TM_(020)模式谐振腔束团长度监测器的设计与仿真（英文）

Design and simulation of TM_(020) cavitybunch length monitor

提出了一种基于高次模式的谐振腔束团长度测量技术,新方法的谐振腔工作于高次本征模式TM0n0。这样的谐振腔拥有更大的腔体半径,从而移除了谐振腔半径必须大于束流管道半径这一原则带来的工作频率限制。为国家同步辐射实验室未来的正电子源设计了一台双腔束团长度监测器,讨论了谐振腔工作频率的选择并推导了束团长度的计算公式,监测器的谐振腔工作于TM020模式,其半径远大于使用TM010模式的传统方法,在CST软件中模拟的结果显示其束团长度测量精度好于7%。

This paper proposes an improved bunch length measurement method based on high order mode cavity.Different from traditional ways,the new method uses the cavity that resonates with higher order mode TM0n0 instead of fundamental mode TM0 1 0 .The operating mode of this new method is alterable,which means that harmonic cavities with larger radius are available and working frequency restriction caused by beam pipe ra-dius is removed.A two-cavity monitor was designed for the linac of future National Synchrotron Radiation La-boratory（NSRL）positron source.Operating frequency selection is discussed and calculation formula of bunch length is derived.The bunch length measurement cavity resonates with mode TM020 at 14.28 GHz,which pro-vides much larger radius than TM0 1 0 mode.A simulation measurement was conducted in CST Particle Studio and the result shows a fairly high accuracy （better than 7%）.