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P: Fachverband Plasmaphysik
P 22: Niedertemperaturplasmen II
P 22.6: Fachvortrag
Friday, March 1, 2013, 11:15–11:40, HS 2
Spatio-temporally resolved N2(A3Σu+) metastables densities in nitrogen barrier discharges — •Sebastian Nemschokmichal and Jürgen Meichsner — Institute of Physics, University of Greifswald
Atmospheric pressure barrier discharges can operate in two discharge modes, the filamentary and the diffuse discharge mode. The transition between these modes depends, e.g., on the feeding gas, the dielectrics, and the discharge voltage. In a barrier discharge in pure nitrogen, driven by a sinusoidal applied voltage, the diffuse mode develops. Adding only 500 ppm oxygen, a transition to the filamentary mode can be observed due to the strong quenching of the N2(A3Σu+) metastables by oxygen molecules. Hence, the metastable molecules are essential for the diffuse mode development, either because of Penning-ionization in the volume or exoemission of electrons at the (charged) dielectrics. To clarify their specific role in these processes, the density of the nitrogen A3Σu+,v=0 metastables was measured by laser induced fluorescence spectroscopy in a discharge gap of 1 mm at a pressure of 500 mbar. The densities are in the order of magnitude of 1013 cm−3. The time resolved measurement after one single microdischarge shows a delay of the metastables population with respect to the microdischarge pulse. In the diffuse mode, the axial density profiles show a maximum shifted to the respective anode. This corresponds to the larger electron density at the anode typical for the Townsend-like discharge mode. Nevertheless, the metastables density does not increase exponentially toward the anode as the electron density.