Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session YP8: Poster Session IX: Ignitor, Supplemental and Postdeadline |
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Room: Plaza ABC |
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YP8.00001: IGNITOR |
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YP8.00002: Improved Confinement Regimes and the Ignitor Experiment* F. Bombarda, B. Coppi, P. Detragiache The Ignitor experiment is the only one designed and planned to reach ignition under controlled DT burning conditions. The machine prameters [1] have been established on the basis of existing knowledge of the confinement properties of high density plasmas. The optimal plasma evolution in order to reach ignition by means of Ohmic heating only, without the contribution of transport barriers has been identified. Improved confinement regimes are expected to be accessible by means of the available ICRH additional heating power and the injection of pellets for density profile control. Moreover, ECRH of the outer edge of the (toroidal) plasma column has been proposed using very high frequency sources developed in Russia. Ignition can then be reached at slightly reduced machine parameters. Significant exploration of the behavior of burning, sub-ignited plasmas can be carried out in less demanding operational conditions than those needed for ignition with plasmas accessing the I or H-regimes. These conditions will be discussed together with the provisions made in order to maintain the required (for ignition) degree of plasma purity. *Sponsored in part by the U.S. DOE.\\[4pt] [1] B. Coppi, et al. IAEA Fusion Energy Conference, OV/P-02 (2012). To be published in Nucl. Fus. 2013. [Preview Abstract] |
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YP8.00003: Plasma Disruption Simulations for the Assessment of the Ignitor Plasma Chamber Design* G. Ramogida, A. Bianchi, B. Coppi The Ignitor Plasma Chamber is designed on the basis of available information about the electro-magnetic (EM) loads coming from relevant experiments and the increasingly accurate numerical models of the eddy and halo currents produced by disruption events. The recently achieved success in the active control of disruptions is also considered as a valuable safety factor in the present design of the plasma chamber. A set of plasma disruption simulations was carried out to verify that the Plasma Chamber can withstand structurally, with proper margins, the EM loads during off-normal events, to complete the assessment of its compliance with the ASME rules and to identify the safe limits of operation that will be targeted by the disruption mitigation system. For this purpose the worst expected plasma disruption, the Vertical Displacement Event at full plasma current, was extensively simulated varying the current decay rate, the halo current region extension and the safety factor limit when the thermal quench occurs. *Sponsored in part by ENEA of Italy and by the U.S. D.O.E. [Preview Abstract] |
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YP8.00004: Auxiliary Heating Systems for the Ignitor Project* M. Sassi, S. Mantovani, B. Coppi Auxiliary plasma heating systems directed at extending the range of plasma regimes that can be accessed by Ohmic heating only are important components of the Ignitor machine. In order to affect the entire plasma column an appropriate ICRH systemhas been designed and components of it have been tested. The adoption of a 280 GHz system affecting, by ECRH, the outer edge of the plasma column has been proposed in order to influence temperature and density profiles in this important region. The ICRH system will operate over the range 80-120 MHz, consistent with magnetic fields in the range 9-13 T. The maximum delivered power goes from 8 MW (at 80 MHz) to 6 MW (at 120 MHz) distributed over 4 ports. A full size prototype of the VTL between the port flange and the antenna straps, with the external support and precise guiding system has been constructed. The innovative quick latching system located at the end of the coaxial cable has been successfully tested, providing perfect interference with the spring Be-Cu electrical contacts. Vacuum levels of $10^{-6}$, compatible with the limit of material degassing, and electrical tests up to 12 kV without discharges have been obtained. Special attention was given to the finishing of the inox surfaces, and to the TIG welds. *U.S. DOE sponsored. [Preview Abstract] |
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YP8.00005: Further progresses in the development of large MgB$_{2}$ Superconducting Coils for the Ignitor Experiment* A. Tumino, G. Grasso, B. Coppi Intermediate temperature superconducting cables have been adopted for the fabrication of the largest poloidal field coils of the Ignitor experiment. This is an important step toward achieving better duty cycles in Ignitor-like machines with innovative magnet technologies compared to traditional superconductors. The commercially available MgB$_{2}$ strands manufactured by Columbus Superconductors can achieve the target specifications for the considered coils, about 5 meters of outer diameter and maximum field on the conductor below 5 T. These cables are also compatible with the Ignitor cryogenic system, which is designed to cool the machine at about 30 K, although MgB$_{2}$ may use colder gas at 10 K. The preliminary cable design includes about 300 MgB$_{2}$ multifilamentary strands of 1 mm in diameter and a copper tube for the He-gas flow in the center. Recently we have succeeded in the development of MgB$_{2}$ strands with a further improvement in design and electrical properties for cable application. Reaching of a higher critical current density and better current sharing properties between the different strands is allowed by the newest design. The implementation of this progress in wire performance and its impact on the coil design will be discussed. *US DOE partly sponsored. [Preview Abstract] |
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YP8.00006: SUPPLEMENTAL |
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YP8.00007: Elasticity of Relativistic Rigid Bodies? Florentin Smarandache In the classical Twin Paradox, according to the Special Theory of Relativity, when the traveling twin blasts off from the Earth to a relative velocity \[ v=\frac{\sqrt 3 }{2}c \] with respect to the Earth, his measuring stick and other physical objects in the direction of relative motion shrink to half their lengths. How is that possible in the real physical world to have let's say a rigid rocket shrinking to half and then later elongated back to normal as an elastic material when it stops? What is the explanation for the traveler's measuring stick and other physical objects, in effect, return to the same length to their original length in the Stay-At-Home, but there is no record of their having shrunk? If it's a rigid (not elastic) object, how can it shrink and then elongate back to normal? It might get broken in such situation. [Preview Abstract] |
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YP8.00008: Non-dimensionalization of Helmholtz equation and the nature of the Alfvenic turbulence Ahmad Reza Estakhr I redefined Reynold number in a different situation, the Helmholtz equation which represents the time-independent wave equation, $\nabla^2 A+k^2 A=0$ Now i consider wave number as Reynold number per linear dimension, $L^2\nabla^2 A+R_e^2 A=0$ the important non-dimensional parameters for MHD are Reynold, Magnetic Reynold and Prandtl numbers, $R_e.P_m=R_{em}$ then we find, $P_m^2L^2\nabla^2 A+R_{e_m}^2 A=0$ where the $\nabla^2$ is laplacian and $A$ is the Amplitude. [Preview Abstract] |
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YP8.00009: Diffusion of 2D Yukawa liquids under a magnetic field Yan Feng, T.P. Intrator, J. Goree, Bin Liu Normal and anomalous diffusion of 2D strongly coupled dusty plasmas without magnetic fields have been studied both theoretically and experimentally in the past decade. Recently, dusty plasma behaviors under magnetic fields have attracted attention, especially the Magnetized Dusty Plasma (MDPX) facility. The gyro motion due to the applied magnetic field will drastically change the collective dynamics of dusty plasmas. Here, Langevin dynamics simulations were performed to study the diffusion of individual charged particles of 2D Yukawa liquids, with a magnetic field perpendicular to the 2D plane. The gyro motion is competing with the thermal motion, and as a result, the diffusion behavior of individual particles will be suppressed by the applied magnetic field. As diagnostics of diffusion, the mean squared displacement and velocity autocorrelation function have been calculated from the simulated particle trajectories. A relationship between the diffusion and the applied magnetic field will be obtained from our simulations. Work supported by DOE, NSF and NASA. [Preview Abstract] |
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YP8.00010: Generating Planetary Interiors in the Laboratory Using Intense Ion Beams in the Proposed LAPLAS Experiments at FAIR at Darmstadt Naeem Ahmad Tahir, Antonio Roberto Piriz, Alaxandar Shutov Importance of planetary physics has increased manifold due to the discovery of over two thousand extra-solar planets. These include gas giants like Jupiter and Saturn, water rich objects like Uranus and Neptune as well as huge earth like rocky planets called super-earths. To understand the structure of these newly discovered members of the planetary club, as well as that of the solar planets, it is necessary to create the very extreme physical conditions that exist in the interiors of these objects. We have proposed a novel technique of imploding samples like hydrogen, water and iron in multi-layered cylindrical targets using intense heavy ion beams that will be generated at the Facility for Antiprotons and Ion Research (FAIR) at Darmstadt. The scheme known as LAPLAS (LAboratory PLAnetary Sciences), employs a multiple shock reflection scheme that leads to a low-entropy compression of the sample material. Simulations have shown that one can generate pressures of the order of 30 Mbar while the temperature remains low (a few kK) in the sample. The LAPLAS experiment is an integral part of the HEDgeHOB scientific proposal for FAIR. Due to the high line density of the target, proton radiography will be used to diagnose the target. [Preview Abstract] |
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YP8.00011: Validating compressible turbulence models under reshock and shear-driven high energy density conditions Eric Loomis, Leslie Welser-Sherrill, Forrest Doss, Kirk Flippo, Jim Fincke The implementation of turbulence models into radiation hydrodynamics codes requires its validation through comparisons with experimental data that isolate different aspects of the model. We are carrying out these validation experiments at the OMEGA laser facility isolating the effects of shear flow and reshock of Richtmyer-Meshkov unstable interfaces. The shear experiment uses the passage of counter-propagating shocks in adjacent CH foam semi-cylinders while the reshock experiment uses the collision of counter-propagating shocks in a single cylindrical foam. We will present recent data and simulations for both of these experiments and summarize our progress towards model validation. [Preview Abstract] |
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YP8.00012: Selective trapping of hydrogen plasma in mirror machine Ilan Be'ery, Omri Seemann, Amnon Fruchtman, Amnon Fisher, Amiram Ron When ablation plasma, consisting mostly of hydrogen and carbon ions and neutral, is injected through the throat of a mirror machine, pure hydrogen plasma is observed to accumulate inside the mirror trap. In this work we study the formation of magnetized plasma beam, the scattering out of the loss cone, and the plasma decay in the mirror trap. The selective accumulation of hydrogen ions is shown to be a result of the difference in the magnetic channeling through a limiter and of difference in scattering probabilities into the trapped regions of phase space. The accumulation of plasma in the trap is limited by centrifugal drift instability, convecting plasma to the walls. [Preview Abstract] |
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YP8.00013: Circularly polarized electromagnetic wave-particle interaction and whistler magnetic polarization Paul Bellan Two recent results on waves are reported: (i) The interaction between a circularly polarized electromagnetic wave and an energetic gyrating particle is described using a relativistic pseudo-potential that is a function of the instantaneous frequency mismatch [1]. The pseudo-potential parametrically depends on the initial mismatch, the normalized wave amplitude, and the initial angle between the wave magnetic field and the particle perpendicular velocity. For zero initial mismatch, the pseudo-potential consists of a single valley, but for finite initial mismatch it can be two valleys separated by a hill. (ii) The circular propagation of the magnetic field of oblique whistler waves previously shown in Ref. [2] is derived using a simple oblique basis set [3]. Whistler propagation is shown to consist mainly of magnetic energy sloshing back and forth between two orthogonal components of wave magnetic field in quadrature; wave electric field energy is small compared to the wave magnetic field energy.\\[4pt] [1] P. M. Bellan, \textit{Phys. Plasmas }20, 042117 (2013).\\[0pt] [2] O. P. Verkhoglyadova, B. T. Tsurutani, and G. S. Lakhina, JGR-Space 115, A00F19 (2010).\\[0pt] [3] P. M. Bellan (submitted). [Preview Abstract] |
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YP8.00014: The Scientific Prototype -- a proposed next step for the American MFE effort Wallace Manheimer The Scientific prototype is the only logical next step for the American~magnetic fusion effort. This poster is divided into two parts. The first is~a description of the scientific prototype, a tokamak about the size of TFTR, JET and JT-60, but which runs steady state in DT and breeds its own tritium. The second is an examination of other proposed approaches for American MFE and why none constitute a viable alternative. W. Manheimer, J. Fusion Energy, 32, 419-421, 2013. [Preview Abstract] |
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YP8.00015: An analytical theory for lateral Rayleigh-Taylor instability of a collimated MHD cylindrical plasma Xiang Zhai, Paul Bellan A Rayleigh-Taylor (RT) instability is observed in the Caltech plasma jet experiment [1], when the current-carrying plasma tube undergoes kink instability and accelerates laterally from the original axis. This acceleration produces perpendicular to the cylindrical plasma an effective gravity that drives a fast, fine-scale RT which results in a fast magnetic reconnection. None of the existing RT theory considers the situation where a quasi-uniform (effective) gravity is perpendicular to a cylindrical magnetized plasma. We have developed an analytical RT model for this configuration. The effective gravity splits and couples an infinite set of azimuthal modes, leading to a dynamics that combines RT instability, current-driven instability, magnetic tension and cylindrical geometry. The theory successfully explains the RT wavelength and growth rate observed in the Caltech experiment.\\[4pt] [1] Moser, A. L. \& Bellan, P. M. Magnetic reconnection from a multiscale instability Cascade. Nature. 482, 379 (2012) [Preview Abstract] |
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YP8.00016: Natural Divertor Spherical Tokamak Plasmas with bean shape and ergodic limiter Celso Ribeiro, Julio Herrera, Esteban Chavez, Kevin Tritz The former spherical tokamak (ST) MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, R\textless 0.14m, a\textless 0.10m, B$_{T}$\textless 0.5T, I$_{p}$\textless 40kA, 3ms pulse) [1] is being recommissioned in Costa Rica Institute of Technology. The main objectives of the MEDUSA-CR project are training and to clarify several issues in relevant physics for conventional and mainly STs, including beta studies in bean-shaped ST plasmas [2], transport, heating and current drive via Alfv\'{e}n wave, and natural divertor STs with ergodic magnetic limiter [2,3]. We report here improvements in the self-consistency of these equilibrium comparisons and a preliminary study of their MHD stability beta limits.\\[4pt] [1] G. D. Garstka, PhD thesis, University of Wisconsin at Madison, September 1997\\[0pt] [2] C. Ribeiro et al., Proc. 25$^{\mathrm{th}}$ Symposium on Fusion Engineering, San Francisco, US, June 2013\\[0pt] [3] C. Ribeiro et al., Proc. 39$^{\mathrm{th}}$ EPS Conf. Contr. Fusion and Plasma Phys., vol. 36F, P1.091, Stockholm, Sweden, July 2012\\[0pt] [4] J. J. E. Herrera-Velazquez, E. C. Alarcon, and C. Ribeiro, 24$^{\mathrm{th}}$ IAEA Fusion Energy Conference, TH-p2-28, San Diego, US, 8-12 October 2012 [Preview Abstract] |
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YP8.00017: Fast Wave Evanescence in Intermittent Edge Plasmas J.R. Myra Radio frequency waves used for heating and current drive in tokamaks must traverse the strongly turbulent and intermittent scrape-off-layer (SOL) and edge plasma; however, usually propagation characteristics are assessed using smooth time-averaged one-dimensional plasma profiles. Here, we address the question of the effective scale length for evanescence of an incident fast wave (FW) between the antenna and the core plasma when there is strong SOL intermittency, i.e. 2D density profiles varying perpendicular to B, with a significant disparity between the average density, the density between intermittent blob-filaments, and the peak blob-filament density. Although the FW wavelength is long compared with the dimensions of the turbulence, the FW does not simply average over the turbulent density, rather the evanescence is usually controlled by the density between blobs. This effect can decrease antenna coupling to the core plasma relative to average-profile estimates. It is expected to be significant when the distance between the antenna and the nominal FW cutoff (where propagation begins) is long, such as in some ITER scenarios. [Preview Abstract] |
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YP8.00018: Coherent nonlinear structures in ITG-Zonal flow system Rameswar Singh, Raghvendra Singh, Predhiman Kaw, Patrick H. Diamond Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG) - Zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of ITG mode and the longer scale zonal mode is described by a dynamical equation for the $m = n =0$ component of the potential. In a moving frame, two populations of trappped and untrapped drift wave trajectories are shown to exist. This novel effect leads to formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radialy propagating modulation envelope structures such as solitons, shocks, nonlinear wave trains, etc. [Preview Abstract] |
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YP8.00019: HYDRA Simulations Relevant to Collisionless Shock Experiments to be Performed at NIF Christopher Plechaty, Channing Huntington, Frederico Fiuza, Dmitri Ryutov, Hye-Sook Park, Steven Ross, Radu Presura, Bruce Remington Collisionless shocks are ubiquitous in the universe, and occur when the thickness of the shock is much smaller than the Coulomb collision mean free path. In astrophysical systems, collisionless shocks lead to the generation of magnetic fields, which are thought to play an important role in several different phenomena, such as particle acceleration, and the structuring of supernova remnants. The development and evolution of these self-generated magnetic fields is not entirely understood. To investigate the microphysics which plays a role in collisionless shock formation and magnetic field generation in the laboratory, experiments will be performed at the National Ignition Facility. In these experiments, two opposing polyethylene (CH2) targets will be each irradiated with $\sim$ 10$^{16}$ W/cm$^{2}$ to produce counter-streaming flows. In preparation for these experiments, in this work we model the plasma flow in the context of radiation hydrodynamics, by employing the Arbitrary Lagrange-Eulerian (ALE) radiation hydrodynamics code HYDRA [1]. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. \\[4pt] [1] M. Marinak, et al., POP 8, 2275 (2001). [Preview Abstract] |
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YP8.00020: ABSTRACT WITHDRAWN |
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YP8.00021: Stationary Flowing Liquid Lithium (SFLiLi) systems for tokamaks Leonid Zakharov, Charles Gentile, Lane Roquemore The present approach to magnetic fusion which relies on high recycling plasma-wall interaction has exhausted itself at the level of TFTR, JET, JT-60 devices with no realistic path to the burning plasma. Instead, magnetic fusion needs a return to its original idea of insulation of the plasma from the wall, which was the dominant approach in the 1970s and upon implementations has a clear path to the DEMO device with $P_{DT}\simeq100$ MW and $Q_{electric}>1$. The SFLiLi systems of this talk is the technology tool for implementation of the guiding idea of magnetic fusion. It utilizes the unique properties of flowing LiLi to pump plasma particles and, thus, insulate plasma from the walls. The necessary flow rate, $\simeq1$ g$^3$/s, is very small, thus, making the use of lithium practical and consistent with safety requirements. The talk describes how chemical activity of LiLi, which is the major technology challenge of using LiLi in tokamaks, is addressed by SFLiLi systems at the level of already performed (HT-7) experiment, and in ongoing implementations for a prototype of SFLiLi for tokamak divertors and the mid-plane limiter for EAST tokamak (to be tested in the next experimental campaign). [Preview Abstract] |
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YP8.00022: The Tearing Stability of High-$\beta_N$ Discharges is Directly Linked to the Ideal MHD Stability Boundary F. Turco, T.C. Luce, A.D. Turnbull, D. Brennan High-$\beta_N$ scenarios in tokamaks are limited by tearing modes (TM) above the no-wall $\beta_N$ limit. It has been shown that the calculated classical stability index $\Delta$' has a pole at the $\beta_N$ ideal-wall limit, due to the proximity to the 1/1 internal kink limit, destabilizing a m/n=3/2 or =2/1 TM. New modeling of several experimental DIII D equilibria shows that this feature is common to all the types of scenarios, e.g. with $q_{min}{\gg 1}$ (no 1/1 internal kink), without a conducting wall, and with a wall in contact with the plasma surface. Systematic changes to the plasma current density and pressure profiles show that the $\Delta$' trends with $\beta_N$ for all the equilibria have a sharp increase at $\sim90\%$ of the ideal (no-wall, with-wall, without vacuum) limit, independently from the proximity to the q=1 surface. In this $\beta_N$ range, small perturbations in the ideal MHD boundary will cause large changes in the tearing stability. This effect may overwhelm the attempts to stabilize the TMs, e.g. with broad or direct ECCD injection. [Preview Abstract] |
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YP8.00023: An External Circuit Model for 3D Electromagnetic Particle-In-Cell Simulations M.C. Lin, C.D. Zhou, D.N. Smithe In this work, an algorithm for coupling external circuit elements to electromagnetic (EM) particle-in-cell (PIC) simulations is developed. The circuit equation including an external voltage or current source, resistance, inductance, capacitance, and a dynamic load is solved simultaneously with the EM PIC updaters through an instant measured voltage across the system to obtain the supplied current for feeding into the system. This external circuit model has been demonstrated and implemented in a 3D conformal finite-difference time-domain PIC code, Vorpal. [Preview Abstract] |
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YP8.00024: Improved Field Emission Algorithms for Modeling Field Emission Devices Using a Conformal Finite-Difference Time-Domain Particle-in-Cell Method M.C. Lin, J. Loverich, P.H. Stoltz, C. Nieter This work introduces a conformal finite difference time domain (CFDTD) particle-in-cell (PIC) method with an improved field emission algorithm to accurately and efficiently study field emission devices. The CFDTD method is based on the Dey-Mittra algorithm or cut-cell algorithm, as implemented in the Vorpal code. For the field emission algorithm, we employ the elliptic function v(y) found by Forbes and a new fitting function t(y)2 for the Fowler-Nordheim (FN) equation. With these improved correction factors, field emission of electrons from a cathode surface is much closer to the prediction of the exact FN formula derived by Murphy and Good. [Preview Abstract] |
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YP8.00025: Historical time-recessive recombinant nucleotidal gene transfer Michael A. Norton Whether conscious of it or not, physicist Tim Berners-Lee basically applied principle of a nuclear chain reaction to electron transport, a remarkable outcome being the world wide web. On a less dense exponential than the nucleus, but still by out of control design (1999), the flow of electrons with high symmetry (hypertext) brought about astonishing new insights to the field. No one in the author's sphere of influence, including the author, ever learned or taught that such chain reactions have a time-recessive trajectory, such that key significant moments in the new science had impact not only the world at present, but on scale overlapping with ancestors. Dr. Chuck Darwin learned man indeed did arise in Africa (brown toastmasters); author suggests his creed ``survival of the fittest'' in post-20th century hindsight, for man initialized nuclear energy in Eurasia (white toastmasters), and nearly brought the world to collapse by dropping nuclear weapons on humans in Asia (yellow toastmasters), be best updated ``survival of the most communicative.'' If true, this informs that the measure of the appended science's power is as equally as important as the measure of its speed,; ergo, there really is no energy crisis. [Preview Abstract] |
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YP8.00026: Length Contraction Should not be Independent of Time Florentin Smarandache In Special Theory of Relativity it looks that the length contraction along the direction of the motion is independent of time, i.e. if a rocket flies one second, or the rocket flies one year the rocket's along-the-motion length contraction is the same, since the contraction factor \[ C(v)=\sqrt {1-\frac{v^{2}}{c^{2}}} \] depends on the rocket's relativistic speed ($v)$ and on the light speed in vacuum ($c)$ only. \newline We find this as unrealistic, incomplete. It is logical that flying more and more it should increase the length contraction. What about the cosmic bodies that continuously travel, do they contract only once or are they continuously contracting? [Preview Abstract] |
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YP8.00027: Impact of Screening and Ionization on Coulomb Coupling in Strongly Coupled Plasmas Liam Stanton, Michael Murillo Coulomb coupling is traditionally defined by the parameter $\Gamma = Q^2/aT$, which is the ratio of a potential energy $Q^2/a$ ($Q$ is the charge and $a$ is the spacing) to a kinetic energy $T$ ($T$ is the temperature in energy units). We examine regimes of strong coupling in dense plasma experiments using a refined definition in which we compute the potential and kinetic energies directly from their thermodynamic definition and include the effects of finite ionization [1] and screening [2], which have recently been shown to have important impacts on coupling. We propose optimal experimental regimes that can be probed with XRTS to examine directly the physics of strong coupling.\\[4pt] [1] M. S. Murillo et al. PRE 87, 063113 (2013).\\[0pt] [2] M. Lyon, S. D. Bergeson, and M. S. Murillo PRE 87, 033101 (2013). [Preview Abstract] |
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YP8.00028: A Gradient-Corrected, Analytic Screening Potential for Dense, Strongly-Coupled Plasmas Liam Stanton, Michael Murillo We generalize the Yukawa potential to allow for moderate spatial variations in the electronic density and non-ideal contributions to the compressibility for both classical and quantum plasmas. Based on a gradient expansion around the Thomas-Fermi limit of density functional theory, the new potential contains a bifurcation that separates purely repulsive behavior from oscillatory, Friedel-like behavior. This potential has no empirical parameters and is valid at arbitrary temperature and density, yet it adds no additional computational complexity. We use this gradient-corrected screening potential to predict properties of warm dense matter that can be validated through XRTS experiments. [Preview Abstract] |
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YP8.00029: POSTDEADLINE |
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YP8.00030: Bootstrap current and the magnetic structure of W7-X A.S. Ware, P.S. Burns, S.P. Hirshman The impact of self-consistent bootstrap current on the magnetic structure of equilibria in computational studies of the W7-X stellarator is examined. While one of the criteria in designing W7-X was the minimization of the bootstrap current, at finite-$\beta$ there will likely still be some residual bootstrap current. Even a small bootstrap current can change the rotational transform profile and thus, change the magnetic configuration, especially in the edge region. In this work, free-boundary equilibria for the W7-X coil configuration have been obtained at a range of $\beta$ values and the bootstrap current has been calculated for each. Equilibria with self-consistent bootstrap current (i.e., where the plasma current is solely from the bootstrap current) have been obtained as well. The impact of both finite-$\beta$ and bootstrap currents on the magnetic structure in the edge is examined using the SIESTA code [Hirshman, {\it et al.}, Phys. Plasmas {\bf 18}, 062504 (2011)]. The formation of islands in the edge regions is indicated as a result of self-consistent bootstrap current. Methods of removing this impact of bootstrap current will be discussed. [Preview Abstract] |
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YP8.00031: Initial coil sets for a high-$\beta$ stellarator-tokamak hybrid B. Schlomann, A.S. Ware, D.A. Spong Magnetic coil configurations have been developed for a drift-optimized, tokamak-stellarator hybrid that is stable to both pressure- and current-driven modes for high values of $\beta$. Previous work on this configuration [A. S. Ware, {\it et al.}, Phys. Rev. Lett, 89, 125003 (2002)] was carried out using a fixed-boundary equilibrium (i.e., with no set of external coils). Here, we present initial work to produce a realizable coil set for such a configuration. This work is done using the COILOPT code to develop an initial coil set and the STELLOPT code to enhance the quality of the resulting free-boundary equilibria. Since this is a hybrid device, the initial modular coil sets have the advantage of being simpler than modular coils from recent stellarator design efforts (such as QPS and NCSX). Ballooning stability is analyzed using the COBRAVMEC code and transport properties are analyzed using the DKES code. [Preview Abstract] |
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YP8.00032: Comparison between Prandtl, Navier-Stokes and Euler solutions for 2D flows in the presence of solid boundaries Marie Farge, Romain Nguyen van yen, Matthias Waidmann, Kai Schneider, Rupert Klein In 1904 Prandtl introduced the notion of boundary layer (BL), assuming all viscous energy dissipation takes place only in the BL (as long as it remains in contact with the body) whose thickness is inversely proportional to the Reynolds number, $Re$. He derived the BL equation and succeeded to asymptotically match its solution with that of an inviscid fluid flow governed by Euler's equation outside the BL. In the poster we address the following question: does energy dissipate when the BL detaches from the solid body? We consider a jet, modeled as a vorticity dipole, impinging onto a wall, that we study by Direct Numerical Simulation to see how solutions behave in the vanishing viscosity limit (equivalent to the limit of large $Re$). Starting from the same initial flow and the same geometry, we compare the solutions obtained for Euler's equation, Prandtl's equation, and Navier-Stokes equation, using different numerical methods. We observe that in the vanishing viscosity limit energy dissipation does not tend to zero, in a BL whose thickness scales as $Re^{-1/2}$ (as predicted by Prandtl's 1904 theory), but produces vortices at the wall which entrain the BL and roll it up to form a dissipative structure, whose thickness scales as $Re^{-1}$ (Kato, 1984), which detaches from the wall. [Preview Abstract] |
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YP8.00033: X-ray Imaging and preliminary studies of the X-ray self-emission from an innovative plasma-trap based on the Bernstein waves heating mechanism C. Caliri, F.P. Romano, D. Mascali, S. Gammino, A. Musumarra, G. Castro, L. Celona, L. Neri, C. Altana Electron Cyclotron Resonance Ion Sources (ECRIS) are based on ECR heated plasmas emitting high fluxes of X-rays. Here we illustrate a pilot study of the X-ray emission from a compact plasma-trap in which an off-resonance microwave-plasma interaction has been attempted, highlighting a possible Bernstein-Waves based heating mechanism. EBWs-heating is obtained via the inner plasma EM-to-ES wave conversion and enables to reach densities much larger than the cut-off ones. At LNS-INFN, an innovative diagnostic technique based on the design of a Pinhole Camera (PHC) coupled to a CCD device for X-ray Imaging of the plasma (XRI) has been developed, in order to integrate X-ray traditional diagnostics (XRS). The complementary use of electrostatic probes measurements and X-ray diagnostics enabled us to gain knowledge about the high energy electrons density and temperature and about the spatial structure of the source. The combination of the experimental data with appropriate modeling of the plasma-source allowed to estimate the X-ray emission intensity in different energy domains (ranging from EUV up to Hard X-rays). The use of ECRIS as X-ray source for multidisciplinary applications, is now a concrete perspective due to the intense fluxes produced by the new plasma heating mechanism. [Preview Abstract] |
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YP8.00034: A new method for computing the gyrocenter orbit in the tokamak configuration Yingfeng Xu Gyrokinetic theory is an important tool for studying the long-time behavior of magnetized plasmas in Tokamaks. The gyrocenter trajectory determined by the gyrocenter equations of motion can be computed by using a special kind of the Lie-transform perturbation method. The corresponding Lie-transform called I-transform makes that the transformed equations of motion have the same form as the unperturbed ones. The gyrocenter trajectory in short time is divided into two parts. One is along the unperturbed orbit. The other one, which is related to perturbation, is determined by the I-transform generating vector. The numerical gyrocenter orbit code based on this new method has been developed in the tokamak configuration and benchmarked with the other orbit code in some simple cases. Furthermore, it is clearly demonstrated that this new method for computing gyrocenter orbit is equivalent to the gyrocenter Hamilton equations of motion up to the second order in timestep. The new method can be applied to the gyrokinetic simulation. The gyrocenter orbit of the unperturbed part determined by the equilibrium fields can be computed previously in the gyrokinetic simulation, and the corresponding time consumption is neglectable. [Preview Abstract] |
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YP8.00035: Particle-in-cell simulation study on turbulence driven parametric instability of the Alfven-ion-cyclotron waves Helen Kaang, Chang-Mo Ryu, Tongnyeol Rhee Nonlinear damping of Alfven-ion-cyclotron (AIC) waves via the parametric instability was investigated by particle-in-cell simulation with low and high beta plasmas. PIC simulation shows same AIC wave damping phenomena regardless of the plasma beta. The excited AIC waves were soon damped via the parametric instabilities; the modulational, decay, and beat instabilities. The ion-acoustic waves and its harmonic mode were excited through the parametric instabilities. The spectrums of ion density and the electromagnetic wave fluctuations showed inverse cascade processes as the results of the continuous excitation of instabilities. These simulation results and the fluid theory showed coherence in low beta plasma, but incoherence in high beta plasma. The fluid theory expects that the AIC waves are unstable for all of the three type parametric instability in low beta plasma, but the only beat instability in high beta plasma. So, this simulation study shows that the plasma kinetic effects which are not considered in the fluid theory lead to the same nonlinear damping phenomena of AIC waves regardless of the plasma beta. [Preview Abstract] |
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YP8.00036: Aluminum X-ray Mass Ablation Rates Relevant to Inertial Confinement Fusion Jonathan Hager, John Kline, David Montgomery, Derek Schmidt, Igor Usov, Richard Olson In indirect-drive inertial confinement fusion (ICF), a spherical target is imploded as a response to x-ray mass ablation of the target's shell. Typical ICF ablator materials include plastic, doped plastic, high density carbon, and beryllium. The equation of state of many ICF ablators are commonly measured using an impedance matching technique where a relative measurement is made compared to a standard material. Aluminum's shocked equation of state has been studied through many absolute and relative measurements making it an excellent and common choice as a standard in these types of experiments. This work proposes to use aluminum as a surrogate ablator material to aid in the benchmarking of the hydrodynamics codes used to design experiments for indirect-drive thermonuclear ignition at the National Ignition Facility (NIF). X-ray mass ablation rates have been measured in aluminum at conditions relevant to indirect-drive inertial confinement fusion (ICF) as a first step in developing this platform. The measurements used the same technique as Olson et al. for typical ablator materials allowing a comprehensive comparison. [Preview Abstract] |
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YP8.00037: Kelvin-Helmholtz instability in non-Newtonian complex plasma Debabrata Banerjee, Sudip Garai, M. Sita Janaki, Nikhil Chakrabarti In dusty plasma, viscosity plays a vital role on the dynamics of dust flow. For Newtonian regime, shear flow takes parabolic form. Strong velocity shear exists in the boundary layer and viscosity for its diffusive nature drives this shear energy to midstream flow to launch the instability. Dusty plasma shows non-Newtonian behaviour where viscosity ($\eta$) depends on velocity shear rate ($\gamma$). Different values of $\epsilon$ (ratio of equilibrium plasma temperature and melting temperature) generate different types of velocity profile and corresponding viscosity profile with shear rate. With numerical eigenvalue analysis, it is shown that shear thinning property enhances the Kelvin-Helmholtz instability but shear thickening property stabilizes it [D. Banerjee et. al., Phys. Plasmas {\bf {20}}, 073702 (2013)]. The maximum growth rate is observed for incompressible limit and the effect of compressibility is found to decrease the growth rate. The dispersion effect of Poisson's equation is also reported. [Preview Abstract] |
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YP8.00038: Laser driven shock and shockless experiments in SG-II laser facility Hua Shu, Sizu Fu, Xiuguang Huang Laser driven shock wave can obtain ultra-high pressure(\textgreater\ 1TPa) and it can be used to obtain high pressure Hugoniot data. But preheat is a crucial problem in laser-driven shock wave experiments which can infact on equation of state measurement results. The study of preheat in directly laser-driven condition is scare. In this paper we will present the experimental results of preheat in directly laser-driven condition. The free-surface expansion velocity(due to preheat) was measured using a double-channel line-imaging VISAR. The free-surface velocity of different heights Al sample was obtained. The maximum free-surface velocity is about 1.2 Km/s. [Preview Abstract] |
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YP8.00039: Generation of well-collimated mono-energetic heavy ion beams by intense laser pulses D. Wu, B. Qiao, C. McGuffey, F.N. Beg We report on the generation of well-collimated quasi-monoenergetic heavy ion beams from ultrathin foil targets irradiated by intense laser pulses. It is found that the field ionization effect plays an important role in the acceleration dynamics of heavy ion species. The heavy ions close to the laser propagation axis are ionized to a higher charge state by the strong laser field within its central focal region, which are favorable to be accelerated by the laser radiation pressure due to larger charge-to-mass ratio. The others located away from the axis are ionized to lower charge states due to the weaker laser field. By choosing an optimal coupling of laser intensity, target material and thickness, a well-collimated mono-energetic high charge state heavy ion beam can be produced. Two-dimensional particle-in-cell simulations shows 300 MeV $\textrm{Al}^{12+}$ ion beam are produced from ultrathin foils by intense laser at intensities of $10^{20}\textrm{Wcm}^{-2}$. Simulations for different target materials, such as Fe and Cu, are also carried out to verify this novel scheme. [Preview Abstract] |
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YP8.00040: Surface morphology changes and damage in hot tungsten by impact of 80 eV - 12 keV He-ions and keV-energy self-atoms Hussein Hijazi, Mark E. Bannister, Predrag S. Krstic, Chad M. Parish, Harry M. Meyer III, Fred M. Meyer We report on measurements of interactions of 50 -- 12,000 eV He ions with heated tungsten surfaces performed at the ORNL MIRF. Surface morphology changes, as well as nano-fuzz formation were investigated as function of flux and total fluence, for both virgin and pre-damaged W-targets. At low fluences, ordered surface structures are observed, with great grain-to-grain variability, together with blisters and pinholes, whose density and size increase with increasing fluence. At larger fluences, individual grain characteristics disappear, and the entire surface assumes a frothy appearance in FIB/SEM, with a multitude of near-surface bubbles with a broad range of sizes, and disordered whisker growth, while in SEM imaging the surface is indistinguishable from nano-fuzz produced on linear plasma devices. These features are evident at progressively lower fluences as the He-ion energy is increased, particularly above 1 keV, where the He beam serves not only to load the near-surface region with He to saturation, but to produce significant near-surface damage sites that can trap He. We also report on observations of the effects on surface morphology changes and nano-fuzz formation of pre-damage created by self-ion impact, and on MD simulations of near-surface damage using self-atoms. [Preview Abstract] |
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YP8.00041: Analysis of RF emissions from laser induced breakdown of atmospheric air and metals Prem Kiran Paturi, Vinoth Kumar Lakshmi, Manikanta Elle, Leela Chelikani The low frequency (RF, microwave) emissions from laser produced plasma (LPP) are of great interest because of their variety of applications. The RF waves emitted by the nanosecond LPP of atmospheric air and metal (Al, Cu) targets were detected using antennas over frequency ranges (30MHz-18GHz) and were monitored using a spectrum analyzer (3Hz-50GHz). With different target materials, the dominant emission lines were observed to fall in different specific frequency ranges within the detection limit. The emissions from Cu were in the higher frequency range (100-200 MHz) than that of Al (30-100 MHz) may be due to the higher electron density of Cu, which contributes to the LPP conductivity. From the LPP of atmospheric air, the RF output was found to be increasing with the input laser energy up to certain value, beyond which almost no emission was observed. This effect is attributed to the modification in the net induced dipole moment due to the multiple plasma sources in the LPP at higher input laser energies. The detected radiation was observed to be dependent on laser and antenna polarization. Further studies may lead to an efficient technique for material identification from the RF characteristic peaks. [Preview Abstract] |
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YP8.00042: Structure formation of thermally driven turbulence Yohei Kawazura, Zensho Yoshida Self-organized structures in plasma turbulence, such as zonal flow and streamer, play important roles in terms of confinement in fusion devices. Recently thermodynamical approaches to dictate self-organization are proposed. Yoshida and Mahajan explained the bifurcation to ``High confinement mode'' in magnetically confined fusion device by using thermodynamic model [1]. The nonexact term available to generate vorticity in equation of motion is baroclinicity ($T\nabla S$). Assuming circulation of the fluid element as cycle of heat engine, fluid mechanics and thermodynamic laws can be connected. In this study, by solving the fluid equation of motion as specific mechanical process, we investigate the connection between thermal driving of turbulence and self-organization of vortical structures. \\[4pt] [1] Z. Yoshida and S. M. Mahajan, Phys. Plasmas 15, 032307 (2008). [Preview Abstract] |
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YP8.00043: Scaling Optimization of the SIESTA MHD Code Sudip Seal, Steven Hirshman, Kalyan Perumalla SIESTA is a parallel three-dimensional plasma equilibrium code capable of resolving magnetic islands at high spatial resolutions for toroidal plasmas. Originally~designed to exploit small-scale~parallelism, SIESTA~has now been scaled to execute efficiently over several thousands of processors P. This scaling improvement was accomplished with minimal intrusion to the execution flow of the original version. First, the efficiency of the iterative solutions was improved by integrating the parallel tridiagonal block solver code BCYCLIC. Krylov-space generation in GMRES was then accelerated using a customized parallel matrix-vector multiplication algorithm. Novel parallel Hessian generation algorithms were integrated and memory access latencies were dramatically reduced through loop nest optimizations and data layout rearrangement. These optimizations sped up equilibria calculations by factors of 30-50. It is possible to compute solutions with granularity N/P near unity on extremely fine radial meshes (N\textgreater 1024 points).~Grid separation in SIESTA, which manifests itself primarily in the resonant components of the pressure far from rational surfaces, is strongly suppressed by finer meshes.~Large problem sizes of up to 300K simultaneous non-linear coupled equations have been solved on the NERSC supercomputers. [Preview Abstract] |
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YP8.00044: Observation and control of shock waves in individual nanoplasmas Daniel D. Hickstein, Franklin Dollar, Wei Xiong, K. Ellen Keister, Jennifer L. Ellis, Chengyuan Ding, Henry C. Kapteyn, Margaret M. Murnane, Jim A. Gaffney, Mark E. Foord, Stephen B. Libby, Brett B. Palm, Jose L. Jimenez, George M. Petrov Using short (40 fs) laser pulses at an intensity of 10$^{14}$ W/cm$^{2}$, we present the first observation of shock waves in nanometer-scale plasmas (nanoplasmas). Nanoplasmas offer enhanced laser absorption compared to either solid or gas targets, and the generation of shock waves presents an appealing method for creating new sources of monoenergetic ions and X-rays from a tabletop scale apparatus. By utilizing an instrument that images photoions from a single nanoparticle, we make the first experimental observation of individual nanoplasmas and observe clear shock waves. We demonstrate that the introduction of a heating pulse prior to the main laser pulse increases the intensity of the shock wave, and produces a strong burst of quasi-monochromatic ions with energies around 100 eV. Numerical hydrodynamic calculations show that the energy of the quasi-monochromatic ions increases with the intensity of the driving laser, suggesting a possible avenue for production of higher-energy monoenergetic ions required for medical applications. Additionally, this observation of well-characterized shock waves in dense, low-temperature plasmas may enable the laboratory control, study, and exploitation of nanoscale shock phenomena with tabletop lasers. [Preview Abstract] |
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YP8.00045: Stochastic advection and landau damping in a collisionless plasma Anjor Kanekar, Alexander Schekochihin, William Dorland, Greg Hammett, Nuno Loureiro We consider a simple model of passive chaotic advection of a kinetic field in a collisionless plasma. We test the fluctuation dissipation theorem for a kinetic field, without stochastic advection as a first result. We then present results discussing the effect of stochastic advection on the evolution of the kinetic field-- specifically, the efficiency of linear Landau damping in this simple model. We observe that the free energy is scattered through phase space, allowing a possibility of return of energy from small velocity scales to large. This is interpreted as a manifestation of the ``plasma echo'' phenomenon in a 3-d nonlinear stochastic system. [Preview Abstract] |
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YP8.00046: Investigating the effect of Argon Pressure on DC and High Power Magnetron Plasmas Baysha Bernales, Rustem Bolat, Andre Anders, Jonathan Slack Smart Glass is fabricated by depositing thin films of specialized material onto a transparent substrate. When a potential is applied across the surface of the Smart Glass, it changes its optical properties. Direct Current Magnetron Sputtering (DCMS) and High Power Impulse Magnetron Sputtering (HiPIMS) are two methods of PVD that are used to fabricate this material. In previous research, it has been noted that magnetron plasmas have localized ionization zones that rotate clockwise in DCMS and counterclockwise in HiPIMS. Not much is known about what causes the change in rotation. This research seeks to investigate what occurs during the first moments of plasma evolution. Both DC and high power magnetron plasmas were observed as Argon pressure was varied. It was found that pressure had a very pronounced effect on the floating-point potential signal that was received from the probes placed in the plasma. It was found that when a high-pressure jet of Argon was injected into the system, that the rotation pattern of the DC magnetron plasma was disrupted. It was also found that at certain pressures, the voltage signal was less indicative of azimuthal rotation and more indicative of z-direction breathing modes. [Preview Abstract] |
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YP8.00047: Evaluation of Runaway Electrons with CQL3D/NIMROD and Validation with Measurements in DIII-D Tokamak M. Choi, V.A. Izzo During plasma disruptions in tokamaks, fast current quench may produce a significant current of runaway electrons (REs) in the plasma. REs lost to the first wall can result in local power dissipations, which can potentially cause localized melting of first wall components. In DIII-D experiments, RE currents were measured from negligible to over 500 kA during Ar pellet injections. However, during Ne gas injections, they were not observed [1]. To understand these observations, the bounce-averaged Fokker-Planck code CQL3D is coupled with the nonlinear MHD code NIMROD. These combined simulation tools enable the evaluation of plasma current profile evolution self-consistently with the evolution of the generation/loss of RE currents during the termination phase of disruptions. In this work, we report validation results of CQL3D/NIMROD with measurements for a set of DIII-D discharges with Ar pellet injections and Ne gas injections.\par \vskip6pt \noindent [1] V.A.\ Izzo, et al., Plasma Phys.\ Control. Fusion {\bf 54} (2012) 095002. [Preview Abstract] |
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YP8.00048: Cylindrical probe in nonequilibrium plasma - new possibilities Alexander Mustafaev, Artiom Grabovskiy, Anastasiya Strakhova This talk presents the method of reconstruction full EVDF in plasmas with arbitrary degree of anisotropy. It will be demonstrated that cylindrical probe allows to determine only even components of the EVDF Legendre expansion. The odd components can be found by solving the kinetic Boltzmann equation, which relate the even- and odd- index coefficients ($f_{0}$, $f_{1})$; ($f_{0}$, $f_{1}$, $f_{2})$ etc., jointly with experimentally obtained even components. \[ \frac{\partial f_{1} }{\partial t}+v\,\left( {\frac{\partial f_{0} }{\partial z}+\frac{2}{5}\frac{\partial f_{2} }{\partial z}} \right)-\frac{eE_{z} }{m}\left[ {\frac{\partial f_{0} }{\partial v}+\frac{2}{5v^{3}}\frac{\partial }{\partial v}\left( {v^{3}f_{2} } \right)} \right]+\nu_{ea}^{t} f_{1} =0 \] The method has been experimentally tested in two dramatically different types of helium discharge: in positive column of glow discharge and in nonlocal plasma of beam discharge. The new possibilities of the proposed method have been illustrated. The reliability of the proposed method has been tested by comparing the experimentally obtained and theoretically calculated data and independent measurements, carried out using the flat single-sided probe. This work was supported by the Ministry of Education of the Russian Federation. [Preview Abstract] |
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YP8.00049: Simulation and Measurement of Ultra-intense, Short-Pulse Gamma Ray Production by Petawatt Lasers Irradiating High-Z Solid Targets Alexander Henderson, Edison Liang, Taylor Clarke, Nathan Riley, Petr Shagin, Kristina Serratto On interaction with a solid target an ultra-intense short pulse high-energy laser, such as the Texas Petawatt Laser in Austin Texas, accelerates a sub-pico-second burst of electrons into the target at relativistic energies. These electrons then undergo bremsstrahlung, producing a beam of high-energy gamma rays. Even for mm thick gold targets, most of the bremsstrahlung gamma rays escape, while many hot electrons do not. Here we attempt to characterize the angular distribution, energy spectrum and total yield of these gamma rays as produced by the Texass Petawatt Laser irradiating mm thick gold and platinum targets using a combination of dosimeters, Filter Stack Spectrometers (FSS) and Forward Compton Electron Spectrometer (FCES). GEANT4 Monte-Carlo simulation results are then used to fit the data and extrapolate the results beyond the limits of the measurements. We will also discuss potential applications of such intense gamma-ray beams. [Preview Abstract] |
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YP8.00050: The Mixed WKB-Full-Wave Approach and Its Application to Lower Hybrid Wave Propagation and Absorption Zhixin Lu, Fulvio Zonca, Alessandro Cardinali The mixed WKB-full-wave approach for the calculation of the 2D mode structure in tokamak plasmas is further developed based on our previous work [1, 2]. A new scheme for numerical implementation of the mixed WKB-full-wave approach is formulated, based on scale separation and asymptotic analysis. Besides its capability to efficiently investigate the initial value problem for 2D mode structures and linear stability, in this work, the mixed WKB-full-wave approach is extended to the investigation of radio frequency wave propagation and absorption, e.g. lower hybrid waves. As a novel method, its comparison with other approaches, e.g. WKB and beam tracing methods, is discussed. Its application to lower hybrid wave propagation in concentric circular tokamak plasmas using FTU parameters is also demonstrated. \\[4pt] [1] A. Cardinali et al., Phys. Plasmas 10, 4199 (2003) \\[0pt] [2] Z. X. Lu et al., Phys. Plasmas, 19, 042104 (2012) [Preview Abstract] |
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YP8.00051: Molecular Dynamics Simulation of Temperature Relaxation in Dense Hydrogen Plasma Zengxiu Zhao, Qian Ma, Jiayu Dai, Dongdong Kang, Jianmin Yuan Temperature relaxation between electrons and ions in dense plasma is regarded as an essential factor in understanding the physics process in laser-plasma interactions. Here, we perform molecular dynamics (MD) simulation to investigate the electron-ion temperature relaxation with semi-classical potentials in fully ionized dense hydrogen plasma. We compare the results of different potentials such as HM potential, Yukawa potential and Coulomb potential with an appropriate cutoff, in addition, a simplified scattering model is used in the MD simulation to overcome the negative effect called Coulomb Catastrophe. The MD simulation is performed with a code using velocity Verlet integration in a box cell with periodic boundary and the electron number density changes from to. The tested particle number N is ranging from N$=$500 to as many as N$=$4000, the results reported here use N$=$1372. Statistical uncertainty for each case is estimated by performing the code from 6 samples of the ensemble and then taking the average and standard deviation. Furthermore, the results of theoretical models, such as LS, GMS and BPS, are also used to compare with the MD results. [Preview Abstract] |
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YP8.00052: Complex transport properties of warm dense Hydrogen: inclusion of nuclear quantum effects Jianmin Yuan, Dongdong Kang, Jiayu Dai, Huayang Sun, Zengxiu Zhao Scattering or Collisions are the key physics in determining the transport properties for electrons and ions. Here we show based on ab initio (path-integral) molecular dynamics simulations, by including the Nuclear quantum effects (NQEs), the transport properties of warm dense hydrogen up to 1 eV can be significantly different from the results without NQEs. With the inclusion of NQEs, ionic diffusions are strongly enhanced by the magnitude from 100{\%} to 15{\%} with increasing temperature, while electrical and thermal conductivities are significantly suppressed. In particular at the temperature of 1 eV, where the NQEs have little effects on the static structures, the diffusion is still much larger than that without NQEs. The significant quantum delocalization of ions introduces expressively different scattering cross section between protons compared with classical particle treatments, which can explain the large alterability of transport behaviors. Furthermore, the Stokes-Einstein relation, energy, pressure, and isotope effects are also greatly influenced by NQEs. The complex behavior shows that NQEs cannot be neglected for dense hydrogen even in the warm dense regime. (arXiv:1304.0953 (2013)) [Preview Abstract] |
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YP8.00053: Quantum molecular dynamics simulation of the formation of warm dense SiH$_{4}$ Jiayu Dai, Huayang Sun, Jianmin Yuan, Dongdong Kang, Zengxiu Zhao The ionic and electronic structures of warm dense silane (SiH$_{4})$ for four densities of 1.795, 2.260, 3.382 and 3.844 g/cm$^{3}$ are studied using quantum molecular dynamics at the temperatures (T) from 1000 K to 3 eV. All the structures melt above 1000 K. The melted states from 1000 K to 4000 K are best characterized as polymeric, and they will convert to dense plasma states at 1 eV. At the polymeric state region, the two low density cases of 1.795, 2.260 g/cm$^{3}$ dissociate and transform to polymeric state via chain states from the initial structures, which is different from those of the higher densities. The present characters can help us to understand how the warm dense matter forms. A rise in conductivity is found when T \textless 1000 K, indicating the nonmetal-to-metal transition. The conductivity decreased slightly when the temperature becomes higher. The formation of warm dense plasma can be characterized as the procedure: firstly, melting from solid phases; secondly, forming polymeric states with large clusters; finally, forming warm dense plasma with dynamic clusters. [Preview Abstract] |
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YP8.00054: Optical Measurements of Hybrid ECR and Helicon discharges Lutfi Oksuz, Ali Gulec, Ahmed M. Hala, Ferhat Bozduman, Erdogan Teke, Melek Kiristi, Erdal Dikmen, Aysegul Oksuz An experimental study was carried to investigate the effects of simultaneously heating of plasma by ECR and Helicon sources. 850 W 2.45 GHz magnetron and axially varying magnetic field produced by permanent magnets were used for ECR system. Also Nagoya type III antenna, which is connected to the rf power source, placed into the magnetic field. The argon plasma was produced separately and simultaneously by ECR and Helicon sources in the same quartz tube at 5 mTorr. The emission spectrum was taken for different rf power. Ar I lines intensities and broadening will be used for plasma electron temperature and density. [Preview Abstract] |
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YP8.00055: Effect of Collisionality on H-mode Pedestal Structure T.H. Osborne, R.J. Groebner, S.P. Smith, P.B. Snyder, D.M. Thomas, Z. Yan Variations in the H$\,$mode pedestal pressure, p$_{\rm PED}$, by a factor of 1.5 are observed in ITER baseline scenario demonstration discharges on the DIII-D tokamak. Higher p$_{\rm PED}$ occurs when the pressure increase between ELMs is primarily due to an increase in density. The variation in p$_{\rm PED}$ can be understood through the effect of collsionality, $\nu \propto n/T^2$, under the EPED model [1]. In this model, the pedestal pressure gradient, $p^\prime$, grows until it triggers a peeling-ballooning mode, PBM, which results in the ELM. Since, in these discharges, ELMs are triggered at the current driven peeling limit, higher $p^\prime$ is achieved at higher collisionality where the associated bootstrap current is reduced. Under EPED, $p^\prime$ between ELMs is constrained by the kinetic ballooning mode, KBM, for which the critical $p^\prime$ increases with pedestal width. The KBM critical $p^\prime$ for a given pedestal width is reduced at increased collisionality, resulting in the $p^\prime$ required to trigger the PBM being reached only at larger width and so larger pressure.\par \vskip6pt \noindent [1] P.B.\ Snyder et al., Phys. Plasmas {\bf 16}, 054118 (2009). [Preview Abstract] |
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YP8.00056: Optical and double probe measurements of helicon argon plasma source in axially varying magnetic field intensity Ali Gulec, Ferhat Bozduman, Erdogan Teke, Ahmed M. Hala, Erdal Dikmen, Aysegul Oksuz, Melek Kiristi, Lutfi Oksuz In the helicon plasma sources the external magnetic field is usually generated by electromagnets coaxial with the source tube. The magnetic fields intensities can be vary from 100 G to 1000 G for different plasma studies. In this work permanent magnets configuration, which is cylindrical and surrounding 20 cm region of a long 5.5 cm diameter cylindrical quartz tube, was used for the magnetic field. The magnet system is producing 650 G magnetic field intensity in the upstream and downstream of the field symmetrically but the intensity is decreasing down to 350 G in the middle of the magnets configuration. Nagoya type III antenna was placed into the magnetic field region over the quartz tube. The antenna was driven by different rf power at 13.56 MHz. The emission spectrum of argon plasma at high and low magnetic field intensity positions will be taken. The axial dependence of plasma temperature and density will be given by the double probe measurements. [Preview Abstract] |
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YP8.00057: Development of a plasma injector for supersonic drag reduction Angus Macnab, Akel Hashim, Robert Graham, Timothy Ziemba, Kenneth Miller Eagle Harbor Technologies, Inc. is developing and optimizing a magnetohydrodynamic (MHD) plasma injector, designed to reduce viscous skin friction of supersonic aircraft. The broad goals are to 1. Computationally investigate and verify the dominant physical mechanisms for MHD plasma drag reduction; 2. Develop a proof of concept plasma injector demo, which performs within the power limitations of an onboard flight-relevant system; and 3. Use insights gained through computational investigations to optimize the performance of our MHD plasma injector for maximum efficiency. This investigation focuses on flight-relevant Reynolds and magnetic Reynolds numbers at low supersonic (\textit{1 \textless M \textless 3}) speeds. We present numerical and experimental results detailing the development of our plasma injector. [Preview Abstract] |
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YP8.00058: Effects of RF Plasma Polymerization Parameters on Polymeric Thin Film Characteristics Melek Kiristi, Erdogan Teke, Ferhat Bozduman, Ali Gulec, Aysegul Uygun Oksuz, Lutfi Oksuz Synthetic monomer derivatives such as aniline, chloroaniline and ethylene aniline were polymerized onto indium tin oxide (ITO)/glass substrate by radio frequency (RF) vacuum plasma at constant duration and pressure. It was applied variety power during polymerization process and compared with each other regarding electrical and morphological properties. Optical emission spectroscopy (OES) measurement was used for determining plasma species. The thin films were characterized by scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The electrochemical properties of thin films were investigated by cyclic voltammetry (CV). It was shown that applied power significantly affected thin film morphology and stability. [Preview Abstract] |
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YP8.00059: Comparison of DC and RF magnetron sputtering systems for Electrochromic W/Ti Thin Film Deposition Erdogan Teke, Melek Kiristi, Aysegul Uygun Oksuz, Ferhat Bozduman, Ali Gulec, Lutfi Oksuz, Ahmed M. Hala In this study electrochromic tungsten-titanium thin films were deposited on ITO (indium thin oxide) glasses by using both DC and RF magnetron sputtering techniques. The discharges have been operated in same discharge power, geometry and argon/oxygen mixture pressure for comparison. The voltage and current characteristics and optical emission spectrums of both plasma systems will be given. The plasma parameters are determined by a double probe. ITO thin films coating electrical, optical and morphological characteristics will be compared. [Preview Abstract] |
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YP8.00060: Formation of a High Energy Density Field Reversed Configuration I. Romadanov Formation of a compact toroid (CT) or field reversed configuration (FRC) [1-2] with a maximum input of energy and the capture of the magnetic field into plasma is an important scientific and technical challenge. The proposed method of formation is similar to the formation of FRC based on $\theta $-pinch [1], but has some differences, which will be described below. One of the main CT formation problems is the low level of the captured magnetic flux. A study of compact torus formation with a longitudinal current was done [3]. This method of formation has not been used before, and was tested for the first time. Experiments showed that this method can significantly increase the energy input into plasma.\\[4pt] [1] R.H. Kurtmullaev, A.N. Malutin, V.I. Semenov. ``Compact torus,'' VINITI. Series ``Plasma Physics'' 7, 80-135 (1985).\\[0pt] [2] S.V. Ryzhkov Features of Formation, ``Confinement and Stability of the Field Reversed Configuration,'' Problems of Atomic Science and Technology. Series: Plasma Physics. 2002. 4 (7). P. 73-75.\\[0pt] [4] I.V. Romadanov, ``Theoretical and experimental research of Field Reversed Configuration,'' Science and Education. 2 (2012). [Preview Abstract] |
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YP8.00061: Reactors Power Balance Based on Compact Toroid I. Romadanov The power balance [1] of the plasma source system based on compact toroid with a pulse mode of formation is considered. Developed model takes into account the time dependence of the processes, in a pulsed mode of operation of the system. Also magnetic configuration shape and nuclei energy distribution fluency were considered [2]. Analytical solution of Grad-Shafranov equation was taken to determine the shape of the separatrix and magnetic fields into the configuration [3]. For practical calculation, program was written. Code is able to calculates volume power reactions in the confined plasma, using as input the geometry of the magnetic field, the cross section of reaction rates and energy distribution of the nuclei.\\[4pt] [1] J.T. Slough, A.L. Hoffman, R.D. Milroy, etc. Transport, energy balance, and stability of a large field-reversed configuration, Phys. Plasmas, V. 2. N 6. 1995. P. 2286-2291.\\[0pt] [2] P.R. Goncharov, Practical Calculation of Nuclear Fusion Power for a Toroidal Plasma Device with Magnetic Confinement Proceedings of ITC18, p. 289-295, 2008\\[0pt] [3] Antoine J. Cerfon and Jeffrey P. Freidberg ``One size fits all'' analytic solutions to the Grad-Shafranov equation, Phys. Plasmas p. 17, 2010. [Preview Abstract] |
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YP8.00062: 3D Global Braginskii Simulations of Plasma Dynamics and Turbulence in LAPD Dustin Fisher, Barrett Rogers 3D global two-fluid simulations are presented in an ongoing effort to identify and understand the plasma dynamics in the Large Plasma Device (LAPD) at UCLA's Basic Science Facility. Modeling is done using a modified version of the Global Braginskii Solver (GBS) [1] that models the plasma from source to edge region on a field-aligned grid using a finite difference method and 4th order Runge-Kutta time stepping. Progress has been made to account for the thermionic cathode emission of fast electrons at the source, the axial dependence of the plasma source, and biasing the front and side walls. Along with trying to understand the effect sheath's and neutrals have in setting the plasma potential, work is being done to model the biasable limiter recently used by colleagues at UCLA [2] to better understand flow shear and particle transport in the LAPD. Comparisons of the zero bias case are presented along with analysis of the growth and dynamics of turbulent structures (such as drift waves) seen in the simulations. \\[4pt] [1] B. Rogers and P. Ricci. Phys. Rev. Lett. 104:225002, 2010\\[0pt] [2] D. A. Schaffner, et. al., Phys. of Plasmas, 20:055907, 2013 [Preview Abstract] |
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YP8.00063: Full-wave Feasibility Study of Magnetic Diagnostic based on O-X Mode Conversion and Oblique Reflectometry Imaging F.A. Volpe, M. Choi, Y. Patel, O. Meneghini We present initial two-dimensional full-wave modeling of an innovative diagnostic of the magnetic field vector as a function of the minor radius in the pedestal region. An angularly broad millimeter-wave beam of ordinary (O) polarization is obliquely injected in the magnetized plasma; part of it converts in the extraordinary (X) mode at the O-mode cutoff, the rest is reflected. The reflected beam pattern, measured with an array of receivers, contains information on the angular-dependent mode conversion, which contains information on the magnetic pitch angle at the cutoff. Measurements at various frequencies provide radially resolved measurements of pitch angle. The new technique proposed does not require the plasma to be an overdense emitter of Electron Bernstein Waves and is applicable whenever reflectometry is applicable. Simulations performed with the finite-element COMSOL Multiphysics code in ``DIII-D-like'' plasma slabs confirmed the presence of a minimum in reflectivity of an externally injected O-mode beam. The dependence of such reflectivity ``hole'' upon magnetic field is under study. Future inclusion of toroidal ripple, density and magnetic fluctuation effects, as well as possible extensions to a fully three-dimensional diagnostic of the magnetic field will be discussed. [Preview Abstract] |
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YP8.00064: Suprathermal Electrons Flux and its Effect on the Radial Electric Field in TJ-II Julio J. Martinell In non-axisimmetric toroidal magnetic configurations such as stellarators the main contribution to neoclassical transport in low collisionality plasmas is due to trapped particles in the magnetic ripples. The unequal ion and electron fluxes result in an ambipolar electric field which is found to be systematically smaller than the one measured by HIBP. We explore the possibility that the cause may be the presence of suprathermal electrons that are created by the ECRH system, pumped out from the center. A kinetic description of the particle transport is followed in which a non-maxwellian velocity distribution is assumed for the electrons having a high velocity component. For the thermal particles, fluxes are computed from previous expressions. Therefore only the contribution from the high energy tail is considered to include the suprathermal contribution in the low collisionality regime. The expression for the electron fluxes is used to obtain the ambipolar radial electric field. This is compared with the electric field obtained from the thermal particles and an estimate of the contribution of the suprathermal electrons is obtained. Experimental comparisons of the radial electric field are made for the TJ-II Heliac-stellarator for which good HIBP measurements are available. [Preview Abstract] |
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YP8.00065: Flux tube train model for toroidal plasma turbulence simulations T.-H. Watanabe, H. Sugama, A. Ishizawa, M. Nunami A flux tube model widely used in gyrokinetic and gyrofulid simulations of toroidal plasma turbulence, where the field line coordinates are applied to a local simulation box placed on a flux surface, is useful for accurately describing the ballooning type mode structure of drift waves. However, if the unstable mode structure widely expands in the poloidal angle, some numerical difficulties arise. While a remedy is to extend the poloidal length of the simulation box, it leads to a sever CFL condition. To overcome the numerical limitation, a ``flux tube train'' model is developed, where a series of flux tubes are connected along the field line. The new simulation model is successfully applied to the ion temperature gradient turbulence even in cases with poloidal correlation lengths longer than $2 \pi$, and is verified by detailed comparisons with the conventional flux tube results. [Preview Abstract] |
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YP8.00066: Gasdynamic Multiple-Mirror Trap Alexei Beklemishev, Andrei Anikeev, Peter Bagryansky, Alexander Burdakov, Dmitrii Gavrilenko, Alexander Ivanov, Sergei Polosatkin, Stanislav Sinitsky The new linear device for confinement of fusion plasmas, GDMT, is being developed at the Budker Institute of Nuclear Physics, Novosibirsk. The facility will combine features of existing GOL-3 and GDT devices: the central GDT-like cell with sloshing NBI ions, and the multiple-mirror plugs for suppression of axial losses. Such combination became feasible due to recent discoveries. In particular, the requirement of flute-mode stability can be relaxed by using vortex confinement, achieved by plasma biasing through open field lines. This allows the use of potentially destabilizing multiple-mirror sections. Another key effect is the enhanced multiple-mirror confinement at low densities, which is due to collective rather than coulomb scattering of ions. Hence the multiple-mirror plugs can work at pressures compatible with magnetic confinement. These two main technologies are supplemented by axial injection of pulsed electron beams. Besides additional plasma heating (like in GOL-3), such injection can be used for induced collective scattering in the multiple-mirror plugs and for plasma biasing. The new device is designed to be superconducting and modular. It will be built in stages, with the first stage, GDMT-T, intended for PMI studies. [Preview Abstract] |
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YP8.00067: Absorption and mode conversion of fast waves at high ion cyclotron harmonics in the helicon frequency range Suwon Cho Recently there has been considerable interest in using fast waves in the helicon frequency range, which corresponds to high ion cyclotron harmonics, for off-axis current drive in tokamaks. The hot plasma dispersion relation shows that the ion Bernstein mode can propagate on the high field side of the harmonic resonance. The launched fast wave can be converted into the Bernstein mode and be absorbed near the resonance layer. In this work, absorption and mode conversion of the fast wave are examined with an one dimensional wave equation, which is converted from the dispersion relation by taking the inverse Fourier transform. In obtaining the relevant equation the hot plasma dispersion relation is cast into a form without any sums using the method of steepest descents and then it is approximated by polynomials in the perpendicular wave number. [Preview Abstract] |
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YP8.00068: First Results from a Charged Fusion Products Diagnostic at MAST Ramona V. Perez, Scott Y. Allan, Werner U. Boeglin, Marco Cecconello, Ken G. McClements, Douglass S. Darrow We designed, built and installed in MAST a 4-channel solid-state detector array for the detection of the charged deuterium-deuterium fusion products protons and tritons. The array has been mounted at the end of the reciprocating probe arm in MAST allowing it to sample a range of radial positions. First data have been taken in August 2013. The detector signals have been digitized with a 60MHz sampling rate and have been continuously recorded during plasma discharges. Protons and tritons were readily identified and counted. The observed count rates showed clear dependence on the neutral beam power and were modulated synchronous with saw-teeth. Comparison with data obtained from the MAST neutron camera and the fission chamber neutron detector is planned. We found that time resolutions as low as at least 1 ms were achievable. The detector performance and first analysis results for various plasma scenarios will be presented. [Preview Abstract] |
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YP8.00069: Characterization of impurity deposition on the first wall of EAST tokamak using LIBS Hongbin Ding Our recent investigations have indicated a potential of laser-induced breakdown spectroscopy (LIBS) for analysis of the co-deposited layers on the first wall in the Experimental Advanced Superconducting Tokamak (EAST) in a vacuum environment. Detailed information of compositions at the superficial and in-depth positions of the first wall of divertor tiles can be obtained by analyzing the spectra from 200-980 nm. The decrease in concentrations of the depositional elements (such as Li) was clearly observed in the depth from 0 to 100 $\mu $m, but the concentrations of the substrate elements were found to be relatively uniform in the depth after dozens of laser pulses. The linear correlation approach has been applied for improving the depth profile accuracy and identifying the interface boundary between the deposition layer and the substrate for the first time. This would help us to develop LIBS method to monitor the fuel retention and impurity. [Preview Abstract] |
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YP8.00070: Plasmonics in Quantum Plasmas with two Species of Free Charge Particles Modjtaba Moaied, Kostya Ostrikov The field of quantum plasma nanoscience is increasing and motivated by its potential applications in modern technology (e.g. metallic and semiconductor nanostructures including metallic nanoparticles, nano-plasmonic devices, quantum dots, thin metal films, quantum well, etc.). The collective oscillations in quantum plasmas have been studied by many theoretical and experimental works. In most of them, plasmonics were investigated in metallic structures and those are collective oscillations of conduction electrons in quantum plasmas with one species of free charge particles. In this work, plasmonics in semiconductors with two types of free charge carriers are investigated taking into account the collision between free charge carriers and lattice. The spectra and damping of plasmonic are analytically and numerically obtained in three referred types of plasmons: (1) Volume or Bulk Plasmons, (2) Surface Plasmon Polaritons, and (3) Localised Surface Plasmons. It shows that weakly damped plasmonics propagate in highly doped semiconductors (e.g., by electron density $n_{e} \gg 10^{15}\mbox{\thinspace cm}^{-3}$ in a N-type Silicon at room temperature) and the energy of plasmonics in semiconductors is significant smaller than that in metals (i.e., in THz renge). [Preview Abstract] |
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YP8.00071: A Lagrangian perspective on the stability of ideal MHD equilibria with flow Yao Zhou, J.W. Burby, Hong Qin We take a careful look at two approaches to deriving stability criteria for ideal MHD equilibria. One is based on a tedious analysis of the linearized equations of motion, while the other examines the second variation of the MHD Hamiltonian computed with proper variational constraints. For equilibria without flow, the two approaches are known to be fully consistent. However, for equilibria with flow, the stability criterion obtained from the constrained variation approach was claimed to be stronger than that derived using the linearized equations of motion. We show this claim is incorrect by deriving and comparing both criteria within the same framework. It turns out that the criterion obtained from the constrained variation approach has stricter requirements on the initial perturbations than the other. Such requirements naturally emerge in our new treatment of the constrained variation approach using the Euler-Poincar\'e structure of ideal MHD, which is more direct and simple than the previous derivation from the Poisson perspective. [Preview Abstract] |
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YP8.00072: Advective turbulent transport in the fluid plasma Byung-Hoon Min, Chan-Yong An, Chang-Bae Kim The Hasegawa-Wakatani model (HWM) has been employed in pedagogical analyses of the physics behind the behavior of the tokamak plasmas. In addition to the geometric simplicity HWM has an appealing feature of sustaining autonomous quasi-steady state, unstable modes providing the power that is being transported by the nonlinear interactions and is eventually dissipated by the collisional damping at small scales. Emergence of the zonal flow out of the turbulence is a main candidate to cause the transition from the low plasma confinement to the high mode. In the study of such LH transition with the HWM, the adiabaticity parameter has been shown to play an important role in forcing the zonal flow that results in the regulation of the drift-wave turbulence. Instead of concentrating on the physics of the feedback loop between the turbulence and the zonal flow the present study focuses on the presence of the advective transport of the energy. Numerical simulations of HWM are performed and the connections between the advective transport and the zonal flow will be presented. [Preview Abstract] |
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YP8.00073: Investigation on a new method to in-situ distinguish the deposition tile with the junction defect tile Laizhong Cai, Jian Liu, Eric Gauthier, Yann Corre The behaviors of plasma facing components(PFC) are major concerns for tokamaks, in particular, for steady state operations. Some PFC tiles show abnormal high surface temperature than others when thermal steady state is reached, which is believed to be caused by the deposition layer on the tile or the junction defect of the sandwich PFC tile. Although carbon deposit tiles and junction defect tiles present similar thermal response, the deposition layer and junction delamination have different effects to the tile lifetime. Delamination could bring a critical failure of the tile and then influence the steady state operation. The defect tile needs to be replaced before failure although the replacement is difficult, whereas the deposition tile does not impact on the PFC lifetime and easy to be cleaned. Therefore, trying in-situ to distinguish deposited tiles and junction defect tiles is crucial to avoid a critical failure. More, the junction defect is related to not only repetitive heat pulses but also manufacture. It is possible a junction defect tile exists in the deposition area or even both junction defect and deposition layer appear on the same tile. This makes the discrimination more complicated and obligatory. In this paper, thermal behaviors of junction defect tiles and carbon deposit tiles are simulated. A modified time constant method is introduce and then the feasibility of discrimination by analyzing the thermal behaviors of tiles is discussed. Requirements of this method for discrimination are also described. [Preview Abstract] |
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YP8.00074: Epitaxial AlN thin film deposited on sapphire substrate by ECR plasma Satoru Kaneko, Hironori Torii, Takashi Tokumasu, Sungkyun Park, Mamoru Yoshimoto We prepared aluminum nitride (AlN) thin film on c-plane sapphire substrate by electron cyclotron resonance plasma-enhanced sputtering deposition (ECR-sputtering). The target Al was placed within a argon plasma generated by the ECR plasma reactor. A lamp heater was used to increase the substrate temperature from room temperature to 500$^{\circ}$C. The microwave (MW) power was set to be 700 W. The size of substrate holder was 4 inches in diameter. X-ray diffraction (XRD) verified the epitaxial growth of AlN films with the full width at half maximum (FWHM) of rocking curve of 0.04 deg. even on the film thickness of 100 nm. XRD also verified slight change of peak position from $\theta$-2$\theta$ scan of AlN film along surface normal. By employed in-plane XRD, the epitaxial AlN films showed lattice constants different than the bulk AlN materials along both surface-normal and in-plane directions. The first principle theory was employed to evaluate stability of total energy with the varied lattice constants. The effect of varied lattice constants on band gap was estimated by using the GW approximation (GWA). To be compared with the theoretical results, the evaluation of band gap is experimentally in progress. [Preview Abstract] |
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YP8.00075: The nano-particle dispersion strengthening of V-4Cr-4Ti alloys for high temperature application in fusion reactors Pengfei Zheng, Jiming Chen, Zengyu Xu, Xuru Duan V-4Cr-4Ti was identified as an attractive structural material for Li blanket in fusion reactors. However, both high temperature and irradiation induced degradation are great challenges for this material. It was thought that the nano-particles with high thermal stability can efficiently strengthen the alloy at elevated temperatures, and accommodate the irradiation induced defects at the boundaries. This study is a starting work aiming at improving the creep resistance and reducing the irradiation induced degradation for V-4Cr-4Ti alloy. Currently, we focus on the preparation of some comparative nano-particle dispersion strengthened V-4Cr-4Ti alloys. A mechanical alloying (MA) route is used to fabricate yttrium and carbides added V-4Cr-4Ti alloys. Nano-scale yttria, carbides and other possible particles have a combined dispersion-strengthening effect on the matrices of these MA-fabricated V-4Cr-4Ti alloys. High-temperature annealing is carried out to stabilize the optimized nano-particles. Mechanical properties are tested. Microstructures of the MA-fabricated V-4Cr-4Ti alloys with yttrium and carbide additions are characterized. Based on these results, the thermal stability of different nano-particle agents are classified. [Preview Abstract] |
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YP8.00076: Optical measurements of helicon, inductive and capacitive RF discharges effects in ECR plasma sources Ferhat Bozduman, Ali Gulec, Erdogan Teke, Lutfi Oksuz, Ahmed M. Hala, Aysegul Uygun Oksuz, Melek Kiristi Low pressure argon plasma was produced by using Rf and ECR simultaneously. 2.45 GHz magnetron and for magnetic field permanent magnets were used for ECR plasma system. ECR-Helicon, ECR-Inductive, ECR-Capacitive plasmas were obtained by 13.56 MHz Rf power. Optical emission spectrums were taken. The plasma electron densities and temperatures will be calculated. Spatial and temporal evolution of plasmas will be investigated by an ICCD camera. A thermocouple will be inserted into the plasma for measurement of plasma gas temperature. Comparisons for three configurations will be given. [Preview Abstract] |
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YP8.00077: Negative ion beam generation in laser plasma interactions Sophie Jequier, Vladimir Tikhonchuk, Sargis Ter-Avetisyan Detection of a large number of energetic negative ions and neutral atoms have been reported in recent intense laser plasma interaction experiments. These particles were produced from fast positive ions (proton, carbon, oxygen) accelerated from a laser produced plasma when they were passing through a cold spray of water or ethanol [S. Ter-Avetisyan et al., Appl. Phys. Lett. 99, 051501 (2011)]. The negative ions formation is strongly related to the fast positive ions, and it is explained by a process of a single electron capture - loss. Double charge exchange, elastic scattering and energy loss phenomena have been neglected since their cross sections are much smaller. Assuming independent atoms approximation, we study populations evolution through the interaction zone analytically and numerically by solving the rate equations using cross sections drawn from literature. Taking into account the energy distribution of the incident ions, the calculations give the final energy distribution for the different species that can be compared to experimental spectra. First results obtained for hydrogen in the water case indicate that this model can explain the main observed features. The results concerning the carbon and oxygen ions will be also presented as well as refinement of the cross sections since some cross sections are missing for these energies. [Preview Abstract] |
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YP8.00078: Symmetry of spherically converging shocks through reflection, relating to the Shock Ignition Inertial Fusion Energy scheme Christopher Davie, Roger Evans Asymmetries in spherically imploding shocks through convergence, bounce and reflection into an outgoing shock wave are examined, to understand how they might contribute to the distortion of the final ignition process in the Shock Ignition (SI) Inertial Fusion Energy scheme, limiting energy output. We find that shock fronts that do not collapse centrally in 3D still reflect, but do so with less compression. Even for quite extreme, 3D perturbations, hydrodynamic shocks are robust; they are stable through convergence and reflection. After reflection, the size and shape of the perturbation returns, broadly, to the size and shape during convergence. [Preview Abstract] |
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YP8.00079: Numerical studies of a technique to create a convergent fast electron source from laser-solid interactions Robbie Scott Relativistically-intense laser-solid experiments and simulations have to-date indicated that the fast electron beam generated by the laser-solid interaction is highly divergent. This work presents a new technique which offers the potential to greatly reduce this divergence, potentially enabling the creation of a \textit{convergent} fast electron source. The results of particle-in-cell simulations using the EPOCH code are presented and the basic scheme outlined. If this technique can be shown to work in the laboratory, it may have significant implications for numerous applications related to the generation of fast electrons, including ion acceleration and the fast ignition inertial confinement fusion scheme. [Preview Abstract] |
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YP8.00080: Experimental and Computational Studies of the RF Plasma Sheath Nathaniel Hicks A new experimental and computational plasma physics program is underway at the University of Alaska Anchorage (UAA). The underlying objective is to equip a new plasma laboratory with basic plasma physics apparatus (vacuum vessel, pulsed power, diagnostics) for general plasma studies that can involve undergraduate researchers. The initial experimental focus will be on low power, low temperature plasma volume production in the presence of RF boundary electrodes in order to study the effects of RF on the edge plasma, plasma sheath, and particle transport. The experimental studies are to be complemented by ongoing computational particle-in-cell modeling of the same problems. Another aspect of the program will be to collaborate with other institutions on the development of plasma diagnostics applicable to a wide range of magnetic confinement devices. Examples and initial computational results from these studies will be presented. [Preview Abstract] |
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YP8.00081: Spatially and Temporally Resolved Electron Density Measurements of Air Breakdown Plasma Utilizing a 1.4 MW, 110 GHz Gyrotron S.C. Schaub, J.S. Hummelt, M.A. Shapiro, R.J. Temkin We present the latest results of the MIT microwave-frequency air breakdown experiment. The experiment utilizes a 1.4 MW, 110 GHz gyrotron producing 3 microsecond pulses. The linearly polarized beam is focused to a 3.2 mm diameter spot size. The resulting breakdown plasma spontaneously forms a two-dimensional array of filaments, oriented along electric field lines, that propagate toward the source.\footnote{A. M. Cook, J. S. Hummelt, M. A. Shapiro, and R. J. Temkin, ``Observation of plasma array dynamics in 110 GHz millimeter-wave air breakdown,'' Physics of Plasmas, Vol. 18, No. 10, 100704 (2011).} Two-wavelength laser interferometry is combined with a 2 nanosecond fast gating ICCD to make spatially and temporally resolved electron density measurements of the filament array. Electron density is measured as a function of incident microwave power in a range of pressures of atmospheric air from 25 to 700 Torr. [Preview Abstract] |
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YP8.00082: Magnetogenesis Through Kinematic Effects Evan Miller The origin of magnetic fields in the universe is a long-standing astrophysical problem. Though many proposed mechanisms will amplify small magnetic fields in the early universe to the scales we observe today, there remains some mystery as to how those seed fields arose in the first place. We present a novel magnetogenesis mechanism, requiring only classical fluid mechanics and applicable to both cosmological and laboratory scales. Importantly, unlike previous models of seed field generation, this theory does not ultimately depend upon the well-known Biermann Battery. We instead focus on the finite electron inertia/response time generating currents as electrons respond to thermal oscillations. [Preview Abstract] |
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YP8.00083: Non Axisymmetric Three-Dimensional Magnetic Bernstein-Greene-Kruskal (BGK) Modes Chung-Sang Ng The theory of three-dimensional (3D) magnetic Magnetic Bernstein-Greene-Kruskal (BGK) modes [L.-J. Chen and G. K. Parks, Geophys. Res. Lett., 29, 1331 (2002)] has been generalized to the non axisymmetric case. While the shape of the electrostatic structure is usually elongated along the direction of the strong large-scale magnetic field, a limiting case with the elongated direction along one of the perpendicular direction is also possible. Essentially this makes the solution 2D with the magnetic field on the 2D plane. Note that such 2D BGK modes are very different from those described by another theory [Ng, Bhattacharjee, and Skiff, Phys. Plasmas, 13, 055903 (2006)], of which the magnetic field is perpendicular to the 2D plane. This theory might explain 2D BGK modes observed in some numerical simulations [Wu et. al, J. Geophys. Res., 115, A10245 (2010)]. [Preview Abstract] |
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YP8.00084: Design and Fabrication of a Magnetic System to Investigate Magnetized Dusty Plasmas Evan M. Bates, Carlos A. Romero-Talamas The interest in researching the dynamics and equilibrium of magnetized dusty plasma crystallization has led to the design and fabrication of a novel experimental setup at UMBC. The proposed magnets will be an important subsystem of this setup, and will produce a uniform magnetic field of several tesla for a duration of several seconds. The magnets will be arranged in the Helmholtz configuration and will have a cooling system for temperature compensation of the coils, as well as the ability to adjust the orientation of the magnetic field with respect to gravity. Planned experiments include propagation of magnetized waves in dusty plasma crystals under various boundary conditions. [Preview Abstract] |
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YP8.00085: Study of nonlinear dynamics among zonal flow, GAM, and turbulence on the HL-2A strongly heated L-mode plasmas Min Xu, Kaijun Zhao, Jun Chen, Jiaqi Dong, Wenyu Hong, Longwen Yan, Qingwei Yang, Xianming Song, Yuan Huang, Laizhong Cai, Wulu Zhong, Zhongbing Shi, Xuantong Ding, Xuru Duan, Yong Liu Experiments to directly measure the nonlinear energy exchange among turbulence, zonal flows, and GAMs were carried out on the HL-2A tokamak at the Southwestern Institute of Physics (SWIP) in China. At various discharge conditions, the turbulent kinetic energy was clearly shown to transfer from turbulence with intermediate frequencies (20-60 kHz) to zonal flows (0-5 kHz) and GAMs ($\sim$10 kHz) and to turbulent fluctuations with high frequencies (\textgreater 60 kHz). The turbulent Reynolds stress $\left\langle {\tilde{{v}}_{r} \tilde{{v}}_{pol} } \right\rangle $ profiles were shown consistent with the time-averaged ExB and TDE (time-delay estimation) poloidal velocity profiles. Other micro statistics, such as particle flux $\left\langle {\tilde{{n}}\tilde{{v}}_{r} } \right\rangle $ and vorticity flux $\left\langle {\tilde{{v}}_{r} \tilde{{\omega }}} \right\rangle $, together with the macro equilibrium profiles at various discharge conditions will also be presented, which form a consistent picture that turbulent vortices mediate turbulent energy and momentum and integrate them into sheared flows across the edge plasmas. [Preview Abstract] |
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YP8.00086: E-beam-based Lithium Flash Evaporator for NSTX\textunderscore U A.L. Roquemore, C.W. Skinner, D. Andruczyk, D. Mansfield, R. Majeski A commercial e-beam evaporator is being utilized as the main component of a lithium (Li) flash evaporator that will coat the upper divertor of NSTX-U. The evaporator system (U-Liter) will be mounted on a horizontal probe drive and will be inserted into NSTX-U in an upper port of one of the midplane port covers. In the retracted position the evaporator will be loaded with $\sim$ 300 mg of Li granules utilizing one of the well-calibrated NSTX Li granular droppers. The evaporator will then be inserted into the vessel and parked in a location well within the shadow of the RF limiters where it can remain in the vessel during the discharge. Resident Helmholtz coils will position the beam into a tungsten crucible, where the total Li inventory will be rapidly heated and completely evaporated in a matter of seconds shortly before a discharge. The need for shutters to prevent Li vapor from coating diagnostic windows is eliminated with this approach. The minimal time between the evaporation and the start of the discharge will avoid the passivation of the lithium by residual gases. The evaporator can easily be withdrawn, reloaded with Li granules, and reinserted during the inter-shot interval. [Preview Abstract] |
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