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522 Matching Results

Start Over Year 1998

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Results: 1 - 24 of 522 next

(open access)

[Calibration methods for neutron diagnostics at Omega]. DOE/NLUF final report

The investigation of Calibration Methods for Neutron Diagnostics at Omega is still underway. The data shown here is a compilation of measurements taken at Omega during the time of the grant. The data set has been updated with additional information taken this year. The neutron yield from an ICF event was determined by measuring the activity of an aluminum sample activated by target-produced DT neutrons. The radioactive nuclei {sup 24}Na and {sup 27}Mg, which were produced via the {sup 27}Al(n,{alpha}){sup 24}Na and {sup 27}Al(n,p){sup 27}Mg direct reactions, beta decay to excited states of {sup 24}Mg and {sup 27}Al respectively. These excited states then emitted gamma rays as the nuclei de-excite to their respective ground states. The gamma rays are detected and counted. From their numbers the neutron yield is determined.

Date: January 15, 1998

Creator: Padalino, S.

Object Type: Report

System: The UNT Digital Library

$In-situ spatially resolved x-ray diffraction mapping of the alpha to beta to alpha transformation in commercially pure titanium arc welds$ (open access)

In-situ spatially resolved x-ray diffraction mapping of the alpha to beta to alpha transformation in commercially pure titanium arc welds

Spatially Resolved X-Ray Diffraction (SRXRD) is used to map the {alpha}{r_arrow}{beta}{r_arrow}{alpha} phase transformation in the heat affected zone (HAZ) of commercially pure titanium gas tungsten arc welds. In-situ SRXRD experiments were conducted on arc welds using a 200 pm diameter x-ray beam at Stanford Synchrotron Radiation Laboratory (SSRL). A map was created which identifies six HAZ microstructural regions that exist between the liquid weld pool and the base metal during welding. The first region is single phase {beta}-Ti that forms in a 2- to 3-mm band adjacent to the liquid weld pool. The second region is back transformed {alpha}-Ti that forms behind the portion of the HAZ where {beta}-Ti was once present at higher temperatures. The third region is completely recrystallized {alpha}-Ti that forms in a 2- to 3-mm band surrounding the single phase {beta}-Ti region. Recrystallized {alpha}-Ti was observed by itself and also with varying amounts of {beta}-Ti. The fourth region of the weld is the partially transformed zone where {alpha}-Ti and {beta}-Ti coexist during welding. The fifth region is directly behind the partially transformed zone and consists of a mixture of recrystallized and back transformed {alpha}-Ti The sixth region is farthest from the weld pool and consists of …

Date: May 15, 1998

Creator: Elmer, J. W., LLNL

Object Type: Article

System: The UNT Digital Library

(open access)

Current 3 {omega} large optic test procedures and data analysis for the quality assurance of National Ignition Facility

A reliable metric is required to describe the damage resistance of large aperture 3{omega} transmissive optics for the National Ignition Facility (NIF) laser. The trend from single site testing to the more statistically valid Gaussian scanning test requires a well modeled experimental procedure, accurate monitoring of the test parameters, and careful interpretation of the resulting volumes of data. The methods described here provide reliable quality assurance data, as well as intrinsic damage concentration information used to predict the performance expected under use conditions. This paper describes the equipment, test procedure, and data analysis used to evaluate large aperture 3{omega} optics for the NIF laser.

Date: December 22, 1998

Creator: Schwartz, S; Feit, M D; Kozlowski, M R & Mouser, R P

Object Type: Article

System: The UNT Digital Library

(open access)

Early-time measurements of laser-plasma conditions in OMEGA-Upgrade ICF Targets. Final report, April 1, 1997--March 31, 1998

Under this FY-97 NLUF grant, we primarily carried out spectral line and continuum diagnostics at early times and in the coronal region of the plasma using our flat-field grazing-incidence spectrograph, improved to incorporate time resolution at wavelengths extending below the carbon K-absorption edge using a gated microchannel plate detector. These experiments were carried out on the OMEGA facility. Fifty-nine beams were focused onto the target, providing nominally 18 kJ of energy in a 1 ns pulse for an irradiance of {approximately}2{times}10{sup 14}/cm{sup 2}. Some beam smoothing, provided by spectral dispersion, was used, but may not have been particularly effective alone, i.e., without the presence of distributed phase plates in the beams. The plastic microballoon targets were nominally 900 {mu}m in diameter with 10- and 20-{mu}m thick walls, and were filled with neon to a pressure of 10 atm. Overcoatings of Mg and Al in thicknesses ranging from 0.2 to 4 {mu}m were applied. A 1-{mu}m thick layer of CH was added in some early shots to reduce the rate of expansion of the metallic coatings. In the extreme ultraviolet (euv) spectral region, we observed n=3 to n=2 emissions from Li-, He- and H-like ions from the Mg and Al coatings. …

Date: April 4, 1998

Creator: Griem, H. R. & Elton, R. C.

Object Type: Report

System: The UNT Digital Library

(open access)

New approaches to the preparation of P(alpha)MS beads as mandrels for NIF-scale target capsules

We report on a new method using heated density gradient columns for preparing spherical poly({alpha} - methylstyrene) (P{alpha}MS) bead mandrels for inertial confinement fusion spherical shell targets. Using 1,2 propane diol/glycerol mixtures, stable density gradient columns for supporting P{alpha}MS beads can be prepared at temperatures as high as 150 {degrees}C. At these temperatures plasticized commercial beads become fluid and spherical, however loss of the plasticizer and very low molecular weight components of the bead due to limited solubility in the column fluid leads to surface finish problems. We also present results on P{alpha}MS beads prepared in an aqueous bath batch mode. Using these techniques beads with maximum out-of-rounds less than 5 {micro}m have been produced.

Date: October 20, 1998

Creator: Buckley, S R; Cook, R C; Fearon, E & Letts, S A

Object Type: Article

System: The UNT Digital Library

(open access)

Early-time measurements of laser-plasma conditions in omega-upgrade ICF targets. Semi-annual report, October 1, 1997--March 31, 1998

Since arrival of FY-98 funding under this grant in December, we have been preparing for our first series of experiments under this grant at the University of Rochester Laboratory for Laser Energetics (LLE) on the Omega laser facility, now scheduled the week beginning May 4, 1998. We will again be fielding our flat-field, grazing-incidence extreme-ultraviolet (euv) spectrograph with a four-channel gated-stripline microchannel plate (MCP) detector, which is mounted on the outside of the vacuum chamber approximately 60 inches from the center. In addition, we will be using for the first time our newly constructed flat field spectrograph covering the spectral range of 30-250 {angstrom} (hv = 50-400 eV), designed to fit into a Ten Inch Manipulator (TIM). As such, it can be located closer to the central target position, with an expected enhancement in sensitivity of at least a factor-of-ten. It is the preparation of this instrument that mainly has occupied our attention so far in this grant period and discussed in this report.

Date: April 4, 1998

Creator: Griem, H. R. & Elton, R. C.

Object Type: Report

System: The UNT Digital Library

(open access)

LLE 1997. Annual report, October 1996--September 1997

The fiscal year ending September 1997 (FY97) concluded the fifth year of the cooperative agreement (DE-FC03-92SF19460) with the U.S. Department of Energy (DOE). This report summarizes research at the Laboratory for Laser Energetics (LLE) and is the final report for the first five years of the cooperative agreement. In September 1997, the cooperative agreement was renewed for an additional five years. We summarize our research during FY97, the operation of the National Laser Users` Facility (NLUF), and the education of high school, undergraduate, and graduate students in LLE programs. A general introduction to LLE`s experimental physics program and a report on recent results are found on pp. 161-167. This article includes a useful summary of the system`s operational capabilities and system parameters after three years of operation. Direct-drive inertial confinement fusion requires precise drive uniformity, the control of hydrodynamic instabilities during the implosion of the fusion target, and accurate target fabrication and characterization. The article summarizes a wide variety of experiments relating to direct-drive laser fusion, from high-yield implosion experiments to planar and spherical Rayleigh-Taylor experiments, laser-imprinting experiments, and laser-plasma interaction experiments. A detailed analysis of the equation of motion for an electron in a plane wave is presented beginning …

Date: January 1, 1998

Creator: unknown

Object Type: Report

System: The UNT Digital Library

(open access)

LLE Review, Quarterly Report: Volume 72, July-September 1997

This volume of the LLE Review, covering the period July--September 1997, begins with a general introduction to LLE`s experimental physics program and a report on recent results. This article includes a useful summary of the system`s operational capabilities and system parameters. Other highlights of the wide variety of research presented in this issue are: a promising method to directly observe the cold compressed shell of an imploding target. The shell is normally observed by backlighting. The proposal described here is to use a high-Z dopant that fluoresces under radiation from the hot core in the K{alpha} line. A study of the instabilities associated with near-forward stimulated Brillouin scattering. It includes a calculation of the saturation times and steady-state gain exponents. A successful program of pulse shaping for the OMEGA laser system. Examples of a variety of pulse shapes that can be programmed are presented. A description of the angular-scattering characteristics of ferroelectric liquid crystal electro-optical devices operating in transient and extended scattering modes. The possibility of applying these devices as modulators in practical IR imaging systems is evaluated. A faster method of shaping and finishing IR materials by the use of magnetorheological fluids. Detailed specifications and test results are included. …

Date: February 1, 1998

Creator: unknown

Object Type: Report

System: The UNT Digital Library

(open access)

Dynamo dominated accretion and energy flow: The mechanism of active galactic nuclei

An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole of every galaxy, and the AGN phenomena has been an elusive goal. The authors suggest here the outlines of such a theoretical understanding and point out where the physical understanding is missing. They believe there is an imperative to the sequence of mass flow and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-{alpha} clouds, ultimately leads to the emission spectra of the phenomenon of AGN, quasars, blazars, etc. The over-arching physical principle is the various mechanisms for the transport of angular momentum. They believe they have now understood the new physics of two of these mechanisms that have previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for the subsequent emission of the gravitational binding energy. The new phenomena described are: (1) the Rossby vortex mechanism of the accretion disk {alpha}-viscosity, and (2) the mechanism of the {alpha}-{Omega} dynamo in the accretion disk. The Rossby vortex mechanism …

Date: December 31, 1998

Creator: Colgate, S.A. & Li, H.

Object Type: Article

System: The UNT Digital Library

(open access)

Shock-induced defects in bulk materials

In this paper examples of the shock-induced defects produced during shock compression which correlate with microstructure/mechanical property changes induced in materials due to shock prestraining are discussed. The characteristics of the shock impulse(peak shock pressure, pulse duration, and rarefaction rate) imparted to the material under investigation and the shock-induced defects produced in numerous metals and alloys are compared with their deformation behavior at ordinary rates of deformation. Examples of the range of defects observed in shock-recovered metals and alloys, include: dislocations, deformation twins, point defects, and residual metastable remnants from pressure-induced phase transformations. Results concerning the influence of interstitial content on the propensity of {omega}-phase formation and its structure in high-purity and A-7O Ti are presented. The influence of shock-wave deformation on the phase stability and substructure evolution of high-purity (low-interstitial) titanium and A-7O (3,700 ppm oxygen) titanium were probed utilizing real-time velocity interferometry (VISAR) and soft shock-recovery techniques. Suppression of the {alpha}-{omega} pressure-induced phase transformation in A-70 Ti, containing a high interstitial oxygen content, is seen to simultaneously correspond with the suppression of deformation twinning.

Date: March 1, 1998

Creator: Gray, G.T.

Object Type: Report

System: The UNT Digital Library

(open access)

Inertial confinement fusion target component fabrication and technology development support. Annual report, October 1, 1996--September 30, 1997

This report documents the technical activities of the period October 1, 1996 through September 30, 1997. During this period, GA and their partner Schafer Corporation were assigned 13 formal tasks in support of the ICF program and its five laboratories. A portion of the effort on these tasks included providing direct {open_quotes}Onsite Support{close_quotes} at Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), and Sandia National Laboratory Albuquerque (SNLA). Over 700 gold-plated hohlraum mandrels were fabricated and delivered to LLNL, LANL and SNLA. More than 1600 glass and plastic target capsules were produced for LLNL, LANL, SNLA and University of Rochester/Laboratory for Laser Energetics (UR/LLE). Nearly 2000 various target foils and films were delivered for Naval Research Lab (NRL) and UR/LLE in FY97. This report describes these target fabrication activities and the target fabrication and characterization development activities that made the deliveries possible. The ICF program is anticipating experiments at the OMEGA laser and the National Ignition Facility (NIF) which will require targets containing cryogenic layered D{sub 2} or deuterium-tritium (DT) fuel. This project is part of the National Cryogenic Target Program and support experiments at LLNL and LANL to generate and characterize cryogenic layers for these targets. During …

Date: March 1, 1998

Creator: Gibson, J.

Object Type: Report

System: The UNT Digital Library

(open access)

Measurements of the deuteron elastic structure function

The deuteron elastic structure function A(Q{sup 2}) has been extracted in the range of 0.7 {le} Q{sup 2} {le} 6.0 (GeV/c){sup 2} from cross section measurements of elastic electron-deuteron in coincidence. Measurements of the elastic deuteron electromagnetic form factors offer unique opportunities to test models of short-range aspects of the nucleon-nucleon interaction, meson-exchange currents, isobaric configurations and, quark degrees of freedom. The elastic electron-deuteron cross section is given by d{sigma}/d{Omega} = {sigma}{sub M}[A(Q{sup 2}) + B(Q{sup 2}) tan{sup 2}({theta}/2)] where {theta} is the electron scattering angle, {sigma}{sub M} = {alpha}{sup 2}E{prime} cos{sup 2} ({theta}/2)/[4E{sup 3} sin{sup 4}({theta}/2)] is the Mott cross section, {alpha} is the fine-structure constant, E and E{prime} are the incident and scattered electron energies and Q{sup 2} = 4EE{prime} sin{sup 2}({theta}/2) is the four momentum transfer squared. The deuteron elastic structure functions A(Q {sup 2}) and B(Q{sup 2}) are given in terms of the charge, quadrupole and magnetic form factors F{sub c}(Q{sup 2}), F{sub 1}(Q{sup 2}) and F{sub m}(Q{sup 2}) by A(Q{sup 2}) = F{sub c}{sup 2}(Q{sup 2}) + (8/9){tau}{sup 2} F{sub 1}{sup 2}(Q{sup 2}) + (2/3){tau}F{sub m}{sup 2}(Q{sup 2}) and B(Q{sup 2}) = (4/3){tau}(1+{tau})F{sub m}{sup 2}(Q{sup 2}) and to resolve inconsistencies in previous data sets by …

Date: June 1, 1998

Creator: Gomez, J.

Object Type: Article

System: The UNT Digital Library

(open access)

HINST: A 2-D Code for High-n TAE Stability

A high-n stability code, HINST, has been developed to study the stability of TAE (Toroidicity-induced Alfvén Eigenmodes) in large tokamaks, such as ITER [International Thermonuclear Experimental Reactor], where the spectrum of unstable TAE modes is shifted toward medium- to high-n modes. The code solves the 2-D eigenmode problem by expanding the eigenfunction in terms of basis functions. Based on the Fourier-ballooning formalism the eigenmode problem is reduced to a system of coupled 1-D equations, which is solved numerically by using the finite element method and a SPARSE matrix solver. The numerical method allows including nonperturbatively non-ideal effects, such as: full ion FLR [Finite Larmor Radius], trapped-electron collisional damping, etc. The 2-D numerical results of TAE and Resonance TAE [RTAE] modes are compared with those from local ballooning calculations and global MHD NOVA code. The results show that for ITER-like plasma parameters, TAE and RTAE modes can be driven unstable by alpha particles for n = 10 - 20. The growth rate for the most unstable mode is within the range lambda divided by omega sub A approximately equal to 0.3 - 1.5%. The most unstable modes are localized near r = a approximately equal to 0.5 and have a broad …

Date: April 1, 1998

Creator: Cheng, C. Z.; Gorelenkov, N. N. & Tang, W. M.

Object Type: Report

System: The UNT Digital Library

(open access)

National Ignition Facility final optics assembly thermal effects of maintenance operations

The National Ignition Facility (NIF), the world`s most powerful laser system, is being built at Lawrence Livermore National Laboratory (LLNL) to study inertial fusion and high-energy-density science. This billion-dollar facility consists of 192 beams focusing 1.8 MJ on a fusion target. The Final Optics Assembly (FOA), the last mechanical apparatus before the target chamber, converts the light from an incoming frequency of 1 {omega} to ia target-ready 3 {omega}, and focuses the laser beam. The performance of the frequency conversion crystals is very sensitive to temperature changes; crystal temperature must be maintained within a 0.1 C of a nominal temperature prior to a laser shot. Maximizing system availability requires minimizing thermal recovery times after thermal disturbances occurring in both normal and maintenance operations. To guide the design, it is important to have estimates of those recovery times. This report presents Computational Fluid Dynamics (CFD) design calculations to evaluate thermal effects of maintenance operations.

Date: April 1, 1998

Creator: Parietti, L. & Martin, R.A.

Object Type: Report

System: The UNT Digital Library

(open access)

Numerical thermal stability studies of the National Ignition Facility final optics assembly

The National Ignition Facility (NIF), the world`s most powerful laser system, is being built at Lawrence Livermore National Laboratory (LLNL) to study inertial fusion and high-energy-density science. This billion-dollar facility consists of 192 beams focusing 1.8 MJ on a fusion target. The Final Optics Assembly (FOA), the last mechanical apparatus before the target chamber, converts the light from an incoming frequency of 1 {omega} to a target-ready 3 {omega}, and focuses the laser beam. The performance of the frequency conversion crystals is very sensitive to temperature changes; crystal temperature must be maintained within a 0.1 C of a nominal temperature prior to a laser shot. To ensure system availability, it is important to have an estimate of the thermal recovery time to operating temperature of the FOA after thermal disturbances caused by normal and maintenance operations. This paper presents Computational fluids Dynamics (CFD) fluid and thermal design calculations for both normal and maintenance operations of the NIF FOA.

Date: December 1, 1998

Creator: Parietti, L. & Martin, R.A.

Object Type: Article

System: The UNT Digital Library

(open access)

TECHNOLOGY DEVELOPMENT FOR IRON FISCHER-TROPSCH CATALYSTS

The goal of the proposed work described in this Final Report was the development of iron-based Fischer-Tropsch catalysts that combined high activity, selectivity and life with physical robustness for slurry phase reactors that will produce either low-alpha or high-alpha products. The work described here has optimized the catalyst composition and pretreatment operation for a low-alpha catalyst. In parallel, work has been conducted to design a high-alpha iron catalyst that is suitable for slurry phase synthesis. Studies have been conducted to define the chemical phases present at various stages of the pretreatment and synthesis stages and to define the course of these changes. The oxidation/reduction cycles that are anticipated to occur in large, commercial reactors have been studied at the laboratory scale. Catalyst performance has been determined for catalysts synthesized in this program for activity, selectivity and aging characteristics.

Date: July 22, 1998

Creator: Davis, B. H.

Object Type: Report

System: The UNT Digital Library

(open access)

Lawrence Livermore National Laboratory's activities to achieve ignition by x-ray drive on the National Ignition Facility

The National Ignition Facility (NIF) is a MJ-class glass laser-based facility funded by the Department of Energy which has achieving thermonuclear ignition and moderate gain as one of its main objectives. In the summer of 1998, the project is about 40% complete, and design and construction is on schedule and on cost. The NIF will start firing onto targets in 2001, and will achieve full energy in 2004. The Lawrence Livermore National Laboratory (LLNL), together with the Los Alamos National Laboratory (LANL) have the main responsibility for achieving x-ray driven ignition on the NIF. In the 1990�s, a comprehensive series of experiments on Nova at LLNL, followed by recent experiments on the Omega laser at the University of Rochester, demonstrated confidence in understanding the physics of x-ray drive implosions. The same physics at equivalent scales is used in calculations to predict target performance on the NIF, giving credence to calculations of ignition on the NIF. An integrated program of work in preparing the NIF for x-ray driven ignition in about 2007, and the key issues being addressed on the current ICF facilities [(Nova, Omega, Z at Sandia National Laboratory (SNL), and NIKE at the Naval Research Laboratory (NRL)] are described.

Date: July 20, 1998

Creator: Bernat, T. P.; Hammel, B. A.; Kauffman, R. L.; Kilkenny, J. D.; Landen, O. L.; Lindl, J. D. et al.

Object Type: Article

System: The UNT Digital Library

(open access)

Accretion onto black holes: The power generating mechanism

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The physical relationships among accretion disks, quasars, black holes, collimated radio sources and galactic dynamos previously has been only weakly related without explicit cause and effect. We have constructed a physical evolution from large, primordial density perturbations to {open_quotes}damped Lyman alpha clouds,{close_quotes} to galaxy formation, to black holes, jets, and the the galactic dynamo. We have derived the general relativistic distortions of radiation emitted from close to the black hole and thereby have a new observational test of the central engine. The physics of accretion disks, the astrophysical dynamo, and magnetic reconnection are the least understood physical phenomena in astrophysics. They are still less understood in the general relativity (GR) field close to the black hole. This lack of physical understanding frustrates a quantitative evaluation of observations that define the evolution from the early universe to star formation. We have made progress in this understanding.

Date: December 31, 1998

Creator: Colgate, S.A.; Hills, J.G. & Miller, W.A.

Object Type: Report

System: The UNT Digital Library

(open access)

Optimization of transparent and reflecting electrodes for amorphous silicon solar cells. Final technical report

Transparent conducting fluorine doped zinc oxide was deposited as thin films on soda lime glass substrates by atmospheric pressure chemical vapor deposition (CVD) at substrate temperatures of 460 to 500 degrees C. The precursors diethylzinc, tetramethylethylenediamine and benzoyl fluoride were dissolved in xylene. This solution was nebulized ultrasonically and then flash vaporized by a carrier gas of nitrogen preheated to 150 degrees C. Ethanol was vaporized separately, and these vapors were then mixed to form a homogeneous vapor mixture. Good reproducibility was achieved using this new CVD method. Uniform thicknesses were obtained by moving the heated glass substrates through the deposition zone. The best electrically and optical properties were obtained when the precursor solution was aged for more than a week before use. The films were polycrystalline and highly oriented with the c-axis perpendicular to the substrate. More than 90% of the incorporated fluorine atoms were electrically active as n-type dopants. The electrical resistivity of the films was as low as 5 x 10/sup -4/ Omega cm. The mobility was about 45 cm ²/Vs. The electron concentration was up to 3 x 10 %sup20;/cm³. The optical absorption of the films was about 3-4% at a sheet resistance of 7 ohms/square. …

Date: September 1, 1998

Creator: Gordon, R. G.; Kramer, K.; Liang, H.; Liu, X.; Pang, D. & Teff, D.

Object Type: Report

System: The UNT Digital Library