Langmuir wave filamentation in the kinetic regime. II. Weak and Strong Pumping of Nonlinear Electron Plasma Waves as the Route to Filamentation

TL;DR

This paper investigates how weak and strong external pumping of Langmuir waves in the kinetic regime leads to filamentation instability, destroying wave coherence with different growth rates for each pumping strength.

Contribution

It introduces a detailed analysis of filamentation instability in nonlinear Langmuir waves under varying pumping conditions, extending previous work to include strong pumping effects.

Findings

Weak pumping yields filamentation growth rates similar to BGK modes.

Strong pumping results in higher filamentation growth rates.

Nonlinear evolution causes loss of transverse coherence in Langmuir waves.

Abstract

We consider two kinds of pumped Langmuir waves (LWs) in the kinetic regime, $k\lambda_D\gtrsim0.2,$ where $k$ is the LW wavenumber and $\lambda_D$ is the Debye length. They are driven to finite amplitude by a coherent external potential whose amplitude is either weak or strong. These dynamically prepared nonlinear LWs develop a transverse (filamentation) instability whose nonlinear evolution destroys the LW's transverse coherence. Instability growth rates in the weakly pumped regime are the same as those of BGK modes considered in Part I, while strongly pumped LWs have higher filamentation grow rates.