Magnetic Field-line Curvature and Its Role in Particle Acceleration by Magnetically Dominated Turbulence

Abstract We employ first-principles, fully kinetic particle-in-cell simulations to investigate magnetic field-line curvature in magnetically dominated turbulent plasmas and its role in particle acceleration through curvature-drift motion along the motional electric field. By varying the fluctuation-to-mean-magnetic-field ratio δB 0 / B 0 , we examine curvature κ statistics and their connection to particle acceleration. The curvature probability densities display broad power-law wings, scaling linearly in κ below the peak and developing hard high- κ tails for δB 0 / B 0 ≳ 1. As the mean field strengthens, the high- κ tails steepen, and large-curvature events are suppressed when δB 0 / B 0 ≪ 1. The probability density functions of magnetic field-line contraction, v E · κ , with v E the field-line velocity, develop power-law tails well described by a symmetric Pareto distribution, characteristic of stochastic and intermittent energy exchanges, with the tails becoming harder as δB 0 / B 0 increases. Our guiding-center analysis shows that curvature-drift acceleration accounts for a substantial fraction of the energization via the motional electric field, and that it strengthens with increasing δB 0 / B 0 . For well-magnetized particles, curvature-drift acceleration typically exceeds ∇ B drift, polarization drift, and betatron contributions. These results identify curvature-drift acceleration as a principal pathway through which magnetized turbulence transfers energy to nonthermal particles in astrophysical plasmas.