2025/10/23 by Sebastian, Samuel, Comisso, Luca
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Plasma Physics (physics.plasm-ph) #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2510.20628
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 δB0/B0, 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 δB0/B0 \gtrsim 1. As the mean field strengthens, the high-κ tails steepen, and large-curvature events are suppressed when δB0/B0 ≪ 1. The probability density functions of magnetic field-line contraction, \bf vE ⋅ \bf κ, with \bf vE the field-line velocity, develop power-law tails well described by a symmetric Pareto distribution, characteristic of stochastic energy exchanges, with the tails becoming harder as δB0/B0 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 δB0/B0. For well-magnetized particles, curvature-drift acceleration typically exceeds \bf∇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.