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TY - CONF AU - Tsai, C.-Y. AU - Wu, J. AU - Yang, C. AU - Yoon, M. AU - Zhou, G. ED - Bishofberger, Kip:Carlsten, Bruce (LANL, Los Alamos, NM, USA)[ORCID:0000-0001-5619-907X] ED - Schaa, Volker RW TI - Sideband Instability in a Tapered Free Electron Laser J2 - Proc. of FEL2017, Santa Fe, NM, USA, August 20-25, 2017 C1 - Santa Fe, NM, USA T2 - International Free Electron Laser Conference T3 - 38 LA - english AB - For a high-gain tapered free electron laser (FEL), it is known that there is a so-called second saturation point where the FEL power growth stops. Sideband instability is one of the major reasons leading to this second-saturation and thus prevents reaching terawatt-level power output in an X-ray FEL. It is believed that a strong taper can effectively suppress the sideband instability and further improve the efficiency and peak power. In this paper, we give quantitative analysis on the necessary taper gradient to minimize the sideband growth. We also discuss the transverse effects of induced electron de-trapping which is yet another major reason for the occurrence of the second-saturation point even with a strong enough taper. The study is carried out analytically together with numerical simulation. The numerical parameters are taken from LCLS-II type electron bunch and undulator system. PB - JACoW CP - Geneva, Switzerland SP - 76 EP - 79 KW - ion KW - electron KW - undulator KW - FEL KW - laser DA - 2018/02 PY - 2018 SN - 978-3-95450-179-3 DO - 10.18429/JACoW-FEL2017-MOP020 UR - http://jacow.org/fel2017/papers/mop020.pdf ER -