The physics of streamer discharge phenomena

In this review we describe a transient type of gas discharge which is commonly called a streamer discharge, as well as a few related phenomena in pulsed discharges. Streamers are propagating ionization fronts with self-organized field enhancement at their tips that can appear in gases at (or close to) atmospheric pressure. They are the precursors of other discharges like sparks and lightning, but they also occur in for example corona reactors or plasma jets which are used for a variety of plasma chemical purposes. When enough space is available, streamers can also form at much lower pressures, like in the case of sprite discharges high up in the atmosphere. We explain the structure and basic underlying physics of streamer discharges, and how they scale with gas density. We discuss the chemistry and applications of streamers, and describe their two main stages in detail: inception and propagation. We also look at some other topics, like interaction with flow and heat, related pulsed discharges, and electron runaway and high energy radiation. Finally, we discuss streamer simulations and diagnostics in quite some detail. This review is written with two purposes in mind: First, we describe recent results on the physics of streamer discharges, with a focus on the work performed in our groups. We also describe recent developments in diagnostics and simulations of streamers. Second, we provide background information on the above-mentioned aspects of streamers. This review can therefore be used as a tutorial by researchers starting to work in the field of streamer physics.Comment: 89 pages, 29 figure

A model study of corona emission from hydrometeors

The maximum measured electric fields in thunderclouds are an order of magnitude less than the fields required for electric breakdown of the air. One explanation for lightning initiation in these low fields is that electric breakdown first occurs at the surfaces of raindrops where the ambient field is enhanced very locally due to the drop geometry. Laboratory experiments [Crabb & Latham, 1974] indicate that colliding raindrops which coalesce to form elongated water filaments can produce positive corona in ambient fields close to those measured in thunderclouds. We calculate the E-field distribution around a simulated coalesced drop pair and use a numerical model to study the positive corona mechanisms in detail. Our results give good agreement with the laboratory observations. At the altitudes (and thus low pressures) at which lightning initiation is observed, our results show that positive corona can occur at observed in-cloud E-fields.Comment: 13 pages, 9 figures, http://www.geophys.washington.edu/Surface/Atmospheric/ Submitted to: Quarterly Journal of the Royal Meteorological Societ

Streamers, sprites, leaders, lightning: from micro- to macroscales

"Streamers, sprites, leaders, lightning: from micro- to macroscales" was the theme of a workshop in October 2007 in Leiden, The Netherlands; it brought researchers from plasma physics, electrical engineering and industry, geophysics and space physics, computational science and nonlinear dynamics together around the common topic of generation, structure and products of streamer-like electric breakdown. The present cluster issue collects relevant articles within this area; most of them were presented during the workshop. We here briefly discuss the research questions and very shortly review the papers in the cluster issue, and we also refer to a few recent papers in other journals.Comment: Editorial introduction for the cluster issue on "Streamers, sprites and lightning" in J. Phys. D, 13 pages, 74 reference

Adaptive multiscale methods for 3D streamer discharges in air

We discuss spatially and temporally adaptive implicit-explicit (IMEX) methods for parallel simulations of three-dimensional fluid streamer discharges in atmospheric air. We examine strategies for advancing the fluid equations and elliptic transport equations (e.g. Poisson) with different time steps, synchronizing them on a global physical time scale which is taken to be proportional to the dielectric relaxation time. The use of a longer time step for the electric field leads to numerical errors that can be diagnosed, and we quantify the conditions where this simplification is valid. Likewise, using a three-term Helmholtz model for radiative transport, the same error diagnostics show that the radiative transport equations do not need to be resolved on time scales finer than the dielectric relaxation time. Elliptic equations are bottlenecks for most streamer simulation codes, and the results presented here potentially provide computational savings. Finally, a computational example of 3D branching streamers in a needle-plane geometry that uses up to 700 million grid cells is presented.Comment: 17 pages, 5 figure

The inception of pulsed discharges in air: simulations in background fields above and below breakdown

We investigate discharge inception in air, in uniform background electric fields above and below the breakdown threshold. We perform 3D particle simulations that include a natural level of background ionization in the form of positive and O$_{2}^-$ ions. When the electric field rises above the breakdown and the detachment threshold, which are similar in air, electrons can detach from O$_{2}^-$ and start ionization avalanches. These avalanches together create one large discharge, in contrast to the `double-headed' streamers found in many fluid simulations. On the other hand, in background fields below breakdown, something must enhance the field sufficiently for a streamer to form. We use a strongly ionized seed of electrons and positive ions for this, with which we observe the growth of positive streamers. Negative streamers were not observed. Below breakdown, the inclusion of electron detachment does not change the results much, and we observe similar discharge development as in fluid simulations

X-Rays from long laboratory sparks in air

This collective book provides a review of research concentrated on runaway electron beams and X-rays in an inhomogeneous electric field with different gases at increased pressure. Attention is also given to supershort avalanche electron beam (SAEB) in the optimal conditions. New experimental techniques and equipment, including those with picosecond time resolutions, were required for diagnostics of electrical and optical signals. The book consists of twenty-four chapters, some of which were written jointly by researchers of different teams. Some chapters consider the range of SAEB applications.Postprint (published version

Technological Aspects: High Voltage

This paper covers the theory and technological aspects of high-voltage design for ion sources. Electric field strengths are critical to understanding high-voltage breakdown. The equations governing electric fields and the techniques to solve them are discussed. The fundamental physics of high-voltage breakdown and electrical discharges are outlined. Different types of electrical discharges are catalogued and their behaviour in environments ranging from air to vacuum are detailed. The importance of surfaces is discussed. The principles of designing electrodes and insulators are introduced. The use of high-voltage platforms and their relation to system design are discussed. The use of commercially available high-voltage technology such as connectors, feedthroughs and cables are considered. Different power supply technologies and their procurement are briefly outlined. High-voltage safety, electric shocks and system design rules are covered.Comment: 39 pages, contribution to the CAS-CERN Accelerator School: Ion Sources, Senec, Slovakia, 29 May - 8 June 2012, edited by R. Bailey, CERN-2013-00

Arc tracking control in insulation systems for aeronautic applications: challenges, opportunities, and research needs

Next generation aircrafts will use more electrical power to reduce weight, fuel consumption, system complexity and greenhouse gas emissions. However, new failure modes and challenges arise related to the required voltage increase and consequent rise of electrical stress on wiring insulation materials, thus increasing the risk of electrical arc appearance. This work performs a critical and comprehensive review concerning arc tracking effects in wiring insulation systems, underlying mechanisms, role of materials and possible mitigation strategies, with a special focus on aircraft applications. To this end an evaluation of the scientific and technological state of the art is carried out from the analysis of theses, research articles, technical reports, international standards and white papers. This review paper also reports the limitations of existing insulation materials, standard test methods and mitigation approaches, while identifying the research needs to comply with the future demands of the aircraft industryPeer ReviewedPostprint (published version

Influence of corona charging in cellular polyethlene film

[En] Cellular polymers have recently attracted attention for their property of exhibiting a piezoelectric constant when they are electrically charged. The electrostatic charge generated in the voids by the internal discharges creates and internal macrodipole which is responsible for the piezoelectric effect. Charging by corona discharge is the most used method for cellular polymers. Many works has been published on polypropylene and polyethylene films mainly focused on the required expansion process or on the results obtained for raw cellular materials electrically activated. Our work is based on commercial polyethylene cellular films which have been physically characterized and electrically activated. The effect of thermal treatment, physical uniaxial or biaxial stretching and corona charging was investigated. The new method of corona charging improved the piezoelectric constant under other activation conditions.This work has been developed under the project Intelligent Materials with Mechanical and Electrical Properties interaction (E-MAT)" which has been submitted for funding with reference number IMDEEA/2011/13 to the call of Technological Centers of IMPIVA Network 2011, Strategic development program (action 1, R+D projects) financed by the Generalitat Valenciana through the Instituto de la Mediana y Pequena Empresa Valenciana (IMPIVA) and the European Regional Development Fund (ERDF).Ortega Braña, GE.; Llovera Segovia, P.; Magraner Bella, F.; Quijano Lopez, A. (2011). Influence of corona charging in cellular polyethlene film. Journal of Physics: Conference Series. 301:1-4. doi:10.1088/1742-6596/301/1/012054S14301Fukada, E. (2000). History and recent progress in piezoelectric polymers. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 47(6), 1277-1290. doi:10.1109/58.883516Sessler, G. M., & Hillenbrand, J. (1999). Electromechanical response of cellular electret films. Applied Physics Letters, 75(21), 3405-3407. doi:10.1063/1.125308Hillenbrand, J., & Sessler, G. M. (2000). Piezoelectricity in cellular electret films. IEEE Transactions on Dielectrics and Electrical Insulation, 7(4), 537-542. doi:10.1109/94.868074Paajanen, M., Välimäki, H., & Lekkala, J. (2000). Modelling the electromechanical film (EMFi). Journal of Electrostatics, 48(3-4), 193-204. doi:10.1016/s0304-3886(99)00065-0Gerhard-Multhaupt, R. (2002). Less can be more. Holes in polymers lead to a new paradigm of piezoelectric materials for electret transducers. IEEE Transactions on Dielectrics and Electrical Insulation, 9(5), 850-859. doi:10.1109/tdei.2002.1038668Wegener, M., & Bauer, S. (2005). Microstorms in Cellular Polymers: A Route to Soft Piezoelectric Transducer Materials with Engineered Macroscopic Dipoles. ChemPhysChem, 6(6), 1014-1025. doi:10.1002/cphc.200400517Hillenbrand, J., Behrendt, N., Mohmeyer, N., Altsadt, V., Schmidt, H.-W., & Sessler, G. M. (s. f.). Charge retention in biaxially-oriented polypropylene films containing various additives. 2005 12th International Symposium on Electrets. doi:10.1109/ise.2005.1612375Xiaoqing Zhang, Sessler, G. M., & Hillenbrand, J. (s. f.). Optimization of Piezoelectric Properties of Cellular Polypropylene Films by Repeated Expansion. 2005 12th International Symposium on Electrets. doi:10.1109/ise.2005.161231

The emission of energetic electrons from the complex streamer corona adjacent to leader stepping

We here propose a model to capture the complexity of the streamer corona adjacent to leader stepping and relate it to the production of energetic electrons serving as a source of X-rays and $\gamma$-rays, manifesting in terrestrial gamma-ray flashes (TGFs). During its stepping, the leader tip is accompanied by a corona consisting of multitudinous streamers perturbing the air in its vicinity and leaving residual charge behind. We explore the relative importance of air perturbations and preionization on the production of energetic run-away electrons by 2.5D cylindrical Monte Carlo particle simulations of streamers in ambient fields of 16 kV cm$^{-1}$ and 50 kV cm$^{-1}$ at ground pressure. We explore preionization levels between $10^{10}$ m$^{-3}$ and $10^{13}$ m$^{-3}$, channel widths between 0.5 and 1.5 times the original streamer widths and air perturbation levels between 0\% and 50\% of ambient air. We observe that streamers in preionized and perturbed air accelerate more efficiently than in non-ionized and uniform air with air perturbation dominating the streamer acceleration. We find that in unperturbed air preionization levels of $10^{11}$ m$^{-3}$ are sufficient to explain run-away electron rates measured in conjunction with terrestrial gamma-ray flashes. In perturbed air, the production rate of runaway electrons varies from $10^{10}$ s$^{-1}$ to $10^{17}$ s$^{-1}$ with maximum electron energies from some hundreds of eV up to some hundreds of keV in fields above and below the breakdown strength. In the presented simulations the number of runaway electrons matches with the number of energetic electrons measured in alignment with the observations of terrestrial gamma-ray flashes. Conclusively, the complexity of the streamer zone ahead of leader tips allows explaining the emission of energetic electrons and photons from streamer discharges.Comment: 29 pages, 11 figures, 2 table