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Experiments with extended three-dimensional dusty plasmas under microgravity conditions were performed to study the complex wave pattern of self-excited dust-density waves and its interaction with the plasma. The simultaneous observation of the dust-density fluctuations and the plasma glow revealed that the observed wave phenomenon affects the plasma in the complete discharge. In particular, our investigations suggest, that self-excited dust-density waves are the product of a self-organized system consisting of the dust cloud, the plasma, and the external circuit. The complex wave pattern is a consequence of partial synchronization of neighboring regions inside the dust cloud and can be modeled by a system of coupled nonlinear oscillators. [ABSTRACT FROM AUTHOR]

This paper gives a survey of recent experiments on Coulomb balls. Starting with typical observations to introduce the Coulomb ball experiment and its diagnostic potential, their structural properties are discussed. Further, the trapping mechanism for the dust is quantified to allow for a systematic comparison of experiment and simulations. Finally, the presented results focus on the question how screening influences the structural properties and how Coulomb balls and other strongly coupled systems are related. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this survey the recently found “Coulomb balls” are discussed, which show an unusual kind of crystalline order. These three-dimensional dust clouds consisting of hundreds or thousands of micrometer-sized dust particles have a spherical shape and exist in a wide range of plasma conditions. Coulomb balls are optically highly transparent and have macroscopic dimensions of several millimeters in diameter. The clouds allow for the observation of each single particle and thus the complete reconstruction of the crystal structure by means of video microscopy techniques. The particles are arranged in distinct nested shells in which they form patterns with mostly five and six neighbors. The confinement of Coulomb balls by dielectric walls involves electric forces, surface charges, ion drag forces, and thermophoretic levitation. The thermophoretic force field is measured with tracer particles and particle image velocimetry (PIV). The electric forces are derived from simulations with the two-dimensional SIGLO-2D code. It is shown the the sum of all confineing forces results in a stable potential well that describes levitation and spherical confinement of the Coulomb ball. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Recently, it was shown that it is possible to confine spherical dust clouds in a plasma. It was found that these dust clouds have a crystalline structure which differs noteably from the well known fcc, bcc and hcp order in extended crystalline systems. The experiments show that the particles arrange in nested shells with hexagonal order on individual shells. The high transparency and the rather slow time scales of Coulomb balls allow to observe individual particles with video microscopy techniques and therefore to determine the structural properties of Coulomb balls with high accuracy. This contribution presents a comparison of experimental results and MD-Simulations. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Dusty plasmas have been confined by glass walls in order to generate void-free particle structures under microgravity conditions. Different types of clouds establish in the cuvette in dependence on the rf power and dc bias applied to the multi-electrode system of the discharge device. The observations can be basically understood when applying standard force models to discharge simulation results. The various dust topologies are proposed to result from a change in the direction of the ion drag — inwards or outwards the cuvette gap. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The interaction of a supersonic projectile with a static dust cloud trapped in an rf discharge under microgravity conditions is examined. It is observed that the projectile forms a dust-free cavity in its wake. The cavity dynamics can be divided into an initial impulse and a subsequent elastic response that can be modeled by a damped harmonic oscillator. [ABSTRACT FROM AUTHOR]

Laboratory experiments with thermophoretic levitation of dust particles for gravity compensation are reported. The observed spatially extended dust clouds were investigated, e.g., the dependence of discharge parameters on the void structure. These investigations lead to the discovery of an extended parameter region where spatially extended void-free clouds can be found. The mechanism of void closure is accompanied by a spontaneous change in the discharge topology. This change becomes evident from a reversal of the wave propagation direction. [ABSTRACT FROM AUTHOR]

A chain of mutually coupled nonlinear and self-sustained oscillators is studied numerically. The simple model allows to explain the topological structure of self-excited dust-density waves under microgravity conditions. The basic properties of the model are presented and compared with experimental studies. [ABSTRACT FROM AUTHOR]

Two novel three-dimensional (3D) diagnostics, stereoscopic imaging and digital holography, enable us to provide a critical comparison of experimental results with simulations and theory and thus to gain a detailed insight into the structural and dynamical properties of strongly coupled dust clouds. Special attention is paid to the influence of screening and the role of metastable states in dust clouds containing just a very few particles. [ABSTRACT FROM AUTHOR]

The dynamical properties of individual particles in a dusty plasma under microgravity conditions are investigated by means of a stereoscopic camera setup. This camera system allows the three-dimensional reconstruction of particle trajectories in a volume of approximately (15×15×15) mm3 in three dimensions. We present measurements in two different regions of a dust cloud on parabolic flights. First, the force field in the void is reconstructed from probe particles in three dimensions. Second, the oscillation of particles at the outer dust cloud surface is evaluated, and the relation to dust-density waves in the dust cloud is investigated. [ABSTRACT FROM AUTHOR]