Publications

Parameterization of predictive models is often complicated by the inability to make measurements at the same scale at which one wishes to perform the analysis. This disparity in scales necessitates the use of some averaging or upscaling model to compute the desired effective media properties. In efforts to better model permeability upscaling, laboratory experiments have been conducted on a series of rock samples with different genetic origins. These experiments involve the collection of exhaustive permeability data sets at different sample supports (i.e., sample volumes) using a specially designed minipermeameter test system. Here the authors present a synopsis of such a data set collected from a block of volcanic tuff.

A mathematical model was developed to quantitatively describe the intermetallic compound (IMC) layer growth that takes place between a Sn-based solder and a noble metal thick film conductor material used in hybrid microcircuit (HMC) assemblies. The model combined the reaction kinetics of the solder/substrate interaction, as determined from ancillary isothermal aging experiments, with a 2-D finite element mesh that took account of the porous morphology of the thick film coating. The effect of the porous morphology on the IMC layer growth when compared to the traditional 1-D computations was significant. The previous 1-D calculations under-predicted the nominal IMC layer thickness relative to the 2-D case. The 2-D model showed greater substrate consumption by IMC growth and lesser solder consumption that was determined with the 1-D computation. The new 2-D model allows the design engineer to better predict circuit aging and hence, the reliability of HMC hardware that is placed in the field.

Understanding the parameters that affect the performance of milliscale and microscale actuators is essential to the development of optimized designs and fabrication processes, as well as the qualification of devices for commercial applications. This paper discusses the development of optical techniques for motion measurements of LIGA fabricated milliengines. LIGA processing permits the fabrication of precision millimeter-sized machine elements that cannot be fabricated by conventional miniature machining techniques because of their small feature sizes. In addition, tolerances of 1 part in 10{sup 3} to 10{sup 4} may be maintained in millimeter sized components with this processing technique. Optical techniques offer a convenient means for measuring long term statistical performance data and transient responses needed to optimize designs and manufacturing techniques. Optical techniques can also be used to provide feedback signals needed for control and sensing of the state of the machine. Optical probe concepts and experimental data obtained using a milliengine developed at Sandia National Laboratories are presented.

The Waste Isolation Pilot Plant (WIPP) is a proposed repository for transuranic wastes constructed in bedded Permian-acre halite deposits in southeastern New Mexico, USA. Site-characterization studies at the WIPP site identified groundwater flow in the Culebra Dolomite Member of the Rustler Formation as the most likely Geologic pathway for radio nuclide transport to the accessible environment in the event of a breach of the WIPP repository through inadvertent human intrusion. The Culebra is a 7-m-thick, variably fractured dolomite with massive and layers. Detailed studies at all scales demonstrated that the Culebra is a heterogeneous medium. Heterogeneity in Culebra properties was incorporated into numerical simulations used for data interpretation and PA calculations in different ways, depending on the amount of data available, the certainty with which the effects of a given approach could be evaluated, and the purpose of the study. When abundant, spatially distributed data were available, the heterogeneity was explicitly included. For example, a stochastic approach was used to generate numerous, equally likely, heterogeneous transmissivity fields conditioned on head and transmissivity data. In other cases, constant parameter values were applied over the model domain. These constant values were selected and applied in two different ways. In simple cases where a conservative bounding value could be identified that would not lead to unrealistically conservative results, that value was used for all calculations. In more complex cases, parameter distributions were developed and single values of the parameters were sampled from the distributions and applied across the entire model domain for each of the PA Monte Carlo simulations. We are currently working to refine our understanding of the multiple rates of diffusion attributable to small-scale spatial variability.

This report summarizes progress from the Laboratory Directed Research and Development (LDRD) program during fiscal year 1997. In addition to a programmatic and financial overview, the report includes progress reports from 218 individual R&D projects in eleven categories. Theses reports are grouped into the following areas: materials science and technology; computer sciences; electronics and photonics; phenomenological modeling and engineering simulation; manufacturing science and technology; life-cycle systems engineering; information systems; precision sensing and analysis; environmental sciences; risk and reliability; national grand challenges; focused technologies; and reserve.

This paper presents a prototype virtual reality (VR) system for training medical first responders. The initial application is to battlefield medicine and focuses on the training of medical corpsmen and other front-line personnel who might be called upon to provide emergency triage on the battlefield. The system is built upon Sandia`s multi-user, distributed VR platform and provides an interactive, immersive simulation capability. The user is represented by an Avatar and is able to manipulate his virtual instruments and carry out medical procedures. A dynamic casualty simulation provides realistic cues to the patient`s condition (e.g. changing blood pressure and pulse) and responds to the actions of the trainee (e.g. a change in the color of a patient`s skin may result from a check of the capillary refill rate). The current casualty simulation is of an injury resulting in a tension pneumothorax. This casualty model was developed by the University of Pennsylvania and integrated into the Sandia MediSim system.

Electrical power generated with the heat from the sun, called solar thermal power, is produced with three types of concentrating solar systems - trough or line-focus systems; power towers in which a centrally-located thermal receiver is illuminated with a large field of sun-tracking heliostats; and dish/engine systems. A special case of the third type of system, a dish/Stirling system, is the subject of this paper. A dish/Stirling system comprises a parabolic dish concentrator, a thermal receiver, and a Stirling engine/generator located at the focus of the dish. Several different dish/Stirling systems have been built and operated during the past 15 years. One system claims the world record for net conversion of solar energy to electric power of 29.4%; and two different company`s systems have accumulated thousands of hours of on-sun operation. Due to de-regulation and intense competition in global energy markets as well as the immaturity of the technology, dish/Stirling systems have not yet found their way into the marketplace. This situation is changing as solar technologies become more mature and manufacturers identify high-value niche markets for their products. In this paper, I review the history of dish/Stirling system development with an emphasis on technical and other issues that directly impact the Stirling engine. I also try to provide some insight to the opportunities and barriers confronting the application of dish/Stirling in power generation markets.

VOLMAX is a three-dimensional transient volumetric Maxwell equation solver that operates on standard rectilinear finite-difference time-domain (FDTD) grids, non-orthogonal unstructured grids, or a combination of both types (hybrid grids). The algorithm is fully explicit. Open geometries are typically solved by embedding multiple unstructured regions into a simple rectilinear FDTD mesh. The grid types are fully connected at the mesh interfaces without the need for complex spatial interpolation. The approach permits detailed modeling of complex geometry while mitigating the large cell count typical of non-orthogonal cells such as tetrahedral elements. To further improve efficiency, the unstructured region carries a separate time step that sub-cycles relative to the time-step used in the FDTD mesh.

A discrete element computer program named DMC{underscore}BLAST (Distinct Motion Code) has been under development since 1987 for modeling rock blasting (Preece {ampersand} Taylor, 1989). This program employs explicit time integration and uses spherical or cylindrical elements that are represented as circles in two dimensions (2-D). DMC{underscore}BLAST calculations compare favorably with data from actual bench blasts (Preece et al, 1993). Buffer Choke blasting is commonly used in surface gold mines to break the rock and dilate it sufficiently for ease of digging, with the assumption of insignificant horizontal movement. The blast designs usually call for relatively shallow holes benches ({lt} 11 m) with small blastholes (approx. 165 mm), small burdens and spacings ({lt}5 m), often with 50% or more of the hole stemmed. Control of blast-induced horizontal movement is desired because the ore is assayed in place from the blasthole drill cuttings and digging polygons of ore and waste are laid out before the blast. Horizontal movement at the ore waste boundary can result in dilution of the ore or loss of ore with the waste. The discrete element computer program DMC{underscore}BLAST has been employed to study spatial variation of horizontal rock motion during buffer choke blasting. Patterns of rock motion can be recognized from the discrete element simulations that would be difficult or impossible to recognize in the field (Preece, Tidman and Chung, 1997). Techniques have been developed to calculate ore waste and dilution from the horizontal movement predicted by DMC{underscore}BLAST. Four DMC{underscore}BLAST simulations of buffer blasting have been performed. The blasts are identical except that the burden and spacing are systematically varied which also changes the powder factor. Predictions of ore waste or dilution are made for each burden in the blast, assuming no horizontal movement, to illustrate the spatial variation observed.

The Office of Environmental Management of the U.S. Department of Energy is responsible for the safe management and disposal of DOE owned defense spent nuclear fuel and high level waste (DSNF/DHLW). A desirable option, direct disposal of the waste in the potential repository at Yucca Mountain, depends on the final waste acceptance criteria, which will be set by DOE`s Office of Civilian Radioactive Waste Management (OCRWM). However, evolving regulations make it difficult to determine what the final acceptance criteria will be. A method of anticipating waste acceptance criteria is to gain an understanding of the DOE owned waste types and their behavior in a disposal system through a performance assessment and contrast such behavior with characteristics of commercial spent fuel. Preliminary results from such an analysis indicate that releases of 99Tc and 237Np from commercial spent fuel exceed those of the DSNF/DHLW; thus, if commercial spent fuel can meet the waste acceptance criteria, then DSNF can also meet the criteria. In large part, these results are caused by the small percentage of total activity of the DSNF in the repository (1.5%) and regulatory mass (4%), and also because commercial fuel cladding was assumed to provide no protection.

This paper describes the design and characterization of several types of micromirror devices to include process capabilities, device modeling, and test data resulting in deflection versus applied potential curves. These micromirror devices are the first to be fabricated in the state-of-the-art four-level planarized polysilicon process available at Sandia National Laboratories known as the Sandia Ultra-planar Multi-level MEMS Technology (SUMMiT). This enabling process permits the development of micromirror devices with near-ideal characteristics which have previously been unrealizable in standard three-layer polysilicon processes. This paper describes such characteristics as elevated address electrodes, individual address wiring beneath the device, planarized mirror surfaces using Chemical Mechanical Polishing (CMP), unique post-process metallization, and the best active surface area to date. This paper presents the design, fabrication, modeling, and characterization of several variations of Flexure-Beam (FBMD) and Axial-Rotation Micromirror Devices (ARMD). The released devices are first metallized using a standard sputtering technique relying on metallization guards and masks that are fabricated next to the devices. Such guards are shown to enable the sharing of bond pads between numerous arrays of micromirrors in order to maximize the number of on-chip test arrays. The devices are modeled and then empirically characterized using a laser interferometer setup located at the Air Force Institute of Technology (AFIT) at Wright-Patterson AFB in Dayton, Ohio. Unique design considerations for these devices and the process are also discussed.

Transient solid dynamics simulations are among the most widely used engineering calculations. Industrial applications include vehicle crashworthiness studies, metal forging, and powder compaction prior to sintering. These calculations are also critical to defense applications including safety studies and weapons simulations. The practical importance of these calculations and their computational intensiveness make them natural candidates for parallelization. This has proved to be difficult, and existing implementations fail to scale to more than a few dozen processors. In this paper we describe our parallelization of PRONTO, Sandia`s transient solid dynamics code, via a novel algorithmic approach that utilizes multiple decompositions for different key segments of the computations, including the material contact calculation. This latter calculation is notoriously difficult to perform well in parallel, because it involves dynamically changing geometry, global searches for elements in contact, and unstructured communications among the compute nodes. Our approach scales to at least 3600 compute nodes of the Sandia/Intel Teraflop computer (the largest set of nodes to which we have had access to date) on problems involving millions of finite elements. On this machine we can simulate models using more than ten- million elements in a few tenths of a second per timestep, and solve problems more than 3000 times faster than a single processor Cray Jedi.

The policy debate that has surrounded the national laboratories of the Department of Energy since the end of the Cold War has been very confusing. Initially, with the passage of the National Competitiveness Technology Transfer Act of 1989, the laboratories were encouraged to form cooperative arrangements with industry to maintain their technology base and give a boost for U.S. industrial competitiveness. But in the 104th Congress, technology transfer programs were severely constrained.

Sandia National Laboratories and several subsystem contractors are developing technologies applicable to multispectral remote sensing from space. A proof of concept multispectral sensor system is under development. The objective of building this sensor is to demonstrate and evaluate multispectral imaging technologies for various applications. The three major subsystems making up the sensor are the focal plane assembly (FPA), the cryocooler, and the telescope. This paper covers the focal plane assembly, which is the basis of the sensor system. The focal plane assembly includes sensor chip assemblies, optical filters, and a vacuum enclosure with cold shielding. Linear detector arrays provide spatial resolution in the cross-track direction for a pushbroom imager configuration. The optical filters define 15 spectral bands in a range from 0.45 microns to 10.7 microns. All the detector arrays are mounted on a single focal plane and are designed to operate at 75 K. No beam splitters are used. The four spectral bands covering the visible to near infrared have roughly 2400 pixels each, and the remaining 11 spectral bands have roughly 600 pixels each. The average total rate of multispectral data from the FPA is approximately 15.4 megapixels per second. At the time this paper is being written, the multispectral focal plane assembly is in the fabrication phase. A thermal/mechanical mockup has been built and tested for the vibration environment and to determine the thermal load. Some of the sensor chip assemblies and filters have been built and tested. Several notable features of the design are covered in the paper as well as preliminary test data.

The Air Force Research Laboratory`s Satellite Threat Warning and Attack Reporting (STW/AR) program will provide technologies for advanced threat warning and reporting of radio frequency (RF) and laser threats. The STW/AR program objectives are: (a) develop cost- effective technologies to detect, identify, locate, characterize, and report attacks or interference against U.S. and Allied satellites. (b) demonstrate innovative, light-weight, low-power, laser and RF sensors. The program focuses on the demonstration of RF and laser sensors. The RF sensor effort includes the investigation of interferometric antenna arrays, multi-arm spiral and butler matrix antennas, wideband receivers, adaptive processors, and improved processing algorithms. The laser sensor effort includes the investigation of alternative detectors, broadband grating and optical designs, active pixel sensing, and improved processing algorithms.

The identification of crystallographic phases in the scanning electron microscope (SEM) has been limited by the lack of a simple way to obtain electron diffraction data of an unknown while observing the micro structure of the specimen. With the development of Charge Coupled Device (CCD) based detectors, backscattered electron Kikuchi patterns (BEKP), alternately referred to as electron backscattered diffraction patterns (EBSP), can be easily collected. Previously, BEKP has been limited to crystallographic orientation studies due to the poor pattern quality collected with video rate detector systems. With CCD detectors, a typical BEKP can now be acquired from a micron or sub-micron-sized crystal using an exposure time of 1-10 seconds with an accelerating voltage of 10-40 kV and a beam current as low as 0.1 nA. Crystallographic phase analysis using BEKP is unique in that the properly equipped SEM permits high magnification images, BEKP`s, and elemental information to be collected from bulk specimens. BEKP in the SEM has numerous advantages over other electron microscopy crystallographic techniques. The large angular view ( 70 degrees) provided by BEKP and the lack of difficult specimen preparation are distinct advantages of the technique. No sample preparation beyond what is commonly used for SEM specimens is required for BEKP.

This paper describes the design and fabrication of optical Microelectromechanical Systems (MEMS) devices using the Sandia Ultra planar Multilevel MEMS Technology (SUMMiT) fabrication process. This state of the art process, offered by Sandia National Laboratories, provides unique and very advantageous features which make it ideal for optical devices. This enabling process permits the development of micromirror devices with near ideal characteristics which have previously been unrealizable in standard polysilicon processes. This paper describes such characteristics as elevated address electrodes, individual address wiring beneath the device, planarized mirror surfaces, unique post-process metallization, and the best active surface area to date.

Since the end of the cold war, as our nuclear stockpile has decreased, the Department of Energy (DOE) has been working rapidly to safely dismantle weapons returned by the military. In order to be retired, weapons must be returned to the Pantex Plant in Amarillo, Texas. There they are reduced to their component parts. Although many of these parts are not hazardous, some, including certain explosive assemblies and radioactive materials, are sufficiently hazardous so that special handling systems are necessary. This paper will describe several of these systems developed by Sandia for Pantex and their technical basis.

The Waste Isolation Pilot Plant (WIPP) is a planned geologic repository for permanent disposal of transuranic waste generated by the U.S. Department of Energy. Disposal regions consist of panels and drifts mined from the bedded salt of the Salado Formation at a depth of approximately 650 m below the surface. This lithology is part of the 225 million year old Delaware Basin, and is geographically located in southeastern New Mexico. Four shafts service the facility needs for air intake, exhaust, waste handling, and salt handling. As the science advisor for the project, Sandia National Laboratories developed the WIPP shaft sealing system design. This design is a fundamental component of the application process for facility licensing, and has been found acceptable by stakeholders and regulatory agencies. The seal system design is founded on results obtained from laboratory and field experiments, numerical modeling, and engineering judgment. This paper describes a field test program to characterize the fluid flow properties in the WIPP shafts at representative seal locations. This work was conducted by Duke Engineering and Services under contract to Sandia National Laboratories in support of the seal system design.

The mission of the Divertor Materials Evaluation System (DiMES) in DIII-D is to establish an integrated data base from measurements in the divertor of a tokamak in order to address some of the ITER and fusion power reactor plasma material interaction issues. Carbon and metal coatings of Be, W, V, and Mo were exposed to the steady-state outer strike point on DIII-D for 4--18 s. These short exposure times ensure controlled exposure conditions, and the extensive arrays of DIII-D divertor diagnostics provide a well-characterized plasma for modeling efforts. Post-exposure analysis provides a direct measure of surface material erosion rates and the amount of retained deuterium. For carbon, these results match closely with the results of accumulated carbon deposition and erosion, and the corresponding deuterium retention of long term exposure tiles in DIII-D. Under the carbon-contaminated background plasma of DIII-D, metal coatings of Be, V, Mo, and W were exposed to the steady-state outer strike point under ELMing and ELM-free H-mode discharges. The rate of material erosion and deuterium retention were measured. As expected, W shows the lowest erosion rate at 0.1 mm/s and the lowest deuterium uptake of 2 {times} 10{sup 20}/m{sup 2}.

The growth of the safeguards inspectorate of the Agency, spanning more than 40 years, has produced a variety of interesting subjects (legal, technical, political, etc.) for recollection, discussion, and study. Although the Agency was established in 1957, the first practical inspections did not occur until the early 1960s. In the early inspections, thee was little C/S equipment available, and no optical surveillance was used. However, by the third decade of the IAEA, the 1980s, many technology advances were made, and the level of C/S equipment activities increased. By the late 1980s, some 200 Twin Minolta film camera systems were deployed by the Agency for safeguards use. At the present time, the Agency is evaluating and beginning to implement remote monitoring as part of the Strengthened Safeguards System. However, adoption of remote monitoring by international agencies cannot occur rapidly because of the many technical and policy issues associated with this activity. A glimpse into the future indicates that an important element of safeguards instrumentation will be the merging of C/S and NDA equipment into integrated systems. The use of modern interior area monitors in International Safeguards also offers a great potential for advancing C/S measures. The research in microsensors is in its infancy, and the opportunities for their reducing the cost, increasing the life time, and increasing the reliability of sensors for safeguards applications are manifold. A period may be approaching in which the terminology of C/S will no longer have its original meaning, as integrated systems combining NDA instruments and C/S instruments are already in use and are expected to be the norm in the near future.

MicroElectroMechanical Systems (MEMS) and their fabrication technologies provide great opportunities for application to micro-optical systems (MOEMS). Implementing MOEMS technology ranges from simple, passive components to complicated, active systems. Here, an overview of polysilicon surface micromachining MEMS combined with optics is presented. Recent advancements to the technology, which may enhance its appeal for micro-optics applications are emphasized. Of all the MEMS fabrication technologies, polysilicon surface micromachining technology has the greatest basis in and leverages the most the infrastructure for silicon integrated circuit fabrication. In that respect, it provides the potential for very large volume, inexpensive production of MOEMS. This paper highlights polysilicon surface micromachining technology in regards to its capability to provide both passive and active mechanical elements with quality optical elements.

This paper describes ongoing testing of two microgrippers for assembly of LIGA (Lithographie Galvanoformung Abformung) parts. The goal is to place 100 micron outside diameter (OD) LIGA gears with a 50 micron inner diameter hole onto pins ranging from 35 to 49 microns. The first micro gripper is a vacuum gripper made of a 100 micron OD stainless steel tube. The second micro gripper is a set of tweezers fabricated using the LIGA process. Nickel, Permalloy, and copper materials are tested. The tweezers are actuated by a collet mechanism which is closed by a DC linear motor.

A numerical algorithm for the efficient solution of the uncoupled quasistatic initial/boundary value problem involving orthotropic linear viscoelastic media undergoing thermal and/or mechanical deformation is briefly outlined.

Interfacial adhesion is of extraordinary technological importance and has long been of intense scientific interest. However, the study of the adhesive bond and its failure is made difficult by the complexity of the interfacial interaction and the problems involved with establishing carefully characterized and controlled interfacial surfaces and that of quantitatively evaluating the bonding after its formation. In the present work, we outline the results of studies using Interfacial Force Microscopy (IFM) to study the adhesive bond formation and failure between (1) differing end-group combinations on self-assembling monolayer (SAM) films covering Au surfaces and (2) between clean surfaces of a W probe and a Au single-crystal sample. The IFM is a scanning probe technique distinguished by its use of a mechanically stable, zero-compliance force sensor. This sensor permits the study of the interfacial force as a function of separation without the mechanical instability giving rise to the {open_quotes}jump-to-contact{close_quotes} seen in all presently used displacement-based sensors, such as the surface forces apparatus and the atomic force microscope. Thus, information can be obtained concerning the details of the adhesive bond formation and failure over the entire range of the interfacial interaction. We demonstrate that such measurements yield valuable quantitative information concerning the individual bond strengths between chemically distinct SAM end groups and show that the clean metal-surface interaction is dominated by surface roughness and plastic deformation.