9. 4. 2014. Семинар: Саша Дујко


У среду, 9. априла 2014. године у 12 часова у сали "Звонко Марић" одржаће семинар

др Саша Дујко
Институт за физику у Београду

High-order fluid model for streamer discharges


Streamers are growing filaments of weakly-ionized non-stationary plasma produced by an ionization front that moves through non-ionized matter. They represent the first mode of electric breakdown of non-ionized matter exposed to strong electric fields. Streamers occur in the initial stages of lightning, in sprite discharges above thunderclouds and in industrial applications such as lighting and gas cleaning.

This presentation focuses on the derivation of a high-order fluid model for streamer all other low temperature plasmas. Using momentum transfer theory, the fluid equations are obtained as velocity moments of the Boltzmann equation; they are closed in the local mean energy approximation and coupled to the Poisson equation for the space charge generated electric field. The high-order tensor in the energy flux equation is approximated by the product of two lower order moments to close the system. The average collision frequencies for momentum and energy transfer in elastic and inelastic collisions for electrons in molecular nitrogen and rare gases are calculated from a multi-term Boltzmann equation solution. I will discuss, in particular, (1) the correct implementation of transport data in streamer models; (2) the accuracy of the two-term approximation for solving Boltzmann’s equation in the context of streamer studies; and (3) the evaluation of the mean-energy-dependent collision rates for electrons required as an input in the high-order fluid model.

Using fluid models of different orders, I will discuss the propagation of positive streamers in air. Special attention will be paid upon the propagation of positive streamers in Venusian atmosphere with the aim of analyzing one of the topical problems in geophysics: Does the lightning exist in the atmosphere of Venus? Using a high-order model, I will illustrate the non-local effects in the profiles of the averaged energy behind the streamer front and emphasize the significance of the energy flux balance equation in modeling. I will consider the negative planar ionization fronts in molecular nitrogen and rare gases. Our results for various streamers properties are compared with those obtained by a Monte Carlo approach. The comparison confirms the theoretical basis and numerical integrity of our high order fluid model for streamers discharges.