Efficient Generation of OH Radicals Using Atmospheric Pressure DC Glow Discharge with Two Intersecting Gas Flows*

An efficient method for the generation of OH radicals using atmospheric pressure plasma was investigated using a DC voltage-driven glow discharge with crossed gas flow. We measured the distribution of OH radical density by laser-induced fluorescence spectroscopy. To obtain the accurate spatial distribution of the OH radical density, we also measured the spatial distributions of the rotational temperature of OH(X²Π) and the quench frequency of laser-excited OH((A²Σ⁺). The dependences of the spatial distribution of the OH density on the discharge current, the gas flow rate, and the distance between two electrodes were examined to understand the production process of OH radicals and to optimize the discharge conditions for obtaining the high OH radical density. When two helium gas streams are crossed, a DC glow discharge is formed along the crossed gas. It was confirmed by laser-induced fluorescence(LIF) that OH radicals were produced not only in the plasma part but also in the spatial afterglow region downstream of the crossed part. The origin of the OH radicals is water vapor in the surrounding gas entrained by the helium gas flow. Efficient gas entrainment occurs at the intersection by using the crossed gas flow. OH in the spatial afterglow region is produced not only by the flow from the plasma section but also by dissociative electron attachment due to H₂O₂ and low electron temperature.