Novel Gas-Doping Technique for Local Spectroscopic Measurements in Pulsed-Power Systems

Abstract

A novel method for doping plasmas in pulsed-power experiments with gaseous elements has been developed. A fast gas valve, a nozzle, and a skimmer are used to generate an ultrasonic gas beam that is injected into a planar-geometry microsecond plasma-opening-switch (POS). An array of ionization probes with relatively high spatial and temporal resolutions was developed for diagnosing the absolute injected-gas density and its spatial profile. The properties of the gas column were also studied using spectroscopy of line emission that results from the interaction of the doped gas with the POS prefilled plasma. The doped column is found to have a width of ~1 cm and a density of (0.8-1.7)*10^14 cm-3. Observations of characteristic emission lines from the doped atoms and their ions allow for various spectroscopic measurements, such as the magnetic field from Zeeman splitting and the ion velocity distributions from Doppler shifts, that are local in three dimensions. It is shown that this gas doping technique can also be used to study proton-dominated plasmas that cannot be studied with simple emission spectroscopy due to the lack of light emitting ions. The variety of gases used with this method, together with the small valve dimensions and its fast opening, make it potentially useful for broad diagnostics of various short-duration plasma experiments.