Determination of the electron temperature in plane-to-plane He dielectric barrier discharges at atmospheric pressure

Abstract

Optical emission spectroscopy (OES) measurements coupled with a collisional-radiative model were used to characterize a plane-to-plane dielectric barrier discharge at atmospheric pressure operated in nominally pure helium. The model predicts the population densities for the n = 3 levels of He excited by electron impact processes from either ground or metastable states and takes into account excitation transfer processes between He n = 3 levels as well as all relevant radiative decays and quenching reactions. Time-resolved OES measurements indicate that line ratios from He n = 3 triplet states (for example, 587.5 nm-to-706.5 nm) and singlet states (for example, 667.8 nm-to-728.1 nm) first sharply rise as the discharge ignites and then slowly decrease as it extinguishes. Assuming that n = 3 levels are first populated only by electron impact on ground state He atoms and then only by electron impact on metastable He atoms as the discharge current and thus the metastable number density rise, triplet and singlet line ratios predicted by the model become in each opposite case solely dependent on the electron temperature T e (assuming Maxwellian electron energy distribution function). The values of T e deduced from the analysis of both ratios were relatively high early in the discharge cycle (around 1.0-1.4 eV) and then much lower near discharge extinction (around 0.15 eV). For analysis of time-integrated (or cycle-averaged) OES measurements, the electron temperatures were closer to the 0.15 eV values near the end of the discharge cycle, in good agreement with the values expected from theoretical predictions in the positive columns of He glow discharges at atmospheric pressure.

Characterization of a plasma source for biomedical applications by electrical, optical, and chemical measurements

“…An estimate of the electron temperature was obtained from He I line emissions following Gangwar et al, who applied a collisional radiative model to an atmospheric pressure He plasma. The electron temperature dependence of the intensity ratio between He I 667.8 and 728.1 nm lines calculated by the model allowed us to deduce an electron temperature of about 0.18 eV, which is similar to the average value of 0.17 eV found for the vibrational temperature.…”

Influence of substrate outgassing on the plasma properties during wood treatment in He dielectric barrier discharges at atmospheric pressure

“…In order to extract information about the plasma parameters such as the electron temperature, Te (assuming Maxwellian electron energy distribution function) and the number density of He metastable atoms, OES measurements were coupled to a CR model recently developed in our laboratory . Briefly, the model takes into account electron impact processes from either the ground or the metastable states of He atoms to predict the n = 3 level population densities giving rise to the emission lines at 587.5, 667.8, 706.5, and 728.1 nm.…”

“…The experimental setup used in this work was described in detail in previous papers . Briefly, the plane‐to‐plane AP‐DBD is sustained in a sealed aluminum chamber between two silver‐based electrodes covered by alumina sheets to prevent transition to an arc.…”

“…However, in all cases the source of these “impurities” was a manual addition, and not a natural release by the substrate itself as with porous wood samples. Furthermore, combination of optical emission spectroscopy measurements (OES) and population models such as collisional radiative (CR) models is a non‐invasive way to characterize plasma sources . In a recent work, for example, such approach was used to analyze the Townsend‐to‐glow transition in He AP‐DBDs .…”

“…Furthermore, combination of optical emission spectroscopy measurements (OES) and population models such as collisional radiative (CR) models is a non‐invasive way to characterize plasma sources . In a recent work, for example, such approach was used to analyze the Townsend‐to‐glow transition in He AP‐DBDs . In the present study, we would like to use this combination of OES measurements with CR modeling to investigate the role of wood substrate outgassing during discharge operation on the properties of He AP‐DBDs.…”