Formation of microwave soliton combs under cyclotron resonance interaction of electron beam with counter-propagating waveguide mode

Abstract

We theoretically study the formation of periodical trains of microwave self-induced-transparency solitons (M\W-SIT soliton combs), which arise under cyclotron resonant interaction of an initially rectilinear electron beam with a steady-state electromagnetic wave counter-propagating in a cylindrical waveguide. Depending on the contained energy, solitons can either propagate toward the electron beam (i.e., in the direction of the unperturbed group velocity) or be entrained by the beam in the direction of its translational motion. As a result, a kind of feedback arises, leading to the appearance of soliton combs emitted from both the left and right boundaries of the system. This process can be described by the non-stationary self-consistent model, which is based on the parabolic equation for the field evolution taking into account the waveguide dispersion. Within the framework of the developed model, it is shown that waveguide dispersion does not prevent the formation of ultrashort solitons with duration of about several dozens wave periods. Moreover, the peak power of the entrained solitons can anomalously increase as the frequency of the incident wave approaches the cutoff frequency of the operating mode.