Spectroscopic investigations of transient processes in self-pulsing microdischarges

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For application of microplasmas at atmospheric pressure long-term stability of the devices is a prerequisite. Thus, operation in the stable homogeneous glow mode is often favored. Understanding of transient processes such as the transition from glow to the constricted arcing operation (GAT) is crucial for stable operation of microplasmas. Non-linearities in the plasma dynamic processes on several significantly different time scales may lead to a periodical appearance of similar transitions between operation modes. The microplasma arrays investigated here show self-pulsing on a micro-second timescale whereas the microscaled atmospheric pressure plasma jet pulses on a millisecond scale. As different as the timescales are the interpretations for the origins of this pulsing. Local thermal instabilities may contribute as much as the local accumulation of metastables or charge carriers at dielectric surfaces. Combined with space and phase resolved optical emission spectroscopy and multi-photon laser diagnostics, the periodicity allows to access otherwise self-destructing operation modes with high temporal resolution and sensitivity. Diagnostics will be synchronized to the self-pulsing frequency allowing the investigation of the stable operation modes, the transitions in between and the underlying instabilities.