Effect of Dielectric Surface Morphology on Dielectric Barrier Discharge Mode in Air at Atmospheric Pressure

In order to study the effect of surface morphology of dielectric materials on features of dielectric barrier discharge (DBD) in air at atmospheric pressure (AP), electrical characteristics and optical emission spectrum are obtained in a 2-mm air gap with quartz glass and ceramic used as the dielectric layer (the capacitance of the used dielectrics is similar). The transition of discharge mode is observed for different dielectric material and surface morphology. Results show that with varying dielectric material and surface morphology, air atmospheric pressure dielectric barrier discharge (APDBD) presents three discharge modes, including a filamentary mode, a homogeneous mode, and a mixed mode of them. Further investigation reveals that the homogenous mode is in a Townsend discharge regime, which is realized in a proper surface morphology of 96% Al2O3 ceramic. Moreover, optical emission spectrum is obtained, which mainly consists of atomic lines of nitrogen and molecular bands originating from the second positive system of N2( $\text{C}^{3}\Pi _{\mathrm {u}}\to \text{B}^{3}\Pi _{\mathrm {g}}$ ). From N2( $\text{C}^{3}\Pi _{\mathrm {u}}\to \text{B}^{3}\Pi _{\mathrm {g}}$ ), molecular vibrational temperature is investigated as a function of surface roughness ( $R_{\mathrm {a}}$ ) of the different dielectric materials. Result reveals that there is a minimal vibrational temperature when the discharge is in the homogeneous mode. With quartz glass used as the dielectric, the vibrational temperature decreases first and then increases with increasing $R_{\mathrm {a}}$ . The minimum value appears at $R_{\mathrm {a}}$ of 215 nm. Besides, the discharge current is the most concentrated in time, and the discharge looks the most homogeneous under this circumstance.