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Lookup NU author(s): Andrew Snodin
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The magnetic field line random walk (FLRW) plays an important role in the transport of energy and particles in turbulent plasmas. For magnetic fluctuations that are transverse or almost transverse to a large-scale mean magnetic field, theories describing the FLRW usually predict asymptotic diffusion of magnetic field lines perpendicular to the mean field. Such theories often depend on the assumption that one can relate the Lagrangian and Eulerian statistics of the magnetic field via Corrsin's hypothesis, and additionally take the distribution of magnetic field line displacements to be Gaussian. Here we take an ordinary differential equation (ODE) model with these underlying assumptions and test how well it describes the evolution of the magnetic field line diffusion coefficient in 2D+slab magnetic turbulence, by comparisons to computer simulations that do not involve such assumptions. In addition, we directly test the accuracy of the Corrsin approximation to the Lagrangian correlation. Over much of the studied parameter space we find that the ODE model is in fairly good agreement with computer simulations, in terms of both the evolution and asymptotic values of the diffusion coefficient. When there is poor agreement, we show that this can be largely attributed to the failure of Corrsin's hypothesis rather than the assumption of Gaussian statistics of field line displacements. The degree of non-Gaussianity, which we measure in terms of the kurtosis, appears to be an indicator of how well Corrsin's approximation works.
Author(s): Snodin AP, Ruffolo D, Matthaeus WH
Publication type: Article
Publication status: Published
Journal: Astrophysical Journal
Year: 2016
Volume: 827
Issue: 2
Print publication date: 20/06/2016
Online publication date: 12/08/2016
Acceptance date: 16/06/2016
ISSN (print): 0004-637X
ISSN (electronic): 1538-4357
Publisher: IOP Publishing Ltd.
URL: https://doi.org/10.3847/0004-637X/827/2/115
DOI: 10.3847/0004-637X/827/2/115
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