Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session YP6: Poster Session IX: Inertial Confinement Fusion and HEDP Experiments, Diagnostics and Drivers; Supplemental; Postdeadline |
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Room: Marsalis A/B, 9:45am - 12:45pm |
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YP6.00001: INERTIAL CONFINEMENT FUSION AND HEDP EXPERIMENTS, DIAGNOSTICS AND DRIVERS |
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YP6.00002: X-ray (17 -- 99-keV) diagnostics for the 200-TW Trident Laser James Cobble, Jonathan Workman, Nalin Vutisalchavakul The sub-ps Trident laser can deliver $>$100 J on target. The target irradiance is $\sim $10$^{20}$ W/cm$^{2}$. X-ray diagnostics include a Laue x-ray spectrograph, a Ross filter pair to measure conversion efficiency of laser light to K-shell emission, and a single-photon-counting x-ray CCD camera. For the Laue instrument, we discuss design features used to limit corruption of the recorded spectra by $\sim $MeV electrons and bremsstrahlung: a tungsten shield in the front, low-Z, thick-wall construction materials, magnetic traps, light traps, and a special sandwich-style film holder. For the Laue geometry where a LiF 200 crystal has a bandpass of 17 - 70 keV, LiF 220 shifts the bandpass to 24 - 99 keV. The sensitivity of Si p-i-n diodes is adequate to record x-ray emission up to $\sim $100 keV. With a carefully matched Ross filter pair, we may estimate the signal between the filter edges of two channels through subtraction of signals. The K-shell emission is expected to exceed the continuum contribution to the signal. These instruments will be employed to optimize the efficiency of x-ray backlighters in this energy range. The x-ray CCD is discussed in a parallel poster. [Preview Abstract] |
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YP6.00003: Monochromatic x-ray backlight imaging for high energy density experiments with lasers Takashi Fujiwara, Minoru Tanabe, Shinsuke Fujioka, Hiroaki Nishimura, Takashi Endo, Norimasa Ozaki, Yuichi Inubushi, Ryosuke Kodama, Hideo Nagatomo, Hiroyuki Shiraga, Hiroshi Azechi, Kunioki Mima X-ray backlighting is one of key techniques to observe rapidly evolving density profiles of hot dense matters created with high power laser, such as imploded core plasma in inertial confinement fusion and shock compressed matter in equation of state research. The heated matters themselves emit brilliant continuum x-ray radiation that superimposes on an x-ray backlight image, degrading the observation accuracy. A monochromatic x-ray backlighting technique has been developed to solve and substantially improves image quality. A spherically bent crystal imager was coupled to an x-ray framing camera to obtain spatially and temporally resolved monochromatic images. Spatial resolution and temporal resolution of the imaging system were measured to be 13 $\mu $m and 100 ps, respectively. It was confirmed experimentally that x-ray self-emission of the plasma is negligibly small compared to that taken with conventional method. Details of the experimental results and analysis will be discussed. [Preview Abstract] |
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YP6.00004: X-ray Imaging Schemes with Matched Pairs of Spherically Bent Crystals M. Bitter, K.W. Hill, S. Scott, R. Feder, Jinseok Ko, A. Ince-Cushman, J.E. Rice, P. Beiersdorfer, S. Glenzer The paper describes two x-ray imaging schemes with matched pairs of spherically bent crystals, which may be of interest for the diagnosis of laser-produced plasmas. The first scheme eliminates the astigmatism and thus allows for a point-to-point, one-dimensional, imaging at almost arbitrarily large angles of incidence with high spectral resolution. The second scheme allows for two-dimensional, point-to-point, imaging with a large magnification at a particular wavelength. An advantage common to both schemes is that the detector can easily be protected from debris. [Preview Abstract] |
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YP6.00005: Time-resolved two-color monochromatic x-ray imagers for fast-ignitor plasmas Minoru Tanabe, Takashi Fujiwara, Shinsuke Fujioka, Hiroaki Nishimura, Hiroyuki Shiraga, Hiroshi Azechi, Kunioki Mima Ultrafast two-dimensional (2D) x-ray imaging is required to investigate the dynamics of fast-heated core plasma in fast ignition research. A novel x-ray imager, consisting of two toroidally bent Bragg crystals and an ultrafast two-dimensional x-ray imaging camera, has been demonstrated in order to measure an electron temperature profile of fast-ignitor plasma. Sequential, two-color, and 2D monochromatic x-ray images of laser-imploded core plasma were obtained with a temporal resolution of 20 ps, a spatial resolution of 31 $\mu$m, and a spectral resolution of over 200, simultaneously. Details of the experimental results and analysis will be discussed [Preview Abstract] |
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YP6.00006: X-ray Phase Contrast Imaging of a Strong Shock in a Dense Plasma D.S. Montgomery, K.A. Flippo, D.C. Gautier, J.B. Workman, J.A. Cobble, J.L. Kline, S.A. Gaillard, N. Vutisalchavakul X-ray phase contrast imaging (XPCI) relies on gradients in an object's phase, rather than absorption, to produce image contrast, and requires sufficient propagation distances to optimize the contrast for a given x-ray source size and wavelength. We report initial experimental results using the TRIDENT 200-TW laser to produce bright K-$\alpha$ x-rays with a source size $\sim$ 12-$\mu$m using Mo or Ag wire targets. This is used as a point backlighter to radiograph static or dynamic targets in the phase contrast regime. For the dynamic experiments, a strong spherical shock is launched in a low-Z target using a 200-J, 1.2 nsec laser focused on the target, which is diagnosed using XPCI with a few psec time resolution. Initial experimental results and comparison to theory will be reported. [Preview Abstract] |
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YP6.00007: Phase Contrast Imaging using Sub-mJ, Kilohertz Femto-Second Laser produced Cu-K$_{\alpha }$ Source Juzer Ali Chakera, Atif Ali, Ying Tsui, Robert Fedosejevs We present an efficient Cu-K$_{\alpha }$ x-ray source produced by a commercial kilohertz fs laser system. The source has a high x-ray conversion of well over 10$^{-5}$ into K$_{\alpha }$ line emission at 8.05 keV. The micro plasma x-ray source is produced by focusing 260 $\mu $J laser pulses of 130 fs (FWHM) on a moving Cu-wire target. The source has a size of $<$ 10$\mu $m providing sufficient spatial coherence for phase contrast imaging applications. An average x-ray photon flux of $>$ 10$^{9}$ ph/sr/s is achieved in the exposure to record the in-line phase contrast images of test samples. This compact source can be developed into a durable low cost operating system for phase contrast imaging of biological specimens. Detailed characterization of the source and analysis of example exposures will be presented. [Preview Abstract] |
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YP6.00008: A Prototype Inline Silicon p-i-n Photodiode-Array CMOS7-Based Multiframe Ultrafast Digital X-Ray Camera, MUDXC: A Progress Report G.R. Bennett, L.D. Claus, B.C. Tafoya-Porras, B.W. Atherton, T.M. Gurrieri, A.H. Hsia, J.L. Porter, D.C. Trotter The Z-Beamlet Laser (ZBL) is a long-pulse, multi-kJ, TW-class device that is routinely used for 2-Frame 6.151-keV curved-bragg-crystal imaging on the Z-Accelerator. For higher energy x-ray imaging requirements, the short-pulse, multi-kJ, PW-class Z-Petawatt Laser (ZPW, 2 kJ in 1-10 ps) is being developed. Presently, time-integrated image plate is our best image-plane detector, but we have initiated a program to develop a prototype inline multriframe ultrafast digital x-ray camera (MUDXC) for more frames, higher sensitivity, and time gating. It will consist of a silicon 256 x 256 pixel p-i-n photodiode array backed with 256 x 256 CMOS7 application specific integrated circuits (ASIC). Each ASIC is capable of four 1 ns gates; 4 images. If successful, the system may be enhanced to a cooled germanium (higher x-ray sensitivity, etc.), multi-megapixel device. As such, it would significantly increase the Z physics return when using either ZBL or ZPW. Progress to date will be reported. [Preview Abstract] |
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YP6.00009: Evaluation of continuum x-ray emission for measuring electron temperatures in ICF implosions John Benage, James Cobble, George Kyrala, Douglas Wilson Though most ICF capsules produce plasma conditions where the electron and ion temperatures are not equal and the electrons serve as a sink for the hotter ions, the electron temperature is rarely measured in ICF experiments. When it is measured, one usually relies on spectral emission from much higher z dopants that are assumed do not perturb the conditions in the implosion. We present here an evaluation of the continuum emission produced in thin glass capsule implosions and compare temperatures determined from the continuum emission to that obtained from K-shell line emission in doped implosions. The dopant used is Kr and the x-ray range evaluated is between 12-17 keV. In this evaluation we consider how these two methods compare at many different dopant and gas fill concentrations and estimate the usefulness of the method when no dopant is present. Correlations are also considered with the uniformity of the x-ray source by considering x-ray framing camera images in the same spectral range. [Preview Abstract] |
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YP6.00010: Measurements of ablator-ion spectra for preheat and compression studies N. Sinenian, J. Frenje, C.K. Li, F.H. Seguin, R. Petrasso, J. Delettrez Measurements of ablator-ion spectra produced at the OMEGA laser facility are presented. The mechanism responsible for the acceleration of these ablator ions is the presence of hot electrons generated by laser-plasma interactions. Modeling, benchmarked by measurements, of the ablator-ion spectra is therefore essential to better understand the generation and transport of these hot electrons and their potentially detrimental effect upon implosion performance. The ablator-ion spectra have been measured routinely by two magnetic charged-particle spectrometers, but these spectrometers cannot always unambiguously separate fast ablator ions with low charge states and slow ablator ions with high charge states. To break this degeneracy, we propose to use a Thomson Parabola Spectrometer that allows for accurate measurements of absolute ablator-proton spectra and more importantly, energy spectra for various charge states of higher-Z ablators such as Carbon. This work was supported in part by DOE, LLE and LLNL. [Preview Abstract] |
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YP6.00011: Characterization of Mono-Energetic, Charged-Particle Radiography for HEDP Experiments M. Manuel, F.H. Seguin, C.K. Li, D. Casey, J. Frenje, J. Rygg, R. Petrasso, O. Gotchev, R. Betti, J. Knauer, V. Smalyuk Charged-particle radiography, which utilizes mono-energetic protons and alphas, has been used to image various High-Energy-Density Physics (HEDP) phenomena of interest, including capsule implosions, laser-plasma interactions, and Rayleigh-Taylor-instability growth. An imploded D$^{3}$He- filled glass capsule -- the backlighter -- provides mono-energetic 15-MeV and 3-MeV protons and 3.6-MeV alphas for radiographing these various phenomena. This technique provides simultaneously information about areal density and electromagnetic fields in the imaged systems. For successful study of these phenomena, the backlighter yield and size need to be optimized for the imaging geometry and detector used. Understanding the experimental parameters that affect it is therefore essential. Empirical studies of backlighter performance under a variety of conditions are presented. GEANT4 is used as well to investigate the limits and capabilities of this technique. This work was performed in part at the LLE National Laser User's Facility (NLUF), and was supported in part by US DOE, LLNL, LLE and the Fusion Science Center at Univ. Rochester. *Currently at LLNL. [Preview Abstract] |
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YP6.00012: GEANT4 and TART modeling of the Magnetic Recoil Spectrometer (MRS) response function for down-scattered and primary neutron measurements at OMEGA D. Casey, J. Frenje, C.K. Li, F.H. Seguin, M. Manuel, R. Petrasso, V. Glebov, D. Meyerhofer, S. Roberts, T.C. Sangster A Magnetic Recoil Spectrometer (MRS) has been installed and activated on OMEGA for measurements of down-scattered and primary neutrons, from which areal density, ion temperature, and yield of cryogenic DT implosions can be inferred. To correctly interpret these measurements, the MRS response function must be well characterized. The Monte Carlo code GEANT4 and MRS activation experiments, which utilized 14.1 MeV DT neutrons and $\sim $15 MeV D$^{3}$He protons, were used for this purpose. Through the use the neutron transport code TART and DT experiments, the MRS background was also characterized. As the detector response is a crucial part of the MRS response function, the newly developed triple coincidence counting technique, which was developed and implemented to reduce the background, is presented. This work was supported in part by DOE, LLE and LLNL. [Preview Abstract] |
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YP6.00013: Energy and Time-resolved Measurements of High Energy Electrons Emitted from a Laser-Plasma Interaction Lee Elberson, Yuan Ping, Ronnie Shepherd, Andrew Mackinnon, Pravesh Patel, Wendell Hill Irradiating materials with high energy, short pulse lasers create rapidly evolving plasma states. Deconvolving the physical mechanisms responsible for the plasma evolution necessitates time-resolved diagnostic measurements. In the high energy density regime, electrons dominate energy transport within the plasma, making them an obvious candidate for study. We recently demonstrated a novel technique for observing time-resolved energy spectra of hot electrons escaping from the target. Exploiting this technique, we measured high energy ($\sim $MeV) electrons accelerated from a solid foil ($\sim $10 micron) irradiated by a high intensity ($>$10$^{19}$ W/cm$^{2})$, short pulse ($\sim $100fs) laser. Preliminary analysis shows hot electron lifetimes on the order of 10 ps. Future experiments will combine the above technique with a time-resolved measurement of K-alpha emission, which gives insight into the refluxing electrons. [Preview Abstract] |
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YP6.00014: High Energy Electron Detectors on Sphinx J.R. Thompson, A. Porte, F. Zucchini, H. Calamy, G. Auriel, P.L. Coleman, F. Bayol, B. Lalle, M. Krishnan, K. Wilson Z-pinch plasma radiation sources are used to dose test objects with K-shell ($\sim $1-4keV) x-rays. The implosion physics can produce high energy electrons ($>$ 50keV), which could distort interpretation of the soft x-ray effects. We describe the design and implementation of a diagnostic suite to characterize the electron environment of Al wire and Ar gas puff z-pinches on Sphinx.\footnote{H.Calamy et al, ``Use of microsecond current prepulse for dramatic improvements of wire array Z-pinch implosion,'' Phys Plasmas 15, 012701 (2008)} The design used ITS\footnote{J.A.Halbleib et al, ``ITS: the integrated TIGER series of electron/photon transport codes-Version 3.0,'' IEEE Trans on Nuclear Sci, 39, 1025 (1992)} calculations to model detector response to both soft x-rays and electrons and help set upper bounds to the spurious electron flux. Strategies to discriminate between the known soft x-ray emission and the suspected electron flux will be discussed. [Preview Abstract] |
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YP6.00015: Development of a thermal X-radiation source using short pulse lasers Kelly Cone, Hector Baldis, Lee Elberson, Hui Chen, Mark May, Marilyn Schneider, Ronnie Shepherd We report on experiments designed to use short pulse lasers to generate a thermal x-radiation source.~ The ideal source has a blackbody-like spectra with the radiation density inside the source equal to the blackbody radiation density. The source we are developing is a thin foil irradiated by a short pulse laser. We report on the initial experiments which vary laser energy, pulse length, and target thickness to maximize the conversion of laser energy into soft x-rays. Later experiments will characterize the heating mechanisms by measuring the temporal evolution of soft x-ray emission as well as the energy distribution of hot electrons leaving the target. Understanding the heating mechanisms is crucial to the development of an x-radiation source and contributes to the field of basic plasma physics under extreme conditions. [Preview Abstract] |
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YP6.00016: Diagnostic issues with measuring electrical conductivity and equation of state data from Ohmically exploded planar foils E.L. Ruden, P. Poulsen, J.F. Camacho, S.K. Coffey, J.E. Beach, D.J. Brown, T.C. Grabowski, C.W. Gregg, M.R. Kostora, B.M. Martinez, J.V. Parker Diagnostic development is underway for the simultaneous dynamic measurement of local electrical conductivity, pressure, density, specific energy, and temperature of an LiF tamped planar metal foil exploded by a 36 $\mu $F, 50 kV capacitor bank discharge. Voltage differentials measure the foil's electric field, a B-dot probe measures surface current density, a laser velocity interferometer (VISAR) measures foil thickness, and a spectrometer measures temperature. From these, the desired properties are inferred. This presentation discusses issues which must be resolved to meaningfully interpret the data such as RF interference from the rail-gap current trigger system, uniformity of the foil properties, planarity of the foil expansion and subsequent LiF pressure wave, thermal conduction and radiation, compression and impedance matching of the (LiF embedded) E and B-dot probes, and emissivity spectral dependence of the foil surface. [Preview Abstract] |
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YP6.00017: Electron Density Profile Measurements of a Translated Field-Reversed Configuration J.F. Camacho, D.J. Brown, E.L. Ruden A four-chord HeNe laser interferometer operating at 632.8 nm is being used to measure the electron density of a field-reversed configuration (FRC) for the magnetized target fusion experiment at the Air Force Research Laboratory. The design of the interferometer has been previously described [{\it Bull.~Am.~Phys.~Soc.}~{\bf 52}, 84 (2007)]. We are focusing our efforts on measuring the radial density profile of an axially translated FRC as a function of time as it emerges from the bore of the conical theta coil in which it is formed. The goal is to perform these measurements where the FRC is moving and then is captured by a magnetic mirror that will serve to trap it inside a cylindrical aluminum liner. The liner will be imploded by the Shiva Star capacitor bank to heat the plasma compressively to a fusion-relevant regime [{\it Bull.~Am.~Phys.~Soc.}~{\bf 52}, 257 (2007)]. Data will be presented showing the density evolution of the FRC while it is in the formation, translation, and compression regions. We also plan to divert one of the four probe beams into a single-mode optical fiber whose collimated output can be used to sample a diameter of the plasma at different axial locations. Progress on obtaining density information as a function of axial position with this technique will also be reported. [Preview Abstract] |
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YP6.00018: Omega experiments Demonstrate Control of Capsule Implosion Symmetry in NIF Scale Hohlraums George A. Kyrala, Achim Seifter, John Kline, Nelson Hoffman, S. Robert Goldman To achieve ignition, indirect drive must implode symmetrically to achieve ignition. For indirect drive implosions, such as designed for the NIF laser, we may adjust the symmetry using many methods. We have use power imbalance [phasing] of three, or of two cones from the OMEGA laser to control the symmetry of an imploded capsule. We used a NIF 0.7 scale vacuum-hohlraum and D$_{2}$-filled 1400 $\mu $m CH and Beryllium capsules to verify the technique. Imaging of the imploded core was used to measure the implosion symmetry and to verify its. We captured images of the emission from the core at different times for different phasing of the laser cones of OMEGA. We verified that the technique works and demonstrated symmetry tuning We also showed that propagation of the inner beam cone is important, even in a vacuum hohlraum, and had the largest effect on the hohlraum energetics. Work supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under Contract DE-AC52-06NA25396. [Preview Abstract] |
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YP6.00019: Double-Shell ignition designs and single-shell designs to study effect of perturbations Glenn Magelssen, Ian Tregillis, Mark Schmitt, James Cooley, Jas. Mercer-Smith At the last APS meeting[1], a renewal of the LANL Double-Shell ignition capsule effort was presented. Using the Double-Shell design by P. Amendt et al.[2], preliminary studies of mix, symmetry and yield were presented. In this talk, fully integrated high yield designs will be presented as well as symmetry and power scan studies. The effect of small localized perturbations, such as fill tubes and mounting tents, on the NIF ignition capsule is an important issue in achieving ignition on NIF. Because of issues of symmetry, shock timing, mix etc. trying to understand the effect of localized perturbations ("defects") on the NIF capsule will be difficult. To begin the study of defects on yield, an exploding pusher has been designed. The exploding pusher is insensitive to symmetry and has a very reproducible yield. At the same time a neutron imager being designed for NIF will be tested on these targets. To achieve the neutron yield necessary, the capsules will be DT filled and directly driven. Preliminary results of the exploding pusher calculations with defects will be shown. 1. Magelssen et al., DPP APS bulletin, p. 66, (2007). 2. P. A. Amendt et al., Phys. Rev. Lett. 94, 65004 (2005). [Preview Abstract] |
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YP6.00020: Concepts for unique laboratory astrophysics experiments on NIF Bruce Remington The ability to experimentally study scaled aspects of the explosion dynamics of core- collapse supernovae (massive stars that explode from the inside out) or the radiation kinetics of accreting neutron stars or black holes on high energy density (HED) facilities, such as the new National Ignition Facility (NIF), is an exciting scientific development. [``Experimental astrophysics with high power lasers and Z pinches,'' B.A. Remington, R.P. Drake, D.D. Ryutov, Rev. Mod. Phys. 78, 755 (2006)] Additional areas of research that could become accessible on NIF are studies of fundamental properties of matter in conditions relevant to the cores giant planets and stars, protostellar jet dynamics, radiatively driven molecular cloud dynamics, hyper-velocity (10-100 km/s) dust-dust collisions, and combined with ultraintense short-pulse lasers, pair plasma generation and dynamics, possibly relevant to gamma-ray burst physics. With the added tool of thermonuclear ignition on the National Ignition Facility, excited state (``multi-hit'') nuclear physics studies, and burn physics studies also become possible. Techniques and methodologies for studying aspects of the physics of such extreme phenomena of the universe in submillimeter scale parcels of matter on NIF will be discussed. [Preview Abstract] |
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YP6.00021: Sensitivity Study of Stopping Power Models in ICF Targets Matthew Terry, Gregory Moses Accurate treatment of fusion product charged particle transport (in particular the 3.5 MeV alpha particles) is very important for the accurate simulation of ICF ignition, bootstrap heating and burn. Many models have been proposed that focus on various aspects plasma conditions (collisionality, wave interaction, Fermi-degeneracy) which have various limitations. Here we present a comparison of several stopping power models, including the models of Trubnikov; Li and Petrasso; Brown, Preston and Singleton; Brysk; and Skupsky. Particular attention is given to regions of validity as they relate to ignition conditions. We present results that highlight the limitations of existing models to semi-Fermi-degenerate plasmas and models with explicit Coulomb logarithms. We also present initial results treating collisional effects in a semi-Fermi-degenerate plasma. [Preview Abstract] |
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YP6.00022: Gold Spectra Measurements from LLNL EBIT Plasmas M. May, G.V. Brown, H. Chen, H.K. Chung, M. Gu, S.B. Hansen, M.B. Schneider, K. Widmann, P. Beiersdorfer Spectra have been recorded from gold that has been injected into the Lawrence Livermore Electron Beam Ion Trap (EBIT-II). Both mono-energetic and experimentally simulated Maxwell-Boltzmann (MB) plasmas were created for these measurements. The beam plasmas had energies of 2.75, 3.0, 3.6, 4.6, 5.5, 6.0, 6.5 keV. The MB plasmas had electron temperatures of 2.0, 2.5 and 3.0 keV. M-band gold spectra (n = 4-3, 5-3, 6-3 and 7-3 transitions) were recorded between 1 - 8 keV from K-like to Kr-like ions in the x-ray. The emission of gold was recorded by crystal spectrometers and a micro-calorimeter from the Goddard Space Flight Center. A full survey of the recorded spectra will be presented along with line emission and charge state modeling from the flexible atomic code (FAC). Some comparisons with laser produced plasmas will be made. *This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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YP6.00023: Transport in magnetized dense plasmas for magneto-inertial fusion Xianzhu Tang Transport in high energy density plasmas embedded in an ultra-high magnetic field with closed magnetic fields or magnetic surfaces is of importance to the magneto-inertial fusion (MIF) in the high energy density laboratory plasmas (HEDLP) program. The energy loss rate by thermal transport and radiation in the magnetized dense plasma of the MIF target determines both the feasibility of the concept (i.e. can the target achieve ignition temperature, $\sim 10$ keV for D-T?) and the efficiency of the scheme (i.e. how much driver power and energy are needed?). A three year LDRD project has been funded at LANL to investigate this physics. Specifically we will assess the transport in dense ( and high energy density) plasmas for three plasma target options, namely the field reversed configuration (FRC), the spheromak, and the spherical tokamak with a plasma center column (ST-PCC). As a first step, the neoclassical transport in the collisional and weakly collisional regime of the high energy density target plasmas will be investigated. Work supported by LANL LDRD. [Preview Abstract] |
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YP6.00024: Status and update of the LMJ construction Francois Jequier, Xavier Maille, Jean-Louis Gaussen The Commissariat \`{a} l'Energie Atomique is currently constructing the Laser MegaJoule (LMJ) at CESTA near Bordeaux in France. The LMJ's primary missions are Inertial Confinement Fusion Research and High energy Density Physics. This facility is designed to produce 1.8 MJ of blue (0.35 $\mu $m) light at 500 TW onto targets to meet the requirements of inertial confinement fusion. The Laser and Target Area Building houses the 240 laser beams in four bays. The beams are directed through 60 ports into a 10-meter diameter spherical target chamber located in the central part of the building, the Target Area Building. This building was ``topped out'' in November 2006 and the first bundles are being installed in the Laser Bay 1. The paper will describe recent activities and update plans for LMJ construction. [Preview Abstract] |
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YP6.00025: Magnetic Intervention: Protection for the first wall in a Laser Fusion Chamber J.D. Sethian, J.L. Giuliani, A.M. Velikovich, A.E. Robson, D.V. Rose, A.R. Raffray One of the challenges in fusion energy is to develop a first wall that can survive the continual onslaught of emissions from the fusion reaction. For direct drive with lasers, 2{\%} of the energy is in x-rays, 28{\%} in ions, and 70{\%} in neutrons. The ions deposit significant energy (88 MJ) in a short distance (5 um). They heat the wall to high temperatures, and the implanted helium ions agglomerate into bubbles that exfoliate the surface. ``Magnetic Intervention'' uses a cusp magnetic field to guide the radially expanding ions into external dumps. The dumps can be flowing liquid metal. As the ions are born in a field free region, conservation of canonical angular momentum guarantees they do not hit the wall. A 1979 experiment demonstrated the physics (1), and we recently modeled the plasma/field motion. We present the main facets of MI, including ion motion simulations, and designs for the magnets, dumps, and chamber. (1) R. E. Pechacek, et al., Phys. Rev. Lett. 45, 256 (1980). [Preview Abstract] |
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YP6.00026: Arrayed Diagnostic Development on the HyperV Plasma Accelerators Samuel Brockington, Andrew Case, Sarah Messer, Richard Bomgardner, F.D. Witherspoon The sparkgap injected plasma accelerator is one of several coaxial railguns constructed at HyperV to accelerate dense plasmas to high velocities. A circumferential array of 112 high voltage tungsten electrodes ablates polyethylene to form and inject a toroidally shaped plasma into the annular breech at the rear of the accelerator. A pulse forming network then applies several hundred kiloamps to the coaxial electrodes to accelerate the plasma. A 4-chord laser deflectometer and a 32-sensor fast photodiode array are being developed to help resolve the structure, density, and velocity of the accelerated plasma jet for different accelerator parameters. We present details of the diagnostic designs and initial data. Work supported by the U.S. DOE Office of Fusion Energy Sciences. [Preview Abstract] |
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YP6.00027: Magnetic and Pressure Probes on the HyperV Contoured Coaxial Plasma Accelerator S. Messer, A. Case, S. Brockington, R. Bomgardner, F.D. Witherspoon, R. Elton Magnetic and pressure data from several contoured-gap coaxial railguns is presented. These plasma guns use an injected plasma annulus and shaped inner and outer electrodes to mitigate the blow-by instability. Passive magnetic probes and photodiodes search for evidence of the blow-by instability and azimuthal asymmetries. Stagnation pressure and velocity are compared for different size guns and for different driving voltages and currents. [Preview Abstract] |
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YP6.00028: Optical Measurements of Dense Hypervelocity Plasmoids from a Coaxial Plasma Accelerator Andrew Case, Sarah Messer, Richard Bomgardner, Sam Brockington, Douglas Witherspoon, R. Elton High velocity dense plasma jets are under continued experimental development for fusion applications including refueling, disruption mitigation, rotation drive, and magnetized target fusion. We present spectroscopic measurements of plasma velocity, temperature and density, along with spatially resolved line-integrated density measurements taken using a two channel quadrature heterodyne HeNe interferometer. Results from these measurements are in agreement with each other and with time of flight measurements taken using photodiodes. Plasma density is greater than $5 \times 10^15 cm^{-3}$, and velocities range up to 100 km/s, with a small component in some cases exceeding 120 km/s. [Preview Abstract] |
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YP6.00029: SUPPLEMENTAL ABSTRACTS |
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YP6.00030: Langmuir Probe Measurements of DC Magnetron Plasma A. Mezzacappa, H.L. Wilkens, A. Nikroo, H.W. Xu DC magnetron sputtering has been used to deposit beryllium in fabrication of shells to be used on ignition experiments on the National Ignition Facility (NIF). The plasma properties of the DC magnetron have profound and critical effects on the structure and hence the properties of the sputtered material. To gain a better understanding of these effects, we have used, a Langmuir probe to measure the properties of a plasma generated by the magnetron gun used in the sputtering process, performed in an argon background. Floating and plasma potential which affect the adatom energies and their surface mobilities, electron and ion densities, and electron temperature were obtained through analysis of the Langmuir probe signals. Spatial variation of these parameters were also measured near the magnetron gun by scanning a Langmuir probe attached to a linear drive along X and Z directions. The operation parameters such as gun powers, argon pressures, substrate biasing, and a biased DC ring, which can influence the plasma and their effects were also measured. The possible relationships between our finding and the quality of the sputtered material will be discussed. [Preview Abstract] |
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YP6.00031: Momentum Diffusivity Estimation via PDE-Constrained Optimization C. Xu, Y. Ou, E. Schuster, D.A. Humphreys, M.L. Walker, T.A. Casper, W.H. Meyer Several experiments around the world have demonstrated that plasma rotation can improve plasma stability and enhance confinement. It has been shown [1] that the critical rotation speed for stabilization is a function of the rotation profile shape, implying a radially distributed stabilizing mechanism. Modeling of the rotational profile dynamics is limited by poor knowledge of the momentum diffusivity coefficient. In this work we use toroidal angular velocity data from experiments where the torque is modulated using neutral beams, and we employ optimization techniques to estimate the momentum diffusivity coefficient for the angular momentum partial differential equation (PDE) that best fits the experimental data. To further investigate the nonlinear dependence of the momentum diffusivity on other physical variables such as temperatures and densities, we introduce techniques from nonlinear regression and machine learning.\par \vskip6pt \noindent [1]~A.C.\ Sontag, et al., Nucl.\ Fusion {\bf 47}, 1005 (2007).\par [Preview Abstract] |
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YP6.00032: Phase-space Analysis of Resistive Wall Mode Dynamics E.J. Strait, A.M. Garofalo, G.L. Jackson, R.J. La Haye, H. Reimerdes, M.J. Lanctot, M. Okabayashi, Y. In Phase-space analysis in the plane of plasma rotation vs. mode amplitude offers a possible approach to studying the dynamics of resistive wall modes (RWMs). Models for the interaction of RWM growth and rotation braking can be characterized by their trajectories and fixed points in the phase plane, allowing a qualitative comparison of the models with each other and with experiment. This technique is well suited to analysis of RWMs in high beta plasmas, where ELMs and other transient events provide ``kicks" away from a stable fixed point in the phase plane. Preliminary results will be presented. [Preview Abstract] |
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YP6.00033: Interplay of electrostatic and electromagnetic instabilities for relativistic electron beams in a plasma D.D. Ryutov The physics of relativistic electron particle beams propagating through the plasma is of a significant interest for laboratory astrophysics, fast ignition, and Z-pinch research. Most attention has been directed towards the analysis of electromagnetic filamentation instabilities. On the other hand, there exists a broad class of very powerful electrostatic instabilities, e.g., the Buneman instability. The author considers in a unified fashion linear theory for both types of instabilities under conditions where there is no magnetic field in an unperturbed state (i.e., the beam current is fully neutralized by the plasma current). The following factors are taken into account: the beam energy and angular spread; plasma non-uniformity; particle collisions in the background plasma. The areas of the parameter domain where particular instability is prevalent are identified; the results are presented in the form of several easy-to-use diagrams. Prepared by LLNL under contract DE-AC52-07NA27344. [Preview Abstract] |
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YP6.00034: How the Weibel instability of a beam/plasma system works O. Polomarov, A. Solodov, R. Betti, I. Kaganovich, G. Shvets The linear and non-linear stages of the collisionless and collisional electromagnetic Weibel instability (WI) are considered analytically by the two-fluid hydrodynamic model and numerically by PIC simulations [1, 2]. Conditions for the saturation of the linear and non-linear stages of the instability are distinguished and analyzed. The self-sustained beam and return current structures created by the collisionless Weibel instability at long times are presented. The role of Alfven current for the collisionless and collisional WI instability is pointed out and the increase/decrease of the magnetic field generated by the WI is related to the merging of filaments with the sub/super-Alfvenic beam currents. Transition from collisionless to collisional regimes of the WI with accompanying changes of the instability scales is considered and the influence of the plasma density gradient and beam/plasma temperatures on the development of the instability is studied. \\[0pt] [1] O. Polomarov et al., Phys. Plasmas, \textbf{14}, 043103 (2007) \\[0pt] [2] O. Polomarov et al., PRL (2008) submitted. [Preview Abstract] |
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YP6.00035: Non-diffusive tracer transport in a zonal flow with finite Larmor radius effects Kyle Gustafson, Diego del-Castillo-Negrete, William Dorland Tracer particle transport simulations reveal non-diffusive transport in a prototypical quasi-two dimensional plasma. The plasma model contains two drift wave modes combined with a zonal {\boldmath $E$} $\times$ {\boldmath $B$} shear flow. Finite Larmor radii chosen from a Maxwellian distribution create gyrocenter tracers, which changes the appearance of the flow. Time evolution of the propagator of particle displacements is split into two regimes. Diagnostics are developed for examining non-diffusive transport in more general flows. For the flow considered here, these diagnostic techniques reveal power law dependence in the following: tails of the particle propagator, the first two statistical moments and the distributions of trapping and flight events. The gyroaveraged flow changes the exponent of the second moment of the tracer propagator as a smooth function of $k_{\perp}\rho_{th}$. Self-similar scaling of the particle propagator is consistent with a fractional diffusion model and good agreement is found between the numerical data and a specific solution of the fractional diffusion equation. [Preview Abstract] |
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YP6.00036: Plasma Technology R{\&}D at SMU Ady Hershcovitch, Andrzej Socha, Radovan Kovacevic A program designed to develop enabling technologies for electron beam materials processing in air centered on plasma shielding was initiated at Southern Methodist University (SMU). Plasma shielding is designed to chemically and thermally shield a target object by engulfing an area subjected to beam treatment with inert plasma. The shield consists of a vortex-stabilized arc that is employed to shield beams and workpiece area of interaction from atmospheric or liquid environment. The vortex is composed of a sacrificial gas or liquid that swirls around and stabilizes the arc. A simpler, low-tech concept, which is a radiation and gas shielding chamber dubbed Shield Box, is also slated to be developed. The box is to be mounted on swivel wheels with suspension to facilitated smooth motion of a workpiece during welding or other processing. Sealing of the gap between the box solid walls and the workpiece is to be made out of flexible x-ray shielding material like bismuth cloth, lead vinyl, Demron fabric, etc. [Preview Abstract] |
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YP6.00037: Compact, Energy Self-Sustaining Neutron Source: Enabling Technology for Various Applications Ady Hershcovitch, W. Horak, B. Johnson, M. Todosow, T. Roser, M. Driscoll In this novel neutron source, a deuterium beam (energy of about 100 keV) is to be injected through a Plasma Window into a tube filled with tritium gas or tritium plasma to generate D-T fusion reactions whose products are 14.06 MeV neutrons and 3.52 MeV alpha particles. At the opposite end of the tube, the energy of deuterium ions that did not interact is recovered. Energy recovery is close to 100{\%}. Mo and Nb walls of proper thickness will absorb 14 MeV neutrons and release 2 -- 3 low energy neutrons. Each ion source and tube forms a module. Larger systems can be formed from multiple units. Beam propagation can be further enhanced with vortex stabilized discharges, electron beams in opposite direction (with energy recovery) or magnetic fields where possible. Unlike current methods, where accelerator based neutron sources require large amounts of power for operation, this neutron source will generated enough power to compensate for the power required to generate the ion beam. Concept description and basic calculation will be presented. Among possible applications for this neutron source concept are sub-critical nuclear breeder reactors and accelerator transmutation of radioactive waste. [Preview Abstract] |
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YP6.00038: Ne spectral emission measurements and theoretical modeling for the ASTRAL helicon plasma Jorge Munoz Burgos, Stuart Loch, Robert Boivin, Andrew Kesterson A review of the atomic data available for the first few ion stages of neon is given. We also present some new atomic data that uses a recently developed code to optimize the atomic structure used in the electron impact excitation calculation. The code adjusts the orbital scale factors to get the best energies and oscillator strengths. We compare our new structure with the level (term) energies, and line strengths given by NIST. Our optimised structure calculation is used in an R-matrix with pseudo-states calculation to compute electron-impact excitation data. Some comparisons are given between the predicted and observed neon spectra from ASTRAL. Recent measurements of neon spectra from the Auburn helicon plasma ASTRAL (Auburn Steady sTate Research fAciLity) are described. A spectrometer which features a 0.33 m Criss-Cross Scanning monochromator and a CCD camera is used for this study. The electron density in the plasma can vary from Ne = 10$^{11}$ to 10$^{13}$ cm$^{-3}$ and the electron temperature can vary from Te = 2 to 10 eV. Spectral emission is seen from neutral Ne and the first two ion stages. A rf compensated Langmuir probe is used to measure Te and Ne. We also present some collisional-radiative modeling results for neon spectra using the ADAS suite of codes. The variation of Ne and Te along the line of sight is included in the model. [Preview Abstract] |
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YP6.00039: Ar II Emission Processes and Emission Rate Coefficients in ASTRAL Helicon Plasmas R.F. Boivin, A. Gardner, O. Kamar, A. Kesterson, S. Loch, J. Munoz, C. Ballance Emission processes for Ar II line emission are described for low temperature plasmas (Te $<$ 10 eV). It is found that Ar II emission results primarily from Ar ion ground state excitation rather than from any Ar neutral state. This suggests that Ar II emission results from stepping processes which includes ionization and then excitation of the neutral Ar atom filling the vacuum chamber. The Ar II emission rate coefficients are measured in the ASTRAL helicon plasma source using a 0.33 m monochromator and a CCD camera. ASTRAL produces Ar plasmas with the following parameters: ne = 1E11 -- 1E13 cm-3 and Te = 2 - 10 eV, B-field $\le $ 1.3 kGauss, rf power $\le $ 2 kWatt. RF compensated Langmuir probes are used to measure Te and ne. In this experiment, Ar II transitions are monitored as a function of Te while ne is kept constant. Experimental emission rates are obtained as a function of Te and compared to theoretical predictions. Theoretical predictions make use of the ADAS suite of codes as well as recent R-matrix electron-impact excitation calculations that includes pseudo-states contributions. Our collisional-radiative formalism assumes that the excited levels are in quasi-static equilibrium with the ground and metastable populations. [Preview Abstract] |
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YP6.00040: Low Velocity Proton Stopping in Negative Hydrogen-Proton Mixtures Claude Deutsch, Marthe Bacal, Bekbolat Tashev We consider a charge neutral plasma target built on binary ionic mixtures (BIM) with classical electrons. Electron and ion contributions to the proton projectile low velocity ion slowing down (LIVSD) for projectile velocity Vp$<$Vthe (Vthe, target thermal electron velocity)are quantitatively estimated within a dielectric formalism restricted to the quadratic dependence in the projectile charge. The target BIM is constituted of hydrogen negative ions and bare protons in any proportion. Proton LIVSD quantitatively documents a monotoneous decay of free electron density with the increasing relative proportion of negative hydrogen ions,up to equi-proportionality. Possible diagnostics of low-temperature plasmas with T~3000-4000$^{\circ}$K with total ion density ranging around 10$^{11}$ cm$^{-3}$ are also discussed. [Preview Abstract] |
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YP6.00041: Dimensionality effects on the emergence of superdiffusion in Yukawa liquids Patrick Ludwig, Torben Ott, Michael Bonitz, Zoltan Donk\'o, Peter Hartmann A three-dimensional Yukawa liquid exhibits normal self-diffusion which is characterized by Fick's law and a time-independent diffusion coefficient D [1]. This quantity can be evaluated from the Einstein relation, $D=\langle r(t)^2\rangle/6t$. If however the mean-squared displacement $\langle r(t)^2\rangle$ grows faster than linearly with time, the diffusion coefficient is not well defined and the systems exhibits superdiffusive behaviour. Recently, superdiffusion has been observed in two-dimensional Yukawa liquids [2]. In this contribution we enter into the question about the occurrence of superdiffusion in the transiton-region from a purely three-dimensional to a quasi 2D system where one dimension is confined [3,4]. \\[0pt] [1] H. Ohta and S. Hamaguchi, Phys. Plasmas \textbf{7}, 4506 (2000) \\[0pt] [2] B. Liu and J. Goree, Phys. Rev. E \textbf{75}, 016405 (2007) \\[0pt] [3] Z. Donk\'o, P. Hartmann and G. J. Kalman, Phys. Rev. E \textbf{69}, 065401 (2004) \\[0pt] [4] T. Ott, Z. Donk\'o, P. Hartmann and M. Bonitz, Submitted to Phys. Rev. E. [Preview Abstract] |
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YP6.00042: Stability of a new toroidal magnetized plasma device with permanent poloidal field induced by a central conductor Steve Jaeger, Thiery Pierre A new toroidal device has been recently established at the Institute for Fusion Physics, CNRS- Univ. Marseille, including a central conductor on the secondary axis of the torus. The large radius is 60 cm and the small radius is 20 cm. The central conductor is made of three toroidal turns of a copper bar bearing 400 Amps. The toroidal magnetic field is lower than 400 Gs, leading to a security factor q=1 at radius r close to 6 cm. The plasma is produced using a small tungsten filament (4 cm length, 0.2 mm diameter) at radius r= 2 cm and applying the discharge voltage between the filament and the central conductor. A high density plasma is obtained due to the efficient confinement and in typical discharges, no instability is recorded in the core plasma. The stability is studied changing both the gas pressure (argon gas) and the shear rate of the poloidal field. [Preview Abstract] |
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YP6.00043: ABSTRACT WITHDRAWN |
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YP6.00044: Assessing SRS-induced electron trapping in ignition hohlraums D.J. Strozzi, E.A. Williams, H.A. Rose, A.B. Langdon, D.E. Hinkel Electron trapping can cause important nonlinearities in stimulated Raman scattering (SRS), including kinetic inflation$^{1,2}$, a nonlinear frequency shift$^3$, and Langmuir-wave bowing and self-focusing$^4$. We quantify the likelihood of such nonlinearity with the number of bounce orbits$^2$, $N_B \equiv \tau_{de}/\tau_B$, that a resonant electron undergoes during a typical detrapping time $\tau_{de}$ ( $\tau_B \equiv 2\pi[\delta n/n_e]^{1/2}/\omega_{pe}$ is the bounce period). We calculate $N_B$, with linear theory, for the detrapping processes of speckle sideloss and collisions (both pitch-angle scattering and parallel diffusion). For typical NIF ignition designs, sideloss is the most effective detrapping process. We use NB to analyze simulations of NIF designs with the paraxial, enveloped propagation code pF3D. We find that trapping should not occur on the outer beams. However, it may occur on the inner beams near the hohlraum wall, where pF3D predicts SRS reflectivities of several percent. In addition, comparison of kinetic simulations with various reduced models of trapping nonlinearities will be presented. $^1$H. X. Vu et al., PRL \textbf{86}, 4306 (2001). $^2$D. J. Strozzi et al., PoP \textbf{14}, 013104 (2007). $^3$G. J. Morales, T. M. O'Neil, PRL \textbf{28}, 417 (1972). $^4$L. Yin et al., PRL \textbf{99}, 265004 (2007) [Preview Abstract] |
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YP6.00045: Propagation and Interaction of Laser Beams with ISI and SSD in inhomogeneous plasmas Mathieu Charbonneau-Lefort, Bedros Afeyan, Andrew Schmitt, Robert Lehmberg We examine the propagation of laser beams in inhomogeneous plasmas which are subject to beam smoothing techniques such as ISI or SSD. We compare and contract these two smoothing techniques including the dependence on bandwidth, color cycling, polarization and susceptibility to filamentation. We calculate the statistical properties of the beams inside the plasma with and without filamentation. We also examine the effects of crossing beams on the statistics of such a pump beam. [Preview Abstract] |
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YP6.00046: KEEN Waves, Multiple Water-Bag Models and Vlasov-Poisson vs Vlasov-Maxwell Simulations Bedros Afeyan, Mathieu Charbonneau-Lefort, Magdi Shoucri KEEN Waves are a manifestation of nonstationary, self-organized, nonlinear, kinetic states prevalent in coherently driven plasmas [1, 2]. We will show reduced models of their evolution in phase space that are reminiscent of multiple water-bag models and capture some of their salient features. In addition, Vlasov-Poisson and Vlasov-Maxwell simulation results will be compared to each other in periodic and non-periodic boundary condition modes. The effect of finite bandwidth (instead of single frequency) drive will be highlighted. [1] B. Afeyan, et al., Kinetic Electrostatic Electron Nonlinear (KEEN) Waves and their interactions driven by the ponderomotive force of crossing laser beams, Proc. IFSA, (Inertial Fusion Sciences and Applications 2003, Monterey, CA), B. Hammel, D. Meyerhofer, J. Meyer-ter-Vehn and H. Azechi, editors, 213, American Nuclear Society, 2004. [2] B. Afeyan, et al., Dynamically Self-Organized Structures in Vlasov Phase Space: Ponderomotively Driven KEEN Waves, Submitted to PRL, 2008. [Preview Abstract] |
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YP6.00047: Improved non-LTE simulation algorithm Michel Busquet, Marcel Klapisch, Denis Colombant, David Fyfe, John Gardner The RAdiation Dependent Ionization Model (RADIOM)- a.k.a Busquet's model-[1] has proven its success in simulating non --LTE effects in laser fusion plasmas [2]. This improved algorithm can take into account Auger effect by a new parameter fitted to SCROLL [3] results. It is independent of the photon binning thanks to a projection on a standard grid. It guarantees smoother convergence to LTE. This algorithm has been implemented in a new way in the hydro-code FASTnD. Hydro simulations on the recent subMJ targets[4], with and without non-LTE corrections will be shown. [1] M. Busquet, Phys. Fluids B 5, 4191(1993). [2] D.G. Colombant et al{\ldots}, Phys. Plas. 7,2046 (2000). [3] A. Bar-Shalom, J. Oreg M. Klapisch, J. Quant. Spectr. Rad. Transf. \textbf{65} ,43 (2000). [4] S. P. Obenschain, D. G. Colombant, A. J. Schmitt et al., Phys. Plasmas \textbf{13}, 056320 (2006). [Preview Abstract] |
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YP6.00048: Experimental studies on nonlinear cyclotron harmonic absorption JaeChun Seol, Yong-Su Na, Jayhyun Kim, A.C.C. Sips Nonlinear electron cyclotron resonance heating (ECRH) is studied experimentally in the ASDEX Upgrade tokamak. Pre-ionization process is measured and analyzed to study nonlinear cyclotron resonance absorption. In the pre-ionization process, electrons are heated from the room temperature. Since cold electrons stay in the microwave beam relatively longer in this case, nonlinear interaction between the microwaves and particles are more likely to happen. The new multi-frequency ECRH system, working at 105 GHz and 140 GHz is used for the experiments. It is found that pre-ionization is more efficient at 105 GHz and than 140 GHz as predicted theoretically. It is the first experimental result that verifies the theory. [Preview Abstract] |
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YP6.00049: Electron transport analysis in TCV W. Horton, J.-H. Kim, E. Asp, L. Porte, S. Alberti, A. Karpushov, Y. Martin, O. Sauter, G. Turri A TCV plasma with high power density (up to 8MW/m%^3$) core deposited ECR heating at significant plasma densities ($\leq7 \times 10^{19}$ m$^{-3}$) is analyzed for the electron thermal transport. The discharge has four distinct high confinement mode (H-mode) phases, an ohmic H-mode with type III edge localized modes (ELMs), a type I ELMy H-mode with the ECRH on, two quasi-stationary ELM-free H-modes, one of which without magneto-hydrodynamics (MHD) and one with. For all four phases both large-scale TEM and ITG modes and small-scale ETG modes are analyzed. For easy comparison of the results, a dimensionless error measure, the so-called average relative variance (ARV) is introduced. According to this method the ETG model explains 70\% of the variation in the electron heat diffusivity whereas the predictive capabilities of the TEM-ITG models are poor. These results for TCV support the conclusion that the ETG model is able to explain a wide range of anomalous electron transport data, in addition to existing evidence from ASDEX, Tore Supra and FTU. [Preview Abstract] |
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YP6.00050: Generation of electromagnetic waves by drift wave -- zonal flow turbulence in magnetically confined fusion plasma W. Horton, C. Correa, J. Kim, G.D. Chagelishvili, V.S. Avsarkisov, R.G. Chanishvili According to recent experiments [1,2], magnetically confined fusion plasma ``drift wave -- zonal flow turbulence'' gives rise to broad bend of electromagnetic waves. Ref. [1] reports abrupt changes in magnetic turbulence during L--H transitions in JET plasmas, i.e. appearance of broad spectra of electromagnetic waves, when zonal flow comes into play. Alfvenic fluctuations appear from \textbf{ExB} flow driven turbulence in experiments on the Large Plasma Device (LAPD) at UCLA [2]. We explain the generation of EM waves in DW-ZF systems on an example of LAPD experiments. Our research is based on a break-through by the hydrodynamic community in the 1990s in understanding the physics of spectrally stable nonuniform flows; these flows are non-normal and result in linear transient growth of perturbations and their coupling. The mode linear coupling in shear flows causes the generation of electromagnetic waves in the considered DW-ZF system. We study dependence of the generation on parameters of the system and show that this phenomenon is universal at high shear rates of ZF and should take place in tokamaks.\\[0pt] [1] Sharapov et al. 21st US TTF Workshop, Boulder, CO, March 2008.\\[0pt] [2] Perez, et al. Phys Plasmas, 13,055701, 2006. [Preview Abstract] |
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YP6.00051: Wave generation and magnetic field amplification in astrophysical shocks Luis Gargate, Ricardo Fonseca, Jacek Niemiec, Robert Bingham, Luis Silva Supernovae remnant shocks, producing Cosmic Rays (CR), and coronal mass ejection shocks, producing Solar Energetic Particles (SEP), have different features, but in both scenarios waves are known to propagate and to amplify the magnetic field and turbulence in the upstream region of the shocks. We analyze Bell's instability [1], in which small-scale non-resonant wave modes are driven by cosmic ray ions streaming in the shock precursor along a background magnetic field B0, and driving a current. We use hybrid simulations to study the feedback of magnetic turbulence produced on cosmic ray trajectories; our results show a significant magnetic field enhancement, strongly dependent on the relative flow velocity of the ion species, and show the formation of plasma-depleted cavities. We find that the saturation of the instability is associated with the sustainability of the current. The non-linear growth phase and the saturation phase are explored in detail, and a discussion of the relevance of the mechanism to the CR and SEP scenarios is also presented. [1] A. R. Bell, Mon. Not. R. Astron. Soc. 353, 550, 2004 [Preview Abstract] |
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YP6.00052: Creating flowing space plasma environments with VASIMR Edgar Bering III, Benjamin Longmier, Tim Glover, Franklin Chang-Diaz, Jared Squire, Michael Brukardt Recent results from the operation of a 125 cubic meter space simulation chamber are presented. The primary role of the vacuum chamber is to support the operation of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR), a high power magnetoplasma rocket, capable of Isp/thrust modulation at constant power. However, magnetospheric and heliospheric plasma environments can be produced with the VASIMR plasma source with a power range of 0.5 to 200 kW, producing a H, D, Ne, or Ar flowing plasma with flow velocities in excess of 20,000 km/s. The plasma is produced by a helicon discharge. The bulk of the energy is added by ion cyclotron resonance heating (ICRH.) Axial momentum is obtained by adiabatic expansion of the plasma in a magnetic nozzle. Particle flux and particle energy can be adjusted independently of each other, which is primarily achieved by the partitioning of the RF power to the helicon and ICRH systems, with the proper adjustment of the propellant flow. Ion dynamics in the flowing plasma is studied using probes, gridded energy analyzers (RPA's), microwave interferometry and optical techniques. [Preview Abstract] |
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YP6.00053: Ideal MHD simulations of laboratory and astrophysical magnetic bubble expansion as a model for extragalactic radio lobes. Wei Liu, Scott Hsu, Hui Li, Shengtai Li, Alan Lynn Nonlinear ideal magnetohydrodynamic (MHD) simulations of the propagation and expansion of a magnetic ``bubble'' plasma into a lower density, weakly-magnetized background plasma are presented. These simulations mimic the geometry and parameters of the Plasma Bubble Expansion Experiment (PBEX), which is studying magnetic bubble expansion as a model for extra-galactic radio lobes. The simulations predict several key features of the bubble evolution. First, the direction of bubble expansion depends on the ratio of the bubble toroidal to poloidal magnetic field, with a higher ratio leading to expansion predominantly in the direction of propagation and a lower ratio leading to expansion predominantly normal to the direction of propagation. Second, an MHD shock and a trailing slow-mode compressible MHD wavefront are formed ahead of the bubble as it propagates into the background plasma. Third, the bubble expansion and propagation develop asymmetries about its propagation axis due to reconnection facilitated by numerical resistivity and to inhomogeneous angular momentum transport mainly due to the background magnetic field. These results will help guide the initial experiments and diagnostic measurements on PBEX. [Preview Abstract] |
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YP6.00054: Fast Photography of Acoustic Shock Waves in Glow Discharge Plasmas A.L. Roquemore, N.K. Podder, A.C. LoCascio A fast imaging camera has been used to record the propagation dynamics of an acoustic shock wave in glow discharge plasmas at a frame rate of 43,000 fps. Measurements are performed in both N$_{2}$ and Ar discharges and for both propagation polarities, i.e, anode-to-cathode and cathode-to-anode propagations. Video frames obtained for the shock wave propagation in the N$_{2}$ plasma indicate that the plasma emissions at the nitrogen shock-front are enhanced by up to 40{\%} over the background, whereas those in the Ar plasma indicate that the plasma emissions at the argon shock-front are suppressed. Analyses of the video frames yield the shock wave propagation velocities, which are compared with the velocities obtained from an existing laser beam deflection method. Additional comparisons between the velocities from the two methods are made for both anode-to-cathode and cathode-to-anode propagations of shock waves in plasmas. For both propagation polarities of the shock waves, the average velocity trend determined from the two methods are in good agreement. [Preview Abstract] |
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YP6.00055: Low temperature refrigeration by using thermal-field emission in a coaxial cylindrical diode Lin Wu, Lay Kee Ang, Wee Shing Koh We explore new possibilities of refrigeration by using thermal-field emission of electrons in a coaxial cylindrical diode with a nanometer scale inner electrode (or cathode). Our calculation shows that it is possible to provide cooling at temperature down to 200 K if the work function of the cathode is about 1 eV. The limitation on the cooling power density and its temperature range is due to the requirement of low work function of the cathode. By applying an external axial magnetic field, an additional potential barrier near anode is created, and the emission of low energy electrons (below the Fermi energy level) is suppressed to enhance the cooling performance. With this extra filtering process, emitters of arbitrary work functions can be used to provide a cooling capability from 300 K down to 10 K. The optimal conditions to achieve maximum cooling power density are determined both numerically and analytically. The space charge effects of the emitted electrons in the gap are included self-consistently. [Preview Abstract] |
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YP6.00056: Hybrid fusion: The only viable development path for tokamaks? Wallace Manheimer The world needs a great deal of carbon free energy, and soon, for civilization to continue. Fusion's goal is to develop such a carbon free energy source. For the last 4 decades, tokamaks have been the best magnetic fusion has to offer. But what if its development stops short of commercial fusion? This paper introduces ``conservative design principles'' for tokamaks. These are very simple, are reasonably based in theory, and have always constrained tokamak operation. Assuming they continue to do so, it is unlikely that tokamaks will ever make it as commercial reactors. This is independent of their confinement properties. However because of the large additional gain in hybrid fusion, tokamaks reactors look like they can make it as hybrid fuel producers, and provide large scale power by mid century or shortly thereafter. [Preview Abstract] |
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YP6.00057: Plasma Injection Experiment at MCX Ilker Uzun-Kaymak, S. Messer MCX uses an axial magnetic field and a radial voltage to drive supersonic azimuthal flows. It has been observed that the high flow velocity and large radial velocity shear suppresses the higher order interchange modes. However, the MCX discharges are currently limited by the charge and current available from the capacitor bank supplying the radial voltage. The High Density Plasma Injection Experiment combines the MCX experiment with a modified coaxial plasma gun to drive rotation in the target vessel. A 32-injector prototype coaxial gun has been designed, constructed and installed at MCX midplane, top tangential port, as alternate means of momentum input. Unlike traditional coaxial plasma jets, the transport of the jet has been optimized via a combination of electrode shaping and tailored armature at HyperV Technologies Corp. in order to prevent the blow-by instability. Data will be presented for a wide range of MCX parameters and the prospects for future injection experiments will be evaluated. [Preview Abstract] |
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YP6.00058: Current research activities and installation status of the X-ray imaging crystal spectrometer for KSTAR S.G. Lee, J.G. Bak, U.W. Nam, M.K. Moon, J.K. Cheon, M. Bitter, K. Hill An X-ray imaging crystal spectrometer (XICS) for KSTAR utilizing a four-segmented position-sensitive two dimensional (2D) multi-wire proportional counter and time-to-digital converter (TDC) based delay-line readout data acquisition system has been fabricated. The XICS provides spatially and temporally resolved measurements of the ion and electron temperatures, toroidal rotation velocity, impurity charge-state distributions, and ionization equilibrium. The four-segmented 2D detector with supporting electronics successfully demonstrated to improve the photon count-rate capability of the XICS system and a position resolution of the detector showed about 0.35 mm. A spectral resolution of the fabricated spectrometer has been measured using an X-ray tube before installation in the KSTAR tokamak. The current research activities and installation status of the spectrometer will be presented. [Preview Abstract] |
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YP6.00059: Nonlinear 3D visco-resistive MHD modeling of fusion plasmas: a comparison between numerical codes D. Bonfiglio, L. Chacon, S. Cappello Fluid plasma models (and, in particular, the MHD model) are extensively used in the theoretical description of laboratory and astrophysical plasmas. We present here a successful benchmark between two nonlinear, three-dimensional, compressible visco-resistive MHD codes. One is the fully implicit, finite volume code PIXIE3D [1,2], which is characterized by many attractive features, notably the generalized curvilinear formulation (which makes the code applicable to different geometries) and the possibility to include in the computation the energy transport equation and the extended MHD version of Ohm's law. In addition, the parallel version of the code features excellent scalability properties. Results from this code, obtained in cylindrical geometry, are compared with those produced by the semi-implicit cylindrical code SpeCyl, which uses finite differences radially, and spectral formulation in the other coordinates [3]. Both single and multi-mode simulations are benchmarked, regarding both reversed field pinch (RFP) and ohmic tokamak magnetic configurations. [1] L. Chacon, Computer Physics Communications \textbf{163}, 143 (2004). [2] L. Chacon, Phys. Plasmas \textbf{15}, 056103 (2008). [3] S. Cappello, Plasma Phys. Control. Fusion \textbf{46}, B313 (2004) {\&} references therein. [Preview Abstract] |
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YP6.00060: Evolution of plasma rotation, radial electric field, MHD activity and plasma confinement in the STOR M tokamak Dallas Trembach, Mykola Dreval Experimental results from the STOR-M tokamak detailing simultaneous behavior of plasma SOL rotation, radial electric field, main plasma column parameters, and MHD activity are presented. In the STOR{\-}M tokamak, fast ($\sim $ 1 ms), well correlated changes in the radial electric field, plasma rotation, and floating potential fluctuations in the periphery are observed. During the correlated phase, the radial electric field changes its sign from positive to negative, the Mach number of toroidal plasma rotation, which is co-current, decreases from M$_{\vert \vert }$= 0.4 to nearly 0. MHD activity in STOR{\-}M tends to be suppressed if the radial electric field is negative. When the electric field is negative, MHD frequency decreases and increases in the average electron density and poloidal beta are observed. [Preview Abstract] |
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YP6.00061: Hybrid PIC modeling of fast electron transport and magnetic collimation in low-Z hot dense plasmas accessible on the Omega EP laser Mingsheng Wei, Farhat Beg, Richard Stephens A large uniform low-Z hot (20 eV - 100 eV) and dense (0.2 g/cc - 1.0 g/cc) plasma can be produced with multiple kJ energies, long pulse laser beams at the Omega-EP facility. Then OMEGA EP short pulse laser can be used to produce fast electrons. Study of fast electron propagation in such plasmas is of great importance to fast ignition of inertial confinement fusion. In this work, we use the hybrid particle-in-cell (PIC) code LSP to systematically investigate the propagation and energy transport of fast electrons produced by the EP ultrahigh intensity short pulse in such hot dense plasmas with the abovementioned plasma densities and temperatures. Preliminary results show resistive collimation and beam filamentation under various plasma conditions. In addition, effects of an externally applied magnetic field (MG) on the collimation of fast electrons beam and the resultant improved energy transport have been observed. [Preview Abstract] |
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YP6.00062: Advanced Scenario Development Using Off-Axis Neutral Beam Current Drive in DIII-D, M. Murakami, J.M. Park, T.C. Luce, C.C. Petty, R. Prater, T.S. Taylor, M.R. Wade A goal of the DIII-D AT program is the development of Advanced Tokamak scenarios in support of ITER and future tokamak reactors. Research on DIII-D has focused on the stationary fully noninductive, high-bootstrap fraction scenario development. One-dimensional self-consistent scenario modeling using both scaled experimental transport and theory-based (GLF23) models shows that the proposed 10-MW off-axis NBCD with high power electron cyclotron and fast wave heating and current drive will allow full noninductive operation at high beta with flat safety factor profile with $q_{min}>2$ for twice the current relaxation time, consistent with $Q=5$ steady-state operation of ITER. The modification of the DIII-D NB system for off-axis NBCD will provide a flexible scientific tool for understanding transport, energetic particles, heating and CD physics, and validating the off-axis NBCD in support of scenarios for ITER and FDF. [Preview Abstract] |
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YP6.00063: Critical toroidal rotation profile for resistive wall modes in tokamaks K.C. Shaing, M. Chu, S.A. Sabbagh, M. Peng A three-mode model including the effects of the toroidal coupling is developed for the resistive wall modes in tokamaks. The modes are basically toroidally coupled resistive wall tearing modes, and they have resonant surfaces inside the plasmas. In the vicinity of the resonant surfaces, the neoclassical effects are employed to describe the physics of the resistive layer. This leads to enhanced plasma inertia and dissipation. The dispersion relation that includes toroidal plasma rotation speed at the resonant surfaces and the mode frequency is derived from the determinant of a 6$\times $6 matrix. The toroidal plasma rotation profile is calculated by solving the toroidal momentum diffusion equation with a momentum source in the regions between the magnetic axis and a resonant surface, between two resonant surfaces (there are two such regions in the model), and between a resonant surface and the plasma boundary. The boundary conditions are the toroidal rotation speeds at the magnetic axis, at the resonant surfaces, and at the plasma boundary. These coupled equations uniquely determine a critical toroidal rotation profile that stabilizes the resistive wall mode. [Preview Abstract] |
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YP6.00064: Global Machine Design and Double X-point Equilibrium Configurations for Ignitor* A. Bianchi, B. Parodi, B. Coppi The detailed design of the Ignitor machine has been carried out by considering extended limiter plasma configurations that are up-down symmetric and whose outer magnetic surfaces follow closely the cavity of the toroidal magnet over most of the vertical cross section. This provision minimizes the out-of- plane forces produced by the plasma current and acting on the toroidal magnet. When, instead, the adopted plasma equilibrium configuration is of the double X-point type the out-of-plane forces increase, and a complete structural analysis to take this increase into account becomes appropriate. The reference maximum plasma current $I_p$, in order to maintain an acceptable magnetic safety factor, is reduced from 11 MA in the extended limiter to 9 MA in the double X-point configuration while the magnetic field on axis ($R_0 \cong 1.32$ m) is maintained at $B_T \cong 13$ T. The reduced scenario involving $I_p \cong 6$ MA and $B_T \cong 9$ T does not present a problem. Both 3D and 2D drawings of each individual machine component are produced using the Dassault Systems CATIA-V software. After their integration into a single 3D CATIA model of the Core (Load Assembly), the electro-fluidic and fluidic lines which supply electrical currents and helium cooling gas to the coils are included and mechanically connected to the main machine components.\\ $^*$Sponsored in part by ENEA of Italy and by the U.S. D.O.E. [Preview Abstract] |
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YP6.00065: Gyrokinetic Formulation of Zonal Flow Momentum Conservation in Drift Wave Turbulence L.T. Katt, P.H. Diamond, T.S. Hahm, O.D. Gurcan, X. Garbet A fully gyrokinetic formulation of a generalized Charney-Drazin theorem for zonal flow momentum evolution is presented. The theorem is based on the intrinsically symplectic structure of the gyrokinetic equation and the GK Poisson equation, which parallels the structure of the quasi-geostrophic potential vorticity equation and the Taylor identity. This approach naturally identifies a phase space wave activity density, the evolution of which is tied to zonal momentum evolution. The constraints on zonal flow evolution in a stationary state are identified. This analysis focuses on a reduced model formulated by Kadomtsev and Pogutse and Darmet, et al., but is generalizeable. This material is based upon work supported by the Department of Energy under Award Numbers DE-FG02-04ER54738 and DE-FC02-08ER54959. [Preview Abstract] |
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YP6.00066: POSTDEADLINE |
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YP6.00067: Dynamo ``$\alpha$ effect'' in the MHD plasma due to noise Chang-Bae Kim Response is studied in the long-time and- large-scale limit of a magnetohydrodynamic plasma driven by a noise that depends on a selective direction $\hat s$, which may be due to the rotation about an axis or to the strong magnetic field. The noise is assumed to represent the short-scale turbulence that is often observed in the experiments and the numerical simulations. In addition to enhanced dissipation (that is, the so-called ``$\beta$ effect'') of the magnetic field contributed from the diagonal part of the noise spectrum, it is found that it also yields the so-called ``$\alpha$ effect,'' the curl of the magnetic field in Ohm's law. It is interesting to note that the term is independent of $\hat s$ although $\hat s$ is a necessity to begin with. Comparisons to the gyrotropic noise model will be discussed at the presentation. [Preview Abstract] |
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YP6.00068: Picosecond electron deflectometry of laser-induced plasmas Martin Centurion, Peter Reckenthaeler, Alexander Apolonskiy, Ferenc Krausz, Ernst Fill We demonstrate a method for real-time imaging of the field distribution in laser-induced plasmas with picosecond temporal resolution. The plasma is generated by a 50 fs laser pulse focused in nitrogen gas jet, and is then probed by a picosecond electron pulse synchronized with the laser. Pump-probe images of the electron beam at different delay times are recorded on a CCD camera. The electric and magnetic fields are reconstructed by comparing the recorded patterns with numerical simulations. We have observed a cloud of hot electrons expanding away from a central core of positively charged ions, and the appearance of strong magnetic fields near the boundaries of the gas jet. In the case of a plasma generated in low density nitrogen (10$^{13}$ cm$^{-3})$, we observed that even low energy electrons can escape from the plasma volume. [Preview Abstract] |
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YP6.00069: Experimental demonstration of x-ray betatron radiation spectrum from laser accelerated electron beams Valentine Leurent, Pierre Michel, Chris Clayton, Bradley Pollock, Tilo Doeppner, Joseph Ralph, Art Pak, Tyan-Lin Wang, Chan Joshi, George Tynan, Laurent Divol, John Palastro, Siegried Glenzer, Dustin Froula New laser wakefield acceleration (LWFA) experiments have been carried out at the Callisto Laser Facility, Lawrence Livermore National Laboratory. We will present results of the first experimental campaign on LWFA. The electron beam energy spectrum was measured with a two-screen spectrometer to avoid ambiguities due to the possible angle of the electron beam at the plasma exit [1]. Electron beams up to 300 MeV were measured. X-ray betatron radiation from the accelerated electrons were also measured. By using a set of filters acting like a spectral step function, the x-ray spectrum was reconstructed from fitting theoretical estimates; the radiation peaks at a few keVs. [1] R. Ischebeck et al., Proceedings of PAC 2007, Albuquerque NM, p. 4168. LLNL-ABS-405251 [Preview Abstract] |
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YP6.00070: Diagnosing the High Energy Deuterium Spectra in IEC Devices Using Doppler Shifted Fusion Products David Boris The UW-Inertial Electrostatic Confinement (IEC) device is comprised of concentric spherical metallic grids within a cylindrical vacuum vessel. The central grid, which can be held at high negative potentials ($\sim $ -100 to -200kV), is the device cathode, while the outer grid, held at ground potential, is the device anode. This configuration accelerates ions, created near the anode, toward the center of the device. A weakly ionized cold plasma, created by a filament assisted DC discharge outside the anode, is the ion source for the device. The fill gas for this device is typically deuterium, thus leading to D-D fusion rates on the order of 10$^8$ fusions/s. The high energy protons and tritons resultant from D-D fusion reactions have been observed using charged particle detectors. These detectors are capable of discerning the Doppler shift on D-D fusion products imparted by the center of mass energy of the deuterium reactants. From the fusion product spectra compiled by a multi-channel analyzer the energy spectra of the deuterium reactants can be calculated. Using this diagnostic the effect, on the deuterium spectra, of varying the parameters of fill gas pressure, cathode voltage, cathode current and grid geometry have been examined. [Preview Abstract] |
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YP6.00071: X-ray Thomson scattering spectra of shock-compressed Be plasmas H.J. Lee, R.W. Falcone, S.H. Glenzer, P. Neumayer, J. Castor, O.L. Landen, T. D\"oeppner, R.W. Lee, B.A. Hammel, D.H. Munro, B.K. Spears, S. Weber, C. Fortmann, R. Redmer, R. Thiele, A.L. Kritcher, D.D. Meyerhofer, S.P. Regan We have measured x-ray Thomson scattering spectra of shock compressed Be for pressures in the range of 10-35 Mbar. 6 keV x-rays have been produced to perform spectrally resolved measurements of the plasmas employing both non-collective and collective scattering at the Omega laser facility. The scattering spectra from two different regimes show Compton and Plasmon features indicating Fermi-degenerate dense plasmas with a Fermi energy in excess of 30 eV and temperatures of 9-15 eV. These findings indicate compression by a factor of three in good agreement with radiation hydrodynamic modeling. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344. [Preview Abstract] |
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YP6.00072: Superheating of a Dusty Plasma Crystal John Goree, Yan Feng, Bin Liu In a laboratory dusty plasma, highly-charged micron-size particles of solid matter are immersed in a weakly-ionized gas, where they are confined indefinitely by ambipolar electric potentials. Individual particles move a few mm/s, and are imaged using video micrography. Due to their large mutual Coulomb repulsion, particles self-organize in a solid, which we melt, by applying laser heating. Applying the heating suddenly, we observe solid superheating, a basic physical phenomenon which until now has been observed only in a handful of experiments with metals. A superheated solid has the structure of a solid, but a temperature higher than the melting point. In metals, solid superheating is short-lived because it is rapidly followed by melting. In our experiment, thanks to the long time scales for the massive charged particles to move, our superheated solid lasts about 0.25 sec before melting ensues. We make time-resolved observations of particle motion and defect development during this rapid heating, in a way that is impossible in experiments with metals. A hysteresis diagram reveals the solid superheating. [Preview Abstract] |
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YP6.00073: XUV Opacity of Warm Dense Aluminum Justin Wark, Sam Vinko, Gianluca Gregori, Bob Nagler, Thomas Whticher, Michael Desjarlais, Patrick Audebert, Richard Lee We present calculations of the free-free XUV opacity of warm, solid-density aluminum at photon energies between the plasma frequency at 15 eV and the L-edge at 73 eV using a semi-classical model in the RPA framework with the inclusion of local field corrections. As the temperature is increased from room temperature to 10 eV, with the ion and electron temperatures equal, we calculate an increase in the opacity in the range over which the degree of ionization is constant. Noticeably, this feature is not reproduced by models based on inverse bremsstrahlung. The physical significance of this increase is discussed in terms of intense XUV-laser matter interactions on both femtosecond and picosecond timescales, and our model compared with detailed quantum molecular dynamics calculations (VASP). [Preview Abstract] |
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YP6.00074: Plasma response to external fields with finite current gradient D. Flanagan, D.P. Brennan The displacement of the plasma edge in response to an external magnetic perturbation is calculated in slab geometry. Experiments in DIII-D have shown that varying the magnetic field imposed by the external coils can cause an edge displacement of approximately 2 cm, roughly 6{\%} the plasma half-width. A previously derived model [A. Cole and R. Fitzpatrick, Phys. Plasmas 13, 032 503 (2006)] for the plasma response to an external field perturbation is extended to include effects essential to explaining this data, where equations describing the drift-MHD stability are extended to apply to an equilibrium in slab geometry with a non-zero current gradient flanked by vacuum regions. This system of equations is solved for the modified ExB velocity in viscous force balance. The maximum displacement of the plasma boundary calculated is comparable to experimental results, but only occurs near the ideal MHD limit. This result indicates that the inclusion of a non-zero current gradient and a vacuum region in the slab equilibrium specification is perhaps the simplest method to calculate realistic plasma displacements due to external fields. [Preview Abstract] |
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YP6.00075: Damaging of Debris Shield Exposed during Laser Matter Experiments on the Lil Facility Didier Raffestin, Jean Luc Rullier, Laurent Lamaignere, Severine Garcia, Stephanie Palmier, Alessandra Ciapponi, Jean Yves Napoli During plasma experiments on high energy laser facility, debris and fragments originating from the target can be responsible for significant damages on optics or equipments. On the LIL facility (the Laser Integration Line, prototype of the LMJ (MegaJoule Laser)), valuable optics are protected using debris shield. This device is exposed to both materials (including radiations) stemming from the target and high intensity laser getting through. In the scope of the maintenance programme of the future LMJ (holding, up to 240 debris shields), it is necessary to quantify the expected evolutions of the shield (aka ``LAE'': lame anti \'{e}clat) with respect to the experimental conditions. For this purpose, two programmes were established. On one hand, the periodic measurement of real LIL LAE exposed, in term of observation (size, number of damage) and 3$\omega$ laser transmission. And on the other hand, the exposition of representative samples in the target chamber in order to determine the direct effect of the target (droplets, shrapnels, debris, {\ldots}) and the consequent sensibility to representative laser irradiation. Intermediate results of these two approaches are further discussed in this paper. [Preview Abstract] |
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YP6.00076: Kinetic effects of energetic particles on resistive MHD stability Ryoji Takahashi, Dylan Brennan, Charlson Kim It is shown that the kinetic effects of energetic particles can play a crucial role in the stability of the 2/1 tearing mode in tokamaks such as JET, JT-60U, and DIII-D, where the fraction of energetic particle $\beta $ is high. Using model equilibria based on experimental reconstructions from DIII-D, the non-ideal MHD stability, linear, and nonlinear evolution of the 2/1 mode is investigated including a delta-f kinetic model for the energetic particles coupled to the MHD solution. The growth of unstable modes is calculated at a series of $\beta _{N}$/4$l_{i}$ and S, spanning from the resistive to the ideal unstable regime of the mode. It is observed that energetic particles have significant damping and stabilization effects at higher energetic paricle fractions ($\beta _{frac})$ and S, and cause precession of the 2/1 mode. Furthermore, our extrapolated results are discussed for implications to ITER, where the effects are projected to be significant. [Preview Abstract] |
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YP6.00077: Particle Emission and Absorption in Cut Cell Geometries of Electromagnetic Particle-in-Cell (PIC) Codes Sudhakar Mahalingam, Chet Nieter, John Loverich, David Smithe, Ming-Chieh Lin Cut cell techniques are frequently used in FDTD (Finite Difference Time Domain) electromagnetics algorithms to better represent complex geometries and achieve improved accuracy. Recent research at Tech-X has been performed to investigate the use of particle emitters and absorbers in complex cut cell geometries. Key issues are the preservation of Gauss's law at the emission and absorption points in electromagnetic simulations without using divergence cleaning techniques such as Hodge projection. Several methods have been developed to properly preserve Gauss's law during emission and absorption from cut cell boundaries and are presented in this work. In addition, results are presented for a variety of complex configurations. Ultimately the research will be applied to beamed energy devices. [Preview Abstract] |
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YP6.00078: Verification of the Coupling Oscillation in a Hall Thruster Hans Pfister, Kristina Gaff, Sean Brannon Plasma thrusters have found increasing application for station keeping of Earth-orbiting satellites and interplanetary missions, yet a few basic plasma physics questions of these thrusters remain unresolved. Recently, we discovered an oscillatory interaction between the discharge current and the current for the radial magnetic field in Dickinson College's closed drift Hall thruster. Similar oscillations were found and reported for the first time by Yu et al. [Plasma Sources Sci. Technol. 16, Sept. 2007], who refer to this interaction as a ``coupling oscillation.'' In this phenomenon, azimuthally E~$\times $~B-drifting electrons create a Hall current, which produces a magnetic field opposing the thruster's applied radial magnetic field. The reduction of this crucial radial magnetic field leads to a diminished discharge current and thus Hall current. As a consequence the ``normal'' radial magnetic field and increased discharge current return, causing the coupled cycle to begin again, thereby producing the oscillatory interaction we observe. Here we present evidence that verifies the connection between the discharge current and the current for the thruster's magnetic field. [Preview Abstract] |
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YP6.00079: A New Matching Method for the Resistive Wall Mode Analysis of Rotating Plasmas Junya Shiraishi, Shinji Tokuda, Nobuyuki Aiba Stabilization of the Resistive Wall Modes (RWMs) by the plasma rotation is one of the most important physical issues for future reactors operated in the advanced tokamak regime [1]. For rotating plasmas, the linear stability problem, which is governed by the Frieman-Rotenberg equation [2], becomes non-self-adjoint, thus the conventional normal mode decomposition is not complete. Therefore, in this study, a new matching method is proposed, which solves the Frieman-Rotenberg equation as an initial value problem. The new method divides the plasma region into outer regions and inner layers as in the conventional asymptotic matching method. The essential difference is that the inner layers of the new method have finite width, thus, the Newcomb equation governing the outer regions has no singularity. The matching condition is numerically satisfied such that the normal components of the Lagrangian displacement are smooth. The new method can study the rotation effect around rational surfaces with high numerical accuracy and short computation time. [1] M. Takechi et al., Phys. Rev. Lett. 98, 055002 (2007). [2] E. Frieman and M. Rotenberg, Rev. Mod. Phys. 32, 898 (1960). [Preview Abstract] |
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YP6.00080: Electron transport in cone targets in high intensity laser-plasma interaction Nathalie Le Galloudec, Emmanuel D'Humieres, Byoung-Ick Cho, Jens Osterholz, Yasuhiko Sentoku, Todd Ditmire Copper cones targets of different roughnesses were irradiated with the Thor laser (0.5J, 40fs, 800nm, 7 micron focal spot, 3.10$^{19}$W/cm$^{2}$) at UT Austin. Hot electron transport in the tip has been diagnosed with Coherent Transition of Radiation (CTR). Progress at the NTF has been made and a new diagnostic is being designed to provide a CTR at both $\omega$ and 2 $\omega$. Results supported by simulations will present the current knowledge and trace a path to future progress. [Preview Abstract] |
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YP6.00081: ABSTRACT WITHDRAWN |
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YP6.00082: Beam-Plasma Interaction and Instabilities in a 2D Yukawa Plasma S. Kyrkos, G. Kalman, M. Rosenberg In a complex plasma, penetrating charged particle beams may lead to beam-plasma instabilities. When either the plasma, the beam, or both, are strongly interacting [1], the features of the instability are different from those in a weakly coupled plasma. We consider the case when a 2D dusty plasma forms a lattice, and the beam is moving in the lattice plane. Both the grains and the beam particles interact through a Yukawa potential; the beam particles are weakly coupled to each other and to the lattice. The system develops both a longitudinal and a transverse instability. Based on the phonon spectrum of a 2D hexagonal Yukawa lattice [2], we determine and compare the transverse and longitudinal growth rates. As a function of the wavenumber, the growth rates exhibit remarkable gaps, where no instability is excited. The gap locations are governed by the ratio of the lattice and the beam plasma frequencies. The behavior of the growth rates also depends on the direction of the beam and on the relationship between the beam speed and the longitudinal and transverse sound speeds. [1] GJ Kalman, M Rosenberg, JPA 36, 5963 (2003). [2] T Sullivan, GJ Kalman, S Kyrkos, P Bakshi, M Rosenberg, Z Donko, JPA 39, 4607 (2006). [Preview Abstract] |
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YP6.00083: Finite element analysis of the plasma needle-biomaterial interaction at atmospheric pressure Yukinori Sakiyama, David Graves The atmospheric pressure RF-excited plasma needle is a non-thermal discharge sustained at the sharp tip of a needle in helium gas flow. The plasma needle has been applied to various biomedical applications. However, the mechanisms of the plasma-biomaterial interaction are only poorly understood. In this study, we focus on influences of humid air diffusing into the discharge domain on plasma chemistry. Our fluid model includes 49 species and over 700 elementary reactions in one-dimensional spherical coordinates. An expected concentration gradient of humid air is assumed to be present due to back diffusion of air against helium convective flow. Our simulation results indicate that O2+ and N2+ are dominant ions at the outer electrode corresponding to the biomaterial surface and that the most abundant neutrals near the outer electrode are O, O2*, and OH radicals. These results suggest that trace amounts of humid air can play a central role in plasma needle treatment. [Preview Abstract] |
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YP6.00084: A Hall Thruster Design with Adjustable Acceleration Channel Depth and Azimuthally Uniform B-field Daniel Barnak, Hans Pfister A Hall Thruster, also known as a Stationary Plasma Thruster (SPT) or a Closed Drift Thruster (CDT), is a gridless plasma propulsion device. In lieu of an accelerating grid a Hall Thruster uses the large potential drop near its exit plane to accelerate the propellant ions. The performance of such a thruster is critically dependent on the uniformity and shape of the thruster's predominantly radial magnetic field and the depth of the acceleration channel. We present here a new design, which features an azimuthally more uniform magnetic field and an adjustable anode location, allowing the investigator to vary the depth of the acceleration channel while the thruster is in operation. [Preview Abstract] |
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YP6.00085: Dynamical Properties of Relativistic Intense Electron Beams in Over-Dense Plasmas Alain Piquemal We investigate the evolution of intense relativistic electron beams when transported in accelerators or in over-dense plasmas. It is generally admitted that in plasmas, a beam goes progressively to a Bennett like profile and a Maxwellian distribution. But the problem is the understanding of the routes the beam follows, from a phase space limited distribution function (d.f.) at the generator output, to a Bennett-Maxwell d.f. after some distance of propagation. For this purpose, we used diagnostics from the chaos mechanics, modified to take into account time-dependent mechanisms. With these powerful tools, properties like ergodicity, mixing and self-similarity were studied. Finally, some ideas about the evolution of the beam internal structure and the mechanisms which drive this transformation, are proposed. [Preview Abstract] |
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YP6.00086: Spectroscopic Diagnosis of a Dense Hydrogen Plasma Source Eric Alderson, Gerald Kulcinski, John Santarius, Joe Khachan, Gregory Piefer, David Boris, Samuel Zenobia Diagnosing an energetic dense plasma source is a unique challenge. A hydrogen discharge in a helicon source has been studied by coupling spectroscopic measurements with a Collisional Radiative model to produce a series of measurements of the plasma, without the complication of exposing a probe to the degrading plasma environment or measurement perturbing magnetic field and RF fields. This plasma diagnosis yielded an electron temperature on the order of 5 eV and electron density in the high 10$^{11}$ cm$^{-3}$ range. The hydrogen gas atomic to molecular ratio was measured between 10 and 27, and the gas temperature was measured by analyzing molecular line emission and found to be on the order of 500K. These results will be useful both in comparing the studied helicon with contemporary helicon sources, and optimizing ion current extraction for use in an Inertial Electrical Confinement fusion device. [Preview Abstract] |
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YP6.00087: Tests of collision operators using measurements of shear Alfv\'en wave dispersion and damping Derek Thuecks, Craig Kletzing, Fred Skiff, Scott Bounds, Stephen Vincena The effects of electron-ion collisions on the parallel phase velocity and damping of shear Alfv\'en waves are examined for a variety of different collisional operators. The results from the inclusion of different collision operators in warm-plasma theory are compared with measurements of the dispersion relation made using the LArge Plasma Device (LAPD) located at UCLA. Theory and measurements are compared for the parallel phase velocity and damping as a function of perpendicular wave number $k_{\perp}$ in both the kinetic ($v_{te}\gg v_A$) and inertial ($v_{te}\ll v_A$) parameter regimes. Results show that in the inertial regime, the best match between measurements and theory occur when a non-conserving Krook operator is used to describe electron-ion collisions. In contrast, using a non-conserving Krook operator in the kinetic regime produces very poor agreement between measurements and theory. In this case, the best agreement is found when collisions are completely ignored. [Preview Abstract] |
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YP6.00088: Interactions of clusters with X-ray free electron laser Yuji Fukuda, Tatsufumi Nakamura, Kengo Moribayashi, Yasuaki Kishimoto In order to investigate the damage of a single bio-molecule when it is irradiated by a strong X-ray free electron laser (XFEL) pulse, time evolution of a single carbon cluster with diameter of 30 nm irradiated with 10-fs XFEL pulse is studied by using particle-in-cell (PIC) code including field-ionization and collisional ionization. The cluster is ionized up to C$^{4+}$ within a femtosecond from the surface by strong sheath fields ($\sim $TV/m). Then, the cluster is gradually ionized to higher charge states by collisional ionization. Target size and XFEL pulse intensity have an effect on ionization processes due to the change of sheath field intensity. This result indicates that the field ionization by strong sheath field plays an important role to the damage of a single bio-molecule. [Preview Abstract] |
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YP6.00089: Helical phase lag between coupled nonlinear resistive MHD instabilities in toroidal flow shear D.P. Brennan, S.E. Kruger, R.J. La Haye Nonlinear initial value computational analyses are presented detailing the reconnection on rational surfaces driven by a fast growing 1/1 internal kink mode in the presence of flow shear. The flow is included in the equilibrium solutions, which is crucial in initial value computations using the NIMROD code. The driven 3/2 mode is the chosen focus of the analyses. The effects of sub-sonic flow on the onset are detailed, where both the inner layer physics and the coupling between surfaces are investigated in the nonlinear driven stage of the n=2 mode. This is done in part by determining the helical phase between components of the mode. Simulations of the nonlinearly coupled onset and evolution of these instabilities are combined with reduced analytic analyses and linear computational results to gain an intuitive understanding of the physics behind these competing influences and experimental observations. [Preview Abstract] |
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YP6.00090: Plasma Diagnostics for a Laser Driven Expansion into a Large Ambient Magnetized Plasma A. Zylstra, C. Constantin, E. Everson, D. Schaeffer, N. Kugland, P. Pribyl, W. Gekelman, S. Vincena, S. Tripathi, C. Niemann The expansion of a laser plasma into a large (17m x 0.6m) magnetized plasma across or at 45$^\circ$ to the 275 G background field is studied with Langmuir and Mach probes. A special probe geometry allows data collection inside a diamagnetic bubble formed during the laser plasma expansion. We also observe Alfv\'en and MHD fast waves far away from the target. In the case of an expansion 45$^\circ$ from the background field we detect fast ion motion in the chamber and present Monte Carlo simulations of the ion trajectories. [Preview Abstract] |
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YP6.00091: Mode conversion and wave mediated reconnection Xiaogang Wang, Chijie Xiao, Zuyin Pu Recent theoretical, experimental and observational developments in space and laboratory plasma studies have shown that whistler modes in the ion initial region and lower hybrid modes in the electron dynamics region may play a crucial role in magnetic reconnection. Based on satellite observations and wave resonance and mode conversion theory, we propose a wave mediated reconnection model to understand the collisionless reconnection process through out the ion and electron dynamics regions. The whistler and lower hybrid modes excitation, anomalous resistivity, and electron layer dynamics are then discussed in the frame of the model. [Preview Abstract] |
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YP6.00092: Modeling and Simulation of Aerodynamic Single Dielectric Barrier Discharge Plasma Actuators Dmitri Orlov, Gabriel Font This work presents different approaches to modeling of the plasma actuator, an electrical flow control device, which is now widely used in aerodynamics for separation control, lift enhancement, drag reduction and flight control without moving surfaces. Study of the physics of the discharge in air at atmospheric pressure was performed using particle (PIC-DSMC) and fluid plasma simulations. Based on the experimentally obtained data electro-static and lumped-element circuit models were developed for engineering purposes. Numerical flow simulations were performed to study the effect of the plasma body force on the neutral fluid. The results agreed well with the experiments. An application of the plasma actuators to the leading-edge separation control on the NACA 0021 airfoil was studied numerically. The results were obtained for a range of angles of attack. Improvement in the airfoil characteristics was observed in numerical simulations at high angles of attack in cases with plasma actuation. [Preview Abstract] |
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YP6.00093: Coherent vortex extraction using proper orthogonal decomposition and wavelets methods. S. Futatani, W.J.T. Bos, D. del-Castillo-Negrete, K. Schneider, S. Benkadda, M. Farge The Proper Orthogonal Decomposition (POD), also known as Karhunen-Loeve expansion, and the wavelet decomposition are two useful techniques to extract coherent structures from data sets. In this work we present a comparative study of the application of both techniques to plasma turbulence. We focus on two-dimensional resistive drift-wave turbulence described by the Hasegawa-Wakatani model. This relatively simple model contains key elements for the study of turbulence including the possibility of cross-field transport and the spontaneous formation of coherent structures. In the POD context, the extraction of the coherent structures is based on low-order truncations of the singular value decomposition of the data sets. The wavelet method is based on the thresholding of the wavelet coefficients. The data is decomposed into an orthogonal wavelet series, a thresholding is applied and the coherent vortices are reconstructed from few strong coefficients. Both approaches are compared in terms of compression rate, retained energy, and enstrophy level of the coherent vortices. [Preview Abstract] |
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YP6.00094: Simulations of self-generated magnetic fields in inertial confinement fusion implosions Po-Yu Chang, Riccardo Betti, Orlin Gotchev Magnetic fields in laser produced plasmas can be self-generated by the so-called $\nabla $n$\times \nabla $T effect and resistive electric fields associated with a neutralizing return current. The $\nabla $n$\times \nabla $T fields can be induced by the fluid vorticity originating at the ablation front and amplified by the Rayleigh-Taylor (RT) instability. They can also be driven by the diamagnetic heat flux that leads to the thermo-magnetic (TM) instability. We present the results of simplified two-dimensional simulations of the $\nabla $n$\times \nabla $T magnetic fields driven by the RT and TM instabilities. We show that the RT-induced B-fields reach megagauss (MG) levels only for short wavelength modes in cryogenic DT ablators. We also show that the Nernst effect causes these fields to be localized near the ablation surface. The magnetic fields driven by the TM instability grow on a time scale of hundreds of picoseconds and can further amplify the RT-produced fields in the coronal plasma. These results are compared with the recent experimental measurements of self-generated B-field in ICF implosions. [Preview Abstract] |
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YP6.00095: Low Temperature Collisional Plasma Simulation with a PIC-DSMC Method Paul S. Crozier In this work we will present the current state of our low temperature plasma simulation code. Its target application regime is low temperature plasmas that straddle the non-continuum to continuum regime, specifically including collisional effects and chemistry. Of particular importance to us is that the code be production quality, applicable to industrial problems. In pursuit of that goal, our code is based on unstructured meshes, is massively parallel, and includes dynamic load balancing. Our plasma model consists of weighted particles for each constituent present (ions and neutrals of differing species, and electrons) coupled to an electrostatic (ES) field. The ES field is computed via the finite element method (FEM) every time step by aggregating particle charges on an element-by-element basis. Particles within an element interpolate the electric field to their position for use in the particle move algorithm. Thus, we are performing a very simple particle-in-cell (PIC) simulation. Subsequent to particle moves, collisions are accounted for via a DSMC method. [Preview Abstract] |
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YP6.00096: ABSTRACT WITHDRAWN |
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YP6.00097: A comparative study of total electron scattering cross sections of plasma processing gasses at intermediate electron energies Prasanga Palihawadana, Gilberto Villela, Wickramasinghe Ariyasinghe A comparison is made between the total electron cross sections (TCS) of Tetrafluoromethane (CF$_{4})$, Trifluoromethane (CHF$_{3})$, Hexafluoroethane (C$_{2}$F$_{6})$, and Octafluorocyclobutane (C$_{4}$F$_{8})$ available in the literature and those recently measured in this laboratory using the linear transmission technique. The present measurements are about 0-20{\%} higher than those in the literature. An empirical formula developed to predict the TCS of plasma processing gases, as a function of incident electron energy, will be presented. [Preview Abstract] |
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YP6.00098: MD Modeling of the Plasma Irradiation of the Hydrogenated Carbon Surface Predrag S. Krstic Usual approach to the molecular dynamics (MD) simulations of the plasma-surface interactions (PSI) is to average results of irradiation of the surface by a particle beam of a fixed energy and impact angle. However, we have found [1] that most of the PSI processes have a strong dependence on the instantaneous target surface microstructure (including hybridization content, in case of carbon), which is determined by the irradiation history, in particular of energy and type of the impacting particles that created the surface. Therefore, the effect of the various initial parameters that create a surface is not necessarily linearly additive: In order to improve the MD results for the experiments with plasma irradiation of the surfaces, randomization of the impact energies and angles is preferred. We use this approach to simulate sputtering and reflection of the hydrogenated carbon surfaces by hydrogen plasma, in range of temperatures 10,000-200,000 K. Isotopic effects of deuterium and tritium plasmas are also considered. \\[0pt] [1] P. S. Krstic, C. O. Reinhold, and S. J. Stuart, New J. of Phys. \textbf{9}, 219 (2007). [Preview Abstract] |
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