The acceleration of electrons at collisionless shocks moving through a turbulent magnetic field

Fan Guo, Joe Giacalone

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

We perform a numerical-simulation study of the acceleration of electrons at shocks that propagate through a prespecified, kinematically defined turbulent magnetic field. The turbulence consists of broadband magnetic fluctuations that are embedded in the plasma and cover a range of wavelengths, the smallest of which is larger than the gyroradii of electrons that are initially injected into the system. We find that when the variance of the turbulent component of the upstream magnetic field is sufficiently large - σ2 ∼ 10 B02, where B0 is the strength of the background magnetic field - electrons can be efficiently accelerated at a collisionless shock regardless of the orientation of the mean upstream magnetic field relative to the shock-normal direction. Since the local angle between the incident magnetic-field vector and the shock-normal vector can be quite large, electrons can be accelerated through shock-drift acceleration at the shock front. In the upstream region, electrons are mirrored back to the shock front leading to multiple shock encounters. Eventually the accelerated electrons are energetic enough that their gyroradii are of the same order as the wavelength of waves that are included in our description of the turbulent magnetic field. Our results are consistent with recent in situ observations at Saturn's bow shock. This study may help us to understand the acceleration of electrons at shocks in space and astrophysical systems.

Original languageEnglish (US)
Article number97
JournalAstrophysical Journal
Volume802
Issue number2
DOIs
StatePublished - Apr 1 2015

Fingerprint

shock
magnetic field
electron
magnetic fields
electrons
upstream
shock fronts
wavelength
Saturn
bows
wavelengths
encounters
energetics
turbulence
astrophysics
plasma
broadband
simulation

Keywords

  • Acceleration of particles
  • Cosmic rays
  • Shock waves
  • Turbulence

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

The acceleration of electrons at collisionless shocks moving through a turbulent magnetic field. / Guo, Fan; Giacalone, Joe.

In: Astrophysical Journal, Vol. 802, No. 2, 97, 01.04.2015.

Research output: Contribution to journalArticle

@article{b63113b90fd345e895f254bb27b08a31,
title = "The acceleration of electrons at collisionless shocks moving through a turbulent magnetic field",
abstract = "We perform a numerical-simulation study of the acceleration of electrons at shocks that propagate through a prespecified, kinematically defined turbulent magnetic field. The turbulence consists of broadband magnetic fluctuations that are embedded in the plasma and cover a range of wavelengths, the smallest of which is larger than the gyroradii of electrons that are initially injected into the system. We find that when the variance of the turbulent component of the upstream magnetic field is sufficiently large - σ2 ∼ 10 B02, where B0 is the strength of the background magnetic field - electrons can be efficiently accelerated at a collisionless shock regardless of the orientation of the mean upstream magnetic field relative to the shock-normal direction. Since the local angle between the incident magnetic-field vector and the shock-normal vector can be quite large, electrons can be accelerated through shock-drift acceleration at the shock front. In the upstream region, electrons are mirrored back to the shock front leading to multiple shock encounters. Eventually the accelerated electrons are energetic enough that their gyroradii are of the same order as the wavelength of waves that are included in our description of the turbulent magnetic field. Our results are consistent with recent in situ observations at Saturn's bow shock. This study may help us to understand the acceleration of electrons at shocks in space and astrophysical systems.",
keywords = "Acceleration of particles, Cosmic rays, Shock waves, Turbulence",
author = "Fan Guo and Joe Giacalone",
year = "2015",
month = "4",
day = "1",
doi = "10.1088/0004-637X/802/2/97",
language = "English (US)",
volume = "802",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

TY - JOUR

T1 - The acceleration of electrons at collisionless shocks moving through a turbulent magnetic field

AU - Guo, Fan

AU - Giacalone, Joe

PY - 2015/4/1

Y1 - 2015/4/1

N2 - We perform a numerical-simulation study of the acceleration of electrons at shocks that propagate through a prespecified, kinematically defined turbulent magnetic field. The turbulence consists of broadband magnetic fluctuations that are embedded in the plasma and cover a range of wavelengths, the smallest of which is larger than the gyroradii of electrons that are initially injected into the system. We find that when the variance of the turbulent component of the upstream magnetic field is sufficiently large - σ2 ∼ 10 B02, where B0 is the strength of the background magnetic field - electrons can be efficiently accelerated at a collisionless shock regardless of the orientation of the mean upstream magnetic field relative to the shock-normal direction. Since the local angle between the incident magnetic-field vector and the shock-normal vector can be quite large, electrons can be accelerated through shock-drift acceleration at the shock front. In the upstream region, electrons are mirrored back to the shock front leading to multiple shock encounters. Eventually the accelerated electrons are energetic enough that their gyroradii are of the same order as the wavelength of waves that are included in our description of the turbulent magnetic field. Our results are consistent with recent in situ observations at Saturn's bow shock. This study may help us to understand the acceleration of electrons at shocks in space and astrophysical systems.

AB - We perform a numerical-simulation study of the acceleration of electrons at shocks that propagate through a prespecified, kinematically defined turbulent magnetic field. The turbulence consists of broadband magnetic fluctuations that are embedded in the plasma and cover a range of wavelengths, the smallest of which is larger than the gyroradii of electrons that are initially injected into the system. We find that when the variance of the turbulent component of the upstream magnetic field is sufficiently large - σ2 ∼ 10 B02, where B0 is the strength of the background magnetic field - electrons can be efficiently accelerated at a collisionless shock regardless of the orientation of the mean upstream magnetic field relative to the shock-normal direction. Since the local angle between the incident magnetic-field vector and the shock-normal vector can be quite large, electrons can be accelerated through shock-drift acceleration at the shock front. In the upstream region, electrons are mirrored back to the shock front leading to multiple shock encounters. Eventually the accelerated electrons are energetic enough that their gyroradii are of the same order as the wavelength of waves that are included in our description of the turbulent magnetic field. Our results are consistent with recent in situ observations at Saturn's bow shock. This study may help us to understand the acceleration of electrons at shocks in space and astrophysical systems.

KW - Acceleration of particles

KW - Cosmic rays

KW - Shock waves

KW - Turbulence

UR - http://www.scopus.com/inward/record.url?scp=84926654609&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84926654609&partnerID=8YFLogxK

U2 - 10.1088/0004-637X/802/2/97

DO - 10.1088/0004-637X/802/2/97

M3 - Article

AN - SCOPUS:84926654609

VL - 802

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 97

ER -