Electrostatic instability in the central lunar wake: A process for replenishing the plasma void?

We report on the WIND observations and subsequent analysis of electrostatic ion beam driven waves in the central lunar wake. Previous reports indicate that ion beams are present in the central lunar wake, these generated by an ambipolar electric field near the wake flanks. We demonstrate that these ion beams are inherently unstable, and thus they are capable of generating the observed broadband electrostatic noise. The beam disruption process may be a dominate mechanism to replace ions in the void trailing the moon. This picture of the wake, with an extended electrostatic tail in the central region is distinctly different from the MHD wake picture discussed previously.