A new method of solution of the Boltzmann equation, able to take into account the full anisotropy of the distribution function, is applied to the calculation of swarm parameters in certain reactive gases. The authors first checked the accuracy of the method on the model gas of Lucas and Saelee (1975) where comparisons can be made with results of other authors. Calculations are then carried out with the authors' method in SF6 using three sets of cross-sections available in the literature. The results obtained are compared with those of the standard two-term approximation. It is seen that large differences occur, mainly for the determination of the attachment and transverse diffusion coefficients. Inconsistencies between the three sets of cross-sections used are demonstrated.
This work is devoted to the analysis of experimental results obtained in dry air at atmospheric pressure in a positive point-to-plane corona discharge under a pulsed applied voltage in the cases of anodic mono-and multi-tips. In the mono-tip case, the peak corona current is analysed as a function of several experimental parameters such as magnitude, frequency and duration of pulsed voltage and gap distance. The variation of the corona discharge current is correlated with the ozone production. Then in the multi-tip case, the electrical behaviour is analysed as a function of the distance between two contiguous tips and the tip number in order to highlight the region of creation active species for the lowest dissipated power. Intensified charge-coupled device pictures and electric field calculations as a function of inter-tip distance are performed to analyse the mutual effect between two contiguous tips. The optical emission spectra are measured in the UV-visible-NIR wavelength range between 200 nm and 800 nm, in order to identify the main excited species formed in an air corona discharge such as the usual first and second positive systems with first negative systems of molecular nitrogen. The identification of atomic species (O triplet and N) and the quenching of NOγ emission bands are also emphasized.
Two numerical solutions of the Boltzmann equation are developed and applied to the calculations of swarm time-of-flight parameters in molecular model gases. It is shown that the two methods not only give near similar results but are in good agreement with calculations carried out by some other authors for the same situations. Errors already pointed out in some other works are confirmed and the need of using high-order methods of solution of the Boltzmann equation is stressed.
A numerical analysis of the neutral dynamics is performed in the case of helium short-gap spark discharges to show the energy memory effect of recurring discharges. The millimetric (4 mm) and submillimetric (0.3 mm) discharges are studied at atmospheric pressure and ambient temperature (293 K). This corresponds to a neutral density of 2.5×1025 m−3. The maximum injected power is either 50 or 3 W with a duration of 1 μs, the relaxation time between the two successive injections is 5 μs. The evolution of the neutral gas is described with the classical transport equations written in a two-dimensional cylindrical geometry with plane electrodes and solved with powerful numerical schemes. The effect of the discharge on the neutral gas is represented by energy and momentum transfers. The neutral gas is no longer considered as an infinite sink dissipating the energy of the electrons and ions acquired from the field. It is shown that the energy and momentum transfer effects initiate and control the variations of temperature, pressure, and neutral population. Concerning the recurring aspect, the neutral memory effect persists during the time lapse between two successive discharges and directly influences the gas dynamics of the following discharge. The specific behavior of the gas dynamics for the shorter gap (0.3 mm) is also discussed in terms of boundary effects. In particular, the influence of the latter on the velocity field is studied.
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