Influence of oxygen addition on the discharge aspects of a diffuse argon plume in an atmospheric pressure plasma jet

Diffuse plasma plumes are desirable in practical applications in contrast to filamentary ones, which are normally formed downstream of atmospheric pressure plasma jets. In this paper, a diffuse plume is formed through increasing bias voltage ( U b ) applied to the downstream electrode of an argon plasma jet excited by a negatively pulsed voltage. Results indicate that the plume is filamentary when U b is low, which transits to the diffuse plume with increasing U b . The discharge initiating at the rising edge of the pulsed voltage attributes to the diffuse plume, while that at the falling edge contributes to the filament in the plume. For the diffuse plume, discharge intensity decreases with increasing oxygen content ( C o ). Fast photography reveals that the diffuse plume results from a negative streamer, which has a dark region near the nozzle with C o =0 %. However, the dark region is absent with C o =0.5 %. From optical emission spectrum, electron density, electron excitation temperature, gas temperature, and oxygen atom concentration are investigated. These results are of great importance to the extensive applications of atmospheric pressure plasma jet.