The structure of ‘electron pick-up ring’ in laser-driven asymmetrical magnetic reconnection

Abstract We investigate the formation and phase-space structure of ‘electron pick-up rings’ in laser-driven asymmetric magnetic reconnection using fully three-dimensional particle-in-cell simulations. The system operates in a strongly magnetized, collisionless regime where the reconnection electric field accelerates electrons within the electron diffusion region, producing closed, non-thermal ring-like structures in momentum space. The pick-up ring originates from electron energization by the localized reconnection electric field followed by momentum redistribution within a three-dimensional magnetic topology. Although electric-field acceleration also contributes to electron energization in asymmetric reconnection observed by MMS, the subsequent evolution in the present laser-driven system leads to a distinct closed ring-like structure in momentum space. Its morphology is determined by the competition between energization along the reconnection electric field and transverse deflection by asymmetric magnetic fields. We quantify this behavior through an empirical scaling relation linking the ring eccentricity to upstream magnetic-field asymmetry, c r ∝ ( B low / B high ) 0.27 . This scaling reproduces the systematic trend observed across multiple laser-driven reconnection cases and indicates that increased magnetic symmetry leads to flatter ring structures and enhanced reconnection efficiency. These results provide a kinetic-level characterization of electron acceleration and momentum-space topology in strongly magnetized, laser-produced reconnection plasmas, offering quantitative guidance for the interpretation and design of future laboratory reconnection experiments.