Plasma Sheath Dynamics in Dielectric Barrier‐Free Atmospheric Pressure Radio‐Frequency Glow Discharges

The atmospheric pressure plasma jet (APPJ) makes use of a dielectric barrier-free atmospheric pressure radio-frequency (RF) glow discharge. In its usual operation mode it produces a uniform glow discharge, filling the gap. This alpha mode of the RF discharge is sustained by bulk ionization by oscillating electrons, as long as the gap spacing is sufficient. At higher RF powers the alpha sheath breaks down and the gamma mode, sustained by secondary electron emission occurs. Present experiments test the above model by taking images with nanosecond time resolution. The experiments clearly showed the differences in the development of the discharge over the RF cycle in correlation with gap spacing and α or γ mode, corroborating the model.