Spectroscopic investigations of the plasma behavior in a plasma opening switch experiment

Spectroscopic diagnostics were used to study the electron density, the electron kinetic energy, and the particle velocities in a coaxial positive-polarity Plasma-Opening-Switch (POS). A gaseous plasma source, mounted inside the inner POS high-voltage electrode, injects the plasma radially outward into the inter-electrode region. A laser evaporation technique was employed to locally seed the plasma with various species to allow for measurements with high spatial, temporal and spectral resolutions. The electron density was determined from the ionization times of a few species. The electron energy was studied using measurements of absolute line intensities and time dependent collisional-radiative calculations. The velocity distributions of various ions were obtained from emission-line Doppler broadenings and shifts. The ion motion was found to start early over most of the plasma. Together with the relatively low ion velocities and the nearly linear velocity dependence on the ion charge-to-mass ratio, this leads to the conclusion that the magnetic field penetrates the plasma early in the pulse. The ion velocity dependence on the axial location and the local electron c1ensity were used to infer the time dependent axial distribution of the magnetic field in the plasma, which indicates the formation of a relatively high current density at the load-side edge of the plasma.