FERMI at ELETTRA is a project aims at the construction of a single-pass user facility for the spectral range from 100 nm to 10 nm. Starting point is the existing 1.2 GeV, 3-GHz linac. Downstream of the linac two undulator beamlines will serve the wavelength range from 100 nm to 40 nm, and 40 nm to 10 nm, respectively. The former beamline will be based on a single-stage HGHG scheme while for the latter a double stage HGHG scheme is foreseen. This paper discusses results from start-to-end simulations for the former beamline, including the option of HGHG. Care has been taken to include realistic models for the injector, accelerating structures, and undulator beamline.

Future FEL operations in the ELETTRA LINAC require a high quality beam with an ultra short bunch. The knowledge of the short-range wakefields in the backward traveling wave (BTW) accelerating structure is needed to predict the beam quality in term of the single bunch energy spread and emittance. To calculate the effect of the longitudinal and transverse wakefileds we have used the time domain numerical approch with a new implicit scheme for calculation of wake potential of short bunches in long structure [1,2]. The wake potentials of the BTW structure are calculated numerically for very short bunches and analytical approximations for wake functions in short and long ranges are obtained by fitting procedures based on analytical estimations.