Laser Plasma Interaction at High Power Laser Flux

Abstract

In presence of self-generated magnetic field the high power laser beam in x- mode decays parametrically into upper hybrid wave (UHW) and the magnetosonic wave (MSW). The efforts have been made to understand amplification and turbulence in magnetic field observed in the laboratory plasma as well as astrophysical phenomena. In the proposed thesis, nonlinear interaction of pump MSW (with frequency not much less than ion gyro-frequency ), with various low frequency ( ) waves like ion acoustic wave (propagating in z direction) or slow Alfvén wave (SAW) (propagating in x -z plane, propagating obliquely to background field) etc. has been studied. The pump magnetosonic wave is considered to be propagating in x direction perpendicular to the background magnetic field which is along the z direction, and in other case pump MSW is propagating in the x-z plane. newline Pump MSW nonlinearly interacts with density perturbation which in turn excites various waves (like ion acoustic wave, slow Alfvén wave etc.) which causes the localization of the MSW. The formation of localized structure, resultant turbulent spectrum and its scaling has been studied. To fulfill this objective, a coupled set of nonlinear dynamical equations has been derived by taking nonlinear ponderomotive force associated with pump wave into account. This nonlinearity causes transfer of energy between different length scales. newline Taking the adiabatic case, the localization of MSW is firstly studied via semi-analytical tool to have physical insight of these structures and later by numerical techniques. Numerical simulation is performed to analyze the dependence of localization upon varying different parameters of pump and perturbation. The rate of energy transfer process is implicated by the spectral index in the turbulent energy spectrum. The spatio-temporal evolution of MSW is also studied by relaxing the adiabatic condition of the density fluctuations as one of the objectives. The relevance of the present investigation of the formation of localized structures, amplification and turbulence scaling has been shown with the observation of various experimental results with laser plasma interaction replicating various astrophysical phenomena. newline newline