Local heating induced by Coherent Harmonic Generation on electron beam dynamics in storage ring

We investigate the dynamical response of an electron bunch in a storage ring to a brief and intense excitation of an external laser. We present a model that simulates the evolution of the electronic distribution in the Coherent Harmonic Generation (CHG) configuration: the energy exchange between photons and electrons occurs within an undulator magnetic field, and further leads to a coherent radiation process. Using those simulations and experimental results on the UVSOR-II CHG free electron laser, we demonstrate that the electronic distribution reaches an equilibrium regime thanks to energy spread relaxation in between two laser injections. We also show that saturation is driven by laser-induced local heating, leading to global effect over the whole bunch.