Non-modal approach to linear theory: marginal stability and the dissipation of turbulent fluctuations

TL;DR

This paper introduces a non-modal linear stability analysis for bi-Maxwellian plasmas, revealing transient growth phenomena near marginal stability and emphasizing its importance for understanding turbulence dissipation in space plasmas.

Contribution

It applies a non-modal approach to plasma stability, highlighting transient effects and challenging traditional marginal stability concepts in anisotropic plasmas.

Findings

Stable equilibria can exhibit transient growth of physical quantities.

Transient effects become significant near marginal stability conditions.

Non-modal analysis offers new insights into turbulence dissipation mechanisms.

Abstract

The non-modal approach for a linearized system differs from a normal mode analysis by following the temporal evolution of some perturbed equilibria, and therefore includes transient effects. We employ a non-modal approach for studying the stability of a bi-Maxwellian magnetized plasma using the Landau fluid model, which we briefly describe. We show that bi-Maxwellian stable equilibria can support transient growth of some physical quantities, and we study how these transients behave when an equilibrium approaches its marginally stable condition. This is relevant to anisotropic plasma, that are often observed in the solar wind with a temperature anisotropy close to values that can trigger a kinetic instability. The results obtained with a non-modal approach are relevant to a re-examination of the concept of linear marginal stability. Moreover, we discuss the topic of the dissipation of turbulent fluctuations, suggesting that the non-modal approach should be included in future studies.