Spectroscopic diagnostics of atmospheric pressure helium dielectric barrier discharges in divergent fields

We present optical emission spectroscopy studies of atmospheric pressure glow discharges in flowing pure helium (He), and He/nitrogen (N-2) mixtures. Two different metallic high-voltage electrode geometries have been examined, namely needle and cylindrical, the grounded dielectric-covered electrode being planar. The axial and radial distributions of gas temperature have been evaluated from rotational spectra of molecular nitrogen ion emissions as a function of the electrode geometries, the gap spacings and the partial pressure of N2 in He. Also, the spatiotemporal distribution of discharge species in the needle-plane geometry and the link between gas temperature and light emission intensity are presented. The physical interpretations of these results are discussed with reference to recent work reported by the present authors and by others.