Randolph, Robert T (2021-11). Measuring Neutral Species in a Plasma Environment Using Dual Color Single-Shot Coherent Rayleigh-Brillouin Scattering. Master's Thesis.
Thesis
Laser diagnostic methods provide a remote, non-perturbative way to accurately measure properties of gas and plasma flows such as velocity, density and temperature, leading to increased understanding of the properties of the flow and ultimately more efficient engineering designs. This work demonstrates the use of a non-linear, non-resonant four-wave mixing laser diagnostic technique known as single-shot coherent Rayleigh-Brillouin scattering (CRBS) to measure neutral density and translational temperature in a partially ionized plasma environment. Using a frequency doubled probe beam, CRBS spectra is obtained in gases and low-temperature plasmas of pressures down to 1-10 Torr. Diagnostics are performed in a xenon DC glow discharge due to its low ionization ratio. Using the CRBS laser system, translational temperature and neutral density are measured radially from the center to edge of the glow at a constant current and in the center of the glow with applied currents between 0-30 mA. Experimentally obtained spectra are compared to simulated spectra from the established Tenti s7 model to show agreement. Successful simultaneous density and temperature measurements in a partially ionized environment such as a glow discharge can help demonstrate the viability of single-shot CRBS in other plasma environments including arc discharges, combustion chambers, and hypersonic vehicles.
