Abstract
Abstract : Low-Mach-number shock waves propagating through a low-pressure, non-equilibrium, positive-column gas discharge have been observed to experience dispersion and velocity changes. These effects are shown to depend on discharge polarity. Optical and electrical measurements are described which demonstrate further polarity-dependent effects in discharge light emission and changes in electrical properties. The axial-population-density profile of 2 3S1 metastable He has also been measured by diode-laser absorption spectroscopy in the double layer formed at an abrupt transition of the tube diameter in a positive column. The diode-laser absorption profiles show enhanced production of triplet metastable He 2 3S1 in the double-layer region, as compared to that of the unperturbed positive column (small diameter), with the magnitude of being strongly dependent on the discharge polarity. The absolute concentration of H-atoms has been measured in the positive column of a pulsed dc discharge by two-photon-absorption laser-induced fluorescence (TALIF) in H2 N2 gas mixtures at constant pressure and current for discharge-pulse durations of 10 μs to 1 ms. The change in H-atom production from the direct-electron-impact dissociation of H2 at short times compared to that from multi-quantum vibrational energy-transfer-induced dissociation of H2 at long times is determined from temporally resolved H-atom-concentration measurements.
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