Density filamentation nonlinearly driven by the Weibel instability in relativistic beam plasmas

TL;DR

This paper investigates how the nonlinear behavior of plasma fluids, driven by the Weibel instability, leads to density filamentation through the gradient of the Lorentz factor, supported by simulations and theoretical analysis.

Contribution

It demonstrates that nonuniform Lorentz factor distributions can cause electrostatic fields and density filaments, providing a new explanation for filamentation in relativistic beam plasmas.

Findings

Lorentz factor gradients induce electrostatic fields.

Density filaments arise from nonlinear Lorentz factor effects.

Simulation results support the theoretical model.

Abstract

Density filamentation has been observed in many beam-plasma simulations and experiments. Because current filamentation is a pure transverse mode, charge density filamentation cannot be produced directly by the current filamentation process. To explain this phenomenon, several mechanisms are proposed such as the coupling of the Weibel instability to the two-stream instability, coupling to the Langmuir wave, differences in thermal velocities between the beam and return currents, the magnetic pressure gradient force, etc. In this paper, it is shown that the gradient of the Lorentz factor can, in fact, represent the nonlinear behavior of a plasma fluid and further that the nonuniform Lorentz factor distribution can give rise to electrostatic fields and density filaments. Simulation results together with theoretical analyses are presented.