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Non-monotonic Distributions of Excited Atoms in the Positive Column of Pulsed Helium Discharges: Dynamic Plasma Regime

By E. V. Barnat (a and V. I. Kolobov (b


Non-monotonic radial distributions of excited helium atoms have been experimentally observed in a positive column (PC) of pulsed helium discharges using planar laser induced fluorescence. The observed effect is attributed to the peculiarities of electron impact populationdepopulation of the excited states under “dynamic discharge ” conditions with strong modulations of the electric field maintaining the plasma [1]. Paradoxical non-monotonic radial distributions of excitation rates in the steady-state PC of rare gases (with the exception of helium) at elevated pressures have been previously predicted in simulations and explained by non-local kinetic effects [2]. Nonmonotonic radial distributions of metastables have been recently observed in simulations of pulsed xenon discharges [3] and ascribed to gas heating. However, no experimental observation of this effect was reported. Measured and simulated radial distributions of excited atoms are shown in Fig. 1 for various pressures and various times during the current pulse. For all pressures, the excited species are initially center peaked and monotonic. For the lowest pressure, the distribution of the excite

Year: 2013
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