arXiv subjects

M. Akbari-Moghanjoughi

Publications and source records attributed to M. Akbari-Moghanjoughi.

50 records · Page 3Linked to original sources

arXiv2011

Spin-induced localized density excitations in quantum plasmas

In this paper the dominant effect of electron inertia on the dynamics of localized density excitations is studied in a quantum plasma in the presence of electron spin effects. Using the quantum magnetohydrodynamics (QMHD) model including electron tunneling and spin polarization phenomena, it is revealed that the quantum effects such as plasma paramagnetism and diamagnetism play inevitable role on soliton existence criteria in quantum plasmas. Furthermore, it is shown that the magnetosonic localized density-excitation stability depends strongly on the quantum system dimensionality. Two distinct region of soliton stability is shown to exist depending on the value of the electron effective mass, where, the soliton amplitude variation with respect to the external magnetic field strength is quite opposite in these regions. Current findings can be important in the study of dynamical nonlinear wave features in dense laboratory or inertial-confined plasmas.

physics.plasm-ph↗

arXiv2011

Comment on "Interaction of two solitary waves in quantum electron-positron-ion plasma" [Phys. Plasmas \textbf{18}, 052301 (2011)]

Recently, Yan-Xia Xu, et al. in the article Ref. [Phys. Plasmas \textbf{18}, 052301 (2011)] have studied the effects of various plasma parameters on interaction of two ion-acoustic solitary waves in an unmagnetized three-dimensional electron-positron-ion quantum plasma. They have used the extended reductive perturbation technique, the so-called, extended Poincare'-Lighthill-Kuo (PLK) technique, to deduce from the model governing the quantum hydrodynamics (QHD) differential equations leading to the soliton dynamical properties, namely, Korteweg-de Vries evolution equations (one for each wave) and coupled differential equations describing the phase-shift in trajectories of solitons due to the two dimensional collision. The variation of the calculated collision phase-shifts are then numerically inspected in terms of numerous plasma fractional parameters. In this comment we give some notes specific to the validity of the results of above-mentioned article and refer to important misconceptions about the use of the Fermi-temperature in quantum plasmas, appearing in this article and many other recently published ones.

physics.plasm-ph↗

arXiv2011

Quantum collapse in ground-state Fermi-Dirac-Landau plasmas

It is revealed that in a relativistically degenerate dense highly-magnetized electron-ion plasma the effective quantum-potential due to the total quantum-force acting on fermions may cancel-out causing a quantum transverse collapse in the ground-state Fermi-Dirac-Landau (GSFDL) plasma. The condition for the plasma transverse collapse is found to be restricted to the minimum relativistic degeneracy parameter and minimum impressed magnetic field strength values satisfied for many superdense astrophysical objects such as white dwarfs and neutron stars. In such plasmas, the magnetization pressure is shown to cancel the lateral electron degeneracy pressure counteracting the existing gravitational pressure. Furthermore, using the Sagdeev pseudopotential method in the framework of quantum magnetohydrodynamics (QMHD) model including spin magnetization it is confirmed that the quantum pressure due to spin-orbit polarization and the electron relativistic degeneracy has significant effects on the existence criteria and the propagation of localized magnetosonic density excitations in GSFDL plasmas. Current findings can have important implications for the density excitations mechanism and gravitational collapse of the highly magnetized astrophysical relativistically dense objects such as white-dwarfs, neutron stars, magnetars and pulsars.

astro-ph.SR↗

arXiv2011

Remarkable paramagnetic features of Fermi-Dirac plasmas

In this paper by using the relativistic magnetic susceptibility of a Fermi-Dirac (relativistically degenerate) plasma, quantum magnetohydrodynamics (QMHD) model is used to investigate the propagation of spin-induced (SI) magnetosonic nonlinear excitations in a normally and relativistically degenerate dense electron-ion plasma in the presence of the spin magnetization effect. Based on the conventional pseudopotential method the matching criterion for the evolution of SI solitary structures is evaluated. It is found that, the plasma mass density and strength of the magnetic field have significant effects on excitation and evolution of magnetosonic nonlinear structures in Fermi-Dirac plasmas. Only rarefactive SI magnetosonic solitary structures are found to excite in such plasmas. Furthermore, fundamental differences are shown to exist in magnetosonic soliton dynamics in the two distinct plasma degeneracy regimes, which is due to interplay between the negative spin paramagnetism pressure-like and positive relativistic degeneracy pressure of electrons. Current investigation can help better understand the electron spin effects on nonlinear wave propagations in strongly magnetized dense astrophysical objects such as white dwarfs and pulsar magnetospheres.

astro-ph.SR↗

arXiv2011

Global limits on kinetic Alfvénon speed in quasineutral plasmas

Large amplitude kinetic Alfvénon (exact Alfvén soliton) matching condition is investigated in quasineutral electron-ion and electron-positron-ion plasmas immersed in a uniform magnetic field. Using the standard pseudopotential method, the magnetohydrodynamics (MHD) equations are exactly solved and a global allowed matching condition for propagation of kinetic solitary waves is derived. It is remarked that, depending on the plasma parameters, the kinetic solitons can be sub- or super-Alfvénic, in general. It is further revealed that, either upper or lower soliton speed-limit is independent of fractional plasma parameters. Furthermore, the soliton propagation angle with respect to that of the uniform magnetic field is found to play a fundamental role in controlling the soliton matching speed-range.

physics.plasm-ph↗

arXiv2011

Propagation of ion-acoustic solitary waves in a relativistic electron-positron-ion plasma

Propagation of large amplitude ion-acoustic solitary waves (IASWs) in a fully relativistic plasma consisting of cold ions and ultrarelativistic hot electrons and positrons is investigated using the Sagdeev's pseudopotential method in a relativistic hydrodynamics model. Effects of streaming speed of 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 that the streaming speed of plasma fluid is larger than that of solitary wave, by increasing the streaming speed of plasma fluid the depth and width of potential well increases and resulting in narrower solitons with larger amplitude. This behavior is opposite for the case where the streaming speed of plasma fluid is smaller than that of solitary wave. On the other hand, increase of the thermal energy results in wider solitons with smaller amplitude, because the depth and width of potential well decreases in that case. Additionally, the maximum soliton amplitude increases and the width becomes narrower as a result of increase in positron density. It is shown that varying the positron temperature does not have considerable effect on the width and amplitude of IASWs. The existence of stationary soliton-like arbitary amplitude waves is also predicted in fully relativistic electron-positron-ion (EPI) plasmas. Effects of streaming speed of plasma fluid, thermal energy, positron density and positron temperature on these kinds of solitons are the same as that for large amplitude IASWs.

physics.plasm-ph↗

arXiv2011

Generalized matching criterion for electrostatic ion solitary propagations in quasineutral magnetized plasmas

Based on the magnetohydrodynamics (MHD) model, an exact arbitrary-amplitude general solution is presented for oblique propagation of solitary excitations in two- and three-component quasineutral magnetoplasmas, adopting the standard pseudopotential approach. It is revealed that the necessary matching criterion of existence of such oblique nonlinear propagations in two and three-fluid magnetoplasmas share global features. These features are examined for the cases of electron-ion and electron-positron-ion magnetoplasmas with diverse equations of state. This study also reveals that for electron-ion magnetoplasmas with plasma-frequencies larger than the cyclotron-frequency ($B_0<0.137\sqrt{n_0}$) a critical-angle of $β_{cr}=\arccos{\left[B_0 /(0.137 \sqrt{n_0})\right]}$ exists, at which propagation of solitary excitation is not possible. Coriolis effect on allowed soliton matching condition in rotating magnetoplasmas is also considered as an extension to this work. Current investigation can have important implications for nonlinear wave dynamics in astrophysical as well as laboratory magnetoplasmas.

physics.plasm-ph↗

arXiv2011

Dynamics of nonlinear ion-waves in Fermi-Dirac electron-positron-ion magnetoplasmas

Oblique propagation and head-on collisions of solitary structures is studied in a dense magnetized plasma comprised of relativistic ultra-cold electrons and positrons and positive dynamic ions using conventional extended multi-scales technique, in the ground of quantum hydrodynamics model. The variations of head-on collision phase-shift as well as the characteristic soliton amplitude and width is evaluated numerically in terms of other plasma parameters such as mass-density, normalized magnetic field strength, its angle with respect to the soliton propagation and the relative positron number-density. The relevance of current investigations, with appropriate plasma parameters for the astrophysical dense magnetized objects such as white-dwarfs, is addressed.

astro-ph.SR↗

arXiv2011

Propagation and oblique collision of electron-acoustic solitons in two-electron-populated quantum plasmas

Oblique interaction of small- but finite-amplitude KdV-type electron-acoustic solitary excitations is examined in an unmagnetized two-electron-populated degenerate quantum electron-ion plasma in the framework of quantum hydrodynamics model using the extended Poincaré-Lighthill-Kuo (PLK) perturbation method. Critical plasma parameter is found to distinguish the types of solitons and their interaction phase-shifts. It is shown that, depending on the critical quantum diffraction parameter $H_{cr}$, both compressive and rarefactive solitary excitations may exist in this plasma and their collision phase-shifts can be either positive or negative for the whole range of the collision angle $0<θ<π$.

astro-ph.SR↗

arXiv2011

Nonlinear ion waves in Fermi-Dirac pair plasmas

Arbitrary amplitude nonlinear ion waves is investigated in an extremely degenerate electron-positron-ion plasma with relativistic electrons/positrons and dynamic cold ions using Sagdeev pseudo-potential method in framework of quantum hydrodynamics model. The matching criteria of existence for ion solitary as well as periodic nonlinear excitations is studied numerically in terms of the relativistic degeneracy parameter, relative positron concentration and the relativistic normalized propagation-speed range of these waves are obtained. It is remarked that the electron relativistic degeneracy and relative positron concentration in such plasmas have significant effects on nonlinear wave propagations in relativistically degenerate Fermi-Dirac plasma. Our results are in good agreement with the previously reported ones obtained using semiclassical Thomas-Fermi approximation in dense plasmas with non-relativistic and ultra-relativistic electrons and positrons. Current findings can be appropriate for the study of astrophysical superdense compact objects such as white dwarfs.

astro-ph.SR↗

arXiv2010

Double-wells and double-layers in dusty Fermi-Dirac plasmas: Comparison with the semiclassical Thomas-Fermi counterpart

Based on the quantum hydrodynamic model, a new relationship between the electrostatic-potential and the electron-density in the ultra-dense plasma is derived. Propagation of arbitrary amplitude nonlinear ion waves is, then, investigated in a completely degenerate dense dusty electron-ion plasma, using this new energy relation, for the relativistic electrons in the ground of quantum hydrodynamics model and the results are compared to the case of semiclassical Thomas-Fermi dusty plasma. Using the standard pseudo-potential approach it is remarked that the Fermi-Dirac plasma, in contrast to the Thomas-Fermi counterpart, accommodates a wide variety of nonlinear excitations such as positive-/negative-potential ion solitary and periodic waves, double-layers and double-wells. It is also remarked that, the relativistic degeneracy parameter which relates to the mass-density of plasma has significant effects on the allowed matching-speed range in dusty Fermi-Dirac plasmas.

astro-ph.EP↗

arXiv2010

Propagation of arbitrary amplitude nonlinear quantum ion-acoustic waves in electron-ion plasmas: Dimensionality effects

Propagation of arbitrary-amplitude ion-acoustic solitary (IASWs) as well as periodic waves (IAPWs) is investigated in a fully degenerate quantum electron-ion plasma consisting of isothermal- or adiabatic-ion species. It is shown that the system dimensionality and degrees of freedom play critical roles in matching criteria for propagation of such waves. Furthermore, it is revealed that for the case of adiabatic-ion unlike isothermal one, in some cases, there exists an upper fractional ion-temperature limit for the existence of IAPWs. It is also shown that, the variations of wave-amplitude with respect to the change in fractional ion-temperature is quite different for the cases of isothermal and adiabatic-ion plasmas.

physics.plasm-ph↗

arXiv2010

Distinctive features of ion-acoustic solitons in EPI super-dense magneto-plasmas with degenerate electrons and positrons

Using the extended Poincaré-Lighthill-Kuo (PLK) reductive perturbation method to study the small-amplitude ion acoustic solitary wave (IASW) dynamics (propagation and interaction), it is shown that in Thomas-Fermi magneto-plasma consisting of inertial-less degenerate electrons and positrons and isothermal ions, distinctive features emerge when the ultra-relativistic degeneracy pressure applies to electrons and positrons. Calculations show that ion-acoustic solitary waves may interact differently in such plasmas under ultra-relativistic degeneracy pressure.

astro-ph.SR↗

arXiv2010

Propagation of arbitrary-amplitude ion waves in relativistically degenerate electron-ion plasmas

We employ the Sagdeev pseudo-potential method to investigate the propagation of nonlinear ion waves in a relativistically degenerate electron-ion plasmas. The matching criteria for existence of such nonlinear excitations are numerically investigated in terms of the relativity measure (relativistic degeneracy parameter) of electrons and the allowed Mach-number range for propagation of such waves is evaluated. It is shown that the electron relativistic degeneracy parameter has significant effects on nonlinear wave dynamics in superdense degenerate plasmas such as that encountered in white dwarfs and the cores of massive planets.

astro-ph.SR↗