Kinetic Simulations of Fast Reconnection in Partially Ionized Plasmas

Magnetic reconnection is an important physical process that results in the release of stored magnetic energy. Although commonly studied in fully ionized plasmas, many space, astrophysical, and laboratory systems are only partially ionized, and the physics of fast reconnection in these systems is not well-understood. Using the first fully kinetic particle-in-cell simulations of partially ionized reconnection, the transition to fast reconnection is studied in viscid, semi-collisional plasmas and found to occur when the current sheet width thins below the ion-inertial length. The local reconnection rate is ionization fraction dependent, in agreement with previous experimental results, and a model for the rate is developed. In contrast, the global rate is determined by the embedding of the diffusion region within the global magnetic field and exhibits a weak dependence on system size. Additionally, we test our model for the reconnection rate by directly comparing with experimental measurements of ion and neutral flows on the Magnetic Reconnection Experiment (MRX).