Self-Focusing of Electromagnetic Beams in Plasmas: Some Recent Investigations
Using the earlier expressions for nonlinear dielectric constant (ε=ε 0+Φ(EE*) of isotropic and magnetoactive plasmas, we have investigated the self focusing of gaussian electromagnetic beams in short (t«τε), and long (t>τε) time scales; τε is the energy relaxation time of electrons with heavy particles and ε 0=ε(EE*=0). The wave equation has been solved in the paraxial ray and WKB approximations by expanding ε as ε=ε a(EE* |r=0)+γr2. Unlike previous analyses1 no restriction has been put on the relative magnitudes of Φ and ε 0. Consequently, the treatment is applicable beyond critical electron density. In a magnetoplasma, the self focusing of extraordinary mode has been studied and the treatment is applicable for all values of plasma frequency. Saturating effects of nonlinearity have been discussed in detail. Special attention to self focusing of whistlers and interpretation of Stenzel’s experimental results has been given. We have also studied the filamentation of a plane uniform whistler and the growth rate of filamentation instability is seen to be a saturating function of the intensity of the beam.
KeywordsGaussian Beam Ponderomotive Force Dielectric Tensor Collisional Plasma Electron Cyclotron Frequency
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