# Radiophysics, electronics, acoustics

## Simulation of a Sub-THz Traveling Wave Tube with Multiple Sheet Electron Beam

**Background and Objectives: **Many applications, such as highdata-rate wireless communications, spectroscopy, high-resolution radar, biomedical imaging, security, etc. require compact highpower sources of sub-THz radiation. Traveling wave tube (TWT) amplifiers are the most promising candidates for such sources combining 10–100 W power and wide b andwidth. Here we present the results of design and simulation of a 0.2 THz TWT with a grating slow-wave structure (SWS) and electron-optical system (EOS) with three elliptic-sha ped beams.

## Negative Dispersion, Refraction and Backward Polaritons: Impedance Approach

**Background and Objectives: **The dispersion equations of surface plasmon-polaritons are derived for the general case of layered dissipative structures. The waves are classified as gliding with energy flow into structure from vacuum and leakage ones. The dispersion equations and conditions for the existence of slow and fast gliding and leaky waves, as well as forward and backward waves are considered.

## Spatiotemporal Structures in an Ensemble of Nonlocally Coupled Nekorkin Maps

**Background and Objectives:** Studying chimera states is a subject of special attention among specialists in nonlinear dynamics, and the issue on the mechanisms for implementing chimeras is today one of the topic directions. In the paper we consider the mechanism for realizing a chimera state regime which is based on the so-called “solitary states” (SSC) and is actively discussed by experts. The problem is solved by analyzing the dynamics of a one-dimensional ring of nonlocally coupled discrete-time systems.

## Linear Model of Surface Terahertz Plasmons Amplification in Two Parallel Graphene Sheets

Amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. It is shown that the antisymmetric mode increment of plasmons in the two parallel graphene monolayers may be several times greater than that in a single graphene layer due to deceleration of the antisymmetric plasmon mode as compared to the plasmon mode in a single graphene monolayer.

## On the Theory of Synchronization of a Two-Mode Electron Maser with a Hard Excitation

**Background and Objectives: **Medium-power (10–100 W) THz continuous-wave electron cyclotron masers (gyrotrons) are of great interest for many applications, such as spectroscopy with dynamic nuclear polarization, plasma diagnostics, non-destructive testing, remote detection of radioactive materials, biomedical applications, etc. For these applications, a high frequency stability is required, with the possibility of frequency tuning within 1–2 GHz.

## Complex Dynamics and Chaos in the Rabinovich – Fabrikant Model

**Background and Objectives:** In the work we consider a finitedimensional three-mode model of the nonlinear parabolic equation. It was proposed in 1979 by M. I. Rabinovich and A. L. Fabrikant. It describes the stochasticity arising from the modulation instability in a non-equilibrium dissipative medium with a spectrally narrow amplification increment. The Rabinovich – Fabrikant system presents some extremely rich dynamics die to the third-order nonlinearities presented in the equations. The considered system is universal.

## Numerical Simulation of a Looped Tube 4-Stage Traveling-Wave Thermoacoustic Engine

**Background and Objectives:** The technology of thermoacoustic energy conversion is one of the most promising technologies for converting thermal energy into electrical one. A brief review of the achievements in development of the multi-stage traveling-wave engines was made. The numerical simulation of a 4-stage engine with a load was done. The aim of research was to determine the engine parameters, required to achieve the maximum of efficiency of the system and the acoustic power on the load.

## Lorenz Attractor in a System with Delay: an Example of Pseudogyperbolic Chaos

**Background and Objectives:** The work contributes to a research direction aimed at search for and construction of physically realizable systems, which could fill the mathematical theory of pseudo-hyperbolic dynamics with physical content. Chaotic attractors belonging to this class generate genuine chaos that does not degrade under small variations of parameters and functions in dynamical equations.

## Synchronization of Chimera States in Ensembles of Nonlocally Coupled Cubic Maps

**Background and Objectives: **Effects of mutual and external synchronization of chimera states are studied in two coupled ensembles of discrete maps. Each of the ensembles is a onedimensional ring of nonlocally coupled cubic maps in the chaotic oscillation mode. In order to create differences in the dynamics of the ensembles when there is no coupling between them, a mismatch is introduced in the parameters of the individual oscillators of the first and second rings. Effects of external and mutual synchronization of chimera states are explored in detail.

## Calculation of Focusing Spin Wave Transducers Using the Method of Micromagnetic Simulation

**Background and Objectives:** Researches in the field of electronic circuit development for microwave informational systems based on magnetization oscillations and waves have been performing since the 1960s of the last century. The surge of interest in spin waves (SW) during the last decade is caused by the perspective to use SW as information carriers on the sub-micromagnetic and nanometer scale that leads to the fabrication of devices on magnonic principles and a significant miniaturization of spin-wave devices.