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。大部分的外加放电都有均匀和连续的工作模式。在均质模式下操作的情况下，电离效率比在非均质模式下高1000倍。因此，在本研究项目中，激发机制，导致不同的操作模式，应阐明，以提高电离的有效性。在第一步中，空气的影响，这是周围的等离子体射流，将通过比较与他作为周围的气体都在均匀的和辅助的空间分辨测量的帮助下模式进行调查。等离子体点燃后，离开毛细管的气流的发散将被改变。 当操作模式从均质变为非均质时，发散度也发生变化，这可能是电离效率降低的原因。可以预期，在均质He等离子体中，大多数离子由N2+离子组成，而在非均质等离子体中，也会出现甚至更多的He 2+和He+离子。在He等离子体中，He 2+以及He+的存在很难或甚至不可能通过光谱法检测，并且通过质谱法不能测量空间依赖性。因此，在由Ar和低浓度的氨和Fluor组成的模型系统的帮助下，将检查该假设。此外，在时间分辨测量的帮助下，将研究等离子体射流是否真的如通常所说的那样是余辉，或者两个等离子体，电极等离子体和等离子体射流是否可以被看作两个耦合的等离子体。这将被调查为不同的极化和依赖于所施加的电压。

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.