density measurement in a dielectric barrier discharge in N₂and N₂with small O₂admixtures

Abstract

This paper deals with the measurement of N 2 (A 3 + u ) metastable state density in a dielectric barrier discharge in nitrogen and nitrogen with small admixtures of oxygen, operating in a Townsend-like discharge regime. The measurement is made by optical-optical double resonance-LIF, calibrated by a method based on the measurement of the ratio of nitrogen second positive system and NO-γ emissions, and of NO density by LIF. A metastable density of the order of 10 13 cm −3 was found in a nitrogen diffuse discharge. Addition of small oxygen concentrations to the discharge drives a transition to the filamentary regime that appears to be caused not by a marked decrease of the metastable density in the discharge but rather by a considerable increase of its quenching rate. Such an increase, due to collision quenching by O 2 and O, strongly reduces the survival of the metastable between two discharge pulses. These observations are consistent with the idea that the diffuse regime can be due to a space charge memory effect due to the nitrogen triplet metastable, which is cancelled by the introduction of oxygen in the gas feed.

Thermoluminescence study of the trapped charge at an alumina surface electrode in different dielectric barrier discharge regimes

“…For instance, the nitrogen discharge can be run in different regime depending on the 48 geometry and other discharge parameters [6,7]. Moreover, the addiction of small quantities of oxygen to a 49 nitrogen discharge transform the regime from glow to filamentary [8]. Conversely, running an helium 50 discharge this will lead to a quite distinct glow regime [9].…”

Optical diagnostics in dielectric barrier discharges at atmospheric pressure

“…We have shown in [13] that this is true also in a DBD at ATP. By the way, the SPS too, in the post-discharge, is produced by an energy transfer process involving the nitrogen metastable, the pooling reaction It was then possible to identify a time region, in the post-discharge between two current cycles, in which the ratio of SPS and NO-γ emissions is proportional through a known constant to the ratio [N 2 (A)]/[NO], giving a way to calibrate OODR-LIF on N 2 (A).…”

“…The N 2 (C 3 Π u ,v) states, from which SPS bands originate, are excited by electron impact in a discharge. A simple collision-radiative model gives the time evolution of the C-state populations C v [3]: (3) where k vj XC is the electron impact rate coefficient for (X, j) → (C,v) excitation that depends on the EEDF, k Q is the collision quenching rate coefficient, A v the radiative rate, k wv is the vibrational relaxation (C,w) → (C,v) rate coefficient. The collision features of N 2 (C,v) in a N 2 bath were measured in great detail in [12], where state-selective excitation by OODR-LIF allowed, for the first time, a clear and accurate measurement of the vibrational relaxation process, that, in this case, is quite strong.…”

“…In [2], for example, OES and surface analysis were combined to interpret emission spectra in a DBD for silane-based coatings. Nitrogen emissions have been used for the estimation of electron temperature [3] or of the reduced electric field E/N [4,5]. To this end, collisionradiative models are necessary that require a detailed knowledge of the collision processes occurring in the electronic states.…”

“…We have explored this realm, touching many of the issues described above by a multidiagnostic approach with time-resolved optical diagnostics, applied to common DBD devices. In this paper, we will briefly review our recent results on • the use of N 2 (C) emission (SPS) for electron temperature estimation by a collision-radiative model, with a complete characterization of the collision processes in the N 2 (C,v) manifold [12]; • optical-optical double resonance (OODR) LIF for N 2 (A) metastable detection [13]; • a combination of time-resolved emission and laser spectroscopy for the investigation of CN violet system emissions in a N 2 -CH 4 discharge [14]; and • the detection of CH in a He-CH 4 discharge, an archetype of all the difficulties one has to face when trying to detect a radical in this kind of discharge [15].…”