Role of the excited electronic states in the ionization of ambient air by a nanosecond discharge

This experimental and numerical study is focused on the formation of fully ionized plasmas in ambient air by nanosecond pulsed discharges, namely the thermal spark. The first contribution of this article is the experimental charaterization of the electron number density during the pulse. The increase of the electron number density from 1016 to 101 cm-3 was measured with sub-nanosecond resolution via three techniques based on optical emission spectroscopy (OES): Stark broadening of Hα, Stark broadening of N+/O+, and the continuum emission of electrons. The discharge diameter is measured with sub-nanosecond resolution using calibrated OES of the N+ and O+ lines. All measurements indicate a transition to a micrometric-size filament of fully ionized plasma in approximately 0.5 ns. The second main contribution of this work is the development of a 0D kinetic mechanism to explain this observation. The mechanism includes 100 reactions, 12 species, and 12 excited electronic states. Particular attention is paid to modeling of N2, N2 +, N, and O electronic state kinetics using the electronic states as additional pseudo-species. Our results show that including the electron-impact ionization of the excited electronic states of N and O, in addition to those of N2, is necessary to explain the experimental results, emphasizing the key role of excited state kinetics in the thermal spark formation.

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

Section: Comparison To Electrical Measurementsmentioning

confidence: 94%

“…Therefore, we define N as the heavy particle density, i.e. N = N ion + N neutral [26,86]. This assumption, initially proposed in [26,86], was also successfully employed in [116].…”

Section: Comparison To Electrical Measurementsmentioning

confidence: 99%

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

Minesi

Mariotto

Pannier

et al. 2023

Plasma Sources Sci. Technol.

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“…We demonstrated in Ref. [34,35] that this process has indeed a significant impact, but that the formation of a fully-ionized plasma by a single nanosecond discharge is rather due to the electronimpact ionization of electronically excited states of N and O. We therefore developed a model of ionization adapted for air discharges, including the ionization of N2, N, and O excited states.…”

Section: Kinetic Model Descriptionmentioning

confidence: 99%

“…For a field of up to 240 Td at ambient conditions, we demonstrated that the discharge ionization is essentially due to the ionization of the first six electronic states of N [34][35][36]. The 0-D plasma kinetics and the gas energy equation are solved using ZDPlasKin [44].…”

Section: Reacmentioning

confidence: 99%

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Ionization Mechanism in a Thermal Spark Discharge

Minesi

Mariotto

Stancu

et al. 2021

AIAA Scitech 2021 Forum

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The formation of thermal sparks generated by nanosecond pulses is studied experimentally and numerically. The increase of the electron number density, up to 10 19 cm -3 , is measured with sub-nanosecond resolution using Stark broadening of N + , Stark broadening of Hα, continuum emission of the electron, and the intensity of N + lines. Our experimental results are then compared to 0-D kinetic simulations including the electron-impact ionization of excited electronic states of N and O. The electron temperature, in equilibrium with the gas temperature, reaches 42,000K, which agrees with our experimental findings and the literature on the thermal spark.

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Effects of plasma kinetic modeling on performance characterization of plasma actuators for active flow control

et al. 2020

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This work focuses on the development of a multiscale computational fluid dynamics (CFD) simulation framework for the investigation of the effects of plasma kinetics on the performance of a microscale dielectric barrier discharge plasma actuator (DBD-PA). To this purpose, DBD-PA multi-scale dual-step modelling approach has been implemented, by considering plasma chemistry and flow dynamic. At first, a microscopic plasma model based on the air plasma kinetics has been defined and plasma reactions have been simulated in zero-dimensional computations in order to evaluate the charge density. At this aim computations have been performed using the toolbox ZDPlasKin, which solves plasma reactions by means of Bolsig+ solver. An alternate current (AC) electrical feeding has been assumed: in particular, the sinusoidal voltage amplitude and the frequency have been fixed at 5 kV and 1 kHz at atmospheric pressure and 300 K temperature in quiescent environment. The predictal charge density has been in a macroscopic plasma-fluid model based on Suzen Dual Potential Model (DPM), which has implemented in the computation fluid dynamic CFD code OpenFoam. Hence, as second step, 2D-CFD simulations of the electro-hydrodynamic body forces induced by the microscale DBDPA have been performed, based on the previously predicted charge densities at the operating conditions. Quiescent flow over a dielectric barrier discharge actuator has been simulated using the plasma-fluid model. The novel modelling framework has been validated with experimental data.

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Role of the excited electronic states in the ionization of ambient air by a nanosecond discharge

Cited by 5 publications

References 37 publications

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

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

Ionization Mechanism in a Thermal Spark Discharge

Effects of plasma kinetic modeling on performance characterization of plasma actuators for active flow control

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