2025/05/12 by Yue Hu, Siyao Xu, Hu, Yue +7 · 2 citations
Physics and Astronomy · Engineering · #Solar and Space Plasma Dynamics #Field-Flow Fractionation Techniques #Cosmology and Gravitation Theories
paper · pdf · doi:10.48550/arxiv.2505.07421
Understanding cosmic ray (CR) diffusion in a partially ionized medium is both crucial and challenging. In this study, we investigate CR perpendicular superdiffusion and parallel transport in turbulent, partially ionized media using high-resolution 3D two-fluid simulations that treat ions and neutrals separately. We examine the influence of neutral-ion decoupling and the associated damping of turbulence on CR propagation in both transonic and supersonic conditions. Our simulations demonstrate that neutral-ion decoupling significantly damps velocity and magnetic field fluctuations at small scales, producing spectral slopes steeper than those of Kolmogorov and Burgers scaling. In supersonic turbulence, large-scale shock motion is not subject to damping and generates small-scale density enhancements. Moreover, the damping of magnetic field fluctuations substantially decreases pitch-angle scattering, which, however, only slightly affects the CR parallel mean free path λ_‖, due to the nonresonant mirror interactions of CRs. In the direction perpendicular to the mean magnetic field, we identify two regimes of the perpendicular superdiffusion of CRs: a diffusive regime (λ_‖L\rm inj), with perpendicular separation scaling as t3/2. At initially large pitch angles, the effects of magnetic mirroring-naturally arising in magnetohydrodynamic turbulence-become significant, enhancing the confinement of CRs and resulting in λ_‖