Elucidation of excitation mechanisms which lead to homogeneous and filamentary modes of a dielectric barrier driven plasma-jet

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In recent years dielectric barrier discharges were applied both for Ambient Air Ionisation and for soft ionization of organic molecules. Most of the applied discharges differ in the homogeneous and filamentary operation mode. In the case of the operation in a homogeneous mode the ionization efficiency is 1000 times higher than in the case of the filamentary one. Therefore, in this research project the excitation mechanisms, which lead to different operation modes, should be elucidated in order to increase the effectivity of the ionisation.In the first step, the influence of the air, which is around the plasma-jet, will be investigated by a comparison with He as surrounding gas both in the homogeneous and the filamentary mode with the help of a spatially resolved measurement. After the ignition of a plasma the divergence of the gas-flow which leaves the capillary will be changed. When the Divergence is also changed when the operation mode is changed from homogeneous to filamentary this might be an explanation for the decrease of the Ionisation efficiency.It can be expected that in an homogeneous He plasma the majority of ions consists of N2+ ions whereas in a filamentary plasma also or even more He2+ as well as He+ ions will be present. In a He plasma the existence of He2+ as well as He+ is hard or even not possible to detect by optical spectroscopy and by mass spectrometry it cannot be measured spatially dependent. Therefore, with the help of a model system consisting of Ar and low concentrations of ammonia and Fluor the assumption will be inspected.Furthermore, with the help of time-resolved measurements it will be investigated if the plasma-jet, as often stated, is really an afterglow or if both plasmas, the electrode plasma and the plasma-jet can be seen as two coupled plasmas. This will be investigated for different polarisations and in dependence on the applied voltage.