Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session JO7: Dusty and Complex Plasmas |
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Chair: Ed Thomas, Auburn University Room: Rosen Centre Hotel Salon 7/8 |
Tuesday, November 13, 2007 2:00PM - 2:12PM |
JO7.00001: {\boldmath $\Gamma$} G. Morfill $\Gamma$, the ratio interaction energy to kinetic energy, is a key quantity in strongly coupled plasma physics. Unfortunately it is also one of the most difficult properties to measure -especially locally at the kinetic level. We combine theory, numerical simulations and experimental results to show how to measure this important quantity in `complex (dusty) plasmas'. [Preview Abstract] |
Tuesday, November 13, 2007 2:12PM - 2:24PM |
JO7.00002: Self-diffusion and random motion in a strongly-coupled dusty-plasma: experiment Bin Liu, J. Goree Self-diffusion and random motion in a two-dimensional (2D) dusty plasma were experimentally measured. A single-layer suspension of microsphere particles was levitated in an rf plasma, forming a strongly-coupled dusty plasma with a Yukawa interparticle potential. A pair of cw laser beams moves around the suspension and exerts radiation pressure forces on particles, providing an external control on particle temperature. A dusty-plasma solid is heated to form a dusty-plasma liquid. Particles are imaged, yielding an accurate measurement of particle position and velocity. Random motion is characterized by mean-square displacement (MSD), yielding an estimate of a diffusion coefficient, $D$. Dependence of $D$ on temperature $T$ is dominated by a power law at high $T$ and an Arrhenius form at low $T$. Particle random motion obeys Gaussian statistics at high $T$, but not at low $T$ as indicated by a probability distribution function (PDF) that resembles a kappa distribution. The PDF is self-similar for times longer than the ballistic time scale. [Preview Abstract] |
Tuesday, November 13, 2007 2:24PM - 2:36PM |
JO7.00003: Self-diffusion and random motion in a strongly-coupled dusty-plasma: MD simulation John Goree, Bin Liu, Zoltan Donk\'{o}, Peter Hartmann A dusty plasma as in the accompanying talk by Liu and Goree is modeled as a 2D Yukawa system, with particles that are constrained to move on a plane and interact with a potential $U (r)=Q\exp(-r/\lambda_{\rm D})/r$, where $Q$ is particle charge and $\lambda_{\rm D}$ is a screening length. We performed two independent molecular dynamics (MD) simulations that are frictionless and under equilibrium conditions, unlike the experiment, which is nonequilibrium driven-dissipative and anisotropic. As in the experiment, we tested the long-time behavior of MSD and VACF. We tested the choice of system size and thermostat on the characterization of diffusion. We compare the simulation MSD to the experiment, finding a match in the ballistic limit, but not in the diffusion limit. The MSD is much more superdiffusive in the simulation than in the experiment. For both the simulation and experiment, motion obeys Gaussian statistics at high $T$, but not at low $T$. [Preview Abstract] |
Tuesday, November 13, 2007 2:36PM - 2:48PM |
JO7.00004: Laser manipulation of dust particles in Coulomb balls Tim Flanagan, J. Goree A dusty plasma is a partially ionized gas that contains small particles of solid matter, or dust. Dust particles become charged by collecting electrons and ions from the plasma, which can cause them to interact with a large potential energy in comparison with their thermal energy. This strong coupling causes dust particles to arrange themselves as a solid or liquid. One type of dusty plasma is the recently discovered Coulomb ball (Arp {\it et al.}, PRL 2004), which is a 3D spherically shaped suspension of dust. The ball becomes trapped due to a balance of three forces: the electric force due to the plasma electric field and a thermophoretic force resulting from a temperature gradient in the gas, which are both directed upward, and gravity. In this experiment, a glow-discharge plasma is used to confine $4.8~\mu \rm{m}$ microspheres forming a Coulomb ball inside a glass box atop a heated electrode. We report experimental results where radiation pressure, from one or more laser beams, is used to push some of the dust particles, creating a flow and reshaping the Coulomb ball. [Preview Abstract] |
Tuesday, November 13, 2007 2:48PM - 3:00PM |
JO7.00005: Heat transport in a two-dimensional complex (dusty) plasma at melting conditions V. Nosenko, A.V. Ivlev, S. Zhdanov, G. Morfill, J. Goree, A. Piel The heat transport in a two-dimensional complex (dusty) plasma undergoing a phase transition was studied experimentally. A single layer of highly charged polymer microspheres was suspended in a plasma sheath. In the absence of manipulation, the suspension forms a 2D triangular lattice. To melt this lattice and form a liquid, we used a laser-heating method. Two focused laser beams were moved rapidly around in the monolayer. The kinetic temperature of the particles increased with the laser power applied, and above a threshold a melting transition occurred. We used video microscopy for direct imaging and particle tracking. The spatial profiles of the particle kinetic temperature were calculated. Using the heat transport equation with an additional term to account for the energy dissipation due to the gas drag, we analyzed the temperature profiles to find a thermal conductivity, which did not depend on temperature. [Preview Abstract] |
Tuesday, November 13, 2007 3:00PM - 3:12PM |
JO7.00006: Investigation of dust vertical dispersion relations Jie Kong, Ke Qiao, Truell Hyde The dust acoustic wave (DAW) was first theoretically predicted in 1990 by Rao et al. [Ref] and later observed experimentally by Barkan, et al. [Ref. 2], Pieper and Goree [Ref. 3] and others. The charge on the dust, Debye length and various other fundamental complex plasma parameters can be obtained experimentally through measurement of the DAW. Since under normal laboratory conditions, ordered structures formed within a complex plasma are generally two dimensional in nature, the majority of experiments to date examining such a system's dispersion relationships have been conducted on the horizontal plane. We will present an experimental method providing for a vertical dispersion relationship measurement, and present corresponding data. References [1]. N. N. Rao, P. K. Shukla, and M. Y. Yu, ``Dust-acoustic waves in dusty plasmas,'' Planet. Space Sci. 38, 543-546 (1990). [2]. A. Barkan, R. L. Merlino, and N. D'Angelo, ``Laboratory observation of the dust-acoustic wave mode,'' Phys. Plasmas, 2, 3563-3565, 1995. [3]. J. B. Pieper, J. Goree, ``Dispersion of Plasma Dust Acoustic Waves in the Strong-Coupling Regime,'' Phys. Rev. Lett., 77, 3137-3140, 1996. [Preview Abstract] |
Tuesday, November 13, 2007 3:12PM - 3:24PM |
JO7.00007: Determination of Plasma Sheath and Dust Parameters from Dust Particle Oscillation Modes Ke Qiao, Jorge Carmona-Reyes, Bernard Smith, Mike Cook, Jimmy Schmoke, Truell Hyde The fundamental parameters of a complex dusty plasma system, including particle charge and dust Debye length, can be determined from the thermally excited oscillation modes of an arbitrary number of dust particles (either a dust cluster or plasma crystal) confined on a 2D plane within the plasma sheath produced above the lower electrode of a GEC reference cell [Ref. 1-2]. This paper will discuss an experimental technique allowing the strength of the confining potential well on the horizontal direction to be determined in the same manner. This technique will be further applied to systems of dust grains comprised of both melamine formaldehyde and ferromagnetic monodisperse particles. [Preview Abstract] |
Tuesday, November 13, 2007 3:24PM - 3:36PM |
JO7.00008: Effect of Dipole-Dipole Charge Interactions on the Coagulation of Fractal Aggregates Lorin Matthews, Truell Hyde The coagulation of charged aggregates consisting of micron-sized dust grains is an important process in fields as diverse as planet formation and plasma processing of silicon wafers for computer chips. The coagulation rate is of particular interest in the plasma and radiative environment of a protoplanetary disk around a newly formed star, as recent evidence suggests that planet formation is very efficient and takes place on a relatively short time scale. Although it would seem intuitively obvious that like-charged grains would repel each other and reduce coagulation rates, the distribution of charge over the fractal structure of the aggregates can play a role in increasing the coagulation rate. In this study, we use a self-consistent N-body code to model the dipole-dipole interactions of charged aggregates during the coagulation process. The charge on the aggregates (monopole and dipole moments) is calculated using a heuristic scheme based on a detailed charging model for fractal aggregates using a modified orbital-motion limited theory. [Preview Abstract] |
Tuesday, November 13, 2007 3:36PM - 3:48PM |
JO7.00009: Modeling of small dust Coulomb crystals in PECVD reactors Mohammad Davoudabadi, Beniamino Rovagnati, Farzad Mashayek Modeling of dust crystal structures in the confining potential wells of laboratory non-equilibrium plasmas is of value from both aspects of theory and application. Motivated by simulation of process of nano-particle coating via Plasma Enhanced Chemical Vapor Deposition (PECVD) technique, whose underlying physics coincides with the dust contamination in PECVD reactors of microelectronics industry, we first simulate the plasma phase in a cylindrical PECVD reactor employing the local-field drift-diffusion model. Using a Lagrangian approach, we then three-dimensionally track a few number of interacting particles in a one-way coupling manner. After the particles reach their equilibrium state, their various multi-shell configurations are directly compared to the pertinent experiments. Meanwhile, a particle along with the ion focusing effect due to the ion flow in the sheath region is modeled as a superposition of the uncompensated residual plasma-shielded monopole, plus a plasma-shielded electric dipole. It is shown that the proposed model can successfully predict the vertically-aligned morphology of multi-layer arrangements of particles. [Preview Abstract] |
Tuesday, November 13, 2007 3:48PM - 4:00PM |
JO7.00010: PIC-MCC study of particle charging in a collisional flowing plasma Beniamino Rovagnati, Mohammad Davoudabadi, Giovanni Lapenta, Farzad Mashayek In the framework of both dusty plasmas and material processing technologies for nanoparticles such as Plasma Enhanced Chemical Vapor Deposition (PECVD), the charging process of a single grain is one of the most important and most studied phenomena. It determines the particle interactions with plasma electrons and ions, with electromagnetic fields, between the particles themselves, and strongly relates to the particle coating growth rate in PECVD processes. In the present study, we model the charging phenomenon of a single particle which is immersed in a collisional flowing plasma via Particle-In-Cell (PIC) method. Both ions and electrons are fully tracked as computational particles and collisional charge-exchange process is accounted for by use of the Collisional Monte Carlo (MCC) approach. We consider a particle radius of the order of the electron Debye length. Particle potential, plasma species distributions and ion drag force are calculated under different operating conditions, such as plasma density and plasma drift velocities. [Preview Abstract] |
Tuesday, November 13, 2007 4:00PM - 4:12PM |
JO7.00011: Density profile and breathing mode of strongly correlated spherical Yukawa plasmas Christian Henning, Kenji Fujioka, Patrick Ludwig, Michael Bonitz The structure of ``Yukawa balls,'' i.e. spherical 3D dust crystals, which recently have been produced [1], is well explained by computer simulations of charged Yukawa interacting particles within an external parabolic confinement [2]. Dynamical properties (e.g. breathing mode) of these systems were investigated by experiment, simulations as well as theoretically by using the ansatz of a uniform ground state density [3]. Here we show analytically that screening has a dramatic effect on the density profile which decreases away from the center [4,5] and which is in excellent agreement with MD simulations of Yukawa balls. This result is used to improve former calculations of the breathing mode [6].\newline References\newline [1] O. Arp et al. Phys. Rev. Lett. 93, 165004 (2004)\newline [2] M. Bonitz et al., Phys. Rev. Lett. 96, 075001 (2006)\newline [3] T. E. Sheridan, Phys. Plasmas 13, 022106 (2006)\newline [4] C. Henning et al., Phys. Rev. E 74, 056403 (2006)\newline [5] C. Henning at al., Phys. Rev. E (2007)\newline [6] C. Henning at al., submitted for publication [Preview Abstract] |
Tuesday, November 13, 2007 4:12PM - 4:24PM |
JO7.00012: Nonlinear Structures in Very Dense Plasmas Padma Kant Shukla, Bengt Eliasson We present numerical studies of the formation and dynamics of dark solitons and vortices in very dense quantum electron plasmas. The electron dynamics in the latter is governed by a pair of equations comprising the nonlinear Schr\"odinger and Poisson system of equations, which conserves the number of electrons as well as their momentum and energy. The present governing equations in one spatial dimension admit stationary solutions in the form a dark envelope soliton. The dynamics of the latter reveals its robustness. Furthermore, we numerically demonstrate the existence of cylindrically symmetric two-dimensional quantum electron vortices, which survive during collisions by forming vortex pairs. The nonlinear structures presented here may serve the purpose of transporting information at quantum scales in ultracold micromechanical systems and dense plasmas, such as those created during intense laser-matter interactions. [Preview Abstract] |
Tuesday, November 13, 2007 4:24PM - 4:36PM |
JO7.00013: The Relativistic Feedback Mechanism of Electrical Breakdown. Hamid Rassoul, Joseph Dwyer In 2003, a new electrical breakdown mechanism, referred to as Relativistic Feedback, was introduced. Relativistic Feedback involves the production of runaway electron avalanches by positive feedback from runaway positrons and energetic photons and allows runaway discharges in gases to become self-sustaining, dramatically increasing the flux of runaway electrons, the accompanying high-energy radiation, and resulting ionization. Based upon detailed Monte Carlo calculations, properties of Relativistic Feedback are presented. It will be shown that once Relativistic Feedback commences, electrical breakdown will occur, and the ambient electric field, extending over cubic-kilometers, will be discharged in as little as 20 microseconds. Furthermore, the flux of energetic electrons and x-rays generated by this mechanism can exceed the flux generated by the standard relativistic runaway electron process by a factor of 10 trillion, making Relativistic Feedback a good candidate for explaining Terrestrial Gamma-ray Flashes and other high-energy phenomena observed in the Earth's atmosphere. [Preview Abstract] |
Tuesday, November 13, 2007 4:36PM - 4:48PM |
JO7.00014: The role of thermal and runaway electrons in lightning initiation M. Bakhtiari, J. R. Dwyer, H.K. Rassoul, Z. Saleh Relativistic runaway breakdown acting on extensive cosmic-ray air showers is one of the proposed mechanisms for solving the mystery of lightning initiation. In this mechanism an air shower creates an avalanche of runaway electrons in neutral air, leaving behind a weakly ionized plasma with a tiny population of thermal electrons. Some researchers have suggested that this weakly ionized plasma produces enough conductivity to develop a lightning leader. In this presentation, we revisit the dynamics of runaway electrons in electrified air, and we obtain a pitch angle scattering term in the single-particle trajectory in momentum- space. This term considerably changes the picture of the single-particle runaway electron trajectory in neutral gases, illustrating the importance of elastic scattering for runaway electron calculations. In addition, we have used a Monte Carlo simulation to investigate whether the number of thermal electrons generated during a runaway electron avalanche is enough to induce the necessary conductivity for developing the lightning leader. [Preview Abstract] |
Tuesday, November 13, 2007 4:48PM - 5:00PM |
JO7.00015: Microwave Plasma Confinement and Alfven Wave Ion Heating Jun-Chieh Wang, Jang-Yu Hsu An incident electromagnetic wave with its reflection from an opposite mirror forming a standing wave can easily be absorbed by electrons [1,2] through linear mode conversion into the Langmuir wave [3]. The collisionless electrons at more than 10KeV responding to the ac electric field could excite an ac current that pinches the plasma and results in a plasma equilibrium. Moreover, the oscillatory electric field may excite an Alfven wave. Since half of the Alfven wave energy is in the ion flow energy, the ion kinetic energy can thus be increased with randomization in the flow velocity. The theory is being developed to compare with the experimental details. \newline \newline [1] K. V. Alexandrov, L. P. Grachev, I. I. Esakov, V. V. Fedorov, K. V. Khodataev, Zhurnal Tekhnicheskoi Fiziki, Vol. 76, No. 11, 2006. \newline [2] L. P. Grachev, I. I. Esakov, K. V. Khodataev , Technical Physics Vol. 48, No. 5, p.557, May 2003. \newline [3] Thomas H. Stix, Phys. Rev. Lett., 15, 878, 1965 [Preview Abstract] |
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