Langmuir wave filamentation instability

TL;DR

This paper develops a Langmuir wave model with Hamiltonian dynamics and rotational invariance, analyzing its modulational instability behavior and identifying conditions for stable large amplitude waves.

Contribution

It introduces a novel LW model consistent with stimulated Raman scattering and explores its unique modulational instability characteristics.

Findings

Unstable wavenumber range first expands then shrinks with increasing wave amplitude.

Large amplitude wave dynamics require hyper-diffraction terms for stability.

The model accounts for all orders in wave amplitude and fluctuation wavenumber expansions.

Abstract

A Langmuir wave (LW) model is constructed whose equilibria are consistent with stimulated Raman scatter optimization, with Hamiltonian dynamics and with rotational invariance. Linear instability analysis includes terms to all orders in wave amplitude and fluctuation wavenumber expansions, deltak. Resultant LW modulational instability is nonstandard: as the LW amplitude increases, unstable deltak range first expands and then shrinks to zero. Large amplitude wave model dynamics requires hyper-diffraction terms if k LambdaD < 0.45, lest artificially small length scales become unstable.