Dartmouth Events

Abstract: Solar flare and magnetotail observations show simultaneous acceleration of ions and electrons
into power-law energy distributions extending to high energy. This suggests a common
magnetic-reconnection acceleration process but the underlying physics is not well understood.
During magnetic reconnection, energetic particles undergo a universal Fermi acceleration
process involving the curvature drift of particles. However, the efficiency of this mechanism is
limited by the trapping of energetic particles within flux ropes. Using 3D fully kinetic
simulations, we demonstrate that the flux-rope kink instability leads to field-line chaos in weak-guide-
field regimes where the Fermi mechanism is most efficient, thus allowing particles to
transport out of flux ropes and undergo further acceleration. As a consequence, both ions and
electrons form clear power laws which contain a significant fraction of the released energy. The
low-energy bounds, which control the nonthermal energy contents, are determined by the
injection physics, while the high-energy cutoffs are limited only by the system size. These results
have strong relevance to observations of nonthermal particle acceleration in both the solar corona
and magnetotail.