Berlin 2005 – scientific programme

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P: Plasmaphysik

P 23: Poster: Magnetischer Einschluß 3, Staubige Plasmen 2, Astrophysikalische Plasmen 1

P 23.21: Poster

Tuesday, March 8, 2005, 16:30–18:30, Poster HU

Tree-dimensional plasma clusters — •Tetyana Antonova, B.M. Annaratone, H.M. Thomas, and G.E. Morfill — Max Planck Institute for extraterrestrial Physics, Giessenbachstrasse, D-85741, Garching

This work presents the analysis of small three-dimensional plasma clusters formed by melamine-formaldehyde particles of 3.4µm size in the RF plasma sheath. Due to a fine balancing of DC and RF voltage on a small pixel of the segmented "adaptive" electrode the particles build structured 3D shapes in a gravity compensated environment. The diameters of the clusters are different (from 0.35mm up to 0.8mm) and depend on the particle number, from 4 up to 73, that can be externally controlled. With a 3D experimental diagnostic and programming analysis the time sequence of the three coordinates of the particles have been calculated. That allows us to determine exactly the cluster structure. Some defects are observed, when the particles number is not "magic" (to build close shells) and the experimental conditions are at the edge of melting. In spite of that in all clusters the pieces of icosahedral geometry can be easily seen. In many cases there is motion between preferential positions and vibration of particles in the structures, which can be explained by the smooth shape of potential confinement and formation of the most energetically preferable states of system (to fill vacancies or to push interstitial defects outside). As we do not see any external confinement in the position of the clusters, neither electrostatic nor from ion drag, the structure is probably kept together by particle-particle, or collective, attractive forces.