Multi-species Ion Acceleration in 3D Magnetic Reconnection with Hybrid-kinetic Simulations

TL;DR

This study uses advanced 3D hybrid simulations to reveal how magnetic reconnection accelerates multiple ion species, including heavy ions, into power-law energy spectra through a Fermi acceleration process, aligning with space observations.

Contribution

First 3D hybrid simulation demonstrating nonthermal heavy-ion acceleration with scale separation and flux rope fragmentation in magnetic reconnection.

Findings

All ion species are accelerated into power-law spectra.

Acceleration efficiency depends on charge-mass ratio.

Results align with in-situ space observations.

Abstract

Magnetic reconnection drives multi-species particle acceleration broadly in space and astrophysics. We perform the first 3D hybrid simulations (fluid electrons, kinetic ions) that contain sufficient scale separation to produce nonthermal heavy-ion acceleration, with fragmented flux ropes critical for accelerating all species. We demonstrate the acceleration of all ion species (up to Fe) into power-law spectra with similar indices, by a common Fermi acceleration mechanism. The upstream ion velocities influence the first Fermi reflection for injection. The subsequent onsets of Fermi acceleration are delayed for ions with lower charge-mass ratios (Q/M), until growing flux ropes magnetize them. This leads to a species-dependent maximum energy/nucleon $\propto(Q/M)^\alpha$. These findings are consistent with in-situ observations in reconnection regions, suggesting Fermi acceleration as the dominant multi-species ion acceleration mechanism.