Multi-Fluid and Kinetic Models of Partially Ionized Magnetic Reconnection

Jara-Almonte, J.; Murphy, N.A.; Ji, H.
Issue date: 2021
Cite as:
Jara-Almonte, J., Murphy, N.A., & Ji, H. (2021). Multi-Fluid and Kinetic Models of Partially Ionized Magnetic Reconnection [Data set]. Princeton Plasma Physics Laboratory, Princeton University.
@electronic{jaraalmonte_j_2021,
author      = {Jara-Almonte, J. and
Murphy, N.A. and
Ji, H.},
title       = {{Multi-Fluid and Kinetic Models of Partia
lly Ionized Magnetic Reconnection}},
publisher   = {{Princeton Plasma Physics Laboratory, Pri
nceton University}},
year        = 2021
}
Abstract:

Magnetic reconnection in partially ionized plasmas is a ubiquitous and important phenomena in both laboratory and astrophysical systems. Here, simulations of partially ionized magnetic reconnection with well-matched initial conditions are performed using both multi-fluid and fully-kinetic approaches. Despite similar initial conditions, the time-dependent evolution differs between the two models. In multi-fluid models, the reconnection rate locally obeys either a decoupled Sweet-Parker scaling, where neutrals are unimportant, or a fully coupled Sweet-Parker scaling, where neutrals and ions are strongly coupled, depending on the resistivity. In contrast, kinetic models show a faster reconnection rate that is proportional to the fully-coupled, bulk Alfv\'en speed, $v_A^\star$. These differences are interpreted as the result of operating in different collisional regimes. Multi-fluid simulations are found to maintain $\nu_{ni}L/v_A^\star \gtrsim 1$, where $\nu_{ni}$ is the neutral-ion collision frequency and $L$ is the time-dependent current sheet half-length. This strongly couples neutrals to the reconnection outflow, while kinetic simulations evolve to allow $\nu_{ni}L/v_A^\star < 1$, decoupling neutrals from the reconnection outflow. Differences in the way reconnection is triggered may explain these discrepancies.