Resonance overlap and non-linear features of the beam-plasma system

TL;DR

This paper investigates the non-linear dynamics of the beam-plasma system, focusing on resonance overlap, phase-space transport barriers, and saturation levels to better understand plasma behavior in various contexts.

Contribution

It refines the understanding of resonance overlap and non-linear features in the beam-plasma instability, introducing phase-space analysis with Lagrangian Coherent Structures.

Findings

Resonance size correlates with spectral overlap at saturation.

Phase-space barriers influence transport regimes.

Mode saturation levels are characterized in detail.

Abstract

The beam-plasma instability can be addressed as a reduced model in several contexts of plasma physics, from space to fusion plasma. In this paper, we review and refine some non-linear features of this model. Specifically, by analyzing the dependence of the non-linear velocity spread as a function of the linear growth rate, we discuss the effective size of the resonance in view of its role in the spectral overlap at saturation. The relevance of this characterization relies on the necessity of a quantitative determination of the overlap degree to discriminate among different transport regimes of the self consistent dynamics. The analysis is enriched with a study of the phase-space dynamics by means of the Lagrangian Coherent Structure technique, in order to define the transport barriers of the system describing the relevant features of the overlap process. Finally, we discuss relevant features related to the mode saturation levels.