Nonlinear physics and energetic particle transport features of the beam-plasma instability

TL;DR

This paper investigates the nonlinear dynamics and transport properties of a beam-plasma system with multiple resonances, using a theoretical framework and numerical simulations to analyze phase space transport and structure formation.

Contribution

It introduces a model with multiple cold beams interacting with Langmuir modes and applies Lagrangian Coherent Structures to analyze transport, advancing understanding of beam-plasma nonlinear dynamics.

Findings

Phase space splits into regions with different transport rates

Lagrangian Coherent Structures effectively identify transport barriers

Numerical simulations confirm theoretical predictions

Abstract

In this paper, we study transport features of a one-dimensional beam-plasma system in the presence of multiple resonances. As a model description of the general problem of a warm energetic particle beam, we assume $n$ cold supra-thermal beams and investigate the self-consistent evolution in the presence of the complete spectrum of nearly degenerate Langmuir modes. A qualitative transport estimation is obtained by computing the Lagrangian Coherent Structures of the system on given temporal scales. This leads to the splitting of the phase space into regions where the local transport processes are relatively faster. The general theoretical framework is applied to the case of the nonlinear dynamics of two cold beams, for which numerical simulation results are illustrated and analyzed.