The effect of small O-2 addition on the properties of a long positive streamer in Ar

Experiments are described in which spark discharges in long non-uniform gap s are studied in Ar with a small addition (1-5%) of O-2 under standard cond itions. The results obtained show that even the addition of 1% O-2 drastica lly reduces the conductivity of the streamer channel and increases the aver age electric field required to bridge the discharge gap by a streamer. Brea kdown, producing short circuiting, is developed through leader propagation in Ar:O-2 mixtures, in contrast to a non-thermal streamer mechanism of brea kdown that was previously observed in pure Ar. A 1.5-dimensional simulation was carried out which supports the general observed properties of streamer s in long gaps in Ar:O-2. An analysis of the simulation results shows that the effect of small O-2 additions on the streamer properties in Ar is expla ined by the quenching of excited Ar atoms by O-2 molecules, which leads to the deceleration of two-step ionization in the streamer channel.