G. De Ninno[1,2], D. Garzella[1,2], M. Hirsch[1,2], L. Nahon[1,2], D. Nutarelli[1], E. Renault[1,2] et M.E. Couprie[1,2]
[1] LURE, bat 209d, Universit
Paris-Sud, BP 34, 91898 Orsay Cedex, France[2] SPAM/DRECAM/DSM, bat 522, CE de Saclay, 91191 Gif sur Yvette Cedex, France
Standard theoretical approaches evaluate the FEL-beam interaction in a storage ring in terms of a statistical action of the FEL pulse on the whole electron bunch. A new theoretical approach is here proposed where only the electrons which superimpose with the FEL pulse (that is several times thinner than the electron bunch) are perturbed. The main result of this localized interaction is a perturbation of both longitudinal distribution which do not maintain their (laser off) gaussian profile. Theoretical results are confirmed by experimental observations performed on the ACO and SuperACO FELs at LURE in Orsay. For the latter storage ring different configurations are tested. This allows one to better understand the different role played by the FEL-beam system parameters (and, in particular, by the momentum compaction) in the distortion of the longitudinal beam distributions.
