• E. Allaria, G. De Ninno
  ELETTRA, Basovizza, Trieste
• A. Antoniazzi, D. Fanelli
  Universita di Firenze, Florence
• F.T. Arecchi
  UNIFI, Sesto Fiorentino (FI)
• R. Meucci
  INOA, Firenze

We numerically investigate the effect of a delayed control method on the stabilization of the dynamics of the Elettra storage-ring free-electron laser in Trieste (Italy). Simulations give evidence of a significant reduction of the typical large oscillations of the laser intensity. Results are compared with numerical and experimental data obtained with a derivative feedback. The possibility of an experimental implementation of the proposed method is also discussed.

• G. De Ninno, B. Diviacco, M. Trovo
  ELETTRA, Basovizza, Trieste
• A. Antoniazzi, D. Fanelli
  Universita di Firenze, Florence
• R. Meucci
  INOA, Firenze

The possibility of establishing and maintaining a stable operation mode of a storage-ring free electron laser finally resides in a deep understanding of the strongly coupled laser-electron dynamics. Such a dynamics may be affected by electron-beam instabilities whose origin can be traced back either to electromagnetic wake fields or to "external" perturbations (e.g. line-induced modulations, mechanical vibrations, etc.). This is the case of the Elettra storage-ring free-electron laser which is significantly affected by a 50-Hz perturbation of the electron beam density. We have developed a simple theoretical model which has been proved to be able to provide insight into the evolution of the laser intensity. In this framework, we have also proposed the possibility of utilizing a derivative closed-loop feedback to create or enlarge the region of stable signal. A feedback of this type has been implemented on the Elettra storage-ring free-electron laser. The obtained results, which fully confirm our predictions, are discussed in this paper.