Active FEL-Klystrons as Formers of Femto-Second Clusters of Electromagnetic Field. Nonlinear Physics of the Transit Section

The classification and the kinematic analysis of parametrical resonant interactions in the transit section of two-stream superheterodyne free electron laser are carried out. It is found out that realization of four types of parametrical resonant interactions is possible. A number of the investigated variants of interactions have plural character - hundreds and more harmonics connected with each other simultaneously participate in a three-wave parametrical resonance. A cubically nonlinear multiharmonic theory of plural parametrical resonant interactions is constructed. It is established that such interactions can substantially influence the development of physical processes in the investigated system. It is offered to use the plural parametrical resonant interactions for the formation of a wide multiharmonic spectrum of waves in cluster two-stream superheterodyne free electron lasers.