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

Scientific coordinators: Ute Ebert, Centre for Mathematics and Computer Science (CWI) Amsterdam, and Department of Applied Physics, Eindhoven Univ. Techn., The Netherlands, Davis D. Sentman, University of Alaska Fairbanks, Geophysical Institute, USA.

Description and aim of the workshop:

Rapid filamentary electrical breakdown is a generic and ubiquitous process in nature and technology; its earliest stage is governed by streamers. They occur in lightning related phenomena in the atmosphere (also on other planets), they are developed for and used in various technical and industrial applications, and they are studied as a fundamental phenomenon in air, pure nitrogen, argon etc., and occur equally in water, oil, semiconductors and other materials. Streamers play a pivotal role by initiating leader or arc discharges; they are the most non-thermal process in this sequence. While these breakdown processes are well known, they are intrinsically hard to measure and to understand, as they are very fast, very far from equilibrium and they evolve on multiple scales: from electrons impacting on single molecules up to macroscopic channel formation in space, and from avalanches to streamers to leaders to arcs or afterglow in time.

In recent years, research methods have made progress in various disciplines: in plasma diagnostics and plasma modeling, in observations and modeling of atmospheric electricity, in electric pulsed power technology, and in multi-scale computing and nonlinear dynamics. The commonality and complexity of the breakdown problem is an incentive to cross disciplinary borders between plasma physics, electro-engineering, industrial applications and geophysics, nonlinear dynamics and computational science. In fact, the frequency of cross-referencing among these disciplines in published research papers has increased considerably in recent years.

The workshop will create a forum for direct knowledge transfer among the various disciplines, and also for further development of methods and concepts within each discipline. It will focus on the following topics relevant for laboratory, industrial and atmospheric discharges: Microscopic mechanisms in different gases, experimental identification and model implementation: photo-ionization, background ionization, attachment, inelastic collisions etc. Scaling with gas density as a key to the similarity of streamers at normal pressure and sprite discharges at high altitudes of the atmosphere. Macroscopic spatial structures: Observation and prediction of single streamers, branching or extinction, and interactions. Experimental methods for discharge observations in the laboratory and atmosphere, analysis and computations of the multi-scale nature of the discharge. Electron energy distribution and consecutive chemistry inside the discharge, its technological use, its impact on atmospheric composition, its spectroscopic signatures, and its potential for X-ray emission. X-ray observations in lightning and the laboratory. Electric properties of the discharge: VLF (very low frequency) electromagnetic emissions in the atmosphere, coupling to pulsed power circuits, measurements of inner electric fields, modeling of charge distribution and transport and electromagnetic radiation. Related processes on earlier or later time scales: discharge initiation, secondary streamers, transition to leaders, glows or arcs, and afterglow effects. Heat and convection.

Location, facilities and organization:

The workshop will take place at the Lorentz Center which is a facility for scientific workshops at the old University of Leiden, The Netherlands. The beautiful historical city of Leiden is 7 km from the sea and can be reached from Amsterdam airport within 15 minutes by train. The Lorentz Center is located on the science campus of the university; it offers not only lecture and discussion rooms, but also 20 offices with computer and library access for participants, for more info see http://www.lorentzcenter.nl/. The formal part of the workshop will consist of two blocks of lectures, about 3 hours in the morning (9:30-12:30) and about 2 hours in the late afternoon (16:00-18:00).