Alina Silvia Chiper

On the Secondary Discharge of an Atmospheric-Pressure Pulsed DBD in He with Impurities

The secondary discharge was induced at the end of a slow-falling voltage flank, when a semisine monopolar pulse voltage excites the dielectric-barrier discharge. Formation and properties of the secondary discharge with respect to different dielectric materials such as glass, ceramic, and polyethylene theraphtalate were studied. The tunable diode laser absorption spectrometry (at 777.194 nm) was used to analyze the time-space distribution of the density of the atomic oxygen in metastable state (35S2 rarr 35P3) in addition to both discharge voltage and discharge current versus time. The secondary discharge is always formed, and its amplitude, as well as the amplitude of the main discharge, depends on surface properties of the dielectric barrier.

Detailed Characterization of 2-Heptanone Conversion by Dielectric Barrier Discharge in N2 and N2/O2 Mixtures

The products of 2-heptanone conversion by dielectric barrier discharge plasma are analyzed under different conditions: alternating current (ac) or pulsed mode of excitation, variable energy, variable composition of the carrier gas. The efficiency of the conversion is higher using a pulse excitation mode than an ac mode. With a small oxygen percentage (about 2-3%) added to nitrogen, 2-heptanone is about 30% more efficiently removed than in pure nitrogen, while the 2-heptanone removal decreases with an oxygen percentage higher than 3%. A new analysis method, based on chemical ionization mass spectrometry, is used for volatile organic compound detection along with chromatography. Several products issued from 2-heptanone conversion with ac excitation are identified in nitrogen and in air, and a chemical scheme is proposed to explain their formation and their treatment by the discharge. It appears that byproducts are issued not only from oxidation reactions, but also from C-C bond cleavage by collisions with electrons or nitrogen excited states.

On the Discharge Parameters of a Glow-Mode DBD at Medium and Atmospheric Pressure

In this paper, we report on the behavior of a glow-mode pulsed barrier discharge working at different gas pressure (25-760 torr) in helium and helium-oxygen gas mixture. The experimental setup consists of a plane-parallel geometry of a dielectric barrier discharge (DBD) system, excited by positive monopolar voltage pulses. The discharge properties were characterized by electrical measurements and emission spectroscopy. Our investigations showed that the discharge consists of two current pulses, with different polarities, corresponding to each voltage pulse. The main results referred to the effect of pressure and oxygen percentage on the discharge parameters. The time-resolved spectroscopy of the DBD plasma working at different pressure pointed out the differences between the discharge mechanism at medium pressure and that close to atmospheric pressure. Moreover, at medium pressure (25 torr), the oxygen atoms are efficiently created for about 2% of molecular oxygen added to gas mixture.

Temporally, spatially, and spectrally resolved barrier discharge produced in trapped helium gas at atmospheric pressure

Experimental study was made on induced effects by trapped helium gas in the pulsed positive dielectric barrier discharge (DBD) operating in symmetrical electrode configuration at atmospheric pressure. Using fast photography technique and electrical measurements, the differences in the discharge regimes between the stationary and the flowing helium are investigated. It was shown experimentally that the trapped gas atmosphere (TGA) has notable impact on the barrier discharge regime compared with the influence of the flowing gas atmosphere. According to our experimental results, the DBD discharge produced in trapped helium gas can be categorized as a multi-glow (pseudo-glow) discharge, each discharge working in the sub-normal glow regime. This conclusion is made by considering the duration of current pulse (few μs), their maximum values (tens of mA), the presence of negative slope on the voltage-current characteristic, and the spatio-temporal evolution of the most representative excited species in the discha...

Influence of the Dielectric Surface Nonhomogeneities on the Dynamic of the Pulsed DBD Plasma

This paper reports on the dual dielectric barrier discharge (DBD) plasma produced in helium at atmospheric pressure. Using a gated (20 ns) intensified charge-coupled detector, short exposure time images were recorded to investigate the time-space evolution of the DBD plasma. Experimental results proved that the surface nonhomogeneities are strongly reflected on the DBD plasma dynamic.

Pulsed Atmospheric-Pressure DBD Plasma Produced in Small-Diameter Tubes

This paper presents the experimental results on the characterization of plasma produced in narrow tubes using a pulsed dielectric barrier discharge (DBD), working in helium or helium-oxygen gas mixture at atmospheric pressure, in a symmetrical configuration of external electrodes. This paper focuses on the effect induced by the total gas flow rate and gas composition on the characteristics of pulsed DBD. Using tunable diode laser absorption spectroscopy, ultraviolet absorption, and optical emission spectroscopy, complementary information on the reactive species (O, O₃, N₂, and N₂⁺ ) present in the discharge has been obtained. It results that the excited species generated by direct electron excitation (as He and N₂) follow the evolution of their precursors with increasing gas flow rate, while those created by chain reactions (as N₂⁺ , O, and O₃) depend on the collective behavior of all their precursors, regardless of the fact that these are originating from the feeding gas or are coming from impurities. At specific energies, between 5 and 50 J/L, and a gas temperature of 315 ± 20 K, the atmospheric-pressure plasma is able to produce 10¹⁴-10¹⁵ m^-3 of O (3⁵S₂) or (1.5-2.8) × 10¹⁵ cm^-3 of O₃, depending on the feeding gas composition and its flow rate. Low gas temperature and high density of reactive species could make the present DBD arrangement suitable for medical applications.