If a material that normally does not conduct electricity, is exposed to strong electric fields, it can develop complex patterns of conducting areas, through which it 'discharges' the field. A group at CWI studies both fundamental and applied aspects of such patterns, in particular in so-called streamer and barrier discharges. The results can be used for combustion gas cleaning, ultrafast power semiconductor switches or for flat computer screens. Streamer-like discharges in doped layered semiconductors can be used for ultrafast switching of high power electric circuits.
Stationary discharges are also possible, the best known example being the neon tube.
Since a discharge is a nonlinear process that easily can form patterns, the homogeneous and stationary glow of the neon tube is by no means trivial, and stays a continued challenge in the development of new energy saving and special purpose light sources, eg, at Philips. Figure 3 shows generic instabilities that can occur in such glow discharges. The enormous increase of electric conductivity in a discharge is due to the multiplication of free charge carriers by an approximately local ionization reaction. It persists as long as the local electric field is high enough. However, conducting matter can redistribute its space charges and hence modify the externally applied electric field.