Ehsan Saberian - Academia.edu (original) (raw)

Papers by Ehsan Saberian

We have formulated the invariant ion-acoustic waves (IAWs) in the astrophysical plasmas including... more We have formulated the invariant ion-acoustic waves (IAWs) in the astrophysical plasmas including the pure thermodynamic features of the background particles. Here, we have used the modern version of the kappa distribution formalism, where it is labeled with an invariant kappa index as of the zero dimensionality spectral index, κ0. Two contexts for studying the invariant IAWs have been employed, i.e., the kinetic theory formalism and the hydrodynamic fluid description. At first, we have employed the Vlasov-Poisson equations at the low frequency band of the weakly damped ion waves, where the most generalized formalism of the ion-sound speed has been confirmed in terms of the extended polytropic indices of the plasma species, γj. Furthermore, the Landau damping of IAWs has been formulated in terms of κ0, the wavelength, and the temperatures of the plasma species. In the hydrodynamic description, we have normalized the fluid parameters by using the extended quantities, including the ge...

Cornell University - arXiv, Apr 17, 2012

Propagation of ion-acoustic solitary waves (IASWs) is studied using the hydrodynamic equations co... more Propagation of ion-acoustic solitary waves (IASWs) is studied using the hydrodynamic equations coupled with the Poisson equation in a warm plasma consisting of adiabatic ions and superthermal (Kappa distributed) electrons in presence of an electron-beam component. In the linear limit, the dispersion relation for ion-acoustic (IA) waves is obtained by linearizing of basic equations. On the other hand, in the nonlinear analysis, an energy-balance like equation involving Sagdeev's pseudo-potential is derived in order to investigate arbitrary amplitude IA solitons. The Mach number range is determined in which, propagation and characteristics of IA solitons are analyzed both parametrically and numerically. The variation of amplitude and width of electrostatic (ES) excitations as a result of superthermality (via) and also the physical parameters (ion temperature, soliton speed, electron-beam density and electron-beam velocity) are examined. A typical interaction between IASWs and the electron-beam in plasma is confirmed. It is also found that ES solitons with both negative polarity (rarefactive solitons) and positive polarity (compressive solitons) can coexist in plasma. Furthermore, the small but finite amplitude limit of IASWs is investigated and it is showed that this limit is restricted to negative potential pulses.

Plasma Physics and Controlled Fusion, 2020

The Open Plasma Physics Journal, 2015

The occurrence and propagation of large amplitude dust-acoustic solitary waves (DASWs) are studie... more The occurrence and propagation of large amplitude dust-acoustic solitary waves (DASWs) are studied in a three-component plasma consisting of negatively charged dust grains and electron-positron pairs by employing a pseudopotential technique. Here, we focus on a superthermal plasma modeled by alike distribution and consider a finite temperature for dust particulates. It is shown that the solitary waves with negative polarity are allowed in the system and there is a critical value for dust charge Z d above/below which the subsonic/supersonic solitary structures can propagate. In the case of negative fullerene ions, Z d = 1, it is observed that subsonic DASWs can propagate in the plasma. In addition, it is revealed that the propagation of double layers is not possible in this plasma system.

Plasma and Fusion Research, 2010

Arbitrary amplitude ion-acoustic solitary waves (IASWs) are studied using Sagdeev-Potential appro... more Arbitrary amplitude ion-acoustic solitary waves (IASWs) are studied using Sagdeev-Potential approach in electron-positron-ion plasma with ultra-relativistic or non-relativistic degenerate electrons and positrons and the matching criteria of existence of such solitary waves are numerically investigated. It has been shown that the relativistic degeneracy of electrons and positrons has significant effects on the amplitude and the Mach-number range of IASWs. Also it is remarked that only compressive IASWs can propagate in both non-relativistic and ultra-relativistic degenerate plasmas.

Physics of Plasmas, 2013

ABSTRACT The propagation of ion-acoustic (IA) solitons is studied in a plasma system, comprised o... more ABSTRACT The propagation of ion-acoustic (IA) solitons is studied in a plasma system, comprised of warm ions and superthermal (Kappa distributed) electrons in the presence of an electron-beam by using a hydrodynamic model. In the linear analysis, it is seen that increasing the superthermality lowers the phase speed of the IA waves. On the other hand, in a fully nonlinear investigation, the Mach number range and characteristics of IA solitons are analyzed, parametrically and numerically. It is found that the accessible region for the existence of IA solitons reduces with increasing the superthermality. However, IA solitons with both negative and positive polarities can coexist in the system. Additionally, solitary waves with both subsonic and supersonic speeds are predicted in the plasma, depending on the value of ion-temperature and the superthermality of electrons in the system. It is examined that there are upper critical values for beam parameters (i.e., density and velocity) after which, IA solitary waves could not propagate in the plasma. Furthermore, a typical interaction between IA waves and the electron-beam in the plasma is confirmed.

Physical Review E, 2013

The Langmuir oscillations, Landau damping, and growing unstable modes in an electron-positron (EP... more The Langmuir oscillations, Landau damping, and growing unstable modes in an electron-positron (EP) plasma are studied by using the Vlasov and Poisson's equations in the context of the Tsallis's nonextensive statistics. Logically, the properties of the Langmuir oscillations in a nonextensive EP plasma are remarkably modified in comparison with that of discussed in the Boltzmann-Gibbs statistics, i.e., the Maxwellian plasmas, because of the system under consideration is essentially a plasma system in a nonequilibrium stationary state with inhomogeneous temperature. It is found that by decreasing the nonextensivity index q which corresponds to a plasma with excess superthermal particles, the phase velocity of the Langmuir waves increases. In particular, depend on the degree of nonextensivity, both of damped and growing oscillations are predicted in a collisionless EP plasma, arise from a resonance phenomena between the wave and the nonthermal particles of the system. Here, the mechanism leads to the unstable modes is established in the context of the nonextensive formalism yet the damping mechanism is the same developed by Landau. Furthermore, our results have the flexibility to reduce to the solutions of an equilibrium Maxwellian EP plasma (extensive limit q → 1), in which the Langmuir waves are only the Landau damped modes.

Canadian Journal of Physics, 2011

The propagation of large amplitude ion-acoustic solitary waves (IASWs) in a fully relativistic pl... more The propagation of large amplitude ion-acoustic solitary waves (IASWs) in a fully relativistic plasma consisting of cold ions and ultra-relativistic hot electrons and positrons is investigated using the Sagdeev pseudopotential method in a relativistic hydrodynamics model. The effects of streaming speed of the plasma fluid, thermal energy, positron density, and positron temperature on large amplitude IASWs are studied by analysis of the pseudopotential structure. It is found that in regions in which the streaming speed of the plasma fluid is larger than that of the solitary wave, by increasing the streaming speed of the plasma fluid, the depth and width of the potential well increase, resulting in narrower solitons with larger amplitude. This behavior is opposite to the case where the streaming speed of the plasma fluid is less than that of the solitary wave. On the other hand, an increase in the thermal energy results in wider solitons with smaller amplitude, because the depth and w...

Astrophysics and Space Science, 2013

The low-frequency acoustic-like modes in a pair plasma (electron-positron or pairion) is studied ... more The low-frequency acoustic-like modes in a pair plasma (electron-positron or pairion) is studied by employing a kinetic theory model based on the Vlasov and Poisson's equation with emphasizing the Tsallis's nonextensive statistics. The possibility of the acoustic-like modes and their properties in both fully symmetric and temperatureasymmetric cases are examined by studying the dispersion relation, Landau damping and instability of modes. The resultant dispersion relation in this study is compatible with the acoustic branch of the experimental data [W. Oohara, D. Date, and R. Hatakeyama, Phys. Rev. Lett. 95, 175003 (2005)], in which the electrostatic waves have been examined in a pure pair-ion plasma. Particularly, our study reveals that the occurrence of growing or damped acoustic-like modes depends strongly on the nonextensivity of the system as a measure for describing the long-range Coulombic interactions and correlations in the plasma. The mechanism that leads to the unstable modes lies in the heart of the nonextensive formalism yet, the mechanism of damping is the same developed by Landau. Furthermore, the solutions of acoustic-like waves in an equilibrium Maxwellian pair plasma are recovered in the extensive limit (q → 1), where the acoustic modes have only the Landau damping and no growth.