Simulation of transient energy distributions in sub-ns streamer formation

Breakdown and streamer formation is simulated in atmospheric pressure nitrogen for a 2D planar electrode system. A PIC code with multigrid potential solver is used to simulate the evolution of the non-equilibrium ionization front on sub-nanosecond timescales. The ion and electron energy distributions are computed, accounting for the inclusion of inelastic scattering of electrons, and collisionally excited metastable production and ionization. Of particular interest is the increased production of metastable and low-energy ions and electrons when the applied field is reversed during the progress of the ionization front, giving insight into the improved species yields in nanosecond pulsed systems

A Monte Carlo simulation of ion transport at finite temperatures

We have developed a Monte Carlo simulation for ion transport in hot background gases, which is an alternative way of solving the corresponding Boltzmann equation that determines the distribution function of ions. We consider the limit of low ion densities when the distribution function of the background gas remains unchanged due to collision with ions. A special attention has been paid to properly treat the thermal motion of the host gas particles and their influence on ions, which is very important at low electric fields, when the mean ion energy is comparable to the thermal energy of the host gas. We found the conditional probability distribution of gas velocities that correspond to an ion of specific velocity which collides with a gas particle. Also, we have derived exact analytical formulas for piecewise calculation of the collision frequency integrals. We address the cases when the background gas is monocomponent and when it is a mixture of different gases. The developed techniques described here are required for Monte Carlo simulations of ion transport and for hybrid models of non-equilibrium plasmas. The range of energies where it is necessary to apply the technique has been defined. The results we obtained are in excellent agreement with the existing ones obtained by complementary methods. Having verified our algorithm, we were able to produce calculations for Ar$^+$ ions in Ar and propose them as a new benchmark for thermal effects. The developed method is widely applicable for solving the Boltzmann equation that appears in many different contexts in physics.Comment: 14 page

On the coupling of electron energy distribution function and excited state distributions in pulsed microwave H

Time evolution of vibrationally and electronically excited states and their coupling with the electron energy distribution function (EEDF) were calculated for microwave pulsed discharges. Different situations have been considered by changing the period and the duty cycle, and considering different pressure values.The main result of this study was to evidence the change in the non-equilibrium character and dynamics of the different distributions depending on the pressure and the pulse period. In particular EEDF strongly deviating from the Maxwell behaviour appear as a consequence of inelastic and superelastic collisions at relatively high pressure and long period. Also, strong oscillation appears on the tail of the H2 vibrational distribution at high pressure discharge conditions. At low pressure, the effect of superelastic and inelastic collisions appears to be less significant and most of the plasma characteristics may be deduced from a time averaged electron energy distribution function

Investigation of Hydrogen Peroxide Formation After Underwater Plasma Discharge

International audienceThis paper reports investigations on the formation of hydrogen peroxide resulting from micro-pulse plasma discharges obtained in pin-to-pin configuration underwater. In particular, this study reports the influence of the discharge regime (cathode regime with and without breakdown, and anode regime) as well as that of the discharge energy (from 10 to 45 mJ per pulse). It has been shown that the H 2 O 2 production is higher for high energy and anode regime. In addition, the variation of the pulse width (from 50 to 500 µs) highlights the dependence of the chemical processes induced by the discharge according to the regime. Considering two different electrode materials (tungsten and platinum), we do not observe any significant influence of the electrode material on the H 2 O 2 production, whereas the injected energy depends on the high voltage electrode material. Finally, the erosion of the electrodes have been studied using in-situ optical microscopy and SEM. It is shown that the erosion mechanisms strongly depend on materials, regimes and the polarity of the electrodes

Analysis of discharge regimes obtained by microsecond underwater electrical breakdown in regard to energy balance

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Time-resolved diagnostics of a pin-to-pin pulsed discharge in water: pre-breakdown and breakdown analysis

International audienceThis paper presents an experimental study of an underwater pulsed plasma discharge in a pin-to-pin electrode configuration. Time resolved refractive index-based techniques and electrical measurements have been performed in order to study the pre-breakdown and breakdown phenomena in water (σ  =  100 µS cm−1). A single high voltage pulse with amplitude of a dozen of kV, rise time of 20 ns and duration of [0.1–1] ms is applied between two 100 µm diameter platinum tips separated by 2 mm. This novel experimental work reports that different cases of electrical discharge in water occurs for a unique set of experimental conditions such as (i) bush-like channels from the cathode that do not span the electrode gap, (ii) bush-like channels from the cathode leading to breakdown and (iii) filamentary structures from the anode leading to a stronger breakdown. Two breakdown mechanisms, anode and cathode regimes, have been clearly identified and related to the two principal schools of thoughts to explain discharge propagation in liquid.Cet article présente une étude expérimentale d'une décharge de plasma pulsé dans l'eau dans une configuration d'électrode de broche à broche. Des techniques basées sur l'indice de réfraction à résolution temporelle et des mesures électriques ont été réalisées afin d'étudier les phénomènes de pré-claquage et de claquage dans l'eau. Une seule impulsion haute tension d'une douzaine de kV et d'une durée de [0,1-1] ms est appliquée entre deux pointes de platine de 100 μm de diamètre séparées de 2 mm. Ce nouveau travail expérimental rapporte que différents cas de décharges électriques dans l'eau se produisent pour un ensemble unique de conditions expérimentales telles que (i) des canaux en forme de buisson de la cathode qui ne couvrent pas l'espace entre les électrodes, (ii) des canaux en forme de buissons cathode conduisant à la dégradation et (iii) des structures filamentaires de l'anode conduisant à une rupture plus forte. Deux mécanismes de décomposition, les régimes d'anode et de cathode, ont été clairement identifiés et reliés aux deux principales écoles de pensée pour expliquer la propagation de décharge dans un liquide

n-hexane soot oxidation reactivity in N

This paper discusses some aspects of n-hexane soot reactivity in a multi-pin to plate pulsed corona discharge working in the nanosecond regime at atmospheric pressure. The soot-discharge interaction was quantified by measuring the densities of CO, CO2, O3 and NO2 out-coming from the discharge cell. Results showed that CO2 is the major product of soot oxidation. They also showed a strong enhancement of soot oxidation for O2 percentage greater than 10% and cathode temperatures above 425 K. The soot reactivity is significantly enhanced when the discharge frequency is increased. The results obtained were interpreted in term of the competition between the kinetics of plasma active species adsorption and oxidation product desorption

Cr(VI) Reduction by Microsecond Pin-to-Pin Discharges Generated in an Aqueous Solution

International audienceThe total reduction of Cr(VI) by microsecond pin-to-pin electric discharge generated in aqueous solution has been reported. [Cr(VI)] and [H 2 O 2 ] were measured simultaneously by UV-vis absorption spectroscopy during the process. The kinetics of the Cr(VI) reduction resulting from the discharges is found to be pseudo zero order rate. The influence of the electron properties has been studied by varying the applied voltage and the electrode gap showing a better reduction for a higher electric field. In addition pH and conductivity of the solution have been measured before and after the process. The analysis of the chemical kinetics has been completed by varying the pulse duration of the discharge. The results show that the reduction occurs both during the plasma and the post plasma phases. It is also noted that the increase of the pulse duration involves a better Cr(VI) reduction, a higher [H 2 O 2 ] production and a more important change in conductivity