Berlin 2001 – scientific programme

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P: Plasmaphysik

P 6: Discharges

P 6.1: Talk

Thursday, April 5, 2001, 16:30–16:45, 2053

Loss mechanisms of negative oxygen ions in an inductively coupled rf discharge — •C. Manthey, H.-M. Katsch und H. F. Döbele — Universiät Essen, Institut für Laser- und Plasmaphysik,Universitätsstraße 5, 45117 Essen

A high fraction of negative ions (approx. 90 %) is observed in a pulsed oxygen rf discharge (13.56 MHz, 10 Pa). At the end of a discharge pulse of 1 ms duration both the axial and the radial density profiles of the negative ions coincide with the density profile of the positive charge carriers. The dominant loss reactions - in particular of the negative ions - can be found from measurements of the temporal decay of the positive and negative charge carriers in the afterglow. Recombination with positive oxygen ions and collisions with atomic oxygen dominate the decay of the negative ions. These observations are consistent with the determination of the atomic oxygen density and determinations of the ion species and their energies (plasma monitor). The discharge changes into an ion-ion-plasma approx. 500 µs after its switch-off. Probe measurements indicate a production of electrons during this late phase. This can be explained by collisions of negative oxygen ions with atoms, whereby oxygen molecules are formed.
This project is supported by the "Deutsche Forschungsgesellschaft" in the frame of SFB 191.