  The Unified Gas-Kinetic Wave-Particle (UGKWP) method is constructed for
partially ionized plasma (PIP). This method possesses both multiscale and
unified preserving (UP) properties. The multiscale property allows the method
to capture a wide range of plasma physics, from the particle transport in the
kinetic regime to the two-fluid and magnetohydrodynamics (MHD) in the near
continuum regimes, with the variation of local cell Knudsen number and
normalized Larmor radius.The unified preserving property ensures that the
numerical time step is not limited by the particle collision time in the
continuum regime for the capturing of dissipative macroscopic solutions of the
resistivity, Hall-effect, and all the way to the ideal MHD equations.The UGKWP
is clearly distinguishable from the classical single scale
Particle-in-Cell/Monte Carlo Collision (PIC/MCC) methods.The UGKWP method
combines the evolution of microscopic velocity distribution with the evolution
of macroscopic mean field quantities, granting it UP properties. Moreover, the
time step in UGKWP is not constrained by the plasma cyclotron period through
the Crank-Nicolson scheme for fluid and electromagnetic field interactions. The
momentum and energy exchange between different species is approximated by the
Andries-Aoki-Perthame (AAP) model. Overall, the UGKWP method enables a smooth
transition from the PIC method in the rarefied regime to the MHD solvers in the
continuum regime. This method has been extensively tested on a variety of
phenomena ranging from kinetic Landau damping to the macroscopic flow problems,
such as the Brio-Wu shock tube, Orszag-Tang vortex, and Geospace Environmental
Modeling (GEM) magnetic reconnection. These tests demonstrate that the proposed
method can capture the fundamental features of PIP across different scales
seamlessly.
