Effect of small admixtures of N2, H2 or O2 on the electron drift velocity in argon: experimental measurements and calculations
The European Physical Journal D, 2011
The electron drift velocity in argon with admixtures of up to 2\% of nitrogen, hydrogen or oxygen... more The electron drift velocity in argon with admixtures of up to 2\% of nitrogen, hydrogen or oxygen is measured in a pulsed Townsend system for reduced electric fields ranging from 0.1 Td to 2.5 Td. The results are compared with those obtained by Monte Carlo simulations and from the solution of the electron Boltzmann equation using two different solution techniques: a multiterm method based on Legendre polynomial expansion of the angular dependence of the velocity distribution function and the S n method applied to a density gradient expansion representation of the distribution function. An almost perfect agreement between the results of the three numerical methods and, in general, very good agreement between the experimental and the calculated results is obtained. Measurements in Ar-O 2 mixtures were limited by electron attachment to oxygen molecules, which contributes to the measured drift velocity. As a result of this attachment contribution, the bulk drift velocity becomes larger than the flux drift velocity if attachment is more probable for electrons with energy below the mean value and smaller in the opposite case. Attachment also contributes to the negative differential conductivity observed in Ar-O 2 mixtures. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
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Papers by Zoltan Donko
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wide range of operating conditions. Very good agreement is found for self-bias and flux- energy distribution of the positive ions at the electrodes, while a fair agreement is reached
for discharge power and ion flux data. The simulated spatial and temporal behaviour of the electric field, electron density, electron power absorption, ionization rate and mean electron energy shows a transition between sheath expansion heating and drift-ambipolar discharge modes, induced by changing either the number of harmonics comprising the excitation waveform or the gas pressure. The simulations indicate that under our experimental conditions the plasma operates at high electronegativity, and also reveal the crucial role of O2(a1∆g) singlet metastable molecules in establishing discharge behavior via the fast destruction of negative ions within the bulk plasma.