Dynamics of an atmospheric pressure planar plume with two naked electrodes excited by an alternating current voltage

A large-scale plasma plume has been generated downstream of an argon flow with two naked electrodes excited by an alternating current voltage. Complicated dynamics under various dissipated powers are investigated for the planar plume. Results indicate that, besides the primary oscillations of the applied voltage at 70 kHz, a secondary oscillation is observed for the amplitude envelope of the gas voltage. Furthermore, the secondary oscillation is composed of an increasing amplitude region and a fluctuating amplitude one. With increasing the dissipated power, the duration time of the increasing amplitude region increases, and that of the fluctuating amplitude region decreases until the latter one disappears completely. The secondary oscillation frequency is investigated as a function of the dissipated power and the gas velocity. Detailed waveforms of the gas voltage, the current, and the integrated light emission are investigated for the two regions. Moreover, comprehensive investigations are performed using fast photography over the planar plume, synchronized with simultaneously recorded waveforms. It is found that the secondary oscillation originates from the dynamical movement of a plasma column, which periodically generates in the vicinity of the outlet and disappears at the plume tail.