Magnetic Reconnection in a Partially Ionized Plasma: Scalings, Structure, and Implications for Understanding the Solar Chromosphere

Partially ionized plasma environments, where release of magnetic energy and topological reconfiguration of magnetic fields via magnetic reconnection is known or conjectured to take place, range from highly collisional, e.g. interstellar medium and lower solar chromosphere with ionization fraction below 0.1%, to weakly collisional, e.g. in the upper solar chromosphere with ionization fraction of 1%-10%. Different plasma processes, such as ionization and recombination, ion-neutral interaction via charge-exchange collisions, Hall currents, and radiative losses can become the dominant factors in determining the reconnection rate and the structure of the reconnection region in different parameter regimes. The HiFi multi-fluid modeling framework has been used to implement all of the above processes in a single self-consistent model and to perform 2D simulations of magnetic reconnection under a variety of plasma conditions. Motivated by the simulations, here we present analytically derived predictions of the reconnection rate, as well as the size, shape, and structure of a 2D magnetic reconnection region in a partially ionized plasma under given conditions. The predictions are tested against the simulation results, and implications for better understanding the dynamics of magnetized chromospheric plasmas are discussed. *This work has been supported by the NASA LWS and SR&T programs. Recombination-assisted magnetic reconnection in a weakly ionized plasma. Current sheet evolution in the presence of a secondary plasmoid instability [Leake et al., ApJ 760, 109 (2012)].