| In recent years, with the development of high-speed high-resolution analog-digital conversion (ADC) and the real-time digital signal processing technique, fully digital beam position measurement system (Digital Beam Position Monitor, DBPM) becomes a favorable choice in the beam diagnostic domain. Compared "with the traditional method based on fully analog signal processing with inevitable noise, non-linearity and mismatch errors, the fully digital method greatly simplifies the system architecture. Besides, this method is also remarkable for its flexibility. The beam signal processing algorithms can be modified easily according to different application requirements.Based on digital In-phase and Quadrature-phase Demodulation method, a digital beam position measurement system is designed for the Turn-by-Turn (TBT) beam measurement in the Storage Ring of Shanghai Synchrotron Radiation Facility (SSRF). After the evaluation and tests of the prototype system, four final instruments are produced and tested2.The first chapter includes the review of the synchrotron radiation accelerator and the introduction of the SSRF, and the purposes of beam diagnostics and basic parameters.The second chapter describes three kinds of front-end detection electrodes and main methods used in beam position measurement. This chapter also discusses the beam measurement development from full analog to digital processing technique, and investigates different position measurement systems in real application.In the third chapter, the input signal characteristics and the system architecture is introduced. The beam signals from the pickups of the BPM in the Storage Ring of SSRF are499.654MHz narrow pulses with a pulse width around100ps, which is further modulated by a693.964kHz square wave with a duty ratio of500:220. When this system is applied in machine research, the input signal amplitude could vary over tens of dB. As for the system structure, it consists of the front end module and a digital processing motherboard. The front end module includes RF manipulation and the ADC circuits, and different sampling clock generation circuits are studied. The implementation of the digital motherboard is also discussed.The fourth chapter first introduces the real time digital processing algorithms in this DBPM system. The signals from the RF manipulation circuits are directly under-sampled by4ADCs, and the high frequency signal is converted to a digital Intermediate Frequency (IF) signal. With the Digital Down Conversion (DDC) algorithms in the FPGA, the IF signal is further down converted to a very low frequency, and then the beam position and intensity can be calculated. All the digital algorithms are integrated in one single FPGA. This system also includes a Single Board Computer (SBC), which is responsible for the communication with the remote system through the100M Ethernet interface; actually, the1000M Ethernet interface and Serial port are also included. This system can handle the processing and transferring seven different data types, including SADC, STBT, BADC, BTBT, PM, FA and BFA.The fifth chapter is about the system tests, which includes the test result of the prototype system both in the laboratory and with the real beam signal in SSRF. Then the system test results of the4final instruments are presented.The sixth Chapter introduces the research on the Bunch-by-Bunch measurement based on the waveform stretching method. Based on the simulation conducted in the Matlab platform, the influence of the different parameters of the Band Pass Filter (BPF) is studied.Since the design of the first prototype system, different versions have been produced with modifications and improvements according to the test results in the laboratory and in SSRF. After finishing the system performance evaluation, four final instruments are produced and tested. The test results indicate that a TBT resolution better than7um is achieved in the input dynamic range from-40dBm to10dBm, which is beyond the application requirement in S SRF. |
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