A calibration method and device for linear accelerator beam position measurement

Abstract

The present invention provides a calibration method and device for linear accelerator beam position measurement, including a reference signal processing module, which obtains real-time temperature and humidity values, receives multi-channel beam and reference signals, adjusts the trigger signal reflecting the delay between the reference and beam signals, and outputs the recombined signal of each beam and reference signal; a beam signal processing electronics part, whose digital signal processing module includes a sampling circuit to obtain a digital signal by sampling; an amplitude calculation unit, which extracts the amplitude of the beam and reference signals; a position calculation unit, which obtains the reference signal optimal amplitude variation coefficient according to the real-time temperature and humidity values, uses the coefficient to correct the reference signal amplitude, and uses the correction result to calibrate the beam signal amplitude, and finally obtains the beam position. The calibration device of the present invention can effectively suppress the influence of channel inconsistency and temperature drift and long drift on position measurement, and improve the position resolution and long-term operation stability of beam measurement.

Description

Technical Field

[0001] The invention relates to the technical field of particle accelerator beam diagnosis, and in particular to a calibration method and equipment for linear accelerator beam position measurement. Background Art

[0002] In particle accelerators, the digital beam position measurement detector (BPM) is a key device for beam position measurement. It mainly includes three main parts: BPM probe, BPM signal processing electronics (including RF signal processing module and digital processing module) and connecting cable, with the purpose of achieving high-precision beam position measurement.

[0003] At present, the beam of the linear accelerator is a single-pass type. In addition to the factors of the beam itself, the inconsistency and slow drift between channels caused by temperature and humidity changes in the electronics part are key factors restricting the BPM measurement accuracy. The inconsistency specifically includes the inconsistency of the impedance of the 4-channel cable from the BPM probe to the front-end RF conditioning circuit and the gain inconsistency of the 4 channels of the front-end RF conditioning circuit. Existing solutions, such as adjusting the device parameters of the 4-channel front-end RF conditioning circuit, are difficult and labor-intensive; adding a cross-link switch at the input end of the RF signal conditioning circuit will reduce the isolation of the electronics channel; using a high-precision constant temperature control cabinet to solve the temperature drift problem requires high temperature control accuracy for the constant temperature cabinet and greatly increases the construction and maintenance costs.

[0004] However, gain inconsistency and slow drift between channels are bound to exist, and the gain of analog devices used for RF signal processing will drift to varying degrees with temperature and time, causing the final measured beam position accuracy to decrease and drift. Summary of the invention

[0005] The purpose of the present invention is to provide a calibration method and equipment for linear accelerator beam position measurement, so as to compensate for the influence of cable disturbance, temperature and humidity changes, and inconsistency of analog devices themselves on the 4-channel beam signal amplitude measurement, and effectively improve the position resolution and long-term operation stability of beam measurement.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a calibration device for linear accelerator beam position measurement, comprising a reference signal processing module and a beam signal processing electronics part; the reference signal processing module is configured to obtain real-time temperature and humidity values ​​during measurement, receive a multi-channel beam signal and a reference signal of a beam position probe, adjust a trigger signal reflecting the delay between the reference signal and the beam signal through a delay module of the reference signal processing module, and control each analog switch of the reference signal processing module through the trigger signal to output a recombined signal of each beam signal and the reference signal; the beam signal processing electronics part comprises a digital signal processing module, The digital signal processing module includes a sampling circuit, an amplitude calculation unit and a position calculation unit; the sampling circuit is configured to obtain a digital signal after ADC sampling; the amplitude calculation unit is configured to extract the amplitude of the beam signal and the amplitude of the reference signal from the digital signal; the position calculation unit is configured to obtain the optimal amplitude variation coefficient of the reference signal of each channel according to the real-time temperature and humidity values ​​during measurement, correct the amplitude of the reference signal using the obtained optimal amplitude variation coefficient, calibrate the amplitude of the beam signal using the corrected amplitude of the reference signal of each channel, and calculate the beam position using the amplitude of the calibrated beam signal through a difference ratio and formula.

[0007] The reference signal processing module includes a temperature and humidity measurement module, a power divider for receiving a reference signal, a delay module for receiving a trigger signal, and an analog switch that controls the input of a single-channel beam signal or a single-channel reference signal by an output signal of the delay module. The analog switch is used to output a recombined signal of each beam signal and the reference signal after power division.

[0008] The beam signal processing electronics part also includes a radio frequency signal processing module, which includes multiple signal processing channels with exactly the same configuration. Each signal processing channel includes a cascaded bandpass filter, a low-noise amplifier, a low-pass filter and an attenuator to achieve amplitude control and filtering of the recombined signal before digital signal processing.

[0009] In another aspect, the present invention provides a linear accelerator beam position measurement calibration method, comprising:

[0010] S1: using a reference signal processing module to obtain a multi-channel beam signal and a reference signal from a beam position probe;

[0011] S2: Using the reference signal processing module, the reference signal is divided into multiple reference signals after power division, the temperature and humidity are changed, and different temperatures and humidities are measured and recorded, and the amplitudes of the multiple reference signals under different temperatures and humidities are measured, and a lookup table of amplitude variation coefficients of the reference signals under different temperatures and humidities is established;

[0012] S3: using the delay module of the reference signal processing module to adjust the trigger signal reflecting the delay between the reference signal and the beam signal, and controlling each analog switch of the reference signal processing module through the trigger signal to output a recombined signal of each beam signal and the reference signal;

[0013] S4: using the RF signal processing module to realize amplitude control and filtering functions of the recombined signal, and then using the sampling circuit of the digital signal processing module to perform ADC sampling to obtain a digital signal, and using the amplitude calculation unit of the digital signal processing module to extract the amplitude of the beam signal and the amplitude of the reference signal from the digital signal;

[0014] S5: using the position calculation unit of the digital signal processing module, combining the real-time temperature and humidity values ​​during measurement and the amplitude variation coefficient lookup table of the reference signal, to obtain the optimal amplitude variation coefficient of the reference signal of each channel;

[0015] S6: Using the position calculation unit, the amplitude of the reference signal of each channel is corrected according to the obtained optimal amplitude variation coefficient, and then the amplitude of the beam signal is calibrated using the corrected reference signal amplitude of each channel, and the beam position is calculated using the calibrated beam signal amplitude through the difference ratio and formula.

[0016] In the step S1, the beam position probe is an orthogonal symmetrical strip beam position probe, and the reference signal is a continuous signal from a high-precision frequency synthesizer system.

[0017] The reference signal processing module also includes a temperature and humidity measurement module and a power divider; in step S2, the reference signal is divided into multiple reference signals through the power divider, the temperature and humidity are artificially changed and the temperature and humidity measurement module is used to measure and record different temperatures and humidities, and the amplitudes of the multiple reference signals under different temperatures and humidities are measured and recorded, thereby establishing a lookup table of amplitude change coefficients of reference signals under different temperatures and humidities as a backup.

[0018] In step S3, the delay module is configured to make the delay between the reference signal and the beam signal passing through the same analog switch be in the order of tens of microseconds; each analog switch is controlled by a trigger signal to switch between the beam signal and the reference signal to obtain a recombined signal composed of the beam signal and the reference signal.

[0019] In step S4, after the amplitude control and filtering functions of the recombined signal are realized by the radio frequency signal processing module, the ADC sampling is performed by the sampling circuit to obtain a multi-channel digital signal; wherein the digital signal processing module receives a trigger signal from the accelerator timing system and a clock signal provided by the frequency synthesis system, the clock signal is used to determine the sampling frequency of the sampling circuit, the trigger signal is used to determine the starting position of the valid data point in the ADC sampling, and the limited number of data points after the trigger signal is intercepted are packaged and entered into the subsequent calculation process;

[0020] The amplitude of the beam signal and the amplitude of the reference signal are extracted from the finite number of packaged data points, specifically including: windowing the finite number of packaged data points to respectively intercept the effective data points of the beam signal and the reference signal, squaring the amplitudes of the effective data points intercepted by the windowing, summing them, and then calculating the square root to obtain the amplitude of the beam signal and the amplitude of the reference signal.

[0021] In step S5, the least squares method is used to fit the data of the amplitude variation coefficient lookup table of the reference signal obtained in step S2 to obtain a least squares fitting model, and then the real-time temperature and humidity values ​​during measurement are substituted into the least squares fitting model to obtain the optimal amplitude variation coefficient of the reference signal of each channel.

[0022] The number of channels is 4;

[0023] In step S6, the calibrated beam signal amplitude of each channel , , , , and the corrected reference signal amplitude of each channel , , , Satisfies the following formula:

[0024] , , , ,

[0025] ， ， ， ,

[0026] , , , ,

[0027] in, , , , is the amplitude of the beam signal of the four channels, , , , is the amplitude of the reference signal of the 4 channels, , , , is the optimal amplitude variation coefficient of the four channels, , , , is the transfer coefficient of the four channels;

[0028] In step S6, the beam position calculated by the difference ratio and formula includes the horizontal position X of the beam signal and the vertical position Y of the beam signal, which are respectively:

[0029] ,

[0030] ,

[0031] Where X is the horizontal position of the beam signal, Y is the vertical position of the beam signal, , are the sensitivity coefficients in the horizontal and vertical directions, respectively; , This is the offset caused by the incomplete coincidence between the electrical center and the mechanical center of the beam position probe.

[0032] In a calibration method for linear accelerator beam position measurement of the present invention, the reference signal is first used to calibrate the beam signal in real time to solve the ADC data amplitude inconsistency and the slow drift problem of long-term operation of the equipment caused by the attenuation inconsistency of the BPM cable and the difference in the 4-channel circuit of the front-end RF conditioning circuit; in addition, when the ADC samples the 4-channel analog signal, the time division multiplexing is realized through the analog switch, which not only increases the utilization rate of the ADC sampling channel, but also unifies the influencing factors of the reference signal and beam signal amplitude measurement. Furthermore, for the inconsistency of the 4-channel reference signals caused by temperature and humidity, the reference signal amplitude variation coefficient lookup table is established by temperature and humidity monitoring, and the least squares fitting evaluation method is used for correction, which ensures the accurate consistency of the 4-channel reference signals and further improves the accuracy of subsequent calibration.

[0033] In summary, the calibration method and equipment for linear accelerator beam position measurement of the present invention compensate for the influence of cable disturbance, temperature and humidity changes, and inconsistency of the analog device itself on the 4-channel beam signal amplitude measurement, and realize automatic diagnosis of the online operation status of BPM, effectively improving the position resolution and long-term operation stability of beam measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the principle of a calibration device for linear accelerator beam position measurement according to an embodiment of the present invention;

[0035] Figure 2 It is a schematic diagram of the overall data processing flow of a linear accelerator beam position measurement calibration method according to an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of the structure of a BPM digital signal processing module according to an embodiment of the present invention;

[0037] Figure 4 is a schematic diagram of the structure of a reference signal processing module according to an embodiment of the present invention;

[0038] Figure 5 FIG. 4 is an ideal waveform diagram of a reconstructed signal after ADC sampling according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0040] The present invention provides a linear accelerator beam position measurement calibration device, which is used for linear accelerator beam position measurement and eliminates the influence of cable disturbance, temperature and humidity changes, inconsistency of analog devices themselves, and slow drift on 4-channel beam signal amplitude measurement, and can realize automatic diagnosis of BPM online operation status.

[0041] like Figure 1 As shown, the calibration device for linear accelerator beam position measurement includes a reference signal processing module 10 and a beam signal processing electronics part 20 .

[0042] like Figure 4As shown, the reference signal processing module 10 includes a temperature and humidity measurement module 11, a power divider 12 for receiving a reference signal, a delay module 13 for receiving a trigger signal, and an analog switch 14 connected to a single-channel beam signal, an output end of the power divider 12, and an output end of the delay module 13, and the analog switch 14 is used to output a recombined signal of each beam signal and the reference signal after power division. The reference signal processing module 10 is configured to obtain real-time temperature and humidity values ​​during measurement, receive a multi-channel beam signal and a reference signal coupled from a beam position probe 100 (i.e., a BPM probe), adjust a trigger signal reflecting the delay between the reference signal and the beam signal through a delay module, and control each analog switch of the reference signal processing module through a trigger signal to output a recombined signal of each beam signal and the reference signal.

[0043] In this embodiment, the beam position probe is preferably an orthogonal symmetrical strip beam position probe.

[0044] The beam signal processing electronics part 20 includes a radio frequency signal processing module 21 and a digital signal processing module 22 .

[0045] The RF signal processing module 21 includes multiple signal processing channels with exactly the same configuration, each of which is composed of a cascaded bandpass filter, a low-noise amplifier, a low-pass filter and an attenuator to achieve amplitude control and filtering of the reconstructed signal before digital signal processing.

[0046] like Figure 3 As shown, the digital signal processing module 22 includes a sampling circuit 221, an amplitude calculation unit 222 and a position calculation unit 223. The sampling circuit 221 is configured to obtain a digital signal after ADC sampling; the amplitude calculation unit 222 is configured to extract the amplitude of the beam signal and the amplitude of the reference signal from the digital signal; the position calculation unit 223 is configured to obtain the optimal amplitude variation coefficient of the reference signal of each channel according to the real-time temperature and humidity values ​​during measurement, and to correct the amplitude of the reference signal using the obtained optimal amplitude variation coefficient, and to calibrate the amplitude of the beam signal using the corrected amplitude of the reference signal of each channel, and to calculate the beam position using the amplitude of the calibrated beam signal through the difference ratio and formula.

[0047] like Figure 2 As shown, the calibration method for linear accelerator beam position measurement of the present invention mainly includes the following steps:

[0048] Step S1: using the reference signal processing module 10 to obtain a multi-channel beam signal and a reference signal from a beam position probe;

[0049] In this embodiment, the beam position probe uses an orthogonal symmetrical strip beam position probe, so the orthogonal symmetrical strip beam position probe is used to couple out 4-channel beam signals, which are pulse signals. The reference signal uses a continuous signal from a high-precision frequency synthesis system. The frequency and amplitude of the reference signal must be within the working range required by the filter, amplifier, and attenuator in the RF signal processing module.

[0050] In other embodiments, if the beam position probe is replaced with another type of beam position probe, the formula for calculating the beam position will also be changed accordingly.

[0051] Step S2: using the reference signal processing module 10, the reference signal is split into multiple reference signals through the power divider 12, the temperature and humidity are changed and the temperature and humidity measurement module 11 is used to measure and record different temperatures and humidities, and the amplitudes of the multiple reference signals under different temperatures and humidities are measured, and a lookup table of amplitude variation coefficients of the reference signals under different temperatures and humidities is established;

[0052] In the present invention, since the reference signal is provided by the frequency synthesis system and is transmitted to the reference signal processing module at the location of the beam probe through a cable, it is divided into four signals by the power divider 12. However, due to the influence of temperature and humidity and the performance limitation of the power divider 12 itself, the four reference signals themselves will inevitably have inconsistencies.

[0053] The temperature and humidity measurement module 11 is placed in the chassis of the reference signal processing module 10, and can measure in real time and display the measurement data on the beam signal processing electronics part 20 at the back end.

[0054] In this embodiment, the number of reference signals after power division is 4, denoted as , , , , if the reference signal is , then the amplitude variation coefficient of the reference signal under different temperature and humidity is:

[0055] , , , ,

[0056] in, , , , is the amplitude variation coefficient of the reference signal under different temperature and humidity conditions; , , , are the amplitude of the reference signal after power division, is the amplitude of the reference signal.

[0057] Therefore, the present invention artificially changes the temperature T and humidity H of the experimental environment, artificially selects n temperature values ​​and n humidity value points for measurement and calculation, and measures the amplitude of the reference signal after multi-path power division under different temperatures and humidities, thereby establishing the amplitude variation coefficient ( , , , ) lookup table.

[0058] Step S3: using the delay module 13 to adjust the trigger signal reflecting the delay between the reference signal and the beam signal, and controlling each analog switch 14 through the trigger signal to output a recombined signal of each beam signal and the reference signal;

[0059] The analog switch is actually a channel switch controlled by an electrical signal. Each analog switch 14 is controlled by a trigger signal to switch between the beam signal and the reference signal to obtain a recombined signal composed of the beam signal and the reference signal.

[0060] In this embodiment, the delay module 13 is configured to make the delay between the reference signal and the beam signal of the same analog switch be in the order of tens of microseconds.

[0061] In the present invention, the trigger signal from the accelerator timing system is provided to the analog switch through the delay module, so as to adjust the delay between the reference signal and the beam signal by adjusting the trigger signal through the delay module 13. Since the delay is in the order of tens of microseconds, the beam signal and the reference signal of the same path can be collected by the ADC and then subsequently processed (that is, the collected data are packaged together and sent to the back-end computing program) without generating signal aliasing.

[0062] Among them, the trigger signal is equivalent to a prompt signal, which changes with the frequency of the electron gun emitting the beam, and is used to mark the arrival time of the beam signal, so as to facilitate the capture of the effective beam signal in the FPGA. The present invention requires that the beam signal and the reference signal collected by the ADC can be packaged together and sent to the beam signal processing electronics part 20, and the beam signal processing electronics part 20 can identify and process the beam signal and the reference signal respectively. Therefore, the present invention drives the channel switching of the analog switch after adding an appropriate delay to the trigger signal through the reference signal processing module 10, so as to obtain two signals in the same data processing.

[0063] Step S4: using the RF signal processing module 21 to realize the amplitude control and filtering function of the recombined signal, and then using the sampling circuit 221 of the digital signal processing module 22 to perform ADC sampling to obtain a digital signal, and using the amplitude calculation unit 222 of the digital signal processing module 22 to extract the amplitude of the beam signal and the amplitude of the reference signal from the digital signal;

[0064] In step S4, before obtaining a digital signal by ADC sampling using the sampling circuit 221 of the digital signal processing module 22, it may also include: processing the recombined signal using the RF signal processing module 21 to achieve amplitude control and filtering of the recombined signal before digital signal processing.

[0065] In this embodiment, the RF signal processing module 21 includes multiple signal processing channels with exactly the same configuration, each of which is composed of a cascaded bandpass filter, a low-noise amplifier, a low-pass filter and an attenuator to achieve amplitude control and filtering functions of the signal.

[0066] In step S4, when the sampling circuit 221 is used for ADC sampling, the sampling circuit 221 of the digital signal processing module 22 performs ADC sampling according to the clock signal provided by the frequency synthesis system, so as to obtain a multi-channel digital signal. The clock signal is used as the sampling clock of the sampling circuit 221 to determine the sampling frequency of the sampling circuit 221. The trigger signal from the accelerator timing system is used to determine the starting position of the valid data point in the ADC sampling, and the limited number of data points after the trigger signal is intercepted are packaged and entered into the subsequent calculation process.

[0067] The calculation process refers to the process in which the FPGA program extracts the amplitude of the beam signal and the amplitude of the reference signal from the finite number of packaged data points after the finite number of packaged data points enter the cache program, specifically including: windowing the finite number of packaged data points to extract the effective data points of the beam signal and the reference signal, squaring the amplitudes of the effective data points intercepted by the windowing, summing them, and then taking the square root to obtain the amplitudes of the beam signal and the reference signal. The specific number of points intercepted by the windowing depends on the ADC model used by the sampling circuit 221.

[0068] In one example, the frequency of the reference signal is 500 MHz, the RF signal processing module 21 selects a bandpass filter with a center frequency of 500 MHz and a bandwidth of 10 MHz, the ADC sampling frequency of the sampling circuit 221 is 105.76 MHz, and the ideal waveform of the digital signal after undersampling is as follows: Figure 5 shown.

[0069] In the step S4, the amplitude of the beam signal and the amplitude of the reference signal are extracted from the digital signal, specifically including: respectively opening a window to intercept valid data points of the beam signal and the reference signal, squaring the amplitudes of the valid data points intercepted by the window, summing them, and then calculating the square root to obtain the amplitude of the beam signal and the amplitude of the reference signal.

[0070] Because the pulse width and amplitude of the beam signal and the reference signal are basically fixed, the amplitude threshold and the total number of valid data points can be set in advance based on advance experiments and empirical data, and then the starting time and width of the window can be determined. Specifically, the sampling point where the signal amplitude exceeds the amplitude threshold is the first point, that is, the starting time of the window. The total number of points is the window width. Generally, the valid data points range from 30 to 80. The optimal time window can be appropriately determined based on the ADC sampling situation and the size and length of the measured signal. The window width is generally around several hundred ns.

[0071] In the present invention, since the number of channels is 4, the 4 channels are recorded as A, B, C, and D in sequence. According to the trigger signal, the effective data points of the beam signal and the reference signal are respectively intercepted by opening a window, and the amplitudes of the data points intercepted by the window are squared, summed, and then the square root is calculated to obtain the amplitude of the beam signal and the amplitude of the reference signal. Among them, the amplitudes of the beam signals of the 4 channels are recorded as , , , , the measured amplitudes of the reference signals of the four channels are recorded as , , , .

[0072] Step S5: using the position calculation unit 223 of the digital signal processing module 22, combining the real-time temperature and humidity values ​​during measurement and the amplitude variation coefficient lookup table of the reference signal, to obtain the optimal amplitude variation coefficient of the reference signal of each channel;

[0073] In this embodiment, the least square method is used to fit the data of the amplitude variation coefficient lookup table of the reference signal obtained in step S2 to obtain a least square method fitting model, and then the real-time temperature and humidity values ​​during measurement are substituted into the least square method fitting model to obtain the optimal amplitude variation coefficient of the reference signal of each channel. Thus, the discrete values ​​of the amplitude variation coefficients of the multi-channel reference signals under different temperatures and humidities set artificially are obtained through the amplitude variation coefficient lookup table of the reference signal in step S2, and the temperature and humidity values ​​that can be actually measured are continuous values. In order to facilitate the acquisition of the optimal amplitude variation coefficients of each channel under any temperature and humidity, the least square method is used to fit the optimal result value.

[0074] Taking channel A as an example, the temperature and humidity and the corresponding reference signal amplitude variation coefficient can be obtained by the lookup table. Therefore, the observation data matrix of the reference signal amplitude variation coefficient of channel A includes the temperature and humidity observation matrix and the reference signal amplitude variation coefficient observation matrix. The temperature and humidity observation matrix of channel A is The observation matrix of the amplitude variation coefficient of the reference signal of channel A They are:

[0075] , ,

[0076] in, is the temperature of the first data point, is the humidity of the first data point, is the amplitude variation coefficient of the reference signal of channel A at the first data point, and so on.

[0077] Assume that the temperature influence coefficient , humidity influence coefficient , random interference is a fixed constant that does not change with temperature and humidity, then the coefficient vector X to be determined is expressed as:

[0078] .

[0079] The least squares fitting model is constructed using sample points. The least squares fitting model is expressed in a matrix as follows: , the target loss function It can be expressed as a matrix:

[0080] ,

[0081] According to the principle of least squares method, the sum of squared errors needs to be minimized, that is, the above objective loss function is obtained The extreme point of , take the derivative and make it equal to 0:

[0082] ,

[0083] Solved ,

[0084] Therefore, using the above formula Obtain the analytical solution of the coefficient vector X that minimizes the sum of squared errors, and construct the least squares fitting model based on the coefficient vector X , that is, construct the optimal Value plane, so that all (T, H) values ​​can find corresponding Then, the real-time temperature and humidity values ​​during measurement are brought into the least squares fitting model to solve the optimal amplitude variation coefficient of multiple channels.

[0085] In this embodiment, since the number of channels is 4, the 4 channels are recorded as A, B, C, and D in sequence. Therefore, the optimal amplitude variation coefficient of the 4 channels is obtained as follows: , , , .

[0086] Step S6: Using the position calculation unit 223, the measurement amplitude of the reference signal of each channel is corrected according to the obtained optimal amplitude variation coefficient, and then the measurement amplitude of the beam signal is calibrated using the corrected reference signal amplitude of each channel, and the beam position is calculated using the calibrated beam signal amplitude through the difference ratio and formula.

[0087] In the present invention, the beam signal that is not affected by the transmission cable disturbance and the inconsistency of the gain of each channel of the RF front end is an unknown quantity, that is, the calibrated beam signal amplitude of each channel that needs to be obtained in the present invention is recorded as , , , .

[0088] The reference signal after power division without transmission and RF signal processing is an unknown quantity, that is, the corrected reference signal amplitude of each channel. , , , .

[0089] The transfer functions of the multiple channels are , , , The transfer function actually represents the ratio of the measured value of the reference signal to the starting value after a series of operations such as channel transmission, RF signal processing, and digital signal processing. Cable attenuation, environmental factors, analog device inconsistency, sampling effects, circuit gain coefficients, noise, etc. will all affect the final measurement.

[0090] The real-time temperature during measurement is T, the real-time humidity is H, and the optimal amplitude variation coefficients obtained in step S5 are , , , , then the beam signal amplitude of each channel after calibration is , , , , and the corrected reference signal amplitude of each channel , , , Satisfies the following formula:

[0091] , , , ,

[0092] , , , ,

[0093] , , , ,

[0094] in, , , , is the measured amplitude of the beam signal of the four channels, , , , Measured amplitude of the reference signal for the 4 channels.

[0095] The beam position calculated by the difference ratio and formula includes the horizontal position X of the beam signal and the vertical position Y of the beam signal, which are:

[0096] ,

[0097] ,

[0098] ,

[0099] ,

[0100] Where X is the horizontal position of the beam signal, Y is the vertical position of the beam signal, , are the sensitivity coefficients in the horizontal and vertical directions, respectively, which are calculated through offline calibration experimental measurements; , This is the offset caused by the incomplete coincidence between the electrical center and the mechanical center of the beam position probe, and is measured during the installation of the BPM probe.

[0101] Since there is an offset in the formula caused by the inconsistency between the electrical center and the mechanical center of the beam position probe, the beam position (X, Y) calculated by the difference ratio and formula is the physical position of the beam, not just a purely electrical quantity.

[0102] In a calibration method for linear accelerator beam position measurement of the present invention, the reference signal is first used to calibrate the beam signal in real time to solve the ADC data amplitude inconsistency and the slow drift problem of long-term operation of the equipment caused by the attenuation inconsistency of the BPM cable and the difference in the 4-channel circuit of the front-end RF conditioning circuit; in addition, when the ADC samples the 4-channel analog signal, the time division multiplexing is realized through the analog switch, which not only increases the utilization rate of the ADC sampling channel, but also unifies the influencing factors of the reference signal and beam signal amplitude measurement. Furthermore, for the inconsistency of the 4-channel reference signals caused by temperature and humidity, the reference signal amplitude variation coefficient lookup table is established by temperature and humidity monitoring, and the least squares fitting evaluation method is used for correction, which ensures the accurate consistency of the 4-channel reference signals and further improves the accuracy of subsequent calibration.

[0103] In summary, the calibration method and equipment for linear accelerator beam position measurement of the present invention compensate for the influence of cable disturbance, temperature and humidity changes, and inconsistency of the analog device itself on the 4-channel beam signal amplitude measurement, and realize automatic diagnosis of the online operation status of BPM, effectively improving the position resolution and long-term operation stability of beam measurement.

[0104] The above specific embodiments further illustrate the purpose, technical solutions and equipment of the present invention. It should be understood that the above description is only a specific embodiment and is not limited to the present invention. Any modification, equivalent replacement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A calibration device for linear accelerator beam position measurement, characterized in that: It includes reference signal processing module and beam signal processing electronics; The reference signal processing module is configured to obtain real-time temperature and humidity values ​​during measurement, receive a multi-channel beam signal and a reference signal from a beam position probe, adjust a trigger signal reflecting the delay between the reference signal and the beam signal through a delay module of the reference signal processing module, and control each analog switch of the reference signal processing module through the trigger signal to output a recombined signal of each beam signal and the reference signal; The beam signal processing electronics part includes a digital signal processing module, which includes a sampling circuit, an amplitude calculation unit and a position calculation unit; the sampling circuit is configured to obtain a digital signal after ADC sampling; the amplitude calculation unit is configured to extract the amplitude of the beam signal and the amplitude of the reference signal from the digital signal; the position calculation unit is configured to obtain the optimal amplitude variation coefficient of the reference signal of each channel according to the real-time temperature and humidity values ​​during measurement, correct the amplitude of the reference signal using the obtained optimal amplitude variation coefficient, calibrate the beam signal amplitude using the corrected reference signal amplitude, and calculate the beam position using the calibrated beam signal amplitude through a difference ratio and formula.

2. The calibration device for linear accelerator beam position measurement according to claim 1, characterized in that: The reference signal processing module includes a temperature and humidity measurement module, a power divider for receiving a reference signal, a delay module for receiving a trigger signal, and an analog switch that controls the input of a single-channel beam signal or a single-channel reference signal by an output signal of the delay module. The analog switch is used to output a recombined signal of each beam signal and the reference signal after power division.

3. The calibration device for linear accelerator beam position measurement according to claim 1, characterized in that: The beam signal processing electronics part also includes a radio frequency signal processing module, which includes multiple signal processing channels with exactly the same configuration. Each signal processing channel includes a cascaded bandpass filter, a low-noise amplifier, a low-pass filter and an attenuator to achieve amplitude control and filtering of the recombined signal before digital signal processing.

4. A calibration method for linear accelerator beam position measurement, characterized in that: include: Step S1: using a reference signal processing module to obtain a multi-channel beam signal and a reference signal from a beam position probe; Step S2: using the reference signal processing module to split the reference signal into multiple reference signals, artificially changing the temperature and humidity, and measuring the amplitudes of the multiple reference signals under different temperatures and humidities, and establishing a lookup table of amplitude variation coefficients of the reference signals under different temperatures and humidities; Step S3: using the delay module of the reference signal processing module to adjust the trigger signal reflecting the delay between the reference signal and the beam signal, and controlling each analog switch of the reference signal processing module through the trigger signal to output a recombined signal of each beam signal and the reference signal; Step S4: using the RF signal processing module to realize amplitude control and filtering functions of the recombined signal, and then using the sampling circuit of the digital signal processing module to perform ADC sampling to obtain a digital signal, and using the amplitude calculation unit of the digital signal processing module to extract the amplitude of the beam signal and the amplitude of the reference signal from the digital signal; Step S5: using the position calculation unit of the digital signal processing module, combining the real-time temperature and humidity values ​​during measurement and the amplitude variation coefficient lookup table of the reference signal, to obtain the optimal amplitude variation coefficient of the reference signal of each channel; Step S6: using the position calculation unit, the amplitude of the reference signal of each channel is corrected according to the obtained optimal amplitude variation coefficient, and then the amplitude of the beam signal is calibrated using the corrected reference signal amplitude of each channel, and the beam position is calculated using the calibrated beam signal amplitude through the difference ratio and formula.

5. The linear accelerator beam position measurement calibration method according to claim 4, characterized in that: In the step S1, the beam position probe is an orthogonal symmetrical strip beam position probe, and the reference signal is a continuous signal from a high-precision frequency synthesizer system.

6. The linear accelerator beam position measurement calibration method according to claim 4, characterized in that: The reference signal processing module also includes a temperature and humidity measurement module and a power divider; in step S2, the reference signal is divided into multiple reference signals through the power divider, the temperature and humidity are artificially changed and the temperature and humidity measurement module is used to measure and record different temperatures and humidities, and the amplitudes of the multiple reference signals under different temperatures and humidities are measured and recorded, thereby establishing a lookup table of amplitude change coefficients of reference signals under different temperatures and humidities as a backup.

7. The linear accelerator beam position measurement calibration method according to claim 4, characterized in that: In step S3, the delay module is configured to make the delay between the reference signal and the beam signal passing through the same analog switch be in the order of tens of microseconds; each analog switch is controlled by a trigger signal to switch between the beam signal and the reference signal to obtain a recombined signal composed of the beam signal and the reference signal.

8. The linear accelerator beam position measurement calibration method according to claim 4, characterized in that: In step S4, the digital signal processing module receives a trigger signal from the accelerator timing system and a clock signal provided by the frequency synthesis system. The clock signal is used to determine the sampling frequency of the sampling circuit, and the trigger signal is used to determine the starting position of the valid data point in the ADC sampling. The limited number of data points after the trigger signal is intercepted and packaged into the subsequent calculation process; The amplitude of the beam signal and the amplitude of the reference signal are extracted from the finite number of packaged data points, specifically including: windowing the finite number of packaged data points to respectively intercept the effective data points of the beam signal and the reference signal, squaring the amplitudes of the effective data points intercepted by the windowing, summing them, and then calculating the square root to obtain the amplitude of the beam signal and the amplitude of the reference signal.

9. The linear accelerator beam position measurement calibration method according to claim 4, characterized in that: In step S5, the least squares method is used to fit the data of the amplitude variation coefficient lookup table of the reference signal obtained in step S2 to obtain a least squares fitting model, and then the real-time temperature and humidity values ​​during measurement are substituted into the least squares fitting model to obtain the optimal amplitude variation coefficient of the reference signal of each channel.

10. The linear accelerator beam position measurement calibration method according to claim 4, characterized in that: The number of channels is 4; In step S6, the calibrated beam signal amplitude of each channel , , , , and the corrected reference signal amplitude of each channel , , , Satisfies the following formula: , , , ， ， ， ， ， , , , ， in, , , , is the amplitude of the beam signal of the four channels, , , , is the amplitude of the reference signal of the 4 channels, , , , is the optimal amplitude variation coefficient of the four channels, , , , is the transfer coefficient of the four channels, is the amplitude of the reference signal; In step S6, the beam position calculated by the difference ratio and formula includes the horizontal position X of the beam signal and the vertical position Y of the beam signal, which are respectively: ， ， Where X is the horizontal position of the beam signal, Y is the vertical position of the beam signal, , are the sensitivity coefficients in the horizontal and vertical directions, respectively; , This is the offset caused by the incomplete coincidence between the electrical center and the mechanical center of the beam position probe.

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