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%\cite{zen:ipac2021-frxa05}
\bibitem{zen:ipac2021-frxa05}
H. Zen, R. Hajima, and H. Ohgaki,
\textquotedblleft{Record High Extraction Efficiency of Free electron Laser Oscillator}\textquotedblright,
% --- abbreviated form (UNpublished paper) - JACoW template Feb 2018 ---
presented at IPAC'21, Campinas, SP, Brazil, May 2021, paper FRXA05, unpublished.