Phase space vortex merging in electron plasma waves is researched by applying a periodically changing electric field in plasma space with Maxwellian velocity distribution. The pump electric field excites the electron plasma wave with large amplitude and electron phase space vortices are formed. The electron plasma wave can be transited to longer wave modes through vortex merging processes. Excepting the fundamental mode of electron plasma waves, two or more modes appear and grow exponentially before vortex merging. After merging, another mode replaces the initial pumping wave as the strongest wave mode. It is verified that the growth of this new strong mode is related to trapping particle instability. Vortex merging is one of the saturation mechanisms of trapped particle instability.

In supersonic flowing plasmas, the auto-resonant behavior of ion acoustic waves driven by stimulated Brillouin backscattering is self-consistently investigated. A nature of absolute instability appears in the evolution of the stimulated Brillouin backscattering. By adopting certain form of incident lights combined by two perpendicular linear polarization lasers or polarization rotation lasers, the absolute instability is suppressed significantly. The suppression of auto-resonant stimulated Brillouin scattering is verified with the fully kinetic Vlasov code.

Stimulated Brillouin scattering (SBS) is a basic problem for laser–plasma interactions. In this work, two perpendicular linear polarization lasers with different frequencies are combined to form a new beam. The polarization of the new beam varies between linear and ellipse, while the intensity remains constant. By adopting this method, a significant suppression of SBS is predicted due to the reduction in the effective wave–wave interaction lengths. Additionally, two linearly polarized beams would be easier to use in an experiment than an alternate approach using two circularly polarized beams. The suppression of SBS is modeled with a nonlinear wave–wave coupling model, and the model is verified with 1D particle-in-cell simulations.

The fast and slow waves in multi-ion species collisionless plasmas have been widely studied, but the collision effect on ion acoustic waves is a difficult problem. In this paper, plasmas with azimuthal symmetry velocity distribution in different collisional regimes are studied by eigenvalue solution of the linearized Fokker–Planck equation. The frequency, damping rate and distribution function from the solutions are consistent with the analytical result in collisionless limit. For the fast wave, the damping rate agrees well with the prediction of both fluid theory in collision limit and kinetic theory in collisionless limit. But for the slow wave, the frequency and damping rate predicted by fluid theory are not accurate. In two-ion species plasmas, the light and heavy ion density perturbation phases of two-ion species are the same for the fast wave, but opposite for the slow wave. Polytropic index of C5H12 plasmas is also calculated, which is simply affected by mean-free paths of ions for the fast wave, but affected by multiple factors, such as mean-free paths, heat transfer and the opposite phases for the slow wave.