Perpendicular electron collisions in drift and acoustic wave instabilities

TL;DR

This paper investigates how perpendicular electron collisions influence drift and acoustic wave instabilities, revealing that the growth rate depends on propagation angle and decreases with smaller parallel wave numbers, contrary to previous expectations.

Contribution

It provides a detailed analysis of perpendicular electron collision effects on drift and acoustic wave instabilities, highlighting the angle dependence of growth rates and the behavior at small parallel wave numbers.

Findings

Growth rate decreases for smaller parallel wave numbers.

Growth rate is angle dependent and peaks at specific propagation directions.

Analysis extends to acoustic perturbations with unmagnetized ions and magnetized electrons.

Abstract

Perpendicular electron dynamics and the associated collisions are discussed in relation to the collisional drift wave instability. In addition, the limit of small parallel wave numbers of this instability is studied and it is shown to yield a reduced wave frequency. It is also shown that in this case the growth rate in fact {\em decreases} for smaller parallel wave numbers, instead of growing proportional to $1/k_z^2$. As a result, the growth rate appears to be angle dependent and to reach a maximum for some specific direction of propagation. The explanation for this strange behavior is given. A similar analysis is performed for acoustic perturbations in plasmas with unmagnetized ions and magnetized electrons, in the presence of a density gradient.