A pinhole camera for imaging X-ray synchrotron radiation from a dipole magnet is now in operation at the Shanghai Synchrotron Radiation Facility （SSRF） storage ring.The electron beam size is derived by unfolding the radiation image and the point spread function （PSF） with deconvolution techniques.The performance of the pinhole is determined by the accuracy of the PSF measurement.This article will focus on a beam-based calibration scheme to measure the PSF system by varying the beam images with different quadrupole settings and fitting them with the corresponding theoretical beam sizes.Applying this method at SSRF,the PSF value of the pinhole is revised from 37 to 44μm.The deviation in beam size between the theoretical value and the measured value isminimized to 4% after calibration.This optimization allows us to observe the horizontal disturbance due to injection down to as small as 0.5μm.
Beam current dependence resulted from nonlinearity and asymmetry of the four channels of digital BPM(Beam Position Monitor) processor deteriorates the BPM performance.A systematic solution based on signal source calibration tactics has been carried out to rectify this defect.It is optimized for implementation in FPGA.Mathematical illustrations of the calibration method,hardware and software design and implementation are presented.A signal source circuit using frequency synthesis technique is designed as calibration standard.Data acquisition system using JAVA web technology and Ethernet is introduced.Integrated FPGA implementation code architecture is presented,and experimental test results show that the method implemented in FPGA is feasible.Compared to other methods,our approach can rectify the nonlinearity and asymmetry simultaneously.The whole solution is integrated into the DBPM processor and can be executed online.
As a third generation light source, Shanghai Synchrotron Radiation Facility (SSRF) has up to 140 beam position monitors (BPM) installed to monitor the beam dynamics on its storage ring. Once the operation mode is chosen, the betatron functions are determined. Since the sinusoidal betatron oscillation is the dominant component of the transverse motion, these BPMs can be used to measure the motion to get the betatron functions. Three methods are compared to calculate the phase advance among the BPMs in this paper, aiming to find one or more feasible ways to check the beam optics in SSRF. Some experiments have also been made to verify the practicality of the phase information.
In this paper,in order to achieve the output signal processing of cavity beam position monitor(CBPM),we develop a digital intermediate frequency receiver architecture based signal processing system,which consists of radio frequency(RF) front end and high speed data acquisition board.The beam position resolution in the CBPM signal processing system is superior to 1μm.Two signal processing algorithms,fast Fourier transform(FFT) and digital down converter(DDC),are evaluated offline using MATLAB platform,and both can be used to achieve,the CW input signal,position resolutions of 0.31μm and 0.10μm at -16 dBm.The DDC algorithm for its good compatibility is downloaded into the FPGA to realize online measurement,reaching the position resolution of 0.49μm due to truncation error.The whole system works well and the performance meets design target.
WANG BaopengLENG YongbinYU LuyangZHOU WeiminYUAN RenxianCHEN Zhichu
Cavity beam position monitor(BPM) is widely used in a precise electron beam position measurement. Based on high performance oscilloscope-embedded EPICS input/output controller,we developed an on-line cavity BPM signal processing system for fast data acquisition solution when designing a cavity BPM.Also,methods for extracting the position information from cavity pickup signals and calibration algorithm are included in this solution.
