Now showing 1 - 6 of 6
• Publication
Coexistence of negative and positive polarity electrostatic solitary waves in ultradense relativistic negative-ion-beam permeated plasmas
(2018)
The criteria for occurrence and the dynamical features of electrostatic solitary waves in a homogeneous, unmagnetized ultradense plasma penetrated by a negative ion beam are investigated, relying on a quantum hydrodynamic model. The ionic components are modeled as inertial fluids, while the relativistic electrons obey Fermi-Dirac statistics. A new set of exact analytical conditions for localized solitary pulses to exist is obtained, in terms of plasma density. The algebraic analysis reveals that these depend sensitively on the negative ion beam characteristics, that is, the beam velocity and density. Particular attention is paid to the simultaneous occurrence of positive and negative potential pulses, identified by their respective distinct ambipolar electric field structure forms. It is shown that the coexistence of positive and negative potential pulses occurs in a certain interval of parameter values, where the ion beam inertia becomes significant.
• Publication
Dissipative high-frequency envelope soliton modes in nonthermal plasmas
(2018)
The linear and nonlinear properties of modulated high-frequency (electron-acoustic) electrostatic wave packets are investigated via a fluid-dynamical approach. A three-component plasma is considered, composed of two types of electrons at different temperatures (“cold” and “hot” electrons) evolving against a cold stationary ion background. A weak dissipative effect is assumed, due to electron-neutral collisions. While the cold electrons are treated as an inertial fluid, the hot electrons are assumed to be in a non-Maxwellian state, described by a kappa ($\kappa$) type distribution. The linear characteristics of electron-acoustic waves are analyzed in detail, and a linear dispersion relation is obtained. Weakly damped electrostatic waves are shown to propagate above a wave number k threshold, whose value is related to dissipation (and reduces to zero in its absence). Long-wavelength values (i.e., for k below that threshold) are heavily damped and no propagation occurs. The nonlinear dynamics (modulational self-interaction) of wave packets in the propagating region is modeled via a dissipative nonlinear Schr{\"{o}}dinger type equation, derived via a multiscale perturbation technique for the wave envelope, which includes a dissipative term associated with the finite imaginary part of the nonlinearity term. The dynamical and structural characteristics (speed, amplitude, width) of dissipative localized modes representing the amplitude of modulated electron-acoustic wave packets in a collisional plasma are thus investigated for various values of relevant plasma (configuration) parameters, namely the superthermality index $\kappa$, the cold-to-hot electron density ratio, and collisionality (strength). Our analytical predictions are tested by computer simulations. A quasilinear perturbation method for near-integrable systems leads to a theoretical prediction for the wave amplitude decay, which is shown to match our numerical result. The results presented in this paper should be useful in understanding the dynamics of localized electrostatic disturbances in space plasmas, and also in laboratory plasmas, where the combined effect(s) of excess energetic (suprathermal) electrons and (weak) electron-neutral collisions may be relevant.
• Publication
Electrostatic shock structures in dissipative multi-ion dusty plasmas
(2018)
A comprehensive analytical model is introduced for shock excitations in dusty bi-ion plasma mixtures, taking into account collisionality and kinematic (fluid) viscosity. A multicomponent plasma configuration is considered, consisting of positive ions, negative ions, electrons, and a massive charged component in the background (dust). The ionic dynamical scale is focused upon; thus, electrons are assumed to be thermalized, while the dust is stationary. A dissipative hybrid Korteweg–de Vries/Burgers equation is derived. An analytical solution is obtained, in the form of a shock structure (a step-shaped function for the electrostatic potential, or an electric field pulse) whose maximum amplitude in the far downstream region decays in time. The effect of relevant plasma configuration parameters, in addition to dissipation, is investigated. Our work extends earlier studies of ion-acoustic type shock waves in pure (two-component) bi-ion plasma mixtures.
• Publication
Kinetic Alfvén solitary waves in a plasma with two-temperature superthermal electron populations: the case of Saturn’s magnetosphere
(2019)
Singh, Manpreet
;
Saini, N S
Thanks to the evidence provided by the Cassini spacecraft mission, it is now established that Saturn’s magnetospheric plasma consists of various types of positive ions, as well as two distinct populations of electrons, at different temperatures. The electron population energy distributions are characterized by long suprathermal tails and have been effectively modelled by kappa-type distributions. Plasma properties are known to vary along the radial direction. A strong magnetic field penetrates the magnetosphere, hence the plasma beta is small, β < 1 for radial distance < 15.2RS (where RS = 60 330 km is the Saturn’s radius). Motivated by these observations, we have investigated the conditions for existence and the dynamics of linear and non-linear kinetic Alfv´en waves (KAWs) in Saturn’s magnetosphere. We have considered a low-β (stronglymagnetized) plasma, comprising of positive ions and two electron populations (‘cold’ and ‘hot’) characterized by non-Maxwellian (kappa) distributions. In the small-amplitude regime, harmonic analysis leads to a linear dispersion relation bearing explicit dependence on the characteristics of the suprathermal components. In the nonlinear regime, large-amplitude stationary profile kinetic Alfv´en solitary wave solutions are obtained via a two-component pseudopotential method, associated with either positive or negative potential structures (pulses) propagating at sub- and super-Alfv´enic speeds, respectively. The effect of various intrinsic plasma configuration properties (hot-to-cold electron density and temperature ratio; superthermality indices κc and κh; plasma beta) as well as propagation parameters (pulse speed, direction of propagation) on the characteristics of KAW solitary waves are discussed
• Publication
On a semiclassical model for ion-Acoustic solitons in ultrarelativistic pair plasmas and its classical counterpart
(2019)
Large ion-acoustic solitary waves are investigated in a multispecies plasma model consisting of warm positive ions in the presence of ultrarelativistic electrons and positrons, in a Sagdeev pseudopotential formalism. A parametric investigation determines existence regions in terms of fractional densities, temperature ratios, and soliton speeds. Various examples of pseudopotential functional forms, as well as those of the resulting soliton and electric field profiles, can then be generated numerically, and some typical illustrations have been included. Rather than adiabatic pressure-density relations for the hot species, the classical nonrelativistic counterpart involves Boltzmann distributions, which differ qualitatively from the literature. Surprisingly, the soliton and electric field profiles show scant differences at the same compositional parameters between the two extremes even though the physical description of the hot species is radically different. A brief comparison has also been included between the fully nonlinear Sagdeev pseudopotential descriptions and their respective associated weak-amplitude limits (treated via a reductive perturbation technique) in which nonlinearities have been truncated to low powers of the electrostatic potential. Again, the soliton profiles are not radically different at comparable amplitudes, leaving the underlying physical reasons for such a similarity an open problem.