• M. Ferianis, P. Craievich, G. D'Auria, S. Di Mitri
  ELETTRA, Basovizza, Trieste
• P. Emma
  SLAC, Menlo Park, California
• W. Graves
  MIT, Middleton, Massachusetts
• M. Poggi
  INFN/LNL, Legnaro, Padova
• A. Zholents
  LBNL, Berkeley, California

Fermi is the fourth generation light source currently under design at ELETTRA: based on the Harmonic Generation (HG) scheme it will generate FEL radiation in the 100-10nm range. The successful implementation of the HG scheme calls also for precise knowledge of electron beam emittances and energy spread as well as for very accurate control on the photon to electron interaction, in the Undulator sections. In this paper we present our design for two fundamental Diagnostics foreseen for the new FERMI LINAC: the Beam Position Monitors (BPM) and the Transverse Deflecting cavity set-up. Sensitivity studies on transverse beam displacement effects on global stability of FEL output radiation dictate the ultimate performance to be provided by the BPM system. Due to non negligible longitudinal occupancy of a cavity type BPM, some efforts have been put to study compact cavity BPM configuration. A proper set-up of RF deflecting cavity combined with the vertical ramp foreseen at the end of the LINAC provide a powerful tool for multiple beam measurement. Furthermore, by implementing the two bunch compressors in the vertical plane the effect of the Coherent Synchrotron Radiation (CSR) on the vertical emittance can be checked for.