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The paper presents experiments on the spatial and temporal structure of the breakdown process of microdischarges (MD). For the first time simultaneous streak and iCCD images of individual filaments in a pulsed driven dielectric barrier discharge (DBD) with 1 mm gap in a gas mixture of 0.1 vol% O2 in N2 at atmospheric pressure are recorded. Furthermore current and voltage measurements with fast probes give access to the electrical discharge characteristics such as transferred charge and power. For asymmetric pulses there is a significant difference in the spatial structure as well as in the temporal behaviour of the MDs between the rising and the falling slopes of the high voltage pulse. If the time between rising and falling slopes is reversed all effects reverse as well. For symmetric pulses there are no significant differences between the MD at rising and falling slopes which is in accordance with a sinusoidal DBD operation.

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Barrier discharges at atmospheric pressure in nitrogen-oxygen mixture powered by high voltage pulses of widths between 10 μs and 200 ns were investigated. The development of the microdischarges on rising and falling slopes was recorded by streak and intensified CCD cameras simultaneously. The breakdown on the falling slope strongly depends on the pulse width. As a result of pulse width variation the starting point of ignition changes and positive and negative streamers occur simultaneously in the falling slope. The observed effect is caused by the electric field rearrangement in the gap due to the different positive ion densities related to their gap crossing times.

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