Research Of Feedback Control Technology Based On FPGA For Synchrotron Beam Stability

As the third generation light source, Shanghai Synchrotron Radiation Facility(SSRF) plays an extremely important role in research of basic science and hightechnology in China. Following the Phase-I seven beamlines in2009, the constructionof Dreamline and Protein facilities with five beamlines were finished in2014. Withthe Phase-II project including16beamlines have been approved, as well as users’investment construction of the5beamlines, to2020, there are nearly40beamlines bebuilt and put into operation in SSRF.Due to the interference factors, such as thermal vibration, mechanical vibration,and mechanical rotation of the optical elements cannot be excluded, the beamintensity and position at samples in the end stations would change and drift with time,which may affect the experimental results. Therefore, the usage of the feedbackcontrol technology to stabilize the beam need to be focused on and solved.After studying the feedback control technology used in the synchrotron radiationbeamlines in the world, this paper finished the whole system design and hasimplemented the PID controller based on FPGA. The main work includes four aspects.1) The scheme design of digital feedback control system was completed, whichcontains PSDs (Position Sensitive Detector) as detecting components, PIEZOs asactuators, and one FPGA as the controller.2) The Verilog and schematic dia gram areadopted to finish the PID control algorithm with the top-down method.3) In thelaboratory building a platform to test the response to the time domain step signal ofthe system, and also test the performance of the feedback system by applying onelaser to imitate the jitter disturbance of the synchrotron beam. Finally, on-line testingthe feedback control system in infrared beamline at SSRF. Separately measuring thetime-domain waveform and the corresponding amplitude spectrum of the synchrotronbeam in the horizontal and vertical orientation. The results show that the stability ofinfrared beam position is much improved by adopting the feedback control system.The effective operating band is450Hz, as well as the steady state error is about several μm.