Collisional ionization and recombination effects on coalescence instability in chromospheric partially ionized plasmas

Abstract

Plasmoid-mediated fast magnetic reconnection plays a fundamental role in driving explosive dynamics and heating, but relatively little is known about how it develops in partially ionized plasmas (PIP) of the solar chromosphere. Partial ionization might largely alter the dynamics of the coalescence instability, which promotes fast reconnection and forms a turbulent reconnecting current sheet through plasmoid interaction, but it is still unclear to what extent PIP effects influence this process. We investigate the role of collisional ionization and recombination in the development of plasmoid coalescence in PIP through 2.5D simulations of a two-fluid model. The aim is to understand whether these two-fluid coupling processes play a role in accelerating reconnection. We find that, in general, the ionization–recombination process slows down the coalescence. Unlike the previous models in Murtas et al. [Phys. Plasmas 28, 032901 (2021)] that included thermal collisions only, ionization and recombination stabilize current sheets and suppress non-linear dynamics, with turbulent reconnection occurring in limited cases: bursts of ionization lead to the formation of thicker current sheets, even when radiative losses are included to cool the system. Therefore, the coalescence timescale is very sensitive to ionization–recombination processes. However, reconnection in PIP is still faster than in a fully ionized plasma environment having the same bulk density: the PIP reconnection rate (MIRIP=0.057) increases by a factor of ∼1.2 with respect to the MHD reconnection rate (MMHD=0.047).