arXiv subjects

A. P. Misra

Publications and source records attributed to A. P. Misra.

82 records · Page 5Linked to original sources

arXiv2010

Localized whistlers in magnetized spin quantum plasmas

The nonlinear propagation of electromagnetic (EM) electron-cyclotron waves (whistlers) along an external magnetic field, and their modulation by electrostatic small but finite amplitude ion-acoustic density perturbations are investigated in a uniform quantum plasma with intrinsic spin of electrons. The effects of the quantum force associated with the Bohm potential and the combined effects of the classical as well as the spin-induced ponderomotive forces (CPF and SPF respectively) are taken into consideration. The latter modify the local plasma density in a self-consistent manner. The coupled modes of wave propagation is shown to be governed by a modified set of nonlinear Schrödinger-Boussinesq-like equations which admit exact solutions in form of stationary localized envelopes. Numerical simulation reveals the existence of large-scale density fluctuations that are self-consistently created by the localized whistlers in a strongly magnetized high density plasma. The conditions for the modulational instability (MI) and the value of its growth rate are obtained. Possible applications of our results, e.g., in strongly magnetized dense plasmas and in the next generation laser-solid density plasma interaction experiments are discussed.

physics.plasm-ph↗

arXiv2010

Nonlinear wave-wave interactions in quantum plasmas

Wave-wave interaction in plasmas is a topic of important research since the 16th century. The formation of Langmuir solitons through the coupling of high-frequency (hf) Langmuir and low-frequency (lf) ion-acoustic waves, is one of the most interesting features in the context of turbulence in modern plasma physics. Moreover, quantum plasmas, which are ubiquitous in ultrasmall electronic devices, micromechanical systems as well as in dense astrophysical environments are a topic of current research. In the light of notable interests in such quantum plasmas, we present here a theoretical investigation on the nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic waves (QIAWs), which are governed by the one-dimensional quantum Zakharov equations (QZEs). It is shown that a transition to spatiotemporal chaos (STC) occurs when the length scale of excitation of linear modes is larger than that of the most unstable ones. Such length scale is, however, to be larger (compared to the classical one) in presence of the quantum tunneling effect. The latter induces strong QIAW emission leading to the occurrence of collision and fusion among the patterns at an earlier time than the classical case. Moreover, numerical simulation of the QZEs reveals that many solitary patterns can be excited and saturated through the modulational instability (MI) of unstable harmonic modes. In a longer time, these solitons are seen to appear in the state of STC due to strong QIAW emission as well as by the collision and fusion in stochastic motion. The energy in the system is thus strongly redistributed, which may switch on the onset of Langmuir turbulence in quantum plasmas.

physics.plasm-ph↗

arXiv2010

Modulational instability of ion-acoustic wave packets in quantum pair-ion plasmas

Amplitude modulation of quantum ion-acoustic waves (QIAWs) in a quantum electron-pair-ion plasma is studied. It is shown that the quantum coupling parameter $H$ (being the ratio of the plasmonic energy density to the Fermi energy) is ultimate responsible for the modulational stability of QIAW packets, without which the wave becomes modulational unstable. New regimes for the modulational stability (MS) and instability (MI) are obtained in terms of $H$ and the positive to negative ion density ratio $β$. The growth rate of MI is obtained, the maximum value of which increases with $β$ and decreases with $H$. The results could be important for understanding the origin of modulated QIAW packets in the environments of dense astrophysical objects, laboratory negative ion plasmas as well as for the next generation laser solid density plasma experiments.

physics.plasm-ph↗

arXiv2010

Double-layer shocks in a magnetized quantum plasma

The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves (QIAWs) obliquely to an external magnetic field is reported in a quantum electron-positron-ion (e-p-i) plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter $H$ associated with the Bohm potential and the positron to electron density ratio $δ$. The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.

physics.plasm-ph↗

arXiv2010

Spin contribution to the ponderomotive force in a plasma

The concept of a ponderomotive force due to the intrinsic spin of electrons is developed. An expression containing both the classical as well as the spin-induced ponderomotive force is derived. The results are used to demonstrate that an electromagnetic pulse can induce a spin-polarized plasma. Furthermore, it is shown that for certain parameters, the nonlinear back-reaction on the electromagnetic pulse from the spin magnetization current can be larger than that from the classical free current. Suitable parameter values for a direct test of this effect are presented.

physics.plasm-ph↗

arXiv2010

Circularly polarized modes in magnetized spin plasmas

The influence of the intrinsic spin of electrons on the propagation of circularly polarized waves in a magnetized plasma is considered. New eigenmodes are identified, one of which propagates below the electron cyclotron frequency, one above the spin-precession frequency, and another close to the spin-precession frequency.\ The latter corresponds to the spin modes in ferromagnets under certain conditions. In the nonrelativistic motion of electrons, the spin effects become noticeable even when the external magnetic field $B_{0}$ is below the quantum critical\ magnetic field strength, i.e., $B_{0}<$ $B_{Q} =4.4138\times10^{9}\, \mathrm{T}$ and the electron density satisfies $n_{0} \gg n_{c}\simeq10^{32}$m$^{-3}$. The importance of electron spin (paramagnetic) resonance (ESR) for plasma diagnostics is discussed.

physics.plasm-ph↗

arXiv2010

Spatiotemporal chaos and the dynamics of coupled Langmuir and ion-acoustic waves in plasmas

A simulation study is performed to investigate the dynamics of coupled Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma. The effects of dispersion due to charge separation and the density nonlinearity associated with the IAWs, are considered to modify the properties of Langmuir solitons, as well as to model the dynamics of relatively large amplitude wave envelopes. It is found that the Langmuir wave electric field, indeed, increases by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model, based on three Fourier modes shows that a transition to temporal chaos is possible, when the length scale of the linearly excited modes is larger than that of the most unstable ones. The chaotic behaviors of the unstable modes are identified by the analysis of Lyapunov exponent spectra. The space-time evolution of the coupled LWs and IAWs shows that the IWN can cause the excitation of many unstable harmonic modes, and can lead to strong IAW emission. This occurs when the initial wave field is relatively large or the length scale of IAWs is larger than the soliton characteristic size. Numerical simulation also reveals that many solitary patterns can be excited and generated through the modulational instability (MI) of unstable harmonic modes. As time goes on, these solitons are seen to appear in the spatially partial coherence (SPC) state due to the free ion-acoustic radiation as well as in the state of spatiotemporal chaos (STC) due to collision and fusion in the stochastic motion. The latter results the redistribution of initial wave energy into a few modes with small length scales, which may lead to the onset of Langmuir turbulence in laboratory as well as space plasmas.

physics.plasm-ph↗

arXiv2010

Temporal dynamics in the one-dimensional quantum Zakharov equations for plasmas

The temporal dynamics of the quantum Zakharov equations (QZEs) in one spatial dimension, which describes the nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic waves (QIAWs) is revisited by considering their solution as a superposition of three interacting wave modes in Fourier space. Previous results in the literature are modified and rectified. Periodic, chaotic as well as hyperchaotic behaviors of the Fourier-mode amplitudes are identified by the analysis of Lyapunov exponent spectra and the power spectrum. The periodic route to chaos is explained through an one-parameter bifurcation analysis. The system is shown to be destabilized via a supercritical Hopf-bifurcation. The adiabatic limits of the fully spatio-temporal and reduced systems are compared from the viewpoint of integrability properties.

physics.plasm-ph↗

arXiv2008

Spin magnetosonic shocks in quantum plasmas

The one-dimensional shock structures of magnetosonic waves (MSWs) propagating in a dissipative quantum plasma medium is studied. A quantum magnetohydrodynamic (QMHD) model is used to take into account the quantum force term due to Bohm potential and the pressure-like spin force term for electrons. The nonlinear evolution (Korteweg de-Vries-Burger) equation, derived to describe the dynamics of small amplitude MSWs, where the dissipation is provided by the plasma resistivity, is solved numerically to obtain both oscillatory and monotonic shock structures. The shock strength decreases with increasing the effects of collective tunneling and increases with increasing the effects of spin alignment. The theoretical results could be of importance for astrophysical (e.g., magnetars) as well as for ultracold laboratory plasmas (e.g., Rydberg plasmas).

physics.plasm-ph↗

arXiv2008

Dust ion-acoustic shocks in quantum dusty pair-ion plasmas

The formation of dust ion-acoustic shocks (DIASs) in a four-component quantum plasma whose constituents are electrons, both positive and negative ions and immobile charged dust grains, is studied. The effects of both the dissipation due to kinematic viscosity and the dispersion caused by the charge separation as well as the quantum tunneling due to the Bohm potential are taken into account. The propagation of small but finite amplitude dust ion-acoustic waves (DIAWs) is governed by the Korteweg-de Vries-Burger (KdVB) equation which exhibits both oscillatory and monotonic shocks depending not only on the viscosity parameters, but also on the quantum parameter H (the ratio of the electron plasmon to the electron Fermi energy) and the positive to negative ion density ratio. Large amplitude stationary shocks are recovered for a Mach number exceeding its critical value. Unlike the small amplitude shocks, quite a smaller value of the viscosity parameter, H and the density ratio may lead to the large amplitude monotonic shock strucutres. The results could be of importance in astrophysical and laser produced plasmas.

physics.plasm-ph↗