Relativistic acceleration and retardation effects on photoemission of intense electron short pulses, in RF-FEL photoinjectors

In high-power free electron lasers, self-field effects in the electron beam are often the most important phenomenon on which the beam quality depends. These effects are generally conceived as space-charge effects, and described by a Poisson equation in a beam frame. In RF-FEL photoinjectors, the electrons of the intense short pulse produced by laser irradiation are submitted, just after their photoemission, to such a strong acceleration that relativistic acceleration and retardation effects must be taken into account. The importance of these effects is discussed, from the rigorous calculation of the Lienard-Wiechert velocity and acceleration electric and magnetic fields, as a function of RF-electric field and beam parameters. The beam pulse is assumed to be axisymmetric, with a constant photoemitted current density.<>