Note on the role of friction-induced momentum conservation in the collisional drift wave instability

TL;DR

This paper reexamines the collisional drift wave instability by incorporating ion response due to friction with electrons, revealing how the instability threshold shifts based on dominant collision processes and momentum conservation.

Contribution

It introduces a modified instability threshold considering ion response and friction effects, highlighting differences between electron-neutral and electron-ion collision regimes.

Findings

Instability threshold shifts to higher frequencies with dominant electron-neutral collisions.

Ion response due to friction affects the instability threshold.

The difference between collision regimes vanishes when ion sound response is negligible.

Abstract

The collisional drift wave instability is reexamined taking into account the ion response in the direction parallel to the magnetic field lines, which appears due to friction with electrons and which can not be omitted in view of the momentum conservation. A modified instability threshold is obtained. In plasmas with dominant electron collisions with neutrals, the instability threshold is shifted towards higher frequencies, compared to the case of dominant electron collisions with ions. The difference between the two cases vanishes when the ion sound response is negligible, i.e., when the instability threshold disappears, and both ions and neutrals react to the electron friction in the same manner.