3-D Particle-in-Cell Simulation of an Electromagnetic Wave Cyclotron Resonance Interaction with a Counterpropagating Electron Beam

Interaction of a monochromatic electromagnetic wave with a counterpropagating, initially rectilinear electron beam under the cyclotron resonance condition is studied. The changes in the regimes of wave propagation with increasing frequency of the input signal are discussed. In the cyclotron absorption band, the input signal decays. As the signal frequency increases, the wave transmission becomes possible, and the signal splits into a train of traveling solitons. This phenomenon is due to the development of modulation instability (MI). At higher frequencies, the MI changes its character from absolute to convective, as a result of which non-stationary self-modulation regimes are replaced by stationary single-frequency signal propagation. The theoretical predictions are verified by 3-D particle-in-cell (PIC) simulation of the electron-wave interaction using the CST Studio Suite software package. 3-D PIC simulation has demonstrated the possibility of converting the 241.3-GHz continuous-wave signal into a periodic train of pulses with a duration of about 3–4 ns. Such a phenomenon is of interest for the generation of frequency combs in the microwave range.