• T. Watanabe, D.F.L. Liu, J.B. Murphy, J. Rose, T.V. Shaftan, T. Tsang, X.J. Wang, L.-H. Yu
  BNL, Upton, Long Island, New York
• P. Sprangle
  NRL, Washington, DC

Funding: Work supported by the Office of Naval Research.

A laser seeded near IR FEL amplifier experiment was initiated at the BNL SDL [1] to explore various schemes of FEL efficiency improvement and generation of short Rayleigh length (SRL) FEL output. The FEL achieved first SASE lasing at 0.8 μm on May 6, 2005. The experimental characterization of the laser seeded FEL output power, spectrum and transverse mode structure evolution will be presented.

[1] A. Doyuran et al., PRSTAB, Vol. 7, 050701 (2004).

• G. Parisi, F. Ciocci, G. Dattoli, L. Giannessi, G. K. V. Voykov
  ENEA C.R. Frascati, Frascati (Roma)

In the framework of the SPARC FEL experiment, a 14-m long undulator divided into six sections is presently under construction (by ACCEL Instruments GmbH). In order to correct the phase difference between the electron beam and the radiation, a tunable device will be inserted at the end of each of the six sections of the undulator. In this paper a preliminary design of this device, performed with RADIA code, is proposed,. The phase shifter consists of two groups of a few permanent magnets, arranged as in the main undulator in a variable gap magnet assembly. Adjusting the gap allows to correct the electron-radiation phase difference. Results from beam dynamics simulation, performed with GENESIS code, show the impact of the phase shifter on the characteristics of the output laser field.