arXiv subjects

D. Loffhagen

Publications and source records attributed to D. Loffhagen.

4 recordsLinked to original sources

arXiv2022

Automated Fluid Model Generation and Numerical Analysis of Dielectric Barrier Discharges Using Comsol

MCPlas is introduced as a powerful tool for automated fluid model generation with application to the analysis of dielectric barrier discharges operating in different regimes. MCPlas consists of a number of MATLAB\textsuperscript{\textregistered} scripts and uses the COMSOL Multiphysics\textsuperscript{\textregistered} module LiveLink\textsuperscript{\texttrademark} for MATLAB\textsuperscript{\textregistered} to build up equation-based COMSOL Multiphysics\textsuperscript{\textregistered} models from scratch. The present contribution highlights how MCPlas is used to implement time-dependent models for non-thermal plasmas in spatially one-dimensional and axisymmetric two-dimensional geometries and stresses out the benefit of automation of the modelling procedure. The modelling codes generated by MCPlas are used to study diffuse and filamentary dielectric barrier discharges in argon at sub-atmospheric and atmospheric pressure, respectively. The seamless transition between different levels of model complexity with respect to the considered model geometry is demonstrated. The presented investigation of a single-filament dielectric barrier discharge interacting with a dielectric surface shows that complex phenomena of high technological relevance can be tackled by using plasma models implemented in COMSOL Multiphysics\textsuperscript{\textregistered} via MCPlas.

physics.plasm-ph↗

arXiv2018

Extending \textit{ab initio} plasma-surface simulations to experimentally relevant scales

The physical processes at the interface of a low-temperature plasma and a solid are extremely complex. They involve a huge number of elementary processes in the plasma, in the solid as well as charge, momentum and energy transfer across the interface. In the majority of plasma simulations these surface processes are either neglected or treated via phenomenological parameters. However, those parameters are known only in some cases, so such an approach is very inaccurate and does not have predictive capability. Therefore, improvements are highly needed. In this paper we briefly summarize relevant theoretical methods from solid state and surface physics that are able to contribute to an improved simulation of plasma-surface interaction in the near future. Full \textit{ab initio} quantum simulations are feasible only for extremely short times and/or small system sizes. A substantial simplification is achieved when electronic quantum effects are not treated explicitly. Then one arrives at semi-classical molecular dynamics (MD) simulations for the heavy particles that have become the main workhorse in surface science simulations. Using microscopically founded potentials and force fields as an input, these MD simulations approach the quality of \textit{ab initio} simulations, in many cases. However, despite their simplified nature, these simulations require a time step that is of the order or below one femtosecond making it prohibitive to reach experimentally relevant scales of minutes. To bridge this gap in length and time scales without compromising the first principles character of the simulations, many physical and computational strategies have been put forward in surface science. This paper presents a brief overview on different methods and their underlying physical ideas, and we compare their strengths and weaknesses.

physics.plasm-ph↗

arXiv2017

Electron transport parameters in CO$_2$: scanning drift tube measurements and kinetic computations

This work presents transport coefficients of electrons (bulk drift velocity, longitudinal diffusion coefficient, and effective ionization frequency) in CO2 measured under time-of-flight conditions over a wide range of the reduced electric field, 15Td <= E/N <= 2660Td in a scanning drift tube apparatus. The data obtained in the experiments are also applied to determine the effective steady-state Townsend ionization coefficient. These parameters are compared to the results of previous experimental studies, as well as to results of various kinetic computations: solutions of the electron Boltzmann equation under different approximations (multiterm and density gradient expansions) and Monte Carlo simulations. The experimental data extend the range of E/N compared with previous measurements and are consistent with most of the transport parameters obtained in these earlier studies. The computational results point out the range of applicability of the respective approaches to determine the different measured transport properties of electrons in CO2. They demonstrate as well the need for further improvement of the electron collision cross section data for CO2 taking into account the present experimental data.

physics.plasm-ph↗

arXiv2008

Particles as probes for complex plasmas in front of biased surfaces

An interesting aspect in the research of complex (dusty) plasmas is the experimental study of the interaction of micro-particles with the surrounding plasma for diagnostic purposes. Local electric fields can be determined from the behaviour of particles in the plasma, e.g. particles may serve as electrostatic probes. Since in many cases of applications in plasma technology it is of great interest to describe the electric field conditions in front of floating or biased surfaces, the confinement and behaviour of test particles is studied in front of floating walls inserted into a plasma as well as in front of additionally biased surfaces. For the latter case, the behaviour of particles in front of an adaptive electrode, which allows for an efficient confinement and manipulation of the grains, has been experimentally studied in dependence on the discharge parameters and on different bias conditions of the electrode. The effect of the partially biased surface (dc, rf) on the charged micro-particles has been investigated by particle falling experiments. In addition to the experiments we also investigate the particle behaviour numerically by molecular dynamics, in combination with a fluid and particle-in-cell description of the plasma.

physics.plasm-ph↗