Positive streamers in air of varying density: experiments on the scaling of the excitation density

Abstract

Abstract. Streamers are rapidly extending ionized finger-like structures that dominate the initial breakdown of large gas volumes in the presence of a sufficiently strong electric field. Their macroscopic parameters are described by simple scaling relations, where the densities of electrons and of excited molecules in the active streamer front scale as the square of the density of the neutral gas. In this work we estimate the absolute density of nitrogen molecules excited to the C 3 Π u state that emit photons in the 2P-N 2 band, by radiometrically calibrated short exposure intensified imaging. We test several pressures (100, 200 and 400 mbar) in artificial air at room temperature. Our results provide a first confirmation for the scaling of the density of excited species with the gas density. The method proposed here is particularly suitable to characterize the excitation densities in sprite streamers in the atmosphere.

Universal nature and specific features of streamers in various dielectric media

“…Another method, based on measuring the refractive index with Results of simulation of air streamers at various pressures, from atmospheric pressure and lower, support the validity of similarity laws for the densities of electrons and excited species. The similarity law for the production of excited species in streamers in air has been confirmed in experiment by Dubrovin et al (2015).…”

Experimental Investigation of the Streamer Zone of Long‐Spark Positive Leader Using High‐Speed Photography and Microwave Probing

“…It is important to note that the well‐studied (e.g., Briels et al, ; Briels et al, ; Briels, Kos, et al, ; Dubrovin et al, ; Kojima et al, ; Nijdam et al, ) streamer corona in short (<10–20 cm or so) gaps, in which the streamers of initial streamer burst cross the gap and come in contact with the opposite electrode, cannot be viewed as representative of the streamer zone developing at the tip of leader in a long air gap. There are several key disparities between streamers (including branched ones) originating from the metallic electrode in a short gap and from the moving leader tip: The leader channel has a narrow hot core surrounded by the so‐called corona sheath whose space charge influences the electric field in the streamer zone originating from the leader tip.…”

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

“…Specifically we are interested in the distribution of the streamers in the reactor, because the high-energy electrons and therefore the radicals needed for air-purification processes are generated in the streamer head and the path of the streamer [28,29,30,31,32,33,34]. Therefore, the distribution of the streamers in the reactor directly influences the chemical activity in the reactor.…”

“…The main motivation to study the development of streamers in our corona-plasma reactor is that we have to visualise the streamer discharge to understand and explain the plasmaprocessing measurements that are performed in the plasma reactor (the topic of [15], ch 8). Specifically, we are interested in the distribution of the streamers in the reactor, because the high-energy electrons and therefore the radicals needed for air-purification processes are generated in the streamer head and the path of the streamer [28][29][30][31][32][33][34]. Therefore, the distribution of the streamers in the reactor directly influences the chemical activity in the reactor.…”