Andrey G. Rozhnev

Guided and leaky modes of complex waveguide structures

The guided and leaky modes of the optical waveguides (fibers) are analyzed by the finite-element method (FEM) with the integral boundary conditions. The initial equations are reduced to the algebraic general eigenvalue problem, which is solved by the Arnoldi algorithm. The mode dispersion characteristics, fields, and cutoff frequencies are calculated for several waveguide structures, including flat and multilayer fibers with different shapes of cross sections.

Modeling and characterization of a slow-wave structure for a sheet-beam sub-THz TWT amplifier

Microfabricated sheet-beam traveling-wave tubes for THz and sub-THz operation have attracted a considerable interest. In this paper we discuss design issues of a double-vane slow-wave structure (SWS) for a 0.2 THz amplifier. A fast and accurate code for calculation of electrodynamic characteristics of the SWS is developed.

FDTD-analysis of the wave diffraction from dielectric waveguide discontinuities

The problem of the guided mode reflection from the planar dielectric waveguide end is studied by the finite difference time domain method. The influence of facet deformations on the scattering characteristics is considered. The reflectivity problem for the system with the nonlinear dielectric waveguide insert is examined.

Properties of electron field emission from a fractal surface

Abstract The results of a numerical simulation of electron field emission from the surface of 2-D fractal object bounded by a Julia set are presented. The calculations show that emission occurs mainly from small parts of the surface close to self-similar small-scale irregularities, where the electrostatic field is enhanced. The results presented confirm the hypothesis, that the unusual field-emission properties of some materials can be explained by taking into account the fractal structure of its surface. The connection between the fractal dimension and the emission properties are discussed. It is found that the emission current depends mainly on the geometry of small-scale irregularities. Nevertheless, the fractal dimension defines the slope of current–voltage characteristics.

High-Dimensional Chaos in a Gyrotron

In this paper, nonstationary and chaotic dynamics of a gyrotron with a nonfixed field structure have been studied. We discuss the mechanism of transition to self-modulation and chaotic oscillations and present the plane of parameters with different kinds of regimes in a gyrotron. For chaotic attractors, the set of Lyapunov exponents has been calculated. We have estimated the dimensions of chaotic attractors from the Kaplan-Yorke formula and found it to be anomalously high. The explanation of this fact is based on the presence of a large number of high-Q eigenmodes in the gyrotron resonator operating near a critical frequency of the electrodynamic system

Study of electrodynamic parameters of the planar meander slow-wave structures for THz band traveling wave tubes

Planar meander line slow-wave structure (SWS) for traveling wave tubes at THz frequency band is studied. The meander SWS circuit at 180-230 GHz frequency band is designed and fabricated. Basic electrodynamic parameters of the SWS are calculated. The simulation shows a rather high coupling impedance.

High-dimensional chaotic attractors in a gyrotron with nonfixed field structure

The chaotic dynamics of a gyrotron with nonfixed field structure is numerically simulated and the Lyapunov exponents of chaotic attractors are calculated. The dimensions of chaotic attractors estimated using the Kaplan-Yorke formula prove to be anomalously high. This fact is related to the presence of a large number of high-Q eigenmodes in the gyrotron resonator operating in the vicinity of a critical frequency of the electrodynamic system.

New 2.5D code for modeling of nonlinear multisignal amplification in a wideband helix traveling wave tube

Broadband high-gain traveling wave tube (TWT) amplifiers are widely employed in communications and other related applications. For design of such devices, numerical modeling and optimization tools are of great importance. In this paper, we describe a new 2.5D code for simulation of a helix TWT.

Complex dynamics of gyrotron with non-fixed structure

In this work the results of nonstationary processes investigation in relativistic electron generator-gyrotron with non-fixed field structure are presented. As distinct from previous works it was taken into account the realistic dependence of reflections coefficient from input and output devices irregularity, which is achieved by using received previously nonstationary non-local in time domain boundary conditions. The numerical simulation of nonstationary processes in gyrotron with non-fixed field structure is carried out.

Frequency Stabilization of a 0.67-THz Gyrotron by Self-Injection Locking

Self-injection locking of a gyrotron by a delayed signal is considered. The results of theoretical analysis and numerical simulations explaining gyrotron frequency stabilization by time-delayed part of the output power are presented. A simple quasi-linear model is studied, and formulas for the frequency-stabilization rate and the locking bandwidth are derived. The theory is verified by a numerical simulation for the 0.67-THz gyrotron.