Showing papers by "Padma Kant Shukla published in 1992"
TL;DR: In this paper, the existence of a low-frequency electrostatic wave in an unmagnetized collisionless dusty plasma is pointed out, and the wave can be used to generate a new low frequency electric current.
Abstract: The existence of a new low-frequency electrostatic wave in an unmagnetized collisionless dusty plasma is pointed out.
1,139 citations
TL;DR: In this article, the wave spectra in the presence of static and non-static charged dust grains are presented and the relevance of their investigation to astrophysical and cometary plasmas is pointed out.
Abstract: Linear properties of low-frequency electrostatic and electromagnetic modes in dusty plasmas are studied. The wave spectra in the presence of static and non-static charged dust grains are presented. The relevance of our investigation to astrophysical and cometary plasmas is pointed out.
245 citations
TL;DR: In this paper, large amplitude ion-acoustic solitons in a plasma with a finite population of negatively charged dust grains are investigated, and the effects of the dust grains on the soliton amplitude and Mach number are examined.
231 citations
TL;DR: A preliminary investigation is presented of electron-positron pair production by means of plasma electrons accelerated by relativistic velocities in a strong wake field, which suggests that the total number of pairs produced is independent of the plasma concentration.
Abstract: A preliminary investigation is presented of electron-positron pair production by means of plasma electrons accelerated by relativistic velocities in a strong wake field. The propagation distance of the plasma wake field, which is determined by the depletion of the short laser pulse due to wake-field generation, is much larger than the pulse length. For this case, the total number of electron-positron pairs produced is independent of the plasma concentration. For achievable parameters of the laser pulse, the total number of pairs may be quite significant ([similar to]10[sup 6][ital Z2], where [ital Z] is the nuclear charge of the plasma ion).
215 citations
TL;DR: In this article, the nonlinear coupling between a large amplitude electromagnetic wave and the slow background motion in a dusty plasma is investigated and the relevance of the results to cometary and astrophysical plasmas is pointed out.
Abstract: The nonlinear coupling between a large amplitude electromagnetic wave and the slow background motion in a dusty plasma is considered. Stimulated scattering instabilities are investigated. The relevance of our investigation to cometary and astrophysical plasmas is pointed out.
97 citations
TL;DR: In this article, two-stream instabilities in an unmagnetized multi-species dusty plasma were investigated and the effect of the dust particles on the instability growth rate and the threshold drift velocity for excitation of the instability were examined.
Abstract: Two-stream instabilities in an unmagnetized multi-species dusty plasma are investigated. Four different plasma models are considered. The effect of the dust particles on the instability growth rate and the threshold drift velocity for excitation of the instability are examined.
68 citations
TL;DR: In this article, the nonlinear interaction of an arbitrarily large-amplitude circularly polarized electromagnetic wave with an unmagnetized electron-positron plasma is considered, taking into account relativistic particle-mass variation as well as large-scale density perturbations created by radiation pressure.
Abstract: The nonlinear interaction of an arbitrarily large-amplitude circularly polarized electromagnetic wave with an unmagnetized electron-positron plasma is considered, taking into account relativistic particle-mass variation as well as large-scale density perturbations created by radiation pressure. It is found that the interaction is governed by an equation for the electromagnetic wave envelope, which is coupled with a pair of equations describing fully nonlinear longitudinal plasma motions. The dynamics of the nonlinear electromagnetic wave packet is studied.
50 citations
TL;DR: In this paper, the existence of arbitrarily large amplitude electrostatic double layers is investigated in a four-component plasma consisting of electrons, two distinct positive ion species of different temperatures, and massive micrometre-sized, negatively-charged dust particles.
47 citations
TL;DR: In this paper, the basic forms of the active arcs can be described within the framework of a nonlinear Alfven wave model, and the auroral forms are then considered as nonlinear two-dimensional Alfven vortex structures that are uniform along the ambient magnetic field.
Abstract: Using analytical and numerical methods, it is shown that all the basic forms of the active arcs can be described within the framework of a nonlinear Alfven wave model. The auroral forms are then considered as nonlinear two-dimensional Alfven vortex structures that are uniform along the ambient magnetic field. They can exist in a cold inhomogeneous plasma, e.g., the Earth's ionosphere. Large-scale spirals and folds can recover the initial form of a typical arc. In the case of a small solitary disturbance of the current density or a sharp bending of the current sheets, vortex chains are formed in the spirals and the folds. >
34 citations
TL;DR: In this paper, the authors derived a set of non-linear mode coupling equations for weakly interacting low-frequency electrostatic fluctuations that are driven by a sheared ion velocity flow in a non-uniform dusty plasma embedded in an external magnetic field.
34 citations
TL;DR: The self-consistent theory, which is based on the recently proposed thermal wave model for relativistic charged-particle beam propagation, is capable of reproducing the main results for the beam-filamentation threshold and the self-pinching equilibrium condition that are already known in the conventional theory of the beam self-interaction in collisionless plasmas.
Abstract: It is shown that the self-consistent interaction between wake fields and the driving electron bunch in a collisionless, unmagnetized, overdense (${\mathit{n}}_{\mathit{p}}$\ensuremath{\gg}${\mathit{n}}_{\mathit{b}}$) plasma is governed by three coupled equations. In the long-beam limit, they reduce to a pair consisting of an appropriate nonlinear Schr\"odinger equation for the a/Ibeam wave function \ensuremath{\Psi}, and an equation for the wake-field potential that is driven by the transverse profile of the beam density, which is proportional to \ensuremath{\Vert}\ensuremath{\Psi}${\mathrm{\ensuremath{\Vert}}}^{2}$. The pair of equations are suitable for studying the beam self-focusing (self-pinching equilibrium) for the case in which the beam-spot size is larger (smaller) than the wavelength of the wake fields. It is demonstrated that our self-consistent theory, which is based on the recently proposed thermal wave model for relativistic charged-particle beam propagation, is capable of reproducing the main results for the beam-filamentation threshold and the self-pinching equilibrium condition that are already known in the conventional theory of the beam self-interaction in collisionless plasmas.
TL;DR: In this article, the presence of electron-positron pairs can drastically reduce the amplitude and wavelength of electrostatic wakefields that are generated by coherent, short electromagnetic wave packets in unmagnetized plasmas.
Abstract: It is shown that the presence of electron-positron pairs can drastically reduce the amplitude and wavelength of electrostatic wakefields that are generated by coherent, short electromagnetic wave packets in unmagnetized plasmas. The relevance of our work to laboratory and cosmic plasmas is pointed out.
TL;DR: In this article, the modulational and filamentational instabilities of two coupled electromagnetic waves have been investigated, taking into account the combined effect of relativistic electron mass variations and nonresonant density fulctuations that are driven by the ponderomotive force.
Abstract: The modulational and filamentational instabilities of two coupled electromagnetic waves have been investigated, taking into account the combined effect of relativistic electron mass variations and nonresonant density fulctuations that are driven by the ponderomotive force. The relevance of our investigation to phenomena related with nonlinear mixing of electromagnetic waves is pointed out.
TL;DR: An alternative system of magnetohydrodynamic equations for relativistically hot electron-positron plasmas is derived and should be useful for studying low-frequency wave motions as well as instabilities in astrophysical systems.
Abstract: An alternative system of magnetohydrodynamic equations for relativistically hot electron-positron plasmas is derived. The results should be useful for studying low-frequency wave motions as well as instabilities in astrophysical systems
TL;DR: In this article, the thermal parametric instability excited by powerful high-frequency (HF) radio waves in the F region of the ionosphere is investigated, where the HF radio waves, propagating through this inhomogeneous, magnetized plasma, are transformed into large-amplitude electrostatic plasma waves, which in turn couple to pseudo-three-dimensional low-frequency density disturbances.
Abstract: The thermal parametric instability excited by powerful high-frequency (HF) radio waves in the F region of the ionosphere is investigated. The HF radio waves, propagating through this inhomogeneous, magnetized plasma, are transformed into large-amplitude electrostatic plasma waves, which in turn couple to pseudo-three-dimensional nonlinear low-frequency density disturbances. This scenario is described by a system of equations consisting of the nonlinear Schrodinger equation for the HF plasma wave envelope, and the nonlinear equations for the electron density and temperature fluctuations, which are reinforced by the nonlinear terms associated with the pondermotive force and the differential Joule heating of the electrons. The formation of three-dimensional density striation structures is analyzed. >
TL;DR: In this paper, it was shown that a powerful radio wave passing through the F region of the auroral ionosphere can modify the ion velocity gradient driven low-frequency electrostatic fluctuation spectra due to parametric interaction processes.
Abstract: It is shown that a powerful radio wave passing through the F region of the auroral ionosphere can modify the ion velocity gradient driven low-frequency electrostatic fluctuation spectra due to parametric interaction processes. These are studied with the help of a nonlinear dispersion relation that includes the ponderomotive and differential Joule heating nonlinearities. Our results show how nonthermal fluctuations can be produced and controlled by a powerful radio wave in the auroral F region plasma.
TL;DR: In this article, the growth rate of the instabilities critically depends on collisions between charged particles and neutral atoms, and it is suggested that the present instabilities could be potential candidates for generating enhanced fluctuations during strong auroral activities in the E region of Earth's ionosphere, in cometary plasmas, as well as in controlled laboratory experiments.
Abstract: Novel electrostatic instabilities are shown to exist in a weakly ionized magnetoplasma having equilibrium density and electron temperature gradients. The growth rate of the instabilities critically depends on collisions between charged particles and neutral atoms. It is suggested that the present instabilities could be potential candidates for generating enhanced fluctuations during strong auroral activities in the E region of Earth’s ionosphere, in cometary plasmas, as well as in controlled laboratory experiments.
TL;DR: In this article, it was shown that ion density holes can be generated by a large-amplitude electrostatic ion cyclotron wave on auroral field lines, which may cause intermittent double layers to be observed in the auroral particle acceleration region.
Abstract: It is shown that ion density holes can be generated by a large-amplitude electrostatic ion cyclotron wave on auroral field lines. The rate at which the ion holes are excited is obtained. The presence of ion holes may cause intermittent double layers to be observed in the auroral particle acceleration region. The predicted scale lengths and velocities of the double layers are in agreement with observations.
TL;DR: In this article, a system of equations describing the two-dimensional nonlinear evolution of two-stream and gradient-drift instabilities in the E-region of the Earth's ionosphere is derived, taking into account turbulent ion viscosity and the nonlinearity associated with the ion inertia.
Abstract: A system of equations describing the two-dimensional nonlinear evolution of the two-stream and gradient-drift instabilities in the E-region of the Earth's ionosphere is derived, taking into account turbulent ion viscosity and the nonlinearity associated with the ion inertia. The linear instabilities are briefly re-examined. Regular nonlinear wave forms are found for both instabilities in the one-dimensional limit. Estimates of characteristic values of amplitudes and wavelengths are also presented.
TL;DR: In this article, free energy stored in the equilibrium electron density and temperature gradients can drive short-wavelength electromagnetic fluctuations in collisional plasmas embedded in a homogeneous magnetic field.
Abstract: It is shown that free energy stored in the equilibrium electron density and temperature gradients can drive short‐wavelength electromagnetic fluctuations in collisional plasmas embedded in a homogeneous magnetic field. The enhanced electromagnetic fluctuations can cause anomalous cross‐field electron energy transport. The present investigation can have relevance to short scale electric and magnetic field fluctuations, as well as anomalous thermal conduction in tokamak edges.
TL;DR: In this paper, the self-modulation of a large-amplitude magnetic electron drift (MED) wave is considered and the dynamics of the modulated wave packet is governed by the cubic Schrodinger equation.
Abstract: The self‐modulation of a large‐amplitude magnetic electron drift (MED) wave is considered. It is found that the dynamics of the modulated wave packet is governed by the cubic Schrodinger equation. Since, in the latter, the product of the group dispersion and the nonlinear frequency shift is negative, it turns out that the one‐dimensional nonlinear modulated MED wave packet propagates in the form of a rarefactional pulse. The present nonlinear structure can possibly be associated with the magnetic cavity observed in the vicinity of the magnetopause.