We investigate the physics and applications of fast, transient discharges and the inception stages of gas discharges. The primary example of such a discharge for us is a streamer discharge, a fast-moving ionization wave through a gas. They occur in nature with lightning and sprites but also have many technological applications.

Controlling nanosecond-scale discharges

Our primary scientific topics are fast, transient discharges and the inception stages of gas discharges. Such discharges are always very far from equilibrium which makes them challenging to understand. This interest has started with one example of such discharges, namely streamer discharges, but in recent years has expanded to a larger range of extreme non-equilibrium discharges.

Still, streamer discharges our scientific focal point. Streamer discharges are the first stages of discharges like sparks and arcs. They can pierce through regions with relatively low electric field and have tree-like shapes. In nature they occur as the first stage of lightning and as so-called sprites and other discharges high above thunderclouds.

We are not limited to one application of streamers and related non-equilibrium discharges. The diversity of applications of such discharges makes this field of science interesting and ensures future-proof funding possibilities, both from fundamental scientific viewpoint as from the utilization viewpoint.

Streamer-like electric discharges form the initial stage of electric breakdown in long gaps; they are ubiquitous in nature and technology. They appear in St. Elmo's fire and recently discovered sprite discharges above lightning clouds and determine the early stages of sparks and lightning.

They are used in corona reactors for dust precipitation, ozone generation, disinfection of water and air, odour removal and various other applications. They also play a role in the (re)ignition of high pressure gas discharge lamps. The action of streamers on a gas or other substrate is three-fold:

• They carry electric current and create a path for further electric breakdown; on their course, they deposit charge in the system that, e.g., can be used for electrostatic precipitation of nanoparticles.
• They generate high energetic electrons in a thin space charge region; these electrons very efficiently catalyze gas-chemical reactions and even lead to X-ray emission.
• They cause convection in the gas through which they are moving, the so-called corona wind.

This project aims to a coordinated experimental and theoretical study of the initial phases of electrical breakdown in gases. The goal is to obtain a thorough physical understanding of the process that will enable us to optimize various technological applications. The methods include detailed theoretical and computational models developed at CWI Amsterdam, time resolved measurements of streamer width, velocity and branching under carefully determined physical conditions in a wide parameter range at the physics department of TUE. Experiments are performed at the physics department with power supplies operative in the 2 to 60 kV range.