The stable homogeneous dielectric barrier discharge (DBD) is obtained in atmospheric 2–3 mm air gap. It is generated using center frequency 1 kHz high voltage power supply between two plane parallel electrodes with specific alumina ceramic plates as the dielectric barriers. The discharge characteristics are studied by a measurement of its electrical discharge parameters and observation of its light emission phenomena. The results show that a large single current pulse of about 200 μs duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two electrodes. The homogeneous discharge generated is a Townsend discharge during discharge. The influences of applied barrier, its thickness, and surface roughness on the transition of discharge modes are studied. The results show that it is difficult to produce a homogeneous discharge using smooth plates or alumina plate surface roughness Ra < 100 nm even at a 1 mm air gap. If the alumina plate is too thin, the discharge also transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. With the increase of air gap distance and applied voltage, the discharge can also transit from a homogeneous mode to a filamentary mode. In order to generate stable and homogeneous DBD at a larger air gap, proper dielectric material, dielectric thickness, and dielectric surface roughness should be used, and proper applied voltage amplitude and frequency should also be used.
In this paper, a detailed study is carried out on an argon plasma jet excited by a biased sinusoidal voltage. Results indicate that, with increasing the biased voltage from negative polarity to positive one, the resultant plume transits from solid to hollow. Through implementing fast photography, a plump guided bullet is found to propagate in the solid plume, in which a negative streamer mechanism is involved. However, a positive streamer mechanism is involved in the hollow plume. It behaves as a thin guided streamer starting out from the driven electrode end, which subsequently evolves into branching streamers propagating in the flow periphery. To investigate the formation mechanism of the two plumes, the intensity ratio of spectral lines is investigated.
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