  Non-equilibrium ionization (NEI) is essentially required for astrophysical
plasma diagnostics once the plasma status departs from ionization equilibrium
assumptions. In this work, we perform fast NEI calculations combined with
magnetohydrodynamic (MHD) simulations and analyze the ionization properties of
a Petschek-type magnetic reconnection current sheet during solar eruptions. Our
simulation reveals Petschek-type slow-mode shocks in the classical Spitzer
thermal conduction models and conduction flux-limitation situations. The
results show that under-ionized features can be commonly found in shocked
reconnection outflows and thermal halo regions outside the shocks. The
departure from equilibrium ionization strongly depends on plasma density. In
addition, this departure is sensitive to the observable target temperature: the
high-temperature iron ions are strongly affected by NEI effects. The
under-ionization also affects the synthetic SDO/AIA intensities, which
indicates that the reconstructed hot reconnection current sheet structure may
be significantly under-estimated either for temperature or apparent width. We
also perform the MHD-NEI analysis on the reconnection current sheet in the
classical solar flare geometry. Finally, we show the potential reversal between
the under-ionized and over-ionized state at the lower tip of reconnection
current sheets where the downward outflow collides with closed magnetic loops,
which can strongly affect multiple SDO/AIA band ratios along the reconnection
current sheet.
