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P: Fachverband Plasmaphysik

P 16: Plasma Diagnostics III

P 16.1: Hauptvortrag

Mittwoch, 15. März 2017, 08:30–09:00, HS 1010

Influence of released surface electrons on the pre-ionization of helium barrier discharges — •Robert Tschiersch, Sebastian Nemschokmichal, and Jürgen Meichsner — Institute of Physics, University of Greifswald, Felix-Hausdorff-Str. 6, 17489 Greifswald

The understanding of the interaction between the plasma species and a dielectric surface is still a fundamental issue in the physics of barrier discharges (BDs). The presented contribution highlights the role of residual surface electrons with low binding energy in acting as a seed-electron reservoir that favors the pre-ionization of diffuse BDs. Here, a glow-like BD was operated in helium at a pressure of 500 mbar in between two plane electrodes each covered with float glass at a distance of 3 mm. The change in the discharge development due to photodesorption of surface electrons by a Nd-YAG laser was studied by electrical measurements and optical emission spectroscopy. Moreover, adapting a 1D numerical fluid simulation of the discharge to the laser-photodesorption effect from the experiment allowed the understanding of the impact of released surface electrons on the reaction kinetics in the volume. When the laser beam hits the cathodic dielectric charged with residual electrons during the discharge pre-phase, the breakdown voltage decreases significantly. According to the adapted simulation, the laser releases only a small amount of surface electrons in the order of 10 pC which, nevertheless, supports significantly the pre-ionization. Moreover, both experiment and simulation emphasize that a further enhancement of the yield of released surface electrons triggers the transition from the glow mode to the Townsend mode.