Transport of charged particles in turbulent magnetic fields
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Magnetic fields permeate the Universe. They are found in planets, stars,
galaxies, and the intergalactic medium.
The magnetic field found in these astrophysical systems are
usually chaotic, disordered, and turbulent.
The investigation of the transport
of cosmic rays in magnetic turbulence is a subject of
considerable interest. ☐ One of the important aspects of cosmic ray transport
is to understand their diffusive behavior and to calculate the diffusion coefficient
in the presence of these turbulent fields.
Research has most frequently concentrated
on determining the diffusion coefficient in
the presence of a mean magnetic field. Here, we will particularly focus
on calculating diffusion coefficients of
charged particles and magnetic field lines in a fully three-dimensional
isotropic turbulent magnetic field
with no mean field, which may be pertinent to many astrophysical
situations. ☐ For charged particles in isotropic turbulence
we identify different ranges of particle energy depending
upon the ratio of the Larmor radius of the charged particle to the
characteristic outer length scale of the turbulence. Different theoretical
models are proposed to calculate the diffusion coefficient,
each applicable to a distinct range of particle energies.
The theoretical ideas are tested
against results of detailed numerical experiments
using Monte-Carlo simulations of particle propagation in
stochastic magnetic fields. ☐ We also discuss two different methods of generating random magnetic field
to study charged particle propagation using numerical
simulation. One method is the
usual way of generating 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 therefore devise a way to generate
synthetic intermittent fields which have many properties of
realistic turbulence.
Possible applications of such synthetically generated intermittent
fields are discussed.
Description
Keywords
Pure sciences, Charged particles, Turbulent magnetic fields