Neutral and Excited Molecules and Atoms Densities in the Positive Column of Flowing N2 DC Discharges

Abstract

We investigated flowing N2 DC discharges both experimentally and theoretically. The discharge gas and N2(X1Σ+g) vibrational temperatures, electron density (ne), reduced electric field (E/N), and radiative state densities were measured by optical emission spectrometry (OES) and Langmuir double probes. We formulated a discharge kinetic numerical model to calculate the densities of nitrogen species as functions of the gas residence time. We combine the experimental parameters measured in the discharge with the kinetic model to analyze different discharge conditions where E/N varies significantly. First, we analyzed the measured and calculated radiative states densities and N2(X1Σ+g) vibrational distributions at the end of the positive column. Results show good agreement between calculated and measured parameters. Then, we studied the excited molecular species densities, and neutral and excited atoms densities as functions of the discharge gas residence time. This work presents for the first time the temporal densities of excited molecular and atomic states from 10−9 to 10−1 s discharge residence times, calculated for experimental conditions where ne presents a low variation and E/N varies from high (94 Td) to relatively low values (48 Td). The discharge experimental conditions are discharge current of 60 mA, gas pressure of 230–530 Pa, and gas flow rate of 0.9 Slm−1.