Electron Bunch Train Excited Higher-Order Modes in a Superconducting RF   Cavity
  Higher-order mode (HOM) based intra-cavity beam diagnostics has been proved effectively and conveniently in superconducting radio-frequency (SRF) accelerators. Our recent research shows that the beam harmonics in the bunch train excited HOM spectrum, which have much higher signal-to-noise ratio than the intrinsic HOM peaks, may also be useful for beam diagnostics. In this paper, we will present our study on bunch train excited HOMs, including the theoretic model and recent experiments carried out based on the DC-SRF photoinjector and SRF linac at Peking University. 
Yongfeng Gao, Senlin Huang, Fang Wang, Liwen Feng, Dehao Zhuang, Lin   Lin, Feng Zhu, Jiankui Hao, Shengwen Quan, Kexin Liu
physics.acc-ph