Numerical simulations of non-thermal electrical discharges in air

Kapitel i bok, 2024

Electrical gas discharges belong to the class of low-temperature plasmas. Depending on particular conditions, they can be equilibrium (thermal) or non-equilibrium (non-thermal) meaning that temperatures/energies of constituting particles (electrons, ions, neutral atoms/molecules) are either nearly equal or different, respectively. Examples of the former are electric arcs, sparks, microwave discharges, where such effects like Joule heating of the gas and its thermal ionization are significant. In contrast, non-thermal discharge plasmas are characterized by presence of highly energetic electrons in "cold" neutral gas and ionic component with temperature close (or slightly higher) to that of gas. Typical examples of these are electron avalanches, glow discharges, streamers, electrical coronas, where the degree of ionization of the gas is much less than unity, the electron density rarely exceeds ~10^14 cm-3 and their mean energy is normally below ~10 eV.
This chapter deals with basic principles of numerical simulations of non-thermal electrical discharges in air, which are predecessors and indispensable attributes of a leader discharge. First, processes in such discharges and a theoretical background of so-called fluid model are considered. Further, numerical approaches utilized for computer implementation of the model are presented. Finally, examples are given including computer simulations of coronas as well as positive and negative streamers.