Kiel 2011 – wissenschaftliches Programm
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P: Fachverband Plasmaphysik
P 9: Poster: Diagnostik technischer Plasmen
P 9.8: Poster
Dienstag, 29. März 2011, 17:00–19:00, Foyer
Electron kinetics in 10 Hz pulsed cc-rf plasmas studied by 160 GHz Gaussian beam microwave interferometry — •Christian Küllig, Kristian Dittmann, and Jürgen Meichsner — Ernst-Moritz-Arndt-University of Greifswald, 17489 Greifswald
The line integrated electron density in the bulk plasma of a 10 Hz (50 % duty cycle) pulsed capacitively coupled radio frequency (cc-rf) plasma in argon and oxygen was measured by means of 160 GHz Gaussian beam microwave interferometry with time resolution of 0.2 µs. The line integrated electron density in the steady state plasma-on phase in argon amounts to between 1015 and 3×1016 m−2, whereas the values for oxygen are between 1014 and 1016 m−2. In particular, it was observed an overshoot in the electron density in the afterglow phase of the oxygen plasma shortly after disabling the rf power. This electron density increase was only seen for low rf power over a wide pressure range from 20 to 100 Pa. In this case it is important to note that the electron density is nearly the same as the density of negative atomic oxygen ions, which was measured by simultaneous laser photodetachment. A 0D model for the afterglow phase was applied considering particle balance equations for six species (O2+, O2−, O−, e, O2(a1Δg), O) and eight reactions. The measured (O−, e)/estimated (others) species densities in the steady state plasma on phase were taken as initial conditions. The model fits very well the measured temporal behaviour of the electron density and reveals that the metastable oxygen molecules O2(a1Δg) are the dominant species for detachment of the negative oxygen ions and electron production in the afterglow.