Sujeet Kumar Agarwal

Focusing of electromagnetic beams in collisional plasmas, with finite thermal conduction

In this paper we present a theoretical investigation of the focusing of coaxial Gaussian electromagnetic beams and of a Gaussian ripple on an electromagnetic beam of uniform irradiance in a collisional plasma (in thermal equilibrium in the absence of the beams). A self consistent solution of the electromagnetic wave equation, the energy balance equation, and Fourier’s equation of heat conduction has been obtained in the paraxial approximation. The nonuniform distribution of the electron density and thereby the dielectric function on account of the nonuniform electron temperature/density distribution causes the focusing/defocusing of the beams. The effect of thermal conduction on the temperature distribution of the electrons, on the critical curves, and the nature of focusing has been specifically studied. In common with earlier studies, three regions in the initial beam width—initial axial irradiance plane, corresponding to steady divergence, self focusing and oscillatory divergence have been characterize...

Self-focusing and cross-focusing of Gaussian electromagnetic beams in fully ionized collisional magnetoplasmas

This paper presents an analysis and subsequent discussion of the phenomena of self-focusing of single electromagnetic Gaussian beams and cross-focusing of multiple coaxial beams in fully ionized magnetoplasma, taking into account the Ohmic heating of the electrons by the beams and loss of energy by electrons due to collision with the ions and electronic thermal conduction; the energy gained by ions in collision with the electrons has been equated to the energy lost on account of ionic thermal conduction. It is seen that the inclusion of the ionic thermal conduction reduces self/cross-focusing for high values of the magnetic field (νe≪Ωc) and enhances the same for low values of the magnetic field (νe≫ωc); here νe is the electron collision frequency and ωc,Ωc are the cyclotron frequencies of electrons and ions, respectively. The wave frequency is assumed to be much higher than the cyclotron frequency of the electrons. The results lead to the conclusion that considerable error occurs by neglecting ionic ther...

Mutual interaction between parallel Gaussian electromagnetic beams in plasmas

In this paper, the interaction between two Gaussian electromagnetic beams in a plasma has been investigated, when the axes of the two beams are initially (z=0) parallel along the z axis in the x-z plane; the beams are initially propagating in the z direction. For the three types of nonlinearities (viz., collisional, ponderomotive, and relativistic) the dielectric function has been expressed as a function of the irradiances of the two beams; this expression for the dielectric function has been substituted in the wave equation and a solution of the resulting nonlinear equation obtained in the paraxial approximation. The paraxial approximation is justified since the phenomena of interest occur when the beams are initially close (2x0≤r0). Further, the absorption of the beam in the plasma has been neglected, which is justified when the electron collision frequency is much less than the frequencies of the beams. Second-order coupled ordinary differential equations have been obtained for the distance between the...

Electric field emission of electrons from spherical metallic dust particles

In this paper, an almost exact expression for the tunneling probability of an electron through the potential barrier on account of a negative charge on a spherical metallic particle has been derived and used to obtain the field emission current density from the surface of the particle. Based on these results a parametric analysis of the phenomenon and comparison with the results of the Jeffreys–Wentzel–Kramers–Brillouin (JWKB) approximation (similar to the Fowler–Nordheim theory) has been presented. It is seen that the JWKB theory underestimates the tunneling probability. The investigation is of relevance to dusty plasmas in space and in the laboratory.

The B−3/2 diffusion in magnetized plasma

Fluid equations with transport effects have been derived from summing up discrete particle effects in the configuration space. The diffusion coefficient takes a form different from, but equivalent to, the Kubo formula. By taking into account the decoherence along the field lines, the diffusive damping in the perpendicular direction, and the finite Larmor radius effect in the cyclotron resonance, it is shown that the diffusion of magnetized 3d plasma has a regime of B−3/2 scaling which lies between the Bohm diffusion of B−1 and the classical diffusion of B−2.

Interaction between parallel Gaussian electromagnetic beams in ionic collision dominated plasmas with thermal conduction

. In this communication the interaction between two Gaussian electromagnetic beams in an ionic collision dominated plasma has been investigated, when the axes of the two beams are initially (z = 0) parallel along the z-axis in the xz plane; the beams are initially propagating in the z-direction. Taking into account the loss of electron energy by collisions and by thermal conduction, the energy balance equation for electrons has been solved to obtain the space dependence of the electron temperature and the dielectric function has been expressed as a function of the electron temperature; this expression for the dielectric function has been substituted in the wave equation and a solution of the resulting nonlinear equation obtained in the paraxial approximation. Second-order coupled ordinary differential equations have been obtained for the distance between the centers of the beams and the beam widths in the x- and y-directions as a function of the distance of propagation along the z-axis. The equations have been solved numerically for a range of parameters and a discussion of the results is presented for the case when the two beams have the same axial irradiance. frequency and width. From simple considerations it is seen that the beams attract each other when 2x 0 < wr 0 and in this situation beams are close enough for the paraxial approximation to be valid.

A condition for simultaneous propagation of coaxial Gaussian electromagnetic beams in a plasma, without convergence or divergence

For coaxial Gaussian electromagnetic beams of equal width, a relation between the weighted sum of axial irradiances and the width of the beams, which corresponds to the propagation in a plasma, without convergence or divergence has been obtained in the paraxial approximation. The collisional (with and without thermal conduction), ponderomotive and relativistic nonlinearities have been separately considered in this investigation. The investigation has relevance to the study and application of multi-wave interaction phenomena such as the growth of combination frequencies, plasma beat wave acceleration and enhanced penetration in an overdense plasma.

Nonlinear interaction of an intense radio wave with ionospheric D/E layer plasma

This paper considers the nonlinear interaction of an intense electromagnetic wave with the D/E layer plasma in the ionosphere. A simultaneous solution of the electromagnetic wave equation and the equations describing the kinetics of D/E layer plasma is obtained; the phenomenon of ohmic heating of electrons by the electric field of the wave causes enhanced collision frequency and ionization of neutral species. Electron temperature dependent recombination of electrons with ions, electron attachment to O 2 molecules, and detachment of electrons from O 2 − ions has also been taken into account. The dependence of the plasma parameters on the square of the electric vector of the wave E 0 2 has been evaluated for three ionospheric heights (viz., 90, 100, and 110 km) corresponding to the mid-latitude mid-day ionosphere and discussed; these results are used to investigate the horizontal propagation of an intense radio wave at these heights.