Effect of discharge polarity on OH density and temperature in coaxial-cylinder barrier discharge under atmospheric pressure humid air

Plasma application for environmental pollution control is desirable, and it is important to clarify the chemical reaction processes in nonthermal plasma. In this study, the discharge polarity dependence of the density and rotational temperature of OH radicals is measured by laser-induced fluorescence (LIF) in coaxial-cylinder pulsed dielectric barrier discharge (DBD) in atmospheric pressure humid air. The density of OH radicals generated by a pulsed positive DBD of +28 kV is estimated to be in the range of 6-10 x 10(14) cm(-3) at 3 mu s after discharge near the central electrode. The rotational temperature rises after the discharge and the rate of temperature rise increases with humidity. In negative discharge, the decay rate of OH density, which directly depends on the initial OH density, is lower than that in positive discharge. The OH amounts contained in the observed area are almost the same in positive and negative discharges. These results indicate that the negative streamer diameter is twice the positive streamer diameter and the OH density in negative DBD is a quarter of that in positive discharge. In the chemical treatments using OH radicals, negative streamer DBD is supposed to be superior to positive streamer DBD from the perspective of ineffective loss. The temperature behavior in negative discharge is similar to that in positive discharge. (C) 2018 The Japan Society of Applied Physics