Synchrotron Radiation Wire Scanner Beam Position Monitor Design

Wire scanner is an important beam position monitor for synchrotron radiation beamlines in Shanghai Synchrotron Radiation Facility(SSRF),it is used to detect the position and size of beam.Now,it takes step sampling style of collecting one simple when motor turns one step,the spatial resolution is about 100?m.The signal to noise ratio is low and the signal is affected by glitch,it results to more errors of curve fitting.The beam signal is recognized and extracted by manual work which brings personal error to the results and wastes more time.To solve above problems,this paper's main contributions are as follows:(1)Design a new work style of collecting data continuously when motor keeps constant velocity and develop matched software and hardware system for wire scanner.The work style can increase the scanning speed,increase the number of samples at unit length,improve the resolution of monitor.By the tests on BL09B beamline in SSRF,the beam center position measurement resolution is 48.34?m,the size measurement resolution is 38.46?m,the data processing time is about 160ms.(2)Develop wire scanner signal processing methods,propose a method of detecting and extracting beam signal automatically based on Short Time Average/Long Time Average and Akaike Information Criterion.According to the characters of the signal,the methods on reducing noise is designed,which consist of finite impulse response low-pass filter,average filter and down sampling,median filter.The methods can eliminate glitch and increase data processing speed,reduce curve fitting errors.Signal amplitude variation characteristics are amplified by Allen function,a automatic beam detection method based on Short Time Average/Long Time Average and Akaike Information Criterion is proposed,the method detects and extracts beam signal automatically instead of manual work.Fitting parameter initial values are determined by energy gradient curve to reduce the time of curve fitting.(3)The relationships between measurement resolution and influencing factors are revealed and relevant reference for design and application of wire scanner monitor is provided.Calculations and analysis are done about the related design parameters of wires to provide reference for the selection and use of wires.By the tests,it is found that high sampling rate and low scan velocity help to improve beam center position measurement resolution,wire with smaller diameter can get better resolution,the resolutions under certain experimental conditions are demonstrated,which provides basis and convenience for design and application of wire scanner monitor.