Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence

F. Fraschetti, Joe Giacalone

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.

Original languageEnglish (US)
Article number114
JournalAstrophysical Journal
Volume755
Issue number2
DOIs
StatePublished - Aug 20 2012

Fingerprint

particle diffusion
autocorrelation
charged particles
turbulence
cosmic rays
diffusion coefficient
magnetic fields
interplanetary space
isotropic turbulence
intergalactic media
simulation
magnetic field
energetic particles
cosmic ray
particle energy
supernovae
power spectra
equations of motion
flux density
shock

Keywords

  • cosmic rays
  • ISM: magnetic fields
  • turbulence

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence. / Fraschetti, F.; Giacalone, Joe.

In: Astrophysical Journal, Vol. 755, No. 2, 114, 20.08.2012.

Research output: Contribution to journalArticle

@article{396d1d3053114dea8f256ec4200ae9a6,
title = "Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence",
abstract = "Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles {"}decorrelate{"} from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.",
keywords = "cosmic rays, ISM: magnetic fields, turbulence",
author = "F. Fraschetti and Joe Giacalone",
year = "2012",
month = "8",
day = "20",
doi = "10.1088/0004-637X/755/2/114",
language = "English (US)",
volume = "755",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

TY - JOUR

T1 - Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence

AU - Fraschetti, F.

AU - Giacalone, Joe

PY - 2012/8/20

Y1 - 2012/8/20

N2 - Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.

AB - Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.

KW - cosmic rays

KW - ISM: magnetic fields

KW - turbulence

UR - http://www.scopus.com/inward/record.url?scp=84864718326&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84864718326&partnerID=8YFLogxK

U2 - 10.1088/0004-637X/755/2/114

DO - 10.1088/0004-637X/755/2/114

M3 - Article

VL - 755

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 114

ER -