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 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.