arXiv subjects

Volodymyr M. Lashkin

Publications and source records attributed to Volodymyr M. Lashkin.

14 recordsLinked to original sources

arXiv2025

Interaction of upper hybrid waves with dust-ion-magnetoacoustic waves and stable two-dimensional solitons in dusty plasmas

We obtain a two-dimensional nonlinear system of equations for the electrostatic potential envelope and the low-frequency magnetic field perturbation to describe the interaction of the upper hybrid wave propagating perpendicular to an external magnetic field with the dust-ion-magnetoacoustic (DIMA) wave in a magnetized dusty plasma. The equations contain both scalar and vector nonlinearities. A nonlinear dispersion relation is derived and the decay and modulation instability thresholds and growth rates are obtained. Numerical estimates show that instability thresholds can easily be exceeded in real dusty plasmas. In the static (subsonic) approximation, a two-dimensional (2D) soliton solution (ground state) is found numerically by the generalized Petviashvili relaxation method. The perturbations of the magnetic field and plasma density in the soliton are nonmonotonic in space and, along with the perturbation in the form of a well, there are also perturbation humps. Such peculiar radial soliton profiles differ significantly from previously known results on 2D solitons. The key point is that the presence of a gap in the DIMA wave dispersion due to the Rao cutoff frequency causes the nonlinearity to be nonlocal. We show that due to nonlocal nonlinearity the Hamiltonian is bounded below at fixed energy, proving the stability of the ground state.

physics.plasm-ph↗

arXiv2024

Modulational instability and collapse of internal gravity waves in the atmosphere

Nonlinear two-dimensional internal gravity waves (IGWs) in the atmospheres of the Earth and the Sun are studied. The resulting two-dimensional nonlinear equation has the form of a generalized nonlinear Schrödinger equation with nonlocal nonlinearity, that is when the nonlinear response depends on the wave intensity at some spatial domain. The modulation instability of IGWs is predicted, and specific cases for the Earth's atmosphere are considered. In a number of particular cases, the instability thresholds and instability growth rates are analytically found. Despite the nonlocal nonlinearity, we demonstrate the possibility of critical collapse of IGWs due to the scale homogeneity of the nonlinear term in spatial variables.

nlin.PS↗

arXiv2024

Three-dimensional solitons in fractional nonlinear Schrödinger equation with exponential saturating nonlinearity

We study the fractional three-dimensional (3D) nonlinear Schrödinger equation with exponential saturating nonlinearity. In the case of the Lévy index $α=1.9$, this equation can be considered as a model equation to describe strong Langmuir plasma turbulence. The modulation instability of a plane wave is studied, the regions of instability depending on the Lévy index, and the corresponding instability growth rates are determined. Numerical solutions in the form of 3D fundamental soliton (ground state) are obtained for different values of the Lévy index. It was shown that in a certain range of soliton parameters it is stable even in the presence of a sufficiently strong initial random disturbance, and the self-cleaning of the soliton from such initial noise was demonstrated.

nlin.PS↗

arXiv2024

Dynamics of multidimensional fundamental and vortex solitons in random media

We study the dynamics of fundamental and vortex solitons in the framework of the nonlinear Schrödinger equation with the spatial dimension $D\geqslant 2$ with a multiplicative random term depending on the time and space coordinates. To this end, we develop a new technique for calculating the even moments of the $N$th order. The proposed formalism does not use closure procedures for the nonlinear term, as well as the smallness of the random term and the use of perturbation theory. The essential point is the quadratic form of the autocorrelation function of the random field and the special stochastic change of variables. Using variational analysis to determine the field of structures in the deterministic case, we analytically calculate a number of statistical characteristics describing the dynamics of fundamental and vortex solitons in random medium, such as the mean intensities, the variance of the intensity, the centroid and spread of the structures, the spatial mutual coherence function etc. In particular, we show that, under the irreversible action of fluctuations, the solitons spread out, i.e., no collapse occurs.

nlin.PS↗

arXiv2024

Nonlinear theory of the modulational instability at the ion-ion hybrid frequency and collapse of ion-ion hybrid waves in two-ion plasmas

We study the dynamics of two-dimensional nonlinear ion-ion hybrid waves propagating perpendicular to an external magnetic field in plasmas with two ion species. We derive nonlinear equations for the envelope of electrostatic potential at the ion-ion hybrid frequency to describe the interaction of ion-ion hybrid waves with low frequency acoustic-type disturbances. The resulting nonlinear equations also take into account the contribution of second harmonics of the ion-ion hybrid frequency. A nonlinear dispersion relation is obtained and, for a number of particular cases, the modulational instability growth rates are found. By neglecting the contribution of second harmonics, the phenomenon of collapse of ion-ion hybrid waves is predicted. It is shown that taking into account the interaction with the second harmonics results in the existence of a stable two-dimensional soliton.

nlin.PS↗

arXiv2024

Self-consistent equilibrium of a helical magnetic flux rope in a finite-pressure plasma

We present an analytical model of the self-consistent equilibrium of a magnetic flux rope which is obtained in cylindrical geometry. The equilibrium azimuthal magnetic field and plasma pressure are determined in a self-consistent way through the current density which is derived as a solution of a nonlinear equation. By minimizing the energy functional, it was shown that the constrained equilibrium state is stable. The obtained results are also applicable to the cylindrical tokamak magnetic configurations. It is shown that the analytically predicted radial profiles of equilibrium quantities are in good agreement with the experimental data.

nlin.PS↗

arXiv2024

Fourth-order modon in a rotating self-gravitating fluid

We present a two-dimensional nonlinear equation to govern the dynamics of disturbances in a rotating self-gravitating fluid. The nonlinear term of the equation has the form of a Poisson bracket (Jacobian), and the linear part contains, along with the Laplacian, a biharmonic operator. A solution was found in the form of a dipole vortex (modon). The solution and all its derivatives up to the fourth order are continuous on the separatrix.

nlin.PS↗

arXiv2023

Nonlinear internal gravity waves in the atmosphere: Rogue waves, breathers and dark solitons

We study nonlinear internal gravity waves (IGWs) in the atmosphere. The reductive perturbation method is used to derive a system of two-dimensional nonlinear equations for the envelope of velocity stream function and the mean flow. In the one-dimensional case, we obtain a nonlinear Schrödinger (NLS) equation corresponding to both horizontal and vertical propagation of IGWs. Depending on the characteristic wavelengths, the NLS equation is focusing or defocusing. In the focusing case, non-stationary solutions in the form of the Peregrine soliton, the Akhmediev breather and the Kuznetsov-Ma breather are considered as potential candidates for the modeling of rogue waves in the atmosphere. In the defocusing case, stationary nonlinear IGWs are considered in the form of nonlinear periodic waves and dark solitons.

nlin.PS↗

arXiv2023

Three-dimensional vortex dipole solitons in self-gravitating systems

We derive the nonlinear equations governing the dynamics of three-dimensional (3D) disturbances in a nonuniform rotating self-gravitating fluid under the assumption that the characteristic frequencies of disturbances are small compared to the rotation frequency. Analytical solutions of these equations are found in the form of the 3D vortex dipole solitons. The method for obtaining these solutions is based on the well-known Larichev-Reznik procedure for finding two-dimensional nonlinear dipole vortex solutions in the physics of atmospheres of rotating planets. In addition to the basic 3D x-antisymmetric part (carrier), the solution may also contain radially symmetric (monopole) or/and antisymmetric along the rotation axis (z-axis) parts with arbitrary amplitudes, but these superimposed parts cannot exist without the basic part. The 3D vortex soliton without the superimposed parts is extremely stable. It moves without distortion and retains its shape even in the presence of an initial noise disturbance. The solitons with parts that are radially symmetric or/and z-antisymmetric turn out to be unstable, although at sufficiently small amplitudes of these superimposed parts, the soliton retains its shape for a very long time.

nlin.PS↗

arXiv2022

Coupling of acoustic and drift modes, harmonic modons in astrophysical dusty plasma and a new mode in the Comet Halley

This manuscript, presents a theoretical study of the linear and nonlinear characteristics of acoustic and drift waves in a bounded inhomogenious dusty plasma which has potential applications in space and lab environments. In this analysis, flow of all plasma particles is assumed to be along the axial direction whereas gradients in velocity are considered to be along the radial direction. First we study coupling of dust modified ion acoustic (DMA) and drift (DMD) waves (linear analysis) at fast time when dynamics of dust remain inactive, later formation of nonlinear vortex like structures are examined. In the second case at slow time when dust participates in dynamics, coupling between ultra low frequency dust acoustic (UDA) and dust drift (ULD) waves is studied and modons like solutions are obtained in the nonlinear analysis. Existence of the vortex solution with azimuthal harmonics higher than the dipole vortex has been studied both analytically and numerically. Later we extend our analysis to consider applications of dust particle's presence in the comet Halley and tropical mesospheric dusty plasma where in earlier case we report that that unexpectedly comet Halley plasma admits a new mode where presence of dust in background does not have any affect, this mode is similar to the convective cell mode where electrostatic drift (ExB) cancels out, density gradients also vanish due to the presence of negative ions and only polarization drift contributes to the mode. For the linear analysis of this mode, there is no coupling observed but this the convective cell mode evolves whereas nonlinear dynamics of this mode are found to obey the vortex-like solution.

physics.plasm-ph↗

arXiv2021

Short-wavelength soliton in a fully degenerate quantum plasma

We present a novel one-dimensional nonlinear evolution equation governing the dynamics short-wavelength longitudinal waves in a nonrelativistic fully degenerate quantum plasma using kinetic equation for the Wigner function. The linear dispersion of the equation has a form of "zero sound" $\sim k\exp (-k^{2})$, where $k$ is the wave number, and it strongly differs from previously known nonlinear evolution equations. We numerically find the corresponding soliton solutions and demonstrate that the collisions between three solitons turn out to be elastic resulting only in phase shifts.

nlin.PS↗

arXiv2020

Stable three-dimensional Langmuir vortex soliton

We present a numerical solution in the form of a three-dimensional (3D) vortex soliton in unmagnetized plasma in the model of the generalized Zakharov equations with saturating exponential nonlinearity. To find the solution with a high accuracy we use two-step numerical method combining the Petviashvili iteration procedure and the Newton-Kantorovich method. The vortex soliton with the topological charge $m=1$ turns out to be stable provided the nonlinear frequency shift exceeds a certain critical value. The stability predictions are verified by direct simulations of the full dynamical equation.

nlin.PS↗

arXiv2017

Stable three-dimensional modon soliton in plasmas

We derive the nonlinear equations that describe coupled drift waves and ion acoustic waves in a plasma. We show that when the coupling to ion acoustic waves is negligible, the reduced nonlinear equation is a generalization of the Hasegawa-Mima equation to the three-dimensional (3D) case. We find an exact analytical solution of this equation in the form 3D soliton drift wave (3D modon). By numerical simulations we study collisions between the modons and show that the collisions can be fully elastic.

nlin.PS↗

arXiv2007

Two-dimensional multisolitons and azimuthons in Bose-Einstein condensates with attraction

We present spatially localized nonrotating and rotating (azimuthon) multisolitons in the two-dimensional (2D) ("pancake-shaped configuration") Bose-Einstein condensate (BEC) with attractive interaction. By means of a linear stability analysis, we investigate the stability of these structures and show that rotating dipole solitons are stable provided that the number of atoms is small enough. The results were confirmed by direct numerical simulations of the 2D Gross-Pitaevskii equation.

nlin.PS↗