Abstract
We investigate the influence of coherent structures on particle acceleration in the strongly turbulent solar corona. By randomizing the Fourier phases of a pseudospectral simulation of isotropic magnetohydrodynamic (MHD) turbulence(Re � 300)andtracingcollisionlesstestprotonsinboththeexact-MHDandphase-randomizedfields,itis foundthatthephasecorrelationsenhancetheaccelerationefficiencyduringthefirstadiabaticstageoftheacceleration process. The underlying physical mechanism is identified as the dynamical MHD alignment of the magnetic field with the electric current, which favors 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 � u< b at a nonadiabatic stage of the acceleration process. We point out that nonphysical parallel electric fields in random-phase turbulence proxies lead to artificial acceleration and that the dynamical MHD alignment can be taken intoaccountonthelevelofthejointtwo-pointfunctionofthemagneticandelectricfieldsandisthereforeamenableto Fokker-Planck descriptions of stochastic acceleration. Subject headings: acceleration of particles — methods: numerical — MHD
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