ION COLLECTION IN A SPACECRAFT WAKE - LABORATORY SIMULATIONS

Data from a laboratory simulation of current collection by a highly bi ased body in a spacecraft wake are presented. Ion collection from the plasma stream is investigated for both axisymmetric and nonaxisymmetri c geometries. Spatially resolved current collection data, obtained by using a segmented collector, are presented for the first time. A thres hold potential for the onset of current collection exists; this thresh old depends strongly on the geometry of the problem and is related dir ectly to the details of the trajectories of the collected ions. Result s from an approximate numerical model of the laboratory experiment as well as the predictions of a simplified analysis are given. The agreem ent of the numerical solution with the experimental data is good.