Fluid nonlinear frequency shift of nonlinear ion acoustic waves in multi-ion species plasmas in small wave number region

TL;DR

This paper investigates the fluid nonlinear frequency shift of ion acoustic waves in multi-ion plasmas using Vlasov simulations and theoretical modeling, revealing dominance in small wave number regions and implications for stimulated Brillouin scattering.

Contribution

It provides a theoretical model for fluid NFS from harmonic generation in multi-ion plasmas and validates it with Vlasov simulation results.

Findings

Fluid NFS can reach nearly 15% at small wave numbers and large amplitudes.

Fluid NFS dominates the total NFS in small wave number regions.

Results have implications for understanding stimulated Brillouin scattering saturation.

Abstract

The properties of the nonlinear frequency shift (NFS) especially the fluid NFS from the harmonic generation of the ion-acoustic wave (IAW) in multi-ion species plasmas have been researched by Vlasov simulation. The pictures of the nonlinear frequency shift from harmonic generation and particles trapping are shown to explain the mechanism of NFS qualitatively. The theoretical model of the fluid NFS from harmonic generation in multi-ion species plasmas is given and the results of Vlasov simulation are consistent to the theoretical result of multi-ion species plasmas. When the wave number $k\lambda_{De}$ is small, such as $k\lambda_{De}=0.1$, the fluid NFS dominates in the total NFS and will reach as large as nearly $15\%$ when the wave amplitude $|e\phi/T_e|\sim0.1$, which indicates that in the condition of small $k\lambda_{De}$, the fluid NFS dominates in the saturation of stimulated Brillouin scattering especially when the nonlinear IAW amplitude is large.