Self-driven magnetic reconnection in large-scale electron-positron plasmas

Many simulations of reconnecting current sheets have shown that the plasmoid instability and/or two-fluid physics can permit fast rates of reconnection. However, these studies typically start from pre-existing long and thin layers that are highly unstable, and do not model the dynamic formation of the current sheet, or its coupling with the large-scale system that supplies the reconnecting flux. Here, we present results from PIC simulations of magnetic island coalescence in large scale electron-positron plasmas for both high-beta and low-beta cases. Despite 'sloshing' behavior of the macroscopic flux-ropes, where the reconnection switches off and on, the dynamics of large systems can become weakly dependent on system-size. The rate of coalescence in the low-beta system is significantly faster than high-beta, with many more secondary islands produced in the thinner current sheet.