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• W150434145 abstract "Les decharges a barriere dielectrique (DBD) a la pression atmospherique font partie des plasmas hors-equilibre thermodynamique. Elles peuvent etre operees en mode « filamentaire » ainsi que Townsend. Une des specificites de cette decharge est qu'une electrode (ou les deux) est recouverte par un materiau dielectrique. Generalement, une DBD a la pression atmospherique est une decharge filamentaire, mais en 1968 Bartnikas a rapporte l'existence d'une decharge luminescente uniforme dans He, maintenant dite « Atmospheric Pressure Glow Discharge (APGD)», c'est-a-dire «decharge luminescente a la pression atmospherique », caracterisee par une seule impulsion de courant par demi-cycle de la tension alternative appliquee. Posterieurement, plusieurs chercheurs ont rapporte des decharges homogenes a la pression atmospherique dans d'autres gaz ou melanges gazeux. La majorite des etudes ont ete faites dans He puisqu'il represente un milieu gazeux inerte, c'est-a-dire essentiellement sans reactivite chimique et sans problemes de decomposition, donc un gaz qui peut etre relativement facilement etudie et modelise, au moins en premiere approximation. Parmi les caracteristiques essentielles du plasma, la temperature du gaz est evidemment un parametre tres important a controler. Par exemple, pour le traitement ou modification de materiaux par plasma, une temperature trop elevee peut causer des dommages substantiels, particulierement aux materiaux thermosensibles comme les polymeres.Les objectifs de cette recherche sont : 1) determiner la temperature du gaz dans une APGD d'un gaz rare (He et Ne), en utilisant la spectroscopie d'emission optique (OES), qui a l'avantage d'etre une technique de diagnostique non perturbatrice. Ceci a ete accompli en utilisant le spectre rotationnel provenant du « First Negative System » (FNS) N2+(B2Σu+,ν′=0→X2Σg+,ν′′=0) qui a l'avantage de pouvoir etre resolu meme avec un spectrographe de resolution moyenne. La temperature rotationnelle, Trot, peut alors etre estimee simplement a partir d'un graphique de Boltzmann ; 2) etudier les effets thermiques lies au transfert de chaleur dans ces deux gaz rares, He et Ne ; 3) Finalement, etudier l'evolution spatio-temporelle de l'emission lumineuse provenant des especes excitees dans les decharges de He et Ne, en utilisant une camera numerique ultra-rapide.La decharge APGD faisant l'objet du present travail, est creee entre une electrode plane recouverte d'une mince (1 mm d'epaisseur) lame dielectrique circulaire d'alumine (Al2O3), reliee----------Abstract The purpose of this research has been to measure temperature, T, in dielectric barrier discharges (DBD) using optical emission spectroscopy (OES), which has the great advantage of being non-intrusive and non-perturbing. This is accomplished by analyzing high-resolution rotational bands in the emission spectra of suitable electronically-excited molecular species in the discharge. Several molecules have in the past been used for this purpose, but the most frequently studied are nitrogen bands from the Second Positive System (SPS) of N2 and the First Negative System (FNS) of N2+. In this work, we measure the temperature, T, of dielectric barrier discharges (DBD) in noble gases using OES by analysing rotational bands in the emission spectra of the FNS of N2+. This has the advantage that rotational structure can be fully resolved even with a spectrograph of average performance, and that the rotational temperature, Trot (~ Tgas), can then be determined from a conventional Boltzmann plot. Ionisation of N2 occurs mainly via Penning transfer from metastable excited states of He (ca. 20 eV) or Ne (ca. 16.6 eV). Using a glass-walled DBD chamber of volume 0.1 litter, we have studied atmospheric-pressure discharges in flowing helium (He) or neon (Ne) containing traces of nitrogen. Discharges were excited by audio-frequency (10 kHz) high voltage (HV) using a needle as the HV electrode and a dielectric (alumina)-covered planar grounded counter-electrode. OE spectra were acquired with a 0.5 m focal length spectrograph, coupled to an intensified charge coupled device (ICCD) detector. Using the (0-0) R-branch of the FNS N2+ (B2Σu+ - X2Σg+) bands near a wavelength of 391.4 nm, we have measured axial (inter-electrode) distributions of Trot in both He and Ne. Trot values were found to be highest at the needle electrode, of about 450 K and 740 K for He and Ne, respectively; in He, Trot dropped to a minimum of about 408 K at the mid-gap position. We conclude that temperatures in noble gas discharges depend critically on thermal conductivities of the particular gases (KHe = 1.9; KNe = 0.6, both in mW.cm-1.K-1) and on other experimental factors that influence heat transfer.Even in flows of nominally very pure He or Ne, N2 impurity at the ppm level is sufficient to yield high enough spectral intensity for accurate Trot measurements, Trot increasing linearly with rising N2 flow. We measured the effect of gas flow rate, D, on T in these atmospheric-pressure discharges: D values were varied between ca. 50 and 400 sccm., and they showed that for both gases the temperature at the mid-point in the gap, z = 1.5 mm, dropped near-linearly with rising" @default.
• W150434145 created "2016-06-24" @default.
• W150434145 creator A5029457988 @default.
• W150434145 date "2010-12-01" @default.
• W150434145 modified "2023-09-26" @default.
• W150434145 title "DÉCHARGES À BARRIÈRE DIÉLECTRIQUE DANS L'HÉLIUM ET LE NÉON À LA PRESSION ATMOSPHÉRIQUE" @default.
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