One of the possible consequences of disruptions is the generation of runaway electrons which can impact plasma facing components and cause damage due to high local energy deposition. This problem becomes more serious as the machine size and plasma current increases. Since large size and high currents are characteristics of proposed future machines, control of runaway generation is an important design consideration. A lumped circuit model for disruption runaway electron generation indicates that control circuitry on strongly influence runaway behavior. A comparison of disruption data from several shots on JET and D3-D with model results, demonstrate the effects of plasma motion on runaway number density and energy. 6 refs., 12 figs.
Benchmarking a network file server introduces some unique considerations over traditional benchmarking scenarios. Since the user is executing on a client system interconnected to the file server, the client and network must be provided for during benchmarking. During a recent procurement action, Sandia National Laboratories was challenged to develop a benchmark suite that would accurately test the network requirements. This paper describes the benchmark design and summarizes the experience gained from the benchmark executions. 8 refs., 2 figs.
The electromagnetic field in a mode-stirred chamber is a random process. Samples of this random process are random variables. Different realizations of this random variable can be obtained by changing the paddle-wheel angle, changing the frequency, or changing the location at which the sample is taken. Correlation widths can be defined for each of these three variables. For examples, the spatial correlation width is the distance a point sensor must be moved to realize an uncorrelated value of the field (paddle-wheel angle and frequency held constant). Likewise, the paddle-wheel correlation width is the angle through which the paddle wheel must turn to yield an uncorrelated value (location and frequency held constant). The frequency correlation width is the frequency change required to yield an uncorrelated value (location and paddle-wheel angle held constant). These values were determined experimentally for the sandia mode-stirred chamber by sampling the field at equal increments (for each variable) and calculating an autocorrelation function. The autocorrelation function is a random process (because it is calculated from a random process) and must be averaged to determine it width. The correlation widths were found to be less than 0.1{degree} for paddle-wheel angle, 50 kHz for frequency, and half a wavelength for spatial location. 4 refs., 3 figs., 2 tabs.
NMR and NQR reveal substantial structural changes in the metallic phase of LA{sub 2}CuO{sub 4+}{delta} which occur below 220 K. The oxygen octahedra in the metallic phase are not tilted at phase separation; upon cooling to 40 K considerable tilt has developed. The low temperature structure is highly disordered. 4 refs., 2 figs.
Although the feasibility of using PZT and PLZT films for optical data processing applications, such as optical storage disks, image comparators, and spatial light modulators, has clearly been established, most of the critical parameters related to the storage and readout processes still need to be evaluated. Optical readout techniques capable of nondestructively determining the value of polarization are based either on the quadratic electrooptic effect or on a photocurrent response. In reflection, large electrooptic retardations (>60{degrees}) have now been achieved with thin PZT films ({approx equal} 0.5 {mu}m) under conditions that optimize interference effects. These results are quite attractive for device applications. Model calculations, based on the equations of reflection ellipsometry, have been used to develop a framework for understanding those results. The magnitude of the photocurrent response has also been used to determine the polarization state. However, the photocurrent always has the same sign, regardless of the sign of the polarization, which suggests the presence of a strong bias field due to at least one of the interfaces. In addition, the accumulation of space charge after a succession of measurements suppresses the photocurrent transient, which severely limits the utility of a photocurrent based readout. 7 refs., 9 figs.
Basic to our knowledge of the science of welding is an understanding of the melting efficiency, which indicates how much of the heat deposited by the welding process is used to produce melting. Recent calorimetric studies of GTAW, PAW, and LBW processes have measured the net heat input to the part thereby quantifying the energy transfer efficiency and in turn permitting an accurate determination of the melting efficiency. It is indicated that the weld process variables can dramatically affect the melting efficiency. This limiting value is shown to depend on the weld heat flow geometry as predicted by analytical solutions to the heat flow equation and as demonstrated by the recent empirical data. A new dimensionless parameter is used to predict the melting efficiency and is shown to correlate extremely well with recent empirical data. This simple prediction methodology is notable because it requires only a knowledge of the weld schedule and the material properties in order to estimate melting efficiency. 22 refs., 16 figs.
The contact of aluminum-based melts with liquid water has been shown to be explosive in many experiments performed by the aluminum industry and in several nuclear reactor experiments and accidents. In order to obtain quantitative information relating to the fuel-coolant interactions that might occur with aluminum-based fuel, a laboratory-scale experimental study is being performed at Sandia National Laboratories. The overall objective of this research program is to provide an understanding of the mechanism of steam explosions with the melt compositions expected in several hypothetical core meltdown accident scenarios in production reactors. In this program it has been demonstrated that rapid exothermic metal-water reactions can accompany the steam explosions under certain conditions resulting in enhanced energy release and in the concomitant generation of hydrogen. 4 refs., 2 figs.
A hydraulic fracture stimulation conducted during 1983-1984 in non-marine, deltaic, Mesaverde strata at a depth of 7100 ft (2164 m) was cored in a deviated well in 1990. The observed fracture consists of two fracture intervals, both containing multiple fracture strands (30 and 8, respectively). While the core had separated across many of the fracture strands during coring, the rock remained intact across 20 of the strands, preserving materials within the fractures. Nine of the remaining intact strands were split open, revealing abundant gel residue on the surfaces of every fracture examined. Of 7 strands associated with major bedding planes, 4 displayed offsets of 1-3 mm at the planes and 3 strands had their growth terminated at the planes, showing the importance of bedding (petrophysical heterogeneities) on fracture propagation. Implications of all these findings for hydraulic fracture design and analysis are also addressed.
The INTEROP Achievement Award will be given to those customer organizations that make the most effective use of internetworking technology to further their own specific business aims. This paper is an application for this award by Sandia National Laboratories. Given are the network application, topology, and the types of systems to which it is applied.(JEF)
One problem with electromagnetic time domain finite-difference simulations in cylindrical coordinates is the rapidly decreasing characteristic dimension of the cells as r approaches zero. In order to satisfy the Courant stability condition a small time step is needed to insure stability, which is undesirable because it increases the cost of the simulation. In our presentation, we will describe a method which uses a rectangular grid and an annular cylindrical grid which overlap to perform electromagnetic simulations of cylindrical geometries. The two grids are connected by interpolating the field at the grid points of one grid using field values from the second grid. 2 refs.
Solder joints in electronic packages are electrical interconnections that also function as mechanical bonds. The solder often constrains materials of different coefficients of thermal expansion that, when thermal fluctuations are encountered, causes the solder joint to experience cyclical deformation. Due to the catastrophic consequences of electrical or mechanical failure of solder joints, a great deal of work has been performed to develop a better understanding of the metallurgical response of solder joints subjected to thermomechanical fatigue. This work reviews the microstructural and mechanical evolution that occurs in solder joints during thermomechanical fatigue. The eutectic Sn-Pb solder alloy is highlighted. Unlike most materials that experience thermomechanical fatigue, solder is commonly used at temperatures of up to nine-tenths of its melting point. Therefore extensive creep, solid state diffusion, recrystallization and grain growth occur in this alloy resulting in the evolution of a heterogeneous coarsened band through which failure eventually takes place. Two other solder alloys are compared with the Sn-Pb eutectic, a Pb-rich Sn-Pb alloy and a ternary near eutectic (40In-40Sn-20Pb, all alloys are given in wt. %). The Pb-rich alloy is a precipitated single phase matrix that does not evolve during thermomechanical fatigue and subsequently has a shorter lifetime. Conversely, the 40In-40Sn-20Pb solder is a two phase eutectic in which the microstructures refines during thermomechanical fatigue giving it a longer lifetime than the eutectic Sn-Pb solder. The microstructural processes that occur during thermomechanical fatigue and final fracture behavior are discussed for the three solder alloys. 47 refs., 14 figs.
The use of ground-based lasers to launch small payloads but large total masses into low-Earth orbit may prove to be the most innovative and potentially economical approach for accomplishing this important mission. Of the several possible schemes for laser propulsion, two are examined: (1) ablative momentum transfer using pulsed lasers; and (2) heat exchanger thrusters in conjunction with CW lasers. For an entry-level payload of {approximately}50 kg it is found that the former yields payload-to-power ratios < 0.5 kg/MW with a requirement for an average laser power of at least 100 MW, whereas the latter might yield 1 to 3 kg/MW with a laser power of several 10s of MW. One of the promising approaches that could yield a driver for such a system is the reactor-pumped laser FALCON, which scales to these power levels with the potential for long run times.
The Space Exploration Initiative (SEI) seeks to reestablish a U. S. program of manned and unmanned space exploration. The President has called for a program which includes a space station element, a manned habitation of the moon, and a human exploration of Mars. The NASA Synthesis Group has developed four significantly different architectures for the SEI program. One key element of a space exploration effort is the power required to support the missions. The Power Specialty Team of the Synthesis Group was tasked with assessing and evaluating the power requirements and candidate power technologies for such missions. Inputs to the effort came from existing NASA studies as well as other government agency inputs such as those from DOD and DOE. In addition, there were industry and university briefings and results of solicitations from the AIAA and the general public as a part of the NASA outreach effort. Because of the variety of power needs in the SEI program, there will be a need for multiple power system technologies including solar, nuclear and electrochemical. Due to the high rocket masses required to propel payloads to the moon and beyond to Mars, there is great emphasis placed on the need for high power density and high energy density systems. Power system technology development work is needed and results will determine the ultimate technology selections.
Shockwave techniques have been used for decades to study the dynamic states of matter in temperature and pressure regimes inaccessible by other methods. These techniques have been employed in a wide variety of scientific, military, and commercial applications. A principal scientific objective has been to determine high-pressure equations of state (EOS) to ultra-high pressures; pressures of tens of Mbar have been reported for several materials. Most recently, these methods have been used for studies of thermophysical properties under shock compression, including phase transition kinetics, and mechanical properties, such as the high-pressure yield strength. In this paper, a brief discussion of recent developments in high velocity launchers is given. Advances in techniques for subjecting materials to a wide range of loading conditions is presented, including selected illustrations of shockwave measurements to Mbar pressures. 54 refs.
The modern investigation of the thermochemical behavior of salt started in the mid-1930's and, for what appears to be a very narrow discipline, salt mechanics'' has acquired considerable technical depth and sophistication. The last three decades have been especially productive in constitutive model development and laboratory investigations of time-dependent creep behavior. This has been largely due to anticipated use of domal or bedded salt deposits as sites for radioactive waste repositories and to expanded need for hydrocarbon and feedstock storage caverns. Salt is an interesting material, in that it is metal like''; and, therefore, constitutive modeling can draw upon a large body of metal deformation information to arrive at appropriate models of behavior. Testing apparatus and methods have centered on either uniaxial or triaxial compression to obtain steady state and transient creep responses. Flow and fracture potentials have been defined. Validation attempts of the models against field data, although limited, have proved promising. 27 refs.
Conference Record - 7th Biennial IEEE-USA Careers Conference: Change and Competitiveness and Careers
James, M.R.
Upward Feedback is a program that gives employees and opportunity to anonymoulsy provide their manager with feedback concerning the manager's job performance. It is an opportunity for managers to receive confidential feedback evaluating their implementation of corporate values and management behaviors as perceived by those who work for them. This feedback can come from employees who report directly to the manager, that is, one level below them (referred to as direct reports), or from those two reporting levels below them (referred to as skip-level reports). Managers then share information with their employees in feedback meetings and develop action plans to address areas of concern. Sandia National Laboratories has developed and implemented an Upward Feedback Pilot Program and follow up survey. This paper discussed the program and the lessons learned.
Typical aerospace joints lead to apertures which are very narrow and thick. We develop a systematic analytical treatment of this type of aperture (precise conditions of validity given in the text), although the results are also applicable to apertures on a thin conducting body. An antenna integral equation with an equivalent antenna radius is used to describe the voltage across a narrow and thick aperture in a perfectly conducting plane. The result shows the voltage across the aperture has very high Q (quality-factor) resonances, because the equivalent radius is exponentially small. Transmitted power also exhibits similar behavior. When metallic and gasket losses are included, a nonlocal antenna model together with a local transmission line model is used to describe the voltage across the aperture. Good metallic walls, such as aluminum, are found to significantly reduce the penetration of an aperture of typical dimensions. Gaskets with relatively small loss tangents also result in significant penetration reductions. A simple transmission line with uniform loading is used to approximate the governing equation described in. In the lossless limit and for moderate fatness parameter this simple transmission line model is comparable in accuracy to King's three-term theory. The loading of the bolts or hinges is demonstrated to act in many cases as a short. Finally, the low frequency penetration for a narrow slot aperture of arbitrary depth is characterized by the equivalent polarizabilities (dominating longitudinal component) as a function of the ratio of the depth to the width and ratio of the length to the width. A general relationship is shown to exist between the equivalent radius and the transverse line dipole moments of a slot aperture with depth. The longitudinal equivalent polarizabilities of antennas and slot apertures are used to derive a coupling energy bound for a step function EMP. 9 refs., 8 figs.
The strength of deuterium bonding to the walls of closed cavities within Si was determined in ion-beam experiments. These studies circumvented an inherent indeterminacy in the analysis of external-surface desorption and thereby allowed the Si-H surface bond energy to be quantified for the first time. The bond energy is 2.5 {plus minus} 0.2 eV for submonolayer coverages. 14 refs., 3 figs.
Scan path testing and debugging offers a structured, proven way to debug and test arbitrarily complex electronic systems. The interface and equipment requirements are far lower than traditional debug and test techniques. The system is also completely testable even when physically remote from the lab where it was originally developed. This report describes our experience using scan techniques to debug the EPSILON-2 processor board, a system with over 300 ICs and over 2500 independently controllable and observable test points. The debug time of the circuit was greatly reduced by the adoption of scan path methodology. The use of expensive test equipment was drastically reduced, and the level of control of the circuitry increased. We have run tests on the processor from physically remote sites. Our experiences are described, and the adoption of scan path techniques is shown to be simple enough that it should be useful in all electronic projects. 8 refs., 12 figs.
Sandia National Laboratories is a large multi-program DOE laboratory. The Recorded Information Management Division (RIM) has an expanding mission to meet Sandia's needs for cost-effective management in information from creation to final disposition in accordance with applicable regulations and requirements. An analysis based on the need to meet requirements and to improve business practice was successful in convincing management to allocate increased resources to the RIM Compliance Project.
Historically, the electronics industry has always attempted to increase the speed of electronic components and decrease the size of electronic assemblies by developing and manufacturing smaller and faster basic level components (e.g., integrated circuits). However, it is now becoming apparent that the next significant advancement in electronic assembly size and speed may come not as a result of smaller and faster devices, but rather as a consequence of smaller and more closely spaced packages. This increased packaging density will occur at early levels of assembly as industry moves towards multichip modules. It will also occur at later packaging steps as industry continues to expand the use of surface mount technology (SMT) and mixed mounting technology (through hole attachment as well as SMT on one circuit board). Furthermore, there will be an increased propensity to use higher packaging density on printed wiring boards (PWB) and to place more PWB's in a given volume at yet the next level of packaging. One class of materials on which this advanced packaging technology will place severe new demands will be the alloys used to join assemblies and subassemblies (e.g. solders and brazes). These materials will be taxed both from the perspective of enhanced manufacturability as well as greater in-service robustness. It is the objective of this paper, through the use of selected case studies, to illustrate how advanced microstructural characterization techniques can be used to improve packaging technology. The specific case studies discussed are: (1) Microstructural Characterization of Solders, (2) Microstructural Characterization of Solder Joint Embrittlement of Leaded, Surface Mount Transistors (3) Microstructural Characterization of Metal/Ceramic Brazes in Electronic Applications, and (4) Microstructural Characterization of Direct Brazing of Graphite to Copper. 25 refs., 16 figs.
A number of models that predict the impulse generated in solid targets by short high-intensity radiation loads are described. It is shown that the impulse is insensitive to the details of the energy deposition and interaction processes. Thus with the proper nondimensionalization and normalization, all the models are known to be very nearly equivalent. 5 refs., 5 figs., 1 tab.