Introduction and verification of FEDM, an open-source FEniCS-based discharge modelling code

This paper introduces the FEDM (Finite Element Discharge Modelling) 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\textsuperscript{\textregistered} 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.Comment: 17 pages, 12 figures, revision submitted to Plasma Sources Science and Technolog

Modeling of Atmospheric-Pressure Dielectric Barrier Discharges in Argon with Small Admixtures of Tetramethylsilane

A time-dependent, spatially one-dimensional fluid-Poisson model is applied to analyze the impact of small amounts of tetramethylsilane (TMS) as precursor on the discharge characteristics of an atmospheric-pressure dielectric barrier discharge (DBD) in argon. Based on an established reaction kinetics for argon, it includes a plasma chemistry for TMS, which is validated by measurements of the ignition voltage at the frequency f=86.2kHz for TMS amounts of up to 200 ppm. Details of both a reduced Ar-TMS reaction kinetics scheme and an extended plasma-chemistry model involving about 60 species and 580 reactions related to TMS are given. It is found that good agreement between measured and calculated data can be obtained, when assuming that 25% of the reactions of TMS with excited argon atoms with a rate coefficient of 3.0×10−16m3/s lead to the production of electrons due to Penning ionization. Modeling results for an applied voltage Ua,0=4kV show that TMS is depleted during the residence time of the plasma in the DBD, where the percentage consumption of TMS decreases with increasing TMS fraction because only a finite number of excited argon species is available to dissociate and/or ionize the precursor via energy transfer. Main species resulting from that TMS depletion are presented and discussed. In particular, the analysis clearly indicates that trimethylsilyl cations can be considered to be mainly responsible for the film formation

Plasma parameters of microarcs towards minuscule discharge gap

This paper describes the behaviour of the plasma parameters of microarcs generated between a cooled copper anode and a ceriated tungsten cathode by means of a one-dimensional unified non-equilibrium model for gap lengths between 15 and 200 μm and current densities from 2 × 105 up to 106 A/m2. The results obtained show that the decrease of the gap length to a few tens of micrometres for a given current density results in a progressive shrinking of the quasi-neutral bulk in the microplasma and its complete disappearance. The decrease of the gap length further leads to an increase of the discharge voltage and the electron temperature and to slightly less heating of the gas. © 2020 The Authors. Contributions to Plasma Physics Published by Wiley-VCH Verlag GmbH & Co. KGa

Formation mechanisms of striations in a filamentary dielectric barrier discharge in atmospheric pressure argon

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.Comment: 18 pages, 15 figures, resubmitted to Plasma Sources Science and Technolog

Schlussbericht des BMBF-Verbundprojekts PT-Grid - Plasma-Technologie-Grid : Berichtszeitraum: 01.05.2009 - 30.04.2012

[no abstract available

Investigation of a pulsed xenon discharge at medium pressure

The pulsed discharge in xenon at pressures between 10 and 50 Torr and a peak current of 130 mA has been analysed by means of a time-dependent, spatially one-dimensional fluid model. Main features of the model of the radially inhomogeneous discharge plasma in a discharge tube with an inner diameter of 6.5 mm are given. The comparison of results of model calculations with experimental data shows good agreement for the axial electric field, and the qualitative behaviour of measured axis densities of low-lying excited states is reproduced well by the model. The analysis of the spatiotemporal variation of the pulsed discharge shows the formation of a constricted column plasma at increasing pressure. In particular, a pronouncedly nonlocal behaviour of the electron component is found, and the densities of the metastable and resonance atoms are predicted to have a radial profile with a maximum out of the axis during the discharge phase

Does the energy transfer from Ar(1s) atoms to N2 lead to dissociation?

Dielectric-barrier discharges (DBDs) in Ar–N2 mixtures, with N2 fractions in 0.1–1% range, would be attractive alternatives to DBDs in pure N2 if energy-transfer reactions between Ar(1s) atoms and N2 molecules were an efficient source of N atoms. Attempts to functionalize polyolefins in flowing postdischarges fed by such DBDs, as well as the search for the First Positive System in the emission spectrum, however, failed. Evidently, the energy-transfer reactions do not produce N atoms. For Ar(1s3) and Ar(1s5) metastable states, this fact has already been reported in the literature. For Ar(1s2) and Ar(1s4) resonant states, a quantitative argument is derived in this paper: energy transfer from Ar(1s) atoms to N2 molecules is not an efficient source of N atoms

On a non-thermal atmospheric pressure plasma jet used for the deposition of silicon-organic films

This work represents a concise overview on the results achieved by the authors over the last years on the plasma of a non-thermal reactive plasma jet at atmospheric pressure and of related thin film formation by plasma enhanced chemical vapour deposition (PECVD). The source was developed considering the application of the plasma self-organization for PECVD. The experimental methods comprise spectroscopic measurements of plasma parameters in the active zone, temperature measurements in the active zone and the effluent as well as the analysis of deposited films at the substrate surface. The theoretical investigations are devoted to a single filament in the active zone using a phase-resolved model and to an overall description of the jet including the substrate using a period-averaged model

Electron attachment to oxygen in nitrogen buffer gas at atmospheric pressure

We have carried out experimental and theoretical studies of three body electron attachment (TBEA) to O2 in N2/O2 mixtures. We have applied three different experimental methods to determine the apparent rate constant k for TBEA to O2 for reduced electric fields E / n from 0.5 Td up to 4.5 Td and O2 concentrations from 0.02% up to 3%. From the apparent rate constant k we have evaluated three body rate constant for electron attachment to O2 in pure O2 (kO₂) and in pure N2 (kN₂). The comparison of present data with former studies shows that the former values of kN₂ overestimated the efficiency of this reaction, while in case of kO₂ we have found agreement with earlier studies. We have solved numerically the Boltzmann equation of the electrons and calculated the values of k, kN₂ and kO₂ using well established cross sections. Using the known collision cross section set for TBEA to O2, very good agreement between calculated and measured results for kO₂ was found, while in the case of k and kN₂ we had to introduce a scaling function, which describes the decrease of the efficiency of TBEA to O2 in presence of N2 and the dependence of the scaling function on E/n was determined

Grundlegende Charakterisierung und Modellierung der VUV-Ausbeute von Xenon-Entladungen : Schlussbericht zum Teilvorhaben

[no abstract available