The results of experimental study of the traveling-wave amplification in the oversized circuit with a nonuniform grating, which has increased depth of every third groove, have been presented and discussed. Measured TWT gain versus both frequency and beam voltage is compared with the calculated dispersion. The peculiarities of the interaction of a sheet electron beam with a traveling wave have been discussed for the region of mode coupling. Obtained results show a good agreement with the preliminary 3D PIC simulations.

The preliminary analysis of operation of the 345 GHz sectioned traveling-wave amplifier with the three-stage nonuniform grating has been presented. The design is based on both the simulation and the experimental results obtained for the W-band amplifier earlier. The THz amplifier is designed for the operation with the nonrelativistic sheet electron beams and the oversized beam-wave system. The result of calculations, carried out with the use of the large- signal theory, demonstrated the power gain up to 23 dB for the frequency region from 335 GHz to 365 GHz in the proposed amplifier. The output power of at least 1 W was predicted for the reasonable level of driving signal, that is less than 50 mW.

The results of the research and design of a new model of clinotron with the non-uniform grating structure. The tube is designed to operate at the several regimes those are promising for efficient excitation of the THz waves. The regime of the hybrid surface-volume mode is considered numerically. The design of the clinotron contains two power outputs: the backward wave (BW) output and the space wave (SW) output. The simulation results demonstrate double magnification of the output power at the SW output compared to the BW output. The experimental prototype of the clinotron has been designed and manufactured according to the simulation results.

Effective operation of a clinotron, as well as any other Cherenkov electron vacuum device, critically depends on electron beam formation quality and velocity spreads. Main results, related with an electron gun analysis and electron beam formation for a clinotron are presented in this paper. To study the longitudinal velocity spreads, the sheet electron beam has been investigated by means of 3D particle tracking simulations. Verification of obtained results was carried out by simulation in CST Particle Studio.