Results of numerical simulation of a miniaturized sub-THz traveling-wave tube amplifier with sheet electron beam and planar grating slow wave structure (SWS) are presented. Cold characteristics of the SWS are calculated. Small-signal and large-signal gain regimes are studied by the 1-D parametric frequency-domain code. The results are verified by simulations using 3-D particle-in-cell codes.

The capabilities of two types of terahertz sources based on stimulated Smith-Purcell radiation of electrons in open cavities are discussed. A series of developed pulsed orotrons provides coherent radiation with an output power of 1-0.1 W in the frequency range of 90-410 GHz, with high frequency stability and broad-band electromechanical frequency tuning. A promising alternative source with smaller currents than that in orotrons is a frequency multiplier based on excitation of a surface wave of a periodic structure and Smith-Purcell radiation of arising electron bunches inside the orotron cavity. In contrast to a number of works where only an open grating is used, exploiting a cavity enables a stimulated radiation process with a much higher power. The developed theory demonstrates the possibility of single-mode generation in such multipliers with wide electron beams.

Within the framework of the average approach and direct 3D PIC (particle-in-cell) simulations, we demonstrate that the gyrotrons operating in the regime of developed turbulence can sporadically emit “giant” spikes with intensities a factor of $100–150$ greater than the average radiation power and a factor of $6–9$ exceeding the power of the driving electron beams. Together with the statistical features such as a long-tail probability distribution, this allows the interpretation of generated spikes as microwave rogue waves. The mechanism of spikes formation is related to the simultaneous cyclotron interaction of a gyrating electron beam with forward and backward waves near the waveguide cutoff frequency as well as with the longitudinal deceleration of electrons.

The excitation of a low-frequency surface wave can provide coherent high-frequency Smith–Purcell radiation due to the frequency multiplication effect. The use of an open cavity allows an additional power increase due to the induced nature of the radiation. A radiation source based on these effects is experimentally demonstrated at a frequency of about 190 GHz.