Effects of ion-channel guiding on the saturation mechanism of a single-pass free-electron laser

In this paper we study the nonlinear dynamics of a single-pass free-electron laser in the presence of an ion-channel guide. A set of coupled nonlinear differential equations in 1D approximation is employed, which governs the self-consistent evolution of an electromagnetic wave in the presence of a cold, cylindrically symmetric electron beam. The electron beam propagates at a relativistic velocity through the combination of a wiggler field and of a channel of immobile ions. The effects of the ion channel on the saturation of an amplifier free-electron laser are illustrated. Numerical simulations are performed using the parameters of the Fermi@Elettra single-pass free-electron laser as a reference. The effect of the ion channel is shown to have an impact on both the saturation length and the output power.