Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session CO7: Dusty Plasma |
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Chair: Lorin Matthews, Baylor University Room: 212 AB |
Monday, October 31, 2016 2:00PM - 2:12PM |
CO7.00001: Development of turbulence in a dusty plasma Mierk Schwabe, Sergey Zhdanov, Christoph R\"ath Complex or dusty plasmas are low temperature plasmas which contain micrometer-sized particles ("dust"). The microparticles obtain high charges and interact with each other, effectively forming a solid, liquid or gas state in which the microparticles take over the role of molecules in conventional systems. Complex plasmas often are in a turbulent state, for instance when instabilities like the "heartbeat" instability or intense waves are present. The movement of the microparticles, the carriers of the turbulent interactions in complex plasmas, can be directly followed, unlike that of atoms and molecules in conventional experiments on turbulence. Here we present results of an experiment on the development of turbulence in a complex plasma in the PK-3 Plus laboratory on board the International Space Station. The microparticle cloud was first stabilized against an instability. Once the stabilization was turned off, the cloud became unstable, and the movement of the particles became turbulent. In the report, we show how the energy spectra evolve during the development of turbulence. In the case of fully developed turbulence, the spectra display multiple cascades explaining well the transport of turbulent energy and enstrophy. [Preview Abstract] |
Monday, October 31, 2016 2:12PM - 2:24PM |
CO7.00002: Critical Point Transitions between Dust Particle Structures in a Complex Plasma. Truell Hyde, Lorin Matthews, Jie Kong, Ke QIao, Jorge Carmona-Reyes, Mudi Chen, Zhiyue Ding, Eva Kostadinova, Bo Zhang In 1934 Wigner predicted theoretically that a gas of electrons, in which the kinetic energy was comparable to the average potential energy, would form a symmetric structure (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 on Earth, for example, the electron structures (Wigner `islands') observed floating on the surface of superfluid helium. To date, most experimentally observed Wigner clusters have assembled in the presence of external system confinement, making the fundamental physics behind these correlation driven effects surprisingly difficult to determine. In this talk it will be argued, using experimental data collected in a complex plasma, that there is a basis set of fundamental parameters which determine the critical point transition for a known set of operating conditions. [Preview Abstract] |
Monday, October 31, 2016 2:24PM - 2:36PM |
CO7.00003: Utilization of Complex Plasma in the Study of Localization Phenomena. Kyle Busse, Eva Kostadinova, Lorin Matthews, Constanze Liaw, Truell Hyde Spatial localization of waves traveling within media of sufficiently high disorder has been studied extensively due to its applicability to condensed matter physics, semiconductor physics, and material science. Complex plasma crystals~exhibit characteristic distance and time scales which are easily observable by video microscopy. As such, these strongly coupled many-particle systems are ideal for the study of localization phenomena. In this work, an $N$-body code simulating a 2D complex plasma crystal is used as an analog for a real crystalline medium. An equilibrium state has been achieved numerically producing a crystal with highly ordered hexagonal crystalline domains. Disorder in the medium is introduced by varying the prevalence of crystalline defects, the amount of thermal coupling, or the charge variance of the dust particles. In order to generate a travelling wave in the crystal, a randomly chosen dust particle is given a Gaussian kick. A recently developed spectral method is then used to determine the presence or absence of localization. The goal of our research is to demonstrate the potential for the complex plasma crystal to act as a macroscopic tool to study localization phenomena. [Preview Abstract] |
(Author Not Attending)
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CO7.00004: Submicron dust clouds for optical charge measurements Andre Melzer, Harald Krüger, Carsten Killer Dusty plasmas consist of particles immersed in gaseous plasmas. The charge of the dust particles that they attain due to the inflow of plasma electrons and ions is a pivotal parameter: the particle charge determines the interaction with the plasma species and among the particles themselves. So far, charge measurements exploit the dust-plasma interaction or the analysis of wave-motion of the particles. Recently, a completely different, optical approach has been suggested, where the charge is extracted from the wavelength shift of the optical phonon resonance due to the charge-modified polarizability of the material. This ``detuning'' of the phonon resonance increases with particle charge and is prominent for nanometer-sized particles. In first experiments, we demonstrate the trapping of nanometric dust particles made of Al$_2$O$_3$. The dust is injected by a gas stream into the plasma. Clouds of particles with diameters around 100~nm can be trapped in the bulk plasma of the discharge. There, the phonon resonance of Al$_2$O$_3$ is measured in-situ in an FTIR spectrometer. [Preview Abstract] |
Monday, October 31, 2016 2:48PM - 3:00PM |
CO7.00005: New Large Diameter RF Complex Plasma Device John Meyer, Volodymyr Nosenko, Hubertus Thomas The Complex Plasma Research Group at the German Aerospace Center (DLR) in Oberpfaffenhofen has built a new large diameter rf plasma setup for dusty plasma experiments. The vacuum chamber is a stainless steel cylinder 0.90 m in diameter and 0.34 m in height with ports for viewing and measurement. A 0.85 m diameter plate in about the center serves as a powered electrode (13.56 MHz) with the chamber walls as the ground. It is pumped on by one of two Oerlikon turbo pumps with a pumping rate of 1100 l/s or 270 l/s. Argon gas is admitted into the chamber by an MKS mass flow meter and pumping is regulated by a butterfly valve to set pressure for experiments. A manual dropper is used to insert dust into the plasma. The dust is illuminated horizontally by a 660 nm 100 mW laser sheet and viewed from above by a Photron FASTCAM 1024 PCI camera. A vertical laser sheet of 635 nm will be used for side imaging. So far, single-layer plasma crystals of up to 15000 particles have been suspended. The particle velocity fluctuation spectra were measured and from these, the particle charge and screening length were calculated. Future experiments will explore the system-size dependence of the plasma crystal properties. [Preview Abstract] |
Monday, October 31, 2016 3:00PM - 3:12PM |
CO7.00006: The Ion Wakefield Inside a Glass Box. Mudi Chen, Lorin Matthews, Truell Hyde The formation of an ion wakefield downstream of dust particles in a complex plasma sheath has long been understood to have strong implications on their structure, stability and dynamics . The presence of the ion wake introduces interesting phenomena such as charge reduction on downstream particles and asymmetric interaction forces between upstream and downstream particles. Many of the self-ordered dust particle structures observed in complex plasma experiments are the result of the combination of the ion-wakefield and the external confinement; unfortunately, few experimental measurements isolating the effect of the wakefield have been conducted. In this experiment, 1-D dust particle structures (i.e., vertically aligned particle chains) are formed in a GEC RF reference cell within a glass box sitting on the powered lower electrode. A diode pumped, solid-state laser is used to perturb individual particles within the particle chain, allowing a map of the ion wakefield inside the glass box to be generated. The implications of these results will be discussed. [Preview Abstract] |
Monday, October 31, 2016 3:12PM - 3:24PM |
CO7.00007: First passage problem of dust charge fluctuations Babak Shotorban Starting from a given grain charge, how long does it take for the grain to reach a specified charge? The answer is concerned with the first passage problem, which is of particular interest in systems with metastable fluctuations with two or more macrostates (Van Kampen 2007). A recent study (B. Shotorban Phys. Rev. E 92, 043101) shows that grain charge fluctuations could be metastable when the secondary electron emission (SEE) mechanism is active. The first-passage time in the grain charging system is investigated and discussed for various scenarios. Specially, the time scales associated with the transition of the system from one macrostate to another are characterized for metastable fluctuations. [Preview Abstract] |
Monday, October 31, 2016 3:24PM - 3:36PM |
CO7.00008: A Quick Method to Determine the Charge on Dust Particles in a Complex Plasma. Zhiyue Ding, Ke Qiao, Lorin Matthews, Truell Hyde The individual levitation height for two, paired dust particles (each having a diameter of 8.89 $\mu $m and mass of 5.55e-13 kg as stated by the manufacturer) was measured inside both 1.0-inch and a 0.5-inch glass boxes, placed on the lower powered electrode within a GEC RF reference cell. These heights were compared to that of a single particle levitated under identical conditions, with the equilibrium position of the upper particle within the pair found to be slightly higher than that of the single particle. The measured difference between the two is small (and assumed to be caused by the repulsive interaction between the dust particles), so although the top particle deviates slightly from its equilibrium position (i.e., the equilibrium position acquired by a single particle under the same conditions) it may still be assumed to be influenced by the normal set of restoring forces. Assuming a simplified Coulomb interparticle interaction, applying a standard force balance calculation provides the charge for each dust particle. In this manner, the particle charge was measured for rf powers between 250 mV and 700 mV at a constant gas pressure of 40 mTorr. The resulting data shows the particle dust charge to remain relatively stable, varying less than 10{\%} from an average charge of 14,000 e-, for powers between 450 mV and 700 mV. However, below 450mV the measured particle charge fluctuates dramatically. The implications of these results will be examined and discussed. [Preview Abstract] |
Monday, October 31, 2016 3:36PM - 3:48PM |
CO7.00009: Temperature Measurement for Dust Particles in a GEC Reference Cell. Jie Kong, Ke Qiao, Lorin Matthews, Truell Hyde The thermal motion of a dust particle levitated in a plasma chamber is similar to that described by Brownian motion in many ways. The primary differences between a dust particle in a plasma system and a free Brownian particle is that in addition to the random collisions between the dust particle and the neutral gas atoms, there are electric field fluctuations, dust charge fluctuations, and correlated motions from unwanted continuous signals originating within the plasma system itself. Correlated motion cannot be qualified as random motion, and therefore should not be included in a measurement of the dust temperature. In this presentation, we discuss how to separate random and coherent motion of a dust particle confined in a glass box within a GEC radio frequency reference cell. Dust particle fluctuation data are obtained experimentally and analyzed using the mean square displacement and other techniques, and temperatures obtained by various methods are compared. [Preview Abstract] |
Monday, October 31, 2016 3:48PM - 4:00PM |
CO7.00010: Spectral Approach to Anderson Localization in a Disordered~2D Complex Plasma Crystal. Eva Kostadinova, Constanze Liaw, Lorin Matthews, Kyle Busse, Truell Hyde In condensed matter, a crystal without impurities acts like a perfect conductor for a travelling wave-particle. As the level of impurities reaches a critical value, the resistance in the crystal increases and the travelling wave-particle experiences a transition from an extended to a localized state, which is called Anderson localization. Due to its wide applicability, the subject of Anderson localization has grown into a rich field in both physics and mathematics. Here, we introduce the mathematics behind the spectral approach to localization~in infinite disordered systems and provide physical interpretation in context of both quantum mechanics and classical physics. We argue that the~spectral analysis is an important contribution to localization theory since it avoids issues related to the use of boundary conditions, scaling, and perturbation.~To test accuracy and applicability we apply the spectral approach~to the case of a 2D hexagonal complex plasma crystal used as a macroscopic analog for a graphene-like medium. Complex plasma crystals~exhibit characteristic distance and time scales, which are easily observable by video microscopy. As such, these strongly coupled many-particle systems are ideal for the study of localization phenomena. The goal of this research is to both expand the spectral method into the classical regime and show the potential of complex plasma as a macroscopic tool for localization experiments. [Preview Abstract] |
Monday, October 31, 2016 4:00PM - 4:12PM |
CO7.00011: An equation for pressure of a two-dimensional Yukawa liquid Yan Feng, Wei Li, Qiaoling Wang, Wei Lin, John Goree, Bin Liu Thermodynamic behavior of two-dimensional (2D) dusty plasmas has been studied experimentally and theoretically recently. As a crucial parameter in thermodynamics, the pressure of dusty plasmas arises from frequent collisions of individual dust particles. Here, equilibrium molecular dynamical simulations were performed to study the pressure of 2D Yukawa liquids. A simple analytical expression for the pressure of a 2D Yukawa liquid is found by fitting the obtained pressure data over a wide range of temperatures, from the coldest close to the melting point, to the hottest about 70 times higher than the melting points. The obtained expression verifies that the pressure can be written as the sum of a potential term which is a simple multiple of the Coulomb potential energy at a distance of Wigner-Seitz radius, and a kinetic term which is a multiple of the one for an ideal gas. Dimensionless coefficients for each of these terms are found empirically, by fitting. The resulting analytical expression, with its empirically determined coefficients, is plotted as isochors, or curves of constant area. These results should be applicable to 2D dusty plasmas. [Preview Abstract] |
Monday, October 31, 2016 4:12PM - 4:24PM |
CO7.00012: Dynamics of bounded self-organized dust flow in a complex plasma Modhuchandra Laishram, Dr. Devendra Sharma, Prof. P. K. Kaw Micron sized, highly charged, dust particles constitute a complex medium that exhibits fluid-like behavior when suspended in a quasineutral plasma either using electrostatic levitation or under the micro-gravity conditions. Although the dust particles interact strongly via a partially screened Coulomb force, when subjected to drivers like plasma drag, thermophoratic force or gradients of plasma parameters, the dust fluid is driven to non equilibrium states and develops self organized flows representable by the standard hydrodynamic model [1]. The present analysis of self organized dust flow formations uses 2D fluid dynamics to recover the analytic dependence of the observables like flow shear at a curvilinear boundary and corresponding Reynolds number on the conventional dust transport coefficients for a bounded dust medium subjected to a volumetric drive. In the linear limit of the 2-dimensional Navier-Stokes flow regime of the medium, the effective boundary layer width is recovered to scale with the dust kinematic viscosity $\mu $ as $\delta $r $\approx \quad \mu $ 1/3 , while the effective Reynolds number follows Re $\approx \quad \mu \quad -$2/3 [2]. At relatively higher Reynolds number the dust flow structures show signatures of nonlinear effects requiring extension of the 2D fluid analysis to the nonlinear regime.\newline 1. Laishram, Sharma, and Kaw, Phys.of Plasma 21 073703(2014)\newline 2. Laishram, Sharma, and Kaw, Phys. Rev. E 91 063110(2015). [Preview Abstract] |
Monday, October 31, 2016 4:24PM - 4:36PM |
CO7.00013: The Interparticle Interaction Between a Vertically Aligned Dust Particle Pair in a Complex Plasma. Ke Qiao, Zhiyue Ding, Jie Kong, Lorin Matthews, Truell Hyde The interaction between dust particles is a fundamental topic in complex plasma. In experiments on earth, the interparticle interaction in the horizontal direction (i.e., perpendicular to the gravitational force) is generally recognized to be a Yukawa potential. However, the interaction in the vertical direction is much more complicated, primarily due to the ion flow in the plasma sheath. In this research, we introduce a non-intrusive method to study the interaction between a vertically aligned dust particle pair confined in a glass box placed on the lower powered electrode within a GEC reference cell. This system is investigated for varying rf powers to obtain the trend of the interparticle interaction strength, which is contrasted with theoretical results. Using spontaneous thermal fluctuations of the neutral gas as the only driving force, we obtain the normal mode spectra of the dust pair, revealing not only the oscillation frequencies, but also the vibration amplitudes of the normal modes. The interaction strength between the upper and lower particle is obtained quantitatively from these mode spectra, showing strong nonreciprocity in both the vertical and horizontal directions. It will also be shown that the resulting horizontal attractive force of the upper particle on the lower particle can be larger than the horizontal confinement produced by the glass box alone. [Preview Abstract] |
Monday, October 31, 2016 4:36PM - 4:48PM |
CO7.00014: Computational framework for nanoparticle growth in low-temperature plasmas Benjamin Santos, Fran\c{c}ois Vidal, Claude Boucher We propose a framework to study nanoparticle growth in low-temperature plasmas. This system represents a challenge because of complexity:nanoparticles can accumulate charge, coagulate and grow while strongly coupled with the plasma. In analogy with aerosol physics, we describe the nanoparticle model using a General Dynamics Equation. In order to follow the evolution of nanoparticle size and charge distribution we must partition it in representative sizes and charges for each point in the spatial domain. Thus, for each combination of charge and size we need to calculate a drift-diffusion equation. As a case of study, we considered a radio frequency capacitively coupled plasma with an Argon-Silane gas mixture. Using a time slicing approach\footnote{P. Agarwal,\textbf{Plasma Sources Sci. Technol.} 21(5)} we can separate the plasma calculations from nanoparticle model. Particle densities are calculated from a drift-diffusion equation with finite difference scheme and the flux calculated by a Scharfetter-Gummel method. Additionally,we decoupled the plasma density calculations and nanoparticle sources in chunks that can be solved using linear solvers with appropriate time step, instead of solving a coupled nonlinear system. Finally, applications to the proposed framework are discussed. [Preview Abstract] |
Monday, October 31, 2016 4:48PM - 5:00PM |
CO7.00015: Kinetics of fluid demixing in complex plasmas: Domain growth analysis using Minkowski tensors Alexander Böbel, Christoph Räth The demixing process of a binary complex plasma is analyzed and the role of distinct interaction potentials is discussed by using morphological Minkowski tensor (MT) analysis of the minority phase domain growth in a demixing simulated binary complex plasma. These MT methods are compared with previous results that utilized a power-spectrum method based on the time-dependent average structure factor. It is shown that the MT methods are superior to the previously used method in the sense of higher sensitivity to changes in domain size. By analysis of the slope of the temporal evolution of MT measures qualitative differences between the case of particle interaction with a single length scale compared to particle interactions with two different length scales (dominating long range interaction) are revealed. After proper scaling the graphs for the two length scale scenarios coincide, pointing towards universal behavior. Thus, Minkowski tensor analysis is likely to become a useful tool for further investigation of this (and other) demixing processes. It is capable to reveal (nonlinear) local topological properties, probing deeper than (linear) global power-spectrum analysis, however, still providing easily interpretable results founded on a solid mathematical framework. [Preview Abstract] |
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