High-resolution electric field and temperature distributions in positive streamers

Abstract

In this work, we aim to take a detailed experimental picture of the positive streamer. We apply optical emission spectroscopy to the first negative system (FNS, B2Σu+→X2Σg+) of N2+ and the second positive system (SPS, C3Πu → B3Πg) of N2. Large, centimeter wide, and highly reproducible streamers are created in pure nitrogen and synthetic air, at pressures ranging from 33 to 266 mbar. Direct time resolved spectral imaging of the space charge layer resulted in spatiotemporal maps of the calculated reduced electric field strength (E/N) and rovibrational temperature in sub-nanosecond and sub-millimetre resolution. The E/N peaks at approximately 540 and 480 Td, directly in front of the space charge layer, for synthetic air and pure nitrogen respectively, as determined by using the intensity ratio method of FNS and SPS. A global model for pure nitrogen in PLASIMO uses the experimentally determined E/N distribution to draw a picture of the gas kinetics around the space charge layer passage. In addition, the results of the global model serve as a reference to interpret the rotational and vibrational temperatures obtained from experimental FNS and SPS emissions.

Remote streamer initiation on dielectric surface

“…The exception is to additionally modify the dependence of Paris et al [30] as suggested in [16,31,33,34]. Such modified curve was used for diagnostics of streamer or nanosecond pulsed discharges [17,35] and is well within the uncertainty interval discussed in [29,31]. To overcome the issue of the R(E/N ) dependence coming from the equilibrated steady-state Townsend discharge, the method may be developed and studied also in a time-dependent case by a theoretical means (see also [15]), i.e.…”

Electric field in APTD in nitrogen determined by EFISH, FNS/SPS ratio, α-fitting and electrical equivalent circuit model

“…The method of electric field determination via the first Townsend coefficient is affected by the presence of nitrogen metastable states. The method of FNS/SPS ratio, while successfully utilized for streamer discharges [6,54], is here at the limit of its applicability, apparently due to the impossibility of fully verifying all the underlying assumptions and the low electric field, which needs to be measured. Nevertheless, the overestimation of the electric field from the line ratio is comparable to the accuracy of the method estimated by the analysis of the molecular data (cross sections, lifetimes etc).…”