S. Koshevaya

Electrostatic spatially limited solitons in a magnetised dusty plasma

Abstract Spatially limited ion-acoustic and dusty-acoustic solitons in a magnetised dusty plasmas are investigated. The form and characteristic velocities of the solitons are studied, as well as the conditions for the existence of rarefactive and compressional solitons. The special case of a plasma consisting of ions and dust grains is also considered. The work is then applied to the creation of condensates in cometary tails and to Saturns rings, where it provides an alternative explanation for spoke formation.

Excitation of plasma waves in the ionosphere caused by atmospheric acoustic waves

The transformation of atmospheric acoustic waves into plasma waves in the ionosphere is investigated. The transformation mechanism is based on plasma wave exitation by growing acoustic waves, when a frequency/wavelength matching situation is reached. The interaction of acoustic and plasma waves occurs through collisions of neutral particles with ions. For the case of ion-sound waves, oscillations on ion cyclotron frequency and Alfvén waves is considered. A peculiarity of Alfvén waves is the wide frequency band which may be stimulated through wave-wave interaction.

Dispersion Relation for Two-Valley QuasiHydrodynamic Models in SCWs Propagation in n-GaAs Thin Films

The space charge wave propagation in thin n-GaAs films has been considered within a framework of different quasi-hydrodynamic balance models. A comparative study of the dependencies k(omega) of a complex longitudinal wave number on frequency, which are obtained from different balance equation models are presented and discussed. It has been demonstrated that the model where the balance equations are written for different valleys directly seems to be the most correct. The balance models based on averaging over the valleys may lead to incorrect results in the case of long distances of propagation of space charge waves. When the thermal conductivity term is taken into account and the length of the system is short, the averaged balance models can get satisfactory results

Superheterodyne amplification of sub-millimeter electromagnetic waves in an n-GaAs film

A superheterodyne amplification of sub-millimeter electromagnetic waves in GaAs due to the negative differential mobility is analyzed. The nonlinearity arises from the modulation of concentration, due to a space charge wave, and from the ponderomotive force, due to electromagnetic waves. The case of resonant interaction of two traveling counter propagating electromagnetic waves and the space charge wave in a thin n-GaAs film placed into a dielectric waveguide is considered. The case of 2D electron gas is also analyzed. The simulation of this nonlinear interaction shows a certain increment of the amplification.

Influence of nonlocality on amplification of space charge waves in n-GaN films

Amplification of space charge waves (SCW) due to the negative differential conductivity (NDC) in n-GaN films of submicron thicknesses is investigated theoretically. An influence of nonlocal dependence of average electron velocity on the electron energy is considered. The simplest nonlocal model is used where the total electron concentration is taken into account. The relaxation momentum and energy frequencies have been calculated. An influence of nonlocality on NDC results in the decrease of absolute value of its real part and appearance of the imaginary part. The simulations of spatial increments of amplification of SCW demonstrate that nonlocality is essential at frequencies f ≥ 100 GHz, and amplification is possible up till the frequencies f ≤ 400…500 GHz.

Nonlinear spatiotemporal focusing of terahertz pulses in the structures with graphene layers

The nonlinear interaction of transversely bounded terahertz pulses with layered structures that include graphene layers is investigated theoretically. The nonlinearity possesses the focusing character both in longitudinal and transverse directions. There exist the optimum input amplitudes and transverse widths of the input pulse to get the maximum pulse compression.

Collapse of nonlinear surface dust sound waves in the dusty plasma–dielectric system

The nonlinear monopulses of surface dust sound waves in the dusty plasma–dielectric system are investigated. The dusty plasma includes positive ions as the light component and negative dust as the heavy one. The set of hydrodynamic equations for dust in addition to the Poisson equation is used. The Boltzmann distribution is used for the ions. Electric and hydrodynamic boundary conditions are applied to the smooth interface. When moderate nonlinearity manifests itself near the interface, variations of dust concentration reach extremely high values, and collapse of the surface dust sound waves occurs. Estimations have demonstrated that the above-mentioned phenomena can be observed in natural dusty plasmas such as under volcano eruptions.

Excitation of vortices using linear and nonlinear magnetostatic waves.

It is shown that stationary vortex structures can be excited in a ferrite film, in the important centimeter and millimeter wavelength ranges. It is shown that both linear and nonlinear structures can be excited using a three-beam interaction created with circular antennas. These give rise to a special phase distribution created by linear and nonlinear mixing. An interesting set of three clockwise rotating vortices joined by one counter-rotating one presents itself in the linear regime: a scenario that is only qualitatively changed by the onset of nonlinearity. It is pointed out that control of the vortex structure, through parametric coupling, based upon a microwave resonator, is possible and that there are many interesting possibilities for applications.

Amplification of space charge waves in n-InN films of THz range

The instability of space charge waves (SCW) of THz range due to the negative differential conductivity (NDC) in n-InN films of submicron thicknesses is investigated theoretically. The influence of the nonlocal dependence of the average electron velocity on the electron energy is considered. The momentum and energy relaxation frequencies are calculated. The influence of the nonlocality on NDC decreases the absolute value of its real part. The nonlocality is essential at the frequencies f ≥ 250 GHz, and the amplification is possible up till the frequencies f ≤ 800 GHz. The increments in n-InN films are 10 times higher than in n-GaN ones, but the frequency range is mainly determined by smaller energy relaxation frequencies in n-InN.

Modulation instability of terahertz electromagnetic pulses in SrTiO 3 paraelectric

It is investigated the modulation instability of terahertz electromagnetic waves in paraelectric crystals SrTiO3 at the temperatures 77 K. The cubic nonlinearity and the frequency dispersion correspond to the existence of bright envelope solitons and the modulation instability of long input pulses. The threshold of modulation instability can be reduced by reflection at the boundaries of the crystal. There is a possibility to generate the sequences of short terahertz pulses due to the modulation instability.