Determination of the accuracy of actinometry and line ratio techniques in an O2 glow discharge: part II, Electric field measurements with Ar and Xe admixtures

A line-ratio method for determining the reduced electric field is benchmarked against independent measurements from electrostatic probes and cavity ring-down spectroscopy (CRDS). The method is applied to oxygen DC glow discharges with trace admixtures of argon and xenon. A corona model incorporating fluorescence quenching by heavy species is used to simulate the emission, with electron-impact excitation rates calculated using the LisbOn KInetics Boltzmann solver (LoKI-B). The excitation cross sections and quenching coefficients are those proposed and validated for actinometry in part one of this combined study. The reduced electric field is determined over a pressure range of 0.55 to 5 Torr (at 40 mA) and a current range of 15 to 50 mA (at 5 Torr). Consistent agreement with measured emission line intensities is achieved when applying a correction factor of K c,Ar=3+-0.5 to the excitation cross sections for the argon lines at 750 nm and 811 nm. With this correction, the reduced electric field values obtained from the line-ratio method are in good agreement with direct measurements. A comparison of different line ratios is presented, showing that the best performance is achieved using the ratio of the Ar 750 nm and Xe 828 nm lines. This ratio is particularly sensitive to changes in the electron energy distribution function, due to the large difference in excitation thresholds, while remaining independent of the knowledge of species densities.