Modélisation électrique de la cellule par une méthode volumes finis

International audienceLa modélisation électrique de la cellule, et en particulier l'obtention de la tension transmembranaire, est un problème important en bio-électromagnétisme (électroporation). Dans ce cadre, une modélisation électro-quasi statique est utilisée pour décrire le problème sous forme d'équation de Poisson. Dans cet article, nous proposons une méthode basée sur les volumes finis pour résoudre numériquement le problème. Elle permet de prendre en compte les discontinuités de façon rigoureuse sur des maillages très déformés. La méthode est testée numériquement sur un modèle 2D d'une cellule circulaire (membrane et cytoplasme) soumise à un champ uniforme, puis à un champ électrique pulsé

The use of commercial thyristors in repetitive high voltage switching devices for plasma sources

This paper presents a commercial high voltage thyristor used as a switch allowing a tank capacitor to discharge in a load. In classical high power pulse technology applications the output voltage pulse has to be characterized mainly by its crest value, its rise-time, the period the thyristor is held in the on-state and the fall-time. These parameters are studied as a function of the power circuit and of the trigger circuit. The thyristor presents two behaviours: the main current is either higher or lower than the latching current. The “low current” behaviour is extensively investigated as it allows repetitive operation of the device. Two pulse power applications triggering electrical discharges are presented. Each one necessitates a specific pulsed power supply using series thyristor stacks or Marx structures. The first pulsed source delivers negative pulses with a crest voltage $V_{oM}=-35$ kV, a turn on capability of $T_{r}=90$ ns and a repetition rate F = 900 Hz. The second is built using Marx structure and is characterized by $V_{oM}=60$ kV, $T_{r}=250$ ns, F = 900 Hz

Numerical simulation of transitions between back discharge regimes

ACLInternational audienceThis paper presents numerical simulations of transitions between back discharge regimes. Back discharge refers to any discharge initiated at or near a dielectric layer covering a passive electrode. In this work, a pinhole in a dielectric layer on a plane anode serves as a model for back discharge activity. We have studied transitions between back discharge regimes by varying the surface charge density on the dielectric layer and the electric field in front of the pinhole. From the variation of these two independent parameters, the back discharge regimes have been depicted as a mode diagram inspired by the experimental study of Masuda and Mizuno. The resulting diagram includes the different discharge regimes that are commonly observed in experiments. The propagation of a positive ionizing wave inside the pinhole toward its edge, and the resulting formation of a plasma zone at its exit constitute the onset stage of back discharge. From this stage, the transitions to volume discharge or surface discharge can occur. The volume discharge regime consists of the propagation of a discharge in space toward the cathode which can be superimposed with the propagation of a discharge above the dielectric layer surface. The diagram reveals the conditions for transitions between back discharge regimes. © 2014 EDP Sciences

Numerical Simulation of Back Discharge: Influence of Pinhole Geometry on the Regime Transitions

International audienceThis paper presents numerical simulation of back discharge activity that is modelled at a pinhole in a dielectric layer on plane anode. First, for a given pinhole geometry, the transitions between back discharge regimes have been depicted as a mode diagram. Then, we have studied the influence of the dielectric layer thickness on the regime transitions. We have shown that increase in the layer thickness (within range of 0.02\textendash0.2 mm) promotes the back discharge development. Finally, we have studied the influence of `crater configuration'. We have shown that `crater shape' favours the back discharge ignition, whereas limits the resulting discharge development

Voltage gain optimization of transmission line transformers

Transmission Line Transformers (TLT) based on the use of ferrite beads are presented. This work aims at optimising the performance of the voltage gain and the compactness of the TLT according to the position, the type and the number of ferrites used. The ferrites have been selected taking into account two main parameters: the maximum currents flowing through the outer conductor of the lines of a TLT without ferrite beads and the current frequencies. The function of these ferrites is to decrease the effect of parasitic short-circuit transmission lines between the outer conductors of the coaxial cables of the TLT. Voltages and secondary currents are measured on each cable. The voltage gain achieved reaches the optimum theoretical value thanks to the use of ferrites for a 2, 4 and 10-stage transmission line transformer. Each cable is shorter than 1.5 meter in length which provides an unquestionable advantage of compactness

Electrical breakdown studies of pressurised nitrogen in non uniform fields

The aim of the present work is to provide data to understand better and quantify the dielectric strength of pure compressed N2 (1 < P < 8 bar). The lack of agreement of results found in the literature leads us to study the electrical and physical characteristics of this gas as a function of a wide set of parameters. Experiments are mainly performed in point to plane nitrogen gaps up to 40 mm length using three different rod radii. Gas conditioning phenomenon in positive polarity and corresponding change in characteristics of discharge mechanism are demonstrated here. In our experimental conditions, no leader is involved in the discharge development whatever the polarity is. The values of the breakdown reduced field $E_{\rm b}/P$ are determined as a function of the pressure. Two different experiments are performed in order to take into account the mechanisms of initiatory electron production: the influence of the γ-ray irradiated N2 and that of the surface roughness of the HV electrode. In negative polarity, the free electrons are provided from the cathode whereas they are provided from the gas under positive polarity. Voltage waveform influences on the U50 breakdown voltage are dealt with in a large pressure range (1 < P < 12 bar). The role of the non-uniformity of the applied electric field on the U50 value is pointed out in both polarities. Finally, the reduced guiding field of negative streamer is experimentally measured

Electric field development in positive and negative streamers on dielectric surface

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Excitation of dielectric barrier discharge using sinusoidal and nanosecond waveform: application to silicon solar cell

International audienceDifferent diffuse dielectric barrier discharges (DBDs) are studied in the same configuration for different applied voltage waveforms: Glow, Townsend-like and radiofrequency (RF) DBD's for a sinusoidal excitation ranging from 50 kHz to 9 MHz and the nano-second repetitive pulsed DBD (NRP-DBD). The power of the RF and the NRP-DBD is 10 to 30 times larger than that of the low frequency DBD's but according to emission spectroscopy the electron energy and thus the energy transfer to the gas are quite different. The consequence on the chemical kinetic is illustrated by the difference in the conditions leading to a SiN:H having the same refractive index