Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge in atmospheric pressure and high plasma-chemical reactivity. To further improve the plasma treatment efficiency and activity, a small amount of admixture can be introduced into working gases (usually Ar, He, N2), while it can affect plasma uniformity significantly. In this paper, oxygen is added into Ar nanosecond (ns) pulsed and AC DBDs DBD and the effect of the added oxygen on the uniformity and reactivity have been investigated with optical and electrical methods. The plasma uniformity is quantitatively analyzed by Gray Value Standard Deviation (GVSD) of discharge images. The optical emission spectroscopy (OES) measurement of the emission lines with different energy thresholds can reveal the tendency of T e under different operation conditions. The n e are estimated from the electrical analysis. It is found that the ns pulsed DBD shows a much better uniformity than AC DBD. With the addition of O2, the uniformity of ns-pulsed Ar DBD gets worse for the O2- negative ions by the attachment of electron on O2 distorts the space electric field and promotes the filamentary formation. While, in AC Ar DBD, the added O2 can reduce the n e and brightness of filaments, which enhances the plasma uniformity. Overdose O2 molecules cause drops of n e and T e to plasma extinction. The results can help to realize the establishment of the reactive and uniform atmospheric low temperature plasma sources.