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A non-equilibrium plasma is created in a micro-capillary quartz tube (800 µ m of internal diameter), by a DC-pulsed micro-dielectric barrier discharge (micro-DBD) and the propagation of an ionisation wave, in mixtures of He/H2O/VOC at atmospheric pressure where the studied volatile organic compounds (VOCs) are representative of molecules belonging to different chemical families: alcohols (methanol, ethanol, isopropanol, tert-butanol), ketones (acetone), nitriles (acetonitrile), and aromatic hydrocarbons (toluene). The conversion efficiency of these VOCs is studied as a function of the applied voltage on the micro-DBD (or electrical energy deposited in the plasma) and of the initial concentration of the molecules in the range from 1 ppm up to 3000 ppm (depending on the molecule), with the help of high-resolution real-time mass spectrometry Fourier transform ion cyclotron resonance associated to chemical ionisation (CI-FTICR) using H3O+ as precursor ion. A variety of by-products resulting from the conversion of VOCs are identified and quantified, emphasising that the micro-capillary plasma is able to induce a complex chemical reactivity. A qualitative analysis of the involved kinetics, based on the existing literature, reveals that helium species (ions and metastable states) and radicals coming from the dissociation of the water molecules (O and OH) are the most probable candidates to explain the formation of all compounds detected by the CI-FTICR apparatus. Quenching processes of the metastable He(23S) by the VOCs, leading to the dissociation of the molecules, are suggested to explain some of the experimental results. [ABSTRACT FROM AUTHOR]

Atmospheric microplasma jets (MPJs) sustained in rare gases have gained increased attention due to their potential to generate highly reactive species. In this paper, we present space- and time-resolved argon metastable densities, Ar(1s5), measured in an atmospheric pressure MPJ operated in Ar and propagating into ambient air using tunable diode laser absorption spectroscopy (1s5 → 2p9 optical transition). The MPJ was produced using a dielectric barrier discharge energized by short duration (230 ns) high-voltage positive pulses (4.2–6.2 kV) at a repetition frequency of 20 kHz. The spectral absorption line profile was recorded and allowed measurements of the absolute metastable Ar(1s5) density integrated in the line-of-sight of the laser beam under various operating conditions of the MPJ. The results reveal a sensitive dependence of the Ar(1s5) density on spatial coordinates, i.e., distance from the exit of the capillary tube of the discharge and from the axis of the argon jet. The highest Ar(1s5) densities of about 3 × 1013 cm−3 were measured at the axis of the argon jet at longitudinal distances between 4 and 5.5 mm downstream from the nozzle of the tube. The temporal distribution of the Ar(1s5) density, which presents three maxima, is thoroughly discussed in this paper. The spatial distribution of the effective Ar(1s5) lifetime (<250 ns) is also reported, giving some insight into the surrounding environment of the argon metastable atoms. The determined spatiotemporal distributions of the Ar(1s5) density can be useful for the optimization of argon MPJs for different applications like surface or biomedical processes. [ABSTRACT FROM AUTHOR]

The breakdown delay times of phototriggered discharges for binary neon/xenon, neon/HCl mixtures and neon/xenon/HCl mixtures were investigated. The results showed that direct ionization from the ground-state atoms and molecules determined the breakdown delay times. However, when the reduced electric field and the concentration in minor gases had low values, Penning effects determined the breakdown delay times.

A microstrip line structure which is capable of efficient pulsed microwave excitation of a high-pressure excimer discharge was presented. The line structure was able to sustain plasmas up to five bars of a He/Xe/HCl mixture with good stability and reproductive characteristics without any preionization needed.

An array of seven micro-hollow cathode discharges (MHCDs) operating in a N2/Ar mixture and ignited by a nanosecond pulsed high voltage is experimentally characterized in this work. Compared to other non-equilibrium discharges, high electron densities can be obtained with this type of microdischarge, and, thus, a high dissociation degree of the molecules is expected to be achieved. This is particularly suited for nitride deposition, which is the targeted application of this work, given that the atomic nitrogen density is a key parameter for this deposition process. The electrical diagnostics reveal that the energy deposited in the plasma during one voltage pulse increases with the Ar fraction in the gas mixture and the voltage pulse repetition frequency. A small effect of the repetition frequency is observed on the voltage and current characteristics of the discharge, while a significant increase in the amplitude of these two electrical parameters is observed with increasing Ar admixture. Consequently, a higher electron density is expected with increasing Ar fraction in the gas mixture and repetition frequency. Time-integrated optical emission spectroscopy is carried out to identify the excited emissive species in the plasma and to determine the time-averaged vibrational and rotational temperatures. For a discharge operating in pure N2, at a repetition frequency of 40 kHz, the time-averaged rotational temperature is found to be 390 K ± 40 K and the time-averaged vibrational temperature is 3580 K ± 200 K, revealing the non-equilibrium nature of the discharge. Both temperatures increase with the Ar fraction in the N2/Ar mixture, while they are almost independent of the repetition frequency. Finally, the different phases of the spatio-temporal evolution of the discharge are mapped using space-time resolved ICCD images. The spatial evolution of the discharge between two consecutive voltage pulses can be decomposed in four phases, corresponding to the different stages of the temporal evolution of the discharge voltage. [ABSTRACT FROM AUTHOR]

Presents a study that examined the influence of radial electron density inhomogeneity on electromagnetic plasma modes. Analysis of the variations of the plasma wave characteristics induced by a dielectric layer surrounding the plasma; Examination of the flat radial profile of the electron density; Evaluation of the propagation of plasma waves in a radially inhomogeneous plasma.

Deals with a low-pressure argon microwave discharge created and sustained by a traveling wave in the presence of an axial static magnetic field. Propagation characteristics of the wave; Influence of the electron-neutral collisions on the characteristics; Axial profile of the electron density.

Focuses on a study which presented a self-consistent theory of a low-pressure gas discharge sustained by a surface wave (SW), which provides a complete description of the plasma density and SW-field distribution both in the radial and the axial directions. Basis for the theory; Status of the plasma column in a SW discharge; Function of the high-frequency power delivered to the launcher; Features of SW discharges.

Presents information on a study that investigated the characteristics of phototriggered discharges in pure argon and neon. Pressures by which the elements were investigated; Definition of breakdown delay time; Influence of very small amounts of easily ionizable impurities in pure neon.

The spatial dynamic of phototriggered discharges in S[F.sub.6] and Ne/S[F.sub.6] mixtures has been studied through gated intensified charge-coupled device camera measurements correlated to current and voltage measurements. Physical mechanisms involved in discharge instabilities, which limit performance of discharge pumped HF/DF lasers using [H.sub.2] or [D.sub.2], are under investigation. It is shown that the high cathodic emission intensity and the discharge bulk glow are separated by a pronounced dark space. Arcs develop at a time which depends upon parameters such as the S[F.sub.6] pressure and the current pulse duration. Index Terms - Instabilities, preionized discharges, pulsed X rays, S[F.sub.6], spatial dynamic.