A method and system for automatic frequency tracking based on a sweep pattern

Abstract

The application discloses a kind of automatic frequency tracking method and system based on sweep mode, frequency is swept by the way of combination of " rough sweep+fine sweep ", first by " rough sweep " of big step, " rough sweep " is the method of difference of adjacent frequency point reflected voltage to judge sweep direction, determine a smaller frequency range containing inflection point, in this frequency range, small step " fine sweep " is used, compare the size of each frequency point reflected voltage, the frequency point corresponding to the minimum reflected voltage is the resonant frequency point of accelerating tube.The application compared with traditional frequency discrimination type automatic frequency tracking method, on the basis of ensuring sweep precision, improve sweep efficiency, can quickly obtain the actual resonant frequency of accelerating tube.

Description

Technical Field

[0001] This invention relates to an automatic frequency tracking method and system based on a frequency sweeping mode, belonging to the field of space microwave technology. Background Technology

[0002] An electron linear accelerator is a device that uses a microwave power source to generate a microwave electric field, accelerating electrons along a linear trajectory to higher energies, which then strike a target to produce X-rays. It is now widely used in radiation therapy, irradiation processing, industrial non-destructive testing, and environmental remediation. During application, the stability and reliability of the electron linear accelerator system are crucial. A standing-wave accelerator tube is actually composed of a series of resonant cavities coupled in a specific way. Each resonant cavity has a small hole in its center for the electron beam to pass through. The inherent resonant frequency of the standing-wave accelerator tube is determined after its manufacturing process. If the phase relationship is appropriate when the accelerated electrons reach each accelerating cavity—that is, when the peak electric field strength of the standing wave coincides with the center of the resonant cavity—then the electrons can be continuously accelerated and gain energy. When the electrons reach the end of the accelerator tube, they have considerable energy and then strike a target to produce a certain dose of X-rays.

[0003] To maximize the electron beam energy output by the accelerator, thus achieving the maximum dose rate, the resonant frequency of the microwave source must match the inherent resonant frequency of the accelerator tube. In this case, almost all the microwave power input from the magnetron to the accelerator tube is fed into the tube, with minimal reflection. However, when the resonant frequencies are inconsistent, the accelerator tube will reflect a certain amount of microwave energy, leading to a decrease in the strength of the standing wave accelerating electric field and the electron beam energy. Due to environmental factors such as temperature, voltage, and magnetic fields, the actual resonant frequency of the accelerator tube may deviate from the designed resonant frequency. When the frequency f of the microwave power source deviates from the resonant frequency of the standing wave accelerator tube, it not only causes a decrease in energy and dose rate but also results in power reflection, and may even render the accelerator tube inoperable.

[0004] A keyword search of domestic and international literature and patent databases revealed no patents or literature specifically related to automatic tracking of the resonant frequency of accelerating tubes. Based on available information, it is inferred that this technology is being extensively researched abroad, with some aspects already showing promise. Domestic research, however, lags behind and is still in the exploratory stage. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose an automatic frequency tracking method and system based on a frequency sweep mode. The method automatically tracks the actual resonant frequency of the accelerator tube by using a frequency sweep mode that combines "coarse sweep + fine sweep" and outputs a microwave signal that meets the operating requirements of the accelerator tube.

[0006] The technical solution of this invention is:

[0007] An automatic frequency tracking method based on a frequency sweeping mode includes:

[0008] Based on the accelerator tube design parameters, determine the frequency sweep range and perform the following frequency sweep operation:

[0009] A coarse scan is performed starting from the starting frequency point of the frequency sweep range to obtain the reflected signal voltage of the accelerator tube at each frequency point; the difference between the reflected signal voltage of the current frequency point and the adjacent previous frequency point is calculated. If the difference is negative, the coarse scan continues; otherwise, the frequency sweep is stopped, and the frequency sweep range is updated to the range between the current frequency point and the second frequency point before the current frequency point. A fine scan is performed starting from the starting frequency point of the frequency sweep range to obtain the reflected signal voltage of the accelerator tube at each frequency point, and the frequency point corresponding to the minimum reflected voltage is selected as the resonant frequency point.

[0010] The obtained resonant frequency is used as the input frequency of the accelerator tube. The reflected voltage value of the accelerator tube is monitored. When the reflected voltage value exceeds the set threshold, the above frequency sweep operation is repeated to obtain a new resonant frequency and use it as the input frequency of the accelerator tube.

[0011] Preferably, the difference between coarse scanning and fine scanning is that the scanning step value is different, with the scanning step value of coarse scanning being greater than that of fine scanning.

[0012] Preferably, the scanning step value for coarse scanning is determined based on the scanning frequency range, and the scanning frequency range is divided equally, selecting 40 to 60 frequency points.

[0013] Preferably, the scanning step value for fine scanning is obtained by performing frequency offset and accelerated tube bundle energy and energy dissipation simulation in ASTRA.

[0014] Preferably, the method for determining the sweep frequency range based on the accelerator tube design parameters is as follows:

[0015] Calculate the maximum frequency difference:

[0016] △f=1.7e -5 *f0*△T

[0017] In the formula, f0 is the design center frequency, and ΔT is the difference between the temperature distribution when it reaches steady state and the initial temperature.

[0018] The frequency sweep range is f0 ± Δf.

[0019] Preferably, the method of scanning from the starting frequency point of the frequency sweep range to obtain the reflected signal voltage of the accelerator tube at each frequency point is as follows: obtain the reflected signal of the accelerator tube with the current frequency point as input, and obtain the reflected signal voltage through A / D sampling and detector.

[0020] Preferably, when performing coarse or fine scanning at each frequency point, the device should remain stationary for a certain period of time until the accelerating tube reaches a stable state before acquiring the reflected signal voltage of the accelerating tube at each frequency point.

[0021] An automatic frequency tracking system based on a frequency sweeping mode includes a coarse sweep module, a fine sweep module, and a reflected signal voltage monitoring module;

[0022] The coarse scan module determines the frequency sweep range based on the accelerator tube design parameters, and starts scanning from the starting frequency point of the frequency sweep range. The current frequency point is input to the reflected signal voltage monitoring module to obtain the reflected signal voltage of the accelerator tube at each frequency point. The difference between the reflected signal voltage of the current frequency point and the adjacent previous frequency point is calculated. If the difference is negative, the scanning continues; otherwise, the frequency sweep is stopped, and the frequency sweep range is updated to the range between the current frequency point and the second frequency point before the current frequency point. The updated frequency sweep range is then sent to the fine scan module.

[0023] The fine scanning module scans from the starting frequency point of the received frequency range, inputs the current frequency point to the reflected signal voltage monitoring module, and obtains the reflected signal voltage of the accelerator tube at each frequency point; selects the frequency point corresponding to the minimum reflected voltage as the resonant frequency point, and outputs the resonant frequency point as the input frequency of the accelerator tube.

[0024] Preferably, the reflected signal voltage monitoring module receives frequency point information, acquires the reflected signal of the accelerator tube with the current frequency point as input, and obtains the reflected signal voltage through A / D sampling and detector.

[0025] Preferably, the scanning step values ​​of the coarse scanning module and the fine scanning module are different, with the coarse scanning module having a larger scanning step value and the fine scanning module having a smaller scanning step value.

[0026] The advantages of this invention compared to the prior art are:

[0027] (1) The present invention automatically tracks the frequency of the accelerating tube based on the frequency sweep mode. Compared with the traditional frequency discrimination automatic frequency tracking method, it can perform digital processing and determine the frequency of the output signal.

[0028] (2) The present invention adopts a frequency sweep mode of “coarse sweep + fine sweep”, which improves the frequency sweep efficiency while ensuring the frequency sweep accuracy, and can quickly obtain the actual resonant frequency of the accelerating tube.

[0029] (3) The present invention provides input to the accelerator tube by obtaining the actual resonant frequency, and continuously monitors the reflected power of the accelerator tube. When the reflected power is greater than a certain set value, it indicates that the frequency of the accelerator tube has drifted, and the frequency sweeping mechanism needs to be triggered to start a new round of frequency sweeping in order to obtain the resonant frequency point after frequency drift.

[0030] (4) Automatic frequency tracking is still in its early stages in China, but its demand is already very urgent and it will surely be widely used in the future. This invention proposes an automatic frequency tracking method based on a frequency sweep mode, which has considerable practicality and meets the requirements of high efficiency and high precision in automatic frequency tracking methods. It can be widely used in accelerator tube systems, which can address the problem of easy frequency drift in accelerator tubes and improve the efficiency of automatic frequency tracking. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0032] Figure 1 This is a graph showing the relationship between the reflected power of the accelerating tube and the frequency point in an embodiment of the present invention;

[0033] Figure 2 This is a flowchart of the coarse scan algorithm according to an embodiment of the present invention;

[0034] Figure 3 This is a flowchart of the frequency sweep mode in an embodiment of the present invention. Detailed Implementation

[0035] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] The resonant frequency of current linear electron accelerators is susceptible to drift due to factors such as temperature and magnetic fields. When the microwave power source and the resonant frequency of the accelerator tube are inconsistent, the accelerator tube will reflect microwaves of a certain power, which will lead to a significant reduction in the output dose rate and affect the overall performance of the accelerator tube. Based on an in-depth analysis of its frequency drift characteristics, this invention proposes an automatic frequency tracking method and system based on a frequency sweep mode, filling the gap in domestic automatic frequency tracking technology. This method can automatically adjust the frequency of the output microwave to ensure that it is consistent with the operating frequency of the accelerator tube.

[0037] This invention employs a combination of coarse and fine scanning to achieve automatic frequency tracking. Figure 3As shown, a large-step coarse scan is first performed, using the difference between reflected voltages at adjacent frequencies to determine the scan direction and identify a small frequency range containing inflection points. Within this frequency range, a small-step "fine scan" is performed, comparing the reflected power at each frequency point. The frequency point corresponding to the minimum reflected power is the resonant frequency of the accelerator tube. After determining the resonant frequency, this frequency is used as the input to the accelerator tube. Simultaneously, the reflected signal voltage is continuously monitored. When the reflected signal voltage exceeds a certain value, it indicates that the frequency has drifted, and the frequency needs to be re-scanned to obtain the resonant frequency after the frequency drift.

[0038] The method specifically includes:

[0039] (1) Using the resonant frequency of the accelerating tube design as the center frequency, set the sweep frequency range and the step values ​​for coarse and fine sweeps. Since the accelerating tube needs time to build up its field and reach a stable state, each sweep frequency point must remain for a certain period of time until it reaches a stable state. The relationship between the magnitude of the accelerating tube's reflected voltage and the frequency is as follows: Figure 1 As shown;

[0040] The sweep frequency range is determined using the empirical formula for temperature-frequency deviation: Δf = 1.7e -5 *Fre*△T, Fre is the designed center frequency f0, △T is the difference between the temperature distribution when it reaches steady state and the initial temperature. The initial temperature changes from room temperature T0, and the final steady state temperature reaches a value T1. The temperature difference △T=T1-T0, so the maximum possible frequency difference △f can be calculated, and the frequency sweep range is f0±△f.

[0041] The coarse scan step can be determined based on the frequency range, generally divided into equal parts, with 50 frequency points selected. The fine scan step value is based on the simulation results of the energy and energy dissipation of the accelerating tube bundle after mid-frequency offset in ASTRA, and should be set at least below 100KHz.

[0042] (2) Scanning is performed using a combination of coarse and fine scanning. Coarse scanning includes... Figure 2 As shown, during scanning, a coarse scan is performed starting from the initial frequency point within the frequency range. A step value provides input to the accelerating tube, and the step value range is relatively large. The microwave signal reflected back from the accelerating tube at each frequency point is monitored, and the reflected signal voltage is obtained through A / D sampling and a detector. Since the reflection curve of the accelerating tube is monotonically decreasing and then monotonically increasing (see...),... Figure 1 Therefore, the difference between the reflected voltage corresponding to each frequency point and the previous frequency point is calculated. By observing the change in the positive and negative values ​​after the difference, a smaller frequency range is determined for the next step of fine scanning.

[0043] When the difference is less than 0, the original scanning direction is maintained; when the difference is greater than or equal to 0, the frequency sweep is stopped, and the frequency point f(n) and frequency point f(n-2) at this time are used as the new frequency sweep range. Then, a small step value is set to perform fine sweep within this range. The step provides input to the accelerator tube and monitors the reflected signal of the accelerator tube. By comparing the magnitude of the reflected voltage at each frequency point, the frequency point corresponding to the minimum reflected voltage is determined as the resonant frequency point of the accelerator tube, i.e., the DDS output frequency.

[0044] (3) Use this resonant frequency point to provide input to the accelerator tube, and monitor the reflected signal voltage of the accelerator tube. When the reflected voltage is greater than the set threshold, it indicates that the accelerator tube has frequency drift. Repeat step (2) to scan and obtain a new resonant frequency point, so as to realize automatic frequency tracking of the accelerator tube.

[0045] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. An automatic frequency tracking method based on a frequency sweeping mode, characterized in that, include: Based on the accelerator tube design parameters, determine the frequency sweep range and perform the following frequency sweep operation: A coarse scan is performed starting from the starting frequency point of the frequency sweep range to obtain the reflected signal voltage of the accelerating tube at each frequency point; the difference between the reflected signal voltage corresponding to the current frequency point and the adjacent previous frequency point is calculated, and if the difference is negative, the coarse scan continues; Otherwise, stop the frequency sweep, update the frequency sweep range to the range between the current frequency point and the second frequency point before the current frequency point, start fine sweep from the starting frequency point of the frequency sweep range, obtain the accelerator tube reflected signal voltage at each frequency point, and select the frequency point corresponding to the minimum reflected voltage as the resonant frequency point. The obtained resonant frequency is used as the input frequency of the accelerating tube. The reflected voltage value of the accelerating tube is monitored. When the reflected voltage value exceeds the set threshold, the above frequency sweeping operation is repeated to obtain a new resonant frequency and use it as the input frequency of the accelerating tube. The difference between coarse scanning and fine scanning is that the scanning step value is different, with the scanning step value of coarse scanning being greater than that of fine scanning. The method for determining the sweep frequency range based on the accelerator tube design parameters is as follows: Calculate the maximum frequency difference: △f = 1.7e -5 f 0 △T In the formula, f 0 is the design center frequency. △T It is the difference between the temperature distribution when it reaches a steady state and the initial temperature; The frequency sweep range is f 0 ±△f ; The scanning step value for coarse scanning is determined based on the frequency range. The frequency range is divided equally, and 40 to 60 frequency points are selected. The scanning step value for fine scanning is obtained by simulating the energy and energy dissipation of the accelerated tube bundle after frequency offset in ASTRA.

2. The automatic frequency tracking method based on a frequency sweeping mode according to claim 1, characterized in that, The scanning starts from the starting frequency point of the frequency sweep range. The method to obtain the reflected signal voltage of the accelerator tube at each frequency point is as follows: obtain the reflected signal of the accelerator tube with the current frequency point as input, and obtain the reflected signal voltage through A / D sampling and detector.

3. The automatic frequency tracking method based on a frequency sweeping mode according to claim 1, characterized in that, When performing coarse or fine scanning at each frequency point, the tube should remain stationary for a certain period of time until it reaches a stable state before acquiring the reflected signal voltage of the tube at each frequency point.

4. An automatic frequency tracking system based on a frequency sweeping mode, characterized in that, Includes a coarse scan module, a fine scan module, and a reflected signal voltage monitoring module; The coarse scan module determines the frequency sweep range based on the accelerator tube design parameters, and starts scanning from the starting frequency point of the frequency sweep range. The current frequency point is input to the reflected signal voltage monitoring module to obtain the reflected signal voltage of the accelerator tube at each frequency point. The difference between the reflected signal voltage corresponding to the current frequency point and the adjacent previous frequency point is calculated. If the difference is negative, the scanning continues. Otherwise, stop frequency scanning, update the frequency scanning range to the range between the current frequency point and the second frequency point before the current frequency point, and send the updated frequency scanning range to the fine scanning module. The fine scanning module scans from the starting frequency point of the received frequency range, inputs the current frequency point to the reflected signal voltage monitoring module, and obtains the reflected signal voltage of the accelerator tube at each frequency point; selects the frequency point corresponding to the minimum reflected voltage as the resonant frequency point, and outputs the resonant frequency point as the input frequency of the accelerator tube; The difference between coarse scanning and fine scanning is that the scanning step value is different, with the scanning step value of coarse scanning being greater than that of fine scanning. The method for determining the sweep frequency range based on the accelerator tube design parameters is as follows: Calculate the maximum frequency difference: △f = 1.7e -5 f 0 △T In the formula, f 0 is the design center frequency. △T It is the difference between the temperature distribution when it reaches a steady state and the initial temperature; The frequency sweep range is f 0 ±△f ; The scanning step value for coarse scanning is determined based on the frequency range. The frequency range is divided equally, and 40 to 60 frequency points are selected. The scanning step value for fine scanning is obtained by simulating the energy and energy dissipation of the accelerated tube bundle after frequency offset in ASTRA.

5. The automatic frequency tracking system based on frequency sweep mode according to claim 4, characterized in that, The reflected signal voltage monitoring module receives frequency information, acquires the reflected signal of the accelerator tube with the current frequency as input, and obtains the reflected signal voltage through A / D sampling and detector.

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