Nonlinear oscillations and waves in multi-species cold plasmas

TL;DR

This paper investigates nonlinear oscillations in multi-species cold plasmas, revealing how ponderomotive forces influence phase mixing and wave behavior, with implications for laboratory and astrophysical plasma studies.

Contribution

It constructs two nonlinear solutions showing different phase mixing behaviors and analyzes the role of ponderomotive forces across various plasma compositions.

Findings

Indirect ponderomotive effects are negligible in electron-ion plasma.

No phase mixing occurs in the second solution without ponderomotive forces.

The second solution results in an undistorted nonlinear traveling wave.

Abstract

The spatio-temporal evolution of nonlinear oscillations in multi-species plasma is revisited to provide more insight into the physics of phase mixing by constructing two sets of nonlinear solutions up to the second order. The first solution exhibits perfect oscillations in the linear regime and phase mixing appears only nonlinearly in the second order as a response to the ponderomotive forces. This response can be both direct and indirect. The indirect contribution of the ponderomotive forces appears through self-consistently generated low frequency fields. Furthermore, the direct and indirect contributions of the ponderomotive forces on the phase mixing process is explored and it is found that the indirect contribution is negligible in an electron-ion plasma and it disappears in the case of electron-positron plasma, yet represents an equal contribution in the electron-positron-ion plasma. However, the second solution does not exhibit any phase mixing due to the absence of ponderomotive forces but results in an undistorted nonlinear traveling wave. These investigations have relevance for laboratory/astrophysical multi-species plasma.