Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session TO7: Dusty Plasma, Multi-Phase Media, and Anti-Matter Plasma |
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Chair: Edward Thomas, Auburn University Room: 203 |
Thursday, November 19, 2015 9:30AM - 9:42AM |
TO7.00001: Coulomb fission of a charged dust cloud in an afterglow plasma Robert Merlino, John Meyer A dust cloud of 1 micron diameter silica microspheres was confined in a DC glow discharge dusty plasma in argon at a pressure of 100 mTorr (13 Pa). Laser sheet illumination and a fast video camera (2000 frames/s) was used to record the dynamics of this cloud following the switch-off of the plasma and confining forces. Due to the rapid decay of the plasma, and the substantial residual charge on the particles in the plasma afterglow, the cloud evolved under the mutual Coulomb repulsion forces. A variety of dynamic evolutions were observed with different clouds and under different conditions including, Coulomb explosion and expansion. In one case, the cloud underwent a Coulomb fission process, fragmenting into two clouds. Observations and analysis of this Coulomb fission event will be presented. [Preview Abstract] |
Thursday, November 19, 2015 9:42AM - 9:54AM |
TO7.00002: First Results from Detailed Electric and Magnetic Field Measurements of the Interaction of a Laser-Produced and Ambient Plasma D.B. Schaeffer, L.R. Hofer, P.V. Heuer, C.G. Constantin, A.S. Bondarenko, E.T. Everson, S.E. Clark, W. Gekelman, C. Niemann Utilizing high-repetition lasers combined with a high-repetition ambient plasma allows for detailed 3D scans of the interaction of the laser-produced and ambient plasmas. We present the first results from experiments combining a newly-commissioned high-repetition (1 Hz) laser with the 1 Hz ambient plasma of the Large Plasma Device (LAPD) at the University of California, Los Angeles. The laser (20 J, 14 ns) was focused on a cylindrical plastic target embedded in the ambient LAPD plasma, resulting in an ablated debris-plasma that expanded perpendicular to the background magnetic field. The debris-ambient plasma interaction was studied with 3-axis magnetic flux probes, mounted on a 3D motion drive for detailed, high-resolution planar scans both along and perpendicular to the background field. Measurements were also taken using filtered fast-gate (ns) imaging, emissive Langmuir probes, and emissive spectroscopy. The results show that the debris ions are de-energized inside the diamagnetic cavity, while the ambient ions are accelerated through laminar electric fields. [Preview Abstract] |
Thursday, November 19, 2015 9:54AM - 10:06AM |
TO7.00003: Diagnostics of Nanodusty Plasma Franko Greiner, Sebastian Groth, Bejamin Tadsen, Alexander Piel The diagnostic of nanodusty plasmas, i.e.\ plasmas including nano-sized dust particles, is a challenging task. For both, the diagnostic of the nanodusty plasma itself, and the in-situ diagnostic of the nanoparticles, no standard diagnostic exist. Nanodust particle size and density can be estimated using light scattering techniques, namely kinetic Mie ellipsometry and extinction measurements. The charge of the nanoparticles can be estimated from the analysis of dust density waves (DDW). Parameters like the electron density, which give information about the plasma itself, may be deduced from the DDW analysis. We present detailed investigations on nanodust in a reactive Argon-Acetylene plasma created in an rf-driven parallel plate reactor at low pressure using the above mentioned portfolio of diagnostic. [Preview Abstract] |
Thursday, November 19, 2015 10:06AM - 10:18AM |
TO7.00004: Critical Point Transitions between Dust Particle ``Phases'' in a Complex Plasma Truell Hyde, Lorin Matthews, Jie Kong, Ke Qiao, Mudi Chen, Bo Zhang, Zhiyue Ding In 1934 Wigner predicted theoretically that a gas of electrons, in which the kinetic energy (temperature) was comparable to the average potential energy, would form a symmetric lattice (i.e., a crystalline phase) at some critical value of the ratio of these energies. Since this time, various Wigner structures have been observed experimentally, for example, the electron structures (Wigner ``islands'') observed floating on the surface of superfluid helium. To date, most experimentally observed Wigner clusters have been observed in the presence of external system confinement, making the fundamental physics behind these correlation driven effects surprisingly difficult to determine. Recently, complex plasmas have proven a versatile analog for the study of such systems. In this talk it will be argued, using experimental data collected for two- and three--particle strings, that there is a basis set of fundamental parameters which determine the critical ``phase'' transition point for a given set of operating conditions. [Preview Abstract] |
Thursday, November 19, 2015 10:18AM - 10:30AM |
TO7.00005: Charged Dust Aggregate Interactions Lorin Matthews, Truell Hyde A proper understanding of the behavior of dust particle aggregates immersed in a complex plasma first requires a knowledge of the basic properties of the system. Among the most important of these are the net electrostatic charge and higher multipole moments on the dust aggregate as well as the manner in which the aggregate interacts with the local electrostatic fields. The formation of elongated, fractal-like aggregates levitating in the sheath electric field of a weakly ionized RF generated plasma discharge has recently been observed experimentally. The resulting data has shown that as aggregates approach one another, they can both accelerate and rotate. At equilibrium, aggregates are observed to levitate with regular spacing, rotating about their long axis aligned parallel to the sheath electric field. Since gas drag tends to slow any such rotation, energy must be constantly fed into the system in order to sustain it. A numerical model designed to analyze this motion provides both the electrostatic charge and higher multipole moments of the aggregate while including the forces due to thermophoresis, neutral gas drag, and the ion wakefield. This model will be used to investigate the ambient conditions leading to the observed interactions. [Preview Abstract] |
Thursday, November 19, 2015 10:30AM - 10:42AM |
TO7.00006: The effect of mechanical vibration on the dust particle kinetic temperature measurement Jie Kong, Ke Qiao, Lorin Matthews, Truell Hyde An important parameter in governing the self-assembly of structures in a complex (dusty) plasma is the coupling parameter $\Gamma $, the ratio of the electrostatic energy of the charged dust to the dust thermal energy. In a GEC rf reference cell, the dust thermal energy can come from collisions with the neutral gas, fluctuations of the confining electric field or changes in the charge on the dust particle itself. Experimentally, the kinetic energy of the dust can be determined using the Gaussian thermal velocity probability distribution. However, recent measurements of the dust particle velocity probability distribution function have shown that external mechanical vibrations of the plasma chamber can have a significant effect on the result. This investigation compares measurements of the dust kinetic temperature with and without external vibrations to the GEC cell. [Preview Abstract] |
Thursday, November 19, 2015 10:42AM - 10:54AM |
TO7.00007: Nonlinear mode coupling and vibrational energy transfer in Yukawa clusters Ke Qiao, Jie Kong, Lorin Matthews, Truell Hyde Nonlinear mode coupling and the subsequent vibrational energy transfer that results is an important topic in chemical physics research, ranging from small molecules consisting of several atoms to macromolecules such as those found in proteins and DNA. Nonlinear mode coupling is recognized as the mechanism leading to ergodicity, which is a foundational tenet of statistical mechanics. Over the past two decades, Yukawa systems of particles such as those found in complex plasma, have been shown to be an effective model across a large number of physical systems. In this research, nonlinear mode coupling in Yukawa clusters consisting of 3-10 particles is examined via numerical simulation of the vibrational energy transfer between modes starting from an initial excited state. The relationship between the energy transfer process and the internal resonance between modes having a specified frequency ratio and the temporal evolution of the system to a state of equal energy across all modes, i.e., the state of ergodicity, will be discussed. [Preview Abstract] |
Thursday, November 19, 2015 10:54AM - 11:06AM |
TO7.00008: The Confinement and Sheath Within a Glass Box Mudi Chen, Michael Dropmann, Jie Kong, Ke Qiao, Jorge Carmona-Reyes, Lorin Matthews, Truell Hyde The confinement structure provided by a glass box placed on the lower powered electrode of a GEC rf Reference Cell is proving to be ideal for the formation of vertically aligned structures which are often difficult to obtain under other types of confinement. A glass box also provides a mechanism for controlling the number of dust particles comprising a particular dust structure as well as their size and symmetry. However, given the small volume of the glass box and the fact that each of the glass panes comprising the box develop a new sheath within the plasma environment, the structure of the overall sheath inside is quite different from that produced by the lower electrode alone. Since both the confinement and sheath structure are vital for producing ordered dust particle structures, a better understanding of the underlying physics is sorely needed. In this experiment, the trajectories of dust particles acting as probes while falling through the glass box under various plasma environments are tracked and analyzed. It will be shown that the resulting data provides a map of both the confining force and the structure of the sheath inside the glass box. [Preview Abstract] |
Thursday, November 19, 2015 11:06AM - 11:18AM |
TO7.00009: On the Anderson localization conjecture in Dusty Plasma Constanze Liaw, Kyle Busse, Lorin Matthews, Truell Hyde In 1958, Anderson suggested that sufficiently large impurities in a semi-conductor could lead to spatial localization of electrons. This idea unfolded into the field of Anderson Localization, one of the most fascinating phenomena in solid-state physics as it plays a major role in the conductive properties of imperfectly ordered materials. The \textit{Anderson Localization Conjecture} claims that random disorder of any strength causes localization of electrons in the medium. The problem has proven to be highly non-trivial. Over the years the community has argued whether spatial localization occurs in 2D for small impurities. From a mathematical standpoint, the conjecture is still considered an open question. In 2013, Liaw challenged the commonly held assumption that localization holds in 2D by introducing a new mathematically more rigorous method to test for extended states, and applying it to the discrete random Schr\"{o}dinger operator. One of the advantages of the underlying method is its versatility. It can be applied to any ordered system such as colloids, crystals, and atomic lattices. In a cross-disciplinary effort we merge this method with a numerical code used to simulate 2D physics systems, in preparation for experimentally testing the theory against complex plasma crystals. [Preview Abstract] |
Thursday, November 19, 2015 11:18AM - 11:30AM |
TO7.00010: Investigation of plasma particle interactions with variable particle sizes Michael Dropmann, Rene Laufer, Georg Herdrich, Lorin Matthews, Truell Hyde In dusty plasmas, the dust particles are subjected to many forces of different origins. Both the gas and plasma directly affect the dust particles through electric fields, neutral drag, ion drag and thermophoretic forces, while the particles themselves interact with one another through a screened coulomb potential, which can be influenced by flowing ions. Recently, micron sized particles have been used as probes to analyze the electric fields in the plasma directly. A proper analysis of the resulting data requires a full understanding of the manner in which these forces couple to the dust particles. In most cases each of the forces exhibit unique characteristics, many of which are partially dependent on the particle size. In this study, five different particle sizes are used to investigate the forces resident in the sheath above the lower electrode of a GEC RF reference cell. The particles are tracked using a high-speed camera, yielding two-dimensional force maps allowing the force on the particles to be described as a polynomial series. It will be shown that the data collected can be analyzed to reveal information about the origins of the various forces. [Preview Abstract] |
Thursday, November 19, 2015 11:30AM - 11:42AM |
TO7.00011: Boundary Conditions in Hydrodynamic Modeling of the Plasma in a Dusty RF Plasma Reactor Althea Wilson, Babak Shotorban Selection of the boundary conditions (BC) for a numerical plasma modeling is an important consideration. Two popular BC's in hydrodynamic plasma simulations are the zero number density BC and the thermal flux BC. They both neglect secondary electron emission; however, it has been suggested that secondary emission may be important for some discharges. This study compares the three different BC's applied to a hydrodynamic simulation of an RF dusty plasma reactor and examines the effect of the BC on the plasma and dust variables. Dust grains are individually traced in the Lagrangian frame. \\ \\ This work is supported in part by NSF through award PHY-1414552. [Preview Abstract] |
Thursday, November 19, 2015 11:42AM - 11:54AM |
TO7.00012: Collisional Charging of Dust in a Collisionless Plasma Presheath Richard Cameron, Michael Coppins Charged dust particles are commonly found near the plasma boundary, where their motion is dominated by the electrostatic presheath and sheath fields. For dust grains smaller than the typical collision lengths of the plasma, collisional effects are often ignored. In this work, Particle In Cell simulations are used to show that if a background of low-temperature neutrals is present, even infrequent charge exchange collisions cause a population of low temperature ions to develop. While of low density, these ions tend to collect in orbit around dust grains. The collection radius for this effect is also shown to be large compared to the dust grain -- of order $T_{e}$/$T_{n}$ dust radii (where $T_{e}$ and $T_{n}$ are the electron and neutral temperatures, respectively). These ions both shield the grain and, since further collisions de-orbit these ions into the grain, provide another source of current to the dust, altering its charge. We extend previous work in the bulk plasma to the presheath/sheath region, where dust is more commonly found. The presheath field causes a high flux of ions past the grain, and even grains much smaller than a Debye length can be entirely shielded by the orbiting population, completely altering their behaviour in this region of the plasma. [Preview Abstract] |
Thursday, November 19, 2015 11:54AM - 12:06PM |
TO7.00013: Investigating the Structure of the Wake of a Dust Particle in the Plasma Sheath Hendrik Jung, Franko Greiner, Alexander Piel Due to the deflection of the ambient streaming ions, a negatively charged dust particle in the plasma sheath forms a wake with a net positive space charge in downstream direction. The wake is characterized by attractive, non-reciprocal forces between negatively charged particles and a charge reduction of a particle in the wake of another particle. In this contribution a two-particle system is used to investigate the ion wake structure behind a dust particle in the plasma sheath of an rf discharge [Jung, PoP 22, 053702 (2015)]. For this purpose, we have used the phase-resolved resonance method [Carstensen, PoP 18, 033701 (2011)] that evaluates the dynamic response of the particle system to small external, sinusoidal perturbations, which allows to measure the wake induces characteristics. Plasma inherent etching processes are used to achieve an increasing levitation height of the lower particle, so that the structure of the wake of the upper particle, which is nearly unaffected by etching, can be probed. In good agreement with theoretical predictions, a significant modification in the plasma sheath to one long potential tail is observed. The presented method is used to investigate the influence of a strong magnetic field on the formation and spatial structure of the wake. [Preview Abstract] |
Thursday, November 19, 2015 12:06PM - 12:18PM |
TO7.00014: Phase Transitions in Quasi-2D Plasma-Dust Systems: Simulations and Experiments Oleg Petrov, Mikhail Vasiliev, Konstantin Statsenko, Xeniya Koss, Elena Vasilieva, Maxim Myasnikov, Evgeny Lisin A nature of phase transition in quasi-2D dusty plasma structures was studied and the influence of the quasi-2D cluster size (a number of particles in it) on the features of the phase transition was investigated. Experiments and numerical simulation was conducted for the systems consisting of small ($\sim$ 10) and large ($\sim$ 10$^{3})$ number of particles. To investigate the phase state of the system with 7, 18 and 100 particles observed in numerical and laboratory experiments, we used the method based on analysis of dynamic entropy. Numerical modeling of small systems was conducted by the Langevin molecular dynamic method with the Langevin force, responsible for the stochastic nature of the motion of particles with a given kinetic temperature. Phase state of systems with the number of elements in the order of 10$^{3}$, was studied using the methods of statistical thermodynamics. Here we present new results of an experimental study of the change of translational and orientational order and topological defects, and the pair interactions at 2D melting of dust cluster in rf discharge plasma. The experimental results have revealed the existence of hexatic phase as well as solid-to-hexatic phase and hexatic-to-liquid transitions. [Preview Abstract] |
Thursday, November 19, 2015 12:18PM - 12:30PM |
TO7.00015: ABSTRACT WITHDRAWN |
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