Contribution of Stark broadening to the Balmer Hα line profile observed from barrier discharges in Ar/H2 gas mixtures

Abstract

Results of line profile studies of the Balmer Hα transition emitted from barrier discharges with a plane-parallel electrode configuration in an Ar/H2 gas mixture (90% Ar, 10% H2) at a pressure of 4 kPa are reported. Polarization and phase sensitive emission measurements are performed for various plasma layers, i.e. for different distances from dielectric surfaces limiting the discharge gap. It is shown that the large broadening of the Hα line is predominantly caused by the Doppler effect as well as by the linear Stark effect arising from the interaction of H-atoms with the electric field generating the discharge. The analysis of the measured profiles is performed assuming that each Stark component is broadened due to the motion of two fractions of H-atoms, with significantly different velocities. The electric field strength distribution E = f(l) in the discharge gap perpendicular to the electrode surfaces is determined. This electric field varies from 19 kV cm−1, in the vicinity of the (momentary) cathode, to nearly zero close to the (momentary) anode. The shapes of the determined distributions perpendicular to the dielectric surfaces (electric field strength, charge density, potential) are similar to those of typical glow discharges.