Townsend Dielectric Barrier Discharge in Atmospheric Pressure Air

In order to experimentally study the possibility of homogenous dielectric barrier discharge(DBD) in atmospheric pressure air as well as its characteristics,the homogenous DBD in 3 mm air gap was obtained at atmospheric pressure,using 1~2 kHz sinusoidal high voltage and no less than 1.5 mm thick alumina as the dielectrics.The discharge was proven as an atmospheric pressure Townsend discharge after analyzing the 10 ns exposure high-speed photographs and the current waveform.The steady breakdown voltage for 3 mm air DBD was calculated to be about 5.7 kV,much lower than 11.2 kV,the static breakdown voltage of 3 mm air gap;Extraordinary extinction was also observed in air just like in nitrogen.Both the two phenomena indicated the existence of the shallow traps and consequently the second-electron emission in the alumina surface,which were important for ignition and maintaining stage of Townsend DBD.It is found that the thickness of alumina is important for air DBD,and the thickness less than 1.5 mm can not avoid the filamentary discharge.If two 1 mm thick quartz plates are used instead of alumina,it is impossible to get homogenous DBD at 670 Pa~0.1 MPa in air.The mechanism of Townsend DBD in 3 mm air gap is attributed to the combined effects of the unique shallow traps in the alumina surface and the current-limitation of the dielectrics.