Study of dielectric barrier townsend discharge in air at atmospheric pressure

Non-thermal plasma produced by diffuse discharge in air at atmospheric pressure has advantages in the industrial application of the plasma surface modification. However, the discharge in atmospheric air usually behaves as filamentary discharge rather than diffuse discharge. It was found that diffuse discharge can be produced in a 3mm gap of air at atmospheric pressure by using two plane parallel electrodes each covered by one specific alumina plate with a thickness of about 2 mm. Based on the discharge photographs of short exposure time taken with an ICCD camera, the diffuse discharge was identified with Townsend discharge. The Townsend breakdown voltage for this 3mm air gap is about 8.3 kV, significantly lower than 11.2 kV, the streamer breakdown voltage of this gap. If the alumina plate is too thin, the discharge transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. The uniqueness of the shallow traps on the surface of the specific alumina plate, as well as the effect of the current limitation by dielectric leads to a Townsend discharge. The detail mechanisms for the formation of Townsend discharge are still under investigation.