Oyn Olivier Guaitella

Plasma–catalyst coupling for volatile organic compound removal and indoor air treatment: a review

The first part of the review summarizes the problem of air pollution and related air-cleaning technologies. Volatile organic compounds in particular have various effects on health and their abatement is a key issue. Different ways to couple non-thermal plasmas with catalytic or adsorbing materials are listed. In particular, a comparison between in-plasma and post-plasma coupling is made. Studies dealing with plasma-induced heterogeneous reactivity are analysed, as well as the possible modifications of the catalyst surface under plasma exposure. As an alternative to the conventional and widely studied plasma–catalyst coupling, a sequential approach has been recently proposed whereby pollutants are first adsorbed onto the material, then oxidized by switching on the plasma. Such a sequential approach is reviewed in detail.

Spatio-temporal breakdown in surface DBDs: evidence of collective effect

This paper presents an experimental investigation of the plasma ignition in a dielectric barrier surface discharge in air at atmospheric pressure. CCD pictures of the discharge are compared with electrical measurements. A detailed study of the current peaks during the positive half period of the applied voltage has been performed. CCD pictures of single discharges events have been taken. They show synchronous breakdowns of plasma filaments, corresponding to current intensities of several amperes. It is shown that each plasma filament transfers a current of about 40 mA. The influence of adsorbed electrons on the synchronization of the plasma filaments is discussed. The length of the filaments increases during the half period and can be plotted as a linear function of the difference between applied and ignition voltages. The differences between the discharges of positive and negative half periods are presented. The discharges of the negative half period consist of diffuse spots of shorter lengths and are characterized by low currents (several milliamperes), and individual breakdowns.

Time-resolved nanosecond imaging of the propagation of a corona-like plasma discharge in water at positive applied voltage polarity

This paper is an experimental study of a pulsed filamentary plasma discharge inside liquid water in pin-to-plane electrode configuration. Time-resolved electrical and imaging diagnostics have been performed. The initiation and the propagation of the discharge have been studied for several experimental parameters. The propagation is continuous and is followed by reilluminations at low water conductivity. The measured propagation velocity of the plasma discharge is 30?km?s?1 for the secondary positive mode. This velocity was found to be surprisingly constant whatever the experimental parameters and especially as a function of the water conductivity.

On electric field measurements in surface dielectric barrier discharge

Analysis of available data on electric field measurements in surface dielectric barrier discharges (DBDs) was carried out. Experimental measurements of emission spectra in triggered and non-triggered sinusoidal surface DBD were performed. The results obtained were used for the calculation of electric field value. The comparison of data obtained and the results published by other authors is presented.

Cavitation in the vicinity of the high-voltage electrode as a key step of nanosecond breakdown in liquids

Fast shadowgraphy of nanosecond discharge in liquids with different dielectric permittivity, namely in water, ethanol and n-pentane, has been performed. Formation of a gas cavity at a nanosecond time scale was observed as a pre-breakdown phenomenon at amplitudes of the high-voltage pulse close to the breakdown threshold. This phenomenon is considered as a possible key step of high-voltage breakdown in polar liquids.

Dynamic of the plasma current amplitude in a barrier discharge: influence of photocatalytic material

For a better understanding of the plasma/photocatalytic material interaction under plasma exposure, a study of the electrical properties of a cylindrical sinusoidal dielectric barrier discharge is performed with and without porous material containing TiO2. The metallic inner electrode is in contact with the gas gap. First, the presence of porous material made of silica fibres coated with nanoparticles of TiO2 leads to a strong increase of the injected energy for the same applied voltage. Then the time evolution of the current amplitude distribution function (CADF) shows two different peak populations on the positive half period (when the metallic inner electrode is positive). Apart from numerous low intensity plasma filaments (around 1 mA amplitude), much larger ones exist (around 1 A). These large current amplitude peaks are responsible for 50–70% of the injected energy depending on the presence of the photocatalytic material. The influence of 900 ppm of C2H2 as well as external ultraviolet irradiation on the CADF is also reported.

Experimentally obtained values of electric field of an atmospheric pressure plasma jet impinging on a dielectric surface

We report on experimentally obtained values of the electric field magnitude on a dielectric surface induced by an impinging atmospheric pressure plasma jet. The plasma plume was striking the dielectric surface at an angle of 45°, at 5 mm from the surface measured at the axis of the jet. The results were obtained using Pockels technique on a BSO (Bi12SiO20) crystal. A coaxial configuration of the plasma jet was used, operating in a stable mode with one bullet per voltage period, at 30 kHz and amplitude of 2 kV. The electric field was shown to be a function of the gas flow (He, at 300, 500 and 700 SCCM) and the manner in which the discharge spreads over the dielectric surface. The maximum value of 11.6 × 105 V m−1 was obtained at the negative half-period of the discharge current measured at the grounded electrode, at the flow of 300 SCCM. The largest electric field averaged over the area of the spreading of the discharge (3.6 × 105 V m−1) was found in the same conditions.

TRIPLE Q: A three channel quantum cascade laser absorption spectrometer for fast multiple species concentration measurements

A compact and transportable three channel quantum cascade laser system (TRIPLE Q) based on mid-infrared absorption spectroscopy has been developed for time-resolved plasma diagnostics. The TRIPLE Q spectrometer encompasses three independently controlled quantum cascade lasers (QCLs), which can be used for chemical sensing, particularly for gas phase analysis of plasmas. All three QCLs are operated in the intra-pulse mode with typical pulse lengths of the order of 150 ns. Using a multiplexed detection, a time resolution shorter than 1 μs can be achieved. Hence, the spectrometer is well suited to study kinetic processes of multiple infrared active compounds in reactive plasmas. A special data processing and analysis technique has been established to account for time jitter effects of the infrared emission of the QCLs. The performance of the TRIPLE Q system has been validated in pulsed direct current plasmas containing N(2)O/air and NO(2)/air.

Heavy species kinetics in low-pressure dc pulsed discharges in air

A time-dependent kinetic model is presented to study low-pressure (133 and 210?Pa) pulsed discharges in air for dc currents ranging from 20 to 80?mA with a pulse duration from 0.1 up to 1000?ms. The model provides the temporal evolution of the heavy species along the pulse within this range time, where the coupling between vibrational and chemical kinetics is taken into account. This work shows that the predicted values for NO(X) molecules and O(3P) atoms reproduce well previous measured data for these two species. A systematic analysis is carried out on the interpretation of experimental results. It is observed that the N2(X, v ? 13) + O ? NO(X) + N(4S) and the reverse process NO(X) + N(4S) ? N2 (X, v ~ 3) + O have practically the same rates for a pulse duration longer than 10?ms, each of them playing a dominant role in the populations of NO(X), N(4S) and, to a lesser extent, in O(3P) kinetics. Our simulations show that for shorter pulse durations, from 0.1 to 10?ms, NO(X) is produced mainly via the processes N2(A) + O ? NO(X) + N(2D) and N(2D) + O2 ? NO(X) + O, while the oxygen atoms are created mostly from electron impact dissociation of O2 molecules and by dissociative collisions with N2(A) and N2(B) molecules.

Evidence for surface oxidation on Pyrex of NO into NO2 by adsorbed O atoms

The surface of a Pyrex discharge tube was treated by a capacitively coupled RF plasma at low pressure. In cases where the plasma contained oxygen, O atoms deposition on the tube surface could be confirmed via the time-dependent conversion of NO to NO2 in a post-plasma experiment. Inside the discharge tube, the evolution of the concentrations of NO and of NO2 was measured using quantum cascade laser absorption spectroscopy in the mid-infrared spectral range. The surface density of atomic oxygen was estimated to be about 2 ? 1014?cm?2 based on NO oxidation in the closed reactor. The production rate of NO2 is in the range of 2 ? 1011?molecules?cm?3?s?1.