SOLEIL, Gif-sur-Yvette
CNRS/CPT, Marseille
ELETTRA, Basovizza
Università di Firenze, Florence
Université Libre de Bruxelles, Center for Nonlinear Phenomena and Complex Systems - CP 231, Bruxelles
The regime of intensity (and bunching) oscillation following the FEL saturation is investigated using the Colson-Bonifacio model. This regime is understood as an out-of-equilibrium metastable state, which slowly relaxes toward thermodynamical (Boltzmann) equilibrium. This dynamics is also characterized by a strong regularity, unexpected for an interaction between waves and large number of particles, as well as by low-dimensional phase-space structures in the electron-beam phase space. In this context, the switch from regimes associated to high gain (for small electron-beam energy spread) or very low gain (for large energy spread) can be interpreted as out-of-equilibrium phase transitions, a phenomenon which was recently explained by a mechanism of entropy maximization.
