Sub-nanosecond delays of light emitted by streamer in atmospheric pressure air: Analysis of N2(C3Πu) and N2+(B2Σu+) emissions and fundamental streamer structure

Abstract

Both experimental and theoretical analysis of an ultra-short phenomena occurring during the positive streamer propagation in atmospheric pressure air is presented. With tens-of-picoseconds and tens-of-microns precision, it is shown that when the streamer head passes a spatial coordinate, emission maxima from N2 and N + 2 radiative states follow with different delays. These different delays are caused by differences in the dynamics of populating the radiative states, due to different excitation and quenching rates. Associating the position of the streamer head with the maximum value of the selfenhanced electric field, a delay of 160 ps was experimentally found for the peak emission of the first negative system of N + 2 . For the first time, a delay dilatation was observed experimentally on early-stage streamers and clarified theoretically. Thus, in the case of second positive system of N2 the delay can reach as much as 400 ps. In contrast to the highly-nonlinear behaviour of streamer events, it is shown theoretically that emission maxima delays linearly depend on the ratio of the streamer radius and its velocity. This is found to be one of the fundamental streamer features and its use in streamer head diagnostics is proposed. Moreover, radially-resolved spectra are synthetized for selected subsequent picosecond moments in order to visualize spectrometric fingerprints of radial structures of N2(C 3 Πu) and N + 2 (B 2 Σ + u ) populations created by streamer-head electrons.

Demonstration of Dynamics of Nanosecond Discharge in Liquid Water Using Four-Channel Time-Resolved ICCD Microscopy

“…The sources of emitted photons remain distributed within the entire volume of the growing and expanding filament. In other words, the dominant sources of the discharge luminosity are not predominantly localised on the moving luminous front, as in the case of classical ionising streamer fronts developing in gaseous dielectrics [22,23]. Similar conclusions are supported by the Event 2 and 3 sequences shown in Figure 6; Figure 9 obtained using MCP gates of gate width 1 ns.…”

Optical and Energetic Investigation of an Advanced Corona Ignition System in a Pressure-Based Calorimeter

“…With the selected framerate and the discharge duration of 300 μs, the streamers are expected to be captured in a number of frames between 23 and 24 for each event. The camera sensor is featured with a good sensitivity in the visible range of the electromagnetic spectrum, which is found to be adequate for the streamer detection: the corona discharge luminosity is related to the first negative system (FNS) of N2 + (B 2 Σu + ) at about 391 nm [26], mainly in the streamer head, which moreover justifies the violet colour of the streamers (Fig. 1 left).…”

Plasma-assisted agriculture: history, presence, and prospects—a review

“…Under this treatment, the samples intersect with the electrodynamic profile of plasma/discharge filaments approximated by the luminous profile of plasma filaments under conditions of filamentary micro-discharges at atmospheric pressure [308,309]. In such a case, the treated samples come into direct contact with the electric fields, energetic electrons/ions, excited species, radicals, and with a full spectrum of radiation (including VUV and UV photons) produced within active plasma regions [178,[310][311][312].…”