A SIMPLE SIMULATION OF A PLASMA VOID - APPLICATIONS TO WIND OBSERVATIONS OF THE LUNAR WAKE

Previously, the formation of the lunar wake was considered from a magn etohydrodynamic perspective. However, recent Wind particle and field o bservations suggest the lunar wake may be formed by kinetic processes: those microphysical processes not considered in an MHD formalism. Unf ortunately, a full multidimensional and self-consistent kinetic simula tion of the lunar wake is beyond current means. However, some elements of the kinetic structure can be simulated via a simple one-dimensiona l electrostatic particle-in-cell simulation. We present a self-consist ent simulation of a cross-sectional element of a plasma void. Essentia lly, wakeward directed ion beams are formed at the flanks of the simul ated void, consistent with the Wind observations of counterstreaming i on beams in the wake region. These wakeward directed beams are generat ed by ambipolar electric fields formed at the wake edges. Other struct ures observed by Wind are also seen in the simulation, including an el ectrostatically turbulent central wake region that causes the wake to fill-in and a rarefaction wave emanating outward from the wake.