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Demonstartion of density dependence of x-ray flux in a laser-driven hohlraum

Description: Experiments have been conducted using laser-driven cylindrical hohlraums whose walls are machined from Ta{sub 2}O{sub 5} foams of 100 mg/cc and 4 g/cc densities. Measurements of the radiation temperature demonstrate that the lower density walls produce higher radiation temperatures than the high density walls. This is the first experimental demonstration of the prediction that this would occur [M. D. Rosen and J. H. Hammer, Phys. Rev. E 72, 056403 (2005)]. For high density walls, the radiation front propagates subsonically, and part of the absorbed energy is wasted by the flow kinetic energy. For the lower wall density, the front velocity is supersonic and can devote almost all of the absorbed energy to heating the wall.
Date: February 11, 2008
Creator: Young, P E; Rosen, M D; Hammer, J H; Hsing, W S; Glendinning, S G; Turner, R E et al.
Partner: UNT Libraries Government Documents Department

Ecloud Build-Up Simulations for the FNAL MI for a Mixed Fill Pattern: Dependence on Peak SEY and Pulse Intensity During the Ramp

Description: We present simulation results of the build-up of the electron-cloud density n{sub e} in three regions of the FNAL Main Injector (MI) for a beam fill pattern made up of 5 double booster batches followed by a 6th single batch. We vary the pulse intensity in the range N{sub t} = (2-5) x 10{sup 13}, and the beam kinetic energy in the range E{sub k} = 8-120 GeV. We assume a secondary electron emission model qualitatively corresponding to TiN, except that we let the peak value of the secondary electron yield (SEY) {delta}{sub max} vary as a free parameter in a fairly broad range. Our main conclusions are: (1) At fixed N{sub t} there is a clear threshold behavior of n{sub e} as a function of {delta}{sub max} in the range {approx} 1.1-1.3. (2) At fixed {delta}{sub max}, there is a threshold behavior of n{sub e} as a function of N{sub t} provided {delta}{sub max} is sufficiently high; the threshold value of N{sub t} is a function of the characteristics of the region being simulated. (3) The dependence on E{sub k} is weak except possibly at transition energy. Most of these results were informally presented to the relevant MI personnel in April 2010.
Date: December 11, 2010
Creator: Furman, M. A.
Partner: UNT Libraries Government Documents Department


Description: We explore the possibility of using two non-scaling FFAG accelerators for a high power heavy-ion driver as an alternative to a superconducting Linac. Ions of Uranium 238 are accelerated to a kinetic energy of 400 MeVIu and a total power of 400 kWatt. Different modes of acceleration have been studied: at 1 and 10 kHz repetition rate, and for Continuous Wave production. The following is a summary of the study. More details of the study can be found in reference 2.
Date: June 25, 2007
Partner: UNT Libraries Government Documents Department


Description: In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.
Date: November 1, 1964
Creator: Marcus, R.A.
Partner: UNT Libraries Government Documents Department

An Improved WRF for Urban-Scale and Complex-Terrain Applications

Description: Simulations of atmospheric flow through urban areas must account for a wide range of physical phenomena including both mesoscale and urban processes. Numerical weather prediction models, such as the Weather and Research Forecasting model (WRF), excel at predicting synoptic and mesoscale phenomena. With grid spacings of less than 1 km (as is required for complex heterogeneous urban areas), however, the limits of WRF's terrain capabilities and subfilter scale (SFS) turbulence parameterizations are exposed. Observations of turbulence in urban areas frequently illustrate a local imbalance of turbulent kinetic energy (TKE), which cannot be captured by current turbulence models. Furthermore, WRF's terrain-following coordinate system is inappropriate for high-resolution simulations that include buildings. To address these issues, we are implementing significant modifications to the ARW core of the Weather Research and Forecasting model. First, we are implementing an improved turbulence model, the Dynamic Reconstruction Model (DRM), following Chow et al. (2005). Second, we are modifying WRF's terrain-following coordinate system by implementing an immersed boundary method (IBM) approach to account for the effects of urban geometries and complex terrain. Companion papers detailing the improvements enabled by the DRM and the IBM approaches are also presented (by Mirocha et al., paper 13.1, and K.A. Lundquist et al., paper 11.1, respectively). This overview of the LLNL-UC Berkeley collaboration presents the motivation for this work and some highlights of our progress to date. After implementing both DRM and an IBM for buildings in WRF, we will be able to seamlessly integrate mesoscale synoptic boundary conditions with building-scale urban simulations using grid nesting and lateral boundary forcing. This multi-scale integration will enable high-resolution simulations of flow and dispersion in complex geometries such as urban areas, as well as new simulation capabilities in regions of complex terrain.
Date: September 4, 2007
Creator: Lundquist, J K; Chow, F K; Mirocha, J D & Lundquist, K A
Partner: UNT Libraries Government Documents Department

Event-by-Event Fission with FREYA

Description: The recently developed code FREYA (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. The presentation first discusses the present status of FREYA, which has now been extended up to energies where pre-equilibrium emission becomes significant and one or more neutrons may be emitted prior to fission. Concentrating on {sup 239}Pu(n,f), we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also briefly suggest novel fission observables that could be measured with modern detectors.
Date: November 9, 2010
Creator: Randrup, J. & Vogt, R.
Partner: UNT Libraries Government Documents Department

An atomistic study of dynamic brittle fracture in silicon

Description: Dynamic fracture has been modeled using a modified embedded atom method (MEAM) potential for silicon. For Mode I dynamic fracture along (1 1 1) crystallographic planes, the molecular dynamics model predicts crack speeds and fracture energies in agreement with previous experimental results [l]. In this orientation, hcture occurs almost exclusively along (1 1 1) planes for energy release rates up to 30 J/m2. For Mode I fracture oriented initially on (1 10) planes, fracture occurs by cleavage on (1 10) planes for a static energy release rate (J,) less than 8 J/m2. For greater values of J,, the fracture surfaces switch to alternating (111) planes, which is in agreement with previous experimental results [2]. Crack speed predictions for the (1 10) orientation are somewhat In the atomistic simulations, the dynamically propagating cracks generate dislocations, which are primarily produced on the (1 1 1) and (1 10) planes. Differences in the type and quantity of dislocations produced have been observed for different orientations. Molecular dynamics has the ability to calculate the energy consumed by dislocations and other lattice defects produced during fracture and the total surface energy of the main crack, side branches and secondary cracks. The sum of the surface energy and the energy consumed by lattice defects determines the dynamic fracture less than the high speeds observed experimentally. toughness, J(v). The dynamic fkacture toughness has been found to vary linearly with J,. For the (111) orientation with cracks propagating in the [211] direction, J(v) asymptotically approached a value of 1/3 of J,. The remainder of the strain energy that is released during fracture is converted into kinetic energy at the crack tip during the fracture process, which occurs atom by atom.
Date: January 1, 2002
Creator: Swadener, J. G. (John G.); Baskes, M. I. (Michael I.) & Nastasi, Michael Anthony,
Partner: UNT Libraries Government Documents Department

Correlation effects in the iron pnictides

Description: One of the central questions about the iron pnictides concerns the extent to which their electrons are strongly correlated. Here we address this issue through the phenomenology of the charge transport and dynamics, single-electron excitation spectrum, and magnetic ordering and dynamics. We outline the evidence that the parent compounds, while metallic, have electron interactions that are sufficiently strong to produce incipient Mott physics. In other words, in terms of the strength of electron correlations compared to the kinetic energy, the iron pnictides are closer to intermediately-coupled systems lying at the boundary between itinerancy and localization, such as V{sub 2}O{sub 3} a or Se-doped NiS{sub 2} , rather than to simple antiferromagnetic metals like Cr. This level of electronic correlations produces a new small parameter for controlled theoretical analyses, namely the fraction of the single-electron spectral weight that lies in the coherent part. Using this expansion parameter, we construct the effective low-energy Hamiltonian and discuss its implications for the magnetic order and magnetic quantum criticality. Finally, this approach sharpens the notion of magnetic frustration for such a metallic system, and brings about a multi band matrix t-J{sub 1}-J{sub 2} model for the carrier-doped iron pnictides.
Date: January 1, 2009
Creator: Zhu, Jian-xin; Si, Qimiao; Abrahams, Elihu & Dai, Jianhui
Partner: UNT Libraries Government Documents Department

Progress in Beam Focusing and Compression for Target Heating and Warm Dense Matter Experiments

Description: The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30 mA K{sup +} ion beam with initial kinetic energy 0.3 MeV, axial compression leading to {approx}50X current amplification and simultaneous radial focusing to a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to NDCX to reach the necessary higher beam intensities, including: beam diagnostics, greater axial compression via a longer velocity ramp; and plasma injection improvements to establish a plasma density always greater than the beam density, expected to be > 10{sup 13} cm{sup -3}.
Date: April 17, 2009
Creator: Seidl, Peter; Anders, A.; Bieniosek, F.M.; Barnard, J.J.; Cohen, R.H.; Coleman, J.E. et al.
Partner: UNT Libraries Government Documents Department

Particle-In-Cell/Monte Carlo Simulation of Ion Back BomBardment in a High Average Current RF Photo-Gun

Description: In this paper, we report on study of ion back bombardment in a high average current radio-frequency (RF) photo-gun using a particle-in-cell/Monte Carlo simulation method. Using this method, we systematically studied effects of gas pressure, RF frequency, RF initial phase, electric field profile, magnetic field, laser repetition rate, different ion species on ion particle line density distribution, kinetic energy spectrum, and ion power line density distribution back bombardment onto the photocathode. Those simulation results suggested that effects of ion back bombardment could increase linearly with the background gas pressure and laser repetition rate. The RF frequency has significantly affected the ion motion inside the gun so that the ion power deposition on the photocathode in an RF gun can be several orders of magnitude lower than that in a DC gun. The ion back bombardment can be minimized by appropriately choosing the electric field profile and the initial phase.
Date: October 17, 2009
Creator: Qiang, J.
Partner: UNT Libraries Government Documents Department


Description: This report describes the use of a target containing polarized protons in a particle-scattering experiment. Positive pions of 246-MeV kinetic energy were scattered from the polarized protons. The parameter P that was measured is equivalent to that determined by analyzing the recoil-proton polarization in scattering from an unpolarized target. It has been measured to a higher accuracy than heretofore achieved in pion-proton scattering, at an energy and at angles inconvenient for double-scattering techniques.
Date: August 7, 1963
Creator: Chamberlain, Owen; Jeffries, Carson D.; Schultz, Claude H.; Shapiro, Gilbert & Van Rossum, Ludwig.
Partner: UNT Libraries Government Documents Department

System size, energy and centrality dependence of strange hadron elliptic flow at STAR

Description: The elliptic flow (v{sub 2}) pattern in terms of hadron mass and transverse momentum p{sub T} is qualitatively described for p{sub T} < 2 GeV/c by ideal hydrodynamics in Au + Au collisions at RHIC. In addition, for p{sub T} = 2-6 GeV/c the measured v{sub 2} follow a universal scaling by the number of quarks explained by quark coalescence/recombination models. These observations suggest that a partonic collectivity develops in the matter in early stage of heavy ion collisions. Centrality as well as system size and energy dependence of the v{sub 2} is important to shed light on the underlying collision dynamics in heavy ion collisions. We present the measurements of centrality dependence of v{sub 2} at {radical}s{sub NN} = 200 and 62.4 GeV in Au + Au and Cu + Cu collisions for K{sub S}{sup 0}, {phi}, {Lambda}, {Xi} and {Omega} at STAR experiment. We focus on the recent Cu + Cu results and discuss the centrality dependence of v{sub 2} as well as the number of quark scaling as a function of transverse kinetic energy at different system size and energies. We also discuss the eccentricity scaled v{sub 2} for identified hadrons and implications that ideal hydrodynamical limit has not been reached at RHIC.
Date: December 21, 2008
Creator: Masui, Hiroshi
Partner: UNT Libraries Government Documents Department

Time-dependent simulations of large-scale quantum mechanical processes

Description: Time dependent linear and nonlinear equations govern the evolution of an extensive set of physical systems and processes describing, to enumerate just a few, Bose-Einstein condensates; soliton propagation in optical and photonic band-gap fibers; quantum control of atomic and molecular collisions and reactions; highly-compressed liquids; and dense and ultracold plasmas. While the media vary substantially, the basic computational procedures have many common features. We focus on the nonlinear Schrodinger equation and discuss two powerful approaches to its propagation: the Arnoldi/Lanczos(AL)l and Real Space Product Formula(RSPF)2. Both provide efficient systematic approximations to the short-time exponential propagator that moves the solution between time steps. We implement the former in a discrete variable representation (DVR)3 both in spatial grid and finite element forms and the latter in a spatial mesh with a finite difference representation of the kinetic energy operator. Both approaches require O(N) operations to propagate the wavefunction between time steps and handle multidimensional systems. We shall also draw connections with Liouville formulations used in quantum molecular dynamics simulations of large collections of atoms and molecules. After briefly outlining these formulations, we shall discuss some of the varied applications.
Date: January 1, 2002
Creator: Collins, L. A. (Lee A.)
Partner: UNT Libraries Government Documents Department

Charged and strange hadron elliptic flow in Cu+Cu collisions at sqrt sNN = 62.4 and 200 GeV

Description: We present the results of an elliptic flow, v{sub 2}, analysis of Cu+Cu collisions recorded with the STAR detector at RHIC at {radical}s{sub NN} = 62.4 and 200 GeV. Elliptic flow as a function of transverse momentum, v{sub 2}(p{sub T}), is reported for different collision centralities for charged hadrons h{sup {+-}}, and strangeness containing hadrons K{sub S}{sup 0}, {Lambda}, {Xi}, {phi} in the midrapidity region |{eta}| < 1.0. Significant reduction in systematic uncertainty of the measurement due to non-flow effects has been achieved by correlating particles at midrapidity, |{eta}| < 1.0, with those at forward rapidity, 2.5 < |{eta}| < 4.0. We also present azimuthal correlations in p+p collisions at {radical}s = 200 GeV to help estimating non-flow effects. To study the system-size dependence of elliptic flow, we present a detailed comparison with previously published results from Au+Au collisions at {radical}s{sub NN} = 200 GeV. We observe that v{sub 2}(p{sub T}) of strange hadrons has similar scaling properties as were first observed in Au+Au collisions, i.e.: (i) at low transverse momenta, p{sub T} < 2 GeV/c, v{sub 2} scales with transverse kinetic energy, m{sub T} - m, and (ii) at intermediate p{sub T}, 2 < p{sub T} < 4 GeV/c, it scales with the number of constituent quarks, n{sub q}. We have found that ideal hydrodynamic calculations fail to reproduce the centrality dependence of v{sub 2}(p{sub T}) for K{sub S}{sup 0} and {Lambda}. Eccentricity scaled v{sub 2} values, v{sub 2}/{var_epsilon}, are larger in more central collisions, suggesting stronger collective flow develops in more central collisions. The comparison with Au+Au collisions which go further in density shows v{sub 2}/{var_epsilon} depend on the system size, number of participants N{sub part}. This indicates that the ideal hydrodynamic limit is not reached in Cu+Cu collisions, presumably because the assumption of thermalization is not attained.
Date: July 5, 2010
Creator: Collaboration, STAR & Abelev, Betty
Partner: UNT Libraries Government Documents Department


Description: The occurrence of a fault April 7 caused a short in the stator winding of one of the main generators. Repairs will require at least one month and the total time the generator will be down can be determined only after a further inspection of the damage. In a week or two, after a thorough inspection of the generator and the ignitron system, Bevatron operation will be continued on one generator. Since the targets of use in a Bevatron experiment will depend greatly on the nature of the experiment and the techniques to be employed the ideas presented here relate primarily to the area of research which involves the detection with counters of heavy mesons emitted in the backward direction in the laboratory system. These mesons and their decay products have low kinetic energy over the entire range of Bevatron energies above threshold for production. For this reason discrimination by means of momentum resolution, collimating slits, ionization density and range will be possible.
Date: April 13, 1954
Creator: Lofgren, E.J.
Partner: UNT Libraries Government Documents Department

An Injection/Extraction Scenario for EMMA

Description: EMMA is an experiment to study beam dynamics in a linear non-scaling fixed-field alternating gradient accelerator (FFAG). It accelerates an electron beam from 10 to 20 MeV kinetic energy. To optimally perform these studies, one must be able to inject the beam at any energy within the machine's energy range. Furthermore, because we wish to study the behavior of large-emittance beams in such a machine, the injection systems must be able to inject the beam anywhere within a transverse phase space ellipse with a normalized acceptance of 3 mm, and the extraction systems must be able to extract from that same ellipse. I describe a computation of kicker and septum fields to achieve all of these requirements, and discuss how this interacts with the hardware constraints.
Date: May 4, 2009
Creator: Berg, J. S.
Partner: UNT Libraries Government Documents Department


Description: The distribution of the kinetic energy of fragments emitted as a result of the neutron-induced fission of Th/sup 232/ has been determined. Incident neutron energies of 1475 plus or minus 35 kev and l600 plus or minus 35 kev were used. The distributions determined at the two incident neutron energies are identical. The measured total average fragment kinetic energy was l55 plus or minus 4.5 Mev. The most probable fragment mass ratio is 1.47 plus or minus 0.05, and the average kinetic energies of the light and heavy fragments are 95 plus or minus 2 and 60 plus or minus 3 Mev, respectively. The experimental results were related to the known systematics of neutron-induced and spontaneous fission. The effect of collective nuclear rotations at the saddle point is discussed, with particular emphasis on fission from specific rotational bands. (auth)
Date: November 1, 1960
Creator: Smith, A.B.; Nobles, R.G. & Friedman, A.M.
Partner: UNT Libraries Government Documents Department

Lattice measurement for Fermilab Main Injector

Description: The installation of seven large aperture quadrupoles during shut-down of 2006 necessitates new lattice measurements to evaluate the state of the machine lattice at energies critical to operation. For Main Injector (MI) this means at 8-GeV kinetic energy for proton and pbar injections, at 150-GeV extraction to Tevatron for collider operation, and at 120-GeV extraction to Numi for nutrino experiment and slow spill to fixed target test beam facility. The results of measurement at these three energies and their comparison to their corresponding calculations will be presented.
Date: June 1, 2007
Creator: Yang, M.J.
Partner: UNT Libraries Government Documents Department

Survey and alignment of the Fermilab Booster Accelerator

Description: The Fermilab Booster is a fast-cycling synchrotron which accelerates protons from 400 MeV to 8 GeV of kinetic energy for injection into the Main Injector and for use by all of the Lab's physics programs. The Booster was originally built in 1970. In 2004, as part of the Booster upgrade, a decision was made to upgrade the Booster survey network by densification with monuments and to survey the main Booster components using modern survey and alignment instruments. This paper discusses the survey and alignment methodology employed for the Booster Accelerator upgrade.
Date: July 1, 2005
Creator: Oshinowo, Babatunde O'Sheg & Kyle, John
Partner: UNT Libraries Government Documents Department

A molecular dynamics simulation study of defect production in vanadium

Description: We performed molecular dynamics simulations to investigate the process of defect production in pure vanadium. The interaction of atoms was described by the EAM interatomic potential modified at short range to merge smoothly with the universal potential for description of the high energy recoils in cascades. The melting point of this EAM model of vanadium was found to be consistent with the experimental melting temperature. The threshold energies of displacement events in the model system are also consistent with experimental minimum threshold in vanadium, and its average was found to be 44 eV. We evaluated the efficiencies of defect production in the displacement events initiated by recoils with kinetic energy up to 5 keV, and found that the probability of cluster formation is smaller than that of simulated events in fcc metals reported in the literature.
Date: January 23, 1995
Creator: Morishita, K. & Diaz de la Rubia, T.
Partner: UNT Libraries Government Documents Department

Intercomparison of the seasonal cycle in 200 hPa kinetic energy in AMIP GCM simulations

Description: The 200 hPa kinetic energy is represented by means of the spherical harmonic components for the Atmospheric Model Intercomparison Project (AMIP) simulations, the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and the European Centre for Medium Range Weather Forecast Reanalysis (ERA). The data used are the monthly mean wind fields from 1979 to 1988. The kinetic energy is decomposed into the divergent (DKE) and rotational (RKE) components and emphasis is placed on examining the former. The two reanalysis data sets show reasonable agreement that is best for the rotational kinetic energy. The largest difference in the divergent kinetic energy occurs during the northern summer. As might be expected, the two analyses are closet in regions where there are sufficient observations such that the effect of the model used in the assimilation cycle are minimized. The observed RKE show only a slight seasonal cycle with a maximum occuring during the northern winter. The DKE, on the other hand, has a very pronounced seasonal cycle with maxima at the solsticial seasons and minima during the equinoctial seasons. The model results show a very large spread in the magnitudes of the RKE and DKE although the models all evince a seasonal variation in phase with that observed. The median values of the seasonal cycle of RKE and DKE for the models are usually superior to those of any individual model. Results are also presented for simulation following the AMIP protocol but using updated versions of the original AMIP entries. In most cases these new integrations show better agreement with the observations.
Date: October 1, 1996
Creator: Boyle, J.S.
Partner: UNT Libraries Government Documents Department

An observational study of turbulence in the SPBL

Description: Turbulence in the stable planetary boundary layer (SPBL) is complicated by intermittency, gravity waves, long time scales and meso-scale forcing. Surface features and topography are also important. This study examines turbulence near the top of the SPBL with data taken from a network of 61 m towers. The focus is on the role of moderately complex terrain on turbulent intermittency and spatial variation. The Savannah River Site is {approx}150 km from the Atlantic Ocean and is characterized by rolling forested hills and an average elevation of {approx}80 m ASL. Typical variations in elevation are 50 m (peak to valley) with a horizontal scale of several km. The most important topographic feature is the Savannah River flood plain, which borders the SRS to the southwest. This flood plain is 3-7 km wide with an average elevation of 40 m ASL. Nine 60 meter towers are located on the SRS, generally at higher elevations (81 - 109 m ASL), except for the D tower which is in the Savannah River flood plain (elevation 43 m ASL). The Cl tower differs from the other 8 towers because it collects data at 2, 18, and 36 m as well as 61 m. The TV tower, located 8 km northwest of the SRS, is instrumented at 8 levels from the surface to 300 m.
Date: September 1, 1997
Creator: Kurzeja, R.
Partner: UNT Libraries Government Documents Department

Establishing isokinetic flow for a plasma torch exhaust gas diagnostic for a plasma hearth furnace

Description: Real time monitoring of toxic metallic effluents in confined gas streams can be accomplished through use of Microwave Induced Plasmas to perform atomic emission spectroscopy, For this diagnostic to be viable it is necessary that it sample from the flowstream of interest in an isokinetic manner. A method of isokinetic sampling was established for this device for use in the exhaust system of a plasma hearth vitrification furnace. The flow and entrained particulate environment were simulated in the laboratory setting using a variable flow duct of the same dimensions (8-inch diameter, schedule 40) as that in the field and was loaded with similar particulate (less than 10 {mu}m in diameter) of lake bed soil typically used in the vitrification process. The flow from the furnace was assumed to be straight flow. To reproduce this effect a flow straightener was installed in the device. An isokinetic sampling train was designed to include the plasma torch, with microwave power input operating at 2.45 GHz, to match local freestream velocities between 800 and 2400 ft/sec. The isokinetic sampling system worked as planned and the plasma torch had no difficulty operating at the required flowrates. Simulation of the particulate suspension was also successful. Steady particle feeds were maintained over long periods of time and the plasma diagnostic responded as expected.
Date: May 1, 1996
Creator: Pollack, B.R.
Partner: UNT Libraries Government Documents Department