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Pitch-angle diffusion coefficients in test particle simulations and the estimation of the particle parallel mean free path

Lookup NU author(s): Dr Andrew Snodin



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


The transport of energetic charged particles in turbulent magnetic fields is a topic of interest in various astrophysical contexts. In order to estimate the mean free path of a particle in the direction parallel to the mean magnetic field, one can use theoretical expressions that employ pitch-angle diffusion coefficients. In this work we review some of the methods used in estimating pitch-angle diffusion coefficients from test particle computer simulations. We examine if these methods and theoretical approaches are able to provide consistent estimates of the parallel mean free path, that can also be obtained directly from computer simulations. We perform test particle simulations for synthetic turbulence models over a range of turbulence parameters and particle energies. From the trajectories of test particles, pitch-angle distribution functions and statistics of pitch-angle displacements are obtained, which are then used to estimate the pitch-angle diffusion coefficients. We find that a method using the pitch-angle flux and derivative of the pitch-angle distribution is able to provide accurate values for the parallel mean free path over the range of parameters considered. Other methods considered are accurate only for a limited range of the turbulent fluctuation strength, or must be evaluated at a specific time to provide a reasonable estimate.

Publication metadata

Author(s): Pleumpreedaporn C, Snodin AP

Publication type: Article

Publication status: Published

Journal: Journal of Physics: Conference Series

Year: 2019

Volume: 1380

Online publication date: 16/12/2019

Acceptance date: 30/07/2019

Date deposited: 25/06/2021

ISSN (print): 1742-6588

ISSN (electronic): 1742-6596

Publisher: IOP Publishing Ltd


DOI: 10.1088/1742-6596/1380/1/012141

Notes: Siam Physics Congress 2019 (SPC2019): Physics beyond disruption society 6–7 June 2019, Songkhla, Thailand


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