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

近年来，介质阻挡放电被应用于环境空气电离和有机分子的软电离。大多数施加的放电在均匀和丝状操作模式下不同。在均匀模式下操作的情况下，电离效率比丝状模式下的电离效率高1000倍。因此，在本研究项目中，为了提高电离的有效性，需要阐明导致不同工作模式的激发机制。在第一步中，将借助空间分辨测量，通过在均匀模式和丝状模式下与作为环境气体的He进行比较来研究等离子体射流周围空气的影响。等离子体点火后，离开毛细管的气流的发散度会发生变化。当操作模式从均匀改变为丝状时，发散也改变，这可能是电离效率降低的原因。可以预期，在均匀的He等离子体中，大多数离子由N_2+离子组成，而在丝状等离子体中，也会出现甚至更多的He2+和He+离子。在He等离子体中，He2+和He+的存在很难或甚至不可能用光学光谱和质谱学来检测，它不能在空间上进行测量。因此，借助于由Ar和低浓度氨和氟组成的模型系统，将检验这一假设。此外，将借助时间分辨测量来研究等离子体-射流是否真的像通常所说的那样是余辉，或者如果两个等离子体、电极等离子体和等离子体-射流可以被视为两个耦合等离子体。这将被研究不同的极化和依赖于施加的电压。

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.