Abstract
Light emissions and Schlieren structures were simultaneously observed from streamers produced by tens of kilovolts 1.2/50 μs impulses, representing the high voltage component of lightning, applied across a 4 cm air gap between a variety of electrode geometries and a ground plane in an unconfined environment. The results demonstrated that the light emissions and Schlieren structures coincide along the same streamer filaments but on different timescales; the light existing only during the microsecond timeframe impulse whereas the Schlieren continued to develop into the millisecond timeframe, moving towards the centre of the air gap whilst diffusing into the surrounding air within 100 ms. If an electrical breakdown did occur, the Schlieren structures outside the arc remained visible. Streamer formation theory for high voltage impulses is subsequently refined to include the observed Schlieren mechanism.
Highlights
Light emissions and Schlieren structures were simultaneously observed from streamers produced by tens of kilovolts 1.2/50 μs impulses, representing the high voltage component of lightning, applied across a 4 cm air gap between a variety of electrode geometries and a ground plane in an unconfined environment
The light emissions observed by the first camera and Schlieren structures observed by the second camera were both seen at the same time as the high voltage field was applied
The light emissions were only observed during the first frame, i.e., they were present for less than 47.62 μs, whereas the Schlieren structures were observed from the first frame onwards
Summary
Light emissions and Schlieren structures were simultaneously observed from streamers produced by tens of kilovolts 1.2/50 μs impulses, representing the high voltage component of lightning, applied across a 4 cm air gap between a variety of electrode geometries and a ground plane in an unconfined environment. Flat or rounded edges, such as around a hemispherical electrode, create highly divergent fields resulting in broader structures The observation of both light emissions and Schlieren structure have traditionally been used to study streamers and other related p henomena[7,8,9], with recent examples including using optical cameras to image streamers in air[10,11,12] and Schlieren imaging to analyse streamer and leader structure[13,14,15,16]. A specialised optical setup using filters, knife edges, mirrors and/or lenses are typically required to capture the effect reliably on camera
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