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Spectroscopic investigations of transient processes in self-pulsing microdischarges

Fachliche Zuordnung Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Förderung Förderung von 2009 bis 2016
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 74729252
 
Erstellungsjahr 2016

Zusammenfassung der Projektergebnisse

The main achievements for the two investigated micro plasma devices are summarised in the following: Micro atmospheric pressure plasma jets. The spatial and temporal distributions and developments have been characterised for the μ-APPJ for a set of parameters and species as O, O3, He, ne and others. Further species could be accessed by models developed within in the research group. The COST jet has been developed providing a work-horse for the plasma community providing reliable power measurement. The α−γ mode transition, being characteristic for atmospheric discharges, has been investigated with the help of the self-pulsing jet modification. Investigations showed that in particular two parameters – flow and temperature – have significant influence on the behaviour of the discharge, but are on the other hand very often neglected in diagnostics as well as in simulation. 2-dimensional simulation combined with diagnostics showed to be indispensable for the understanding of these phenomena. The discharge transition into the constricted, very bright mode (γ or arcing mode) was characterised. Processes that are responsible for the instabilities igniting jet devices could be discriminated. Secondary electron emission and sheath variation for mode transitions as underlying mechanisms have been investigated in the wedge-shaped electrode gap of the self-pulsing jet. For future research, it would be interesting to investigate the influence of surface processes on the constricted discharge and especially on the sheath-breakdown dynamics at atmospheric pressure. This can be realised by changing the electrode material. The SP-μ-APPJ in combination with synchronised phase-resolved emission spectroscopy setup offers the opportunity to study the complete evolution of a γ-mode-like discharge by recording only one image while propagating. Micro cavity discharge arrays. In the first project phase, we concluded that self-pulsing of the plasma arrays as well as reignition after each voltage reversal are determined by long-living species as metastables and ions. The appearance of excitation waves propagating across the arrays with velocities of several km/s is attributed to transport of species and photon-induced secondary electron emission. This was revealed by a model developed project B1. To discriminate the transport properties, we investigated the characteristics of a single cavity by varying cavity geometry, dimension, and depth, gas composition, and pressure. After that, we investigated the interaction between cavities of different widths arranged in sub-arrays. Positive and negative half period of the AC excitation as well as successive cycles have been shown to correlate. The reignition is determined by longliving species surviving within the cavities. Due to wall interactions their lifetime is dependent on the dimension of the cavities. By this, the ratio between cavity dimension and distance determines the propagation of the excitation waves across the arrays. The investigation of metal based arrays with dielectric coating and planar counter-electrode may open a field of extremely robust devices. First experiments showed self-pulsing as well as wave-like emission features indicating a kind of an universal feature for these devices. The influence of the much lower resistivities – compared to silicon – on operation is an interesting feature to be investigated and compared in the future.

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