CN111650634B - Beam position detector mechanical center calibration method based on longitudinal phase measurement - Google Patents
Beam position detector mechanical center calibration method based on longitudinal phase measurement Download PDFInfo
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- CN111650634B CN111650634B CN202010442664.9A CN202010442664A CN111650634B CN 111650634 B CN111650634 B CN 111650634B CN 202010442664 A CN202010442664 A CN 202010442664A CN 111650634 B CN111650634 B CN 111650634B
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- G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
Abstract
The invention relates to a method for calibrating a mechanical center of a beam position detector based on a longitudinal phase relationship, which comprises the following steps: firstly, connecting cables to different electrode probes of a beam position detector, connecting the cables to a measuring end of an oscilloscope, and simultaneously recording electric signals of all electrodes; secondly, cutting the electric signals of each electrode according to the interval time T to obtain a plurality of single cluster signals, and splicing corresponding functions of the electrode signals; then measuring the longitudinal phase of the beam group corresponding to each electrode signal according to the corresponding function of the electrode signal; and finally, judging whether the longitudinal phases of the beam groups corresponding to the electrode signals are equal or not, and finishing the calibration of the mechanical center. The invention can accurately calibrate the mechanical center of the beam position detector under the condition that the beam position detector is installed on the accelerator and the accelerator normally operates, and does not influence the operation state of the beam. In addition, the invention can further measure the differential loss of the intermediate element by fully utilizing the mechanical center.
Description
Technical Field
The invention relates to a particle accelerator physical beam diagnosis technology and instrument state analysis, in particular to a beam position detector mechanical center calibration method based on a longitudinal phase relation.
Background
A four-electrode beam position detector (BPM) is widely used for detecting the beam position of a storage ring accelerator, and as shown in fig. 1, four electrodes are symmetrically distributed on a vacuum wall, and the beam position is usually obtained by performing a difference ratio and operation using voltage values of the four electrodes.
The mechanical center of the four-electrode beam position detector is the midpoint of two symmetrical electrodes, that is, the mechanical center in a certain direction is equidistant from the centers of the two electrodes in the direction. The confirmation of the mechanical center has great influence on the performance parameters of the beam position detector. Before the beam position detector is not mounted on the accelerator, we can calibrate the mechanical center by some relatively simple method. However, when the beam position detector is already installed on the accelerator and the accelerator is operating normally, it is very difficult to measure the mechanical center, and in a less detailed experiment, the electrical center of the beam position detector is often regarded as the mechanical center, and the electrical center is searched by comparing the signal amplitudes of different electrodes. In a more precise experiment, the parameters of the front four-stage magnet need to be changed, and the mechanical center is found through the coupling between the four-stage iron parameters and the electrode signals of the beam position detector. The disadvantage of this method is that the magnet parameters need to be changed, which affects the beam current behavior.
In addition, the difference loss of the electronic components is inevitable, and the mechanical center calibration is inaccurate due to the existence of the difference loss, so that the difference loss of the accurate measurement system is also very important work.
Disclosure of Invention
The invention provides a beam position detector mechanical center calibration method based on a longitudinal phase relation, and aims to solve the problem that the mechanical center of a beam position detector cannot be accurately calibrated when a accelerator operates in the prior art.
The invention provides a method for calibrating a mechanical center of a beam position detector based on a longitudinal phase relationship, which comprises 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;
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.
The cable delay times used in step S1 are the same.
The interval time T in step S2 is calculated as T ═ 1/f, where T is the interval time of the current adjacent beam group, and f is the accelerator rf frequency corrected in real time until there is no significant linear drift in the beam group by group phase.
The step S2 further includes:
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.
In step S3, the beam longitudinal phase corresponding to each electrode signal is measured by the zero-crossing method.
The zero-crossing method comprises the following steps:
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 position of the horizontal axis at the zero crossing point.
In step S3, the beam longitudinal phase corresponding to each electrode signal is measured by using a correlation lookup table.
The relevancy table look-up method comprises the following steps:
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.
The mechanical center calibration method of the beam position detector further comprises the following steps: in step S5, the difference in signal amplitude between the electrodes is measured.
The sampling rate of the oscilloscope is higher than 10 GHz.
The sampling rate of the oscilloscope is 20 GHz.
The invention respectively searches the longitudinal phase of the beam group by utilizing the matching of the corresponding functions of each electrode of the beam position detector, and calibrates the mechanical center of the beam position detector by comparing the difference of the longitudinal phases obtained by each electrode. The invention can accurately calibrate the mechanical center of the beam position detector under the condition that the beam position detector is installed on the accelerator and the accelerator normally operates, and does not influence the operation state of the beam. In addition, the invention can further measure the differential loss of the intermediate element by fully utilizing the mechanical center.
Drawings
Fig. 1 is a schematic diagram of an electrode type beam position detector.
Fig. 2 is a flow chart of a method of machine center calibration according to the present invention.
Fig. 3 is a waveform diagram of the corresponding function of the electrode of the beam position detector measured by the calibration method of the invention.
Fig. 4 is a diagram of beam group phase measurement according to the present invention.
FIG. 5 is a diagram illustrating the correlation sorting of the table lookup result according to the correlation function method of the present invention.
FIG. 6 is a schematic diagram of a method of machine center calibration of the present invention.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The invention provides a method for calibrating a mechanical center of a beam position detector based on a longitudinal phase, which comprises the following steps as shown in figure 2:
and step S1, connecting four cables with the same delay time to four different electrode probes of the beam position detector respectively, connecting the other ends of the cables to the measuring end of the oscilloscope, and recording electric signals of the four electrodes simultaneously. The purpose of the same delay time of each cable is to eliminate the source of phase difference and ensure that the propagation time of signals to a receiving end is the same. In addition, considering the short cycle of the beam bunch, an oscilloscope with a sampling rate higher than 10GHz is required to acquire enough sampling points when one beam bunch passes by. In this embodiment, the sampling rate of the oscilloscope is 20 GHz.
And step S2, cutting the electric signals of each electrode, wherein the cutting length is T, and the cutting is performed once every T time, so that the cutting time length is ensured to just cover the electric signals generated when the beam passes through the beam position detector, thereby obtaining a plurality of single beam signals, and splicing corresponding functions of the electrode signals of the beam position detector, wherein the functions reflect the shape characteristics of the electric signals excited when the beam passes through the electrodes.
Due to the problems of temperature drift, geological shift and the like of the accelerator, the interval time between the clusters is constantly changed, which means that the radio frequency of the accelerator drifts along with the time, the time scale of cutting is influenced, and the radio frequency phase has bias, so that the interval time T needs to be corrected in real time. 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 accelerator radio frequency. The principle of real-time correction of the interval time T is as follows: and when the loop-by-loop phase of the beam group has no obvious linear drift, taking the interval time at the moment as the corrected interval time T of the adjacent beam groups.
The method for splicing the corresponding functions of the electrode signals of the beam position detector specifically comprises the following steps: and step S21, carrying out dislocation splicing on the obtained single bunch of signals to obtain the number of sampling points with the sampling rate higher than the original sampling rate of the oscilloscope, namely obtaining a function with a more dense sampling point number.
And step S3, according to the corresponding function of the electrode signals, measuring the longitudinal phase of the beam group corresponding to each electrode signal by using a zero crossing point method or a correlation degree table look-up method.
The zero crossing point method is to find the zero point of an electric signal acquired by each circle of oscilloscope and obtain the relative beam longitudinal phase through the zero point position, and specifically comprises the following steps:
step S311, finding out a zero crossing point of a corresponding function of the electrode signal through 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 degree table look-up method refers to cross-correlation degree matching between the electric signals acquired by the oscilloscope each time and the spliced corresponding functions, and specifically comprises the following steps:
step S321, sparse sampling is carried out on the corresponding functions of the electrode signals in the step S2, and a lookup table corresponding to the longitudinal phases of different clusters is established;
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, wherein when the correlation degree is maximum, the electric signal is the longitudinal phase of the current beam group.
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.
When the beam is at the mechanical center, the signal amplitudes measured by the electrodes should be the same, and if they are different, they represent a difference loss in the intermediate elements such as cables. Therefore, the present invention also includes: and step S5, measuring the difference of signal amplitudes between the electrodes, wherein the difference of the measured signal amplitudes is the differential loss value of the element.
The principles of the present invention are explained in detail below.
When the beam group passes through the beam position detector, induced voltages are excited on the electrodes, a corresponding induced curve can be obtained by measuring the induced voltages of the electrodes, and the induced curve is drawn to obtain a corresponding function of the electrodes, as shown in fig. 3.
The longitudinal phases of the bunch in different electrode eyes can be obtained by comparing signal waveforms generated when the same bunch passes through by each electrode. In the present embodiment, a cross correlation method is employed. The cross-correlation method is an existing mathematical analysis method and is widely applied to the fields of statistics, measurement and the like. However, in the field of accelerators, technicians in the prior art only use the method to process signal data, and never use the method as a measurement means to analyze beam peak amplitude information. According to the method, a lookup table is established by using a corresponding function, and the longitudinal phase is obtained by matching the lookup table. The results for the best matched set are shown in fig. 4, and it can be seen that the set matches the measured oscilloscope signal to a greater degree. In addition, the relevancy ranking of the entire lookup table is shown in FIG. 5.
The difference of the longitudinal phases seen by different electrodes is caused by the eccentricity of the beam cluster, i.e. the balance point of the beam cluster at the transverse position is not on the mechanical center of the beam position detector. Since the propagation speed of the electromagnetic field is the speed of light, the signal of the beam bunch seen by each electrode needs a time t delay. t is equal to the beam cluster to electrode distance divided by the speed of light. Then the measured longitudinal phase of each electrode will be different if the transverse position of the beam cluster is not at the mechanical center. By this theory, the mechanical center of the detector can be calibrated based on the longitudinal phase.
Fig. 6 shows the case of two symmetrical electrodes when passing through a beam cluster that does not pass through the center of the machine. Wherein the bunch flies at a speed v from left to right, the distance between the bunch orbit and the A electrode is d1, and the distance between the bunch orbit and the C electrode is d 2. When d1 equals d2, this position is the mechanical center, the four-pointed star in the figure. When the beam bunch deviates from the mechanical center, the electric field signal of the beam bunch is received by the A electrode for the propagation time of t1 (t1 ═ d1/C), and is received by the C electrode for the propagation time of t2 (t2 ═ d2/C), wherein C is the speed of light. Then if d1 is not equal to d2, i.e. the beam does not pass through the mechanical center, the two electrodes will receive signals at different times, i.e. the longitudinal phase of the beam bunch will be different. Otherwise, the beam group passes through the mechanical center, and the calibration of the mechanical center position is completed.
Mechanical center means that the cluster is equidistant from the electrodes. Then if there is no loss of signal. The signal amplitude measured by each electrode should be the same, i.e. amp1 ═ amp2, see fig. 6. If there is a difference in amplitude, the difference in losses from the electronic components during transmission. The difference in signal amplitude measured by each electrode as the beam bunch passes through the center of the machine is the relative difference loss.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.
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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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1066930A (en) * | 1991-02-08 | 1992-12-09 | 德国汤姆森-勃朗特有限公司 | Optical scanner |
| EP0862169A1 (en) * | 1996-04-22 | 1998-09-02 | Fujitsu Limited | Optical storage apparatus |
| CN107478144A (en) * | 2017-07-27 | 2017-12-15 | 中国科学院高能物理研究所 | A kind of silk thread positioner and method based on quadrupole electromagnet and vibration line technology |
| CN109782331A (en) * | 2018-12-24 | 2019-05-21 | 西北核技术研究所 | A kind of beam position detector electrfic centre caliberating device and scaling method |
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| US7580331B2 (en) * | 2005-10-25 | 2009-08-25 | Lsi Corporation | Center error mechanical center adjustment |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1066930A (en) * | 1991-02-08 | 1992-12-09 | 德国汤姆森-勃朗特有限公司 | Optical scanner |
| EP0862169A1 (en) * | 1996-04-22 | 1998-09-02 | Fujitsu Limited | Optical storage apparatus |
| CN107478144A (en) * | 2017-07-27 | 2017-12-15 | 中国科学院高能物理研究所 | A kind of silk thread positioner and method based on quadrupole electromagnet and vibration line technology |
| CN109782331A (en) * | 2018-12-24 | 2019-05-21 | 西北核技术研究所 | A kind of beam position detector electrfic centre caliberating device and scaling method |
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Effective date of registration: 20221212 Address after: 201800 Shanghai city Jiading District Road No. 2019 Patentee after: SHANGHAI INSTITUTE OF APPLIED PHYSICS, CHINESE ACADEMY OF SCIENCES Patentee after: Shanghai Alliance Investment Ltd. Address before: 201800 Shanghai city Jiading District Road No. 2019 Patentee before: SHANGHAI INSTITUTE OF APPLIED PHYSICS, CHINESE ACADEMY OF SCIENCES |