INTRA UNDULATOR SCREEN DIAGNOSTICS FOR THE FERMI@Elettra FEL

The FERMI@Elettra seeded FEL poses demanding requirements in terms of intra undulator diagnostics due to the short wavelength of its FEL radiation and to the coexistence of the electron and photon FEL beams. An advanced multi-beam screen system has equipped both FEL1 and FEL2. The system has been designed for transverse size and profile measurement on both the electron beam and the FEL radiation. Challenging design constrains are present: COTR suppression, seed laser suppression, FEL wavelength range and minimization of the ionizing radiation delivered to the undulators. This paper describes the novel design and the obtained performance with the FERMI intra undulator screen system (IU-FEL).