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P: Plasmaphysik

P 10: Poster II

P 10.35: Poster

Tuesday, March 18, 2003, 17:30–19:15, Foyer

Dynamical balance of forces acting on free-falling particles in a plasma column — •Ciprian Zafiu, Andre Melzer, and Alexander Piel — Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40-60, 24098 Kiel, Germany

Under microgravity conditions, central particle-free regions, the so-called plasma voids, have been described as result of the dominance of the ion drag and thermophoresis over the confining electric field force. In our experiments micrometer-sized spherical particles are dropped freely through a long plasma column, the weight force being balanced by the neutral gas friction. The interesting forces (ion drag, thermophoresis, and electric field force) act horizontally, leading to an inwards or outwards motion of the dust particles. The observed particle behaviour under various experimental conditions (high or low pressures) is observed and the forces acting on the particles are measured. These measured forces are compared with the theoretical models for ion drag and thermophoresis. The experimentally observed transition from particle repulsion to focussing has been qualitatively and quantitatively related to the transition from dominant outwards-oriented ion drag and thermophoresis to dominance of the focussing electric field force.