• D. Filippetto, D. Alesini, M. Bellaveglia, R. Boni, M. Boscolo, M. Castellano, E. Chiadroni, L. Cultrera, G. Di Pirro, M. Ferrario, L. Ficcadenti, V. Fusco, A. Gallo, G. Gatti, C. Marrelli, M. Migliorati, A. Mostacci, E. Pace, L. Palumbo, B. Spataro, C. Vaccarezza, C. Vicario
  INFN/LNF, Frascati (Roma)
• A. Bacci, A.R. Rossi, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• A. Cianchi
  Università di Roma II Tor Vergata, Roma
• L. Giannessi, M. Labat, M. Quattromini, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• B. Marchetti
  INFN-Roma II, Roma
• J.B. Rosenzweig
  UCLA, Los Angeles, California
• M. Serluca
  INFN-Roma, Roma

The optimization of the beam brightness is one of the main objectives of the research and development efforts in rf-photoinjectors devoted to short wavelength FELs. The velocity bunching experiment at SPARC has recently demonstrated the possibility of increasing the beam current via RF compression at low energies, while compensating the self-fields induced emittance degradation by means of continuous magnetic focusing. The result is an increase of the beam brightness by about one order of magnitude. Stable compression ratio up to a factor 12 has been observed. Characterization of longitudinal phase spaces an measure of projected and slice emittances, as a function of the injection phase in the first accelerating structure and for different solenoids field values are presented. Comparisons with simulations are also reported.

Slides

• M. Labat, F. Ciocci, G. Dattoli, M. Del Franco, A. Doria, G.P. Gallerano, L. Giannessi, E. Giovenale, A. Petralia, M. Quattromini, C. Ronsivalle, E. Sabia, I.P. Spassovsky, V. Surrenti
  ENEA C.R. Frascati, Frascati (Roma)
• D. Alesini, M. Bellaveglia, R. Boni, M. Boscolo, M. Castellano, E. Chiadroni, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Mostacci, E. Pace, L. Palumbo, B. Spataro, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• A. Bacci, V. Petrillo, A.R. Rossi, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• F. Briquez, M.-E. Couprie
  SOLEIL, Gif-sur-Yvette
• B. Carré, D. Garzella
  CEA, Gif-sur-Yvette
• A. Cianchi, B. Marchetti
  INFN-Roma II, Roma
• G. Marcus, J.B. Rosenzweig
  UCLA, Los Angeles, California
• M. Mattioli, M. Serluca
  INFN-Roma, Roma

The SPARC FEL can be operated in both SASE and seeded modes. A major part of the second stage of the commissioning, currently in progress, is dedicated to the characterization of the SASE radiation. Simultaneously, we are finalizing the experimental setup for seeding. We present an in-situ characterization of the two input seeds that are foreseen: both are obtained via harmonic generation, the first one in crystal (400 and 266 nm) and the second in rare gas (Argon). We also describe the specific diagnostics implemented for the electron-seed overlap in the undulator, together with the diagnostics for radiation analysis (2D spectrometer and FROG). The seeding will enable the operation of the SPARC FEL in original cascaded configurations.