An investigation into the role of metastable states on excited populations of weakly ionized argon plasmas, with applications for optical diagnostics.

Abstract

Performing spectroscopic measurements of emission lines in relatively cold laboratory plasmas is challenging because the plasma is often neutral-dominated and is not in thermal equilibrium. However, these types of plasma do offer a unique opportunity for benchmarking the finer details of atomic physics, helping researchers gain a better understanding of fundamental atomic processes in plasmas. In this thesis, we report on a new set of atomic data, from which rate coefficients for the electron-impact excitation of neutral argon, along with dielectronic recombination of Ar+ -- Ar5+ are determined. This data is used to calculate synthetic emission spectra, which are compared to experimental measurements in the ALEXIS device. The goal is to identify emission lines that are sensitive to variations in temperature and density and to use this data to develop new optical density and temperature diagnostics for a low-temperature, neutral-dominated argon plasma. A key component of this is to first determine the metastable fraction in ALEXIS. It is likely that a lack of knowledge on the metastable fraction has been the main limiting factor in the general use of neutral Ar spectral diagnostics. A new spectroscopic method to measure the neutral argon metastable fractions is developed. We also present preliminary density and temperature diagnostics made using our atomic data, with comparisons to standard probe based measurement, and will discuss further efforts to improve and extend our models to other plasmas.