• L. Palumbo
  Rome University La Sapienza, Roma
• D. Alesini, M. Bellaveglia, S. Bertolucci, M.E. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, D. Filippetto, V. Fusco, A. Gallo, A. Ghigo, S. Guiducci, M.  Migliorati, A. Mostacci, L. Pellegrino, M.A. Preger, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stella, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario
  INFN/LNF, Frascati (Roma)
• F. Alessandria, A. Bacci
  INFN/LASA, Segrate (MI)
• F. Broggi, S. Cialdi, C. De Martinis, D. Giove, C. Maroli, M. Mauri, V. Petrillo, M. Rome, L. Serafini
  INFN-Milano, Milano
• L. Catani, E. Chiadroni, A. Cianchi, C. Schaerf
  INFN-Roma II, Roma
• F. Ciocci, G. Dattoli, A. Doria, F. Flora, G.P. Gallerano, L. Giannessi, E. Giovenale, G. Messina, P.L. Ottaviani, G. Parisi, L. Picardi, M. Quattromini, A. Renieri, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• P. Emma
  SLAC, Menlo Park, California
• M. Mattioli
  Universita di Roma I La Sapienza, Roma
• P. Musumeci
  INFN-Roma, Roma
• S. Reiche, J.B. Rosenzweig
  UCLA, Los Angeles, California

The first phase of the SPARX project, now funded by MIUR (Research Department of Italian Government), is an R&D activity focused on developing techniques and critical components for future X-ray FEL facilities. This project is the natural extension of the activities under development within the ongoing SPARC collaboration. The aim is the generation of electron beams characterized by an ultra-high peak brightness with a linear accelerator based on the upgrade of the existing Frascati 800 MeV LINAC and to drive a single pass FEL experiment in the range of 3-5 nm, both in SASE and SEEDED FEL configurations, exploiting the use of superconducting and exotic undulator sections. In this paper we discuss the present status of the collaboration.

• V. Petrillo, C. Maroli
  Universita' degli Studi di Milano, MILANO
• A. Bacci, L. Serafini
  INFN-Milano, Milano
• M. Ferrario
  INFN/LNF, Frascati (Roma)

Funding: Università degli Studi di MIlano-INFN Via Celoria,16 MIlano (Italy)

Collective effects in the radiation emission process via Thomson back-scattering of an intense optical laser pulse by high brightness electron beams are analyzed. The micro-bunching of the electron beam on the scale of the emitted radiation wavelength and the consequent free-electron-laser instability may enhance significantly the total number of emitted photons. Scalings of the radiation properties, both in the collective and in the incoherent spontaneous regime, versus laser and electron beam parameters are discussed. Transverse effects due to radiation diffraction, finite emittance of the beam, and transverse distribution of the laser energy are studied.