On the self-pulsating behavior of dc-driven streamer coronas

Impulsive coronas, driven by dc voltage, can be traced back to the classical works of Loeb and his school. Despite the dc voltage, the discharge is a superposition of a localized glow corona, characterized by electrical and visual stability, and impulsive discharges of a few hundred ns-duration that develop at high repetition rates (1-10 kHz in the positive polarity for point-to-plate geometry, cm-gaps, in atmospheric pressure air). The self-pulsating behavior has been generally attributed to space charge shielding by the ion cloud generated by a streamer burst and gradual field recovery driven by the ion drift motion. However, up until recently, direct confirmation of this effect was not feasible. In this contribution, we report on direct measurements of the electric field at several locations within the discharge, using the Electric Field-Induced Second Harmonic (E-FISH) technique, to quantitatively explore this phenomenon. Unexpectedly, the measurements do not show a monotonically increasing field during the inter-pulse period, but rather hint a propagating wave-like feature from the plate-cathode to the tip-anode. Future work will explore these observations from a theoretical perspective.