Zahida Ehsan

A specific property of electromagnetic waves interacting with dust-laden plasma

The propagation pattern of electromagnetic waves (EMWs) in dusty plasmas is quite different from that in electron-ion plasmas. For instance, here the ponderomotive force acts on dust grains as a negative pressure, and a nonlinear Schrodinger equation with an additional nonlinear term is obtained. Based on this equation, the modulation instability is examined and it is shown that the growth rate becomes maximum when that additional term compensates the diffraction term. The main part of this work is devoted to the localization of the grains by the EMW. Considering both subsonic and supersonic regimes, it has been shown that under certain conditions the grains are localized and the ions circumnavigate the grains, whereas the electrons escape from the region of localization. Further, the localization of grains by the EMW is found to be shape-dependent of the pulse. Comparing pancake and light bullet shaped pulses in the supersonic regime, and it is shown that only the light bullet shape leads to the compress...

Solar wind driven dust acoustic instability with Lorentzian kappa distribution

In a three species electron-ion-dust plasma following a generalized non-Maxwellian distribution function (Lorentzian or kappa), it is shown that a kinetic instability of dust-acoustic mode exists. The instability threshold is affected when such (quasineutral) plasma permeates through another static plasma. Such case is of interest when the solar wind is streaming through the cometary plasma in the presence of interstellar dust. In the limits of phase velocity of the waves larger and smaller than the thermal velocity of dust particles, the dispersion properties and growth rate of dust-acoustic mode are investigated analytically with validation via numerical analysis.

Two types of lower-hybrid waves in dusty plasmas and cusp solitons

A theoretical model is presented for the excitation of ultralow frequency dust-lower hybrid mode (DLH) oscillating at frequency Ωlhd=(Zdndo∕nio)ΩciΩcd by employing the decay of a relatively high frequency dust-modified lower-hybrid (DMLH) wave into a relatively lower frequency DMLH and DLH based on three-wave resonant interaction. A coupled nonlinear Schrodinger (NLS) equation for the DMLH wave and Zakharov equation for the DLH wave are derived. The nonlinear contribution in the NLS equation comes from the DLH density fluctuations. Modulational instabilities of DMLH waves are investigated and its growth rates are studied. Additionally, one-dimensional nonlinear localized structures of bright solitons and nonlinear nonlocal structures like cusp solitons are obtained. It is shown that, when the phase velocity resonates with the dust sound speed (ω∕κ∼vo), the nonlocal nonlinearity leads to the generation of cusp solitons.

Acceleration of soliton by nonlinear Landau damping of dust-helical waves

The problem of nonlinear Landau damping of helicon waves in dusty plasma in particular emphasis to the acceleration of soliton is presented here. This in the framework of a collisionless, anisotropic homogeneous dusty plasma in one dimension, can be well described by two coupled dynamical equations of the generalized Zakharov type, with one extra nonlocal term coming from Landau damping. Nonlinear-nonlocal term gives rise to essential contributions relative to the local term. Then under different conditions, kinetic nonlinear Schrodinger equation is constructed and nonlinear decrement is obtained for two cases. It is noticed that the time dependant term in the ponderomotive force plays a significant role for this kind of damping. Additionally, it is shown that nonlinear Landau damping leads to the amplitude modulation of dust helicon waves, further modulational instability, and maximal growth rate is obtained when the group velocity of the helicon wave reaches the dust-acoustic speed. It is demonstrated t...

Possible colloid crystal formation in a magnetized and inhomogeneous semiconductor plasma

We investigate the detailed properties of the modification of the Debye-Huckel and the consequent oscillatory wake potentials in the presence of a density inhomogeneity and external static uniform electric and magnetic fields in an ion-implanted n-type piezoelectric semiconductor. It is found that the external fields and the density nonuniformity have significant effects on the static and dynamical electrostatic potentials. The possibility of the long-ranged order formation of colloids of the implanted ions, leading to modification of the electrical, thermodynamic, and optical properties of the “soft matter,” has been pointed out. The periodic wakefields besides the usual static Coulombian Debye-Huckel potential may cause the long-range ordered structures of the charged colloidal particulates within the semiconductor to show various additional properties.

Wake potential in a nonuniform self-gravitating dusty magnetoplasma in the presence of ion streaming

A detailed investigation of the electrostatic asymmetric shielding potential and consequent generation of the dynamical oscillatory wake potential has been examined analytically in an inhomogeneous self-gravitating dusty magnetoplasma in the presence of uniform ion streaming. It is found that the wake potential depends significantly on the test particle speed, ambient magnetic field, ion streaming velocity, and the plasma inhomogeneity. The periodic oscillatory potential might lead to an alternative approach to the Jeans instability for the formation of dust agglomeration leading to gravitational collapse of the self-gravitating systems.

Acceleration of dust particles by vortex ring

It is shown that nonlinear interaction between large amplitude circularly polarized EM wave and dusty plasma leads to a non-stationary ponderomotive force, which in turn produces a vortex ring and magnetic field. Then the ensuing vortex ring in the direction of propagation of the pump wave can accelerate the micron-size dust particles, which are initially at rest and eventually form a non-relativistic dust jet. This effect is purely non-stationary and unlike linear vortices, dust particles do not rotate here. Specifically, it is pointed out that the vortex ring or closed filament can become potential candidate for the acceleration of dust in tokamak plasmas. In the past there have been fairly extensive investigations in the field of nonlinear interaction of high-frequency EM waves or short-pulse laser beams with an electron- ion plasma (1-18). Such interactions can produce various types of phenomena, like self-focusing Brilliouin or Raman scattering, filamentation or modulational instability, collisionless shock waves or solitons, wave breaking, absorption of EM waves, generation of vortex rings, quasi-static magnetic fields etc. Spontaneously generated magnetic fields are not only important for laboratory-produced plasmas but also in many cosmic environments, in our Universe as well as in galactic and intergalactic spaces (19-25). A mechanism for the generation of large quasi- static magnetic fields and vortex ring by a non-potential ponderomotive force resulting from the time-dependent amplitude of EM waves in electron-ion plasma was discussed in Ref. (5). This way the production of magnetic field can essentially affect the transport phenomena as well as the absorption of an EM field in inertial confinement fusion (ICF) schemes. Indeed, the vortex ring phenomena can have profound influence on laser experimental research (26-28), and at the same time its behavior can be described within the main equations of a continuous medium (13-15). Most significantly, once this vortex is generated, it develops only under the effect of its own dynamics. Unlike straight vortex filament that is a static phenomenon of plasma, the vortex ring moves relative to the plasma, and at the same time expands noticeably in the process.

Existence of Dust Atoms & Modified OML Theory

Based on adiabatic model and nonlinear screening of the dust grains immersed in electron‐ion plasma, an important relation is obtained between the maximum potential (and therefore the charge) of the dust grain and the temperature of the electrons. A Thomas‐Fermi equation suggesting the existence of dust atom with a well‐defined atomic radius is also derived. Briefly a new approach for obtaining floating potential has been introduced. This novel approach is valid for those cases when the standard OML theory is not applicable.

A new property of electromagnetic wave interacting with dust-laden plasma

The propagation pattern of electromagnetic waves (EMW) in dusty plasmas is quite different from that in electron-ion plasmas. For instance, here the ponderomotive force acts on dust grains as a negative pressure and that a nonlinear Schrodinger equation with an additional nonlinear term is obtained. Based on this equation, the modulation instability is examined and it is shown that the growth rate becomes maximum when that additional term compensates the diffraction term. The main part of this work is devoted to the localization of the grains by the EMW. Considering both subsonic and supersonic regimes it has shown that under certain conditions the grains are localized and the ions circum navigate the grains whereas the electrons escape from the region of localization. Further, the localization of grains by the EMW is found to be shape-dependent of the pulse. Pancake and light bullet shaped pulses have considered in the supersonic regime and have shown that only the light bullet shape leads to the compression of grains. Finally, investigating nonstationary solution, it is shown that for some parameters the nonlinear wave breaking and the formation of shock wave can take place.