Research Progress on SEPs on the Fine Structures of the Large Temporal-spatial Current Sheets in Solar Flares/CMEs

During intense solar atmospheric activity—such as major solar flares and geomagnetic storms—magnetic energy is converted into plasma kinetic and thermal energy through three-dimensional turbulent magnetic reconnection within large-scale, extended current sheets. This process releases enormous amounts of stored energy, often accompanied by the rapid ejection of high-energy particles into interplanetary space. These high-energy particles include electrons, protons, helium nuclei, and heavier ions, forming a complex multi-component, multi-abundance, and multi-isotopic population. Their energies span from ~100 keV to ~100 MeV and even into the GeV range, making them a primary driver of space weather hazards. Understanding the sources and acceleration mechanisms of these particles remains one of the most critical challenges in space weather research. Previous studies have shown that high-energy particle acceleration is highly complex, involving multiple species, a variety of mechanisms, and interactions across scales. It remains an open and challenging problem in solar and plasma physics. This paper provides a systematic review and forward-looking perspective on recent advances in high-energy particle acceleration during the fine-scale evolution of large-scale current sheets. The discussion is organized around three key pillars: theory, observations, and numerical simulations. First, we summarize the turbulence-fractal model as it applies to typical solar atmospheric events. We focus on acceleration mechanisms in turbulent magnetic reconnection within large spatiotemporal current sheets, with particular emphasis on: Turbulent (second-order) Fermi acceleration, Turbulent shock acceleration, and Turbulent wave-particle resonant acceleration. These mechanisms operate synergistically in the turbulent environment generated by reconnection, enabling efficient energy transfer to particles. Second, we review recent progress in coupling macroscopic (hydrodynamic and magnetohydrodynamic) dynamics to microscopic kinetic processes in high-energy particle acceleration. This includes multi-scale modeling of turbulence, reconnection, and particle transport. Finally, we outline promising future research directions, including improved multi-spacecraft observations, higher-resolution simulations that incorporate kinetic effects, and integrated models that bridge MHD turbulence and particle-in-cell approaches. We also highlight several urgent unresolved issues, such as the relative contributions of different mechanisms across energy regimes, the role of fractal structures in particle trapping and escape, and the origin of observed abundance enhancements in heavy ions. This review synthesizes recent theoretical, observational, and computational developments to provide a comprehensive framework for understanding high-energy particle acceleration in large-scale turbulent current sheets, with implications for solar flares, space weather forecasting, and broader astrophysical plasma processes.