Transport of Charged Particles in Turbulent Magnetic Fields

PARASHAR, T.; SUBEDI, P.; SONSRETTEE, W.; BLASI, P.; RUFFOLO, D. J.; MATTHAEUS, W. H.; MONTGOMERY, D.; CHUYCHAI, P.; DMITRUK, P.; WAN, M.; CHHIBER, R.

New Orleans

Congreso; American Geophysical Union Fall Meeting 2017; 2017

AGU

Magnetic fields permeate the Universe. They are found in planets, stars,galaxies, and the intergalactic medium. The magnetic field found inthese astrophysical systems are usually chaotic, disordered, andturbulent. The investigation of the transport of cosmic rays in magneticturbulence is a subject of considerable interest. One of the importantaspects of cosmic ray transport is to understand their diffusivebehavior and to calculate the diffusion coefficient in the presence ofthese turbulent fields. Research has most frequently concentrated ondetermining the diffusion coefficient in the presence of a mean magneticfield. Here, we will particularly focus on calculating diffusioncoefficients of charged particles and magnetic field lines in a fullythree-dimensional isotropic turbulent magnetic field with no mean field,which may be pertinent to many astrophysical situations. For chargedparticles in isotropic turbulence we identify different ranges ofparticle energy depending upon the ratio of the Larmor radius of thecharged particle to the characteristic outer length scale of theturbulence. Different theoretical models are proposed to calculate thediffusion coefficient, each applicable to a distinct range of particleenergies. The theoretical ideas are tested against results of detailednumerical experiments using Monte-Carlo simulations of particlepropagation in stochastic magnetic fields. We also discuss two differentmethods of generating random magnetic field to study charged particlepropagation using numerical simulation. One method is the usual way ofgenerating random fields with a specified power law in wavenumber space,using Gaussian random variables. Turbulence, however, is non-Gaussian,with variability that comes in bursts called intermittency. We thereforedevise a way to generate synthetic intermittent fields which have manyproperties of realistic turbulence. Possible applications of suchsynthetically generated intermittent fields are discussed.