Review of recent results on streamer discharges and discussion of their relevance for sprites and lightning

It is by now well understood that large sprite discharges at the low air densities of the mesosphere are physically similar to small streamer discharges in air at standard temperature and pressure. This similarity is based on Townsend scaling with air density. First the theoretical basis of Townsend scaling and a list of six possible corrections to scaling are discussed; then the experimental evidence for the similarity between streamers and sprites is reviewed. We then discuss how far present sprite and streamer theory has been developed, and we show how streamer experiments can be interpreted as sprite simulations. We review those results of recent streamer research that are relevant for sprites and other forms of atmospheric electricity and discuss their implications for sprite understanding. These include the large range of streamer diameters and velocities and the overall 3D morphology with branching, interaction and reconnection, the dependence on voltage and polarity, the electron energies in the streamer head and the consecutive chemical efficiency and hard radiation. New theoretical and experimental results concern measurements of streamer spectra in air, the density dependence of streamer heating (hot leaders are unlikely at 80 km altitude and cold streamers are unlikely in liquids), and a discussion of the influence of magnetic fields on thermal electrons or on energetic electrons in streamers or sprites.Comment: 38 pages, 4 figures, article accepted for publication in J. Geophys. Res. - Space Physic

Three-dimensional numerical modelling of gas discharges at atmospheric pressure incorporating photoionization phenomena

International audienceA three-dimensional (3D) numerical model for the characterization of gas discharges in air at atmospheric pressure incorporating photoionisation through the solution of the Helmholtz equation is presented. Initially, comparisons with a two-dimensional (2D) axi-symmetric model are performed in order to assess the validity of the model. Subsequently several discharge instabilities (plasma spots and low pressure inhomogeneities) are considered in order to study their effect on streamer branching and off-axis propagation. Depending on the magnitude and position of the plasma spot, deformations and off-axis propagation of the main discharge channel were obtained. No tendency for branching in small (of the order of 0.1cm) overvolted discharge gaps was observed

Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

International audienceThis paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r. Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge

SIMULATION SUR ORDINATEUR DE LA FORMATION DE L'ARC TRANSITOIRE ENTRE UNE POINTE POSITIVE ET UN PLAN DANS L'AIR A PRESSION ATMOSPHERIQUE

Sous l'effet d'un front d'onde ionisant -très localisé- un filament conducteur est crée, joignant finalement les deux électrodes. Trois équations, tenant compte de l'attachement, sont proposées, décrivant l'évolution du filament. Après discussion sur la signification et la détermination des conditions aux limites, une résolution sur ordinateur permet la comparaison des courants calculés et de la distribution de lumière calculées avec l'expérience.Under the effect of a small ionizing wave front -the streamer- a conducting filament is created joining finaly both electrodes. Three equations, taking attachment into account, are proposed, describing the filament evolution. After a discussion on the meaning and the determination of the boundary conditions, a solution, given by a computer, allow a comparison between calculated currents and calculated light distribution with the experiment

TRANSITION PRÉIONISATION-ARC, ÉTUDIÉE A L'AIDE D'UNE CAMÉRA ULTRA-RAPIDE, DANS L'AIR A PRESSION ATMOSPHÉRIQUE, EN POINTE POSITIVE-PLAN AUX COURTES DISTANCES

A photographic study of the luminous evolution which takes place between the streamer and the spark is presented. A breakdown criterion is proposed. The events being periodic, the influence of the residual ionization left by the preceding event on the one following is studied.Une photographie présentant l'ensemble de l'évolution lumineuse entre la descente du dard (streamer) et l'arc est présentée. Un critère de claquage est dégagé. Les phénomènes étant, périodiques, l'influence de l'ionisation résiduelle laissée par un phénomène sur le suivant est étudiée