Combined spectroscopic methods for electron-density diagnostics inside atmospheric-pressure glow discharge using He/N2 gas mixture

We investigated the spatiotemporal structures of electron density inside an atmospheric-pressure glow discharge in a gaseous medium of He with small N-2 impurity using a parallel-plate dielectric barrier discharge configuration. To reveal the spatial distributions of temporal-peak electron density, we combined the measurement results of two spectroscopic diagnostics applied to the same plasma source: CO2-laser heterodyne interferometry and millimetre-wave transmission methods. Laser absorption and optical emission spectroscopy methods were also performed to analyse the detailed plasma characteristics, and we calculated the total ionization frequency to discuss the influence of N-2 impurity on the discharge. The experimental and calculated results suggest that the localization of the electron density near the dielectric barriers was caused by the formation of a high excited-species density region near the temporal cathode, and the total ionization frequency was maximized around 0.25% of the N-2 impurity ratio.