A study of binary ion plasma expansion into laboratory generated plasma wakes

Plasma expansion into the wake of a large rectangular plate immersed in a collisionless, supersonic, binary ion plasma has been investigated. A new plasma source has been developed to generate equivelocity, binary ion plasma flows, which allows access to regions of parameter space that have previously been unavailable for laboratory studies. A krypton-neon plasma (mass ratio of 4.15) is used, and the ambient density ratio of neon to krypton is varied more than an order of magnitude. The expansion is limited to early times by the combination of plasma density, plasma drift speed, and vacuum chamber size. No previous experimental results exist for such early expansion times. New experimental results include: (1) the propagation of a rarefaction wave for each ionic component into the ambient plasma; (2) the formation of a plateau-like region in the neon (the lighter mass) ion current density when the neon ions are the minor ionic species in the ambient plasma; and (3) the acceleration of both ionic species, with neon accelerating at a higher rate than krypton. Results indicate that the plasma expansion process is the dominant filling mechanism of the near wake of a body under these experimental conditions.<>