Polarized 3D Synthetic Turbulence I: Magnetic Field Line Random Walk

TL;DR

This study investigates how magnetic field line diffusion in synthetic turbulence depends on polarization configurations, revealing significant differences from isotropic cases and aligning with theoretical predictions and recent simulations.

Contribution

It introduces polarized synthetic turbulence models and analyzes the impact of polarization on magnetic field line diffusion properties, highlighting new scaling laws and dependencies.

Findings

Field line wandering strongly depends on polarization configurations.

Sub-diffusive phase is highly polarization-dependent and matches theoretical predictions.

Asymptotic diffusion coefficient scales as $( ext{delta} B/B)^4$ in magnetosonic-like polarization.

Abstract

The behavior of magnetic field lines in a turbulent plasma is a key property of the medium, with important consequences for plasma dynamics and charged-particle transport. We study the diffusion properties of magnetic field lines in synthetic turbulence featuring different polarization configurations for the magnetic perturbations, as prescribed by the existing magnetohydrodynamic modes (namely, Alfv\'enic and magnetosonic). These turbulent field realizations are then compared with the isotropic (or, random) polarization case, which is the one typically adopted in the literature. We construct polarized synthetic turbulence simulations and study the properties of field lines through the running diffusion coefficient. Our key findings can be summarized as follow: (i) field line wandering is strongly dependent on polarization configurations, (ii) we unveil that the sub-diffusive phase of field line is highly dependent on the polarization and is well reproduced by theoretical predictions based on Corrsin's hypothesis in the low turbulence level regime, (iii) in particular the scaling of the asymptotic diffusion coefficient in magnetosonic-like polarization is $(\delta B/B)^4$ at odd with the $(\delta B/B)^2$ scaling found in the quasi-linear regime for random polarization, (iv) interestingly we note that the subdiffusive phase of field line transport in the magnetosonic-like polarization follows closely the one observed in recent high resolution MHD turbulence simulations, we end giving a word of caution when FL transport is investigated in such simulations.