Jetting axial flow induced by nanosecond repetitively pulsed discharges in quiescent ambient air

Abstract

This study investigates the phenomenon of jetting axial flow induced by nanosecond repetitively pulsed discharges (NRPD) in quiescent ambient air in a pin-to-pin electrode configuration. Axial stratification of discharge parameters (electron number density, temperature, specific energy, etc.) influences the hydrodynamic effects leading to directed gas flow from the cathode towards the anode. The experimental results presented in this paper were obtained using schlieren imaging, optical emission spectroscopy, and electrical measurements of the deposited energy. A jetting axial flow was induced for all considered gap distances (0.5 - 5 mm) and pulse repetition frequencies of ≧ 10 kHz. The direction of the induced flow is defined by the polarity of the applied high-voltage pulses. It was found that the flow does not arise immediately after the initiation of the first pulse of the applied burst but is induced after a certain number of pulses. Using temporally and spatially resolved optical emission spectroscopy the electron densities and temperatures were measured in the vicinity of the cathode and anode before and after the generation of the axial flow. A model explaining the generation and maintenance of the axial flow in NRPD and the role of the inhomogeneities of plasma parameters along the plasma channel on hydrodynamic effects is suggested and discussed.

Kinetic mechanism and sub-ns measurements of the thermal spark in air

“…N = N ion + N neutral [26,86]. This assumption, initially proposed in [26,86], was also successfully employed in [116].…”

“…However, some experimental results demonstrated that the filaments formation (step 2 and 3) were synchronized within 0.5 ns[47,116]. As underlined by[36,47,116], the electrode curvature and surface quality plays a role in the filament formation.…”

“…However, some experimental results demonstrated that the filaments formation (step 2 and 3) were synchronized within 0.5 ns[47,116]. As underlined by[36,47,116], the electrode curvature and surface quality plays a role in the filament formation. The presence of a strong ionic current near one of the electrodes could foster beneficial conditions, such as surface topology or temperature, that could lead to earlier filament formation.…”