Electric fracture: growth and branching of ionized channels (CTF.6501)

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: 1) 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. 2) 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. 3) They might convect the gas through which they are moving.

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, and the development of a large scale pulsed power corona system at the electrical engineering department of TUE. The electrical engineering department also supports the experiments at the physics department with power supplies operative in the 10 to 60 kV range while experiments in the MV range are carried out in the electrical engineering lab. Two major applications are under investigation: bad odour removal from exhaust gases and tar removal from biogas.