Ion orbit class transitions and phase-space holes in collisionless magnetic reconnection

The origin of anomalous ion heating in collisionless magnetic reconnection has been a longstanding problem. It was previously shown via fluid analyses, kinetic anlyses, kinetic simulations, and test-particle simulations that stochastic heating is responsible for such ion heating for up to moderate guide fields. It was also previously shown that a thinning current sheet involves particle orbit class transitions from the non-crossing to the double-well orbit class. Here we show via kinetic simulations and real-time test-particle simulations that inflowing ions during magnetic reconnection undergo orbit class changes and form phase-space holes. We then show how the orbit class changes are related to stochastic heating.