Growth Rate Of Filamentation Instability Research Articles

Smoothing scheme for intensity sweep and polarization rotation at a subpicosecond timescale

A novel scheme for decreasing the scattering levels of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), as well as for improving illumination uniformity of focal spots, is proposed. In this scheme, four beamlets in a laser quad are frequency shifted, spatial phase shaped by conjugate phase plates, and counter-rotating circularly polarized by polarization control plates before being focused by wedged lenses. Consequently, the intensity sweep and the polarization rotation of the focal spot in the timescale of a subpicosecond are achieved, resulting in the reduction of the scattering level of SRS and SBS, and also the improvement of the illumination uniformity when the frequency shift among beamlets is comparable to the parametric backscattering growth rate and the filamentation instability growth rate. The theoretical model of the novel smoothing scheme has been established, and the influences of some key parameters including spatial modulation type, peak-to-mean value of phase distortion, and frequency shift have been discussed. Results show that the uniformity of the focal spot of this novel scheme is improved much faster than that of the conventional temporal smoothing scheme, i.e., smoothing by spectral dispersion. The parametric instabilities are significantly reduced and both phase distortion and modulation depth of the laser quad have a large tolerance, opening a new dimension for controlling the incident light in laser plasma interaction.

Influence of non-linearity of medium on the laser induced filamentation instability in magnetized plasma

The effects of non-linearity of a medium on the growth rate of filamentation instability in a magnetized plasma interacting with an intense laser pulse is investigated. The non-linearity of the medium, modeled by Kerr non-linearity, is an important factor, which determines the rate of instability growth. The sensitivity of the rate of filamentation growth to the Kerr non-linear coefficient could be adjusted by the external magnetic field and the laser intensity.

Modulation and filamentation instability of ultrarelativistic electromagnetic waves in electron-positron-ion plasma

In this study, we have analytically investigated the effects of nonlinear Landau damping on the temporal growth rate of modulation and filamentation instabilities. Here, the nonlocal nonlinear Landau damping phenomena is appearing due to the nonlinear interaction between ultrarelativistic electromagnetic (UREM) wave (having wave vector normal to the beam) and electron-positron-ion plasma. We found that the ultrarelativistic ponderomotive force is linear, while usually it is nonlinear in relativistic case. We construct three dimensional kinetic nonlinear Schrödinger equation for a slowly varying spatio and temporal amplitude of UREM waves. The equations are then Fourier analyzed to obtain dispersion relation, which admit both modulation and filamentation instabilities. It is shown that nonlinear Landau damping is the main source of modulation instability, for a particular condition taking into account later one the maximum growth rate of modulation instability obtained as a function of amplitude of UREM waves and is displayed graphically. Further, it is shown that for an oscillating density profile, plane wave of uniform intensity becomes unstable and gets filamented. Growth rate of stationary state filament is found to be a function of amplitude of UREM waves and is emphasized that the maximum value of growth rate of filamentation instability is further increased in the presence of nonlinear Landau damping term. Finally, the growth rate of non stationary state filamentation instability is calculated and is shown that the characteristic growth length increases both with perpendicular wave vector and the amplitude of UREM waves.

Filamentation instability of an intense laser beam in axially inhomogeneous plasma

The present paper deals with the filamentation instability of a linearly polarized laser beam propagating in an axially inhomogeneous plasma. A nonlinear wave equation for the laser field driven by relativistic nonlinearity is set up. The laser amplitude is considered to be perturbed in a transverse plane. Assuming an appropriate form of the perturbed amplitude, the perturbed wave equation is solved to give the growth rate of filamentation instability for a laser beam propagating in different axially varying plasma density structures.

Filamentation Instability of Electromagnetic Radiation in Magnetized Plasma

The filamentation instability (FI) of electromagnetic waves traveling across an ambient magnetic field in a plasma has been investigated. The general dispersion relation of the FI growth rate in the presence of a perpendicular dc magnetic field has been derived, and an analytical expression for the growth rate in a weakly magnetized plasma has been obtained. The result shows reduction in the instability growth rate by the magnetic field.

Cumulative effect of the Weibel-type instabilities in symmetric counterstreaming plasmas with kappa anisotropies

Counterstreaming plasma structures are ubiquitous in laboratory experiments and astrophysical systems, and they are investigated either to prevent unstable modes arising in beam-plasma experiments or to prove the existence of large scale magnetic fields in astrophysical objects. Filamentation instability arises in a counterstreaming plasma and is responsible for the magnetization of the plasma. A filamentationally unstable mode is described by assuming two symmetric counterstreaming plasmas, each with an isotropic Lorentzian (kappa) distribution. In this case, the filamentation instability growth rate can reach a maximum value markedly larger than that for a plasma with a Maxwellian distribution function. This behavior is opposite to what was observed for the Weibel instability growth rate in a bi-kappa plasma, which is always smaller than that obtained for a bi-Maxwellian plasma. The approach is further generalized for a counterstreaming plasma with a bi-kappa temperature anisotropy. In this case, the filamentation instability growth rate is enhanced by the Weibel effect when the plasma is hotter in the streaming direction, and the growth rate becomes even larger. These effects significantly improve the efficiency of the magnetic field generation, and provide further support for the potential role of the Weibel-type instabilities in the fast magnetization scenarios.

Temporal growth rate of filamentation instability in a strongly ionised magnetoplasma

Presents an investigation of the temporal growth rate of filamentation instability of a uniform laser beam propagating along and perpendicular to the static magnetic field in a strongly ionised plasma. The nonlinearity of the dielectric constant arises on account of diffusion of non-uniformly heated carriers (on account of fluctuations in the intensity of the main beam). Both the mechanism of energy loss of electrons, namely the thermal conduction and collisions with heavy particles have been taken into consideration.

Growth of laser ripple in a plasma and its effect on plasma wave excitation

An investigation of the growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in a collisionless unmagnetized plasma is presented. The effect of the position and the width of the ripple on its growth has been studied in some detail. In a special case, the growth rate of the ripple is seen to be comparable to the growth rate of filamentation instability. In addition to the growth of the ripple, the effect of the presence of the ripple on the excitation of an electron plasma wave has also been studied.

Filamentation of a Gaussian laser beam in a plasma

Investigates the growth of filamentation instability arising from the interaction of an ion-acoustic wave with a Gaussian laser beam using the two fluid model of plasma and the paraxial approximation. The pump wave (laser beam) on account of its non-uniform character modifies the carrier density and thereby gets self-focused provided its initial power exceeds the critical value. This process further modifies the growth rate of filamentation instability.

Temporal growth of filamentation instability in plasmas

In this paper we have derived an expression for the growth rate of filamentation instability, valid for arbitrary intensity of the electromagnetic wave and upto plasma resonance (ωp?ω0 here ωp and ω0 are the field free plasma frequency and EM wave frequency respectively). In a collisionless plasma and on the short time scale (tτε, τε being the energy relaxation time) in a collisional plasma, the nonlinearity arises on account of pondermotive force and consequent depletion of electrons in regions of large wave amplitude. On the time scale of energy relaxation time in a collisional plasma, the dominant nonlinearity arises on account of preferential heating electrons. It is found that (i) maximum growth rate attains it’s maximum for an optimum intensity of the beam (ii) filamentation is predicted in the over dense plasmas (ωp≳ω0).