Simple Analytical Model of the Anodic Streamer

In this work, an analytical model is used to study the formation of the anodic streamer in high pressure electrical discharge. This model enabled us to see the space variations of the characteristics of the streamer such as the electric field and the propagation velocity of streamer. The validity of the analytic approach is demonstrated by comparing the model results to the data from the literature. A qualitative concord was found. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasma Chemical and Electrical Modeling of a Dielectric Barrier Discharge in Kr–Cl2 Gas Mixtures

This paper reports the study of the Kr–Cl₂ plasma chemistry in terms of the homogenous model of a dielectric barrier discharge and for two kinds of the applied voltage excitation shape. The effect of Cl₂ concentration in the gas mixture, as well as gas pressure and power frequency on the discharge efficiency and the 222 nm photon generation, under typical experimental operating conditions, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to ultraviolet emission in the lamp is in the range of 4.4–12 %, and it will be very affected at high chlorine percentage (>1 %) and high gas pressure (>200 Torr). A comparison between the sinusoidal and the burst excitation waveforms reveals that the burst excitation method provides an enhanced light source performance compared to the sinusoidal wave.     

Investigation of plasmas produced by laser ablation using single and double pulses for food analysis demonstrated by probing potato skins

We report on investigations of plasmas produced by laser ablation of fresh potatoes using infrared nanosecond laser radiation. A twin laser system consisting of two Nd:YAG oscillators was used to generate single or double pulses of adjustable interpulse delay. The potatoes were irradiated under ambient air with moderate pulse energies of about 10 mJ. The expansion dynamics of the ablation plume was characterized using fast imaging with a gated camera. In addition, time-resolved optical emission spectroscopy was applied to study the spectral line emission of the various plasma species. The electron density was deduced from Stark broadening, and the plasma temperature was inferred from the relative emission intensities of spectral lines. The relative concentrations of metals were estimated from the comparison of the measured emission spectra to the spectral radiance computed for a plasma in local thermal equilibrium. It is shown that the plasma produced by double pulses has a larger volume and a lower density. These properties lead to an increase of the signal-to-noise ratio by a factor of 2 and thus to an improved measurement sensitivity.     

Electrical Approach of Homogenous High Pressure Ne/Xe/HCl Dielectric Barrier Discharge for XeCl (308 nm) Lamp

This paper reports the investigation of the excimer UV emission efficiency in Ne/Xe/HCl mixture in terms of the homogenous model of a dielectric barrier discharge. The computer model developed is based on the Ne/Xe/HCl gas mixture chemistry, the circuit and the Boltzmann equations. The effects of operating voltage, HCl concentration in the mixture as well as gas pressure on the discharge efficiency and the 172, and 308 nm photon generation, under typical experimental operating conditions, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to VUV emission in the lamp is greater than 27%, and it will be very affected at high voltage amplitude and high gas pressure with a significant dependence on the HCl concentration in the gas mixture.     

Theoretical Kinetics Investigation of Krypton Dielectric Barrier Discharge for UV Lamp

Plasma Chemistry and Plasma Processing - This work presents an electric and kinetic study of homogeneous dielectric barrier discharge (DBD) in pure krypton (Kr). The electrical characterization and...     

Ortho-Quinone Methide Driven Synthesis of New O,N- or N,N-Heterocycles

To synthesize functionalized Mannich bases that can serve two different types of ortho-quinone methide (o-QM) intermediates, 2-naphthol and 6-hydroxyquinoline were reacted with salicylic aldehyde in the presence of morpholine. The Mannich bases that can form o-QM and aza-o-QM were also synthesized by mixing 2-naphthol, 2-nitrobenzaldehyde, and morpholine followed by reduction of the nitro group. The highly functionalized aminonaphthol derivatives were then tested in [4+2] cycloaddition with different cyclic imines. The reaction proved to be both regio- and diastereoselective. In all cases, only one reaction product was obtained. Detailed structural analyses of the new polyheterocycles as well as conformational studies including DFT modelling were performed. The relative stability of o-QMs/aza-o-QM were also calculated, and the regioselectivity of the reactions could be explained only when the cycloaddition started from aminodiol 4 . It was summarized that starting from diaminonaphthol 25 , the regioselectivity of the reaction is driven by the higher nucleophilicity of the amino group compared with the hydroxy group. 12H-benzo[a]xanthen-12-one ( 11 ), formed via o-QM formation, was isolated as a side product. The proton NMR spectrum of 11 proved to be very unique from NMR point of view. The reason for the extreme low-field position of proton H-1 could be accounted for by theoretical calculation of structure and spatial magnetic properties of the compound in combination of ring current effects of the aromatic moieties and steric compression within the heavily hindered H(1)-C(1)-C(12b)-C(12a)-C(12)=O structural fragment.     

Sheath formation study in Ne–Xe DBD discharge

The sheath is formed near the cathode immediately after applying the voltage across the electrodes. This formation is mainly due to the depopulation of this region by electrons. Using the one-dimensional model of the sheath region and the kinetic model coupled to the dielectric barrier discharge discharge electric circuit, we studied the formation of the cathode sheath and its evolution during the first pulse in Ne–Xe mixture for 10% and 20% of xenon at a total gas pressure of 400 Torr and for an applied voltage of 3 kV. The results illustrate the discharge behaviors as well as the evolution of the electric field and the charged particles in the cathode region. The effect of the xenon concentration is also studied and discussed.     

Radiative Emissions in Visible–IR of Krypton Excilamp: Experimental and Theoretical Interpretations

Plasma Chemistry and Plasma Processing - The paper presents an experimental and theoretical study of the radiative emission in the pure krypton lamp excited by dielectric barrier discharge....     

Numerical and theoretical calculation of breakdown voltage in the electrical discharge for rare gases

This work has been devoted to a numerical and analytical calculus of the voltage breakdown in electrical discharge for several rare gases such as argon, krypton, neon, xenon and helium. It was performed using a fluid model 2D, which is based on the numerical solution of the two Boltzmann equations (equation of continuity and momentum), coupled to Poisson's equation to measure the breakdown voltage according to the product of the electrode spacing and the pressure. This study allowed a better comprehension of the physical phenomena occurring in the discharges. We, thus, developed a calculation, based on the empirically Paschen's law, allowing the determination of the breakdown voltage, which describes the transition from insulating gas to the conductive state. Paschen's curves of the different gases are plotted and a comparison between numerical and experimental as well as analytical results is also presented and analyzed.