Electromagnetic turbulence driven by the mixed mode instability

TL;DR

This paper investigates the nonlinear evolution of electromagnetic turbulence driven by the mixed mode instability in relativistic counter-streaming plasmas, revealing wave power transfer and isotropization processes relevant to astrophysical shock emissions.

Contribution

It extends previous studies by analyzing the nonlinear regime of the mixed mode instability and its impact on turbulence spectra in relativistic plasmas.

Findings

Wave power peaks on the mixed mode branch initially.

Wave power transfers to other wave numbers during late evolution.

Turbulence spectra become nearly isotropic and partially electromagnetic.

Abstract

In continuation of previous work, numerical results are presented, concerning relativistically counter-streaming plasmas. Here, the relativistic mixed mode instability evolves through, and beyond, the linear saturation -- well into the nonlinear regime. Besides confirming earlier findings, that wave power initially peaks on the mixed mode branch, it is observed that, during late time evolution wave power is transferred to other wave numbers. It is argued that the isotropization of power in wavenumber space may be a consequence of weak turbulence. Further, some modifications to the ideal weak turbulence limit is observed. Development of almost isotropic predominantly electrostatic -- partially electromagnetic -- turbulent spectra holds relevance when considering the spectral emission signatures of the plasma, namely bremsstrahlung, respectively magneto-bremsstrahlung (synchrotron radiation and jitter radiation) from relativistic shocks in astrophysical jets and shocks from gamma-ray bursts and active galactic nuclei.