Two-stream superheterodyne free electron lasers as formers of ultrashort electromagnetic clusters

We develop a cubic nonlinear self-consistent theory of multiharmonic two-stream superheterodyne free electron lasers (TSFEL) of a klystron type, designed to form powerful ultrashort clusters of an electromagnetic field. We have considered plural three-wave parametric resonant interactions of wave harmonics. We used the TSFEL regime in which the first harmonic of a space-charge wave (SCW) is much smaller than the critical frequency of two-stream instability for forming of the powerful ultrashort clusters of electromagnetic waves. Amplitude, phase and spectral analyses of the processes occurring in such devices have been carried out. We found out the conditions needed for the forming of the ultrashort electromagnetic field clusters. We demonstrate the possibility of the ultrashort electromagnetic cluster formation in the multiharmonic TSFEL-type systems.