of the positive dc bias is the off-line value that ensures the electron beam is generated. Due to the intrinsic nature of the hardware, the ratio of the magnitudes of the positive and negative dc biases when this condition is satisfied is a varying value. When a higher current is required, the amplitude of the forward bias can be preset to be higher than the lower line value which is different and larger than the amplitude of the forward bias, so that the required high-voltage pulse waveform can be obtained when the high-voltage switch is triggered. The high-voltage pulse waveforms of n2p2 to nnpn are similar to n1p1, the asymmetry is also represented by the ratio of the positive amplitude to the negative absolute value, the actual experimental values depend on the characteristics of hardware, and the high-voltage pulse waveform in fig. 3-b is a waveform obtained under different frequencies, pulse widths and direct current biases than those of the trigger signals in fig. 3-a. In a specific experimental test practice, the process of setting synchronization of the trigger signal and the dc bias control signal is as follows: firstly, determining parameters such as frequency, pulse width and the like of a required asymmetric high-voltage pulse waveform to form a control sequence command, then determining positive and negative direct current bias amplitudes, starting a modulation system control command, obtaining a high-voltage pulse waveform on a control electrode, and modulating a direct current electron beam into a pulse electron beam with synchronously changed intensity, frequency and pulse width.
Fig. 4 is a schematic diagram of modulating a dc electron beam into a time-domain, discontinuous series of electron clusters by a pulse modulation voltage, and studying the suppression of the instability of the ion beam by using the longitudinal kisk effect of the space charge field generated by each electron cluster on the ion beam.
The modulation system triggers the high-voltage switch by a trigger signal, and generates a corresponding high-voltage pulse waveform by adjusting the frequency, the pulse width and the amplitude of the asymmetric high-voltage pulse waveform. The asymmetry value of the asymmetric high voltage pulse waveform is derived from the relative values of the dc bias to turn the electron beam on and off, wherein the magnitude of the negative pulse voltage depends on the value of the electron beam fully off and the magnitude of the positive pulse voltage depends on the minimum value of the electron beam generated; when the required beam intensity increases, the amplitude is adjusted from the minimum value of the positive pulse DC bias to the positive direction, so that the asymmetric proportion of the pulse voltage is increased, thereby changing the amplitude of the pulse electron beam.
⑶ calculating the high voltage pulse signal frequency based on the ion beam cyclotron frequency.
Calculating the cyclotron frequency of the heavy ion beam according to the energy of the heavy ion beamf i ：
；
In the formula:βis a relativistic factor;cat the speed of light 3 x 108m/s ；CIs the storage ring perimeter;
due to the difference of energy, when the frequency of the pulsed electron beam is required to be equal to or an integral multiple of the cyclotron frequency of the heavy ion beam for heavy ion beams with the cyclotron frequency of 0.2MHz to 1.6MHz, a longitudinal kick can be effectively formed on the heavy ion beams by the space electric field generated by the pulsed electron beam in a cyclotron period, as shown in fig. 5, a strong waveform diagram of the pulsed electron beam is shown.
⑷ sets the modulation period T within one injection period.
One injection period may correspond to one or several modulation periods, and a basic modulation mode or a combined modulation mode may be adopted in one modulation period.
⑸ setting the frequency f of the trigger signaleAnd a pulse width Um.
The parameters of the high-voltage pulse signal depend on the trigger signal when the frequency f of the trigger signaleWhen the pulse width Um is determined, the high voltage pulse signal is synchronized with it.
⑹ sets the DC bias amplitudes + U and-U.
The dc bias amplitude is set such that firstly modulation is enabled at a minimum beam, and when the modulation depth is changed, the lowest value of + U is the down-line value at which the beam is generated and-U is the up-line value at which the beam is turned off.
⑺ sets the start time T of the synchronous timing control command for each modulation cyclesAnd a termination time Te。
Starting time T of synchronous sequential control instructionsSynchronized with the start time, the end time T, of each modulation periodeSynchronized with the end time of each modulation period.
⑻ sets the modulation mode.
The modulation mode employed during one injection period is set.
⑼ trigger the modulation system.
The trigger time of the modulation system is synchronized with the implantation time of the heavy ion beam and is related to the modulation period.
The invention aims at heavy ions with different energies to design an asymmetric high-voltage pulse modulation waveform, which can be realized by adjusting the frequency or pulse width of a trigger driving signal of a high-voltage switch, and adjusting the amplitudes of positive direct current bias and negative direct current bias, when a time sequence control instruction is started, the high-voltage switch and the direct current bias control complete a modulation period according to a preset mode, the most basic working mode is that the amplitude of the direct current bias is not changed along with the advance of a time sequence after the direct current bias is ready according to a preset value, the frequency and the width of a high-voltage modulation pulse are correspondingly changed according to the change of the frequency and the pulse width of the trigger signal, the working mode is a basic modulation mode, the basic modulation mode is as shown in figure 6, under the mode, each electron beam group is basically consistent with the longitudinal kick of the heavy ion beam, the general effects of modulation are similar, the method and strategy for researching and inhibiting the instability of the heavy ion beam are single, and through observation and analysis of a basic modulation mode, a further research scheme is that under the synergistic action of synchronous driving signals, the frequency and pulse width of a trigger signal of a high-voltage switch are changed at the initial moment of starting each modulation period, and the amplitude of direct current bias is synchronously changed once, so that gradient modulation pulse voltage corresponding to a plurality of modulation periods in one injection period can be formed, fig. 7 is a schematic diagram of the pulse voltage waveform of the combined modulation mode, and fig. 7-a is a waveform schematic diagram of direct current bias and high-voltage pulse waveform amplitude in a plurality of modulation periods responding to a control timing command in a gradient descending manner; FIG. 7-b is a waveform diagram of the DC bias and the amplitude of the high voltage pulse waveform in response to a control timing command in a gradient ascending manner for several modulation periods; this mode of operation is a monotonic modulation mode; the modulation mode combination generates a dynamically-changed high-voltage pulse modulation waveform in different modulation periods in an injection period, and the generated pulse electron beam group acts with a heavy ion beam, so that a method and a technical means for testing, analyzing and inhibiting beam instability are added. The electric field generated by the space charge of the pulsed electron beam cluster is transferred along the electron beam to the heavy ion rail, this longitudinal electric field will generate a certain longitudinal kick for the heavy ion beam and is related to the length, frequency, amplitude of the pulsed electron beam cluster, the following examples illustrate two different shapes of high voltage pulse modulated waveforms.
Example 1: the narrow pulse modulates a voltage waveform.
The trigger signal triggers the high-voltage switch, the direct current bias is monotonically increased to obtain a group of examples of asymmetric high-voltage pulse modulation waveforms, as shown in fig. 8, in fig. 8-a, the positive amplitude of the direct current bias is 600V, the absolute value ratio of the negative bias amplitude is-400 is 1.5:1, and the pulse width is 1 us; in FIG. 8-b, the DC bias has a positive amplitude of 1200V, a negative bias amplitude of-400V, an absolute ratio of 3:1, and a pulse width of 50 us.
Example 2: the wide pulse modulates the voltage waveform.
The trigger signal triggers the high-voltage switch, the direct current bias is monotonically increased to obtain a group of examples of asymmetric high-voltage pulse modulation waveforms as shown in fig. 9, in fig. 9-a, the positive amplitude of the direct current bias is 600V, the absolute value ratio of the negative bias amplitude is-400 is 1.5:1, and the pulse width is 1 ms; in FIG. 8-b, the DC bias has a positive amplitude of 1200V, a negative bias amplitude of-400V, an absolute ratio of 3:1, and a pulse width of 200 us.
The above embodiments describe the characteristics of an asymmetric high voltage modulated pulse waveform, with the parameters listed as examples being varied accordingly with experimental test requirements.
Claims (1)
1. The method for modulating the electron beam based on the asymmetric pulse voltage for inhibiting the beam instability comprises the following steps:
⑴ the DC bias of the control electrode is modulated into pulse voltage by high voltage pulse signal, other basic DC parameters of the system are changed correspondingly according to the modulation requirement;
⑵ a logic driving circuit for triggering the high-voltage switch by a trigger signal, determining the frequency of the high-voltage pulse signal and the pulse width of the high-voltage pulse according to the frequency and the pulse width of the trigger signal;
when the frequency of the high-voltage pulse signal, the amplitude of the high-voltage pulse and the pulse width of the high-voltage pulse are changed, the high-voltage switch is synchronous with the trigger signal, and the high-voltage switch outputs the high-voltage pulse signal;
⑶ calculating the frequency of the high voltage pulse signal according to the cyclotron frequency of the ion beam;
⑷ setting a modulation period T within one injection period;
⑸ setting the frequency f of the trigger signalePulse width Um;
⑹ setting DC bias amplitude + U and-U;
⑺ sets the start time T of the synchronous timing control command for each modulation cyclesAnd a termination time Te；
⑻ setting a modulation mode;
⑼ trigger the modulation system.
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| CN2596404Y (en) * | 2002-11-23 | 2003-12-31 | 中国科学院近代物理研究所 | High frequency transmitter screen-grid switch power source device |
| CN101652017A (en) * | 2009-01-12 | 2010-02-17 | 中国科学院近代物理研究所 | Synchronous acceleration method of high frequency variable harmonics and control device thereof |
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| CN2596404Y (en) * | 2002-11-23 | 2003-12-31 | 中国科学院近代物理研究所 | High frequency transmitter screen-grid switch power source device |
| CN101652017A (en) * | 2009-01-12 | 2010-02-17 | 中国科学院近代物理研究所 | Synchronous acceleration method of high frequency variable harmonics and control device thereof |
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