Nonlinear evolution of kinetic Alfvén waves and the turbulent spectra.

This paper presents the model equation governing the nonlinear dynamics of the kinetic Alfvén wave (KAW) in the low-β plasmas (β≪me/mi) and intermediate-β plasmas (me/mi≪β≪1), where β is thermal pressure to background magnetic pressure ratio, me/mi is the electron to ion mass ratio. When the ponderomotive and Joule heating nonlinearities are incorporated in the KAW dynamics, the model equation turns out to be a modified nonlinear Schrödinger equation. Numerical solution of this has been obtained when the incident pump KAW is having a small perturbation. Energy exchange between main KAW and perturbation and the resulting filamentary structures of the KAW have been studied. More detail diagnostics reveal that the dynamics of the wave is chaotic. We have presented a simplified model also to explain some of the features of this evolution. Nonlinear saturation of the instability in the form of localized structures and the resulting power spectra of the magnetic field has also been studied. [ABSTRACT FROM AUTHOR]