The Effect of Coherent Structures on Stochastic Acceleration in MHD Turbulence

Abstract

We investigate the influence of coherent structures on particle acceleration in the strongly turbulent solar corona. By randomizing the Fourier phases of a pseudo-spectral simulation of isotropic MHD turbulence (Re $\sim 300$), and tracing collisionless test protons in both the exact-MHD and phase-randomized fields, it is found that the phase correlations enhance the acceleration efficiency during the first adiabatic stage of the acceleration process. The underlying physical mechanism is identified as the dynamical MHD alignment of the magnetic field with the electric current, which favours parallel (resistive) electric fields responsible for initial injection. Conversely, the alignment of the magnetic field with the bulk velocity weakens the acceleration by convective electric fields $- \bfu \times \bfb$ at a non-adiabatic stage of the acceleration process. We point out that non-physical parallel electric fields in random-phase turbulence proxies lead to artificial acceleration, and that the dynamical MHD alignment can be taken into account on the level of the joint two-point function of the magnetic and electric fields, and is therefore amenable to Fokker-Planck descriptions of stochastic acceleration.

arXiv commentaccepted for publication in ApJ

References in corpus (9)

• Particles and fields in fluid turbulence
• Simulations of MHD Turbulence in a Strongly Magnetized Medium
• Statistical Theory of Magnetohydrodynamic Turbulence: Recent Results
• The spectral evolution of impulsive solar X-ray flares
• Decay laws for three-dimensional magnetohydrodynamic turbulence
• Particle Acceleration in Multiple Dissipation Regions
• Non-gaussian probability distribution functions in two dimensional Magnetohydrodynamic turbulence
• Acceleration and Enrichment of 3He in Impulsive Solar Flares by Electron Firehose Waves
• Initial Condition Sensitivity of Global Quantities in Magnetohydrodynamic Turbulence

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