Creating unstable velocity-space distributions with barium injections

Ion velocity-space distributions resulting from barium injections from orbiting spacecraft and shaped charges are discussed. Active experiments confirm that anomalous ionization processes may operate, but photoionization accounts for the production of the bulk of the barium ions. Pitch-angle diffusion and/or velocity-space diffusion may occur, but observations of barium ions moving upwards against gravity suggests that the ions retain a significant enough fraction of their initial perpendicular velocity to provide a mirror force. The barium ion plasmas should have a range of Alfven Mach numbers and plasma betas. Because the initial conditions can be predicted these active experiments should permit testing plasma instability hypotheses.