H. Saleem

Ruhr-Universität Bochum, Bochum, North Rhine-Westphalia, Germany

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Publications (121)194.66 Total impact

  • S. Ali Shan, Q. Haque, H. Saleem
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    ABSTRACT: It is shown that the sheared flow of electrons and ions in the presence of heavy stationary dust gives rise to unstable Alfvén waves. The coupling of newly studied low frequency electrostatic current-driven mode with the electromagnetic Alfvén and drift waves is investigated. The instability conditions and the growth rates of both inertial and kinetic Alfvén waves are estimated. The theoretical model is applied to the night side boundary regions of Jupiter’s magnetosphere which contain positive dust. The growth rates increase with increase in sheared flow speed. In the nonlinear regime, both inertial and kinetic Alfvén waves form dipolar vortices whose speed and amplitude depend upon the magnitude of the zero-order current.
    Astrophysics and Space Science 01/2014; · 2.06 Impact Factor
  • S. Ali Shan, H. Saleem
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    ABSTRACT: The current-driven electrostatic solitons and shocks are investigated in flowing plasmas having stationary dust and non-Maxwellian electrons. The propagation of solar wind parallel to the external magnetic field in the boundary regions of dusty magnetospheres of planets can give rise to drift type unstable electrostatic waves and nonlinear structures even if density is homogeneous. These waves can be produced in laboratory plasma experiments as well. Here the theoretical model is applied to Saturn’s magnetosphere.
    Astrophysics and Space Science 01/2014; 349(1). · 2.06 Impact Factor
  • S. Ali Shan, H. Saleem
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    ABSTRACT: Small amplitude ion-acoustic double layers in an unmagnetized and collisionless plasma consisting of cold positive ions, q-nonextensive electrons, and a cold electron beam are investigated. Small amplitude double layer solution is obtained by expanding the Sagdeev potential truncated method. The effects of entropic index q, speed and density of cold electron beam on double layer structures are discussed.
    Physics Letters A. 01/2014;
  • Ali Ahmad, H. Saleem
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    ABSTRACT: The soliton formation by the current-driven drift-like wave is investigated for heavier ion (such as barium) plasma experiments planned to be performed in future. It is pointed out that the sheared flow of electrons can give rise to short scale solitary structures in the presence of stationary heavier ions. The nonlinearity appears due to convective term in the parallel equation of motion and not because of temperature gradient unlike the case of low frequency usual drift wave soliton. This higher frequency drift-like wave requires sheared flow of electrons and not the density gradient to exist.
    Physics Letters A 12/2013; 377(43):3128-3130. · 1.63 Impact Factor
  • W. Masood, H. Saleem
    11/2013; 79(06).
  • Nazia Batool, H. Saleem
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    ABSTRACT: The linear and nonlinear dynamics of pair-ion (PI) and pair-ion-electron plasmas (PIE) have been investigated in a cylindrical geometry with a sheared plasma flow along the axial direction having radial dependence. The coupled linear dispersion relation of low frequency electrostatic waves has been presented taking into account the Guassian profile of density and linear gradient of sheared flow. It is pointed out that the quasi-neutral cold inhomogeneous pure pair ion plasma supports only the obliquely propagating convective cell mode. The linear dispersion relation of this mode has been solved using boundary conditions. The nonlinear structures in the form of vortices formed by different waves have been discussed in PI and PIE plasmas.
    Physics of Plasmas 10/2013; 20(10):2304-. · 2.38 Impact Factor
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    ABSTRACT: It is pointed out that interactions between the solar wind and the dusty magnetospheres of planets and comets give rise to nonlinear electrostatic drift waves. It is assumed that after transient processes a local steady state is attained with the same sheared flow of electrons and ions Vi0(x) = Ve0(x) = V0(x) z^ along the initial constant component of B0z of the total sheared magnetic field B0=B0z z^+B0y (x ) y^. The nonlinear perturbation caused by the electron temperature gradient forms solitary and shock structures, depending upon the dominant role of either the wave dispersion or dissipation, respectively. The theoretical model has been applied to the magnetosphere of Jupiter that contains positively charged dust grains. This investigation predicts the formation of short scale electrostatic solitons having width of the order of 1 m and shocks having widths of the order of 2 m.
    Journal of Geophysical Research 08/2012; 117(A8):8220-. · 3.17 Impact Factor
  • Ali Ahmad, H Saleem
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    ABSTRACT: Nonlinear equations for an electrostatic perturbation in hybrid frequency range are derived in a magnetized heavier ion plasma assuming that the electrons are flowing with a sheared velocity along the initial external constant magnetic field B 0z ^ z. As a result of this current, the total zero-order magnetic field becomes sheared as B 0 ¼ B 0z ^ z þ B 0y ðxÞ^ y. Such a system can give rise to unstable electrostatic waves under certain conditions. The solutions of the nonlinear equations are obtained in the form of dipolar vortices, which can play an important role in plasma transport across field lines. This work can be useful for the future experiments on sheared electron flows. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700177]
    Physics of Plasmas 04/2012; 19:042107. · 2.38 Impact Factor
  • H. Saleem, P.K. Shukla
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    ABSTRACT: We present nonlinear properties of the low-frequency nonlinear electrostatic waves in a nonuniform bounded magneto-plasma with the equilibrium density and parallel ion velocity gradients along the radial direction. The existence of electrostatic global vortices in a cylindrical magnetoplasma is established. The present results should help to understand the properties of coherent vortical structures in the presence of a magnetic field-aligned ion flow with a radial ion velocity gradient in laboratory magnetoplasmas that are bounded and nonuniform.
    Physics Letters A 01/2012; 376(4):497–499. · 1.63 Impact Factor
  • Source
    H Saleem, S. Ali, S. Poedts
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    ABSTRACT: A mechanism of self-heating of solar corona is pointed out. It is shown that the free energy available in the form of sheared flows gives rise to unstable electrostatic waves which accelerate the particles and heat them. The electrostatic perturbations take place through two processes (a) by purely growing sheared flow-driven instability and (b) by sheared flow-driven drift waves. These processes occur throughout the corona and hence the self-heating is very important in this plasma. These instabilities can give rise to local electrostatic potentials $\varphi$ of the order of about 100 volts or less within $3\times10^{-2}$ to a few seconds time if the initial perturbation is assumed to be about one percent that is $\frac{e\varphi}{T_{e}}\simeq10^{-2}$. The components of wave lengths in the direction perpendicular to external magnetic field $\textbf{B}_{0}$ vary from about 10m to 1m. The purely growing instability creates electrostatic fields by sheared flows even if the density gradient does not exist whereas the density gradient is crucial for the concurrence of drift wave instability. Subject headings: Sun: self-heating of corona, sheared flow-driven instability, drift waves.
    The Astrophysical Journal 01/2012; 748(2). · 6.73 Impact Factor
  • S. Mahmood, H. Saleem
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    ABSTRACT: Solitary inertial Alfvén wave in the presence of positively and negatively charged dust particles is studied. It is found that electron density dips are formed in the super Alfvénic region and wave amplitude is increased for the case of negatively charged dust particles in comparison with positively charged dust particles in electron-ion plasmas.
    11/2011;
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    H. Saleem
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    ABSTRACT: The ambiguity involved in the use of Maxwell's equation particularly in electron plasmas is discussed. It is pointed out that in the slow time scale perturbations the displacement current is ignored but it does not imply that the electron density fluctuations vanish. The contradictions in the assumptions and approximations used in the literature on this subject are discussed. A new low frequency electromagnetic wave is described which is a normal mode of non-uniform magnetized electron plasmas. This wave can couple with plasma hybrid oscillations if ion dynamics is taken into account. It is stressed that the electron magnetohydrodynamics (EMHD) model seems to be simple but in fact its use is subtle and its scope is very limited.
    07/2011;
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    Hamid Saleem, Zensho Yoshida
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    ABSTRACT: A theory of two-dimensional plasma evolution with Beltrami-like flow and field due to baroclinic effect has been presented. Particular solution of the nonlinear two-fluid equations is obtained. This simple model can explain the generation of magnetic field without assuming the presence of a seed in the system. Coupled field and flow naturally grow together. The theory has been applied to estimate B-field in laser-induced plasmas and the result is in good agreement with experimental values.
    Physics of Plasmas 06/2011; 11. · 2.38 Impact Factor
  • Source
    Hamid Saleem
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    ABSTRACT: A criterion to define a pure pair-ion (PI) plasma is presented. It is suggested that the lighter elements (like H and He) are more suitable to produce PI plasmas. The observation of ion acoustic wave (IAW) in recent experiments with fullerene plasmas clearly indicates the presence of electrons in the system. A set of two coupled non-linear differential equations has been obtained for PI plasma dynamics. In moving frame, it can be reduced to a form similar to Hasegawa-Mima equation but it does not contain drift wave.
    AIP Conference Proceedings. 06/2011; 1061(1).
  • H. Saleem, N. Batool, S. Poedts
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    ABSTRACT: The shear flow-driven electrostatic instabilities are investigated in ideal low density, low temperature pair-ion-electron and pure pair-ion plasmas in several different cases, including homogeneous and inhomogeneous density effects. In uniform pair-ion-electron plasma, when the shear flow is of the order of the acoustic speed, the purely growing D’Angelo mode can give rise to electrostatic fields. In the case of an inhomogeneous plasma, the drift wave becomes unstable. The presence of negative ions, however, reduces the growth rate. If the positive and negative ions are not in thermal equilibrium with each other, then the shear flow also gives rise to an electrostatic instability in pure pair-ion plasma.
    Physics of Plasmas 05/2011; 18(5). · 2.38 Impact Factor
  • Hamid Saleem, Bengt Eliasson
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    ABSTRACT: It is found that the zero-order current associated with electron shear flow produces a drift wave in magnetized plasmas, which can become unstable under certain conditions. This wave will be particularly important in low density and low temperature plasmas of heavy ions. As an example, numerical estimates are presented for a barium plasma with parameters compatible with experiments.
    Physics of Plasmas 05/2011; 18(5):052103-052103-4. · 2.38 Impact Factor
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    Hamid Saleem
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    ABSTRACT: It is pointed out that the unmagnetized inhomogeneous plasmas can support a low frequency electromagnetic ion wave as a normal mode like Alfven wave of magnetized plasmas. But this is a coupled mode produced by the mixing of longitudinal and transverse components of perturbed electric field due to density inhomogeneity. The ion acoustic wave does not remain electrostatic in non-uniform plasmas. On the other hand, a low frequency electrostatic wave can also exist in the pure electron plasmas. But the magnetic field fluctuations in both electron as well as in electron-ion plasmas are coupled with the electrostatic perturbations in unmagnetized case. The main instability condition for these low frequency electrostatic and electromagnetic modes is the same ${2/3}\kappa_n < \kappa_T$ (where $\kappa_n$ and $\kappa_T$ are inverse of the scale lengths of density and electron temperature, respectively).
    02/2011;
  • Source
    Hamid Saleem
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    ABSTRACT: A new analytical solution of the set of highly nonlinear two-fluid equations is presented to explain the mechanism for the generation of "seed" magnetic field and plasma flow by assuming the density n to have a profile like an exponential in xy-plane and temperature profiles of electrons (ions) to be linear in yz-plane. {It is shown that the baroclinic vectors - $\nabla\Psi\times\nabla T_{j}$ (where $\Psi = ln\bar{n}, \bar{n}$ is normalized density, and $T_{j}$ denote the temperatures of electrons and ions for j = e, i) can generate not only the magnetic field but the plasma flow as well.} It is also pointed out that the electron magnetohydrodynamics (EMHD) model has inconsistencies because it does not take into account the ion dynamics while the magnetic field is produced on slow time scale. The estimate of the magnitude of the magnetic field in a classical laser plasma using this model is in agreement with the experimental observations.
    Physics of Plasmas 02/2011; 17(9). · 2.38 Impact Factor
  • H. Saleem
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    ABSTRACT: The flow of electrons and ions with the same sheared velocity introduces new type of electrostatic drift waves and instabilities due to non-uniform zero-order current in plasmas having stationary dust. One of the modes is flute-like and the other also includes ions motion parallel to the background magnetic field. This investigation has applications in the phenomena of solar wind interaction with the dusty plasmas of planets and comets.
    Physics Letters A 01/2011; 375(44):3877-3879. · 1.63 Impact Factor
  • S. Ali, H. Saleem
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    ABSTRACT: Drift wave is studied in pair-ion plasmas in the presence of electrons using the Vlasov–Poisson set of equations. The growth rate of this universal instability depends on the concentration of electrons. The real frequency and the growth rate are reduced as the number density of electrons decreases. If the laboratory produced pair-ion plasmas contain relatively small amount of electrons then very low frequency almost stable drift waves can be produced which will indicate that the plasma is not a pure pair-ion plasma. The present investigation can be useful for future experiments on pair-ion plasmas and low density low temperature industrial plasmas which contain negative ions.
    Physics of Plasmas 09/2010; 17(9):092101-092101-5. · 2.38 Impact Factor

Publication Stats

697 Citations
194.66 Total Impact Points

Institutions

  • 1992–2012
    • Ruhr-Universität Bochum
      • • Faculty of Physics and Astronomy
      • • Institut für Theoretische Physik I
      Bochum, North Rhine-Westphalia, Germany
  • 1985–2012
    • Quaid-i-Azam University
      • Department of Physics
      Islāmābād, Islāmābād, Pakistan
  • 2003–2011
    • COMSATS Institute of Information Technology
      • Department of Physics
      Islāmābād, Islāmābād, Pakistan
  • 2007
    • Pakistani Institute of Nuclear Science and Technology
      Islāmābād, Islāmābād, Pakistan
  • 2002
    • The University of Tokyo
      • Graduate School of Frontier Sciences
      Tokyo, Tokyo-to, Japan