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Measurements of thermal distortion of the submarine intermediate reactor "Mark A" moderator tube

Description: Report presenting a moderator tube of the Submarine Intermediate Reactor (SIR) ("Mark A") subjected to temperature gradients considered to be representative of those occurring in the reactor during operation. The distortion of the tube was measured under two conditions: with the ends of the tube retained in the same manner at the reactor and with the ends of the tube simply supported.
Date: December 1952
Creator: Kemp, R. H. & Morgan, W. C.
Partner: UNT Libraries Government Documents Department

Generation of Compositionally Graded Ga{sub 1-x}In{sub x}Sb Seed by Solute Diffusion

Description: Compositionally graded single crystalline <100> seed of Ga{sub 1-x}In{sub x}Sb has been grown in a single experiment using a solute diffusion method. The present technique is simple and less time consuming compared to the conventional boot-strapping approach previously used for generating ternary seeds. Starting from an InSb <100> single crystalline seed, a seed of Ga{sub 0.6}In{sub 0.4}Sb has been grown. The effect of temperature gradient on the crystalline quality of seeds grown using this method has been discussed.
Date: August 29, 2002
Creator: Dutta, P.S.; Rajagopalan, G.; Gutmann, R.J. & Nichols, G.
Partner: UNT Libraries Government Documents Department

Sound Propagation Into the Shadow Zone in a Temperature-Stratified Atmosphere Above a Plane Boundary

Description: Note presenting an investigation of the sound field about a point source over a plane boundary in the presence of a vertical temperature gradient, which represents one phase of a general program of research in atmospheric acoustics. In this report, geometrical ray acoustics is employed to derive the ray paths and intensity distribution about a source located in a uniformly stratified medium. Results indicate that the existence of a temperature gradient, which leads only to a simple refraction of sound rays, can be in conjunction with the ground boundary result in the formation of a "shadow zone".
Date: October 1955
Creator: Pridmore-Brown, David C. & Ingard, Uno
Partner: UNT Libraries Government Documents Department

Thermal, Electrical and Mechanical Response to a Quench in Nb3Sn Superconducting Coils

Description: During a quench, significant temperatures can arise as a magnet's stored energy is dissipated in the normal zone. Temperature gradients during this process give rise to localized strains within the coil. Reactive forces in the magnet structure balance the electromagnetic and thermal forces and maintain on equilibrium. In this paper we present a complete 3D finite element analysis of a racetrack coil. Specifically, the analysis focuses on thermal, electrical and mechanical conditions in a 10T Nb{sub 3}Sn coil built and tested as part of LBNL's Subscale Magnet Program. The study attempts to simulate time history of the temperature and voltage rise during quench propagation. The transient thermal stress after the quench is then evaluated and discussed.
Date: October 1, 2003
Creator: Ferracin, P.; Caspi, S.; Chiesa, L.; Gourlay, S.A.; Hafalia, R.r.; Imbasciati, L. et al.
Partner: UNT Libraries Government Documents Department

Determination of the Evaporation Coefficient of D2O

Description: The evaporation rate of D{sub 2}O has been determined by Raman thermometry of a droplet train (12-15 {micro}m diameter) injected into vacuum ({approx}10{sup -5} torr). The cooling rate measured as a function of time in vacuum was fit to a model that accounts for temperature gradients between the surface and the core of the droplets, yielding an evaporation coefficient ({gamma}{sub e}) of 0.57 {+-} 0.06. This is nearly identical to that found for H{sub 2}O (0.62 {+-} 0.09) using the same experimental method and model, and indicates the existence of a kinetic barrier to evaporation. The application of a recently developed transition state theory (TST) model suggests that the kinetic barrier is due to librational and hindered translational motions at the liquid surface, and that the lack of an isotope effect is due to competing energetic and entropic factors. The implications of these results for cloud and aerosol particles in the atmosphere are discussed.
Date: March 26, 2008
Creator: Drisdell, Walter S.; Cappa, Christopher D.; Smith, Jared D.; Saykally, Richard J. & Cohen, Ronald C.
Partner: UNT Libraries Government Documents Department

Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Description: Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.
Date: May 1, 1996
Creator: Kiggans, J.O.: Tiegs, T.N. & Kimrey, H.D.
Partner: UNT Libraries Government Documents Department

Simulation of ion-temperature-gradient turbulence in tokamaks

Description: Results are presented from nonlinear gyrokinetic simulations of toroidal ion temperature gradient (ITG) turbulence and transport. The gyrokinetic simulations are found to yield values of the thermal diffusivity significantly lower than gyrofluid or IFS-PPPL-model predictions. A new phenomenon of nonlinear effective critical gradients larger than the linear instability threshold gradients is observed, and is associated with undamped flux-surface-averaged shear flows. The nonlinear gyrokineic codes have passed extensive validity tests which include comparison against independent linear calculations, a series of nonlinear convergence tests, and a comparison between two independent nonlinear gyrokinetic codes. Our most realistic simulations to date have actual reconstructed equilibria from experiments and a model for dilution by impurity and beam ions. These simulations highlight the need for still more physics to be included in the simulations
Date: October 14, 1998
Creator: Cohen, B I; Dimits, A M; Kim, C; Mattor, N; Nevins, W M; Parker, S E et al.
Partner: UNT Libraries Government Documents Department

Finite Element Modeling of a Microhotplate for Microfluidic Applications

Description: A hand-held chemical laboratory ({mu}ChemLab) is being developed that utilizes a silicon- nitride-supported microhotplate in the front-end, gas sampling and preconcentration stage. Device constraints include low-power (<200mW at 5V), rapid heating (<20msec), and a relatively uniform temperature distribution throughout the heated area ({approximately}3mm{sup 2}). To optimize for these criteria, the electro-thermal behavior of the microhotplate was modeled using Thermal Analysis System (TAS). Predicted steady-state and transient behavior agree well with infrared (IR) microscope data and measured transient response for a low-stress silicon nitride thermal conductivity of k{sub n} = 6.4 x 10{sup {minus}2} W x (cm x {degree}C){sup {minus}1} and a convection coefficient of h{sub cv} = 3.5 x 10{sup {minus}3} W x (cm{sup 2} x {degree}C){sup {minus}1}. The magnitude of h{sub cv} is framed in the context of vacuum measurements and empirical data. Details and limitations of the IR measurement are discussed. Finally, the efficacy of methods for reducing thermal gradients in the microhotplate's active area is presented.
Date: March 9, 1999
Creator: Benson, D.A.; Frye-Mason, G.C.; Manginell, R.P. & Rosato, D.A.
Partner: UNT Libraries Government Documents Department

Shear flow effects on ion thermal transport in tokamaks

Description: From various laboratory and numerical experiments, there is clear evidence that under certain conditions the presence of sheared flows in a tokamak plasma can significantly reduce the ion thermal transport. In the presence of plasma fluctuations driven by the ion temperature gradient, the flows of energy and momentum parallel and perpendicular to the magnetic field are coupled with each other. This coupling manifests itself as significant off-diagonal coupling coefficients that give rise to new terms for anomalous transport. The authors derive from the gyrokinetic equation a set of velocity moment equations that describe the interaction among plasma turbulent fluctuations, the temperature gradient, the toroidal velocity shear, and the poloidal flow in a tokamak plasma. Four coupled equations for the amplitudes of the state variables radially extended over the transport region by toroidicity induced coupling are derived. The equations show bifurcations from the low confinement mode without sheared flows to high confinement mode with substantially reduced transport due to strong shear flows. Also discussed is the reduced version with three state variables. In the presence of sheared flows, the radially extended coupled toroidal modes driven by the ion temperature gradient disintegrate into smaller, less elongated vortices. Such a transition to smaller spatial correlation lengths changes the transport from Bohm-like to gyrobohm-like. The properties of these equations are analyzed. The conditions for the improved confined regime are obtained as a function of the momentum-energy deposition rates and profiles. The appearance of a transport barrier is a consequence of the present theory.
Date: March 1, 1995
Creator: Tajima, T.; Horton, W.; Dong, J.Q. & Kishimoto, Y.
Partner: UNT Libraries Government Documents Department

X-ray radiography of fracture flow and matrix imbibition in Topopah Spring Tuff under a thermal gradient

Description: A method of imaging the flow of liquid in fractures and matrix imbibition in tuff using x-ray radiography has been developed and a formulation for the calculation of saturation in the matrix based on x-ray radiography is presented. Experiments were performed using different thermal gradients and hydrostatic heads. The distance that liquid penetrates the boiling region was found to be dependent on hydrostatic head: during the highest-head experiment, liquid water penetrated the entire fracture and continued to pass through the boiling region. For experiments where flow stopped at the boiling region, x-ray images indicate crystal deposition along the fracture. In some cases, when the sample was cooled, fracture flow resumed, and in other cases the fractures were sealed and flow did not continue.
Date: March 1, 1997
Creator: Roberts, J.J., Lin, W.
Partner: UNT Libraries Government Documents Department

Studies of impurity mode and ITG mode in toroidal plasmas

Description: The impurity mode and {eta}{sub i} mode driven by impurity ions with outwardly peaked density profiles, just as it is at the boundary of tokamak plasmas, and the ion temperature gradient, respectively, are studied in high temperature toroidal plasmas. The gyrokinetic theory is applied and finite Larmor radius effects of both hydrogenic and impurity ions are included. It is found that the impurity mode is enhanced by the ion temperature gradient. In addition, the impurity ions with outwardly peaked density profiles are demonstrated to have destabilizing effects on the {eta}{sub i} mode. These two modes are strongly coupled to each other so that it is impossible to distinguish between them when both the driving mechanisms axe strong enough to drive the corresponding mode unstable independently. The correlation of the results with nonlinear simulations and the experimental observations are discussed.
Date: April 1, 1995
Creator: Dong, J.Q. & Horton, W.
Partner: UNT Libraries Government Documents Department

Using Multispectral Imaging to Measure Temperature Profiles and Emissivity of Large Thermionic Dispenser, Cathodes

Description: Thermionic dispenser cathodes are widely used in modern high-power microwave tubes. Use of these cathodes has led to significant improvement in performance. In recent years these cathodes have been used in electron linear accelerators (LINACs), particularly in induction LINACs, such as the Experimental Test Accelerator at Lawrence Livermore National Laboratory and the Relativistic Test Accelerator at Lawrence Berkeley National Laboratory. For induction LINACs, the thermionic dispenser cathode provides greater reproducibility, longer pulse lengths, and lower emittance beams than does a field emission cathode. Los Alamos National Laboratory is fabricating a dual-axis X-ray radiography machine called dual-axis radiograph hydrodynamic test (DARHT). The second axis of DARHT consists of a 2-kA, 20-MeV induction LINAC that uses a 3.2-MeV electron gun with a tungsten thermionic-dispenser cathode. Typically the DARHT cathode current density is 10 A/cm{sup 2} at 1050 C. Under these conditions current density is space-charge limited, which is desirable since current density is independent of temperature. At lower temperature (the temperature-limited regime) there are variations in the local current density due to a nonuniform temperature profile. To obtain the desired uniform current density associated with space-charge limited operation, the coolest area on the cathode must be at a sufficiently high temperature so that the emission is space-charge limited. Consequently, the rest of the cathode is emitting at the same space-charge-limited current density but is at a higher temperature than necessary. Because cathode lifetime is such a strong function of cathode temperature, there is a severe penalty for nonuniformity in the cathode temperature. For example, a temperature increase of 50 C means cathode lifetime will decrease by a factor of at least four. Therefore, we are motivated to measure the temperature profiles of our large-area cathodes.
Date: September 2001
Creator: Simmons, D. F.; Fortgang, C. M. & Holtkamp, D. B.
Partner: UNT Libraries Government Documents Department

Laboratory and Field Studies Related to Radionuclide Migration at the Nevada Test Site in Support of the Underground Test Area Program and Hydrologic Resources Management Project October 1, 1999-September 30, 2000

Description: This report details the work of Chemistry Division personnel from Los Alamos National Laboratory in FY 2000 for the US Department of Energy/Nevada Operations Office under their Defense Programs and Environmental Restoration Divisions. Los Alamos is one of a number of agencies collaborating in an effort to describe the present and future movement of radionuclides in the underground environment of the Nevada Test Site. This fiscal year we collected and analyzed water samples from a number of expended test locations at the Nevada Test Site. We give the results of these analyses and summarize the information gained over the quarter century that we have been studying several of these sites. We find that by far most of the radioactive residues from a nuclear test are contained in the melt glass in the cavity. Those radionuclides that are mobile in water can be transported if the groundwater is moving due to hydraulic or thermal gradients. The extent to which they move is a function of their chemical speciation, with neutral or anionic materials traveling freely relative to cationic materials that tend to sorb on rock surfaces. However, radionuclides sorbed on colloids may be transported if the colloids are moving. Local conditions strongly influence the distribution and movement of radionuclides, and we continue to study sites such as Almendro, which is thermally quite hot, and Bilby where radionuclides do not appear to have moved a short distance from the cavity. We have begun field use of a tool that allows us to measure important groundwater properties in situ. We conclude our report by noting document reviews and publications produced in support of this program.
Date: January 1, 2001
Creator: Finnegan, David L. & Thompson, Joseph L.
Partner: UNT Libraries Government Documents Department

Corrosion of structural materials by lead-based reactor coolants.

Description: Advanced nuclear reactor design has, in recent years, focused increasingly on the use of heavy-liquid-metal coolants, such as lead and lead-bismuth eutectic. Similarly, programs on accelerator-based transmutation systems have also considered the use of such coolants. Russian experience with heavy-metal coolants for nuclear reactors has lent credence to the validity of this approach. Of significant concern is the compatibility of structural materials with these coolants. We have used a thermal convection-based test method to allow exposure of candidate materials to molten lead and lead-bismuth flowing under a temperature gradient. The gradient was deemed essential in evaluating the behavior of the test materials in that should preferential dissolution of components of the test material occur we would expect dissolution in the hotter regions and deposition in the colder regions, thus promoting material transport. Results from the interactions of a Si-rich mild steel alloy, AISI S5, and a ferritic-martensitic stainless steel, HT-9, with the molten lead-bismuth are presented.
Date: November 16, 2000
Creator: Abraham, D. P.; Leibowitz, L.; Maroni, V. A.; McDeavitt, S. M. & Raraz, A. G.
Partner: UNT Libraries Government Documents Department

Vapor CdCl2-Optimization and Screening Experiments for an All Dry Chloride Treatment of CdS/CdTe Solar Cells

Description: A dry vapor treatment of CdCl2 is being developed as an alternative approach to the conventional solution CdCl2 treatment of CdS/CdTe devices. In this alternative process, the CdS/CdTe substrates are vapor treated in a close-spaced sublimation configuration. A 16-run Plackett-Burman screening experiment identified source temperature, substrate temperature, and treatment time as being the most significant parameters in the process. Subsequently, a 20-run Central Composite Design showed that a source temperature of 380-390 C, a temperature gradient (DT) of 5 C, and a time of 10 minutes provides the most process tolerant combination, yielding a total-area efficiency of 12.6%. A strong interaction between DT and treatment time was also identified. The model indicated that for a small DT, device performance improved with decreasing time, whereas at larger values of DT, performance increased with increasing time.
Date: October 1, 1998
Creator: Mahathongdy, Y.; Wolden, C. A.; Baldwin, R. M. & Albin, D. S.
Partner: UNT Libraries Government Documents Department

Performance of cryogenically cooled, high-heat-load silicon crystal monochromators with porous media augmentation

Description: The performance of two Si crystal x-ray monochromators internally cooled with liquid nitrogen was tested on the F2-wiggler beamline at the Cornell High Energy Synchrotron Source (CHESS). Both crystals were (111)-oriented blocks of rectangular cross section having identical dimensions. Seven 6.4-mm-diameter coolant channels were drilled through the crystals along the beam direction. In one of the crystals, porous Cu mesh inserts were bonded into the channels to enhance the heat transfer. The channels of the second crystal were left as drilled. Symmetric, double-crystal rocking curves were recorded simultaneously for both the first and third order reflections at 8 and 24 keV. The power load on the cooled crystal was adjusted by varying the horizontal beam size using slits. The measured Si(333) rocking curve of the unenhanced crystal at 24 keV at low power was 1.9 arcsec FWHM. The theoretical width is 0.63 arcsec. The difference is due to residual fabrication and mounting strain. For a maximum incident power of 601 W and an average power density of about 10 W/MM{sup 2}, the rocking curve was 2.7 arcsec. The rocking curve for the enhanced crystal at low power was 2.4 arcsec. At a maximum incident power of 1803 W and an average power density of about 19 W/mm{sup 2} the rocking curve width was 2.2 arcsec FWHM. The use of porous mesh augmentation is a simple, but very effective, means to improve the performance of cryogenically cooled Si monochromators exposed to high power x-ray beams.
Date: January 1, 1996
Creator: Rogers, C.S.; Mills, D.M.; Assoufid, L. & Graber, T.
Partner: UNT Libraries Government Documents Department

Study of micro-instabilities in toroidal plasmas with negative magnetic shear

Description: The micro-instabilities driven by a parallel velocity shear, and a temperature gradient of ions are studied in toroidal plasmas with negative magnetic shear. Both the fluid and the gyro-kinetic formulations are investigated. It is found that for a broad range of parameters, the linear growth rates of the modes are lower, and the threshold temperature gradient {eta}{sub icr} is higher for plasmas with negative magnetic shear compared to plasmas with positive magnetic shear of equal magnitude. The reduction in the growth rate (with negative shear), although not insignificant, does not seem to be enough to account for the dramatic improvement in the confinement observed experimentally. Other possible physical mechanisms for the improved confinement are discussed.
Date: March 1, 1996
Creator: Dong, J.Q.; Zhang, Y.Z.; Mahajan, S.M. & Guzdar, P.N.
Partner: UNT Libraries Government Documents Department

Experimental issues in in-situ synchrotron x-ray diffraction at high pressure and temperature by using a laser-heated diamond-anvil cell

Description: An integrated technique of diamond-anvil cell, laser-heating and synchrotron x-ray diffraction technologies is capable of structural investigation of condensed matter in an extended region of high pressures and temperatures above 100 GPa and 3000 K. The feasibility of this technique to obtain reliable data, however, strongly depends on several experimental issues, including optical and x-ray setups, thermal gradients, pressure homogeneity, preferred orientation, and chemical reaction. In this paper, we discuss about these experimental issues together with future perspectives of this technique for obtaining accurate data.
Date: December 1, 1997
Creator: Yoo, C.S.
Partner: UNT Libraries Government Documents Department


Description: The electron temperature gradient (ETG) mode is a likely contributor to electron thermal transport in tokamaks. The ETG modes are dominantly unstable for poloidal wavelengths shorter than the ion gyroradius (high-k) where the ion response is adiabatic. Thus, they do not directly produce ion thermal or momentum transport or particle transport. Two potential mechanisms whereby ETG modes could produce transport in these channels are explored in this paper: a nonlinear coupling between high-k ETG modes and ions at low-k and a direct coupling when ETG modes and ion temperature gradient (ITG) modes are unstable in overlapping wavenumber ranges. It will be shown that the particle and momentum transport required to match experiment is small compared to the ETG driven electron thermal transport. Even quasilinearly ETG modes can produce ion transport if the ITG and ETG modes are both unstable at low-k. The implications of this for transport will be explored at the quasilinear level. A new gyro-Landau-fluid (GLF) closure model has been constructed in order to build a transport model which can include the coupling between electron and ion modes including trapped particles. The first growth rate spectra from this model will be shown to give an accurate approximation to the kinetic linear growth rates of drift-ballooning modes in tokamaks.
Date: July 2, 2004
Partner: UNT Libraries Government Documents Department

Length Scale Correlations of Cellular Microstructures in Directionally Solidified Binary System

Description: In a cellular array, a range of primary spacing is found to be stable under given growth conditions. Since a strong coupling of solute field exists between the neighboring cells, primary spacing variation should also influence other microstructure features such as cell shape and cell length. The existence of multiple solutions is examined in this study both theoretically as well as experimentally. A theoretical model is developed that identifies and relates four important microstructural lengths, which are found to be primary spacing, tip radius, cell width and cell length. This general microstructural relationship is shown to be valid for different cells in an array as well as for other cellular patterns obtained under different growth conditions. The unique feature of the model is that the microstructure correlation does not depend on composition or growth conditions since these variables scale microstructural lengths to satisfy the relationship obtained in this study. Detailed directional solidification experimental studies have been carried out in the succinonitrile-salol system to characterize and measure these four length scales. Besides the validation of the model, experimental results showed additional scaling laws to be present. In the regime where only a cellular structure is formed, the shape of the cell, the cell tip radius and the length of the cell are all found to scale individually with the local primary spacing. The presence of multiple solutions of primary spacing is also shown to influence the cell-dendrite transition that is controlled not only by the processing variables (growth velocity, thermal gradient and composition) but also by the local cell spacing. The cell-dendrite transition was found not to be sharp, but occurred over a range of processing conditions. Two critical conditions have been identified such that only cells are present below lower critics condition, and only dendrites are formed above the upper ...
Date: August 1, 2002
Creator: Shen, Yunxue
Partner: UNT Libraries Government Documents Department

Effect of Surface Condition and Heat Treatment on Corrosion of Type 316L Stainless Steel in a Mercury Thermal Convection Loop

Description: Two thermal convection loops (TCLs) fabricated from 316L stainless steel and containing mercury and a variety of 316L coupons representing variable surface conditions and heat treatments have been operated continuously for 2000 h. Surface conditions included surface ground, polished, gold-coated, chemically etched, bombarded with Fe to simulate radiation damage, and oxidized. Heat treatments included solution treated, welded, and sensitized. In addition, a nitrogen doped 316L material, termed 316LN, was also examined in the solution treated condition. Duplicate TCLs were operated in this experiment--both were operated with a 305 C peak temperature, a 65 C temperature gradient, and mercury velocity of 1.2 m/min--but only one included a 36 h soak in Hg at 310 C just prior to operation to encourage wetting. Results indicate that the soak in Hg at 310 C had no lasting effect on wetting or compatibility with Hg. Further, based on examination of post-test wetting and coupon weight loss, only the gold-coated surfaces revealed significant interaction with Hg. In areas wetted significantly by Hg, the extreme surface of the stainless steel (ca 10 {micro}m) was depleted in Ni and Cr compared to the bulk composition.
Date: October 17, 2000
Creator: Pawel, S.J.
Partner: UNT Libraries Government Documents Department