Streamer discharges, their initiation and electric field*

Streamer discharges are present in many fields of science. They are basic components of atmospheric electricity and frequently utilized sources of non-equilibrium plasmas, both in fundamental research and applications. Three cases from the physics of streamer discharges are discussed in this presentation. In a free space, the quasi-stationary phase of the streamer development is a well understood phenomenon. Nevertheless the very first stages of the initiation of the streamer in pulse driven discharges lack an experimental understanding, mostly due to the diagnostical challenges connected with the high streamer velocity and its stochastic occurence. Here, we offer an approach for such detailed diagnostics. In a similar way, the complexity and high velocity of streamer discharges developing on dielectric surfaces is the reason for unanswered questions or lack of experimental data in the field. We offer experimentally based answers to two such questions: What amplitudes can the electric field strength reach during the streamer-surface interaction? What is the initiation mechanism of long plasma filaments in surface barrier discharges? We apply the time-correlated single-photon counting-based optical emission spectroscopy to surface and coplanar barrier discharges in atmospheric air to study such phenomena. We show experimentaly that the electric field amplitude reaches values of 400 kV/cm as the positive streamer propagates directly on the surface in a coplanar discharge arrangement. Furthermore, we reveal an ultra-fast development of a remotely initiated streamer cascade in the case of surface barrier discharge operated at high overvoltage. We show that this previously unknown mechanism leads to the generation of an intense cathode spot, which is a crucial condition for plasma transition to a highly-ionized state.