The modelling was performed for the DBD in an asymmetric arrangement with a 1.5 mm gap, electrode radius of 2 mm and 0.5 mm thick dielectric (alumina, relative permittivity 9) covering grounded electrode, driven by sinusoidal voltage (voltage amplitude of 1.3 kV and frequency of 60 kHz, corresponding to a period of T = 16.67 microseconds).
\n" }, "medium": { "name": "Ar", "properties": "Pure argon, gas pressure is 760 Torr, constant gas temperature of 300 K
\n" }, "target": [], "diagnostics": { "name": "fluid-Poisson model, plasma chemical model", "properties": "Model: Fluid-Poisson model in cylindrical geometry;
\nComputational software: COMSOL Multiphysics\u00ae v. 5.6 (www.comsol.com, COMSOL AB, Stockholm, Sweden);
\nNumerical method: Finite element method;
\nElement type: Linear Lagrange elements for particle balance equations, quadratic Lagrange elements for Poisson equation, linear discontinuous Lagrange elements for the surface charge density balance equation;
\nTime-stepping: Backward differentiation formula (BDF), with automatically adapted time-step size and the BDF order (in the range from 1 to 2);
\nSolver: Fully coupled constant Newton solver, with the direct linear solver (PARDISO);
\nTolerance: in range from 0.0001 to 0.001 (varied to prevent small time-stepping during the discharge in negative half-period);
\nMesh: Manual remeshing was done to reduce calculation time, where the continuation of the calculations from the last calculated time step was performed after each remeshing. The mesh had in average 500 000 elements and about 3 million degrees of freedom (noting that coarser mesh was used during the off-phase).
An atmospheric-pressure DBD in argon is investigated by means of time-dependent and spatially two-dimensional fluid-Poisson modelling in an axisymmetric geometry. The object of interest was formation of the striations along the discharge channel. The model comprises a set of balance equations for the particle number densities of electrons and the most important argon species (atomic Ar+ and molecular Ar2+ ions, as well as the lumped excited atomic Ar\u2217 and molecular Ar2\u2217 states of argon), Poisson\u2019s equation for the electric potential and field, the electron energy balance equation and a balance equation for the surface charge density. The quasi-neutral initial conditions and physically-based boundary conditions, accounting for thermal flux and partial reflection of the particles, are used. The additional term describing the ion-induced emission of secondary electrons is included into the boundary conditions for the balance equations for the particle number density and energy density of electrons. The analysis of the spatiotemporal evolution of the particle species, electric field, mean electron energy and rates of electron production after reaching the quasi-periodic state was performed to determine the origin of the striations. The voltage and electric current, as well as the number densities, electric field and electron production rates were exported using LiveLink\u2122 for MATLAB\u00ae (https://www.comsol.com/livelink-for-matlab) and post-processed using python3 (https://www.python.org) and Matplotlib (https://matplotlib.org).
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