Research of Key Radicals for Plasma Chemical Reaction in Atmospheric Pressure Discharges

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Streamer coronas at atmospheric pressure are widely used in the non-thermal plasma processing of harmful gases. It is well known that hydroxyl (OH) radicals play an important role for the plasma chemical reactions in the reactor. Therefore, the direct study of the radicals in non-thermal plasma reactors is of great interest. Laser-induced fluorescence (LIF) is a useful diagnostic method for in-situ observation of the phenomena during the non-thermal plasma processing of gaseous pollutants.The OH radicals generated by the discharges have time transient characteristics (i.e. there are generation period and decay period during/after the discharge), and the lifetime is very short. While the DC streamer corona discharge consists of more of less regular self-repetitive current pulses (streamers) with the pulse duration up to several hundred nanoseconds and repetition frequency in the range of 1 to 100 kHz. In this study, taking into account on these time dependent characteristics, the time-r … More esolved and time-averaged behaviors of OH radicals were investigated.The LIF detection of the OH radicals was performed in the nozzle-to-plane electrode configuration (the radical injection and radical shower systems) during the steady-state positive streamer corona discharge at atmospheric pressure. For monitoring the ground-state OH radicals, the scheme with excitation at 282 nm and detection at 309 nm was used. The time relationship between the regular streamer coronas, laser pulse, OH fluorescence and laser-induced streamer was measured. The time dependence of OH radicals between the successive streamers was measured for the evaluation of OH dynamics. The two-dimensional OH distribution around the streamer corona region was also observed. As a result, it was found that the LIF could apply to the measurement of OH radicals generated by a DC streamer corona discharge at atmospheric pressure. The ground-state OH radicals were generated and stayed mainly in the region where streamers propagated between the electrodes. Less