Plasmoid statistics in relativistic magnetic reconnection

Abstract

Plasmoids, quasi-spherical regions of plasma containing magnetic fields and high-energy particles, are a self-consistent by-product of the reconnection process in the relativistic regime. Recent two-dimensional particle-in-cell (PIC) simulations have shown that plasmoids can undergo a variety of processes (e.g. mergers, bulk acceleration, growth, and advection) within the reconnection layer. We developed a Monte Carlo (MC) code, benchmarked with the recent PIC simulations, to examine the effects of these processes on the steady-state size and momentum distributions of the plasmoid chain. The differential plasmoid size distribution is shown to be a power law, $N(w)\propto w^{-χ}$, ranging from a few plasma skin depths to $\sim 0.1$ of the reconnection layer's length. We demonstrate numerically and analytically that the power law slope $χ$ is linearly dependent upon the ratio of the plasmoid acceleration and growth rates and that it slightly decreases (from $\sim 2$ to $\sim 1.3$) with increasing plasma magnetization (from 3 to 50). We perform a detailed comparison of our results with those of recent PIC simulations and briefly discuss the astrophysical implications of our findings through the representative case of flaring events from blazar jets.