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Title: The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares

Abstract

The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze this approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport ofmore » electrons along the magnetic field of a flaring loop can be modeled rather effectively as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.« less

Authors:
;  [1];  [2]
  1. School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom)
  2. Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101 (United States)
Publication Date:
OSTI Identifier:
22663899
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COLLISIONS; CORRECTIONS; DIFFUSION; DISTRIBUTION FUNCTIONS; EMISSION; ENERGY ABSORPTION; ENERGY LOSSES; FLARING; GAMMA RADIATION; HARD X RADIATION; MAGNETIC FIELDS; MEAN FREE PATH; RANDOMNESS; SCATTERING; SOLAR FLARES; SPATIAL DISTRIBUTION; SUN; TAIL ELECTRONS; VELOCITY

Citation Formats

Bian, Nicolas H., Kontar, Eduard P., and Emslie, A. Gordon, E-mail: nicolas.bian@glasgow.gla.ac.uk, E-mail: emslieg@wku.edu. The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/262.
Bian, Nicolas H., Kontar, Eduard P., & Emslie, A. Gordon, E-mail: nicolas.bian@glasgow.gla.ac.uk, E-mail: emslieg@wku.edu. The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares. United States. doi:10.3847/1538-4357/835/2/262.
Bian, Nicolas H., Kontar, Eduard P., and Emslie, A. Gordon, E-mail: nicolas.bian@glasgow.gla.ac.uk, E-mail: emslieg@wku.edu. Wed . "The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares". United States. doi:10.3847/1538-4357/835/2/262.
@article{osti_22663899,
title = {The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares},
author = {Bian, Nicolas H. and Kontar, Eduard P. and Emslie, A. Gordon, E-mail: nicolas.bian@glasgow.gla.ac.uk, E-mail: emslieg@wku.edu},
abstractNote = {The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze this approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport of electrons along the magnetic field of a flaring loop can be modeled rather effectively as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.},
doi = {10.3847/1538-4357/835/2/262},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}