LIF Imaging of OH radicals in Atmospheric DC Glow Discharge Using Miniature Gas Flow and Electrolyte Cathode
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LIF Imaging of OH radicals in Atmospheric DC Glow Discharge Using Miniature Gas Flow and Electrolyte Cathode Shusuke Nishiyama, Hiroaki Ishigame, Tomoki Komori, and Koichi Sasaki Division of Quantum Science and Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan ABSTRACT In this paper, we report the spatial distribution of OH radical density in atmospheric-pressure DC glow discharge using a miniature helium flow and an electrolyte cathode. Laser-induced fluorescence imaging was applied for the measurement of the OH radical density. The effect of collisional quenching was considered in obtaining the spatial distribution of the OH density. The spatial distribution of the OH radical density showed that the peak of the OH density was located at a separated distance from the electrolyte surface. However, the OH radicals kept contact with the electrolyte surface. It was suggested that the OH radicals were generated mainly in a region separated from the electrolyte surface and some fraction of the generated OH radicals reached to the liquid phase. INTRODUCTION Recently, atmospheric-pressure non-equilibrium plasmas attract much interest in its applications such as material processing, pollution control, biological and medical applications because many of these applications contain liquid phase and atmospheric-pressure nonequilibrium plasma can be exposed to liquid materials easily1. A stable DC glow discharge can be generated with noble gas flow in air2. Shirai et al. reported many properties of DC glow discharge with miniature gas flow and electrolyte cathode3-4. Li et al. reported the density of hydroxyl (OH) radicals, which is an important reactive species, in the core of micro-flow discharge in He, Ar, and N2 with a water electrode by laser induced fluorescence (LIF) spectroscopy5. However, the origin of OH radicals in this discharge configuration has not been clarified yet. In this study, we have investigated the spatial distribution of OH radicals in the gas phase of miniature gas flow DC discharge and electrolyte cathode by LIF imaging spectroscopy. EXPERIMENT Figure 1 shows the experimental setup for LIF imaging of OH radicals in miniature gas flow DC glow discharge. The electrolyte cathode was 1% NaCl solution which filled a square acryl vessel with quarts windows. A stainless-steel nozzle anode with 0.7 mm outer diameter and 0.48 mm inner diameter was placed above the electrolyte surface with 4 mm gap distance. The working gas, helium, was fed through the nozzle and the gas flow rate was controlled to 70-350 sccm using a mass flow controller. A DC power supply was connected via a 100 k ballast register between the nozzle anode and a platinum wire immersed in the electrolyte cathode. The
discharge current was controlled to 10-40 mA using the DC power supply in constant current mode. The light source in the LIF measurement was an optical parametric oscillator (SpectraPhysics MOPO-HF), which generated a tunable intense pulsed laser beam. The typical pulse width and the energy were
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