Spectroscopic characterization of a He/N₂ dielectric barrier discharge for determination of plasma parameters and estimation of impurity content*

Optical emission spectroscopy (OES) is among the most convenient methods for plasma diagnostics, as it allows to investigate a plasma without physical intervention. In this study, absolutely calibrated optical emission spectroscopy is used together with a collisional radiative model to determine the electron density, reduced electric field and gas temperature in a low temperature volume dielectric barrier discharge (vDBD) in helium with small admixtures of nitrogen. The vDBD is operated in an enclosed chamber at atmospheric pressure to control all necessary environmental conditions. Nevertheless, nitrogen emission is observed even without intentional addition to the chamber. To better understand the discharge properties, OES is also used to estimate the air impurity content in the chamber. A fitting procedure is used to separate overlapping emission bands and estimate the gas temperature. The ratio of the fitted N₂(C-B) and N₂⁺(B-X) emission is then used to calculate the reduced electric field. Using the absolute emission intensity, the electron density is then calculated. Calculated electron densities and the impurity of the setup are found to be in the range of 1x10⁹ - 1x10¹⁰ cm⁻³ and ~750ppm, respectively.