Study On Several Key Techniques In Upgrading Of The Diagnostic Beam Line At Shanghai Synchrotron Radition Facility

Synchrotron radiation monitor,uses synchrotron light to measure the transverse and longitudinal cross-section of beam,is a key tool in beam instrumentation.This method has no blocking on the moving beam,can accurately and truly reflect the charge distribution in the bunch,and can directly obtain the time structure of the electron bunch.In order to meet the requirement for tuning and operation of the accelerator,synchrotron radiation monitors are widely used to monitor the beam of the storage ring.Shanghai Synchrotron Radiation Facility has built two diagnostic beam lines in the first phase of the project.One for the X-ray band and one for the visible light band.The visible light diagnostic beam line consists of five sub-systems: a streak camera used to measure the length of the bunch;a spatial interferometer method used to measure the horizontal and vertical beam size;the focused imaging system used to monitor the beam position and shape.An X-ray pinhole camera is used to measure beam size and emittance at X-ray diagnostic beam line.At present,those two beam lines runs well and plays a very important role in the operation of SSRF.However,those existing beam lines still need to be optimized.The performance of the X-ray pinhole camera is determined by the width of the point spread function.The existing point spread function calibration method needs to be completed at a specific machine study time;at the same time,the second phase of the light source construction will add a new X-ray diagnostic beam line,the new design needs to consider the advantages and disadvantages of both the existing beamlines and the new developed measurement methods;the deformation of the visible light extraction mirror has always been the common problem of this diagnostic beam line.Shanghai synchrontron radiation facility has established a calibration target to measure the distortion of the mirror surface,but this method intercepts the synchrontro light,and the measurement system cannot be used at same time;the spatial interferometer currently uses the commonly used fixed-slot spacing,and the accuracy is better in the measurement where the beam spot size does not change greatly.However,for different beam spot sizes,the resolution will change,especially in the small spot size measurement will introduce a larger error;in the context of increasing demand for high-speed beam size measurement,the current 2Hz data refresh rate of the spatial interferometer can not meet the demand.In this context,this article selects the research and discussion of key technologies in the upgrade and reconstruction of Shanghai synchrontro radiation facility as the main research content of the project.The resolution of the X-ray pinhole camera is determined by the point spread function width.The existing point spread function calibration method requires a specific machine study time.In the process of upgrading,an X-ray quasi-monochromator was installed.Combined with this monochromator,a novel calibration method was employed to calibrate the point spread function of pinhole camera.The distorition of the extraction mirror,due to the high engery X-ray,is an important issue at visible light diagnostic beam lines around the world.Actually,other optical devices in the optical path also introduce wavefront distortion.In order to overcome this problem,a wavefront sensor was installed at the end of the optical path to measure the w avefront distortion of the synchrotron light.Adptive optics was employed to correct the distortion.Another development direction of diagnostic beamline is high-speed measurement.At present,the Diamond light source and Cornell University have adopted coded aperture to realize high-speed measurement.Hefei light source and Shanghai light source adopt visible light direct focus imaging method in the visible light band,cooperate with photomultiplier tube and data acquisition card to perform high-speed measurement.However,the visible light focusing imaging has a larger point spread function due to diffraction,and is not suitable for accurate measurement.The measurement of the X-ray band requires higher cost.Therefore,this paper focuses on the high-speed measurement of the visible light band.The interferometer has high accuracy in the measurement of the transverse beam size,but its light transmission is small and the light intensity is weaker,which is not suitable for high-speed measurement.This article proposes the use of multi-slit imaging method to measure the transverse beam size.In general,this article studies some key technologies for the upgrade of diagnostic beam line at Shanghai synchrotron facility.The main contents include: Combined with the X-ray quasi-monochromator,a novel calibration method was employed to calibrate the point spread function of pinhole camera;Adptive optics was introduced to correct the wavefront distorition;Silt spacing rapid scanning system was installed at the sp atial interferometer;4)Design of a multi-slit imaging method was expected to achieve high-speed beam size measurement.