Characterization of the downstream plasma in a microsecond conduction time POS

Summary form only given, as follows. It is generally accepted that near the end of the conduction phase of a POS a small fraction of the injected plasma is accelerated axially downstream from the switch region to high velocities (/spl sim/0.5 cm/ns). In previous experiments using a POS plasma composed of hydrogen, the evidence suggested that the downstream plasma component was a significant fraction of the injected plasma and downstream propagation comprised one third of the total conduction phase. This may pose a serious limitation to this type of switch. Currently, experiments are underway to characterize the dynamics of the plasma downstream from the switch injection region. Magnetic probes, charge collectors, and an interferometer have been used to determine the density and velocity of the plasma as well as the velocity of the current sheet/magnetic field. The experiments indicate that the magnetic field eventually propagates through the moving plasma and the switch "opens" as plasma continues to flow in the transmission line. Experiments with other plasma compositions are also planned. The experiments will be conducted on a cylindrical POS with a peak current of 350 kA and a quarter cycle time of 1.2 /spl mu/s. The load is a short circuit, which may be as long as 40 cm from the center of the switch. The gas driven inverse pinch plasma source is used to operate the POS.