Ion thermal effects in oscillating multi-ion plasma sheath theory

TL;DR

This paper investigates ion thermal effects in oscillating multi-ion plasma sheaths, comparing fluid and kinetic models, and introduces a fluid model that accurately captures ion acoustic modes and damping phenomena.

Contribution

It presents a fluid model that overcomes limitations of approximative kinetic descriptions, accurately capturing multiple ion acoustic modes and their damping.

Findings

Approximative kinetic models fail to describe the additional acoustic mode.

Approximative kinetic models inaccurately predict Landau damping.

The proposed fluid model captures both fast and slow ion acoustic modes and their damping.

Abstract

The effects of ion temperature are discussed in a two-ion electron plasma and for a model applicable to the oscillating sheath theory that has recently been much in the focus of researchers. The differences between the fluid and kinetic models have been pointed out, as well as the differences between the approximative kinetic description (which involves the expansion of the plasma dispersion function), and the exact kinetic description. It is shown that the approximative kinetic description, first, can not describe the additional acoustic mode which naturally exists in the plasma with an additional ion population with a finite temperature, and, second, it yields an inaccurate Landau damping of the bulk ion acoustic mode. The reasons for these two failures are described. In addition to this, a fluid model is presented that is capable of capturing both of these features that are missing in the approximative kinetic description, i.e., two (fast and slow) ion acoustic modes, and the corresponding Landau damping of both modes.