The frequency and damping of ion acoustic waves in hydrocarbon (CH) and two-ion-species plasmas

TLDR

Ion‑acoustic waves in multi‑ion‑species plasmas are studied using kinetic theory, with a focus on hydrocarbon (CH) plasmas common in laser–plasma experiments. The authors compute the frequencies and Landau damping of the two dominant ion‑acoustic modes in CH plasmas by numerically solving the kinetic dispersion relation. Analytical expansions and fluid models disagree with the numerical results in practical regimes; when ion temperatures exceed 0.2 T_e, the mode with the smaller phase velocity becomes the least damped and dominates the ponderomotive response.

Abstract

The kinetic theory of ion-acoustic waves in multi-ion-species plasmas is discussed. Particular application is made to hydrocarbon (CH) plasmas, which are widely used in laser–plasma experiments. The mode frequencies and Landau damping of the two, dominant, ion-acoustic modes in CH plasmas are calculated by numerical solution of the kinetic dispersion relation. In addition, some useful results are obtained analytically from expansions of the kinetic dispersion relation and from fluid models. However, these results disagree with the numerical results in domains of particular practical interest. When ion temperatures exceed two-tenths of the electron temperature, the least damped mode is the one with the smaller phase velocity, and this mode is then found to dominate the ponderomotive response of the CH plasma.