Research On Mono-light Position Stability Measurement Based On Fluorescent Screen Image

Synchrotron radiation is a very versatile light source that can be used in a variety area for fundamental frontier research,synchrotron radiation facilities play a major role in promoting the development of various disciplines.The performance of Shanghai Synchrotron Radiation Facility(SSRF)ranks at the international advanced level,some important achievements have been made in the frontier basic research and high-tech research,such as life sciences,condensed matter physics,materials science,chemistry,energy and environmental sciences.Beam position monitor(BPM)is one of the most important devices of the beamline in SSRF,it is used to measure the beam position of the X-ray and its spot size,and help experiment user to get thus messages,even to realize feedback control for stability X-ray spot.There are four kinds of BPM at SSRF: blade BPM,fluorescent screen BPM,quadrant BPM and wire-scanning BPM.And they are all different with their measurement principles,working environment,measurement accuracy etc.you can select the appropriate detector to do according to your different needs.Because of its convenient and intuitive,fluorescent screen BPM is widely employed in SSRF.However,when the fluorescent screen detector is in operation,then its target of CVD or YAG will completely inset in the X-ray path,so that the most of X-ray cannot continue to go downstream,mean it cannot achieve real-time position measurement of X-rays beam.But this paper improves on the use of traditional fluorescent screen BPM,measuring the position change of X-ray beam by using only image of the spot edge portion from the fluorescent screen BPM.And this use method does not affect the normal test of X-ray at the experimental station,but also achieve real-time measurement of the beam position.This type of detector is used in SSRF for the first time,and is estimated to achieve measurement resolution on the order of micrometers.It mainly depends on the optical magnification of the image collection system and the pixel size of the CCD.The paper beginning is brief introduction with the structure of the fluorescent screen BPM,then according to their working principle and to bring about a new use method of the fluorescent screen BPM by controlling the fluorescent target which is a YAG slice,to place in the edge portion of the mono X-ray spot.Thus,fluorescent screen BPM will not affect the X-ray to go downstream,can also generate fluorescent images to measure position change of the mono X-ray beam in real-time.In the thesis,some images of fluorescent screen BPM from BL17 U and BL03 U in SSRF is analyzed and processed,and the relevant toolbox function of MATLAB software for processing spot image is simply introduced,According to the characteristics of the spot image,a suitable image processing method is proposed,which includes image filter,Laplacian enhancement,image segmentation and so on,so that it can accurately calculate the position change of the spot in the image by means of the change of the average of the 10 height near most high point of the spot edge.The position change of the traditional fluorescent screen BPM can only reach the order of millimeters,and the position change of the spot can reach the micron level by using the method of image processing.The accuracy of the image processing method is verified by many simulation tests of different light spots,and the feasibility of real-time measurement of the beam position of the fluorescent screen BPM is further proved.Experience has been accumulated for high-precision position measurement and real-time position feedback of fluorescent screen BPM.