On Ω Mode in Radio-Frequency Atmospheric Discharges Controlled by Dielectric Barriers

In atmospheric radio-frequency (RF) discharges, two discharge modes, namely alpha and beta modes, have been deeply discussed by experimental measurements and computational data, and another mode, known as Omega mode, has also been reported in the electronegative gas. In this paper, we present a fluid model to investigate the formation and dynamics of Omega mode in atmospheric RF discharges but controlled by dielectric barriers with pure helium as working gas. The simulation results show that the Omega mode can be observed right after the breakdown event, and only sustained in a very narrow voltage range; then, the discharge will enter into the Omega mode as the applied voltage is further increased. Compared with the alpha mode, the numerical data reveal that in the Omega mode, a relatively larger electric fields are sustained in the bulk plasma to ensure the continuity of discharge current due to the lower electron density, consequently the Ohmic heating and ionization processes mainly take place in the central region of discharge gap.