EXPERIMENTAL STUDY OF AN ULTRA-FAST ATMOSPHERIC PRESSURE AIR DISCHARGE IN A PIN-TO-PLATE GEOMETRY
Résumé
In this work, a pin-to-plate reactor operating in air at ambient temperature and pressure is investigated. Driven with a high-voltage (HV) ns pulse generator with sub-ns rise time excitation up to 50 kV, the discharge is ignited within a gap ranging from 0.5 to 25 mm. Although pin-to-plate discharges have been widely studied over the last century, the system offers the advantage to ignite the discharge in the over-voltage regime allowing for minimizing gas heating (at least in the single shot regime) and the production of highly energetic electrons due to the intense electric field (EF). As already shown, the discharge expends in very large and homogeneous volume (up to 20 mm diameter) within the gap. This is of high interest for atmospheric pressure volume treatment concerning either degradation of pollutants, assisted combustion ignition or activation of materials1.
Various diagnostics have been applied to study this ultra-fast discharge, including ICCD imaging, EOS, time resolved spectroscopy, Schlieren and electric field measurement. With this contribution, we will report on excited species time evolution in positive and negative polarity arrangements, in correlation with electric field time evolution, measured with an electro optic sensor based on the Pockels effect2, and ICCD imaging that allows to follow the discharge development. We will emphasize on the effect of discharge frequency (from single shot to 10Hz) which affect the initial conditions of the discharge development in the inter-electrode gap. There are strong modifications in the air canal where the plasma occurs, especially at the highest frequencies that can lead to kinetics changes due to local gas pressure changes. These results are of significant interest for the comparison with numerical simulations which at the present time generally do not includes fluid mechanics. Furthermore, values of strength EF will help to validate a better description of the ionization mechanisms taking place in the over-voltage regime.
1. Tardiveau P. et al. Sub-nanosecond time resolved light emission study for diffuse discharges in air under steep high voltage pulses. PSST 25, 054005 (2016).
2. Gaborit, G. et al. Single Shot and Vectorial Characterization of Intense Electric Field in Various Environments with Pigtailed Electrooptic Probe. IEEE Trans. Plasma Sci. 42, 1265–1273 (2014).