Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session XP8: Poster Session IX: Supplemental and Post-Deadline Posters |
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Room: Grand Hall East |
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XP8.00001: SUPPLEMENTARY ABSTRACTS |
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XP8.00002: Neoclassical Toroidal Plasma Viscosity in the Vicinity of an Island in Tokamaks N.T. Island, K.C. Shaing, S.A. Sabbagh, M.S. Chu It is known that the broken toroidal symmetry in $\vert $\textbf{\textit{B}}$\vert $ spectrum caused by the presence of the error fields and magnetohydrodynamic (MHD) activities in tokamaks enhances totoidal flow damping rate through the neoclassical toroidal viscosity. Recent extensions of the theory for the neoclassical toroidal plasma viscosity for non-resonant perturbations are generalized to calculate the symmetry breaking induced plasma viscosity in the vicinity of a rotating island. Specifically, the effects of orbit squeezing, collisional boundary layer, collisionless detrapping-retrapping, drift resonance caused superbananas, and bounce-transit and drift resonance are now included to complete the original theory. The results can be compared with experimental measurements of the flow damping rate in the vicinity of the islands. This extensive theory will form a basis for the further development of the island rotation theory in tokamaks. [Preview Abstract] |
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XP8.00003: EUV Measurements and Analytic Models of a Laboratory Solar Coronal Loop Simulation R.J. Perkins, P.M. Bellan Solar coronal loops typically erupt abruptly after long quiescent periods. Such eruptions might be initiated by interactions between adjacent loops; this was explored in a laboratory experiment where two plasma-filled flux tubes merge in either a co- or counter-helicity arrangement (J.F. Hansen, S.K.P. Tripathi, and P.M. Bellan, Phys. Plasma 2, 3177(2004)). The latter arrangement produces a bright region with enhanced soft x-ray emission. We investigate such mergings with a new array of EUV photo-detectors (based on S.J. Zweben, R.J. Taylor, Plasma Physics, Vol. 23, No. 4(1981)), and with analytic studies of particle orbits. The EUV array provides spatially and temporally resolved measurements of radiation between 10 and 120 nm needed to observe the bright regions. Precautions are taken against capacitive coupling, incoming plasma, and noise. We model the orbits of individual particles to understand the merging process. These models suggest two classes of trajectories: those confined to a single flux tube and those that move symmetrically between adjacent flux tubes, and how trajectories transition from these classes. [Preview Abstract] |
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XP8.00004: Dusty Modes in Nano-technological Plasmas Steven Bekhor An updated set of dispersion relations for dust acoustic, ion-acoustic and magneto-acoustic waves as well as the linear instabilities and dust charge relaxation processes associated with certain electrostatic and electromagnetic waves is presented using typical parameters for nano-technological plasmas based on a multi-fluid treatment. In the future, these may be used in an assessment of the optimal parameters for dynamical self-organization in multi-component plasmas used in the plasma enhanced chemical vapor deposition (PECVD) of self-assembled vertically aligned nanostructures. [Preview Abstract] |
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XP8.00005: H-1NF: The Australian National Plasma Fusion Facility: Results and Upgrade Plans B.D. Blackwell, J. Howard, M.J. Hole, D.G. Pretty, J.W. Read, H. Punzmann, S.T.A. Kumar, M. McGann, R.L. Dewar, C.A. Nuehrenberg The H-1 National Plasma Fusion Research Facility will be upgraded to support the development of world-class diagnostic systems for application to international facilities in preparation for ITER.~~ The upgrade will include new heating systems and deliver access to new magnetic configurations relevant to development of edge and divertor plasma diagnostics for next generation devices. ~ The Facility plan will be presented, including target parameters and configurations, modelling results and the relation to the strategic plan for Australian fusion research, developed by the Australian ITER Forum.~ New results from some of the optical imaging and magnetic diagnostics underpinning the upgrade plans will be presented, including a new method of coherence imaging of ion temperatures and flows. Synchronous imaging of MHD mode structure using fast optical emission imaging promises to supplement data from two poloidal arrays of Mirnov coils and a precision step-scanned interferometer to provide detailed information about radial and toroidal mode structure. Comparisons with theory will include a CAS3D study. [Preview Abstract] |
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XP8.00006: Superdiffusion in strongly coupled 2D Yukawa plasmas Michael Bonitz, Torben Ott Numerical simulation results for the mass transport by diffusion in dusty plasmas are presented and compared to experimental measurements, e.g. [1, 2]. For a wide range of parameters, an anomalous behaviour of the diffusion process, i.e., ``superdiffusion,'' is shown to exist for monolayer systems. In such superdiffusive systems, the mean-squared displacement does not obey the Einstein relation $\langle \vert \vec r(t) - \vec r(t_0)\vert^2\rangle\sim t^\alpha$ with $\alpha=1$. In contrast, the diffusion exponent is greater than unity on large time scales. The dependence of $\alpha$ on the plasma conditions has been investigated by varying the temperature, the screening and the dissipation in the numerical simulations, thus providing detailed predictions for the superdiffusion process in dusty plasmas [3,4]. In addition, we present results for the persistence of superdiffusion, i.e., we adress the question whether superdiffusion extends to arbitrarily long time scales. [1] B. Liu and J. Goree, \textit{Physical Review Letters} \textbf{100}, 055003 (2008) [2] W.-T. Juan and L. I, \textit{Physical Review Letters} \textbf{80}, 3073 (1998) [3] T. Ott, M. Bonitz, P. Hartmann, subm. to \textit{Physical Review Letters} [4] T. Ott \textit{et al.}, \textit{Physical Review E} \textbf{78}, 026409 (2008) [Preview Abstract] |
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XP8.00007: Progress in the SciDAC FSP Prototype Center for Plasma Edge Simulation (CPES) C.S. Chang The present status of and the future plans for the SciDAC FSP Prototype Center for Plasma Edge Simulation (CPES) will be reported. The full-f XGC1 gyrokienetic edge turbulence code evaluates 5D edge turbulence in realistic tokamak geometry, with the inner boundary pushed all the way to the magnetic axis to study edge pedestal effect on core turbulence. Full-f XGC0 is a kinetic-based transport modeling code in realistic 3D magnetic geometry, which is designed to predict plasma transport behavior on experimental time scale, in integration with MHD codes to include large scale instability events (such as ELMs) on plasma profile evolution. DEGAS2 code is integrated into XGC for higher fidelity neutral transport. The code integration is achieved by computer science means on EFFIS framework (End-to-end Framework for Fusion Integrated Simulation). [Preview Abstract] |
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XP8.00008: Envelope equation of a plasma jet Chiping Chen A self-consistent phase-space moment description is developed for high-energy-density plasma jets in the context of plasma jet approaches to high-energy density physics (HEDP). The phase-space moment theory is the truncated moment average of the kinetic equation. Using the phase-space moment theory, the root-mean-square (rms) envelope equations, which describe the orientation and size of the plasma jet, are derived for high-energy-density plasma jets. The envelope equations are demonstrated to agree with the virial theorem. In the regime where the internal field energy density is negligibly small compared with the thermal energy density and the internal flow energy density (Zhou and Chen, 2008), the rms envelope and density profiles for a plasma jet column are determined analytically, and used to predict the characteristics of a plasma jet column under compression. [Preview Abstract] |
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XP8.00009: Particle-in-cell simulations of the excitation mechanism for fusion-product-driven ion cyclotron emission from tokamaks Richard Dendy, James Cook, Sandra Chapman Suprathermal ion cyclotron emission (ICE) was the first collective radiative instability, driven by fusion products, observed on JET and TFTR. Strong emission occurs at sequential cyclotron harmonics of the energetic ion population at the outer mid-plane. Its intensity scales linearly with fusion reactivity, including its time evolution during a discharge. The emission mechanism is probably the magnetoacoustic cyclotron instability (MCI), involving resonance between: fast Alfv\'{e}n waves; cyclotron harmonic waves supported by the energetic particle population and by the background thermal plasma; and a subset of the centrally born fusion products, just inside the trapped-passing boundary, whose drift orbits make large radial excursions. The linear growth rate of the MCI has been intensively studied analytically, and yields good agreement with several key observational features of ICE. To address outstanding issues in the nonlinear ICE regime, we have developed a particle-in-cell code which self-consistently evolves electron and multi-species ion macroparticles and the electromagnetic field. We focus on the growth rate of the MCI, as it evolves from the linear into the nonlinear regime for JET-like parameters. [Preview Abstract] |
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XP8.00010: ICF Fast Ignition with Ultra-Relativistic Electrons Claude Deutsch, Jean-Pierre Didelez In contradistinction to the main-stream fast ignition scenario based on collisional stopping in the compressed DT-fuel of relativistic electron beams(REB) in the 1-2 Mev energy range(ER) [1], we consider an ultra-relativistic extension of the Malkin- Fisch [2] attempt at using REB in the several tenths of MeV ER, and stopping them in target through strong induced Langmuir turbulence. We stress therefore the additional and substantial contribution to REB stopping of strongly inelastic reactions such as the Trident production of electron-positron pairs as well as the many ways of electro-desintegrating deuterons and tritons, firstly in nucleons and eventually at higher energy with negative pion production included. In the latter case, it seems attactive to consider pion-catalyzed DT-fusion in a very dense and hot plasma with no sticking. This claim is supported by preliminary estimates based on Debyelike diatomic plasma orbitals.\\[4pt] [1] C. Deutsch, H. Furukawa, K. Mima, M. Murakami and K. Nishihara Phys.Rev.Lett. 77, 2483 (1996) and also K.V. Starikov and C. Deutsch, Phys.Plasmas 14, 022704 (2007)\\[0pt] [2] V.N. Malkin and N.J. Fisch, Phys.Rev.Lett. 89, 125004 (2002) [Preview Abstract] |
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XP8.00011: Diagnostic Systems of the Princeton MRI Experiment E.M. Edlund, H. Ji, K. Garot, M.D. Nornberg, A.H. Roach, E.J. Spence The MRI experiment at the Princeton Plasma Physics Laboratory is a Taylor-Couette device for the study of rotational instabilities in sheared flows of a magnetized liquid metal GaInSn alloy [1]. Four components of the containment vessel (the inner and outer cylinders, and segmented top and bottom plates) may be rotated independent of each other to tailor the fluid rotation profile. External azimuthal coils produce vertical magnetic fields up to 5 kG. The primary signatures of rotational turbulence are found in the fluctuations of the magnetic field and fluid velocity. An array of 72 externally mounted magnetic pick-up coils detects global magnetic perturbations and can distinguish low order axial and azimuthal mode numbers. A proposed additional coil may be mounted in a fin and inserted into the fluid for measurement of local magnetic perturbations. An outer wall mounted transducer, acting as both transmitter and receiver, operates at 4 MHz in a pulse-echo configuration and measures both the equilibrium and fluctuating fluid velocity. We will present plans for a novel diagnostic to measure the torque at the fluid-wall interface, employing strain gauges between the outer wall and a coaxial sleeve. Work supported by the US DOE, NASA and the NSF.\\[4pt] [1] E. Schartman, H. Ji and M.J. Burin, RSI 80, 24501 (2009). [Preview Abstract] |
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XP8.00012: Turbulence and magnetic field generation by magnetic electron drift vortex modes in a nonuniform plasma Bengt Eliasson, Padma K. Shukla, Vladimir P. Pavlenko We present a simulation study of the dynamical evolution of nonlinearly interacting two-dimensional magnetic electron drift vortex modes in a nonuniform plasma. Depending on the equilibrium density and temperature gradients, the system can either be stable or unstable. The unstable system reveals spontaneous generation of magnetic fields from noise level, and large-scale magnetic field structures are formed. When the system is linearly stable, one encounters magnetic electron drift vortex (MEDV) mode turbulence in which there is a competition between zonal flows and streamers. For large MEDV mode amplitudes, one encounters the formation of localized and small-scale magnetic vortices and vortex pairs with scale sizes of the order of the electron skin depth. The MEDV turbulence exhibits non-Kolmogorov and anisotropic spectra for different sets of plasma parameters. [Preview Abstract] |
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XP8.00013: ABSTRACT WITHDRAWN |
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XP8.00014: Focusing and neutralization of intense ion beams with a metallic funnel E. Henestroza, F.M. Bieniosek, F. Hernandez The phenomenon of grazing incidence reflection of MeV ion beams from a metallic surface and the production of secondary electrons from this interaction is the basis for a proposal to provide additional focusing and neutralization using a metallic funnel for the ion beams of the Neutralized Drift Compression Experiments (NDCX1 and NDCX2) at LBNL; these beams will be used to heat targets to high temperatures for the study of matter under warm dense matter (WDM) conditions. The present design of the final focus system provides a high-field solenoid and an injected neutralizing plasma to focus the beam onto the target. The addition of a metallic funnel inserted in close proximity to the target will concentrate the ions and provide additional secondary electrons for neutralization in the region of high compression. We will present Particle-in-Cell simulations of the dynamics of the ion beam as it propagates through the funnel and onto the target for cases where the inner bore of the cone may have a straight or curved profile, and compare with initial experiments to focus ion beams with a gold cone in the NDCX1 accelerator. [Preview Abstract] |
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XP8.00015: Optical Comparison of Single and Double Dielectric barrier plasma actuators Noah Hershkowitz, Lutfi Oksuz, Alan Hoskinson Time resolved ICCD pictures are taken for double and single surface barrier discharge plasma actuator for thick and thin powered electrodes. The filament and jet propagation minimum speeds are measured for both single and double barrier actuators. Optical emission spectra are measured using a monochromator. In a typical OES spectrum, O$_{2}$, O$^{+}$, CO, OH, N, N$_{2}$, N$_{2}^{+}$ and also optical emission lines from exposed electrodes (stainless steel, copper and tungsten lines) were observed for single barrier actuators. The optical data are fit by SPECAIR code$^{1}$. The translational and rotational temperatures are found to be approximately room temperature while the vibrational temperatures were1700 K and 1200 K, the electron temperatures were 3200 K and 2400 K for thick and thin electrode respectively. The different regimes in a discharge will be discussed. [Preview Abstract] |
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XP8.00016: Manipulation of Laser-generated Proton Beam Energy Distribution for (p,n) Neutron Production D.P. Higginson, J.M. McNaney, D.C. Swift, T. Bartal, H. Chen, D.S. Hey, S. Le Pape, A.J. Mackinnon, N. Nakanii, H. Nakamura, F.N. Beg Laser-accelerated proton beams have many applications including proton fast ignition, oncology, and neutron production. Neutrons can be created from (p,n) type reaction and in many elements this reaction is at relatively low proton energy (e.g. $^{7}$Li(p,n)$^{7}$Be peaks at $\sim $0.5 barns at 2-6 MeV). Thus the ability to increase the low energy protons (i.e. decrease the temperature) while keeping the conversion efficiency constant will lead to higher neutron production. In this experiment, the Titan laser (4x10$^{19}$ W/cm$^{2})$ was used to accelerate protons from 25 $\mu $m thick Cu foils. Laser pulse length (0.7 to 10 ps) and intensity were systematically varied to show a change in the proton energy distribution. These protons then struck various (p,n) converter materials to create neutrons. Experimental results will be discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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XP8.00017: Short-time behavior of a spherically trapped Yukawa plasma Hanno Kaehlert, Michael Bonitz The formation of correlations in non-ideal plasmas and the associated heating or cooling effects have attracted considerable attention in recent years~[1-4]. These results were obtained for macroscopic plasmas. Here, this question is reconsidered for charged particles confined by a spherical trap. Langevin dynamics simulations are used to study the correlation buildup and the formation of a strongly correlated Coulomb liquid when starting from a completely uncorrelated state. We observe an oscillatory behavior of the potential energy with the signature of a breathing oscillation of the whole cluster and a strong dependence of the maximal heating effect on the initial density profile. Results are also presented for the temperature relaxation to equilibrium.\\[4pt] [1] M. Bonitz, D. Semkat and D. Kremp, Phys. Rev. E \textbf{56}, 1246 (1997)\newline [2] D. Semkat, D. Kremp, and M. Bonitz, Phys. Rev. E \textbf{59}, 1557 (1999) [3] D.O. Gericke, M.S. Murillo, D. Semkat, M. Bonitz, and D. Kremp, J. Phys. A: Math. Gen. \textbf{36}, 6087-6093 (2003)\newline [4] D. Semkat et al., Progress in Nonequilibrium Green's functions II, p. 83, M. Bonitz and D. Semkat (Eds.), World Scientific Publ. (2003) [Preview Abstract] |
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XP8.00018: Variational approach for the fully three-dimensional quantum Zakharov system Padma Kant Shukla, Fernando Haas The three-dimensional quantum Zakharov system is derived from a two time-scales technique and hydrodynamic equations. The Lagrangian formalism as well as the pertinent conservation laws are identified. In the adiabatic and semiclassical case, the quantum Zakharov system reduces to a quantum modified vector nonlinear Schrodinger (NLS) equation for the envelope electric field. The variational structure is used to investigate the dynamics of localized, Gaussian shaped solutions, via the Rayleigh-Ritz variational method. The formal classical limit is considered in detail. Quantum corrections are shown to prevent the collapse of localized Langmuir envelope fields, in both two and three-spatial dimensions. Moreover, the quantum terms can produce a breather-like, oscillatory behavior of the width of the approximate Gaussian solutions. The variational method is shown to preserve the essential conservation laws of the quantum modified vector NLS equation. The possibility of laboratory tests in the next generation intense laser-solid plasma compression experiment is discussed. [Preview Abstract] |
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XP8.00019: Self-consistent effects and breather mode in semiconductor quantum wells Padma Kant Shukla, Fernando Haas, Giovanni Manfredi, Paul-Antoine Hervieux A novel breather mode in the self-consistent electron dynamics in semiconductor quantum wells is identified and characterized. The breather solution corresponds to coherent oscillations of the size of the electron gas around a self-consistent equilibrium. A non-perturbative time-dependent variational formalism is used to describe the relevant properties of the breather mode, both in the linear and nonlinear regimes, in the context of a quantum hydrodynamic model. The time-dependent Wigner-Poisson or Hartree equations are shown to be in excellent agreement with our analytical results. For asymmetric quantum wells, a signature of the breather mode is observed in the dipole response, which can be detected by standard optical means. The present approach should equally apply to metal nanoparticles and carbon-based systems such as fullerenes. [Preview Abstract] |
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XP8.00020: Negative energy modes and the quantum two-stream instability Padma Kant Shukla, Fernando Haas, Antoine Claude Bret The quantum two-stream instability is a benchmark displaying many of the particularities of quantum plasmas, including a new unstable branch of the dispersion relation for large wave- numbers and almost stationary, quasineutral, nonlinear oscillations without analog in classical plasmas. The unexpected features of the two-stream instability in electrostatic quantum plasmas are interpreted in terms of the coupling of approximate fast and slow waves. This is accomplished thanks to the factorization of the dispersion relation into different sectors carrying positive or negative energy. The concept of negative and positive energy waves, therefore, is shown to be useful not only for classical, but for quantum plasmas as well. The analysis can in principle be carried on in similar problems, like for the quantum beam- plasma instability or the case of parallel propagating quantum beams. [Preview Abstract] |
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XP8.00021: Experimental Investigation of Trigger Problem in Magnetic Reconnection N. Katz, J. Egedal, W. Fox, A. Le, A. Vrublevskis, J. Bonde, M. Porkolab In order for magnetic reconnection to be explosive there must be a sudden transition from slow to fast reconnection. This so- called ``trigger mechanism,'' which is responsible for the spontaneous and explosive release of magnetic energy in solar flares, magnetospheric substorms, and sawtooth crashes in magnetic fusion devices, is not yet well-understood. We use the Versatile Toroidal Facility (VTF) at MIT to study this transition [1], focusing specifically on its 3D nature. To this end, we use multiple arrays of Langmuir probes, magnetic probes, and Rogowski coils to map out the full 3D structure of the reconnecting plasma. The emerging picture is one in which a global plasma mode ($q=2$ or $q=3$) plays a key role in the onset of reconnection, by breaking the axi-symmetry of the device and allowing 3D effects to arise.\\[1ex] [1] J.~Egedal et al., Phys.~Rev.~Lett.~{\bf 98}, 015003 (2007). [Preview Abstract] |
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XP8.00022: Ideal Magnetohydrodynamic Simulations of Low Beta Compact Toroid Injection into a Hot Strongly Magnetized Plasma Wei Liu, Scott Hsu, Hui Li We present results from three-dimensional ideal magnetohydrodynamic simulations of low beta compact toroid (CT) injection into a hot strongly magnetized plasma, with the aim of providing insight into CT fueling of a tokamak with parameters relevant for ITER (International Thermonuclear Experimental Reactor). A regime is identified in terms of CT injection speed and CT-to-background magnetic field ratio that appears promising for precise core fueling. Shock-dominated regimes, which are probably unfavorable for tokamak fueling, are also identified. The CT penetration depth is proportional to the CT injection speed and density. The entire CT evolution can be divided into three stages: (1)~initial penetration, (2)~compression in the direction of propagation, and reconnection with the background magnetic field, and (3)~coming to rest and spreading in the direction perpendicular to injection. Tilting of the CT is not observed due to the fast transit time of the CT across the background plasma. [Preview Abstract] |
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XP8.00023: Long Term Evolution of Magnetized Bubbles in Galaxy Clusters Wei Liu, Hui Li, Scott Hsu, Shengtai Li We have performed nonlinear ideal MHD simulations of the long term evolution of a magnetized low-density ``bubble'' plasma formed by a radio galaxy in a stratified cluster medium. It is found that about 3.5\% of the initial magnetic energy remains in the bubble after 8 billion years, and the initial magnetic bubble expansion is adiabatic. The bubble can survive for at least 8 billion years due to the stabilizing effect of the bubble magnetic field on Rayleigh-Taylor and Kelvin-Holmholtz instabilities, possibly accounting for ``ghost cavities'' as observed in Perseus-A. A filament structure spanning about 500 kpc is formed along the path of bubble motion. The mean value of the magnetic field inside this structure is 0.88 micro Gauss at 8 billion years. Finally, the initial bubble momentum and rotation have limited influence on the long term evolution of the bubble. [Preview Abstract] |
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XP8.00024: Dynamical Screening and Wake Effects in Spherical Dusty Plasmas Patrick Ludwig, Michael Bonitz, Glenn Joyce, Martin Lampe Previous investigations have shown that 3D dusty plasma balls [1] can be well described by a one-component model with a static Yukawa-type pair interaction [2]. However, the multi-component plasma environment requires a systematic investigation of collective many-particle effects on the crystal formation. In particular the effect of streaming ions (i.e. a dynamically-screened Coulomb potential) can strongly influence structure and dynamics of a strongly-coupled dusty plasma. In a plasma with ions streaming at a uniform velocity, the dust-dust potential takes the form of a wake structure, which results in attractive forces between the similarly charged dust grains [3]. Of central interest are therefore the remarkable structural and dynamical consequences for 3D plasma crystals due to the non-reciprocal forces of the wakefield. The considered simulation model comprises an accurate representation of all plasma properties, including screening, wake effects, ion and electron thermal effects, Landau damping, as well as collisional damping.\\[4pt] [1] Arp et al., Phys. Rev. Lett. 93, 165004 (2004)\\[0pt] [2] Bonitz et al., Phys. Rev. Lett. 96, 075001 (2006)\\[0pt] [3] Lampe et al., Phys. Plasmas 7, 3851 (2000) [Preview Abstract] |
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XP8.00025: Quest for impact ignition and its future prospect Masakatsu Murakami, H. Azechi, T. Watari, T. Sakaiya, K. Ohtani, K. Takeda, H. Shiraga, K. Shigemori, S. Fujioka, H. Nagatomo, T. Johzaki, J. Gardner, J. Bates, A. Velikovich, Y. Aglitskiy, M. Karasik, J. Weaver, S. Obenschain Since the impact ignition has been proposed [1], we have achieved such crucial milestones under the operation of Gekko XII (ILE) and NIKE (NRL) laser systems as super-high-velocity acceleration of foils ranging 700-1000 km/s and hundred-fold increase in neutron yield by impact collision [2]. For the latter achievement, the kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of ~ 1.6 keV. The use of Bromine-doped plastic target are key measure to suppress Rayleigh-Taylor instabilities and thus to achieve effective collisions. Based on these preliminary results, we have done two-dimensional hydrodynamic simulations to demonstrate that ignition occurs when impactor with a velocity beyond 1500 km/s and a density of ~ 50 g/cm3 collides with main fuel with a density of 400 g/cm3, when the maximum impactor kinetic energy is 10 kJ.\\[4pt] [1] M. Murakami and H. Nagatomo, Nucl. Inst. \& Meth. Phys. Res. A544, 67 (2005).\\[0pt] [2] H. Azechi, et al., Phys. Rev. Lett. 102, 235002 (2009). [Preview Abstract] |
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XP8.00026: Quasi-Static Magnetic Filed Generation in Interaction of Circularly Polarized Laser Pulses with Underdense Plasma Neda Naseri, Valery Yu. Bychenkov, Wojciech Rozmus The excitation of quasi-static axial magnetic field by circularly polarized laser pulses in plasma channels due to inverse Farday effect is studied. The distribution of axial quasi-static magnetic filed is found numerically for different laser intensity and plasma channel distributions. To check that magnetic field changes its sign with change of left to right circular polarization, we performed 3D PIC simulations with right-hand and left-hand circularly polarized laser light and found that the excited magnetic filed due to inverse Faraday effect changes its sign with the change of polarization as predicted from theory. The distribution of quasi-static axial magnetic filed is found numerically by adopting the distribution of the laser intensities and density channels from our 3D simulations and compared with quasi-static magnetic filed calculated from the simulation. [Preview Abstract] |
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XP8.00027: Off-axis stability of intense continuous relativistic beams Renato Pakter, Luciano C. Martins, Felipe B. Rizzato This paper investigates the stability of off-axis continuous intense relativistic beams propagating inside a circular conducting pipe. The equations of motion for the centroid and the envelope of slightly off-axis beams are derived and used to determine equilibrium and stability conditions for the beam transport. It is shown that depending on the parameters of the system, beams propagating along the pipe axis may become unstable due to the presence of the wall, imposing a fundamental limitation in the effective area that an equilibrium beam can occupy inside the conductor. Self-consistent $N$-particle simulations are used to verify the findings. [Preview Abstract] |
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XP8.00028: Generation of Langmuir turbulence and stochastic acceleration in laser beat wave process Prerana Sharma, R.P. Sharma This paper investigates the filamentation process of two co-axially propagating laser beams in a collisionless plasma. On account of the ponderomotive nonlinearity, two laser beams affect the dynamics of each other and cross-focusing takes place. The initial Gaussian laser beams are found to have non-Gaussian structures in the plasma. Using the laser beam and the plasma parameters, appropriate for beat wave process, the filaments of the laser beams have been studied. Using these results, the Langmuir wave (LW) excitation at the beat wave frequency (when the laser beams are having filamentary structures) has been studied. The excited LW is modeled with the help of a driven oscillator and it is found that the excited LW is not a plane wave; rather it has a turbulent structure. We have obtained the power spectrum of the excited beat wave (Langmuir wave) and calculated the spectral index. The stochastic electron acceleration has been studied in the presence of this Langmuir turbulence and relevance of these results to beat wave process has been pointed out. [Preview Abstract] |
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XP8.00029: Effect of Laser Beam Filamentation on Second Harmonic Spectrum in Laser Plasma Interaction Prerana Sharma, R.P. Sharma This paper presents the laser beam filamentation at ultra relativistic laser powers, when the restriction on the beam is relaxed during filamentation process. On account of laser beam intensity gradient and background density gradients in filamentary regions the electron plasma wave (epw) at pump wave frequency is generated, this epw is found to be highly localized on account of the laser beam filaments. Interaction of incident laser beam with these epw leads to second harmonic generation. The second harmonic spectrum has also been studied in detail and its correlation with the filamentation of the laser beam has been established. Starting almost with a monochromatic component of laser beam propagation, the second harmonic spectrum becomes more complicated and broadened as the laser beam propagates further, and filamentation takes place. For the typical laser beam and plasma parameters: $\lambda _{0}$= 1064 nm, power flux (10$^{22}$ W/cm$^{2})$,$\omega _p =0.03\omega _0 $, $v_{th} =0.1c$, n$_{0}$=1.9$\times $10$^{19}$. We found that conversion efficiency comes out to be (E$_{2}$/E$_{0})$ = 8$\times $10$^{-3}$, and the spectrum is quite broad which depends upon the laser beam propagation distance. The results (specifically, second harmonic spectral feature) presented here may be used for the diagnostics of laser produced plasmas. [Preview Abstract] |
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XP8.00030: Nonlinear Simulations of the inhomogeneous magnetic electron drift vortex mode turbulence P.K. Shukla, Dastgeer Shaikh, B. Eliasson A simulation study of the magnetic electron drift vortex (MEDV) mode turbulence in a magnetoplasma in the presence of inhomogeneities in the plasma temperature and density, as well as in the external magnetic field, is presented. The study shows that the influence of the magnetic field inhomogeneity is to suppress streamer-like structures observed in previous simulation studies without background magnetic fields. The MEDV mode turbulence exhibits non-universal (non-Kolmogorov type) spectra for different sets of the plasma parameters. In the presence of an inhomogeneous magnetic field, the spectrum changes to a 7/3 power law, which is flatter than without magnetic field gradients. The relevance of this work to laboratory and cosmic plasmas is briefly mentioned. [Preview Abstract] |
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XP8.00031: Dark and grey electromagnetic electron-cyclotron envelope solitons in an electron-positron magnetoplasma P.K. Shukla, R. Bingham, A.D.R. Phelps, L. Stenflo We present an investigation of the amplitude modulation of an external magnetic field-aligned right-hand circularly polarized electromagnetic electron-cyclotron (EMEC) wave in a strongly magnetized electron-positron plasma. It is shown that the dynamics of the modulated EMEC wave packet is governed by a cubic nonlinear Schr\"{o}dinger equation. The latter reveals that a modulated wave packet can propagate in the form of either a dark or a grey envelope soliton. This result could have relevance to the transport of electromagnetic wave energy over long distances via envelope solitons in the magnetospheres of pulsars and magnetars. [Preview Abstract] |
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XP8.00032: An Interpretation of ``Puff \& Pump'' Radiative Divertor Experiments in DIII-D W.M. Stacey, T.W. Petrie A series of ``puff \& pump'' experiments in which argon is injected into the private flux region to achieve a radiative divertor, and deuterium is puffed into the chamber to achieve an enhanced gas flow in the scrape-off layer (SOL), intended to entrain and sweep escaping argon into the divertor, have been performed on DIII-D [1]. A calculational model [2] for particle flows and drifts in the SOL has been modified to represent the puff and pump experimental situation. We focus here on the effectiveness of varying the deuterium gas puff rate on argon accumulation in the core plasma, particularly with respect to how the $\nabla B$ drift impacts these results. Our analysis will be compared with experimental results.\par \vskip8pt \noindent [1] T.W.\ Petrie, {\em et al.}, Nucl.\ Fusion {\bf 49}, 065013 (2009).\par \noindent [2] W.M.\ Stacey, Phys.\ Plasmas {\bf 16}, 042502 (2009). [Preview Abstract] |
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XP8.00033: Reduced Modeling of Electron Trapping Nonlinearity in Raman Scattering D.J. Strozzi, R.L. Berger, H.A. Rose, A.B. Langdon, E.A. Williams The trapping of resonant electrons in Langmuir waves generated by stimulated Raman scattering (SRS) gives rise to several nonlinear effects, which can either increase or decrease the reflectivity. We have implemented a reduced model of these nonlinearities in the paraxial propagation code pF3D [R. L. Berger et al., Phys. Plasmas 5 (1998)], consisting of a Landau damping reduction and Langmuir-wave frequency downshift. Both effects depend on the local wave amplitude, and gradually turn on with amplitude. This model is compared with 1D seeded Vlasov simulations, that include a Krook relaxation operator to mimic, e.g., transverse sideloss out of a multi-D, finite laser speckle. SRS in these runs develops from a counter-propagating seed light wave. Applications to ICF experiments will also be presented. [Preview Abstract] |
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XP8.00034: EBW Heating in the Pegasus Spherical Experiment F. Volpe, R. Fonck, A. Redd, T. Bigelow, S.J. Diem Electron Bernstein Wave (EBW) heating (H) and current drive (CD) are strong candidates for the growth of ST plasmas initiated by helicity injection up to become appropriate targets for neutral beam H{\&}CD. Additionally they can improve beta, help sustaining the plasma current and tailor its profile, possibly in synergy with the high harmonic fast wave system. A 2.45GHz, 1MW EBW H{\&}CD system is presently under consideration for a proposal for Pegasus. It would rapidly and cost-effectively address the applicability and scalability of EBW techniques to larger STs such as NSTX and a future component test facility. Two klystrons and part of the hardware originally deployed for lower hybrid heating in the PLT tokamak could serve for this purpose. It is proposed to explore both the ordinary-extraordinary-Bernstein and extraordinary-Bernstein conversion by means of a new launcher capable of oblique, adjustable launch, probably combined with a local limiter to steepen the density profile and so improve the mode conversion efficiency. A phase shifter would make the polarization elliptical, as required for modal purity. [Preview Abstract] |
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XP8.00035: ABSTRACT WITHDRAWN |
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XP8.00036: Modeling of turbulent transport and flow generation in the HELCAT experiemnt A.S. Ware, M. Olsen, M. Breyfogle, M. Gilmore, E. Schuster This work investigates modeling of transport and flow generation in a linear plasma device using a 1-D transport code. The goal is to model the HELCAT experiment including the use of biased concentric rings as control elements for the radial electric field profile. By varying the bias voltages, the local {\bf E}$\times${\bf B} flow can be modified. The effect will be identical to a source of {\bf E}$\times${\bf B} flow in the limit of zero $\beta$ (i.e., when diamagnetic flows are negligible). By varying the momentum sources a sheared radial electric field can be generated that can suppress turbulent particle and heat transport. Analysis of drift wave turbulence models will be used to derive models for the growth rate and Reynolds stress parameterization in the transport model. We will test the impact of different numerical models for the momentum sources and compare the results with experimental measurements of the radial electric field in the HELCAT experiment. [Preview Abstract] |
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XP8.00037: POST-DEADLINE ABSTRACTS |
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XP8.00038: SVD Techniques Applied to Modulated ECH Data on DIII-D D.F. Meyerson, M.E. Austin, K.W. Gentle, T.C. Luce, C.C. Petty Sawtooth contamination is a serious problem that interferes with modulated electron cyclotron heating (MECH) induced heat pulse propagation analysis. To address this issue we apply system identification SVD techniques (SI-SVD) to separate the effect of sawteeth and MECH. DIII-D ECE data with and without sawtooth contamination is analyzed and compared to assess the validity of the method. While the different sources separated out by this method are assumed to have the ability to excite the same eigenmodes of the linearized energy transport equation, the sources themselves are assumed to be independent of one another. It is well known that the location of MECH deposition can alter the character of sawtooth instability; to quantify to what degree the location of deposition alters the results we consider on-axis as well as off-axis MECH shots. Additionally the technique gives a means of verifying the power deposition profile of the relevant sources. The results are compared with local power balance calculations as well as calculations of absorption profiles. [Preview Abstract] |
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XP8.00039: Relativistic MHD Jets Hui Li We present the formulation of relativistic MHD flows, likely occurring in the environment of accretion onto supermassive black holes. Three-dimensional relativistic MHD simulations will be presented on how the energy outflow will partition among different physical components and on the collimation and stability of such systems. The interaction between such flows with their environment, e.g., the intra-cluster medium, will be discussed. [Preview Abstract] |
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XP8.00040: Application of Hilbert-Huang Transform for the determination of instantaneous low frequency of Plasma waves Ekong Nathaniel, Natasha Beloff, Andrew Buckley Downstream of a quasi-perpendicular bow shock of the Earth, various wave modes associated with the different boundaries have been confirmed and different methods have been used to find frequency and instantaneous frequency of the different modes. We applied Hilbert-Huang Transform in the determination of instantaneous frequency by decomposing the data observed by in-situ spacecraft in certain region in space called the Magnetosheath into intrinsic mode functions (IMFs) using empirical mode decomposition (EMD) technique of Huang et al., 1998. Instantaneous frequencies for the different IMFs were computed using Hilbert transform. The determined instantaneous frequency supports the non-stationary and non-linear nature of the data. The instantaneous wave vector was then computed. The observed data were taken from FGM instrument on Cluster II mission which provides 3-dimensional advantage for this analysis, and the results compared with the instantaneous frequency computed using simple Hilbert transform with electric field measurements of Cluster II mission already carried out. [Preview Abstract] |
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XP8.00041: ABSTRACT WITHDRAWN |
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XP8.00042: Magnetic spectrometry of deuteron spectra in plasma focus device Mahmud Vahdat Roshan, Alireza Talebitaher, Rajdeep Singh Rawat, Paul Lee, Stuart Victor Springham Magnetic spectrometry using polymer nuclear track detectors is used for high-resolution measurement of the energy spectrum of deuterons emitted from the pinch-column of the NX2 plasma focus (PF). The spectrum is measured for single PF shots. A 25~$\mu $m pinhole images the deuteron source on the spectrometer. Deuteron tracks are measured with an automated scanning system. The recognized and counted tracks are accumulated in a histogram of track displacement in bins representing equal energy stripes on the detector. A very distinct neutrals spot is clearly visible for each spectrum, resulting from uncharged deuterons passing through the spectrometer in straight-line paths and producing a densely tracked zone. The deuteron trajectory in the magnetic field is calculated in order to obtain the deuteron energy as a function of the distance from the neutrals spot on the detector. The deuteron spectrum $d^{2}$\textit{N/dEd$\Omega $ }is derived from the track displacement histogram. The deuteron spectrum is used to estimate the beam-target contribution for fusion neutron production. The number of Nitrogen-13 nuclides in the activation of graphite through $^{12}C(d,n)^{13}N$ is estimated using the deuteron spectra and the thick target yield. [Preview Abstract] |
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XP8.00043: Nonlinear Landau damping and edge electron heating of electron Bernstein waves John R. Cary, Nong Xiang In 1D simulations, it has been shown that nonlinear wave- particle interactions such as parametric decays and nonlinear Landau damping play an important role in electron Bernstein wave (EBW) propagations and absorptions. In this work, 3D particle-in-cell simulations are conducted with taking the wave antenna structure into account. The wave coupling and propagation around the mode-conversion layer are extensively studied. It is found that for typically experimental EBW heating parameters, if the incident frequency is larger than the second harmonic electron cyclotron frequency near the upper hybrid resonance (UHR), the incident wave may decay to an electron cyclotron wave whose frequency equals the electron gyro-frequency near the UHR, and an EBW at a lower frequency. As a result, a significant portion of the incident wave power will be absorbed at the plasma edge and electrons are strongly heated. This nonlinear Landau damping could much reduce the electron heating efficiency in the core plasma, and significantly affect the edge plasma properties. [Preview Abstract] |
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XP8.00044: Plasma instability driven by noise Chang-Bae Kim Plasma response to an external noise is explored in the long-time and- large-scale limit. External noise is assumed to depend on a particular direction that may simulate the strong magnetic field or the gradient of the density and the temperature. The noise is thought to represent the short-scale background turbulence of certain physical origins whose spectrum is a transverse tensor to the wave vector. It is found that noise generates two effects: One is to enhance the dissipation by the isotropic spectrum and the other is a destabilizing term due to the anisotropic part. Depending on the relative strength of the anisotropic noise to the isotropic part the plasma may be unstable for small $k$ modes. Potential relevance to the large-scale flows like the zonal flow and the streamer will be discussed in the presentation. [Preview Abstract] |
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XP8.00045: Physics validation for design change of KSTAR passive stabilizer Y.M. Jeon, J.Y. Kim, Y.K. Oh, H.L. Yang, W.C. Kim, H.K. Kim, S.A. Sabbagh, J.M. Bialek, D.A. Humphreys, A.S. Welander, M.L. Walker Recently, the design of the passive stabilizer in KSTAR has been changed to improve controllability of the active control system and reduce the possibility of producing an additional error field. Originally the passive stabilizer in KSTAR was designed for RWM and vertical instability (or VDE) stabilizations and plasma startup efficiency, so that current bridges were designed and combined through 3D saddle-loop connections. Since the key design change is removing the current bridges, it's essential to assure satisfactory control performance for these instabilities under the design change. Control capability for n=1 RWM and achievable $\beta _{N}$ will be addressed as a primary goal of the passive stabilizer together with vertical instability control and effects on plasma startup. In addition, the changes in electro-magnetic force on conducting structures will be discussed qualitatively as a key engineering issue of the design change. [Preview Abstract] |
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XP8.00046: Ion acceleration with a picosecond CO$_{2}$ laser Igor Pogorelsky, Marcus Babzien, Mikhail Polyanskiy, Karl Kusche, Peter Shkolnikov, Michael Ispirian, David Neely, Paul McKenna, David Carroll, Nizar Najmudin, Joerg Schreiber, Charlotte Palmer, Nicholas Dover, Vitaly Yakimenko The ion acceleration experiment at BNL explores the laser wavelength scaling from optical to mid-IR region. 10$^{16}$ W/cm$^{2}$ of a CO$_{2}$ laser intensity focused on a 8 $\mu $m Al foil produced a 1-MeV proton beam. This observation agrees with predicted scaling of the proton energy E$_{p}\sim I^{1/2}$\textit{$\lambda $}. We now initiated new ion acceleration runs where a gas jet is a target. At the CO$_{2}$ laser wavelength (\textit{$\lambda $}=10 \textit{$\mu $}m), a critical plasma density is 100 times lower (10$^{19}$ cm$^{-3})$ than for a glass laser. This opens new opportunities for time-resolved interferometric optical diagnostic of over-critical laser/plasma interactions. We present the latest results from both foil and gas jet ion acceleration experiments and give an outlook on possibilities of attaining multi-terawatt femtosecond pulses with CO$_{2}$ lasers. [Preview Abstract] |
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XP8.00047: Direct measurements of the magnetic field inside the magnetospheric plasma RT-1 Yoshihisa Yano, Zensho Yoshida, Junji Morikawa, Haruhiko Saitoh, Tatsunori Mizushima The magnetospheric plasma experiment RT-1 (Ring trap -1) has achieved stable confinement of high-beta plasma produced by electron cyclotron resonance heating (ECH). The observed diamagnetic signals ($\sim$3mWb) correspond to the maximum local beta values exceeding 40\%, according to the MHD equilibrium analysis. (Soft X-ray measurements confirmed the existence of high energy electrons of Te $\sim$ 10 keV, which is consistent to the estimated plasma pressure.) As a diagnostic of internal profile of the plasma pressure, we developed a multi-channel magnetic probe system and carried out direct measurement of the diamagnetic signals inside the plasma. We found that the pressure profile peaks steeply near the ECH resonance surface and has dependence on the fueling gas pressure. [Preview Abstract] |
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XP8.00048: The relativistic virial theorem in plasma EOS calculations Joseph Oreg, Avraham Barshalom A method for enhancing EOS calculations is presented. Our model combines the two pressure representations: the basic definition - as the volume derivative of the free energy $F$, and the ``virial pressure'' $P_{v}$ = [$E - c^{2}B$] / 3V derived from the relativistic virial theorem, where $B$ is the lower component contribution to the electronic density. The model takes into account the deviation $\delta $ between the two representations and presents an exact differential equation for $F$ that provides analytic expressions for both $F$ and $P$, in terms of $M=\delta +c^{2}B$ - \textit{TS}. Using the LDA approximation for $M$ in these exact expressions, together with a boundary condition at the normal density, improves the EOS LDA results significantly. We present a survey of comparisons with experiments showing excellent agreements with the calculations. [Preview Abstract] |
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XP8.00049: Spectrally Resolved X-ray Scattering from Implosion Targets Andrea Kritcher, Tilo Doeppner, Hae Ja Lee, Paul Davis, Otto Landen, Siegfried Glenzer Spectrally resolved x-ray Thomson scattering has been applied at the Omega Laser Facility to investigate the capsule adiabat of cone-in-shell targets. The technique of scattering from implosion targets was developed and tested for use as a diagnostic at the National Ignition Facility (NIF), LLNL. Measurement of the adiabat is applied to test low-adiabat pulse shaping methods, designed for optimum compressibility and stability. Theoretical equation of state models (EOS) can also be studied for conditions encountered during implosion. In these experiments, the noncollective, or microscopic behavior of the plasma, was probed with a Zn He-alpha x-ray source at a scattering angle of 113$^{\circ}$. For these degenerate plasmas, the width of the inelastic scattering peak is proportional to the Fermi energy, and thus the electron density. The electron temperature is obtained from the measured intensities of the elastic and inelastic features. In-flight scattering measurements yielded electron densities of $\sim $ 1.2x10$^{24}$cm$^{-3}$, temperatures of $\sim $10 eV, and an ionization state of C(+4)H(+1). This work was performed under the auspices of the DOE by LLNL under Contract No. DE-AC52-07NA27344, LDRD 08-ERI-003, and the Nat. Lab. User Fac. Prog. [Preview Abstract] |
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XP8.00050: The effect of the Hall term on Jeans instability in quantum magnetoplasma with resistive effects Zhengwei Wu, Haijun Ren, Paul Chu The Jeans instability in dense quantum plasmas is investigated by taking into account the Hall term and resistive effect in the presence of two dimensional (2-D) magnetic fields. The general dispersion relation is presented. The presence of Hall term is shown to induce a frequency shift and have no effect on the instability criterion. The resistance is shown to introduce both damping and destabilizing effect on the system in different cases. The analytical expressions of the growth/damping rate of Jeans instability are obtained for both the finite and remarkable resistive effects cases in the absence of Hall term. [Preview Abstract] |
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XP8.00051: Magnetothermal instability of plasmas in a horizontal magnetic field Haijun Ren, Zhengwei Wu, Jintao Cao, Paul Chu The linear buoyancy instability in a magnetized plasma, generally referred to as magnetothermal instability (MTI), is investigated by considering anisotropic heat conduction. The external magnetic field is assumed to be horizontal and background heat flux is not taken into account. The general dispersion relationship of the convective instability is derived. The growth rate of the MTI in fixed boundary condition is presented and discussed. The effect of density special gradient on the MTI is investigated. The magnetic field is shown to suppress the MTI and even quench the instability when the magnetic field is strong enough. Under the standard Wentzel- Kramaers-Brillouin (WKB) approximation, our results could be simplified to a brief form reported by one previous paper (E.Quataert, Astrophys. J. {\bf673}, 758 (2008)). [Preview Abstract] |
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XP8.00052: Reply to ``Notes on Pioneer Anomaly Explanation by Satellite-Shift Formula of Quaternion Relativity'' Vic Chrisitanto, Florentin Smarandache In the present article we would like to make a few comments on a recent paper by A. Yefremov in Progress in Physics international journal. It is interesting to note here that he concludes his analysis by pointing out that using full machinery of Quaternion Relativity it is possible to explain Pioneer XI anomaly with excellent agreement compared with observed data, and explain around 45{\%} of Pioneer X anomalous acceleration. We argue that perhaps it will be necessary to consider extension of Lorentz transformation to Finsler-Berwald metric, as discussed by a number of authors in the past few years. In this regard, it would be interesting to see if the use of extended Lorentz transformation could also elucidate the long-lasting problem known as Ehrenfest paradox. Further observation is of course recommended in order to refute or verify this proposition. [Preview Abstract] |
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XP8.00053: Towards Recombination Pumped H-Like N X-Ray Laser Itay Gissis, Asaf Lifshitz, Nir Kampel, Avi Rikanati, Ilan Beery, Uri Avni, Amit Ben-Kish, Amnon Fisher, Amiram Ron The recombination pumping scheme for soft X-Ray lasers has better energy scaling, in comparison to the collisional pumping scheme. Implementation of an H-like $3\to 2$ Nitrogen recombination laser, at $\lambda \sim $13.4 nm requires initial conditions of 50{\%} fully stripped Nitrogen, Te$\sim $140eV and N$_{e}\sim $10$^{20}$cm$^{-3}$. The cooling period to below 60eV should be faster than the typical three-body recombination time. Here we study the possibility to achieve the required plasma conditions using a capillary discharge Z-Pinch apparatus. The experimental setup includes a 90mm long ceramic capillary with an inner diameter of 5mm, coupled to a pulsed power generator supplying a peak current of $\sim $60 kA, with a quarter-period of 60 ns. We used various diagnostics techniques to measure the plasma dynamics including X-Ray diodes, time-integrated spectrometry and time-resolved pin-hole imaging (using a framing MCP camera). Analysis of the results shows a rapid cooling period to a temperature below 60eV, demonstrating the feasibility of recombination-pumped capillary discharge lasers. [Preview Abstract] |
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XP8.00054: Nonlinear Landau damping, and nonlinear envelope equation, for a driven plasma wave Didier Benisti, Olivier Morice, Laurent Gremillet, David Strozzi A nonlinear envelope equation for a laser-driven electron plasma wave (EPW) is derived in a 3-D geometry, starting from first principles. This equation accounts the nonlinear variations of the EPW Landau damping rate, frequency, and group velocity, as well as for the nonlinear variations of the coupling of the EPW to the electromagnetic waves. All these quantities are moreover shown to be nonlocal because of nonlocal variations of the electron distribution function. Each piece of our model is carefully tested against Vlasov simulations of stimulated Raman scattering (SRS), and very good agreement is found between the numerical and theoretical results. Our envelope equations for both, the electrostatic and electromagnetic waves, are solved numerically, and comparisons with Vlasov simulations regarding the growth of SRS are provided. Finally, from our theory we can straightforwardly deduce a nonlinear gain factor which provides an alternate, simpler and faster method to quantify the SRS reflectivity. First results using this method will be shown. [Preview Abstract] |
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XP8.00055: Lateral Propagation of MeV Electrons Generated by Femtosecond Laser Irradiation John Seely, Csilla Szabo, Patrick Audebert, Erik Brambrink, Emeric Tabakhoff, Lawrence Hudson Using high-resolution hard x-ray spectroscopy, the propagation of MeV electrons generated by intense ($\approx $10$^{19}$ W/cm$^{2})$ femtosecond laser irradiation, in the lateral direction perpendicular to the incident laser beam, was studied using targets consisting of irradiated metal wires and neighboring spectator wires embedded in electrically conductive (aluminum) or resistive (teflon) substrates. It was found that electron propagation through teflon was inhibited, compared to aluminum, implying a relatively weak return current and incomplete space-charge neutralization. The energetic electron propagation in the direction parallel to the electric field of the laser beam was larger than perpendicular to the electric field. Such lateral electron propagation to distance up to 1 mm from the focal spot can be detrimental to fast-ignition fusion and hard x-ray backlighter radiography. [Preview Abstract] |
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XP8.00056: Charge dependence of impurity peaking factor Sara Moradi, M.Z. Tokar, Boris Weyssow The experimentally found dependence of impurity transport characteristics, such as diffusivity and pinch velocity, on the impurity ion charge $Z$, remains unexplained both by neoclassical and anomalous theoretical predictions. In this contribution the model for the impurity anomalous transport due to the ITG/TE unstable modes has been developed further by taking into account the effects of impurity ion collisions with the main plasma components becoming more and more important with increasing impurity charge. In linearized transport equations these effects are included as friction and thermal forces and collision energy exchange affecting perturbations of impurity ion parallel velocity and temperature, correspondingly. For the plasma conditions examined here, where the magnetic shear is low, the collisional effects are dominant in the pinch velocity and result in a very strong Z dependence of the impurity peaking factor. The sign and magnitude of the pinch-velocity and $p$ depends essentially on the instability mechanism, i.e., ITG or TE drive. The results of calculations are compared with the experimental observations. [Preview Abstract] |
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XP8.00057: Observation of Neutral Depletion in High Power Helium-Helicon Plasmas Saeid Houshmandyar, Saikat Chakraborty Thakur, Stephanie Sears, Jerry Carr, Earl Scime Helicon plasmas are known for their high plasma density. However, the effects of neutral atoms on wave dispersion cannot be neglected, even in the high density core, $e.g.$ Alfv\'{e}n wave propagation in helicon plasmas. Laser Induced Fluorescence (LIF), a noninvasive diagnostic tool, was used to measure the neutral density profile of helium atoms in high-density, helium helicon plasmas. At 578.725 nm (vacuum), the LIF signal of neutral helium atoms resulting from injection of the laser along the magnetic field, exhibits a dip, at the Doppler shifted central wavelength, that results from the finite optical depth of the plasma at that wavelength [51$^{st}$ APS-DPP, GP8.00133]. In a series of experiments performed in WVU HELIX (Hot hELIcon eXperiment), the neutral density profile and optical depth are measured for different ambient magnetic fields, radial positions and driving frequencies of the helicon source. As a result, the optimum plasma performance ($i.e.$, largest neutral depletion cases) for helium-helicon plasmas was determined. [Preview Abstract] |
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XP8.00058: Characterization of Low frequency zonal flow in linear magnetized plasma Jinlin Xie, Ran Chen, Tao Lan, Adi Liu, Wandong Liu, Changxuan Yu A low frequency, poloidally symmetrical potential structure that peaks near zero frequency is observed in a steady linear magnetized plasma device. The complete 3D spectral features of this structure have been identified to have the characteristics expected for the low frequency zonal flow (LFZF). The analysis of the nonlinear interaction between the LFZF and ambient drift turbulence suggests that the LFZF may be generated in energy-conserving nonlinear interactions with the turbulence. The LFZF frequency bandwidth is found to scale inversely with the square root of the ion mass, which implies that the collisional damping mechanism dominates the saturation of the LFZF in our case. [Preview Abstract] |
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XP8.00059: Observations of geodesic acoustic modes and low-frequency zonal flow in the edge of HL-2A and HT-7 tokamaks T. Lan, C.X. Yu, H.L. Zhao, D.F. Kong, A.D. Liu, L.W. Yan, Wenyu Hong, K.J. Zhao, J.Q. Dong, J. Qian, J. Cheng, D.L. Yu, Q.W. Yang, X.R. Duan, B.N. Wan, X. Gao, J.G. Li Zonal Flows, including Low-Frequency Zonal Flow (LFZF) and geodesic acoustic mode (GAM), had both been characterized in the HL-2A tokamak and the HT-7 tokamak. The radial spectral features of GAM fluctuations were measured using two radial rake probe arrays separated toroidally. The GAMs with a fixed mode frequency were located within a radial distance inside the LCFS; the amplitude, radial wavenumber, phase velocity and group velocity profiles had all been measured. The radial wavenumber of GAM had been observed to decrease with increasing radial position. The group velocity of GAM had also been observed to spread outward with a tuning position from which the GAM propagated inward. The spectral characteristics of density and electron temperature fluctuations of GAM had been studied in detail as well. [Preview Abstract] |
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XP8.00060: First real-time detection of surface dust in a tokamak C.H. Skinner, L. Roquemore, H.W. Kugel, R. Marsala, T. Provost Dust accumulating in the vacuum vessel from plasma surface interactions has important consequences for the operation and safety of next-step devices such as ITER. Local measurements of dust are part of the ITER dust strategy, but to date no real time measurements of dust on internal tokamak surfaces have been reported. We will present the first measurements of dust in the NSTX vessel using an novel electrostatic surface dust detector. A fine grid of interlocking circuit traces was biased to 50 v. Impinging dust particles create a temporary short circuit and the resulting current pulse is recorded by counting electronics. Techniques used to increase the sensitivity to match NSTX dust levels while suppressing electrical pickup will be presented. Results from a separate experiment to gauge the mobilization of dust from ITER-scale castellations will also be reported. [Preview Abstract] |
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XP8.00061: Self-Similar Decay of Enstrophy in an Electron Plasma Douglas Rodgers, Sergio Servidio, William Matthaeus, Travis Mitchell The similarity solution for energy decay in 3D hydrodynamic turbulence, due to Taylor and von Karman [1], based on the self preservation hypothesis for the shape of the two point correlation, implies that the energy E decays as dE/dt = - a Z$^3$/L, where a is a constant, Z is the turbulence amplitude and L is a similarity length scale. Extensions of this idea to MHD [2] have been of great utility in solar wind and coronal heating studies. While the hydrodynamic case is well studied experimentally, we are not aware that similarity decay has been examined in a laboratory plasma. Here we conduct an experimental study of this idea in the context of two dimensional electron plasma turbulence. Specifically, we propose an expression for the decay of enstrophy of a single-signed-vorticity fluid which is analogous to the von Karman decay of energy in 3D turbulence, and compare this to the dynamical relaxation of a pure electron plasma in a Malmberg-Penning (MP) trap [3]. Results show good agreement between the proposed decay law and the MP experiments. [1] G. I. Taylor, Proc. Roy. Soc. Lon. A, 151:421, 1935; T. de Karman and L. Howarth, Proc. Roy. Soc. Lon. A, 164:192, 1938. [2] W. H. Matthaeus, G. P. Zank and S. Oughton. J. Plas. Phys., 56:659, 1996. [3] D. J. Rodgers et al, Phys. Rev. Lett., 102(24):244501, 2009. [Preview Abstract] |
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XP8.00062: Characterization of Meta-Stable Equilibria of a Electron Plasma: Relaxation Towards Minimum Enstrophy and Maximum Entropy States Douglas Rodgers, Sergio Servidio, William Matthaeus, David Montgomery, Travis Mitchell Dynamical relaxation of a pure electron plasma in a Malmberg-Penning trap is studied, comparing experiments and statistical theories of weakly dissipative two-dimensional turbulence [1]. Statistical analysis of many experimental runs favors a theoretical picture of relaxation to a near-maximum entropy state with constrained energy, circulation and angular momentum, rather than to a minimum enstrophy state [2]. However it is possible to vary experimental parameters continuously so that the results move from near-equal accord with the two theories to more strongly favoring maximum entropy. One way to accomplish this is to vary the initial distribution so that more complex electron patches are produced; this generally appears to increase the level of turbulent activity, favoring maximum entropy over minimum enstrophy. Research supported in part by USDOE Grant No. DE-FG02-06ER54853. [1] D. J. Rodgers et al, Phys. Rev. Lett., 102(24):244501, 2009. [2] X. -P. Huang, C. F. Driscoll, Phys. Rev. Lett., 72(14):2187, 1995 [Preview Abstract] |
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XP8.00063: Recyclable Solid Blanket for a Fusion Reactor M.V. Umansky Neutron damage and tritium inventory will limit the lifetime of inner wall components of a fusion reactor, leading to increased operation cost and possibly making it economically unattractive. Thick liquid walls may be a solution to this; however, at present the feasibility of forming and maintaining thick liquid walls remains to be demonstrated for a tokamak configuration. Here it is proposed to construct inner wall components of a reactor using a meltable material. During the normal operation the blanket is maintained in the solid state. After some period of operation, when a critical level of neutron damage and tritium inventory in the blanket is accumulated, the structure is melted and drained out of the reactor chamber. After that, by bringing in fresh liquid blanket material and freezing it to the solid state on the walls, the blanket is rebuilt. Thus the blanket is periodically replaced without opening up the reactor chamber, relatively easily compared to a solid blanket. Preliminary calculations demonstrate that such system can satisfy the basic requirements of thermal transport and tritium breeding in a reactor. [Preview Abstract] |
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XP8.00064: Magnetic Reconnection in Electron Magnetohydrodynamics Huishan Cai, Ding Li The dissipation mechanisms of magnetic reconnection, pressure anisotropy effects and guide field gradient effects on magnetic reconnection and tearing mode instability are investigated, respectively. It is found that the conditions either pressure-based dissipation or electron inertia-based dissipation dominant depend on the relative magnitude between electron thermal Larmor radius and electron inertial skin depth.The dissipation mechanisms have a great relation with the magnitude of guide field. The effects of pressure gradient depend on the relative magnitude between the parallel and perpendicular pressure gradients. The guide field gradient can affect significantly on tearing mode. In the small guide field gradient limit, namely the guide field gradient is smaller than the magnetic field shear at the magnetic null plane, the growth rate of tearing mode instability is enhanced by the guide field gradient. In the large guide field gradient limit, the guide field gradient can destabilize tearing mode instability dramatically and the growth rate is proportional to the guide field gradient. [Preview Abstract] |
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XP8.00065: Study of the heating and expansion of spherical nanoplasmas Gianni Coppa, Roberta Mulas, Elisabetta Boella, Gian Luca Delzanno The present work deals with the analysis of the interaction between a laser pulse and a gas cluster. The phenomenon is characterized by three different phases: 1) electron ionization and heating by the laser radiation; 2) escape of the most energetic electrons; 3) ion acceleration due to the positive charge inside the sphere. Although these three phases have different timescales, for a rigorous analysis they cannot be studied as completely separated. In the poster, results obtained by means of a numerical code developed by the Authors are presented. In the code a three-dimensional particle technique for electrons and positive ions is employed, in which the electric field is calculated considering a perfect spherical symmetry by resorting to the Gauss' law. The method has two advantages: 1) it preserves the symmetry of the problem; 2) a grid is not necessary and, consequently, the calculation of the electric field requires little computational effort. In the code, a simplified model for the electron heating is introduced by considering collisions between electrons and fictitious energetic particles. [Preview Abstract] |
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XP8.00066: Diffusion and energization of charged particles in time-dependent chaotic magnetic field Gang Li, Brahmananda Dasgupta, Abhay Ram Chaotic magnetic field can be obtained from simple steady state current system consisting of straight wires and loops in an asymmetric configuration. Since in solar flares macroscopic and time varying currents in the form of filaments and/or loops commonly exist, the resulting magnetic field must be chaotic. Consequently, to understand solar flare phenomena, studying particle motion in a time-dependent chaotic magnetic field is of fundamental importance. These currents, time-varying, can induce electric fields. Therefore, electrons and ions are subject to potential (2nd order Fermi) acceleration. We report recent results on charged particle motion in a chaotic electric and magnetic fields. Particle trajectories are followed using the Lorentz equation with a $4$-th order Runge-Kutta skeme. The running diffusion coefficient, particle spectrum, and the chaotic magnetic field spectrum are obtained. Implications of our result to particle acceleration and heating at a flare site are discussed. [Preview Abstract] |
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XP8.00067: An Empirical Model for the Interaction of Ultra-Intense Laser Pulses with Fully Ionized Plasmas Including Electrostatic Effects J.-H. Yang, R.S. Craxton This work investigates the capability of ultrafast lasers with irradiance $I \ge $ 10$^{18}$ W cm$^{-2}$ to produce highly energetic electron beams in a Gaussian focus in a low-density plasma. A simple particle simulation code including a physical model of collective electrostatic effects in relativistic plasmas has been developed. Without electrostatic fields, free electrons escape from the Gaussian focal region of a 10-ps petawatt laser pulse very quickly, well before the laser field reaches its maximum amplitude. In this case very small net energy transfer occurs, indicating that free electrons cannot extract enough energy for ignition. However, it has been demonstrated that the electrostatic field generated by the electron flow is able to strongly modify the range and direction of the laser-generated MeV electrons by allowing trapped electrons to experience much higher laser-intensity peaks along their trajectories and, therefore, be accelerated to higher velocities, drifting along the laser direction. This modeling predicts some collimation, but not enough to meet the requirements of fast ignition. This work was supported by the U. S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
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XP8.00068: Improving the Dynamic Range of CR39 Detectors for ICF Experiments Through Multiple Track Overlap Detection Algorithms A. Zylstra, N. Sinenian, M. Manuel, H.G. Rinderknecht, M.J. Rosenberg, D.T. Casey, J.A. Frenje, C.K. Li, F.H. Seguin, R.D. Petrasso CR39 based nuclear detectors are in widespread use for Inertial Confinement Fusion (ICF) experiments [1,2]. Current analysis methods only count scanned shapes of single tracks, limiting the standard dynamic range of the detector to approximately 100. We present simulations and experimental studies at the MIT accelerator of methods for accurately determining the total particle count when overlapping tracks are a non-negligible fraction of the total. Advancements in analysis algorithms to accurately count at higher track densities through these methods could significantly increase the dynamic range of CR39 based detectors at OMEGA and the NIF.\\[4pt] [1] F. H. Seguin et al., Rev. Sci. Instrum 74 (2003) 975.\\[0pt] [2] C.K. Li et al, Phys. Rev. Lett. 100, 225001 (2008). [Preview Abstract] |
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XP8.00069: Modeling of the Lightning Plasma Channel Stroke to a Spacecraft during Ascent Alfonso Tarditi, John Norgard Lightning protection is an important aspect of modern aerospace design: the increased use of composite materials (\textit{vs.} metals) reduces the shielding and robustness of the conducting path that the outer shell of a vehicle can present to a lightning discharge. A spacecraft during ascent becomes vulnerable to lightning strokes immediately after leaving the launch pad: in addition to natural lightning conditions, there is the possibility of triggered lightning events, caused by a perturbation of the atmospheric electric field [1]. The purpose of this study, in support of the NASA Constellation program, is to determine the evolution of the plasma current and its distribution on the spacecraft surface. Following earlier ``gas dynamic'' approaches [2], the model considers a plasma channel attached to the ascending spacecraft after a return stroke is established. The conductive exhaust plume [3] is an integral part of the model. The \textit{NIMROD} 3D plasma fluid code [4] is used to model the plasma channel, reproducing the full transient due to the self-consistent magnetic field and the possibility of sweeping of the attachment point along the moving structure [5]. \textbf{References}: [1] M.A. Uman, Proc. IEEE, 76, 1548 (1988). [2] V. A. Rakov, M. A. Uman, IEEE Trans. EMC, EMC-2940, 403 (1998). [3] J. D. Norgard, G.S. Smith, IEEE Trans. EMC, EMC-29, 157 (1987) [4] C. R. Sovinec \textit{et al.}, J. Comput. Phys. 195, 355 (2004). [5] Larsson \textit{et al}., J. Phys. D, 33, 1876 (2000) [Preview Abstract] |
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XP8.00070: FRC Formation and Stability in an Accelerated Plasma Flow Alfonso G. Tarditi ~ Electric propulsion concepts based on FRC's and acceleration of compact tori (CT) have been considered in the past [$e.g.$ 1-5], particularly due to FRC's attractive properties in term of stability and low beta. Unlike previous CT concepts, the present study focuses on the formation of FRC plasmoids in an accelerated plasma column [6]. The 3D fluid code \textit{NIMROD} [7] is used to explore the formation of an FRC from a plasma accelerated through a magnetic nozzle, effectively producing a detachment of the plasma from the guiding magnetic field.~The stability of the detached FRC and the energy balance are investigated. \textbf{References}: [1] K Miller, APS-DPP Conf. New Orleans (LA) 1998, Bull. APS (1998). [2] M.J. Schaffer, Proc. NASA Advanced Propulsion Workshop in Fusion Propulsion, Huntsville, AL, Nov. 2000. [3] Slough, J., AIAA paper 2001-3674 (2001). [4] S. J. Koelfgen, AIAA paper 2003-4992 (2003). [5] T. Weber, this conference. [6] A. G. Tarditi, Int. Sherwood Fus. Theory Conf., Stateline NV, April 2005. [7] C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004). [Preview Abstract] |
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