Particle acceleration and energy partition in global simulations of magnetic reconnection

Magnetic reconnection is frequently invoked as a mechanism to explain efficient particle acceleration and plasma heating in a variety of astrophysical plasma environments. As reconnection occurs in highly localized current sheets, its dynamics fundamentally involve the multi-scale coupling between the global system and plasma-kinetic scales. Despite this, it remains poorly understood how the particle acceleration, heating, and partition of released energy are mediated by these cross-scale interactions. Here, we present a detailed investigation of this physics using particle-in-cell simulations of coalescing magnetic islands in a strongly magnetized, relativistic pair plasma. This simple example of a global reconnecting system includes self-consistent current sheet formation due to the motions of the islands, as well as feedback on the macroscales via the reconnection outflows. At large system sizes, reconnection becomes bursty as islands bounce and turbulent downstream regions driven by the outflows dominate the global energy dissipation. Remarkably, because these regions remain active as reconnection slows, dissipation is both spatially and temporally delocalized from the dynamics at the primary reconnection site. The resulting particle spectra indicate an energy partition which differs substantially from similar simulations of a force-free current sheet, with a hotter thermal bulk component and a sub-dominant, non-thermal power-law tail.