Measurement of PEOS plasma temperatures and densities using laser induced fluorescence

In order to understand the operation of the plasma erosion opening switch (PEOS) many basic parameters of the switch plasma, such as electron and ion density distributions, plasma temperatures, and magnetic field contours, must be experimentally determined. A program is in progress to measure these properties using laser induced fluorescence (LIF), resonance holographic interferometry and emission spectroscopy. A flashboard coated with colloidal carbon doped with barium oxide is used as a plasma source for a planar PEOS having an electrode separation of 2 cm. The intensities of the 465nm CIII, 535nm Bal, and 493nm BaI, lines emitted by the flashboard plasma were measured with a monochromator. The ground state density of the barium ion was inferred from the fluorescence intensities obtained by saturating the 493nm transition with a pulsed dye laser. Plasma temperatures can be inferred from the relative population of two atomic energy levels. The standard technique for determining the relative population level has been the intensity measurement of two optical emission lines. The LIF counterpart in this technique is to use two laser wavelengths to excite two optical transitions. Both of these require the simultaneous recording of two wavelengths in a pulsed plasma that is not very reproducible. In the simplified approach used herein, the density of the lower state of a transition is determined from the LIF measurement while the upper state density is inferred from collisionally induced emission measured when the laser is off. With this approach all the required data is taken in one shot with only one laser and detector. The relative population levels are related to a plasma temperature using a specific equilibrium model (LTE or coronal).