%\cite{Emma:FEL2015-WEP075} \bibitem{Emma:FEL2015-WEP075} C.~Emma, Y.~Ding, Z.~Huang, A.A.~Lutman, G.~Marcus, A.~Marinelli, and C.~Pellegrini, % C. Emma \emph{et al.}, \textquotedblleft{Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam}\textquotedblright, % in \emph{Proc. FEL2015}, WEP075, pp. 722--725, % in \emph{Proc. FEL2015}, Daejeon, Republic of Korea, August 2015, paper WEP075, pp. 722--725, in \emph{Proc. 37th International Free Electron Laser Conference (FEL2015)}, Daejeon, Republic of Korea, August 2015, paper WEP075, pp. 722--725, ISBN: 978-3-95450-134-2, \url{http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/wep075.pdf}, doi:10.18429/JACoW-FEL2015-WEP075, 2015.