Gyro-viscosity and linear dispersion relations in pair-ion magnetized plasmas

TL;DR

This paper develops a fluid theory incorporating gyro-viscosity to analyze wave propagation in pair-ion magnetized plasmas, successfully explaining experimental observations and providing a simpler alternative to kinetic theory.

Contribution

It introduces a fluid model with gyro-viscosity that simplifies the understanding of wave dispersion in pair-ion plasmas, aligning with experimental results.

Findings

Gyro-viscosity causes a transition from forward to backward wave propagation.

The derived dispersion relations match experimental observations.

The fluid theory offers a transparent alternative to kinetic models.

Abstract

A fluid theory has been developed by taking account of gyro-viscosity to study wave propagation characteristics in a homogeneous pair-ion magnetized plasma with a cylindrical symmetry. The exact dispersion relations derived by the Hankel-Fourier transformation are shown comparable with those observed in the experiment by Oohara and co-workers. The gyro-viscosity is responsible for the change in propagation characteristics of the ion cyclotron wave from forward to backward by suppressing the effect of the thermal pressure which normally causes the forward nature of dispersion. Although the experiment has been already explained by a kinetic theory by the present authors, the kinetic derivations are so involved because of exact particle orbits in phase space, finite Larmor radius effects, and higher order ion cyclotron resonances. The present fluid theory provides a simple and transparent structure to the dispersion relations since the gyro-viscosity is renormalized into the ion cyclotron frequency which itself indicates the backward nature of dispersion. The usual disadvantage of a fluid theory, which treats only fundamental modes of eigen-waves excited in a system and is not able to describe higher harmonics that a kinetic theory does, is compensated by simple derivations and clear picture based on the renormalization of the gyro-viscosity.