The role of the plasma composition in the magnetic field evolution in plasma opening switches

High spatial- and temporal-resolution spectroscopic methods are employed to perform fundamental studies of the interaction between the propagating magnetic field and a multiion species plasma. The experiment is performed in a plasma opening switch configuration, in which a 150-kA current of /spl sim/400 ns duration is conducted through a plasma. Spatial resolution of /spl sim/0.5 cm along the line of sight is achieved using plasma doping techniques. Three doping methods are implemented, capable of producing either neutral or ionized dopant-species columns. Recent observations demonstrated a new phenomenon of simultaneous rapid magnetic field penetration into the heavy-ion plasma and specular reflection of the light-ion plasma leading to ion-species separation. Additionally, noticeable inconsistencies between experimental results and theories were found. The magnetic field was found to propagate faster than expected from diffusion. The observed broad current channel, as well as the nondependence of the magnetic field evolution on the current polarity, disagree with treatments based on the Hall-field effect. The ion separation phenomenon, not accounted for in present theories, indicates that the plasma composition might play a substantial role in the magnetic field evolution and ion dynamics. In order to systematically investigate the effect of the plasma composition, efforts are currently invested in developing techniques for producing plasmas with controllable compositions. These include spatial species separation and electrode heating. In addition, a novel application of laser spectroscopy is used to achieve submm 3D resolved measurements of the plasma properties and the electric fields. Using this method it was possible to determine, spectroscopically for the first time, the properties of plasma with a density down to /spl cong/ 10/sup 13/ cm/sup -3/, with ns-time-resolution. These studies are believed to be highly important for improving the understanding of var- ous high-current experiments such as plasma switches, high-power transmission lines, and particle-beam diodes.