The separation of ions and fluxes in nonlinear ion-acoustic waves

TL;DR

This paper investigates how nonlinear ion-acoustic waves in multi-species plasmas can induce ion fluxes that enable ion separation, with potential applications in plasma processing and diagnostics.

Contribution

It provides new calculations of ion fluxes in various plasma models, revealing mechanisms for ion separation driven by nonlinear wave dynamics.

Findings

Ion fluxes in electron-ion plasma oppose wave phase speed.

Fast waves co-direct ion fluxes, drift against wave.

Slow waves cause ions to drift in opposite directions.

Abstract

The multi-species plasma of natural or laboratory origin is often considered to host nonlinear ion-acoustic waves. We present calculations of ion fluxes induced by nonlinear ion-acoustic waves in a plasma consisting of multiple ion populations, electrons, and dust. The following plasma models are considered: an electron-ion plasma with cold ions, a bi-ion plasma with two types of warm positively charged ions, and a dusty bi-ion plasma. It is found that in the electron-ion plasma, the wave-induced ion flux is directed oppositely to the phase speed of the nonlinear ion-acoustic wave. In the bi-ion plasma, there are two modes of ion-acoustic waves which are fast and slow waves. In the nonlinear fast ion-acoustic wave, the fluxes of both types of ions are found to be co-directed and drift against the wave. In a slow wave, the nonlinear fluxes of ions are directed in opposite directions. This result demonstrates the possibility to use these nonlinear wave-induced ion fluxes for effective separation of ions in the plasma. In a dusty bi-ion plasma, the ion separation process can be intensified by a super-nonlinear regime of slow ion-acoustic waves.