Insight into theory-experiment comparisons of wake measurements in the plasmasphere

Abstract

Calculated results from a modified one-dimensional time-dependent plasma expansion model are compared with wake measurements of low energy H + ions made in the plasmasphere which consists of 77–90% H + and 23 10% H e +. The variation of the theoretical-to-experimental results with the H + ionic Mach number (S H+) in the range 0.5 < S H+ < 1.2 is shown. It is found that the theoretical model used overestimates the particle flux in the wake by factors of 2 to 6. Possible causes for these differences are examined. Discussions regarding; (1) the shortcomings of using one-dimensional models and other simplifications commonly used in theoretical modeling, (2) the use of measurements from probes having finite angular acceptance in wake studies, and (3) a relative comparison between a three-dimensional neutral approximation and the modified one-dimensional model used here are given. This comparison shows that for the plasmaspheric parameters used here, the application of a neutral particle model yields reasonable results, since the ion thermal motion rather than the local electric field dominates the filling of the wake (particularly for weakly charged bodies). These discussions provide additional insight into such theory-experiment comparisons and should be of practical use.