Transformation superplasticity is a deformation mechanism induced by thermally-cycling a polymorphic material through the phase transformation range while simultaneously applying an external biasing stress. Unlike microstructural superplasticity, which requires a fine, equiaxed grain structure, this mechanism can be applied to coarse-grained alloys and composites. In this article, we review our research on transformation superplasticity of Ti-6Al-4V/TiB-whisker reinforced composites, during thermal cycling through the titanium {alpha}/{beta} transformation range. The composites exhibit Newtonian flow and superplastic extension under these conditions. We describe the constitutive behavior of composites containing 0, 5 and 10 vol% reinforcing whiskers, and consider the effects of load transfer from matrix to whisker on superplastic deformation using existing rheological models. Additionally, strain hardening due to gradual whisker alignment is observed, and rationalized in terms of increased load transfer for aligned whiskers.

The properties of highly charged ions and their interaction with electrons and atoms is being studied in-situ at the LLNL electron beam ion traps, EBIT-II and SuperEBIT. Spectroscopic measurements provide data on electron-ion and ion-atom interactions as well as accurate transition energies of lines relevant for understanding QED, nuclear magnetization, and the effects of relativity on complex, state-of-the-art atomic calculations.

The appearance of denuded zones following low stress creep in particle-containing crystalline materials is both a microstructural prediction and observation often cited as irrefutable evidence for the Nabarro-Herring mechanism of diffusional creep. The denuded zones are predicted to be at grain boundaries that are orthogonal to the direction of the applied stress. Furthermore, their dimensions should account for the accumulated plastic flow. In the present paper, the evidence for such denuded zones is critically examined. These zones have been observed during creep of magnesium, aluminum, and nickel-base alloys. The investigation casts serious doubts on the apparently compelling evidence for the link between denuded zones and diffusional creep. Specifically, denuded zones are clearly observed under conditions that are explicitly not diffusional creep. Additionally, the denuded zones are often found in directions that are not orthogonal to the applied stress. Other mechanisms that can account for the observations of denuded zones are discussed. It is proposed that grain boundary sliding accommodated by slip is the rate-controlling process in the stress range where denuded zones have been observed. It is likely that the denuded zones are created by dissolution of precipitates at grain boundaries that are simultaneously sliding and migrating during creep.

We review concurrent multiscale simulations of dynamic and temperature-dependent processes found in nanomechanical systems coupled to larger scale surroundings. We focus on the behavior of sub-micron Micro-Electro-Mechanical Systems (MEMS), especially microresonators. These systems are often called NEMS, for Nano-Electro-Mechanical Systems. The coupling of length scales methodology we have developed for MEMS employs an atomistic description of small but key regions of the system, consisting of millions of atoms, coupled concurrently to a finite element model of the periphery. The model, Coarse-Grained Molecular Dynamics (CGMD), builds a generalized finite element formalism from the underlying atomistic physics in order to ensure a smooth coupling between regions governed by different length scales. The result is a model that accurately describes the behavior of the mechanical components of MEMS down to the atomic scale.

The possibility of fast ignition of thermo-nuclear fusion is stimulating research interest and activity worldwide. Fast ignition (FI) offers significantly higher gain than conventional spark ignition and the high gain opens the way to an efficient fusion energy producing cycle with laser drivers. The key to FI is the efficient transport of energy from a short pulse laser beam, the igniter, to a small ignition spark in compressed deuterium-tritium fuel. The primary candidate process enabling such energy transfer, is the absorption of laser light and its conversion into a beam of relativistic electrons, which heats the spark. Theory has predicted self-induced magnetic collimation of the electron beam, which could enable efficient transport from the absorption point to the ignition spark. Experiments are required to understand this highly complex process which involves currents in the electron beam, which greatly exceed the Alfven current limit6 (at which the Larmor radius of an electron in the magnetic field associated with by the current is smaller than the radius of the beam). Almost complete current compensation by cold electron return current is therefore required. The oppositely directed hot and cold electron flows initiate strong growth of the Weibel instability, which causes the currents to …

This paper surveys theory issues associated with inducing convective cells through divertor tile biasing in a tokamak to broaden the scrape-off layer (SOL). The theory is applied to the Mega-Ampere Spherical Tokamak (MAST), where such experiments are planned in the near future. Criteria are presented for achieving strong broadening and for exciting shear-flow turbulence in the SOL; these criteria are shown to be attainable in practice. It is also shown that the magnetic shear present in the vicinity of the X-point is likely to confine the potential perturbations to the divertor region below the X-point, leaving the part of the SOL that is in direct contact with the core plasma intact. The current created by the biasing and the associated heating power are found to be modest.

(1) LLNL measured the material removal rate from stainless steel, silicon carbide, rhenium, N5, hastalloy X, and titanium as a function of pulse fluence at a wavelength of 810 nm for pulse durations of 150 fs, 1.5 ps, 20 ps, and 500 ps. The spot size of the beam used was 150 microns in diameter and the nominal material thickness was 1-2 mm. These experiments were performed on the existing 1 kHz laser system. Holes of different penetration depths were obtained to ascertain change in removal rate as a function of depth. Measurements included electron microscopy of selected samples. (2) The experiments in I were repeated for all materials but select pulse durations with the sample in a vacuum of base pressure 10 mTorr to determine if hole quality and ablation rate is improved. (3) LLNL measured material removal rate from stainless steel, silicon carbide, rhenium, N5, hastalloy X, and titanium as a function of pulse fluence at a wavelength of 532 nm for pulse duration at 200 ns. The spot size of the beam used was 200 microns in diameter and the material thickness was the same as in task I. Holes of different penetration depths were obtained to …

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During last twenty years, a number of models have been used to calculate the change of conductivity and dielectric strength in materials caused by the passage of high-energy photons, such as Gamma-rays and X-rays. In these models, the electromagnetic fields generated in the electronic system created by the high-energy photons have not been investigated. That is, the solution of Maxwell's equations has not been obtained for these kinds of problems. We constructed a theoretical model, described by a set of equations to solve such a problem. The model includes the equations that describe the physics of the recombination and generation of electron-hole pairs by the high-energy photons in the dielectric materials, the Compton electron generation rates, and Maxwell's equations. When a beam of gamma photons penetrates into a transmission line or cables, energetic electrons and holes (carriers) are created in the metals and dielectrics of the system by the Compton and photoelectric effects. These energetic electrons and holes in turn create many low-energy holes and electrons through the interaction of the high-energy electrons with the atoms in the solids. Since the density of the solids is very high, the mean free path of the high-energy electrons is very short. In …

Metal matrix composites (MMCs) containing matrices with nanometer grain sizes have been produced from pure aluminum nano-powders (particle sizes 50-200 nm) with SiC reinforcement (particle sizes 3-10 {micro}m). The pure Al nano-powders were produced using an exploding wire technique. Dynamic loading using a magnetic impulse technique has been used to compact the MMC to high density. The dynamic compaction process results in excellent wetting of the SiC particles by the nanocrystalline Al powders, and the retention of a nano-crystalline grain size in the MMC. Microstructural analysis of the resulting MMC showed a highly uniform distribution of Sic particles with no visible defects or pores and the absence of deleterious phases (such as Al{sub 4}C{sub 3}) at the interfaces between the aluminum nano-grains and the SiC particles. The microstructures produced and the evolution of microstructure during dynamic compaction has also been studied using TEM and found to progress in three stages. These three stages are described.

Solid-state lasers have held great promise for the generation of high-average-power, high-quality output beams for a number of decades. However, the inherent difficulty of scaling the active solid-state gain media while continuing to provide efficient cooling has limited demonstrated powers to <5kW. Even at the maximum demonstrated average powers, the output is most often delivered as continuous wave (CW) or as small energy pulses at high pulse repetition frequency (PRF) and the beam divergence is typically >10X the diffraction limit. Challenges posed by optical distortions and depolarization arising from internal temperature gradients in the gain medium of a continuously cooled system are only increased for laser designs that would attempt to deliver the high average power in the form of high energy pulses (>25J) from a single coherent optical aperture. Although demonstrated phase-locking of multiple laser apertures may hold significant promise for the future scaling of solid-state laser systems,1 the continuing need for additional technical development and innovation coupled with the anticipated complexity of these systems effectively limits this approach for near-term multi-kW laser operation outside of a laboratory setting. We have developed and demonstrated a new operational mode for solid-state laser systems in which the cooling of the gain …

This newsletter is prepared for the NARUC Subcommittee on Renewable Energy to promote information sharing on state-level renewable electric activities. It is sponsored by the Office of Power Technologies of the U.S. Department of Energy.

The second axis accelerator of the Dual Axis Radiographic Hydrodynamic Test (DARHT-II) facility will produce a 2-kA, 20-MeV, 2-{micro}s output electron beam with a design goal of less than 1000 {pi} mm-mrad normalized transverse emittance. In order to meet this goal, both the beam breakup instability (BBU) and transverse ''corkscrew'' motion (due to chromatic phase advance) must be limited in growth. Using data from recent experimental measurements of the transverse impedance of actual DARHT-II accelerator cells by Briggs et al., they have used the LLNL BREAKUP code to predict BBU and corkscrew growth in DARHT-II. The results suggest that BBU growth should not seriously degrade the final achievable spot size at the x-ray converter, presuming the initial excitation level is of the order 100 microns or smaller. For control of corkscrew growth, a major concern is the number of ''tuning'' shots needed to utilize effectively the ''tuning-V'' algorithm. Presuming that the solenoid magnet alignment falls within spec, they believe that possibly as few as 50-100 shots will be necessary to set the dipole corrector magnet currents. They give some specific examples of tune determination for a hypothetical set of alignment errors.

Embedded gold and mechanical deformation in silica were used to investigate initiation of laser-induced damage at 3.55-nm (7.6 ns). The nanoparticle-covered surfaces were coated with between 0 and 500 nm of SiO{sub 2} by e-beam deposition. The threshold for observable damage and initiation site morphology for these ''engineered'' surfaces was determined. The gold nanoparticle coated surfaces with 500nm SiO{sub 2} coating exhibited pinpoint damage threshold of <0.7 J/cm{sup 2} determined by light scattering and Nomarski microscopy. The gold nanoparticle coated surfaces with the 100nm SiO{sub 2} coatings exhibited what nominally appeared to be film exfoliation damage threshold of 19 J/cm{sup 2} via light scattering and Nomarski microscopy. With atomic force microscopy pinholes could be detected at fluences greater than 7 J/cm{sup 2} and blisters at fluences greater than 3 J/cm{sup 2} on the 100 nm-coated surfaces. A series of mechanical indents and scratches were made in the fused silica substrates using a nano-indentor. Plastic deformation without cracking led to damage thresholds of -25 J/cm{sup 2}, whereas indents and scratches with cracking led to damage thresholds of only {approx}5 J/cm{sup 2}. Particularly illuminating was the deterministic damage of scratches at the deepest end of the scratch, as if the scratch acted …

We describe the design and MPI implementation of two benchmarks created to characterize the balanced system performance of high-performance clusters and supercomputers: b{_}eff, the communication-specific benchmark examines the parallel message passing performance of a system, and b{_}eff{_}io, which characterizes the effective 1/0 bandwidth. Both benchmarks have two goals: (a) to get a detailed insight into the Performance strengths and weaknesses of different parallel communication and I/O patterns, and based on this, (b) to obtain a single bandwidth number that characterizes the average performance of the system namely communication and 1/0 bandwidth. Both benchmarks use a time driven approach and loop over a variety of communication and access patterns to characterize a system in an automated fashion. Results of the two benchmarks are given for several systems including IBM SPs, Cray T3E, NEC SX-5, and Hitachi SR 8000. After a redesign of b{_}eff{_}io, I/O bandwidth results for several compute partition sizes are achieved in an appropriate time for rapid benchmarking.

Energetic oxetane polymers have shown promise as performance-enhancing ingredients in gun and missile propellants. In order to correctly predict the performance of energetic materials containing these polymers, it is important to have accurate, experimentally determined values for the polymer heats of formation ({Delta}H{sub f}). In support of a theoretical study on gun propellant performance, heats of combustion were experimentally determined for a series of oxetane polymers and monomers (see below) using combustion calorimetry, and from these, {Delta}H{sub f} values were calculated. Polymers included BAMO/AMMO, BAMO/NMMO (polyol and TPE), and BNMO/NMMO mixtures. In order to calculate the {Delta}H{sub f} of the polymers from heat of combustion data, a number of assumptions were made regarding the polymer structure and molecular weight. A comparison of the {Delta}H{sub f} values for the monomers and polymers were made, and these values were compared to heats of formation measured elsewhere.

A spare NASA/GSFC Astro-E microcalorimeter has been installed, tested, and run successfully on EBIT-II at the Lawrence Livermore National Laboratory. A brief overview of results including measurements by the microcalorimeter of absolute excitation cross sections, time dependent spectra, and spectra as a function of Maxwellian temperature are discussed.

Parallel optical interconnects based on multimode fiber ribbon cables are emerging as a robust, high-performance data link technology that enhances throughput by using parallel arrays of fibers. While this technology has primarily been implemented as single wavelength point-to-point links, it can be significantly enhanced by wavelength division multiplexing (WDM). WDM enables both increased point-to-point bandwidth as well as more complex interconnect topologies and routing approaches that are particularly attractive for massively parallel processing (MPP) systems. Exploiting the advantages of WDM interconnects requires multi-wavelength sources, a low loss routing fabric, and small footprint wavelength selective filter modules. The Lambda-connect project ({gamma}- Connect) at Lawrence Livermore National Laboratory is a technology development and proof-of-principle demonstration of the enabling hardware for WDM parallel optical interconnects for use in massively parallel processing systems and other high-performance data link applications. This dissertation demonstrates several key system components and technologies for {gamma}-Connect.

Free electron lasers have the promise of producing extremely high-intensity short pulses of coherent, monochromatic radiation in the 1-10 keV energy range. For example, the Linac Coherent Light Source at Stanford is being designed to produce an output intensity of 2 x 10{sup 14} W/cm{sup 2} in a 230 fs pulse. These sources will open the door to many novel research studies. However, the intense x-ray pulses may damage the optical components necessary for studying and controlling the output. At the full output intensity, the dose to optical components at normal incidence ranges from 1-10 eV/atom for low-Z materials (Z < 14) at photon energies of 1 keV. It is important to have an understanding of the effects of such high doses in order to specify the composition, placement, and orientation of optical components, such as mirrors and monochromators. Doses of 10 eV/atom are certainly unacceptable since they will lead to ablation of the surface of the optical components. However, it is not precisely known what the damage thresholds are for the materials being considered for optical components for x-ray free electron lasers. In this paper, we present analytic estimates and computational simulations of the effects of high-intensity x-ray pulses …

The purpose of this document is to describe the National Ignition Facility (NIF) Project Organization and the top level roles and responsibilities of the managers charged with executing the Project.

The purpose of this White Paper is to outline the benefits we expect to receive from Model-Based Engineering and Manufacturing (MBE/M) for the design, analysis, fabrication, and assembly of nuclear weapons for upcoming Life Extension Programs (LEPs). Industry experiences with model-based approaches and the NNSA/DP investments and experiences, discussed in this paper, indicate that model-based methods can achieve reliable refurbished weapons for the stockpile with less cost and time. In this the paper, we list both general and specific benefits of MBE/M for the upcoming LEPs and the metrics for determining the success of model-based approaches. We also present some outstanding issues and challenges to deploying and achieving long-term benefit from the MBE/M. In conclusion, we argue that successful completion of the upcoming LEPs--with very aggressive schedule and funding restrictions--will depend on electronic model-based methods. We ask for a strong commitment from LEP managers throughout the Nuclear Weapons Complex to support deployment and use of MBE/M systems to meet their program needs.

Underground coal mining (down to {approx}0.75 km depth) in the contiguous Wasatch Plateau (WP) and Book Cliffs (BC) mining districts of east-central Utah induces abundant seismicity that is monitored by the University of Utah regional seismic network. This report presents the results of a systematic characterization of mining seismicity (magnitude {le} 4.2) in the WP-BC region from January 1978 to June 2000-together with an evaluation of three seismic events (magnitude {le} 4.3) associated with underground trona mining in southwestern Wyoming during January-August 2000. (Unless specified otherwise, magnitude implies Richter local magnitude, M{sub L}.) The University of Utah Seismograph Stations (UUSS) undertook this cooperative project to assist the University of California Lawrence Livermore National Laboratory (LLNL) in research and development relating to monitoring the Comprehensive Test Ban Treaty (CTBT). The project, which formally began February 28, 1998, and ended September 1, 2000, had three basic objectives: (1) Strategically install a three-component broadband digital seismic station in the WP-BC region to ensure the continuous recording of high-quality waveform data to meet the long-term needs of LLNL, UUSS, and other interested parties, including the international CTBT community. (2) Determine source mechanisms--to the extent that available source data and resources allowed--for comparative seismic characterization …

A model-based detector is developed to process shallow water ocean acoustic data. The function of the detector is to adaptively monitor the environment and decide whether or not a change from normal has occurred. Here we develop a processor incorporating both a normal-mode ocean acoustic model and a vertical hydrophone array. The detector is applied to data acquired from the Hudson Canyon experiments at various ranges and its performance is evaluated.