Anomalous, nonGaussian 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 nonGaussian, with superdiffusion along the average magnetic field and subdiffusion perpendicular to it. In addition, the spatial distribution of particles is clearly nonGaussian. Such regimes are characterized by a Levy statistics, with diverging secondorder 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 »
 Authors:
 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, nonGaussian 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, nonGaussian transport of charged particles in anisotropic magnetic turbulence. United States. doi:10.1063/1.2434795.
Pommois, P., Zimbardo, G., and Veltri, P. Mon .
"Anomalous, nonGaussian transport of charged particles in anisotropic magnetic turbulence". United States.
doi:10.1063/1.2434795.
@article{osti_20960099,
title = {Anomalous, nonGaussian 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 nonGaussian, with superdiffusion along the average magnetic field and subdiffusion perpendicular to it. In addition, the spatial distribution of particles is clearly nonGaussian. Such regimes are characterized by a Levy statistics, with diverging secondorder 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 nonGaussian 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}
}

Collisionless magnetohydrodynamic Turbulence is common in large scale astrophysical environments. The determination of the transport of charged particles both parallel and perpendicular in such a system is of considerable interest. Quasilinear analysis or direct numerical simulation can be used to find the effects of the turbulent magnetic field on the transport of charged particles. A number of different magnetic turbulence models have been proposed in the last several decades. We present here the results of studying particle transport in synthesized, anisotropic turbulence and compare the results with those obtained using the standard isotropic turbulence model in a series of papers.more »

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