Browsing by Author "Jovanović, Aleksandar P."

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    Formation mechanisms of striations in a filamentary dielectric barrier discharge in atmospheric-pressure argon
    (Bristol : IOP Publ., 2023) Jovanović, Aleksandar P.; Hoder, Tomáš; Höft, Hans; Loffhagen, Detlef; Becker, Markus M.
    Formation mechanisms of striations along the discharge channel of a single-filament dielectric barrier discharge (DBD) in argon at atmospheric pressure are investigated by means of a time-dependent, spatially two-dimensional fluid-Poisson model. The model is applied to a one-sided DBD arrangement with a 1.5 mm gap using a sinusoidal high voltage at the powered metal electrode. The discharge conditions are chosen to mimic experimental conditions for which striations have been observed. It is found that the striations form in both half-periods during the transient glow phase, which follows the streamer breakdown phase. The modelling results show that the distinct striated structures feature local spatial maxima and minima in charged and excited particle densities, which are more pronounced during the positive polarity. Their formation is explained by a repetitive stepwise ionisation of metastable argon atoms and ionisation of excimers, causing a disturbance of the spatial distribution of charge carriers along the discharge channel. The results emphasise the importance of excited states and stepwise ionisation processes on the formation of repetitive ionisation waves, eventually leading to striations along the discharge channel.
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    Introduction and verification of FEDM, an open-source FEniCS-based discharge modelling code
    (Bristol : IOP Publ., 2023) Jovanović, Aleksandar P.; Loffhagen, Detlef; Becker, Markus M.
    This paper introduces the finite element discharge modelling (FEDM) code, which was developed using the open-source computing platform FEniCS (https://fenicsproject.org). Building on FEniCS, the FEDM code utilises the finite element method to solve partial differential equations. It extends FEniCS with features that allow the automated implementation and numerical solution of fully coupled fluid-Poisson models including an arbitrary number of particle balance equations. The code is verified using the method of exact solutions and benchmarking. The physically based examples of a time-of-flight experiment, a positive streamer discharge in atmospheric-pressure air and a low-pressure glow discharge in argon are used as rigorous test cases for the developed modelling code and to illustrate its capabilities. The performance of the code is compared to the commercial software package COMSOL Multiphysics® and a comparable parallel speed-up is obtained. It is shown that the iterative solver implemented by FEDM performs particularly well on high-performance compute clusters.
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    Simulation of the statistical and formative time delay of Townsend-mechanism-governed breakdown in argon at low pressure
    (Weinheim : Wiley-VCH, 2023) Jovanović, Aleksandar P.; Stankov, Marjan N.; Marković, Vidosav Lj.; Stamenković, Suzana N.
    Understanding the breakdown process is important both from fundamental and practical perspectives. One of the most important quantities that characterize the breakdown is the breakdown time delay. In this article, numerical models for self-consistent simulation of the statistical and formative time delay of the electric breakdown in argon at low pressure have been proposed. The first model, based on the Monte Carlo simulation of the electron avalanche development, is used to simulate the statistical time delay. The model is designed for low-pressure breakdowns when the Townsend mechanism is dominant. The electric breakdown is then governed by ion-induced secondary electron emission from the cathode. In that case, the statistical time delay to breakdown is determined by tracking the waiting time of emission of the primary electron that initiates the electron avalanche and the number of ions produced in it. On the other hand, the formative time delay is determined by simulating the electric current waveform (Formula presented.) using the fluid model. To test whether the proposed models can be used for discharges operating under various conditions, the voltage dependence is simulated for both the statistical and the formative time delay. The results of the simulations show good agreement with the experimental results and theoretical models.
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    Streamer-surface interaction in an atmospheric pressure dielectric barrier discharge in argon
    (Bristol : IOP Publ., 2022) Jovanović, Aleksandar P.; Loffhagen, Detlef; Becker, Markus M.
    An atmospheric-pressure dielectric barrier discharge (DBD) in argon is investigated using a time-dependent and spatially two-dimensional fluid-Poisson model in axisymmetric geometry. The focus is on the streamer-surface interaction and the cathode-layer formation during the first discharge event in the single-filament DBD driven by sinusoidal voltage. A characteristic structure consisting of a volume streamer propagating just above the dielectric and simultaneous development of an additional surface discharge near the cathode is observed. The analysis of the electric field, electron production and loss rates, and surface charge density distribution shows that the radial deflection of the volume streamer is driven by free electrons remaining in the volume from the Townsend pre-phase and guided by the radial component of the electric field. The surface discharge occurring between the deflected volume streamer, which acts as virtual anode, and the dielectric surface is governed by ion-induced secondary electron emission and the surface charges accumulated on the dielectric.