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 gyroadii 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 -- ${\sigma }^2\sim$ 10 $B_0^2$, where $B_0$ 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 \textit{in situ} observations at Saturn's bow shock. The study may help understand the acceleration of electrons at shocks in space and astrophysical systems.

7 pages, 5 figures. Accepted for publication in the Astrophysical Journal

References in corpus (7)

• A kinetic approach to cosmic ray induced streaming instability at supernova shocks
• Confirmation of strong magnetic field amplification and nuclear cosmic ray acceleration in SN 1006
• Off-limb Solar Coronal Wavefronts From SDO/AIA EUV Observations - Implications For Particle Production
• Nonrelativistic collisionless shocks in weakly magnetized electron--ion plasmas: two-dimensional particle-in-cell simulation of perpendicular shock
• Simulations of Electron Acceleration at Collisionless Shocks: The Effects of Surface Fluctuations
• A critical Mach number for electron injection in collisionless shocks
• Particle-in-cell simulations of particle energization from low Mach number fast mode shocks

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• Non-thermal particle acceleration at highly oblique non-relativistic shocks
• Non-linear diffusive shock acceleration: A recipe for injection of electrons
• An in situ comparison of electron acceleration at collisionless shocks under differing upstream magnetic field orientations
• Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks: Effects of Preexisting Nonthermal Electrons
• Electron Energization in Quasi-Parallel Shocks: Test-Particle-Electrons in a Proton Driven Turbulence
• Variable Ion Compositions of Solar Energetic Particle Events in the Inner Heliosphere: A Field-line Braiding Model with Compound Injections
• Non-linear Diffusive Shock Acceleration of Cosmic Rays -- Quasi-thermal and Non-thermal Particle Distributions
• The mechanism of efficient electron acceleration at parallel non-relativistic shocks
• Transport of electrons in tangled magnetic fields