Cosmic Ray Diffusion in Magnetic Fields Amplified by Nonlinear Turbulent Dynamo
Year: 2024
Type: article
Abstract: The diffusion of cosmic rays (CRs) in turbulent magnetic fields is fundamental to understanding various astrophysical processes. We explore the CR diffusion in the magnetic fluctuations amplified by the nonlinear turbulent dynamo in the absence of a strong mean magnetic field. Using test particle simulations, we identify three distinct CR diffusion regimes: mirroring, wandering, and magnetic moment scattering (MMS). With highly inhomogeneous distribution of the dynamo-amplified magnetic fields, we find that the diffusion of CRs is also spatially inhomogeneous. Our results reveal that lower-energy CRs preferentially undergo the mirror and wandering diffusion in the strong-field regions, and the MMS diffusion in the weak-field regions. The former two diffusion mechanisms play a more important role toward lower CR energies, resulting in a relatively weak energy dependence of the overall CR mean free path (MFP). In contrast, higher-energy CRs predominantly undergo the MMS diffusion, for which the incomplete particle gyration, i.e., the limit case of mirroring, in strong fields has a more significant effect than the scattering by small-scale field tangling/reversal. Compared with lower-energy CRs, they are more poorly confined in space and their MFPs have a stronger energy dependence. We stress the fundamental role of magnetic field inhomogeneity of nonlinear turbulent dynamo in causing the different diffusion behavior of CRs compared to that in sub-Alfvénic magnetohydrodynamic turbulence.
Source: The Astrophysical Journal
Authors: Chao Zhang, Siyao Xu
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: G1588448908, G1693976111, Track 4: Advanced CI Coordination Ecosystem: Monitoring and Measurement Services, G2452989760, G2595738051, G2815302120, G3245429106, G3339971651, G3398237449, G4248962021, G4437173897, ACO: An Open CI Ecosystem to Advance Scientific Discovery (OpenCI), G4689434848, Track 3: COre National Ecosystem for CyberinfrasTructure (CONECT), G6128126499, Kavli Institute for Theoretical Physics, Programs on Critical Problems in Physics, Astrophysics and Biophysics at the Aspen Center for Physics, G7976526739, G8250941178, Track 2: Customized Multi-tier Assistance, Training, and Computational Help (MATCH) for End User ACCESS to CI
OpenAlex ID: W4403776253