Active FEL-Klystrons as Formers of Femto-Second Clusters of Electromagnetic Field. Description of the Models Based on “Ordinary” FEL Sections

The qualitative properties discussion of the Femto-second active cluster FEL-klystrons, which are designed on the basis of “ordinary” FEL sections, is performed. Theoretical models of two different types of such devices are proposed. The main difference between them consists in the acceleration block arrangement. Namely, in the model with intermediate acceleration, a part of the acceleration sections is placed between the modulation and energy-transformation sections. The formulation of the problem is done. The basic system of truncated equations (in the cubic-nonlinear approximation) for the complex amplitudes of harmonics of resonantly-interacting waves is obtained.