Publications

Results are presented of a detailed survey of the present state of scientific understanding of cloud electrification processes and lightning warning technology. A review is given of the principles of operation and demonstrated performance factors of lightning strike location technologies and associated commercial products. Emphasis is given to the local lightning warning problem, which is divided into two categories: detection and tracking of active storms that originate outside of and move into the declared safety zone, and early detection of cloud electrification that initiates within the zone. A prototype single-station warning system design is presented that is intended to accumulate data simultaneously from a complement of different types of sensors during intervals immediately preceding the onset of lightning conditions within the area of coverage. The resultant data base will be analyzed statistically to identify the most promising combinations of early warning indicators and to quantify their reliability as a function of the warning intervals they provide.

Multiple sources of variation will often affect the stability of a manufacturing process. Items from different batches may vary because of variation both within a batch and among different batches. Potential sources of variation include within run, run-to-run and week-to-week differences in a manufacturing process. If multiple sources of variation are present, traditional control chart methods may not be appropriate. In this report we develop control charts for monitoring these sources of variation as well as the process average. An example of how to use the control charts is given, using Field 89 data from functional testing of the MC3854 neutron tube.

GROPE is a program that examines the input to a finite element analysis (which is in the GENESIS database format) or the output from an analysis (in the EXODUS database format). GROPE allows the user to examine any value in the database. The display can be directed to the user`s terminal or to a print file.

A Quality Management System was defined by Sub-Process teams within Data Analysis Department 2722. Each of the processes is concerned with a different phase of work for intemal customers (members of the Department) and for external customers (Sandians external to the Department, or agencies outside of Sandia). This report identifies and defines the crucial Work Processes of the Department, where each Process is documented in a separate ``Chapter.`` This report documents the effort of the Data Analysis Department to effectively provide services to its customers and to assess/improve these services. Thus this report is intended to be a ``living document`` for the Department and each member of the Department is expected to follow its guidelines.

Solar heat gain inside a radiation-shielded forklift operator compartment can be a significant problem due to the ``greenhouse effect``. Battery power prohibits the use of a refrigerant type of air-conditioning system, which limits the interior temperature to be approximately equal to the outside ambient temperature through alternative cooling methods. A heat transfer analysis is performed to determine the amount of solar heat gain in this type of mobile vehicle shelter. Various results are presented that depend on exterior surface finish and temperature difference between inside and outside ambient. An amount of forced air flow along with several design recommendations are then specified to rid the compartment of this excess heat.

Sandia National Laboratories operates the Primary Standards Laboratory for the Department of Energy, Albuquerque Operations Office (DOE/AL). This report summarizes metrology activities that received emphasis in the first half of 1992 and provides information pertinent to the operation of the DOE/AL system wide Standards and Calibration Program.

Aprepro is an algebraic preprocessor that reads a file containing both general text and algebraic, string, or conditional expressions. It interprets the expressions and outputs them to the output file along with the general text. The syntax used in Aprepro is such that all expressions between the delimiters and are evaluated and all other text is simply echoed to the output file. Aprepro contains several mathematical functions, string functions, and flow control constructs. In addition, functions are included that, with some additional files, implement a units conversion system and a material database lookup system. Aprepro was written primarily to simplify the preparation of parameterized input files for finite element analyses at Sandia National Laboratories; however, it can process any text file that does not use the characters.

Calculations of residual stresses in braze joints are required to validate designs for a variety of metal/ceramic joining applications. In particular, finite element analysis (FEA) codes have the capability of incorporating either elastic-plastic or minimum creep rate constitutive models for the braze material. This paper presents both elevated temperature mechanical properties correlations for the eutectic Ag-Cu alloy, along with FEA results which use this data in calculating residual stresses in a generic metal/ceramic ``shear'' type braze joint. Three constitutive relations have been developed for eutectic Ag-Cu alloy: (i) an elastic/plastic correlation incorporating temperature-dependent yield stress and work hardening data, (ii) a high temperature minimum creep rate correlation with a temperature-dependent stress exponent and (iii) a minimum creep rate correlation using the Garofalo hyperbolic sine (sinh) equation. FEA calculations are presented for a eutectic Ag-Cu braze joint between metallized alumina ceramic and either Fe-29Ni-17Co or Fe-27Ni-25Co alloys using the three different constitutive relations for the brazement. The two creep correlations, since they are time-dependent, permit a study of the effect of various cooldown cycles on the maximum residual stress in the alumina ceramic. For the cooldown profiles studied in this paper, lower residual stresses are predicted in the ceramic-relative to the elastic-plastic model - when either of the two creep models are used as the constitutive law for the eutectic Ag-Cu braze joint. A second important result is that the simulations which incorporate the Fe-29-Ni-17Co alloy show higher peak stresses than the Fe-27Ni-25Co alloy at 420°C, along with much lower peak stresses compared to Fe-27Ni-25Co alloy at room temperature. The reason for this somewhat surprising behavior can be understood in terms of the coefficient of thermal expansion for the two Fe-Ni-Co alloys.

GJOIN is a two- or three-dimensional mesh combination program. GJOIN combines two or more meshes written in the GENESIS mesh database format into a single GENESIS mesh. Selected nodes in the two meshes that are closer than a specified distance can be combined The geometry of the mesh databases can be modified by scaling, offsetting, revolving, and mirroring. The combined meshes can be further modified by deleting, renaming, or combining material blocks, sideset identifications, or nodeset identifications. GJOIN is one of the mesh generation tools in the Sandia National Laboratories Engineering Analysis Code Access System (SEACAS). GJOIN is typically used with the other SEACAS mesh generation codes GEN3D, GENSHELL, GREPOS, and Aprepro.

A description of ion-irradiation-induced reduction in the photoluminescence (PL) signal from porous silicon is given and a simple model which is consistent with a nanocrystalline Si structure is presented. Ion irradiation with 250 keV Ne is used to controllably reduce the integrated PL signal by 20% after a fluence of 4*1012 Ne cm-2 and completely eliminate the PL signal after a fluence of 4*1013 Ne cm-2. The use of vacuum and air annealing to recover ion-induced damage is also described, but the high temperatures for annealing cause elimination of the PL signal.

Pyro shock loads are generated in many missile or rocket systems when stages are separated or shrouds are removed. These shocks are localized, of short rise time (10's of ns) and of very high stress level. This paper will document some anomalous behavior that occurs when pyro shock accelerometers (Endevco 7270A) are exposed to levels of high frequency shock that is higher than the manufacturer's recommended limits. Such shocks occur in many pyro shock events. Standard, accepted recording techniques can produce totally erroneous data with no obvious indicator that the data is in error. Wide band data recording, along with Fourier Analysis of the data, and dynamic analysis, made by the gage manufacturer of the transducer, allow recognition of some of the non-standard response modes excited but no method of quantifying the corrupted data has been developed. Wide band recording, which will preserve the data in the gage resonance range and above, are required to insure understanding of these pyro shock events.

We have measured the efficiency (tracks per incident neutron) of pure CR-39 for detecting DD and DT neutrons. Neutrons having average energies of 2.9 MeV (DD) and 14.8 MeV (DT) were produced by a 200-keV electrostatic accelerator and the neutron yields were measured using the associated particle counting technique. All CR-39 samples irradiated by DD or DT neutrons were etched for 2 h in a 70°, 6.25-N- NaOH bath. For bare CR-39, the efficiencies for detecting 2.9- and 14.8-MeV neutrons were found to be (1.3±0.4)×10 -4 and (5.0±1.8)×10-5, respectively. We also investigated using CR-39 and polyimide as proton radiators. For detecting 2.9-MeV neutrons, the radiators had no significant effect on efficiency; but for detecting 14.8-MeV neutrons the polyimide radiator increased the efficiency to (7.8±2.8)×10-5.

This report describes preliminary probabilistic sensitivity analyses of long term gas and brine migration at the Waste Isolation Pilot Plant (WIPP). Because gas and brine are potential transport media for organic compounds and heavy metals, understanding two-phase flow in the repository and the surrounding Salado Formation is essential to evaluating long-term compliance with 40 CFR 268.6, which is the portion of the Land Disposal Restrictions of the Hazardous and Solid Waste Amendments to the Resource Conservation and Recovery Act that states the conditions for disposal of specified hazardous wastes. Calculations described here are designed to provide guidance to the WIPP Project by identifying important parameters and helping to recognize processes not yet modeled that may affect compliance. Based on these analyses, performance is sensitive to shaft-seal permeabilities, parameters affecting gas generation, and the conceptual model used for the disturbed rock zone surrounding the excavation. Brine migration is less likely to affect compliance with 40 CFR 268.6 than gas migration. However, results are preliminary, and additional iterations of uncertainty and sensitivity analyses will be required to provide the confidence needed for a defensible compliance evaluation. Specifically, subsequent analyses will explicitly include effects of salt creep and, when conceptual and computational models are available, pressure-dependent fracturing of anhydrite marker beds.

Iterative, annual performance-assessment calculations are being performed for the Waste Isolation Pilot Plant (WIPP), which is a planned underground repository in southeastern New Mexico for the disposal of transuranic radioactive waste. The performance-assessment calculations estimate long-term (10,000-year) radionuclide releases from the disposal system to the accessible environment. The estimation of the releases is probabilistic in nature, requiring system parameters to be described with probability distributions. Because direct experimental data in some areas are presently insufficient or unavailable to form the required distributions, researchers at Sandia National Laboratories have used a formalized expert-judgment elicitation procedure to determine the state of knowledge in these areas. Expert judgment was used to estimate the concentrations of specific radionuclides in a repository brine that might be forced up an intruding borehole, and also to estimate the distribution coefficients to determine the retardation of radionuclides in the overlying Culebra Dolomite. The variables representing these concentrations and coefficients have been shown by 1990 sensitivity analyses to be among the set of parameters making the greatest contribution to the uncertainty in WIPP performance assessment predictions. Using available information, the experts (one expert panel addressed concentrations and a second panel addressed retardation) were briefed on the problem of insufficient experimental data and were formally elicited to obtain probability distributions that characterize the uncertainty in fixed, but unknown, quantities. The probability distributions developed by the experts were incorporated into the 1991 and 1992 performance-assessment calculations.

Progress in Z-pinch experiments at Sandia's Saturn facility have underscored a need for an absolute yield measurement for DD fusion neutrons. The technique chosen for making this absolute yield measurement was neutron activation of indium metal samples. To calibrate the technique, a 175-keV deuteron beam was allowed to impinge on a 3.0-μm-thick erbium deuteride target, producing neutrons through the 2H(d,n)3He fusion reaction. The neutron flux produced at 0° and incident on nominal 5-g indium samples was determined by the associated particle method. This method employed protons measured from the 2H(d,p)3H reaction to infer the neutron flux produced. After neutron irradiation, the activity of the indium samples was measured with a Ge gamma-ray detector. The total activity of the metastable state 115mIn (336.23 keV) was measured, compared with the total incident flux, and a calibration factor (indium counts/neutron/gram of indium) determined. For completeness, a calibration factor for DT neutrons from the 3H(d,n)4He fusion reaction was also obtained through the measured activity of the metastable state 114mIn(190.29 keV). The experiment and the measured calibration factors for both reactions are described in the paper.

The CR-39/range-filter technique measures ion energy by determining the maximum filter thickness which ions can penetrate. CR-39 located behind the filter records the ions. This method is used to measure peak voltage in pulsed power accelerators. We investigated range and straggling effects in this diagnostic by exposing it to 8- and 15-MeV protons for both Al and Ta filters. The range agreed with published values to better than ±6%. The range straggling decreased for higher incident ion energy and lower atomic number, as expected, although there were differences up to a factor of 1.7 between the experimental values and predictions. The dependence of the track diameter distribution on ion energy enabled us to establish a signature which is characteristic of ions which penetrate a filter, via straggling. These results can be used to evaluate the errors present when this diagnostic is used to measure accelerator voltage.

In recent proton beam experiments on PBFA-II, foam-filled gold targets and gas-filled spherical exploding pushers were shot as physics targets. Surrounding these targets were gold foils used to characterize the beam. The target fabrication and characterization are presented in this paper.

Because a direct measurement of the voltage (V) in pulsed power bremsstrahlung sources can be difficult, the energy spectrum of x rays emitted is sometimes used to infer V. Both the voltage and current in such sources vary with time. Moreover, for modern x-ray simulators with multiple cathodes, multiple voltages may exist simultaneously. We demonstrate here how such sources lead to systematic errors in several types of simple-to-field x-ray voltage measurements, especially those with broad spectral response functions, when calibrated against constant-potential bremsstrahlung spectra.

The laser-initiated LEVIS source is intended to provide an active source in the PBFA II ion diode by generation of a preformed lithium anode plasma. Visible spectra recorded with a streaked spectrograph are used to help evaluate the source performance. The absence of Stark shifting of the Li I 2p-3d and 2s-2p light confirms that a plasma is created over the anode surface. At lower LEVIS laser intensities this plasma erodes back toward the anode as the ion beam current grows. Considerable improvements in anode plasma purity have been noted when the anode is heated for several hours. The LEVIS source microdivergence estimated from the carbon ion transverse energy is less than 14 mrad, meeting the near term requirements for PBFA II target experiments. © 1992 National Technical Information Service.

Helium removal experiments were conducted in TEXTOR with a small helium self-pumping module located in a modified ALT-I limiter head. The module contained two heated nickel alloy trapping plates, a nickel deposition filament array, a Langmuir probe, flux probe, and thermocouples. The experiment examined plasma helium removal via trapping of helium ions in the deposited nickel surfaces. Such helium removal was successfully observed, with about 10% of the helium in a 10% He/D plasma being removed in a ∼1 s period. The module was found to be compatible with overall tokamak operation with essentially no sputtered nickel entering the core plasma. The temperature rise on the ion-exposed inner trapping plate, during a plasma shot, is consistent with a local sheath potential of ∼3kTe. Post-tokamak test examination of the trapping plates shows helium atom concentrations in the deposited nickel consistent with the observed helium removal, and shows very small D concentrations. © 1992 Elsevier Science Publishers B.V. All rights reserved.

We present results from initial experiments with a high impedance applied-B extraction diode on the SABRE ten stage linear induction accelerator (6 MV, 300 kA). We have demonstrated efficient coupling of power from the accelerator through an extended MTTL (Magnetically Insulated Transmission Line) into a high intensity ion beam. Both MITL electron flow in the diode region and ion diode behavior, including ion source turn-on, virtual cathode formation and evolution, enhancement delay, and ion coupling efficiency, are strongly influenced by the geometry of the diode insulating magnetic field. For our present diode electrode geometry, electrons from the cathode feed play a large role in the evolution of the virtual cathode. Both experimental data and particle-in-cell numerical simulations show that a uniform radial distribution of these feed electrons is required for uniform ion emission and efficient diode operation. © 1992 National Technical Information Service.

An active ion source, LEVIS (Laser Evaporation Ion Source), using a short pulsed Nd laser (1.06 m, 8ns) to form a thin Li vapor layer and a tuned dye laser (670.8nm, μsec) for ionization is being developed at Sandia. The LEVIS process has been developed and characterized in the laboratory. Initial experiments using these ion sources on PBFA-II produced ion beams with a low fraction of lithium ions and with low voltages. Recent experiments using improved distribution optics and anode cleaning techniques are described. © 1992 National Technical Information Service.

Significant progress in the generation and focusing of ion beams generated by PBFA-II has enabled us to begin experiments in ion beam coupling and target physics. Data from these experiments indicates that we can reproducibly deliver 50 KJ of 5 MeV protons at an average power intensity of 3.5 TW/cm 2 to a 6 mm diameter by 6 mm tall cylindrical target. The implosion of spherical exploding pusher targets and the radiation production from foam-filled cylindrical thermal targets were studied in these experiments. They demonstrated that high quality target data can be obtained on PBFA-II. Specific deposition rates of about 100 TW/g were achieved in these experiments. This deposition rate marks the boundary between the regime where enhanced ion deposition and equation-of-state (EOS) physics are studied (10-100 TW/g) and the regime where radiation-conversion and radiation-transport physics are studied (100-1000 TW/g). Experiments in the radiation-conversion regime are now of primary importance in our program because these experiments will test the target physics basis for ion-driven ICE Experiments using a thin film LiF source have produced an intensity of 1 TW/cm 2 of lithium ions. This beam has a potential specific deposition rate of 300-400 TW/g in hydrocarbon foams. However, radiation conversion experiments will require an increased total energy content of this beam in order to overcome the specific internal energy of the foam. Further increases in ion beam intensity and energy content are being pursued in a multi-pronged attack. Understanding and controlling ion beam divergence is the highest program priority. Present understanding indicates that instabilities in the electron sheath cause significant ion beam divergence. Our understanding suggests that this contribution to the ion divergence can be decreased by operating the diode at a low enhancement through the use of high applied magnetic fields or by modifying the electron distribution near the anode via electron limiters. The new 9 cm radius Compact Diode has the capability of generating 8 T applied magnetic fields which will enable divergence experiments in the low-enhancement, high-B regime. Experiments with the LEVIS (Laser Evaporation Ion Source) lithium source have demonstrated the existence of a preformed plasma, as determined by visible-emission spectroscopy of the anode plasma. Work on improving lithium purity with this source is in progress. This active anode plasma will be used in experiments testing the effectiveness of electron limiters in controlling ion beam divergence. We are also working to understand the interrelation between accelerator coupling, diode physics, and ion beam focusing in order to optimize the diode configuration to maximize the power intensity on target. Success in these experiments will provide an adequate lithium beam for performing target experiments exploring radiation conversion and radiation transport physics in ion-driven ICF. © 1992 National Technical Information Service.

We have built a five-channel, x-ray detector array based on diamond photoconducting detectors (PCDs). The diamond elements have dimensions of 3 mm × 1 mm × 1 mm (or 0.5 mm). We use diamond PCDs for their stability, flat spectral response, and low leakage currents. The good time response of diamond PCDs is due to the 100-ps electron/hole recombination time. Filters were designed to give information in the 1-10-keV spectral region. Calibration of the diamond PCDs showed sensitivities between 4 and 7 × 10-4 A/W for a bias of 100 V. We shall present data from z-pinch experiments on Saturn.

Using concepts of decision analysis, this paper examines how government policy makers might consider and evaluate the contribution of additional inspection, openness, and confidence-building measures to diplomatic questions involving compliance with arms control agreements. During the current debate among parties to the Biological Weapons Convention as to what constitutes effective verification of compliance with that Convention, these analytical concepts were employed to evaluate some proposed inspection or confidence-building measures. Some of the salient points not bound up in the confidentiality of on-going negotiations will be summarized here.