Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session PO6: Dusty and Strongly-Coupled Plasmas |
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Chair: Edward Thomas Jr., Auburn University Room: 555AB |
Wednesday, October 31, 2012 2:00PM - 2:12PM |
PO6.00001: Long-range correlation of nanoparticle growth in in low pressure reactive VHF discharge plasmas Masaharu Shiratani, Kunihiro Kamataki, Yasuo Morita, Hyunwoong Seo, Haho Itagaki, Giichiro Uchida, Kazunori Koga We report experimental results on long-range correlation of growth of nanoparticles in capacitively-coupled VHF discharges with amplitude modulation (AM) obtained using two dimensional laser light scattering method [1-3]. AM gives an artificial plasma fluctuation, which brings about 100{\%} increase of density of nanoparticles, 23{\%} decrease of their size, and narrower size dispersion. The growth of nanoparticles show strong time and spatial correlation for discharges with AM, where as it has little time and spatial correlation for discharges without AM. The long-range correlation over the whole plasma region brings about narrow size distribution of nanoparticles. The long-range correlation is not explained by transport of nanoparticles. Coupling between nanoparticles and other species can be the key to the long-range correlation.\\[4pt] [1] K. Kamataki, et al., J. Inst. 7 (2012) C04017.\\[0pt] [2] K. Kamataki, et al., Thin Solid Films in press.\\[0pt] [3] K. Kamataki, et al., Jpn. J. Appl. Phys. in press. [Preview Abstract] |
Wednesday, October 31, 2012 2:12PM - 2:24PM |
PO6.00002: Synchronization of self-excited dust acoustic waves W.D. Suranga Ruhunusiri, John Goree Synchronization is a nonlinear phenomenon where a self-excited oscillation, like a wave in a plasma, interacts with an external driving, resulting in an adjustment of the oscillation frequency. Dust acoustic wave synchronization has been experimentally studied previously in laboratory and in microgravity conditions, e.g. [Pilch PoP 2009] and [Menzel PRL 2010]. We perform a laboratory experiment to study synchronization of self-excited dust acoustic waves. An rf glow discharge argon plasma is formed by applying a low power radio frequency voltage to a lower electrode. A 3D dust cloud is formed by levitating 4.83 micron microspheres inside a glass box placed on the lower electrode. Dust acoustic waves are self-excited with a natural frequency of 22 Hz due to an ion streaming instability. A cross section of the dust cloud is illuminated by a vertical laser sheet and imaged from the side with a digital camera. To synchronize the waves, we sinusoidally modulate the overall ion density. Differently from previous experiments, we use a driving electrode that is separate from the electrode that sustains the plasma, and we characterize synchronization by varying both driving amplitude and frequency. [Preview Abstract] |
Wednesday, October 31, 2012 2:24PM - 2:36PM |
PO6.00003: Highly nonlinear dust acoustic waves and secondary dust density wave growth Jonathon Heinrich, Su-Hyun Kim, John Meyer, Robert Merlino, Marlene Rosenberg In a moderately coupled DC discharge dusty plasma, dust acoustic waves were excited by a modest ion drift. These dust acoustic waves grew to very large amplitude (n$_{d}$/n$_{d0}>$2) and developed into highly nonlinear waves (with over 35{\%} of the wave energy in the second harmonic). Dust particles in the presences of these high amplitude, nonlinear waves underwent large coherent particle displacement due to the nonlinear wave potential. As the displaced dust particles restored to their equilibrium positions, secondary dust density waves were excited in the wave troughs of the primary dust acoustic waves. The primary dust acoustic wave profiles were averaged and compared to second-order wave theory. The frequency and wavelengths of the secondary dust density waves are compared to a dust-dust streaming instability. [Preview Abstract] |
Wednesday, October 31, 2012 2:36PM - 2:48PM |
PO6.00004: Collective Phenomena in Extended Particle Chains within a Complex Plasma Truell Hyde, Jie Kong, Mudi Chen, Ke Qiao, Brandon Harris, Angela Douglass, Jorge Carmona Reyes, Lorin Matthews Examination of collective phenomena within dusty plasma allows investigation into the fundamental physics behind the strong correlation effects observed across a broad range of systems. Recently, research into the micro-excitations of dust in vertical chain bundles has increased due to interest in other 2+1 D liquids sharing similar characteristics. This is particularly true for systems providing external field alignment of the bundle. Most such chain motion is created due to (a) strong vertical interparticle coupling creating particle alignment within the chain, (b) topological constraints arising from the structure of the confinement and (c) thermal perturbations and/or local strain-induced stresses which can induce particle hopping and overall chain motion. This paper will discuss the manner in which strong vertical and horizontal coupling tends to align vertical chain bundles and the topological constraints that arise from the resulting anisotropic confinement. Employing a glass box placed on the lower electrode of a GEC rf reference cell, a vertical dust chain bundle will be shown to undergo phase transitions from a single 1D vertical chain to a 2-fold zigzag structure to 3-, 4-, and 5-fold helical structures. Both theoretical and experimental results will be presented to better define the role the vertical interparticle force and overall system confinement plays in the physics underlying overall chain behavior. [Preview Abstract] |
Wednesday, October 31, 2012 2:48PM - 3:00PM |
PO6.00005: Mode coupling and resonance instabilities in a horizontal finite dust chain Ke Qiao, Jie Kong, Zhuanhao Zhang, Lorin Matthews, Truell Hyde Mode couplings and resonance instabilities in plasma crystals have recently received increased attention both theoretically and experimentally. The ion wakefield downstream of the dust particles created by the vertical ion flow within the sheath has been shown to be the main cause of this mode coupling. In this research, the normal modes are investigated for a horizontal finite chain consisting of 3-10 dust particles in a complex plasma, employing a molecular dynamic (MD) simulation. Considering the ion wakefield downstream of each particle, the resultant mode coupling and resonance instabilities are analyzed and compared to experimental results from the CASPER lab. [Preview Abstract] |
Wednesday, October 31, 2012 3:00PM - 3:12PM |
PO6.00006: Elastic Turbulence in strongly coupled dusty plasma medium Amita Das, Sanat Kumar Tiwari, Vikram Singh Dharodi, Bhavesh G. Patel, Predhiman Kaw The dusty plasma medium can be often found in a strongly coupled state when the Coupling parameter defined by the ratio of the inter-particle coulomb energy to the thermal kinetic energy of the particle exceeds unity. At the intermediate values of the parameter, the dusty plasma medium behaves like a visco -elastic fluid. The visco - elastic nature has been captured by a Generalized Hydrodynamic model for the dust momentum equation. This is coupled with the Poisson equation, in which the Boltzmann response of electron and ion species has been retained. The study of the evolution of random fluctuation for this particular set of model equation has been carried out in two dimensions. The spectral evolution shows that in this case short scale fluctuation persists, unlike the inverse spectral cascade behavior associated with typical Navier stokes dynamics. Other interesting aspects such as recurrence of sharp scale structures have also been observed and will be reported. [Preview Abstract] |
Wednesday, October 31, 2012 3:12PM - 3:24PM |
PO6.00007: Characteristics of a strongly coupled ultracold neutral Ca$^{2+}$ plasma Mary Lyon, Abigail Wilkins, Scott Bergeson Ultracold neutral plasmas are formed by ionizing laser-cooled atoms at threshhold. They are strongly coupled Coulomb systems. Disorder-induced heating limits the strong coupling parameter to values of $\Gamma \leq 4$. A recent simulation predicted that higher values of the strong coupling parameter in ultracold neutral plasmas can be realized if the plasma ions are excited to higher ionization states. The maximum value of $\Gamma$ depends on the time at which the second ionization pulse arrives. We have built an experiment to test this prediction in laser-cooled calcium. This talk will describe the experiment and recent results. [Preview Abstract] |
Wednesday, October 31, 2012 3:24PM - 3:36PM |
PO6.00008: Avalanche Ionization of a Frozen Rydberg Gas Embedded in an Ultracold Neutral Plasma, with Possibilities for Stronger Coupling Patrick McQuillen, Xinyue Zhang, Trevor Strickler, Thomas Killian Ultracold neutral plasmas (UNPs) are well controlled, exotic plasmas with unusually low temperatures ($T_i \sim$ 1K-5K and $T_e \sim$ 20K-1000K) that permit detailed study of strongly coupled dynamics. Frozen Rydberg gases are highly interactive quantum systems with dynamics dictated by their unusually large dipole moments. They exhibit many interesting effects, such as the Rydberg blockade, the suppression of subsequent Rydberg excitations within a blockade radius of the first. By combining the two systems, it seems that spatial correlations induced by the blockade could be used to lessen disorder induced heating (DIH), and extend UNPs into stronger coupling. To this goal, we added the capability of exciting Rydberg states to our apparatus. We studied the dynamics of spontaneous ionization in strontium frozen Rydberg gases, in both space and time, with and without a collocated UNP. We have observed that ionization rates of a solitary Rydberg gas follow the expected dependence on density and interatomic potentials. We see rapid avalanche ionization with a ``seed'' UNP and show its utility in counting Rydberg excitations. We will discuss optical imaging of the Rydberg core, similar to Sr UNP imaging, but complicated by l-mixing collisions and autoionization concerns. [Preview Abstract] |
Wednesday, October 31, 2012 3:36PM - 3:48PM |
PO6.00009: Pseudo-Potentials in Dense and He-like Hot temperature Plasmas Claude Deutsch, Hamid Rahal Extending our former derivations in dense and high temperature plasmas of hydrogenic effective interactions mimiking the Heisenberg uncertainty principle [1,2], we worked out in a canonical ensemble, effective interactions in He-like plasmas where an orbital 1s electron remains strongly tighted to the He-like ions. The plasma electrons are then taken into account through appropriate Slater sums obtained in the most economical hydrogenic extension of the He-like bound and scattered states with angular orbital momentum l$<$3. Ground states are described by a multi-parametric HF approximation [3]. We thus obtain Diffraction-corrected electron-ion pseudo-potentials taking into account of a polarizable and nonpointlike ion core. Very large enhancements and discrepancies are obtained when they are contrasted to their H-like homologs with ion charge Z=2,10 and 92. These results are of obvious significance for He-like warm dense matter plasmas.Ionization is also considered.\\[4pt] [1] C. Deutsch, Phys. Lett. A60, 317 (1977)\\[4pt] [2] C. Deutsch, Y. Furutani and M.M. Gombert, Phys. Rep. 69,86 (1981)\\[0pt] [3] E. Clementi and C. Roetti, Atomic Data and Nucl. Data Tables, 14,177(1974) [Preview Abstract] |
Wednesday, October 31, 2012 3:48PM - 4:00PM |
PO6.00010: Simulation Studies of Hydrodynamic Tunneling of 440 GeV Protons Generated by Super proton Synchrotron at CERN N.A. Tahir, J. Blanco Sancho, A. Shutov, R. Schmidt, A.R. Piriz Super Proton Synchrotron (SPS) is used as injector to the Large Hadron Collider (LHC) at CERN. Each LHC beam carries 362 MJ energy, sufficient to melt 500 kg copper. Safety of operation is thus a critical issue and simulations have been performed to study the damage caused by full impact of one LHC beam on solid materials. In order to validate these simulations, similar work has been carried out using the SPS beam which will be compared with the fixed target experiments at the HiRadMat facility using the SPS beam. The simulations have shown that the range of the LHC as well as the SPS protons is substantially increased due to hydrodynamic tunneling, an extremely important phenomenon. This work has shown that the beam heated region of the targets are converted into strongly coupled plasma which suggests that the HiRadMat facility can also be used to study Warm Dense Matter. [Preview Abstract] |
Wednesday, October 31, 2012 4:00PM - 4:12PM |
PO6.00011: Probe Induced Dust Cavities in Complex Plasma Brandon Harris, Lorin Matthews, Truell Hyde Spherical, micrometer particles within a Coulomb crystal levitated in the sheath above the powered lower electrode in a GEC reference cell are perturbed using a vertical probe attached to a Zyvex S100 nanomanipulator. The probe is positioned within the cell over a range of locations and used to produce a series of user-controlled potentials that interact with the dust within the complex plasma. As the probe is lowered toward the dust layer, or its potential increased in absolute magnitude, a circular cavity devoid of dust is produced within the crystal. A horizontal force balance is shown to exist between the horizontal confinement, the interparticle repulsion, and the probe. Low density dust regions induced by the probe will be compared to those forming naturally at higher pressures and the 3-D voids observed in complex plasmas on the International Space Station. Finally, dust~density waves produced by oscillation of the probe potential will be analyzed and discussed. [Preview Abstract] |
Wednesday, October 31, 2012 4:12PM - 4:24PM |
PO6.00012: Particle Hopping within an Extended Vertical Chain in a Complex Plasma Mudi Chen, Jie Kong, Ke Qiao, Jorge Carmona-Reyes, Brandon Harris, Lorin Matthews, Truell Hyde Research into the micro-excitations of dust in vertical chain bundles has recently increased due to interest in the generic micro-behaviors of other 2+1 D liquids sharing similar characteristics. This is particularly true for systems providing external field alignment (for example, due to the ion wakefield) of the chain bundle. Most such chain motion is created due to (a) strong vertical interparticle coupling creating particle alignment within the chain, (b) topological constraints arising from the structure of the confinement which can ``cage'' the motion of the particle, and (c) thermal perturbations and/or local strain-induced stresses which can induce particle hopping and overall chain motion. This paper will discuss the third of these, i.e., the manner in which thermal perturbations and/or local strain-induced stresses can induce particle hopping and overall chain motion. Using a glass box placed on the lower powered electrode of a GEC rf reference cell to provide strong horizontal confinement, a vertical dust chain will be perturbed employing a diode pumped solid state laser (Coherent VERDI). The resulting particle hopping and overall chain motion will be examined theoretically and the manner in which the vertical interparticle force and the overall confinement impacts the underlying physics will be discussed. [Preview Abstract] |
Wednesday, October 31, 2012 4:24PM - 4:36PM |
PO6.00013: Using Falling Dust Particles as In-Situ Probes to Measure the Vertical Electric Force Distribution in a Complex Plasma Jie Kong, Ke Qiao, Jorge Carmona-Reyes, Angela Douglass, Zhuanhao Zhang, Lorin Matthews, Truell Hyde A free-falling dust particle within a complex plasma acts as an in-situ probe, providing a minimally perturbative diagnostic for the measurement of the electric force distribution. This technique is particularly important for particles confined within a glass box placed on the lower electrode, as the electric potential within this structure is not yet well-understood. In this experiment, falling particle trajectories within and without a glass box placed on the lower electrode in a GEC reference cell were recorded and analyzed and the electric forces exerted on the dust particles derived and compared. It will be shown that without a glass box, only a single force balance point (i.e., the position where the gravitational force is balanced by the electric force) exists in the vertical direction, while within a glass box this force balance spans an extended vertical range. [Preview Abstract] |
Wednesday, October 31, 2012 4:36PM - 4:48PM |
PO6.00014: Singular Longitudinal Waves in Nonlinear Viscoelastic Liquids Predhiman Kaw, Sanat Tiwari, Amita Das, Abhijit Sen Many fluid materials with strong correlations and memory possess properties which can be described by hydrodynamic equations with viscoelastic transport coefficients, namely, equations of generalized hydrodynamics (Frenkel). Examples of such materials are strongly coupled dusty plasmas, strongly dense astrophysical plasmas, complex fluids, colloidal suspensions, polymeric liquids, blood flowing in arteries etc. We examine the generalized hydrodynamic equations for longitudinal disturbances in the limit of large memory relaxation time. Here longitudinal disturbances propagate as shearless elastic waves and the nonlinear effects arise dominantly through inertial terms. For small amplitude waves, we carry out a reductive perturbation expansion and show that the nonlinear disturbances are described by the Hunter-Saxton equation, an equation with a dual Hamiltonian structure and an infinite number of conservation laws. Nonlinear propagating step like solutions leading to ``shock waves of zero strength'' are the novel solutions of this equation. For arbitrary amplitudes, exact equations are solved with a stationarity ansatz somewhat different from the standard moving frame ansatz. Exact cusp like solutions with an integrable singularity in the energy like integral, are found. [Preview Abstract] |
Wednesday, October 31, 2012 4:48PM - 5:00PM |
PO6.00015: ABSTRACT WITHDRAWN |
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