Experimental study of homogeneous dielectric barrier discharge in air at atmospheric pressure

Summary form only given. The dielectric barrier discharge (DBD) in air at atmospheric pressure was investigated with electrical measurement and fast photography. Homogeneous DBD without filaments was obtained in a gap of a length as long as 3 mm, which has never been reported in previous literatures. The air gap was in between two plane-parallel electrodes of 50 mm in diameter, each covered by a specific ceramic plate with a thickness of 1.5∼3.25 mm. By subtracting the displacement current from the total current, there appears one current peak per half cycle of the applied sinusoidal voltage, which is typical for homogeneous DBD. The current peak is 1 mA in amplitude and about 85 µs in FWHM (full width at half magnitude). Side-view photographs with 10 ns exposure time taken at the time about the peak of the current pulse showed that there were no filaments in the discharge gap. A luminous layer close to the instantaneous anode was observed, indicating the homogeneous DBD was a Townsend discharge. When choosing a ceramic thinner than 1.5 mm, some filaments randomly appeared in the gap, as was called a mixed mode of homogenous and filamentary DBD. This was because in DBD the dielectric capacitance played an important role in the limitation of the discharge current. A smaller capacitance would help to avoid an electron avalanche overdeveloping to a streamer. When a stable Townsend discharge was maintained, the breakdown voltage was determined to be only 8.3 kV, much lower than the static breakdown voltage of 11.2 kV for the same air gap of 3 mm in length. The formation of Townsend discharge was attributed to the uniqueness of the shallow traps on the surface of the specific ceramic plate and the common effect of the current limitation by dielectric.