Abstract: Magnetic reconnection in asymmetric environments such as the solar corona and Earth’s magnetosphere exhibits distinct particle acceleration behavior compared to symmetric cases, due to differences in plasma density and magnetic field across the current sheet. Using 3D hybrid and particle-in-cell simulations, we explore how this asymmetry influences particle acceleration. We find that increasing asymmetry leads to a systematic reduction in particle acceleration efficiency. The energy spectra display a distinct shoulder associated with the early stages of nonthermal acceleration, which shifts to lower energies in asymmetric reconnection due to reduced outflow velocities. This weakened acceleration is linked to a misalignment between magnetic curvature and reconnection outflows, resulting in softer spectral slopes. Based on these results, we develop a theoretical model that quantitatively predicts how particle acceleration rates and spectral indices scale with reconnection asymmetry.
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