Study Of Bunch Length Measurement Technology Using Two-frequency Method

X-ray Light Source Accelerator has been developed for four generation,and Synchrotron Radiation Light Source with many insertion devices and Free Electron Laser with high energy enhancement are major solution facilities for X-ray Light Source.The topic of this thesis is study of bunch length measurement technology using two-frequency method,which is applied at Shanghai Synchrotron Radiation Facility and Shanghai Soft X-ray Free Electron Laser.This topic is chosen for actually status of applied facilities and all kinds of investigated bunch length measurement methods with their measurement accuracy and merits and drawbacks considered.The research work is aiming to construct a two-frequency bunch length measurement system and realize bunch-by-bunch length measurement with excellent measurement error.Theoretical foundation of system design consists of two-frequency bunch length measurement formula derived from Gauss bunch model,demand analysis of bunch-by-bunch measurement.500 MHz and 3GHz are chosen as system working frequencies because of spectrum response of button-type electrode and practical experience.The system is constructed based on consideration of magnitude of signals,main parameters of radio frequency devices and above points.Experiment about the relationship between bunch length and charge is executed using steak camera and two-frequency system for probe simultaneously,and with the contrast between their measurement results,the formula of bunch length has been revised in both single bunch and multiple bunches filling mode and systemic parameter K has been calibrated.Mathematical simulation work of bunch length synchrotron oscillation process has revealed the rule and time-frequency domain characteristics of bunch length vibrating in bunch refilling process.Experimental results of injection event at single bunch and multiple bunches status match with simulation work very well,and bunch length synchrotron osc illation process has been observed in two experiments.This oscillation process would be more obvious when we use a hybrid device to subtract 500 MHz and 3GHz signals at intermediate frequency and observe the subtracted one.The random measurement error of two-frequency bunch length measurement in single bunch filling mode has been demonstrated better than 0.2ps;the bunch-by-bunch random measurement error is less than 0.5ps.Bunch length measurement with charge of less than 5nC is linear,and if we choose analog devices with high input power,the systemic measurement dynamic range would be enlarged and system could be applicable to proton and heavy ion accelerator.The transverse magnetic field mode 010 of cavity has high signal accuracy that can satisfy measurement demand of bunch length at FEL when one designs two cavities of different working frequencies.The two-frequency and two-cavity method hasn't been accomplished except system design and analog front-end circuit because of schedule of foundation project.Laboratory test of entire linearity and each component can ensure the validity of analog front-end circuit.