Investigation of instabilities and striation structures in single filament dielectric barrier discharges in argon at atmospheric pressure

• Applicant: Dr. Markus Becker
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407462159

• Final Report Year: 2023

Final Report Abstract

Dielectric barrier discharges (DBDs) operated under atmospheric pressure are commonly used to generate non-thermal plasmas for a wide area of applications. These include, for example, ozone generation, decontamination, the functionalisation of surfaces and plasma medicine. Atmospheric pressure DBDs operate in different modes depending on the gas composition used, the power supply and the discharge geometry. These modes are not only characterised by differences in the plasma parameters, such as the current and electron density, but also have an impact on their applicability and efficiency for practical plasma applications. Despite the widespread use of DBDs, the causal mechanisms that lead to the occurrence of the different discharge modes under the influence of the aforementioned operating parameters are not yet fully understood and are the subject of ongoing investigations. In this context, the subject of the project was the numerical analysis of instabilities and striated structures in DBDs at atmospheric pressure. For this purpose, a self-consistent hydrodynamic plasma model was developed for the time-dependent, spatial two-dimensional description of a single-filament DBD in argon at atmospheric pressure and used to investigate experimentally observed phenomena. In particular, it was investigated which physical processes are responsible for the formation of different discharge modes and the occurrence of a stratified discharge channel, i.e. the occurrence of localised emission maxima (striations). Furthermore, the influence of oxygen admixtures on the discharge behaviour was analysed. One result of the project is the new simulation programme FEDM, which was developed and used for the analysis of the single-filament DBD but can also be used for modelling other non-thermal plasmas. Here, FEDM stands for “Finite Element Discharge Modeling” and is based on the open-source platform FEniCS. The source code of the programme has been extensively documented and published as opensource for reuse. In addition to FEDM, the commercial software package COMSOL Multiphysics was used for the simulations and code verification. The results of the modelling and parameter studies show that the formation of the spatial structures along the discharge channel is triggered by repetitive ionisation waves, which disturb the spatial distribution of the electrons and modulate the electric field. The main contributions to electron production are the ionisation of metastable argon atoms and excimers. The number density and spatial distribution of the excited atoms and molecules thus directly determine the occurrence and position of the local maxima of electron production. Parameter studies based on a statistical design of experiments have shown that the formation of instabilities and striated structures along the discharge channel is favoured by smaller electrode gaps, thinner dielectrics and higher frequencies, and that the influence of the voltage amplitude is comparatively small. The addition of oxygen to the argon discharge reduces the formation of striations due to the additional loss rates for metastable argon atoms and excimers in collision processes with oxygen molecules.

Publications

• “Modeling of electrical discharges using fenics” 72nd Annual Gaseous Electronics Conference (GEC), College Station, Texas, USA, October 28–November 1, 2019
  Jovanović A. P.; Loffhagen D. & Becker M. M.
  
• “Verification and performance test of electric discharge modeling code developed in FEniCS”
  Jovanović A. P.; Loffhagen D. & Becker M. M.
  
• Automated Fluid Model Generation and Numerical Analysis of Dielectric Barrier Discharges Using Comsol. IEEE Transactions on Plasma Science, 49(11), 3710-3718.
  Jovanovic, Aleksandar P.; Stankov, Marjan N.; Loffhagen, Detlef & Becker, Markus M.
  
• “Plasma modelling using FEniCS and FEDM” Proceedings of FEniCS
  Jovanovic A. P.; Loffhagen D. & Becker M. M.
  
• Streamer–surface interaction in an atmospheric pressure dielectric barrier discharge in argon. Plasma Sources Science and Technology, 31(4), 04LT02.
  Jovanović, Aleksandar P.; Loffhagen, Detlef & Becker, Markus M.
  
• “Fluid-modelling analysis of striated structures in a single-filament dielectric barrier discharge in argon at atmospheric pressure” ESCAMPIG XXV, Paris, France, July 19–23, 2022
  Jovanović A. P.; Hoder T.; Loffhagen D. & Becker M. M.
  
• “Modelling of streamer inception in pulseddriven dielectric barrier discharges at atmospheric pressure” DPG Spring Meeting, Mainz, Germany, March 28–April 1, 2022
  Jovanović A. P.; Hoft H.; Loffhagen D. & Becker M. M.
  
• Formation mechanisms of striations in a filamentary dielectric barrier discharge in atmospheric-pressure argon. Plasma Sources Science and Technology, 32(5), 055011.
  Jovanović, Aleksandar P.; Hoder, Tomáš; Höft, Hans; Loffhagen, Detlef & Becker, Markus M.
  
• Introduction and verification of FEDM, an open-source FEniCS-based discharge modelling code. Plasma Sources Science and Technology, 32(4), 044003.
  Jovanović, Aleksandar P.; Loffhagen, Detlef & Becker, Markus M.
  
• Simulation of the statistical and formative time delay of Townsend‐mechanism‐governed breakdown in argon at low pressure. Contributions to Plasma Physics, 63(3-4).
  Jovanović, Aleksandar P.; Stankov, Marjan N.; Marković, Vidosav Lj. & Stamenković, Suzana N.