[institut] Seminar: Saša Dujko

[Zoran Petrović]

Postovane koleginice i kolege,

pozivamo Vas na seminar Laboratorije za gasnu elektroniku, koji će u 
sredu 09. Aprila 2014. god. u 12:00 u velikoj sali Zvonko Maric održati

dr Saša Dujko.

Naslov siminara je:

High-order fluid model for streamer discharges

Abstract

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.


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