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Polarizability of the low frequency excitations in disordered solids. [Polymethylmethacrylate]

Description: An attempt to find manifestations of an electric dipole moment associated with the low-temperature thermal properties of glasses has enabled the setting of very low limits for GeO/sub 2/ and PMMA, 0.06 and 0.16 Debye respectively. Measurements of the temperature dependence of the dielectric constant and the electric field dependence of the thermal conductivity of SiO/sub 2/ in conjunction with dielectric measurements by Schickfus et al. has pinned down some of the features of a tunneling systems model. The potentials must be nearly symmetric (..delta../sub 0/>> ..delta../sub A/) and the distribution of these states, n(..delta..)/sub tun/, must be considerably more uniform than one would calculate from measurements of the specific heat of SiO/sub 2/, n(..delta..)/sub C/sub p/. (auth)
Date: October 1, 1975
Creator: Stephens, R.B.
Partner: UNT Libraries Government Documents Department

Lattice vibrations in noncrystalline solids

Description: The specific heat of noncrystalline solids differs from that predicted by the Debye model by amounts much larger than is known for crystalline solids. This deviation is most pronounced at temperatures below 1 deg K. Near 0.1 deg K. the experimental specific heat approaches a linear temperature dependence and is up to 30 times larger than predicted by the Debye model. This paper describes Brillouin scattering experiments, and also measurements of the thermal conductivity in thin glass fibers. This work is aimed at elucidating the nature of the excitations responsible for this large specific heat. It is concluded that Debye phonons have sufficiently long lifetimes to be considered as good normal modes in noncrystalline solids and also that these phonons are the main carriers of heat at low temperatures. (11 figures. 29 references) (auth)
Date: August 1, 1973
Creator: Pohl, R.O.; Love, W.F. & Stephens, R.B.
Partner: UNT Libraries Government Documents Department

Analysis of integrating sphere performance for IR enhanced DT layering

Description: Absorbed IR energy can supplement the beta decay energy from DT ice to improve the driving force toward uniform layers. A significant problem with this approach has been to deliver the added IR energy with sufficient uniformity to enhance rather than destroy the uniformity of the ice layers. Computer modeling has indicated that one can achieve {approximately}1% uniformity in the angular variation of the absorbed power using an integrating sphere containing holes large enough to allow external inspection of the ice layer uniformity. The power required depends on the integrating sphere size, a 25 mm diameter sphere requires {approximately}35 mW of IR to deposit as much energy in the ice as the 50 mW/cm{sup 3}(35 pW total) received from tritium decay in DT. Power absorbed in the plastic can cause unacceptable ice-layer non-uniformities for the integrating sphere design considered here.
Date: June 1, 1997
Creator: Stephens, R.B., & Collins, G.W.
Partner: UNT Libraries Government Documents Department

Studies of the top quark with the D0 detector

Description: The observation of the top quark by the D0 experiment, at Fermilab`s Tevatron proton-antiproton collider, is briefly reviewed. The analysis of the top quark mass in the lepton plus jets decay channels, resulting in m{sub t} {approx} 200 GeV/c{sup 2} is reviewed; and a preliminary mass analysis from the dilepton decay channels resulting in m{sub t} = 145 {plus_minus} 25 (statistical) {plus_minus} 20 (systematic) GeV/c{sup 2} is presented. These mass measurements are compared with Standard Model limits from CERN`s LEP experiments and the published CDF measurement. Preliminary observation of top quark-W boson correlation is shown.
Date: January 1, 1996
Creator: Stephens, R.W.
Partner: UNT Libraries Government Documents Department

Final Activities for NLUF Grant "Examination of the cone in shell tartget compression concept for Asymmetric Fast Ignition"

Description: In an x-ray driven reentrant cone fast ignition target the x-ray spectrum contains a high energy component that causes preheating of the reentrant cone and mixing of gold into the collapsing shell. Direct laser drive might avoid this problem.
Date: March 2, 2005
Creator: Stephens, R.B.
Partner: UNT Libraries Government Documents Department

Study to determine the technical and economic feasibility of reclaiming chemicals used in micellar polymer and low tension surfactant flooding. Final report. [Ultrafiltration membranes and reverse osmosis membranes]

Description: Energy Resources Company has developed a technology for use with enhanced oil recovery to achieve emulsion breaking and surfactant recovery. By using ultrafiltration membranes, the Energy Resources Company process can dewater an oil-in-water type emulsion expected from enhanced oil recovery projects to the point where the emulsion can be inverted and treated using conventional emulsion-treating equipment. By using a tight ultrafiltration membrane or a reverse osmosis membrane, the Energy Resources Company process is capable of recovering chemicals such as surfactants used in micellar polymer flooding.
Date: February 1, 1978
Creator: Stephens, R.H.; Himmelblau, A. & Donnelly, R.G.
Partner: UNT Libraries Government Documents Department

Studies of QCD at the Tevatron with the D0 detector

Description: QCD studies at Fermilab`s Tevatron encompass a rich variety of topics. We present some of the latest results from the D0 experiment including probes of the standard model given by the inclusive jet cross section, the dijet invariant mass spectrum and several studies with direct photons. To complement these probes, we also present new results from precision examinations of the color interactions including studies of color coherence and jet azimuthal decorrelation. 22 refs., 14 figs.
Date: December 1, 1996
Creator: Stephens, R.W.
Partner: UNT Libraries Government Documents Department


Description: OAK-B135 Inertial confinement fusion shells have previously been evaluated on the basis of microscopic examination for local defects and limited surface profiling to represent their average fluctuation power. Since defects are local, and don't always have visible edges, this approach both misses some important fluctuations and doesn't properly represent the spatially dependent surface fluctuation power. they have taken the first step toward correcting this problem by demonstrating the capability to completely map the surface of a NIF shell with the resolution to account for all modes. This allows complete accounting of all the surface fluctuations. In the future this capability could be used for valuable shells to generate a complete r({theta},{psi}) surface map for accurate 3-D modeling of a shot.
Date: June 1, 2003
Partner: UNT Libraries Government Documents Department

Representative surface profile power spectra from capsules used in NOVA and Omega implosion experiments

Description: Typical surface profile power spectra of capsules used in Nova and Omega implosion experiments are presented. All Nova capsules are essentially identical in size and composition; their differences reflect small shell-to-shell variations. Differences among the Omega capsule power spectra can be attributed to changes in material properties with doping and (very importantly) differences in processing experience. These capsule power spectra accurately reflect past and current production, but are only a starting point for future capabilities.
Date: October 20, 1998
Creator: Cook, R. C.; McEachern, R. L. & Stephens, R.
Partner: UNT Libraries Government Documents Department

X-ray imaging to characterize MeV electronics propagation through plastic targets

Description: A high intensity laser pulse incident on an overdense plasma generates high energy electrons at the critical surface which propagate into the plasma. The details of this propagation is critical to the Fast Ignition process. The energetic electrons emerge as a jet on the far side, but the spread and propagation direction of the jet within the plasma is not well known. By embedding several thin high Z layers in a CH film one can directly image the progress of the electron beam. It loses enough energy to heat the medium through which it travels to hundreds of eV. At that temperature a film, even buried under CH, emits sufficiently hard thermal x-rays to allow imaging the heated area with an x-ray pinhole camera. The film can be thin enough to also see the emissions from another layer near the front of the film. If these two images are visible simultaneously, one can measure the beam spread and propagation direction within the plastic.
Date: September 3, 1999
Creator: Key, M H; Stephens, R B; Koch, J & Pennington, D
Partner: UNT Libraries Government Documents Department


Description: OAK-B135 Inertial Confinement Fusion (ICF) shells are mesoscale objects with nano-scale dimensional and nano-surface finish requirements. Currently, the shell dimensions are measured by white-light interferometry and an image analysis method. These two methods complement each other and give a rather complete data set on a single shell. The process is, however, labor intensive. They have developed an automation routine to fully characterize a shell in one shot and perform unattended batch measurements. The method is useful to the ICF program both for production screening and for full characterization. It also has potential for Inertial Fusion Energy (IFE) power plant where half a million shells need to be processed daily.
Date: June 1, 2003
Partner: UNT Libraries Government Documents Department

Implosion of indirectly driven reentrant cone shell target

Description: In an x-ray driven reentrant cone fast ignition target the x-ray spectrum contains a high energy component that casuses preheating of the reentrant cone and mixing of the gold into the collapsing shell. Direct laser drive might avoid this problem.
Date: October 31, 2003
Creator: Stephens, R.B.; Hatchett, S.P.; Turner, R.E.; Tanaka, K.A. & Kodama, R.
Partner: UNT Libraries Government Documents Department

Attritioning of Temple Mountain Ore

Description: Abstract: The results of both dry and wet attritioning of Temple Mountain ore are presented. In order to obtain effective attritioning on this ore, the amphaltite must be removed before attritioning. With the asphaltite present, dry attritioning causes a build-up of asphaltite on the surface of sand grains, with consequent loss of uranium values. In wet attritioning, the asphaltite is not broken down or attritioned, because of its low specific gravity and resilience.
Date: June 19, 1953
Creator: Butler, John Nicholson, III; Stephens, R. W. & Ehrlinger, H. P.
Partner: UNT Libraries Government Documents Department

Hydrodynamics of Conically-Guided Fast-Ignition Targets

Description: The fast ignition (FI) concept requires the generation of a compact, dense, pure fuel mass accessible to an external ignition source. The current baseline FI target is a shell fitted with a re-entrant cone extending to near its center. Conventional direct or indirect drive collapses the shell near the tip of the cone and then an ultra-intense laser pulse focused to the inside cone tip generates high-energy electrons to ignite the dense fuel. Theoretical investigations of this concept with a modest 2-D calculational scheme have sparsely explored the large design space and the tradeoffs available to optimize compaction of the fuel and maintain the integrity of the cone. Experiments have generally validated the modeling while revealing additional complexities. Away from the cone, the shell collapses much as does a conventional implosion, generating a hot, low-density inner core plasma which exhausts out toward the tip of the cone. The hot, low-density inner core can impede the compaction of the cold fuel, lowering the implosion/burn efficiency and the gain, and jetting toward the cone tip can affect the cone integrity. Thicker initial fuel layers, lower velocity implosions, and drive asymmetries can lead to decreased efficiency in converting implosion kinetic energy into compression. Ignition and burn hydrodynamic studies have revealed strategies for generating additional convergence and compression in the FI context. We describe 2-D and 1-D approaches to optimizing designs for cone-guided fast-ignition.
Date: September 29, 2005
Creator: Hatchett, S P; Clark, D; Tabak, M; Turner, R E; Stoeckel, C; Stephens, R B et al.
Partner: UNT Libraries Government Documents Department

Measurements of deep heating generated by ultra-intense laser-plasma interactions

Description: We measure 300 eV thermal temperatures at near-solid densities by x-ray spectroscopy of tracer layers buried up to 30 pm inside CH slabs which are irradiated by a 0.5 kJ, 5 ps laser. X-ray imaging data suggest that collimated electron transport produces comparable temperatures as deep as 200 pm, and unexpectedly show the heated regions to be 50-120 pm-diameter rings. The data indicate that intense lasers can directionally heat solid matter to high temperatures over large distances; the results are relevant for fast-ignition inertial-confinement fusion and hot, dense plasma research
Date: August 25, 1999
Creator: Hatchett, S P; Key, M H; Koch, J A; Lee, R W; Pennington, D; Stephens, R B et al.
Partner: UNT Libraries Government Documents Department

The case for fast ignition as an IFE concept exploration program

Description: The fast ignition (FI) concept is a variant of inertial fusion in which the compression and ignition steps are separated. Calculations suggest this would allow a substantial improvement in target gain, and could form the basis of a very attractive power plant. Transporting the energy to ignite a target involves the physics of light-driven relativistic plasmas; a subject which is not well understood. A concept exploration effort to understand the energy transport physics, and also to clarify the merits of a FI IFE power plant could justify a proof-of-principle program on the National Ignition Facility.
Date: September 23, 1999
Creator: Key, M. H.; Stephens, R. B.; Meier, W.; Moir, R. & Tabak, M.
Partner: UNT Libraries Government Documents Department

Compression dynamics of an indirect drive fast ignition target

Description: In an x-ray driven reentrant cone fast ignition target the x-ray spectrum contains a high energy component that cause preheating of the reentrant cone and mixing of its gold into the collapsing shell. Direct laser drive might avoid this problem.
Date: November 12, 2002
Creator: Stephens, R.B.; Hatchett, S.P.; Turner, R.E.; Tanaka, K.A.; Kodama, R.; Kodama, R. et al.
Partner: UNT Libraries Government Documents Department

A Bremsstrahlung Spectrometer using k-edge and Differential Filters with Image plate dosimeters

Description: A Bremsstrahlung spectrometer using k-edge and differential filtering has been used with Image Plate dosimeters to measure the x-ray fluence from short-pulse laser/target interactions. An electron spectrometer in front of the Bremsstrahlung spectrometer deflects electrons from the x-ray line of sight and simultaneously measures the electron spectrum. The response functions were modeled with the Monte Carlo code Integrated Tiger Series 3.0 and the dosimeters calibrated with radioactive sources. Electron distributions with slope temperatures in the MeV range are inferred from the Bremsstrahlung spectra.
Date: May 2, 2008
Creator: Chen, C; Mackinnon, A; Beg, F; Chen, H; Key, M; King, J A et al.
Partner: UNT Libraries Government Documents Department

Electron-Heated Target Temperature Measurements in Petawatt Laser Experiments Based on Extreme Ultraviolet Imaging and Spectroscopy

Description: Three independent methods (XUV spectroscopy, imaging at 68 eV and 256 eV) have been used to measure planar target rear surface plasma temperature due to heating by hot electrons. The hot electrons are produced by ultra-intense laser plasma interactions using the 150 J, 0.5 ps Titan laser. Soft x-ray spectroscopy in the 50-400 eV region and imaging at the 68 eV and 256 eV photon energies were used to determine the rear surface temperature of planar CD targets. Temperatures were found to be in the 60-150 eV range, with good agreement between the three diagnostics.
Date: May 2, 2008
Creator: Ma, T; Beg, F; Macphee, A; Chung, H; Key, M; Mackinnon, A et al.
Partner: UNT Libraries Government Documents Department

Hot dense matter creation in short-pulse laser interaction with tamped foils

Description: The possibility of producing hot dense matter has important applications for the understanding of transport processes in inertial confinement fusion (ICF) [1] and laboratory astrophysics experiments [2]. While the success of ICF requires the correct solution of a complex interaction between laser coupling, equation-of-state, and particle transport problems, the possibility of experimentally recreating conditions found during the ignition phase in a simplified geometry is extremely appealing. In this paper we will show that hot dense plasma conditions found during ICF ignition experiments can be reproduced by illuminating a tamped foil with a high intensity laser. We will show that temperatures on the order of kiloelectronvolts at solid densities can be achieved under controlled conditions during the experiment. Hydrodynamic tamping by surface coatings allows to reach higher density regimes by enabling the diagnosis of matter that has not yet begun to decompress, thus opening the possibility of directly investigating strongly coupled systems [3]. Our experimental diagnostics is based on K-shell spectroscopy coupled to x-ray imaging techniques. Such techniques have recently become prevalent in the diagnosis of hot dense matter [4]. By looking at the presence, and relative strengths, of lines associated with different ionization states, spectroscopy provides considerable insight into plasma conditions. At the same time, curved crystal imaging techniques allow for the spatial resolution of different regions of the target, both allowing for comparison of heating processes with the results of Particle-In-Cell (PIC) and hybrid simulation codes.
Date: August 15, 2006
Creator: Chen, S; Pasley, J; Beg, F; Gregori, G; Evans, R G; Notley, M et al.
Partner: UNT Libraries Government Documents Department

Fast Ignition relevant study of the flux of high intensity laser generated electrons via a hollow cone into a laser-imploded plasma

Description: An integrated experiment relevant to fast ignition is described. A Cu doped CD spherical shell target is imploded around an inserted hollow Au cone by a six beam 600J, 1ns laser to a peak density of 4gcm{sup -3} and a diameter of 100 {micro}m. A 10 ps, 20TW laser pulse is focused into the cone at the time of peak compression. The flux of high-energy electrons through the imploded material is determined from the yield of Cu K{alpha} fluorescence by comparison with a Monte Carlo model and is estimated to carry 15% of the laser energy. Collisional and Ohmic heating are modeled. An electron spectrometer shows significantly greater reduction of the transmitted electron flux than is due to binary collisions and Ohmic potential. Enhanced scattering by instability-induced magnetic fields is suggested.
Date: October 11, 2005
Creator: Key, M; Adam, J; Akli, K; Borgheshi, M; Chen, M; Evans, R et al.
Partner: UNT Libraries Government Documents Department