Design And Simulation Of A Cavity Bunch Length Monitor

In this thesis, a cavity bunch length monitor system (CBLM) is studied and designed. Measurable bunch length ranges from 5 to 10 ps. The device could be used to accomplish a number of important tasks, including setting the rf amplitude of bunching cavities, monitoring rf phase stability. Compared with other bunch length measurement methods, CBLM is compact, real-time and noninvase. And its measurement accuracy increases with the development of electronics. The promising method has attracted much more attention recently.The study history and latest progress of CBLM are summarized, and the design schemes of Jefferson Lab and IHEP are presented. The linac of NSRL future positron source that this design relying on is introduced. And the basic principles of CBLM are reviewed, including bunch length calculation, coupling structure, operating frequency selection. The traditional CBLM method is improved, the new method uses harmonic cavity that works at higher order mode TMono instead of TM010, which means harmonic cavities with larger radius is available and work frequency restriction caused by beam pipe radius is removed.The CBLM was designed and loaded with virtual beam to give a measurement simulation in CST Particle Studio. An improved bunch length calculation method was proposed and calculation result shows a fairly high accuracy better than 7%.