Padma Kant Shukla

Electron-acoustic solitary waves in dense quantum electron-ion plasmas

A quantum hydrodynamic (QHD) model is used to investigate the propagation characteristics of nonlinear electron-acoustic solitary waves (EASWs) in a dense quantum plasma whose constituents are two groups of electrons: one inertial cold electrons and other inertialess hot electrons, and the stationary ions which form the neutralizing background. By using the standard reductive perturbation technique, a Kadomtsev-Petviashvili (KP) equation, which governs the dynamics of EASWs, is derived in both spherical and cylindrical geometry. The effects of cold electrons and the density correlations due to quantum fluctuations on the profiles of the amplitudes and widths of the solitary structures are examined numerically. The nondimensional parameter δ=nc0∕nh0, which is the equilibrium density ratio of the cold to hot electron component, is shown to play a vital role in the formation of both bright and dark solitons. It is also found that the angular dependence of the physical quantities and the presence of cold elec...

Surface waves on a quantum plasma half-space

Surface modes are coupled electromagnetic/electrostatic excitations of free electrons near the vacuum-plasma interface and can be excited on a sufficiently dense plasma half-space. They propagate along the surface plane and decay in either sides of the boundary. In such dense plasma models, which are of interest in electronic signal transmission or in some astrophysical applications, the dynamics of the electrons is certainly affected by the quantum effects. Thus, the dispersion relation for the surface wave on a quantum electron plasma half-space is derived by employing the quantum hydrodynamical (QHD) and Maxwell-Poison equations. The QHD include quantum forces involving the Fermi electron temperature and the quantum Bohm potential. It is found that, at room temperature, the quantum effects are mainly relevant for the electrostatic surface plasma waves in a dense gold metallic plasma.

Oblique modulation of electron-acoustic waves in a Fermi electron-ion plasma

The oblique modulational instability (MI) of electron-acoustic waves (EAWs) in a quantum plasma whose components are two distinct groups of electrons (one inertial cold electrons and other inertialess hot electrons) and immobile ions is investigated, by using a quantum hydrodynamic model. The analysis is carried out through the derivation of the nonlinear Schrodinger equation for the modulated EAW packets. The effects of obliqueness, the quantum diffraction (H), and the equilibrium density ratio of the cold to hot electron component (δ) on the MI of EAWs are numerically examined. At quantum scales, these parameters are found to significantly modify the MI domain in the plane of wave number and the angle (θ) between the modulation and the propagation direction. The relevance of our results in astrophysical environments, as well as in intense laser-solid density plasma interaction experiments is discussed.

The Formation of a Relativistic Partially Electromagnetic Planar Plasma Shock

Relativistically colliding plasma is modeled by particle-in-cell simulations in one and two spatial dimensions, with an ion-to-electron mass ratio of 400 and a temperature of 100 keV. The energy of an initial quasi-parallel magnetic field is 1% of the plasma kinetic energy. Energy dissipation by a growing wave pulse of mixed polarity, probably an oblique whistler wave, and different densities of the colliding plasma slabs result in the formation of an energetic electromagnetic structure within milliseconds. The structure, which develops for an initial collision speed of 0.9c, accelerates electrons to Lorentz factors of several hundred. A downstream region forms, separating the forward and reverse shocks. In this region, the plasma approaches an energy equipartition between electrons, ions, and the magnetic field. The electron energy spectrum -->N(E) resembles a power law at high energies, with an exponent close to –2.7, or -->N(E) E−2.7. The magnetic field reflects upstream ions, which form a beam and drag the electrons along to preserve the plasma quasineutrality. The forward and reverse shocks are asymmetric due to the unequal slab densities. The forward shock may be representative for the internal shocks of gamma-ray bursts.

Amplitude modulation of electron plasma oscillations in a dense electron-hole plasma

By using a quantum hydrodynamic model, the amplitude modulation of electron plasma oscillations (EPOs) in an unmagnetized dense electron-hole (e-h) quantum plasma is investigated. The standard reductive perturbation technique is used to derive one-dimensional nonlinear Schrodinger equation for the modulated EPO wave packet. The effects of the quantum diffraction, charged dust impurities and the effective e-h mass ratio on the propagation of linear dispersive EPOs, as well as on the modulational stability/instability of finite amplitude EPOs are examined. It is found that these parameters significantly affect the propagation of the EPOs as well as the nonlinear stability/instability domain of the wave vector, quite distinct from the classical and quantum electron-ion or electron-positron plasmas. The relevance of our investigation to semiconductor plasmas is discussed.

Parametric study of nonlinear electrostatic waves in two-dimensional quantum dusty plasmas

The nonlinear properties of two-dimensional cylindrical quantum dust-ion-acoustic (QDIA) and quantum dust-acoustic (QDA) waves are studied in a collisionless, unmagnetized and dense (quantum) dusty plasma. For this purpose, the reductive perturbation technique is employed to the quantum hydrodynamical equations and the Poisson equation, obtaining the cylindrical Kadomtsev–Petviashvili (CKP) equations. The effects of quantum diffraction, as well as quantum statistical and geometric effects on the profiles of QDIA and QDA solitary waves are examined. It is found that the amplitudes and widths of the nonplanar QDIA and QDA waves are significantly affected by the quantum electron tunneling effect. The addition of a dust component to a quantum plasma is seen to affect the propagation characteristics of localized QDIA excitations. In the case of low-frequency QDA waves, this effect is even stronger, since the actual form of the potential solitary waves, in fact, depends on the dust charge polarity (positive/negative) itself (allowing for positive/negative potential forms, respectively). The relevance of the present investigation to metallic nanostructures is highlighted.

Lie symmetry analysis of the quantum Zakharov equations

The Lie point symmetries of the one-dimensional quantum Zakharov (qZ) system of equations are considered, which is a general model to describe the coupling between the Langmuir and the ion-acoustic waves in a quantum setting. It is demonstrated that the Lie symmetries of the qZ system are exactly similar to those of the classical Zakharov equations. Further, similarity reductions are conducted based on the obtained Lie symmetries. A pure general periodic similarity ion-acoustic wave solution is obtained with the presence of constant linear and time-dependent nonlinear shears and time-dependent background, where the quantum effect increases the period of the waves.

Ion-temperature-gradient driven modes in very dense magnetoplasmas

By employing the quantum magnetohydrodynamic-Poisson model, a general dispersion relation for low-frequency electrostatic ion-temperature-gradient (ITG) modes in a very dense Fermi plasma is derived. The growth rate is found to be higher in the presence of ion-temperature gradients and electron corrections due to quantum fluctuations. Two new ITG driven modes in the Fermi plasma are found. These ITG modes are associated with an electron density response that differs from the Boltzmann law. It is expected that newly found ITG modes can play an important role in anomalous cross-field ion energy transport in the next-generation laser-solid density plasma experiments as well as in dense astrophysical bodies (e.g., neutron stars and the interior of white dwarfs).

Child-Langmuir flow in a planar diode filled with charged dust impurities

The Child–Langmuir (CL) flow in a planar diode in the presence of stationary charged dust particles is studied. The limiting electron current density and other diode properties, such as the electrostatic potential, the electron flow speed, and the electron number density, are calculated analytically. A comparison of the results with the case without dust impurities reveals that the diode parameters mentioned above decrease with the increase of the dust charge density. Furthermore, it is found that the classical scaling of D−2 (the gap spacing D) for the CL current density remains exactly valid, while the scaling of V3∕2 (the applied gap voltage V) can be a good approximation for low applied gap voltage and for low dust charge density.

Modulational instabilities of surface plasmons on metallic plasma surfaces with nanoparticles

The nonlinear coupling between high-frequency surface plasmons (SPs) and low-frequency ion oscillations on metallic plasma surfaces with charged nanoparticles is considered. It is shown that a finite-amplitude SP wave is modulationally unstable against the excitation of non-resonant ion oscillations. The growth rates and thresholds of the modulational instabilities are presented.