Multi-species Ion Acceleration in 3D Magnetic Reconnection

Magnetic reconnection can efficiently accelerate particles into nonthermal energy spectra, including not only electrons and protons but also multi-species heavier ions. Multi-species nonthermal ions contain key information of the underlying particle acceleration process, but are poorly understood. Here we use 3D large-scale hybrid reconnection simulations to capture the challenging multiscale multi-species ion acceleration process. Our simulations, for the first time, achieve efficient acceleration of all ion species into nonthermal power-law spectra. We find that the 3D reconnection layers consist of fragmented kinking flux ropes, growing in size over time, as part of the reconnection-driven turbulence. Different species are injected by Fermi reflection at the Alfvenic reconnection exhausts influenced by the different initial thermal speeds, which determines the low energy bound shoulders of spectra. Then they start a universal Fermi acceleration process at different times when they are magnetized by growing magnetic flux ropes and exhausts. This gives different species similar power-law indices (p~4.5) but different maximum energy per nucleon that follows (Q/M)^α (α~0.6). These results agree reasonably with the range of heliospheric current sheets and magnetotail observations.