CN111650634B - Beam position detector mechanical center calibration method based on longitudinal phase measurement - Google Patents

Abstract

The invention relates to a method for calibrating the mechanical center of a beam position detector based on a longitudinal phase relationship. The electrical signal of each electrode; secondly, the electrical signal of each electrode is cut according to the interval time T to obtain several single bundle signals, and the corresponding function of the electrode signal is spliced; then the longitudinal phase of the bundle corresponding to each electrode signal is measured according to the corresponding function of the electrode signal; Finally, it is judged whether the longitudinal phases of the bundles corresponding to the electrode signals are equal, and the calibration of the mechanical center is completed. The invention can accurately demarcate the mechanical center of the beam position detector under the condition that the beam position detector has been installed on the accelerator and the accelerator is running normally, and the operation state of the beam current is not affected. In addition, the present invention can make full use of the mechanical center to further measure the differential loss of the intermediate element.

Description

A Beam Position Detector Mechanical Center Calibration Method Based on Longitudinal Phase Measurement

technical field

The invention relates to particle accelerator physical beam current diagnosis technology and instrument state analysis, and more particularly to a beam position detector mechanical center calibration method based on longitudinal phase relationship.

Background technique

Four-electrode beam position detectors (BPM) are widely used in the beam position detection of storage ring accelerators. As shown in Figure 1, four electrodes are symmetrically distributed on the vacuum wall. The difference ratio sum operation yields the beam position.

The mechanical center of the four-electrode beam position detector refers to the midpoint of two symmetrical electrodes, that is, the mechanical center in a certain direction is the same distance from the center of the two electrodes in that direction. The confirmation of the mechanical center has a great influence on the performance parameters of the beam position detector. Before the beam position detector is installed in the accelerator, we can calibrate the mechanical center by some relatively simple methods. However, when the beam position detector has been installed on the accelerator and the accelerator is operating normally, it is very difficult to measure the mechanical center. In less elaborate experiments, the electrical center of the beam position detector is often regarded as the mechanical center, Find the electrical center by comparing the signal amplitudes of different electrodes. In a more sophisticated experiment, it is necessary to change the parameters of the front quaternary magnet, and find the mechanical center through the coupling between the quaternary iron parameters and the signal of the beam position detector electrode. The disadvantage of this method is that the magnet parameters need to be changed, which will affect the operating state of the beam.

In addition, the loss of electronic components is unavoidable. Due to the existence of the loss, the calibration of the mechanical center is not accurate. Therefore, it is also a very important task to accurately measure the loss of the system.

SUMMARY OF THE INVENTION

In order to solve the problem in the prior art that the accelerator cannot accurately calibrate the mechanical center of the beam position detector during operation, the present invention provides a method for calibrating the mechanical center of the beam position detector based on the longitudinal phase relationship.

The present invention provides a method for calibrating the mechanical center of a beam position detector based on a longitudinal phase relationship, comprising:

Step S1, connecting a plurality of cables to different electrode probes of the beam position detector respectively, connecting the other end of the cables to the measuring end of the oscilloscope, and simultaneously recording the electrical signals of each electrode;

Step S2, cutting the electrical signals of the electrodes according to the interval time T to obtain several single-cluster signals, and splicing the single-cluster signals to obtain the corresponding function of the electrode signal of the beam position detector;

Step S3, measuring the longitudinal phase of the bundle corresponding to each electrode signal according to the corresponding function of the electrode signal;

Step S4, determine whether the longitudinal phases of the bundles corresponding to the electrode signals are equal, if they are equal, it means that the bundles pass through the mechanical center of the detector; if not, change the position of the pre-magnet, and repeat the above steps until the measured The longitudinal phase of the bundle corresponding to each electrode signal is equal to complete the calibration of the mechanical center.

The delay time of each cable used in the step S1 is the same.

The interval time T in the step S2 is calculated according to T=1/f, where T is the interval time of the current adjacent bundles, and f is the accelerator radio frequency that is corrected in real time until the phase of the bundles has no obvious linear drift from turn to turn. frequency.

The step S2 also includes:

Step S21 , performing dislocation splicing on the single-cluster signal obtained by cutting, and obtaining a corresponding function of the electrode signal with the sampling rate higher than the sampling point number of the original sampling rate of the oscilloscope.

In the step S3, the longitudinal phase of the bundle corresponding to each electrode signal is measured by the zero-crossing method.

The zero-crossing method includes:

Step S311, find out the zero-crossing point of the corresponding function of the electrode signal by fitting;

In step S312, the relative longitudinal phase is obtained according to the horizontal axis position at the zero-crossing point.

In the step S3, a correlation look-up table method is used to measure the longitudinal phase of the bundle corresponding to each electrode signal.

The correlation look-up table method includes:

Step S321, performing sparse sampling on the corresponding function of the electrode signal in the step S2, and establishing a look-up table corresponding to the longitudinal phase of different bundles;

In step S322, the cross-correlation method is used to compare the electrical signal of the current bundle sampled by the oscilloscope with the look-up table in step S321, and when the correlation is the largest, it is the longitudinal phase of the current bundle.

The method for calibrating the mechanical center of the beam position detector according to the present invention further includes: step S5, measuring the difference between the signal amplitudes between the electrodes.

The sampling rate of the oscilloscope is higher than 10 GHz.

The sampling rate of the oscilloscope was 20 GHz.

The invention uses the matching of the corresponding functions of each electrode of the beam position detector to find the longitudinal phase of the beam cluster respectively, and calibrates the mechanical center of the beam position detector by comparing the longitudinal phase difference obtained by each electrode. The present invention can accurately demarcate the mechanical center of the beam position detector under the condition that the beam position detector has been installed on the accelerator and the accelerator is running normally, and the operation state of the beam current is not affected. In addition, the present invention can make full use of the mechanical center to further measure the differential loss of the intermediate element.

Description of drawings

FIG. 1 is a schematic diagram of an electrode-type beam position detector.

FIG. 2 is a flow chart of a method for calibrating a machine center according to the present invention.

FIG. 3 is a waveform diagram of the corresponding function of the electrode of the beam position detector measured according to the calibration method of the present invention.

FIG. 4 is a graph of the phase measurement of the bunch according to the present invention.

FIG. 5 is a schematic diagram of sorting the correlation degree of the table lookup results according to the correlation function method of the present invention.

FIG. 6 is a schematic diagram of the mechanical center calibration method of the present invention.

Detailed ways

Below in conjunction with the accompanying drawings, preferred embodiments of the present invention are given and described in detail.

The method for calibrating the mechanical center of the beam position detector based on the longitudinal phase provided by the present invention, as shown in FIG. 2 , includes the following steps:

In step S1, four cables with the same delay time are respectively connected to four different electrode probes of the beam position detector, and the other end is connected to the measurement end of the oscilloscope, and the electrical signals of the four electrodes are recorded simultaneously. Among them, the purpose of the same delay time of each cable is to eliminate the source of the phase difference and ensure the same propagation time of the signal to the receiving end. In addition, considering the short period of the cluster, an oscilloscope with a sampling rate higher than 10 GHz is required to collect enough sampling points when a cluster passes by. In this embodiment, the sampling rate of the oscilloscope is 20 GHz.

Step S2, cutting the electrical signals of the electrodes, the cutting length is T, and the cutting is performed once every time T to ensure that the cutting time length just covers the electrical signals generated by the bundles passing through the beam position detector, thereby obtaining several single beams. The cluster signal is obtained, and the corresponding function of the electrode signal of the beam position detector is spliced out, and the function reflects the shape characteristics of the excited electrical signal when the beam cluster passes through the electrode.

Due to the problems of temperature drift and geological offset of the accelerator, the interval time between the clusters is constantly changing, which means that the RF frequency drifts with time, which will affect the time scale of cutting, so that the RF phase is biased. Therefore, the interval time T needs to be corrected in real time. The interval time T is calculated as T=1/f, where T is the interval time between the current adjacent bunches, and f is the radio frequency of the accelerator. The principle of real-time correction of the interval time T is as follows: the interval time T is corrected by using the characteristic that the turn-by-turn phase of the same bundle in a certain period of time will oscillate in a range. When the turn-by-turn phase of the bundle has no obvious linear drift, The interval time at this time is taken as the corrected interval time T of adjacent bundles.

Wherein, the method for splicing the corresponding function of the electrode signal of the beam position detector is specifically: Step S21, performing dislocation splicing on the obtained single-beam signal to obtain the number of sampling points whose sampling rate is higher than the original sampling rate of the oscilloscope, that is, the number of sampling points is obtained denser function.

In step S3, according to the corresponding function of the electrode signal, the longitudinal phase of the bundle corresponding to each electrode signal is measured by the zero-crossing method or the correlation look-up table method.

Among them, the zero-crossing method refers to finding the zero point of the electrical signal collected by the oscilloscope of each circle, and obtaining the relative longitudinal phase of the beam cluster through the zero point position, including:

Step S311, find out the zero-crossing point of the corresponding function of the electrode signal by fitting;

In step S312, the relative longitudinal phase is obtained according to the position of the horizontal axis at the zero-crossing point in step S311.

The correlation look-up table method refers to the cross-correlation matching between the electrical signal collected by the oscilloscope and the corresponding spliced function, including:

Step S321, perform sparse sampling on the corresponding function of the electrode signal in step S2, and establish a look-up table corresponding to the longitudinal phase of different bundles;

In step S322, the cross-correlation method is used to compare the electrical signal of the current bundle sampled by the oscilloscope with the look-up table in step S321, and when the correlation is the largest, it is the longitudinal phase of the current bundle.

Step S4, judge whether the longitudinal phase of the bundle corresponding to each electrode signal is equal, if it is equal, it means that the bundle passes through the mechanical center of the detector; if not, change the position of the pre-magnet, and repeat the above steps until the measured The longitudinal phase of the bundle corresponding to the electrode signal is equal, and the calibration of the mechanical center is completed.

When the bundle is in the center of the machine, the signal amplitudes measured by each electrode should be the same. If they are different, it means that there is a difference in the intermediate components such as cables. Therefore, the present invention further includes: step S5, measuring the difference between the signal amplitudes between the electrodes, and the measured signal amplitude difference is the difference loss value of the element.

The principle of the present invention will be described in detail below.

When the beam group passes through the beam position detector, an induced voltage will be excited on each electrode. By measuring the induced voltage of the electrode, the corresponding induction curve can be obtained, and the corresponding function of the electrode can be obtained by drawing the induction curve. ,As shown in Figure 3.

Using each electrode to compare the signal waveforms generated when the same bundle passes through, the longitudinal phase of the bundle in the eyes of different electrodes can be obtained. In this embodiment, the cross-correlation method is used. Cross-correlation method is an existing mathematical analysis method, which is widely used in statistics, measurement and other fields. However, in the field of accelerators, technicians in the prior art only use this method to process signal data, and have never used this method to analyze beam peak amplitude information. According to this method, a look-up table is established by using the corresponding function, and the longitudinal phase is obtained by matching the look-up table. The results of the best matched group are shown in Figure 4. It can be seen that this group has a high degree of matching with the measured oscilloscope signal. In addition, the correlation ranking of the entire lookup table is shown in FIG. 5 .

The longitudinal phase seen by different electrodes is different. This phenomenon originates from the eccentricity of the bundle, that is, the balance point of the lateral position of the bundle is not on the mechanical center of the beam position detector. Since the propagation speed of the electromagnetic field is the speed of light, each electrode needs a delay of time t to see the signal of the cluster. t is equal to the distance from the cluster to the electrode divided by the speed of light. Then, if the balance point of the transverse position of the bundle is not on the mechanical center, the longitudinal phase measured by each electrode will be different. With this theory, the mechanical center of the detector can be calibrated based on the longitudinal phase.

Figure 6 shows two symmetrical electrodes passing through a bundle that does not pass through the mechanical center. Among them, the bundle flies from left to right at a speed v, the distance between the bundle track and the A electrode is d1, and the distance from the C electrode is d2. When d1 is equal to d2, this position is the mechanical center, which is the four-pointed star in the figure. When the bundle deviates from the mechanical center, the electric field signal of the bundle needs a propagation time of t1 to be received by the A electrode (t1=d1/c), and received by the C electrode requires a propagation time of t2 (t2=d2/c), where c is the speed of light. Then if d1 is not equal to d2, that is, the beam does not pass through the mechanical center, the time at which the two electrodes receive the signal will be different, that is, the longitudinal phase of the beam cluster is different. On the contrary, it means that the bunch passes through the mechanical center, thus completing the calibration of the mechanical center position.

Mechanical center means that the bundle is equidistant from each electrode. Then if there is no signal loss. The signal amplitudes measured by each electrode should be the same, that is, amp1=amp2, see Figure 6. If there is an amplitude difference, it comes from the loss of electronic components during transmission. When the bundle passes through the mechanical center, the difference between the signal amplitudes measured by each electrode is the relative loss.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Various changes can be made to the above-mentioned embodiments of the present invention. That is, all simple and equivalent changes and modifications made according to the claims and descriptions of the present invention fall into the protection scope of the claims of the present invention. What is not described in detail in the present invention is conventional technical content.

Claims (10)

1. A beam position detector mechanical center calibration method based on longitudinal phase relation is characterized by comprising the following steps:

step S1, connecting a plurality of cables to different electrode probes of a beam position detector respectively, connecting the other ends of the cables to a measuring end of an oscilloscope, and recording electric signals of all electrodes simultaneously;

step S2, cutting the electric signals of each electrode according to the interval time T to obtain a plurality of single beam group signals, and splicing the single beam group signals to obtain a corresponding function of the electrode signals of the beam position detector; the interval time T is calculated according to T = 1/f, wherein T is the interval time of the current adjacent beam group, and f is the radio frequency of the accelerator when the real-time correction is carried out until the loop-by-loop phase of the beam group does not have obvious linear drift;

step S3, measuring the beam group longitudinal phase corresponding to each electrode signal according to the corresponding function of the electrode signal;

step S4, judging whether the longitudinal phases of the beam groups corresponding to the electrode signals are equal, if so, indicating that the beam groups pass through the mechanical center of the detector; if not, changing the position of the front magnet, and repeating the steps until the longitudinal phases of the beam groups corresponding to the measured electrode signals are equal, thereby completing the calibration of the mechanical center.

2. The method for calibrating the mechanical center of the beam position detector according to claim 1, wherein the delay time of each cable used in the step S1 is the same.

3. The method for calibrating the mechanical center of the beam position detector according to claim 1, wherein the step S2 further comprises:

and step S21, carrying out dislocation splicing on the single bunch of signals obtained by cutting to obtain a corresponding function of the electrode signals of the number of sampling points with the sampling rate higher than the original sampling rate of the oscilloscope.

4. The method for calibrating the mechanical center of the beam position detector according to claim 1, wherein in step S3, the longitudinal phase of the beam corresponding to each electrode signal is measured by using a zero-crossing method.

5. The method for calibrating the mechanical center of the beam position detector according to claim 4, wherein the zero-crossing point method comprises:

step S311, finding out a zero crossing point of a corresponding function of the electrode signal through fitting;

and step S312, obtaining the relative longitudinal phase according to the horizontal axis position at the zero crossing point.

6. The method for calibrating the mechanical center of a beam position detector according to claim 1, wherein in step S3, the beam longitudinal phase corresponding to each electrode signal is measured by using a correlation lookup table.

7. The method of claim 6, wherein the correlation lookup table comprises:

step S321, performing sparse sampling on the corresponding functions of the electrode signals in the step S2, and establishing a lookup table corresponding to longitudinal phases of different clusters;

step S322, comparing the electric signal of the current beam group sampled by the oscilloscope with the lookup table in the step S321 by adopting a cross-correlation method, and determining the longitudinal phase of the current beam group when the correlation degree is maximum.

8. The method for calibrating the mechanical center of the beam position detector according to claim 1, further comprising: in step S5, the difference in signal amplitude between the electrodes is measured.

9. The method for calibrating the mechanical center of the beam position detector according to claim 1, wherein the sampling rate of the oscilloscope is higher than 10 GHz.

10. The method for calibrating the mechanical center of the beam position detector according to claim 8, wherein the sampling rate of the oscilloscope is 20 GHz.

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