Precise optical registration of fine-structured electrical sparks and related challenges

Abstract

Fine-structured sparks naturally formed in electrical gas discharges are challenging objects of optical research. The veracity of the spark structure image obtained by laser probing techniques is still a subject for discussion due to possible distortions introduced by the employed optical setup. We thoroughly analyze this issue by simulating the spark image formation and evaluating the effect of the setup response function on the spark pattern quality. The latter turns out to dramatically suffer from the defocusing effect, whereas the spark fine structure is reliably resolved only by optics having a spatial resolution close to several micrometers.

Thin Luminous Tracks of Particles from Electrodes with a Small Radius of Curvature in Pulsed Nanosecond Discharges in Air and Argon

“…Microchannels in the plasma of pulsed discharges in atmospheric air in tip-plane gaps of a few millimeters long was also found in [14][15][16] for both voltage pulse polarities. Therewith, jets with a high concentration of ionized particles were detected near the electrodes in the case of spark breakdown.…”

“…It was confirmed, see [8], those bright spots appear first on the electrode with a small radius of curvature. It was established in [15,16] using multi-frame laser interferometry with a high temporal resolution that, in short gaps and high electric field on an electrode with a small radius of curvature, the breakdown is caused by the rapid (within 1 ns) explosive appearance of micron-sized cathode and anode spots. The spots were found to consist of highly ionized plasma with an electron number density ne ~ 10 19 -10 20 cm -3 , and spark channels of small diameter are formed from these spots.…”

“…The spots were found to consist of highly ionized plasma with an electron number density ne ~ 10 19 -10 20 cm -3 , and spark channels of small diameter are formed from these spots. However, the stages of formation of primary streamers and a diffuse discharge with ne ≤ 10 14 cm -3 were not studied and there was no information about the observation of particle tracks in [14][15][16]. No registration of runaway electrons or X-rays was reported, which contribute to the formation of diffuse discharges in atmospheric air and other gases, as well.…”

Thin Luminous Tracks of Particles Released from Electrodes with A Small Radius of Curvature in Pulsed Nanosecond Discharges in Air and Argon

“…Microchannels in the plasma of pulsed discharges in atmospheric air in point-plane gaps of a few millimeters long were also found in [14][15][16] for both voltage pulse polarities. Therewith, jets with a high concentration of ionized particles were detected near the electrodes in the case of spark breakdown.…”

“…It was confirmed (see, e.g., [8]) that those bright spots appear first on the electrode with a small radius of curvature. It was established in [15,16] using multi-frame laser interferometry with a high temporal resolution, that in short gaps and at high electric field strength near an electrode with a small radius of curvature, the breakdown is caused by the rapid (within 1 ns) explosive appearance of micron-sized cathode and anode spots. The spots were found to consist of highly ionized plasma with n e ~10 19 -10 20 cm −3 , and spark channels of small diameter are formed from these spots.…”