A two-dimensional density distribution of metastables [Formula Presented] (in Paschen notation) in an inductively coupled plasma (ICP) reactor in argon, driven by one-turn radio-frequency current coil at 13.56 MHz, has been investigated by laser absorption spectroscopy. Measurements were made over a pressure range of 15–300 mTorr, and powers between 20 and 400 W. In these conditions, metastable density varied between [Formula Presented] and [Formula Presented] Even for the the position far from the coil, 140 mm far from the source region, metastable density remained comparatively high (of the order of [Formula Presented] As the power increases the metastable density drops down significantly especially for the center of the discharge where the highest electron density is anticipated. In general, the metastable profiles can be explained by combining the expected profile of efficient excitation with diffusion and with the radial dependence of the density of the electrons that can quench the metastable levels by inducing transitions to higher excited states. Therefore we have compared the data for metastable profiles with the excitation rates for one radiative level with a relatively short lifetime and with the radial dependence of electron density obtained by using a Langmuir probe.
|Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics
|Published - 1998
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