Characteristics of atmospheric pressure plasma jets emerging into ambient air and helium

An investigation of atmospheric pressure helium plasma jets emerging into ambient air and helium was carried out with the aim of shedding light on the mechanism for the formation of extended plasma plumes. By electron multiplying charge coupled device imaging, it is shown that the geometrical shape of the jet in ambient helium is not an arrow-like shape as that in ambient air, but a diffusive one. In ambient helium, the jet length increased continuously with the applied voltage. For ambient air, the jet length was determined by both the helium flow rate and the applied voltage. In addition, the N₂ (C-B) band and the lines dominate the emission spectra of the jet in ambient air. The Penning ionization between metastable He atoms and N₂ molecular may be the main source of .