%\cite{Davidyuk:FEL2015-WEP051} \bibitem{Davidyuk:FEL2015-WEP051} I.V.~Davidyuk, O.A.~Shevchenko, V.G.~Tcheskidov, and N.~Vinokurov, \textquotedblleft{The Prototype of New Variable Period Undulator for Novosibirsk Free Electron Laser.}\textquotedblright, % in \emph{Proc. FEL2015}, WEP051, pp. 677--680, % in \emph{Proc. FEL2015}, Daejeon, Republic of Korea, August 2015, paper WEP051, pp. 677--680, in \emph{Proc. 37th International Free Electron Laser Conference (FEL2015)}, Daejeon, Republic of Korea, August 2015, paper WEP051, pp. 677--680, ISBN: 978-3-95450-134-2, \url{http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/wep051.pdf}, doi:10.18429/JACoW-FEL2015-WEP051, 2015.