Maksimenko O. Interaction of helical electron beams with electromagnetic fields in gyrotron resonators in the terahertz range

The studies consider the interaction of helical electron beams with electromagnetic fields in gyrotron resonators in the terahertz range. For a resonator with perfectly conducting walls, the radius of which is described by a sinusoidal-periodic dependence with respect to the azimuthal angle, it was shown for the first time by analytical and numerical calculations that non-transmission bands, in which there are no resonator vibrations, appear near the intersection points of neighboring harmonics. To determine the parameters of a gyrotron without taking into account the effect of the beam, it was first proposed to apply the decomposition of the longitudinal components of electromagnetic fields under conditions of the significant mode conversion and ohmic losses. To make it possible to account for the electron beam, the well-known method based on the decomposition of the transverse components of electromagnetic fields in the case of significant ohmic losses was generalized. Using this method, a generalized starting current formula was obtained for the first time in the case of the significant mode conversion in the approximation of a given field. For self-consistent accounting of an electron beam, a method that reduces the equations of motion and the equations of electromagnetic fields to a spectral task was developed. The conducted studies are based on modern methods of gyrotron electrodynamics, which take into account mode conversion and ohmic losses. The results obtained will be useful for further theoretical and experimental studies of subterahertz and terahertz gyrotrons.