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TY - CONF AU - Wei, J.H. AU - Baboi, N. AU - Shi, L. ED - Schaa, Volker RW TI - Long Term Beam Phase Monitoring Based on HOM Signals in SC Cavities at FLASH J2 - Proc. of IBIC2018, Shanghai, China, 09-13 September 2018 CY - Shanghai, China T2 - International Beam Instrumentation Conference T3 - 7 LA - english AB - The accelerating RF fields in superconducting cavities must be controlled precisely in FEL (Free Electron Laser) facilities to avoid beam energy spread and arrival time jitter. Otherwise the beam quality is degraded. The LLRF (Low Level Radio Frequency) system controls the RF field and provides a highly stable RF reference. A new type of beam phase determination technique based on beam-excited HOMs (Higher Order Modes) in cavities has been implemented. The two special couplers installed at both ends of each cavity, pick up the signals containing both the leakage of the accelerating field and the HOM signals. Therefore the signals can be used to calculate the beam phase directly with respect to the RF phase. We analysed the factors which may affect the result of the beam phase on a long-term based on an experimental platform at FLASH. Some phase drifts between the HOM-BPhM (Beam Phase Monitor) and the LLRF system phase measurement were observed and the reason will be further studied. PB - JACoW Publishing CP - Geneva, Switzerland SP - 388 EP - 391 KW - HOM KW - cavity KW - controls KW - electron KW - FEL DA - 2019/01 PY - 2019 SN - 978-3-95450-201-1 DO - DOI: 10.18429/JACoW-IBIC2018-WEPA09 UR - http://jacow.org/ibic2018/papers/wepa09.pdf ER -