Olivier Guaitella

Influence of the charges deposition on the spatio-temporal self-organization of streamers in a DBD

At atmospheric pressure, dielectric barrier discharges (DBDs) are mainly constituted of unstably triggered non-equilibrium transient plasma filaments, also called microdischarges. A self-organization of plasma filaments and their interaction with the deposited charges upon the dielectric material has been studied previously for frequencies on the order of a few kilohertz (for example see Guikema et al (2000 Phys. Rev. Lett. 85 3817) and Chirokov et al (2004 Plasma Sources Sci. Technol. 13 623–35)). In this paper we realized a DBD in the configuration cylinder-tip to dielectric plate biased by a low frequency power supply (50 Hz) in synthetic air. Using a CCD camera coupled with electrical diagnostics we observed collective behaviour of plasma filaments in the gas gap, as already observed for asymmetric surface dielectric barrier discharges (ASDBD) in Allegraud et al (2007 J. Phys. D: Appl. Phys. 40 7698–706) and predicted in Guaitella et al (2006 J. Phys. D: Appl. Phys. 39 2964–72). We also show how the surface charge deposited upon the dielectric plate modifies the spatial organization of microdischarges in this experimental device. In parallel, we made an electrostatic model of the experimental device which gave results consistent with the experimental measurements and with the assumption we made on the role of the deposited charges for their impact on the subsequent discharges during a positive half-cycle.

Ozone kinetics in low-pressure discharges: vibrationally excited ozone and molecule formation on surfaces

A combined experimental and modeling investigation of the ozone kinetics in the afterglow of pulsed direct current discharges in oxygen is carried out. The discharge is generated in a cylindrical silica tube of radius 1?cm, with short pulse durations between 0.5 and 2?ms, pressures in the range 1?5?Torr and discharge currents ?40?120?mA. Time-resolved absolute concentrations of ground-state atoms and ozone molecules were measured simultaneously in situ, by two-photon absorption laser-induced fluorescence and ultraviolet absorption, respectively. The experiments were complemented by a self-consistent model developed to interpret the results and, in particular, to evaluate the roles of vibrationally excited ozone and of ozone formation on surfaces. It is found that vibrationally excited ozone, , plays an important role in the ozone kinetics, leading to a decrease in the ozone concentration and an increase in its formation time. In turn, the kinetics of is strongly coupled with those of atomic oxygen and O2(a?1?g) metastables. Ozone formation at the wall does not contribute significantly to the total ozone production under the present conditions. Upper limits for the effective heterogeneous recombination probability of O atoms into ozone are established.

Electric field measurement in the dielectric tube of helium atmospheric pressure plasma jet

The results of the electric field measurements in the capillary of the helium plasma jet are presented in this article. Distributions of the electric field for the streamers are determined for different gas flow rates. It is found that electric field strength in front of the ionization wave decreases as it approaches to the exit of the tube. The values obtained under presented experimental conditions are in the range of 5–11 kV/cm. It was found that the increase in gas flow above 1500 SCCM could induce substantial changes in the discharge operation. This is reflected through the formation of the brighter discharge region and appearance of the electric field maxima. Furthermore, using the measured values of the electric field strength in the streamer head, it was possible to estimate electron densities in the streamer channel. Maximal density of 4  × 1011 cm−3 is obtained in the vicinity of the grounded ring electrode. Similar behaviors of the electron density distributions to the distributions of the elec...

A spectroscopic study of ethylene destruction and by-product generation using a three-stage atmospheric packed-bed plasma reactor

Using a three-stage dielectric packed-bed plasma reactor at atmospheric pressure, the destruction of ethylene, a typical volatile organic compound, and the generation of major by-products have been studied by means of Fourier Transform Infrared Spectroscopy. A test gas mixture air at a gas flow of 1 slm containing 0.12% humidity with 0.1% ethylene has been used. In addition to the fragmentation of the precursor gas, the evolution of the concentration of ten stable reaction products, CO, CO2, O3, NO2, N2O, HCN, H2O, HNO3, CH2O, and CH2O2 has been monitored. The concentrations of the by-products range between 5 ppm, in the case of NO2, and 1200 ppm, for H2O. By the application of three sequentially working discharge cells at a frequency of f = 4 kHz and voltage values between 9 and 12 kV, a nearly complete decomposition of C2H4 could be achieved. Furthermore, the influence of the specific energy deposition (SED) on the destruction process has been studied and the maximum value of SED was about 900 J l−1. Th...

Distribution of surface electric charge in a surface DBD

Summary form only given. For more than one decade, the surface dielectric barrier discharge (SDBD) has been extensively studied in aerodynamic applications as electro-hydrodynamic (EHD) actuators [1]. The SDBD was also largely studied for air pollution treatment due to the lower discharge ignition voltage and the larger contact surface with catalyst than the volume DBD [2]. The propagation and expansion mechanism of discharge on the dielectric surface is the key point for the understanding of the plasma-gas flow interaction. The electric charges deposited on the dielectric surface play an important role in the discharge mechanism, and it has an important influence on the SDBD physics. A lot of works were performed on this topic, for example: the collective effect [3]; self-synchronized breakdown effect due to photodesorption [4]; the surface potential in a SDBD [5], etc.