Entrainment, stopping, and transmission of microwave solitons of self-induced transparency in counter-propagating magnetized electron beam.

Based on numerical simulations of a boundary problem, we study various scenarios of microwave soliton formation in the process of cyclotron resonance interaction of a short electromagnetic pulse with a counter-propagating initially rectilinear electron beam taking into account the relativistic dependence of the cyclotron frequency on the electrons' energy. When a certain threshold in the pulse energy is exceeded, the incident pulse can propagate without damping in the absorbing beam, similar to the effect of self-induced transparency in optics. However, mutual motion of the wave and electrons can lead to some novel effects. For relatively small energy of the incident pulse, the microwave soliton is entrained by the electron beam opposite to the direction of the wave's group velocity. With an increase in the pulse energy, soliton stopping occurs. This regime is characterized by the close-to-zero pulse velocity and can be interpreted as a variety of the "light stopping." High-energy microwave solitons propagate in the direction of the unperturbed group velocity. Their amplitude may exceed the amplitude of the incident pulse, i.e., nonlinear self-compression takes place. A further increase in the incident energy leads to the formation of additional high-order solitons whose behavior is similar to that of the first-order ones. The characteristics of each soliton (its amplitude and duration) correspond to analytical two-parametric soliton solutions that are to be found from consideration of the unbounded problem.

Generation of Subterahertz Superradiance Pulses Based on Excitation of a Surface Wave by Relativistic Electron Bunches Moving in Oversized Corrugated Waveguides.

The first experiments on the observation of short pulsed superradiant (SR) emission with the excitation of a surface wave by a relativistic electron bunch moving in an oversized corrugated waveguide were performed. Subterahertz SR pulses with a central frequency of 0.14 THz, an ultrashort duration of 150 ps, and an extremely high peak power of 50-70 MW were generated. The experiments were based on a theoretical consideration including the quasioptical approach and direct particle-in-cell simulations.

3D quasioptical theory of terahertz superradiance of an extended electron bunch moving over a corrugated surface.

We consider the superradiance of an extended relativistic electron bunch moving over a periodically corrugated surface for the generation of multimegawatt terahertz pulses. To study the above process we have developed a three-dimensional, self-consistent, quasioptical theory of Cherenkov stimulated emission which includes a description of the formation of an evanescent wave over a corrugated surface and its excitation by rf current induced in the electron bunch.

High-power terahertz-range planar gyrotrons with transverse energy extraction.

To increase the output power of terahertz gyrotrons to several hundred kilowatts, we suggest using a planar geometry of interaction space with a sheet electron beam and transverse energy extraction. An advantage of this scheme in comparison with conventional cylindrical geometry is the possibility to ensure effective mode selection over the open transverse coordinate in combination with radiation outcoupling that leads to a substantial reduction of Ohmic losses. Similar to unstable resonators in optics for further growth of the radiation power it is beneficial to introduce waveguide tapering.