Effect of pressure on the fundamental parameters' spatio-temporal evolution in a µs pulsed-power glow discharge in low vacuum as studied via laser scattering techniques

Laser scattering (LS) plasma-diagnostic techniques (Thomson, Raman, and Rayleigh) have inherent spatio-temporal resolution, minimal-to-no plasma perturbation, and do not require local thermodynamic equilibrium assumptions. While LS instrumentation can be complex for low-density plasmas, e.g. low vacuum glow discharge (GD), they are the method of choice when available, given all their advantages.

Here, a home-built LS system featuring a transmission-type triple grating spectrograph will be used to obtain spatiotemporally resolved maps of electron temperatures/densities, pertaining to a variety of GD operating conditions relevant to different applications, e.g. materials characterization via optical emission spectroscopy. A method for the spatial/spectral correction of the imaging system based on simulated Raman Scattering will be presented. Also, the instrument performance with different camera types will be discussed. Finally, the effects of pressure/RF power on the fundamental parameters will be examined as a function of spatial position and time along the plasma pulse. These studies will allow obtaining necessary insights into plasma underlying mechanisms, and serve as a baseline for future studies to elucidate the changes induced by coupling with external microwave radiation.