Particle acceleration at a flare termination shock: Effect of large-scale magnetic turbulence

Fan Guo, Joe Giacalone

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

We investigate the acceleration of charged particles (both electrons and protons) at collisionless shocks predicted to exist in the vicinity of solar flares. The existence of standing termination shocks has been examined by flare models and numerical simulations. We study electron energization by numerically integrating the equations of motion of a large number of test-particle electrons in the time-dependent two-dimensional electric and magnetic fields generated from hybrid simulations (kinetic ions and fluid electron) using parameters typical of the solar flare plasma environment. The shock is produced by injecting plasma flow toward a rigid piston. Large-scale magnetic fluctuations - known to exist in plasmas and known to have important effects on the nonthermal electron acceleration at shocks - are also included in our simulations. For the parameters characteristic of the flaring region, our calculations suggest that the termination shock formed in the reconnection outflow region (above post-flare loops) could accelerate electrons to a kinetic energy of a few MeV within 100 ion cyclotron periods, which is of the order of a millisecond. Given a sufficient turbulence amplitude level (δB 2/B 2 0 0.3), about 10% of thermal test-particle electrons are accelerated to more than 15keV. We find that protons are also accelerated, but not to as high energy in the available time and the energy spectra are considerably steeper than that of the electrons for the parameters used in our simulations. Our results are qualitatively consistent with the observed hard X-ray emissions in solar flares.

Original languageEnglish (US)
Article number28
JournalAstrophysical Journal
Volume753
Issue number1
DOIs
StatePublished - Jul 1 2012

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particle acceleration
flares
turbulence
shock
electron
solar flares
electrons
plasma
simulation
electron acceleration
protons
magnetohydrodynamic flow
effect
particle
ion
pistons
cyclotrons
charged particles
ions
equations of motion

Keywords

  • acceleration of particles
  • shock waves
  • Sun: flares
  • turbulence

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Particle acceleration at a flare termination shock : Effect of large-scale magnetic turbulence. / Guo, Fan; Giacalone, Joe.

In: Astrophysical Journal, Vol. 753, No. 1, 28, 01.07.2012.

Research output: Contribution to journalArticle

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