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We propose a novel method of determination of the dust particle spatial distribution in dust clouds that form in three-dimensional (3D) complex plasmas under microgravity conditions. The method utilizes the data obtained during the 3D scanning of a cloud and provides a reasonably good accuracy. Based on this method, we investigate the particle density in a dust cloud realized in gas discharge plasma in the PK-3 Plus setup onboard the International Space Station. We find that the treated dust clouds are both anisotropic and inhomogeneous. One can isolate two regimes, in which a stationary dust cloud can be observed. At low pressures, the particle density decreases monotonically with the increase of the distance from the discharge center; at higher pressures, the density distribution has a shallow minimum. Regardless of the regime, we detect a cusp of the distribution at the void boundary and a slowly varying density at larger distances (in the foot region). A theoretical interpretation of obtained results is developed that leads to reasonable estimates of the densities for both the cusp and foot. The modified ionization equation of state, which allows for violation of the local quasineutrality in the cusp region, predicts the spatial distributions of ion and electron densities to be measured in future experiments., Comment: 37 pages, 13 figures

Two-dimensional complex plasma crystals are an ideal model system to study dynamic processes [1]. Recently, synchronized motion of alternating in-phase and anti-phase particle lines was observed during mode-coupling instability (MCI), where the out-of-plane mode couples to the longitudinal mode [2]. The coupling allows energy to be transferred from the flowing ions in the plasma sheath to the crystal until the crystal melts. While MCI is equally strong in three directions for an ideal hexagonal lattice [3], it was observed in only two directions in Ref. [2]. Here, we demonstrate with molecular dynamics simulations that an asymmetry in the horizontal confinement of the plasma crystal can cause an anisotropic ignition of MCI. The confinement asymmetry leads to a deformation of the hexagonal lattice that is typically observed in experiments. The instability is accompanied by synchronized particle motion that is characterized by a new order parameter. Depending on the orientation of the confinement asymmetry, MCI and synchronized motion are observed in one or two directions. The good agreement of simulation and experiment suggests that the confinement asymmetry can be used to explain the synchronized motion observed in experiments. [1] Morfill G. E. and Ivlev A. V., Rev. Mod. Phys., 81 1353 (2009). [2] L. Couëdel, S. Zhdanov, V. Nosenko, A. V. Ivlev, H. M. Thomas, and G. E. Morfill, Phys. Rev. E 89, 053108 (2014). [3] S. K. Zhdanov, A. V. Ivlev, and G. Morfill, Phys. Plasmas 16, 083706 (2009).

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We report the first observation of the Mach cones excited by a larger microparticle (projectile) moving through a cloud of smaller microparticles (dust) in a complex plasma with neon as a buffer gas under microgravity conditions. A collective motion of the dust particles occurs as propagation of the contact discontinuity. The corresponding speed of sound was measured by a special method of the Mach cone visualization. The measurement results are incompatible with the theory of ion acoustic waves. The estimate for the pressure in a strongly coupled Coulomb system and a scaling law for the complex plasma make it possible to derive an evaluation for the speed of sound, which is in a reasonable agreement with the experiments in complex plasmas., 5 pages, 2 figures, 1 table

Diese Dissertation befasst sich mit neuen experimentellen Möglichkeiten zur strukturellen und dynamischen Manipulation finiter Staubwolken in einem Plasma. Derartige Partikelsysteme sind aufgrund ihrer besonderen Eigenschaften hervorragend für umfassende Untersuchungen von Korrelationseffekten in stark gekoppelten Systemen geeignet und daher Gegenstand intensiver Forschungsanstrengungen der letzten 20 Jahre. Im Rahmen dieser Arbeit werden verschiedene Vorgehensweisen verfolgt. Zum einen wird eine globale Anregung dynamischer Prozesse mittels umlaufender elektrischer Felder sowie mit einer rotierenden Neutralgassäule untersucht. Letztgenannte Methode wird genutzt, um einen scherinduzierten Schmelzprozess zu erforschen. In diesem Zusammenhang werden sowohl der Einfluss der Partikelwechselwirkung als auch der Einschlussgeometrie auf die Dynamik rotierender Systeme untersucht. Zum anderen liegt ein weiterer Schwerpunkt der Arbeit auf der Lasermanipulation, die eine kontrollierte Manipulation von Staubsystemen ohne signifikante Beeinflussung des Plasmahintergrunds ermöglicht. Am Beispiel der Laserheizung wird hierbei eine weitere globale Manipulationsmethode in Form eines idealen Thermostaten für Staubcluster vorgestellt. Es wird ferner nachgewiesen, dass die diffuse Reflexion eines Laserstrahls nicht nur signifikanten Einfluss auf Staubpartikel haben kann, sondern auch gezielt für eine globale sowie teil-lokalisierte Anregung dynamischer Prozesse genutzt werden kann. Es wird gezeigt, dass hiermit eine selektive Anregung weniger Eigenmoden von Clustern möglich ist und diese bei geeigneter Topologie und passender Anregungsfrequenz resonant getrieben werden können. Schließlich wird mit einer auf die Anwendung in staubigen Plasmen angepassten optischen Falle ein neues und vielseitiges Werkzeug vorgestellt, mit dem Staubpartikel in einem Laserstrahl eingefangen werden können. Es werden damit zum einen die Folgen intensiver Laserbestrahlung auf die Partikeleigenschaften untersucht und zum anderen wird gezeigt, dass mit dieser Laserpinzette einzelne Partikel in Vielteilchensystemen kontrolliert werden können. Es werden Anwendungen vorgestellt, mit denen die Auswirkungen einer lokalen Manipulation von Struktur und Dynamik auf das kollektive Partikelverhalten in Staubclustern analysiert werden. This thesis addresses novel experimental methods of structural and dynamic manipulation of finite dust clouds in plasmas. Due to their unique nature such particle systems are exceptionally suited for extensive studies of correlation effects in strongly coupled systems, and hence have been subject to intensive research work over the past 20 years. Within the scope of this work different approaches are taken. On the one hand a global excitation of dynamic processes is studied by means of rotating electric fields as well as using a rotating neutral gas column. The latter method is used to explore a shear-induced melting process. In this context both the role of the particle interaction ands the influence of the confinement geometry are studied. On the other hand emphasis is placed on laser manipulation, which allows for a well-controllable manipulation of particle systems without a significant perturbation of the plasma background. By the use of laser heating a further form of global manipulation is demonstrated which can be regarded as an ideal thermostat for dust clusters. Furthermore, it is shown that the diffuse reflection of a laser beam may not only have significant impact on dust particles but can also be used for a purposeful excitation of dynamical processes in either a global or a partially localized manner. With the help of this method a selective excitation of few normal modes in a cluster is demonstrated, which can be driven resonantly in case of a suitable topology and appropriate excitation frequencies. Finally, an optical trap adapted for the use in dusty plasmas is introduced. This novel and versatile tool allows to trap single particles in the beam of a laser. By the use of this trap, the impact of the exposure of a microparticle to intensive laser irradiation on its properties is studied. Further, it is shown that single grains in a many-particle system can be effectively trapped and controlled by this laser tweezer. Applications of this method are presented and used to analyze the effects of a local manipulation of structure and dynamics on the collective response of strongly coupled particle systems.

Network analysis was used to study the structure and time evolution of driven three-dimensional complex plasma clusters. The clusters were created by suspending micron-size particles in a glass box placed on top of the rf electrode in a capacitively coupled discharge. The particles were highly charged and manipulated by an external electric �eld that had a constant magnitude and rotated uniformly in the horizontal plane. Depending on the frequency of the applied electric �eld, the clusters rotated in the direction of the electric �eld or remained stationary. The three-dimensional positions of all particles were measured using stereoscopic digital in-line holography. The network approach was used to elucidate the structural changes in the cluster consisting only of a very limited number of particles (64). The Analysis revealed an interplay between two competing symmetries in the cluster. Spherical and cylindrical ordering of the particles was examined by comparing network measures of the experimental data with null models. The null models were arti�cial data with a certain number of points in perfectly spherical order, and the rest in cylindrical order. The well established network measures local connectivity, clustering coe�cient and average path length were considered. Network analysis of the clusters showed that the rotating cluster was more cylindrical than the nonrotating cluster. These �ndings were in agreement with the estimate of the radial con�nement with the aid of a dynamical force balance. Neglecting friction and inertial forces due to the low particle velocities in the cluster, the pro�le of the electrical con�nement could be estimated by calculating the repulsing Yukawa-type interaction between the particles. The radial con�nement was shown to be stronger in the case of cluster rotation, increasing the cylindricity of the cluster. The emergence of vertical strings of particles was also con�rmed by using a network analysis. While the traditional method of a �xed threshold has limitations such as erroneously including passing by particles and a somewhat arbitrary threshold, community �nding algorithms yield a more elegant approach of �nding structures in complex systems. With the aid of multislice networks, it is possible to examine the whole time series at once and thus resolve the time evolution of the strings. As we demonstrated, network analysis is a powerful tool to analyze the structure of complex plasma clusters and may have numerous applications in other complex systems where the characertization of the spatial structure plays a vital role. 1

A test for nonlinearity based on network measures of recurrence networks is proposed and compared to a powerful measure for nonlinearity, namely the nonlinear prediction error. Simulated time series from the Lorenz System and light curves from Active Galactic Nuclei are studied. The new test based on networks shows similar discrimination power. Both tests detect induced phase correlations in so-called surrogate data produced by two established algorithms. In a second part, two promising applications of network analysis to complex plasma clusters are described. The detection of vertical strings with the aid of a community-finding algorithm has proven an elegant way of examining stable units in complex structures. Network analysis also enables a throughout study of the global structure of the clusters. For the relatively small clusters of about 60 particles a significant diverence between the well-studied case of nonrotating clusters and dynamically driven clusters is demonstrated.

In dieser Dissertation werden zwei Stoßrichtungen verfolgt, die eng miteinander verflochten sind, nämlich die Untersuchung staubakustischer Wellen (DAW) und ein Verständnis des Einschlusses von Staub in einem Laborplasma. Es wird der Versuch unternommen, durch Sondendiagnostik und mit Hilfe eines selbstkonsistenten Modells für das einschließende Plasma zu einer quantitativen Erklärung beider Phänomene zu gelangen. In dem Experiment wird Staub in einem anodischen Plasma gefangen. Aufgrund der hohen elektrischen Feldstärke und des niedrigen Gasdrucks driften die Ionen mit einer schwach überthermischen Geschwindigkeit. Lage und Größe der Staubwolke können durch ein effektives Fallenpotential, das durch die elektrische Feldkraft und die Ionenwindkraft in dem überthermischen Regime definiert wird, gut beschrieben werden. Staubakustische Wellen treten in dem untersuchten Regime spontan auf und breiten sich in Richtung der Ionenströmung aus. Durch Synchronisation der selbsterregten Wellen mit einem externen Signal werden Dispersionsrelationen experimentell bestimmt. Für die Auswertung der mit einer Kamera gemessenen Dichtefluktuationen wird die Singulärwertzerlegung (SVD) benutzt. Systematisch werden unter Zuhilfenahme der SVD-Methode lokale Wellenzahlen und Anwachsraten gemessen. Erstmals werden im überthermischen Regime gemessene DAW-Dispersionsrelationen mit einer ionenkinetischen Theorie verglichen. Es wird gefunden, dass ein Wellenmodell mit Bhatnagar-Gross-Krook-Ionenstößen eine gute Vorhersage der gemessenen mittleren Wellenzahlen ergibt, allerdings werden die Anwachsraten überschätzt. Weitergehende Untersuchungen machen eine nichtinvasive Diagnostik der Dichte der freien Elektronen im staubigen Plasma erforderlich. Eine Methode, die dies leistet, ist die Resonanzkegeldiagnostik, die Whistlerwellen bei Ausbreitung unter einem Winkel zum Magnetfeld benutzt. Es wird gezeigt, dass Resonanzkegel auch im staubigen Plasma angeregt werden können. Simultane Messungen mit der Resonanzkegelmethode und einer Langmuir-Sonde liefern übereinstimmende Ergebnisse für die Verarmung der Elektronen durch Staub. Der Mechanismus der Elektronenverarmung wird mit der zusätzlichen, inneren Verlustfläche des Staubs erklärt.

keine dt.-spr. Zusammenfassung vh. The ion drag force on micrometer sized particles in a plasma was investigated. Acting on these particles was the gravitational force and the drag force of an ion beam with ion energies ranging from 3...45 eV, and an ion drift with ion velocities of approx. 500 m/s. As both ion flows are in a horizontal direction, the ion drag force could be measured from the deflection of the free falling microspheres from the vertical direction. By a thorough diagnostics of the background plasma parameters and the ion density and energy, a comparison with theoretical models was possible. At high ion energies, a good agreement was found with the standard model (Barnes 1992), when using the Debye length as a cut-off parameter. At low energies however, a better agreement is found with recent numerical models (Khrapak 2003). In particular, it is found, that the standard model overestimates the collection radius for low ion energies and particle sizes comparable to the screening length (Debye length), due to a neglection of the shielding properties of the plasma.