Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session TO5: Strongly-coupled/Dusty Plasmas |
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Chair: James Danielson, University of California, San Diego Room: 202AB |
Thursday, October 26, 2017 9:30AM - 9:42AM |
TO5.00001: Structural and dynamical properties of recombining ultracold neutral plasma Sanat Kumar Tiwari, Nathaniel R. Shaffer, Scott D. Baalrud An ultracold plasma (UCP) is an evolving collection of free charges and bound charges (Rydberg atoms). Over time, bound species concentration increases due to recombination. We present the structural and dynamical properties of an evolving UCP using classical molecular dynamics simulation. Coulomb collapse is avoided using a repulsive core with the attractive Coulomb potential. The repulsive core size controls the concentration of bound states, as it determines the depth of the potential well between opposite charges. We vary the repulsive core size to emulate the quasi-static state of plasma at different time during the evolution. Binary, chain and ring-like bound states are observed in the simulation carried out at different coupling strengths and repulsive core size. The effect of bound states can be seen as molecular peaks in the radial distribution function (RDF). The thermodynamic properties associated with the free charges can be analyzed from RDF by separating free from bound states. These bound states also change the dynamical properties of the plasma. The electron velocity auto-correlation displays oscillations due to the orbital motion in bound states. These bound states act like a neutral species, damping electron plasmon modes and broadening the ion acoustic mode. [Preview Abstract] |
Thursday, October 26, 2017 9:42AM - 9:54AM |
TO5.00002: Radial Distribution Functions of Strongly Coupled Two-Temperature Plasmas Nathaniel R. Shaffer, Sanat Kumar Tiwari, Scott D. Baalrud We present tests of three theoretical models for the radial distribution functions (RDFs) in two-temperature strongly coupled plasmas. RDFs are useful in extending plasma thermodynamics and kinetic theory to strong coupling, but they are usually known only for thermal equilibrium or for approximate one-component model plasmas. Accurate two-component modeling is necessary to understand the impact of strong coupling on inter-species transport, e.g., ambipolar diffusion and electron-ion temperature relaxation. We demonstrate that the Seuferling-Vogel-Toeppfer (SVT) extension\footnote{P.~Seuferling, J.~Vogel, and C.~Toepffer, Phys.~Rev.~A \textbf{40} (1989).} of the hypernetted chain equations not only gives accurate RDFs (as compared with classical molecular dynamics simulations), but also has a simple connection with the Yukawa OCP model. This connection gives a practical means to recover the structure of the electron background from knowledge of the ion-ion RDF alone. Using the model RDFs in Effective Potential Theory\footnote{S.~D.~Baalrud and J.~Daligault, Phys.~Rev.~Lett.~\textbf{100} (2013)}, we report the first predictions of inter-species transport coefficients of strongly coupled plasmas far from equilibrium. [Preview Abstract] |
Thursday, October 26, 2017 9:54AM - 10:06AM |
TO5.00003: Equilibration rates in a dual-species ultracold neutral Ca/Yb plasma Tucker Sprenkle, Adam Dodson, Quin McKnight, Scott Bergeson We study energy relaxation in a strongly-coupled neutral plasma of calcium and ytterbium ions at temperatures near 1 K. The ion temperature is determined by disorder-induced heating, and denser plasmas have higher temperatures. The electron temperature is determined by the wavelength of the ionizing laser, and is typically 20 to 200 K. We control the plasma stoichiometry and overall plasma density in order to vary the temperatures of the two ion species. We control the electron temperature to adjust the electron screening length and the plasma expansion rate. We will present measurements of energy relaxation rates in this mixed-species plasma. [Preview Abstract] |
Thursday, October 26, 2017 10:06AM - 10:18AM |
TO5.00004: Abstract Withdrawn
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Thursday, October 26, 2017 10:18AM - 10:30AM |
TO5.00005: Strongly coupled plasmas from compressed gases with controllable coupling Gautham Dharuman, Liam G. Stanton, Michael S. Murillo We propose a method for creating strongly coupled plasmas (SCPs) with controllable coupling and relatively low density. Strong coupling in plasmas created from neutral gases is hindered by the process of disorder induced heating (DIH), as shown in ultracold neutral plasmas (UCNPs) [1]. Mitigating DIH requires the neutral system to be pre-correlated [2]. Using molecular dynamics simulations we examine the formation of SCPs from cool gases that are pre-correlated using high gas pressures. By changing the initial pressure over orders of magnitude, we examine the variations in continuum lowering, ionization state, Coulomb coupling, degeneracy, Coulomb collisional processes, and species partial pressures. We are able to vary and control the effective Coulomb coupling over a wide range and much higher than the measured values in UCNPs [2]. This method has significant advantages over experiments in dense plasmas because of the lower energy-density environments that are produced. Further, the method has the advantage of varying the properties listed above by varying the electron and ion temperatures independently.[1] Phys. Rev. Lett. 83, 4776 (1999) [2] Phys. Rev. Lett. 87, 115003 (2001) [Preview Abstract] |
Thursday, October 26, 2017 10:30AM - 10:42AM |
TO5.00006: Coupling of non-crossing wave modes in a two-dimensional plasma crystal John Meyer, Ingo Laut, Sergey Zhdanov, Vladimir Nosenko, Hubertus Thomas We report an experimental observation of coupling of the transverse vertical and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex plasma crystal in the absence of mode crossing. A new large diameter (90 cm) rf plasma chamber was used to suspend the plasma crystal. The observations are confirmed with molecular-dynamics simulations. The coupling manifests itself in traces of the longitudinal mode in the measured transverse vertical spectra and vice versa. We calculate the expected ratio of the trace to the principal mode with a theoretical analysis of the modes in a crystal with finite temperature and find good agreement with the experiment and simulations. [Preview Abstract] |
Thursday, October 26, 2017 10:42AM - 10:54AM |
TO5.00007: Lattice wave transport in a 2D complex plasma graphene analogue. Eva Kostadinova, Constanze Liaw, Lorin Matthews, Kyle Busse, Truell Hyde We present a numerical study of Anderson localization in à 2D complex plasma crystal. In the classical regime, Anderson localization is the absence of diffusion of certain wave frequencies due to scattering from lattice defects. The appropriate condition for localization is (known as the modified Ioffe-Regel criterion), where is the wavevector and is the mean free path. As , the wave cannot perform even a single oscillation between successive interactions with defects, which eliminates the propagation. Here we examine transport of in-plane lattice waves through a 2D dusty plasma crystal, which is used as a graphene analogue. The lattice disorder is controlled in two ways: i) through variation of particle size (and thus particle density and interparticle separation) and ii) through variation of the radial confinement force. This allows us to compare the transport properties of the crystal in the weak and strong interaction regimes, which provides valuable information on the effects of strong interactions in the crystal. [Preview Abstract] |
Thursday, October 26, 2017 10:54AM - 11:06AM |
TO5.00008: Mode spectra measurement of particle-particle interaction and upstream potential around dust particles in a plasma sheath. Ke Qiao, Zhiyue Ding, Jie Kong, Lorin Matthews, Truell Hyde The interaction potential between dust particles is a fundamental topic in complex plasmas. It is of particular interest for particles in the plasma sheath due to modification of the potential around a dust particle by the ion flow. In this research, we introduce a non-intrusive mode spectra method [1] to study the interaction between a vertically aligned dust particle pair confined in a glass box in a GEC reference cell. The interaction strength between the two particles is measured simultaneously in both the vertical and horizontal directions. The results show an interaction with strong nonreciprocity in both directions and gives a quantitative value for the horizontal attraction on the bottom particle. The method also finds an upstream potential with effective screening length in the vertical direction $\lambda_{\mathrm{v}}$ greater than $\lambda_{\mathrm{h}}$ in the horizontal direction. This is in agreement with previous predictions [2] and has to our knowledge, never before been observed experimentally. [1] Ke Qiao, Zhiyue Ding, Jie Kong, Mudi Chen, Lorin S. Matthews, Truell W. Hyde \underline {\textbf{arXiv:1705.01982}} [2] P. Ludwig, W. J. Miloch, H. K. Ahlert, and M. Bonitz, New Journal of Physics, 14 053016 (2012). [Preview Abstract] |
Thursday, October 26, 2017 11:06AM - 11:18AM |
TO5.00009: Dust particle pair correlation functions and the non-linear effect of interaction potentials. Jie Kong, Ke Qiao, Lorin Matthews, Truell Hyde Dust temperature is a measure of the energy of the stochastic motion of a dust particle, which is a result of the combination of Brownian motion and fluctuations in between the dust charge and the confining electric field. This presentation will provide results of our recent investigation into the relationship between the dust particle temperature as derived using two different analysis techniques: the mean square displacement and the distribution of displacements obtained from the random motion of the dust particle. Experimental results indicate that the harmonic confinement potential acting on the dust particle can be obtained by combining the two methods, allowing the non-linear effect of the confining force to be investigated. [Preview Abstract] |
Thursday, October 26, 2017 11:18AM - 11:30AM |
TO5.00010: Nonlinear response of vertical particle chains to driven oscillations. Zhiyue Ding, Ke Qiao, Jie Kong, Lorin Matthews, Truell Hyde Vertical chain structures of two or more particles were formed inside a glass box placed on the lower electrode of a modified GEC reference cell. Vertical oscillations of the particles were driven by a sinusoidal potential applied to the lower electrode, and the particle response was studied for various driving parameters. While the particle response generally increases linearly with the driving amplitude, a range of driving amplitudes was found where the particle response is inversely proportional to the driving amplitude. The specific range can vary depending on the experiment parameters. This work explores the possibility that this behavior is due to two regions within the plasma sheath and the different characteristics of the electric field in each region. [Preview Abstract] |
Thursday, October 26, 2017 11:30AM - 11:42AM |
TO5.00011: The Relationship between Dust Particle Structures and Confinement. Mudi Chen, Jie Kong, Ke Qiao, Jorge Carmona-Reyes, Lorin Matthews, Truell Hyde The structure of dust particle systems immersed in plasma is determined by both the particle-particle interaction and the external confinement. Here we present recent experimental results obtained from exploring the relationship between the external confinement and the symmetry of the structures formed by the dust particles. Various structures such as vertical chains, zigzag and helical structures, and horizontal layers have previously been formed experimentally [1] using varying confinement methods (e.g. a circular cutout placed on the lower electrode and a 1/2or 1\textunderscore glass box placed on the lower electrode). In the case at hand, after forming a specific structure single dust particles were used as probes to map the local confinement allowing determination of the ratio between the horizontal and vertical confinement. [1] Truell Hyde, Jie Kong and Lorin Matthews, Physical Review E,87 053106 (2013). [Preview Abstract] |
Thursday, October 26, 2017 11:42AM - 11:54AM |
TO5.00012: Steady equilibrium co-rotating dust vortices in complex plasma Modhuchandra Singh Laishram, Devendra Sharma, kaw P.K. Dust clouds suspended in a plasma represent the simplest model for various living/active systems of nature which are inherently complex and thermodynamic non-equilibrium. Dynamics of such dust clouds confined in an axis symmetric cylindrical setup and in dynamic equilibrium with the background plasma is analyzed using hydrodynamic formulation for wide range of Reynolds numbers(Re). It revealed that any non-conservative forces associated with a species in a complex flow causes vortex flow of another slowly moving species in the system. Also in the nonlinear regimes(high Re), the dust flow structure mainly depend on the Re and aspect ratio ($L_{z}/L_{r}$) of the confined domain. For ($L_{z}:L_{r}\ge1$), the flow structure is characterized by symmetric and elongated circulation at linear regime (low Re), and is turned into new antisymmetric pattern in nonlinear regime (high Re). Further increase in Re produce a spontaneous structural change through a critical parameter Re* by the nonlinear phenomena called structural bifurcation. Then the flow structure spontaneously turn into a system of identical structure co-rotating vertices's of almost uniform core region and surrounded by shear layers.\\ \\1. Laishram, Sharma, and Kaw, Phys. of Plasma 21 073703(2014).\newline 2. Laishram, Sharma, and Kaw, Phys. Rev. E 91 063110(2015).\newline 3. Laishram, Sharma, Prabal and Kaw, Phys. Rev. E 95 033204(2017). [Preview Abstract] |
Thursday, October 26, 2017 11:54AM - 12:06PM |
TO5.00013: Interparticle / Interchain Forces in Field-Aligned Chains within a Complex Plasma. Truell Hyde, Lorin Matthews, Peter Hartmann, Oleg Petrov, Vladimir Nosenko, Marlene Rosenberg, Jie Kong, Ke Qiao Since predicted in 1934, various Wigner structures have been observed experimentally. To date, most have assembled under the presence of external system confinement, making the fundamental physics behind these correlation driven effects difficult to determine. Complex plasmas have proven a versatile analog for the study of such systems, particularly where global behavior is determined by the combined effect of the particles' low temperature/kinetic energy, interparticle interaction, global/local confinement and streaming ion flow. Of these the ion wakefield force, although of fundamental importance, is generally weaker than the others leaving its effects partially masked by gravity for terrestrial experiments. In this talk, a recently funded NASA/NSF project proposing examination of field-aligned chains formed in PK-4 microgravity experiments, where the ion flow and resulting interparticle potential can be controlled by tuning an alternating DC bias, will be discussed. [Preview Abstract] |
Thursday, October 26, 2017 12:06PM - 12:18PM |
TO5.00014: Molecular Dynamics Simulations of Magnetized Dusty Plasmas C. A. Romero-Talamas, E. M. Bates, W. J. Birmingham, W. F. Rivera, R. P. Smith, M. Lacarra Molecular Dynamics (MD) simulations of dusty plasma particles under various B and E x B configurations, where E and B are electric and magnetic fields, are presented. The numerical algorithm solves Poisson’s equation dynamically throughout the simulation to account for time-changing conditions such as inter-particle distance and time-dependent functions of ion temperature, and E and B fields. Simulations are run in 2D and 3D, and the results are being used to explore dust crystallization, quenching, and heating under intense B fields and high E x B drift velocities. The MD code is used to explore scenarios for E x B experiments planned with dust immersed in argon plasmas resulting from a combination of RF and DC glow discharges with the B-field produced by a Bitter-type electromagnet under development called ALPHA (Adjustable Long Pulse High-Field Apparatus) capable of sustaining fields up to 10 T from seconds to minutes. Particle tracking and stereoscopic reconstruction algorithms to be used on experimental data are also being tested with MD simulated particle position and velocity for ensembles that range from tens to hundreds of particles. The hardware and diagnostic setup planned for the experiments are also presented. [Preview Abstract] |
Thursday, October 26, 2017 12:18PM - 12:30PM |
TO5.00015: Effect of Stochastic Charge Fluctuations on Dust Dynamics Lorin Matthews, Babak Shotorban, Truell Hyde The charging of particles in a plasma environment occurs through the collection of electrons and ions on the particle surface. Depending on the particle size and the plasma density, the standard deviation of the number of collected elementary charges, which fluctuates due to the randomness in times of collisions with electrons or ions, may be a significant fraction of the equilibrium charge. We use a discrete stochastic charging model to simulate the variations in charge across the dust surface as well as in time. The resultant asymmetric particle potentials, even for spherical grains, has a significant impact on the particle coagulation rate as well as the structure of the resulting aggregates. We compare the effects on particle collisions and growth in typical laboratory and astrophysical plasma environments. [Preview Abstract] |
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