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Title: Anomalous, non-Gaussian transport of charged particles in anisotropic magnetic turbulence

Abstract

The transport of energetic particles in a mean magnetic field and in the presence of anisotropic magnetic turbulence is studied numerically, for parameter values relevant to astrophysical plasmas. A numerical realization of magnetic turbulence is set up, in which the degree of anisotropy is varied by changing the correlation lengths l{sub x}, l{sub y}, and l{sub z}. The ratio {rho}/{lambda} of the particle Larmor radius {rho} over the turbulence correlation length {lambda} is also varied. It is found that for l{sub x},l{sub y}>>l{sub z}, and for {rho}/{lambda} < or approx. 10{sup -2} transport can be non-Gaussian, with superdiffusion along the average magnetic field and subdiffusion perpendicular to it. In addition, the spatial distribution of particles is clearly non-Gaussian. Such regimes are characterized by a Levy statistics, with diverging second-order moments. Decreasing the ratio l{sub x}/l{sub z}, nearly Gaussian (normal) diffusion is obtained, showing that the transport regime depends on the turbulence anisotropy. Changing the particle Larmor radius, normal diffusion is found for 10{sup -2} < or approx. {rho}/{lambda} < or approx. 1 because of increased pitch angle diffusion. New anomalous superdiffusive regimes appear when {rho}/{lambda} > or approx. 1 showing that the interaction between particles and turbulence decreases in thesemore » cases. A new regime, called generalized double diffusion, is proposed for the cases when particles are able to trace back field lines. A summary of the physical conditions which lead to non-Gaussian transport is given.« less

Authors:
; ;  [1]
  1. Physics Department, University of Calabria, Arcavacata di Rende, 87036 Rende (Italy)
Publication Date:
OSTI Identifier:
20960099
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2434795; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANISOTROPY; CHARGED PARTICLES; CORRELATIONS; DIFFUSION; LARMOR RADIUS; LENGTH; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; NUMERICAL ANALYSIS; PARTICLES; PLASMA; SPATIAL DISTRIBUTION; STATISTICS; TURBULENCE

Citation Formats

Pommois, P., Zimbardo, G., and Veltri, P. Anomalous, non-Gaussian transport of charged particles in anisotropic magnetic turbulence. United States: N. p., 2007. Web. doi:10.1063/1.2434795.
Pommois, P., Zimbardo, G., & Veltri, P. Anomalous, non-Gaussian transport of charged particles in anisotropic magnetic turbulence. United States. doi:10.1063/1.2434795.
Pommois, P., Zimbardo, G., and Veltri, P. Mon . "Anomalous, non-Gaussian transport of charged particles in anisotropic magnetic turbulence". United States. doi:10.1063/1.2434795.
@article{osti_20960099,
title = {Anomalous, non-Gaussian transport of charged particles in anisotropic magnetic turbulence},
author = {Pommois, P. and Zimbardo, G. and Veltri, P.},
abstractNote = {The transport of energetic particles in a mean magnetic field and in the presence of anisotropic magnetic turbulence is studied numerically, for parameter values relevant to astrophysical plasmas. A numerical realization of magnetic turbulence is set up, in which the degree of anisotropy is varied by changing the correlation lengths l{sub x}, l{sub y}, and l{sub z}. The ratio {rho}/{lambda} of the particle Larmor radius {rho} over the turbulence correlation length {lambda} is also varied. It is found that for l{sub x},l{sub y}>>l{sub z}, and for {rho}/{lambda} < or approx. 10{sup -2} transport can be non-Gaussian, with superdiffusion along the average magnetic field and subdiffusion perpendicular to it. In addition, the spatial distribution of particles is clearly non-Gaussian. Such regimes are characterized by a Levy statistics, with diverging second-order moments. Decreasing the ratio l{sub x}/l{sub z}, nearly Gaussian (normal) diffusion is obtained, showing that the transport regime depends on the turbulence anisotropy. Changing the particle Larmor radius, normal diffusion is found for 10{sup -2} < or approx. {rho}/{lambda} < or approx. 1 because of increased pitch angle diffusion. New anomalous superdiffusive regimes appear when {rho}/{lambda} > or approx. 1 showing that the interaction between particles and turbulence decreases in these cases. A new regime, called generalized double diffusion, is proposed for the cases when particles are able to trace back field lines. A summary of the physical conditions which lead to non-Gaussian transport is given.},
doi = {10.1063/1.2434795},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}