Particle Acceleration in Alfvénic Turbulence with a Strong Guide Field

Abstract Magnetically dominated Alfvénic turbulence creates an effective environment for particle acceleration. However, when a strong mean field is present, traditional mechanisms like mirror and curvature acceleration become inefficient at explaining nonthermal particle energy distributions. Based on numerical and phenomenological study, we propose that in such turbulence, particles are accelerated in charge-starved current sheets, corresponding to current velocities approaching the speed of light. The distributions of the electric currents, plasma density, and fluctuations of electric charge, as well as the energy distributions of accelerated particles, approximately follow lognormal statistics. Nonthermal particle distributions thus arise from particle acceleration in these charge-starved current sheets rather than from conventional Fermi-type particle acceleration by turbulent eddies.