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TY - UNPB AU - Penco, G. ED - Chin, Yong Ho ED - Zhao, Zhentang ED - Petit-Jean-Genaz, Christine ED - Schaa, Volker RW TI - Two-Bunch Operation With ns Temporal Separation at FERMI J2 - Proc. of FLS2018, Shanghai, China, 5-9 March 2018 C1 - Shanghai, China T2 - ICFA Advanced Beam Dynamics Workshop T3 - 60 LA - english AB - In the last decade a continuous effort has been spent to improve the capability of existing free-electron lasers (FELs) operating in the X-ray and VUV regimes. Together with the possibility to provide sub-ps and fs photon pulses with an intensity ten order of magnitude larger than the past generation light sources, new modes of operation have been conceived. In this framework, generation of two-color (or multi-colour) FEL pulses, temporally separated, had an unprecedented impact on the scientic community, pave the way for new pump-and-probe experiments. A number of two-color two-pulse schemes have been already implemented in several labs but with a limited time-separation from 0 to few hundreds of fs. We present a new design tested at the FERMI FEL machine, able to produce two independent electron bunches temporally separated from hundreds of ps to few ns. Measurements and characterisation of this two-bunch mode operation are presented, including trajectory control, impact of longitudinal and transverse wakefields, manipulation of the longitudinal phase space and finally a demonstration of suitability of the scheme to provide extreme ultra-violet light by using both bunches. PB - JACoW Publishing CP - Geneva, Switzerland ER -