Nanosecond repetitively pulsed discharges in N₂–O₂mixtures: inception cloud and streamer emergence

Abstract

We evaluate the nanosecond temporal evolution of tens of thousands of positive discharges in a 16 cm point-plane gap in high purity nitrogen 6.0 and in N 2-O 2 gas mixtures with oxygen contents of 100 ppm, 0.2%, 2% and 20%, for pressures between 66.7 and 200 mbar. The voltage pulses have amplitudes of 20 to 40 kV with rise times of 20 or 60 ns and repetition frequencies of 0.1 to 10 Hz. The discharges first rapidly form a growing cloud around the tip, then they expand much more slowly like a shell and finally after a stagnation stage they can break up into rapid streamers. The radius of cloud and shell in artificial air is about 10% below the theoretically predicted value and scales with pressure p as theoretically expected, while the observed scaling of time scales with p raises questions. We find characteristic dependences on the oxygen content. No cloud and shell stage can be seen in nitrogen 6.0, and streamers emerge immediately. The radius of cloud and shell increases with oxygen concentration. On the other hand, the stagnation time after the shell phase is maximal for the intermediate oxygen concentration of 0.1% and the number of streamers formed is minimal; here the cloud and shell phase seem to be particularly stable against destabilization into streamers.

The 2017 Plasma Roadmap: Low temperature plasma science and technology

“…The rapidity with which these nascent subfields of plasma physics have progressed from fundamental research to societal benefit underscores the unique properties of low temperature plasmas confined to mesoscopic spatialscale cavities or produced in fluids such as SCF. With regard to the future, exotic plasmas such as SCFs, microcavity plasmas, and short time-scale plasmas present an exquisite challenge for diagnostics and modeling that will require the cross-disciplinary efforts of experimentalists and theorists from disparate fields such as sub-wavelength imaging, condensed matter physics, short pulse power electronics and nanotechnology [18]. [19,20].…”

Spatiotemporally resolved imaging of streamer discharges in air generated in a wire-cylinder reactor with (sub)nanosecond voltage pulses

“…The majority have used pointplate geometries which are very useful for fundamental streamer research because of optical accessibility and reproducibility [5,22,8,9,38,39,10,3,40,43,44,4,47]. Some used wire-plate geometries [6,7] and only a few have looked at coaxial geometries [2,12,11,52].…”

“…Streamer development 1.1.1. Streamer propagation velocity There are many studies on streamer development under pulsed voltage conditions [2,5,6,12,22,7,8,9,38,39,10,3,11,40,41,42,43,44,45,46,4,47,48]. For instance, several researchers have reported on streamer propagation velocities for a range of voltages and rise times.…”

Pulsed positive discharges in air at moderate pressures near a dielectric rod

“…The radius of the inception cloud is roughly halved to ∼25-30 mm (compared to 75 mbar). This value is again somewhat lower than the theoretical maximum (see equation 1), and the scaling with pressure is maintained [19]. After stagnating, the inception cloud breaks up into separate channels.…”

“…This cylindrically symmetric inception cloud then can destabilize and break up into separate streamer filaments that then obviously break the cylindrical symmetry. The concept of inception cloud and its breaking into streamers is described in [18][19][20].…”