A. P. Misra

Ion-acoustic shocks in quantum electron-positron-ion plasmas

Nonlinear propagation of quantum ion-acoustic waves (QIAWs) in a dense quantum plasma whose constituents are electrons, positrons, and positive ions is investigated using a quantum hydrodynamic model. The standard reductive perturbation technique is used to derive the Korteweg–de Vries–Burger (KdVB) equation for QIAWs. It is shown by numerical simulation that the KdVB equation has either oscillatory or monotonic shock wave solutions depending on the system parameters H proportional to quantum diffraction, μi the effect of ion kinematic viscosity, and μ the equilibrium electron to ion density ratio. The results may have relevance in dense astrophysical plasmas (such as neutron stars) as well as in intense laser solid density plasma experiments where the particle density is about 1025−1028m−3.

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...

Nonlinear wave modulation in a quantum magnetoplasma

Amplitude modulation of ion-acoustic waves (IAW) in a magnetized electron-ion quantum plasma is investigated. For this purpose, a three-dimensional (3D) quantum magnetohydrodynamic model is considered in the limit of small mass ratio of the charged particles. By using the standard reductive perturbation technique, a 3D nonlinear Schrodinger equation containing the magnetic field and the quantum effects is derived. The importance of quantum corrections is described through a nondimensional parameter H which is proportional to quantum diffraction effects. Some important and new modulational instability criteria of 3D IAW, quite distinct from the classical one, are obtained and analyzed.

Modulational instability of magnetosonic waves in a spin 1/2 quantum plasma

The modulational instability (MI) of magnetosonic waves (MSWs) is analyzed, by using a two-fluid quantum magnetohydrodynamic model that includes the effects of the electron-1/2 spin and the plasma resistivity. The envelope modulation is then studied by deriving the corresponding nonlinear Schrodinger equation from the governing equations. The plasma resistivity is shown to play a dissipative role for the onset of MI. In the absence of resistivity, the microscopic spin properties of electrons can also lead to MI. In such a situation, the dominant spin contribution corresponds to a dense quantum plasma with the particle number density, n(0)greater than or similar to 10(28) m(-3). Also, in such a dissipative (absorbing) medium, where the group velocity vector is usually complex for real values of the wave vector, the role of the real group velocity in the propagation of one-dimensional MSW packets in a homogeneous absorbing medium is reported. The effects of quantum spin on the stability/instability conditions of the magnetosonic envelope are obtained and examined numerically. From the nonlinear dispersion relation of the modulated wave packet it is found that the effect of the spin (plasma resistivity) is to decrease (increase) the instability growth rate provided the normalized Zeeman energy does not exceed a critical value. The theoretical results may have relevance to astrophysical (e.g., magnetars) as well as to ultracold laboratory plasmas (e.g., Rydberg plasmas).

Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption

Optical chaos is a topic of current research characterized by high-dimensional nonlinearity which is attributed to the delay-induced dynamics, high bandwidth and easy modular implementation of optical feedback. In light of these facts, which add enough confusion and diffusion properties for secure communications, we explore the synchronization phenomena in spatiotemporal semiconductor laser systems. The novel system is used in a two-phase colored image encryption process. The high-dimensional chaotic attractor generated by the system produces a completely randomized chaotic time series, which is ideal in the secure encoding of messages. The scheme thus illustrated is a two-phase encryption method, which provides sufficiently high confusion and diffusion properties of chaotic cryptosystem employed with unique data sets of processed chaotic sequences. In this novel method of cryptography, the chaotic phase masks are represented as images using the chaotic sequences as the elements of the image. The scheme drastically permutes the positions of the picture elements. The next additional layer of security further alters the statistical information of the original image to a great extent along the three-color planes. The intermediate results during encryption demonstrate the infeasibility for an unauthorized user to decipher the cipher image. Exhaustive statistical tests conducted validate that the scheme is robust against noise and resistant to common attacks due to the double shield of encryption and the infinite dimensionality of the relevant system of partial differential equations.

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 backreaction 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.

Alfvén surface modes in dusty spin 1/2 quantum magnetoplasmas

The dispersion properties of electromagnetic surface modes propagating at the planar interface between two structured quantum magnetoplasmas composed of electrons, positrons, and charged dust grains of different densities and between a plasma and free space with spin quantum effects are studied. It is shown that even in the absence of charged dust impurities, the spin quantum effects can lead to a new low frequency (in comparison to the electron/positron gyrofrequency) Alfven surface modes which otherwise do not exist. The important applications to plasmas in the vicinity of pulsars and magnetars as well as in the dense astrophysical plasma environments where the particle density is about 1020–1025m−3 are discussed.

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 ...

Quantum electron-acoustic double layers in a magnetoplasma

Using a quantum magnetohydrodynamic (QMHD) model, the existence of small but finite amplitude quantum electron-acoustic double layers (QEADLs) is reported in a magnetized collisionless dense quantum plasma whose constituents are two distinct groups of cold and hot electrons, and the stationary ions forming only the neutralizing background. It is shown that the existence of steady state solutions of these double layers obtained from an extended Korteweg-de Vries (KdV) equation depends parametrically on the ratio of the cold to hot electron unperturbed number density (δ), the quantum diffraction parameter (H), the obliqueness parameter (lz), and the external magnetic field via the normalized electron-cyclotron frequency (Ω). It is found that the system supports both compressive and rarefactive double layers depending on the parameters δ and lz. The effects of all these parameters on the profiles of the double layers are also examined numerically.

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.