R&D Of Bunch-by-bunch Charge And Tune Measurement Technology Using Digital Beam Signal Processor

Shanghai Synchrotron Radiation Facility(SSRF)electronic storage ring has a circumference of 432 m for storing 3.5 GeV electron beams and emitting high-quality synchrotron radiation.There are 720 RF buckets in the full ring at 500 MHz frequency.The beam diagnostic system is an important tool for the synchrotron radiation and commission process.With the advancement of fast electronics technology,beam diagnostics has been developed from the initial multi-turn average measurement to the turn-by-turn measurement.Nowadays,with the high-performance digital beam signal processor,bunch-by-bunch diagnostic technology has become one of the most important development directions.The second phase upgrade of SSRF will introduce many Insert Devices,which makes the coupling instability caused by the beam wake field more serious.It is urgent to use the bunch-by-bunch diagnostic tool to achieve the study of bunch instability,machine impedance and wake field.On the other hand,the bunchby-bunch diagnostic system can also provide a reference tool for accelerator physicists to study the physical processes of beam dynamics.Bunch-by-bunch diagnostic techniques are increasingly demanding and increasingly effective in researching accelerator performance and observing coupled beam instability.The beam instrumentation group at SSRF has focused on the study of bunch-by-bunch diagnostic since 2009,and has built a multi-parameter bunch-by-bunch diagnostic platform including position,bunch length and transeversal beam size.The technology has achieved good results in three-dimensional position measurement and three-dimensional bunch size measurement in the operation of user mode and machine research.However,it is limited by the measurement accuracy of instruments,traditional signal acquisition methods and traditional data processing methods.The previous work has not been thoroughly studied in the direction of the high precision measurement of the bunch charge,the beam lifetime,and the tune measurement without stimulation.The research of this thesis is focused on these directions.The technical requirements of the digital beam signal processor are summarized and analyzed.Moreover,the influence of crosstalk between bunches and crosstalk between the processor's channels is discussed in detail.The test evaluation method and the compensation algorithm that can be used in the beam signal processor are discussed,and several application examples have been shown in the thesis.A precise bunch-by-bunch beam current monitor system has been developed at the SSRF.Utilizing the advantages of the high data refresh rate and the high resolution of the beam signal processor,we can extract the bunch charge information from the sum signal of the button BPM.In order to avoid the influence of the longitudinal oscillation on the amplitudes of the sampling points,a method called two-point equilibrium sampling is introduced.The results,obtained during routine operation time,show that the relative resolution of the measurement of the bunch charges is better than 0.02%,which is significantly higher than the original BCM system resolution(0.1%).With the high resolution,the new BCM system is now able to monitor the bunch-by-bunch beam lifetime.By using the filling pattern information,the Touschek lifetime and the vacuum lifetime can also be calculated.In this thesis,the principle of the new method and the experiments is presented in detail.Traditional tune measurements usually need to excite the beam.In order to decrease the influence on the beam,the unexcited or perturbed tune measurement methods in an electron storage ring were investigated.Referring to the new method called baseband tune(BBQ)used in the heavy ion storage ring,the method was simulated and substituted into the SSRF storage ring parameters,and the PCB board was developed for preliminary beam experiment.Both of the simulation and the experiment results show that the BBQ method is not effective for the SSRF storage ring.On this basis,another tune measurement method based on bunch-by-bunch signal acquisition and processing is proposed: collecting the bunch-by-bunch beam position and using harmonic analysis.We also designed a confirmatory experiment.The beam experiment results show that the bunch-by-bunch tune measurement system can achieve the perturbation tune measurement during routione operation time in the SSRF.