Turbulence-driven magnetic reconnection is increasingly recognized as a crucial mechanism for accelerating cosmic rays (CRs) to ultra-high energies (UHEs) in magnetized astrophysical environments, ranging from compact sources to more extended regions. In this contribution, we provide an overview of this acceleration process and present a comparative analysis of 3D magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulation results.
We explore how cosmic ray acceleration unfolds across both microscopic and macroscopic scales, drawing insights from 3D PIC kinetic simulations, hybrid 3D MHD-PIC models, and large-scale 3D MHD simulations. While micro-scale simulations are essential for understanding the initial stages of particle acceleration—commonly referred to as the injection problem—macro-scale MHD models help determine the maximum energies particles can reach. We briefly summarize the key similarities and differences between these regimes, their influence on acceleration rates and spectral properties, and the transition from microscopic to macroscopic scales.
Furthermore, we examine how 3D turbulence-driven reconnection efficiently CRs to high energies primarily in a Fermi process and its implications for astrophysical sources, particularly AGN accretion disks and jets. This mechanism offers a compelling explanation for the observed gamma-ray and neutrino emissions from magnetized regions, in sources such as TXS 0506+056, Mrk 501, and NGC1068.