ELECTROSTATIC INSTABILITY IN THE CENTRAL LUNAR WAKE - A PROCESS FOR REPLENISHING THE PLASMA VOID

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