The spontaneous filamentation of a dielectric barrier glow discharge plasma (Townsend, not streamer breakdown), i.e., an instability of the homogeneous state has been simulated and understood with the help of a self-consistent two-dimensional fluid model of the discharge. The formation of self-organized or solitary filaments observed experimentally and described in previous papers can be explained in terms of electron and ion transport coefficients only, without including gas heating, plasma chemistry or surface effects. The conditions favoring the plasma filamentation are discussed.

We report on a new type of interaction between solitary current density spots observed in an ac-driven gas discharge system. These spots behave as independent particles as long as they are far apart from each other. Upon collision, in most cases one of the spots is extinguished. However, we also observe the formation of stable bound pairs of spots that move rather fast. We argue that both the rapid motion and the binding itself are due to a pronounced symmetry breaking with respect to size and breakdown phase of the individual spots. Basic features of pairs of spots traveling due to a true two-spot mechanism are discussed.

A summary is given for the work that has been done on pattern formation in planar ac-and dc-gas-discharge systems with high ohmic and dielectric barrier respectively at the Institute of Applied Physics at the University of Muenster. WeIl defined stationary and moving solitary filaments are observed that may be referred to as selforganized quasiparticles. Among others, filaments can be scattered, generated, or annihilated, and the formation of filament clusters ("molecules") is observed. For appropriate parameters filaments in the "gaseous" phase are observed, and the condensation of large assemblies to "crystalline" phase and "liquid" phase is recorded, too. Filaments may generate superstructures e.g. domain patterns. The experimental work demonstrates that a filament is a generic pattern. In addition, reference is made to non-filamentary patterns. Finally, a list of references referring to models and numerical treatment is presented.The evolution of self -organized patterns in gas-discharge systems is well known since the middle of the 18th century. It is amazing to observe that so far little attention has been payed to a systematic investigation of these patterns from the point of view of modern Nonlinear Dynamics and Pattern Formation. T o fill this gap at the Institute of Applied Physics at the University of Muenster extensive experimental, theoretical and numerical investigations have been carried out for lateral acand dc-gas-dicharge systems. In this paper we mainly concentrate on the experimental results thereby emphazising spatially welllocalized large amplitude patterns that behave like quasiparticles as it turns out. A detailed discussion of the experimental results in terms of recent qualitative and quantitative models and reference to other work that is related to the work carried out at the Institute of Applied Physics will be done elsewhere.Due to the spatial extension, because of the dissipation of electric energy and as result of the intrinsic nonlinearities of transport processes gas discharge systems may generate self-organized transient patterns and attractors. As electronic systems they can easily be driven far away from thermodynamic equilibrium. Also the formation of spatial patterns is supported by the absence of a reference system in the discharge gap in contrast e.g. to the rigid ion lattice in solid state devices. These properties make gas-discharge systems exceptional for studying self-organized patterns.