Metallurgical Analyses of Niobium for Superconducting Radio Frequency Cavities

Superconducting radio frequency cavities have gained use in accelerator systems for particle physics research. Careful production of the cavities has the greatest influence on their efficiencies as uniform interior surfaces are required for high accelerating gradients. Small variations in the surfaces of these cavities, such as inclusions, voids, and cracks, cause large deficiencies in the accelerating gradients. Processes to remove such deficiencies usually include eddy current scanning, buffered chemical polishing, and electropolishing. These methods do not provide a consistent means of producing a uniform interior surface. The effectiveness of tumbling as a mass finishing technique was analyzed. This process completely removed the weld line. The effects of weld line removal on cavity efficiencies will be examined.

Developing a Routing Priority Map for Geospatial Modeling of CO2 Pipeline Deployment in the People's Republic of China

Carbon capture and sequestration (CCS) technologies are currently being researched as a potential component of a global portfolio of technologies to help reduce anthropogenic emissions of carbon dioxide (CO2) to the atmosphere. In China, currently a leading emitter of CO2 and a potentially critical player in future carbon emissions reduction strategies, it is important to evaluate the economic feasibility of CCS to understand its potential for large-scale deployment. This paper describes the development of a high resolution geospatial model to assist in efforts to estimate the construction costs of pipelines for transport of CO2from sources to storage sites. The model assigns relative weights to geographic features throughout mainland China to form a relative prioritization map that may be used to model pipeline routing along paths that are likely to represent the lowest cost paths. The final routing priority map (RPM) differentiates between areas according to their relative cost for routing from sources to sinks. The RPM represents the weighted combination of all overlapping geographic and cultural features included in the model. By using the RPM in conjunction with a routing protocol, grid cells with low priority values (i.e., those for which construction and/or societal costs would be higher) would be avoided in favor of cells with higher priority values, all else equal. This mode of estimating least-cost pipeline routing could represent a significant enhancement to existing methodologies used to estimate CO2 transport costs for CCS in China.

Creating Improved Cathode Materials for Lithium-Ion Batteries

Lithium-ion (Li-ion) batteries are key to the development of Hybrid Electric Vehicles (HEVs) and Plug-in Hybrid Electric Vehicles (PHEVs). One challenge to overcome that will lead to better-working and longer-lasting batteries for more efficient hybrid vehicles is to change and refine the cathode material. The objective of the research was to create a new cathode material that could overcome the constraints associated with the traditional LiCoO2 cathode by reducing or eliminating the amount of costly cobalt and adding a combination of nickel and manganese to the transition metal layer. The compound Li[Ni0.5Mn0.5]O2 has previously been shown to increase the capacity and energy of the battery while still retaining the layered formation of the LiCoO2. The precursor material, which consisted of either nickel cobalt manganese hydroxide or nickel manganese carbonate, was reacted with sodium carbonate in an oven at varying temperatures. The Na[M]O2, with M being the combination of cobalt, nickel, and manganese, underwent an ion exchange in hexanol with an excess of lithium bromide to obtain Li[M]O2. Initial rate tests examining the performance and life of the batteries have demonstrated that this new cathode material operates slightly better than the current baseline material and has the potential to lead to better batteries for HEVs and PHEVs. Further studies must be done to continue to maximize the performance of these materials.

Implementation of Viscous Effects in RELAP5-3D Thermal Hydraulics Code

The Reactor Excursion Leak Analysis Program (RELAP5-3D) is a world class thermal hydraulics safety analysis code developed at the Idaho National Laboratory (INL) to address safety concerns in light water nuclear reactors. The purpose of this project is to implement viscous effects into the current RELAP5-3D code. Viscous effects have been thoroughly studied and implemented in many Computational Fluid Dynamics (CFD) codes. However, because of the original purpose of RELAP5-3D, viscous effects on fluid dynamics were not implemented during initial code development. As demand for coupling RELAP5-3D with CFD codes increases, implementing viscous effects in RELAP5-3D is becoming more important both for calculation accuracy and code coupling stability. The momentum flux equations used in RELAP5 resemble the Navier-Stokes Equations (NSE) but doesn't include the viscous contributions. Therefore, a double central finite difference method is used to discretize second order differentials of the viscous terms in both Cartesian and cylindrical geometries. A total of 20 new terms were introduced and the original RELAP5 wall boundary condition was changed from free slip to no slip. The original code architecture was not changed during any of the coding to avoid introducing new limitations.

Post-Deposition Induced Conductivity in Pulsed Laser Irradiated Metal Doped Zinc Oxide Films

he optical and electrical properties of doped solution-deposited and rf sputter-deposited thin metal oxide films were investigated following post deposition pulsed laser irradiation. Solution deposited films were annealed at 450 ºC. Following the heating regiment, the transparent metal oxide films were subjected to 355 nm pulsed Nd:YAG laser irradiation (4 nsec pulsewidth) at fluences between 5 and 150 mJ/cm2. Irradiation times at pulse frequencies of 30 Hz ranged from seconds to tens of minutes. Film densification, index change and a marked increase in conductivity were observed following irradiation in air and under vacuum of Al:ZnO (AZO), Ga:ZnO (GZO), and In:ZnO (IZO) films deposited on silica substrates. Despite the measured increase in conductivity, all films continued to show high transparency on the order of 90% at wavelengths from the band edge well into the near infrared region of the spectrum. Laser energies required for turning on the conductivity of these films varied depending upon the dopant. Irradiations in air yielded resistivity measurements on the order of 16 Ω•cm. Resistivities of films irradiated under vacuum were on the order of 0.1 Ω•cm. The increase in conductivity can be attributed to the formation of oxygen vacancies and subsequent promotion of free carriers into the conduction band. All irradiated films became insulating again after around 24 hours. Oxygen atoms in air became reduced by electrons in the metal conduction band and diffused into vacancies in the lattice. The rate of this reduction process depends on the type of dopant. This work also sheds light on the damage threshold, correlating the optical properties with the presence of free carriers that have been introduced into the conduction band. All films were characterized by means of UV-VIS-NIR transmission spectroscopy, visible and UV Raman spectroscopy and Hall measurements. Analysis of interference fringes in measured transmission spectra allowed film density and refractive index to be evaluated while the Raman measurements showed an increase in LO mode intensity with respect to the TO mode intensity as the films became more conducting. Results of this study are not only important for the continued development of transparent conducting oxide films that find use in photovoltaic cells and solid state lighting modules, but also provide evidence for the role of free carriers in initiating the laser damage process in these wide bandgap metal oxide films.

Correcting the Energy Reconstruction of Photons Detected in the Electromagnetic Calorimeter

The outermost layer of the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility consists of an electromagnetic calorimeter (EC). The EC is composed of alternating layers of scintillator strips and lead sheets and covers a large portion of the angular range. The EC is used to detect particles,such as electrons, photons, and neutrons,that meet a certain energy threshold. When a particle enters the EC, it loses some of its energy and creates a shower of light that is picked up by the scintillators. The location and amount of this detected light is then used to help identify where and with what energy a particle entered the EC. However, this system has some inefficiency built into it; for example, its layers of lead absorb some of the light instead of recording it. Since the EC contains some unavoidable inefficiency and particles do not always deposit all of their energy, the energy recorded in the EC needs to be analyzed periodically to determine what corrections need to be made to identify the true energy of incident photons. Creating the correction helps to better identify photons and to better understand the intrinsic inefficiency in the EC. The focus of this project was to create a correction for the energy of photons detected in the EC and then use this correction to understand EC inefficiency. To do this, a reaction was picked that involves only electrons, protons, and neutral pi mesons that decay into two photons. The invariant mass of the photon pairs, which were considered to have originated from the same decay, was then compared to the known theoretical mass of the neutral pi meson. The known mass was used to identify how the energy of photons needed to be corrected for different energy levels. It was found that a correction function could be created to increase the accuracy of photon reconstruction. The correction function that was discovered varies considerably from a previous correction that was implemented in 2006. The new correction will be used to analyze data that contain photons at 0.3 GeV and greater. With this new correction implemented, the efficiency of assigning energy to incident photons in the EC has increased. Also, we used this information to estimate the overall efficiency of the EC in detecting photons,a process that hasn't been performed previously on CLAS.

Physical Modeling of Spinel Crystals Settling at Low Reynolds Numbers

The crystallization of large octahedral crystals of spinel during the high-level waste (HLW) vitrification process poses a potential danger to electrically heated ceramic melters. Large spinel crystals rapidly settle under gravitational attraction and accumulate in a thick sludge layer that may partially or completely block the glass discharge riser of the melter. The settling of single particles of different sizes and the motion of hindered settling front of different particle volume fraction suspensions were studied in stagnant, transparent-silicone oils at room temperature to help predict the settling behavior of spinel crystals in the riser. The dimensions and terminal settling velocities of single particles were measured using an optical particle-dynamics-analyzer. The data yielded an experimental shape factor for glass beads that differed only 0.73% compared to the theoretical shape factor for a perfect sphere. The experimental shape factor for the spinel crystals was smaller than that of the beads given the larger drag force caused by the larger surface area to volume ratio of the octahedral crystals, but matched the theoretically predicted value to within 10%. In the hindered settling experiments, both the glass bead and spinel suspensions were found to follow the predictions of the Richardson-Zaki equation with higher particle volume fractions settling at a slower rate. Particle concentration profiles obtained from color threshold analysis (CTA) indicated that for a given volume fraction the rate of clarification increases with an increase in settling vessel angle with respect to the vertical as predicted by the Ponder, Nakamura and Kuroda (PNK) model. The Stokes', Richardson-Zaki and PNK equations can adequately predict the accumulation rate of spinel crystals in the vertical or inclined glass discharge riser of HLW melters.

The Extreme C-terminus of Xeroderma pigmentosum group G protein Mediates Protein-Protein Interactions

Organisms across the evolutionary scale are equipped with complex and interconnected DNA repair pathways that are regulated by multifunctional proteins. These proteins mediate interactions by conformational changes and protein hand-offs in order to coordinate lesion detection and removal with vital cellular processes such as DNA replication, transcription and recombination. Mutations that disrupt repair protein functioning can lead to genomic instability, developmental and immunological abnormalities, and cancer and aging. Xeroderma pigmentosum group G (XPG) is one such multifunctional protein that plays a critical role in maintaining human genome stability. Point mutations in the XPG gene gives rise to an inherited photosensitive disorder, Xeroderma pigmentosum (XP) and truncation mutations cause the profound neurological and developmental disorder Cockayne syndrome (CS) combined with XP. The molecular basis of XPG in XP is well understood because XPG contains structure specific 3ˈ endonuclease activity that is critical to the repair of ultraviolet-damaged DNA in the nucleotide excision repair (NER) pathway. However, the clinical features of CS in XPG-CS patients are difficult to explain on the basis of defects in NER, which suggests that XPG possesses several poorly understood roles that are regulated by its unstructured non-enzymatic recognition (R) and carboxyl (C) terminal domains. These domains have been shown to mediate interactions with over fifteen proteins from multiple repair pathways. Studies conducted on these regions have identified novel scaffolding roles for XPG in transcription-coupled (TCR) and base excision (BER) repair, and recently a replication-associated function with proteins that process damaged replication forks. How XPG is involved in multiple pathways is of considerable interest. Considering the role of the XPG C-terminus in protein-protein interaction, this study involved bacterially expressing and purifying three sequential C-terminal subdomain constructs and screening interactions with seven proteins representing roles in different DNA replication and repair pathways. All seven proteins were found to interact with the same region of the C-terminus, which provides information critical towards identifying the amino acids uniquely required by each protein partner. This will allow one to genetically dissect the molecular basis of XPG in order to elucidate and remedy its involvement in the complex disease phenotype of XP-CS.

Thermal Conductivity Measurements of Graphite Samples

All materials have a property of thermal conductivity (k). As a measure of ability to conduct heat energy, k is a valuable number in heat transfer design and analysis. Knowing a material's value of thermal conductivity allows for proper selection in its use. The Applied Engineering Technology group at Los Alamos National Laboratory wishes to measure the thermal conductivity of various solid samples with minimal error. An apparatus was built in an attempt to measure a large range and variety of samples using a method combined from ASTM standards and the writer's ideas. The sample was heated on one end and cooled on the other. The temperature distribution across the sample was measured and a value of k calculated. Using Fourier's Law the results of the one material tested, graphite, produced a k value of 129.16 4.69 W/mK the first time, 126.63 2.90 W/mK the next and 127.31 2.27 W/mK in the final run. The expected result based on the manufacturer's data sheet was 130 W/mK. The apparatus can now be used to measure various samples. Additionally, methods have been developed to estimate the errors associated with each new measurement.

Power Measurement and Modulization in the Network Protocol Independent Performance Evaluator (NetPIPE)

In order to provide a more user-friendly environment and a clearer benchmark for computational efficiency and to promote America's energy security through reliable, clean and affordable energy, a version of the Network Protocol Independent Performance Evaluator (NetPIPE) was created, which was written completely in the object-oriented Python language. NetPIPE performs simple ping-pong tests for increasing message sizes to determine network bandwidth and latency. The base code created last year by Science Undergraduate Laboratory Internship student Torrey Dupras, which implemented NetPIPE using Python and a Python module written in C, was modified to be purely Python, and its efficiency was compared with the previous version. The NetPIPE package was also modified to include code which documents power use during a NetPIPE experiment and outputs the results of a NetPIPE run using the Python matplotlib module to show graphs of various data. The power data was obtained by using a Watts up? PRO meter which registers the base power consumption of a device once per second. The results of the investigation revealed that, for both the implementations, there appeared to be a correlation between network bandwidth and rate of energy consumed. Further, the Python module had about one-half the peak bandwidth of the C module; however, it was much more portable to operating systems other than Linux. As energy rather than computing speed becomes the dominant factor in computer performance, these experiments could provide a base for efficiency measurements in the future and also a greater ease of access for those wishing to perform those measurements.

Cadmium Sulfide and Titanium Dioxide Thin Film Nanostructures for Nanocrystal-Based Solar Cells

New solar cell architectures leverage nanostructured materials in attempting to achieve high light-to-electricity conversion efficiencies using low-cost materials and processes. One such example is a dye sensitized solar cell, wherein light is absorbed by an organic dye sensitizer (rather than by a semiconductor, as in a traditional solar cell), and the photogenerated charge transports out of the device through a nanostructured percolating titanium dioxide (TiO2) network. Because organic dyes have a limited spectral absorption range, they are not readily suited to capture all incident solar energy. Inorganic semiconductor quantum dots represent an alterative solar cell sensitizer with potential advantages because their spectral light absorption can be controlled by their size and composition. In principle, one can design a device having a spectral absorbance range well-matched to the incident solar spectrum by using an array of differently sized quantum dots – thereby providing a pathway to higher performance efficiencies. We use solution-phase chemistry to synthesize cadmium sulfide (CdS) quantum dots with precise diameter control over the range of 2 to 10 nanometers, and corresponding control of peak optical absorption from 320nm to 365nm. We produce CdS particles using a reverse micelle method using a surfactant (AOT in heptane) allowing further integration into thin film devices using solution processing. We have characterized the optical properties of thin films of both CdS and TiO2 nanocrystal using ultraviolet-visible spectroscopy in order to determine their absorbance. We have measured the nanocrystal film morphologies (size, structure, and thickness) using scanning electron microscopy and profilometry in order to understand the effects of different methods of film deposition (spin coating versus doctor-blading). Spin coating of both CdS and TiO2 nanocrystals yields uniform, three-dimensional nanocrystalline thin films. We have fabricated nanocrystal thin film devices by sandwiching nanocrystalline films of either CdS or TiO2 between a transparent indium-tin oxide electrical contact and an aluminum contact deposited by thermal evaporation. In both CdS and TiO2 nanocrystal devices, the device current increases with applied voltage. Under simulated solar illumination, the conductance of both CdS and TiO2devices increases, consistent with excitation of photogenerated carriers in the semiconductor nanocrystal film network.

Enzymatic Hydrolysis of Pretreated Corn Stover at High Solids Loadings

Biochemically produced cellulosic ethanol holds promise for the future of renewable liquid transportation fuels. Cellulosic ethanol must demonstrate an economic and large-scale viability in order to realize its full potential, and therefore intermediate processes such as enzymatic cellulose digestion must be more fully understood. In this study, the digestibility of dilute sulfuric acid pretreated corn stover was explored with respect to pretreatment severity, particle size, and regimen of pH adjustment before enzymatic hydrolysis. A series of experiments were performed at 20% insoluble solids weight, which is considered a high solids concentration because the material has an appreciable yield stress. Conversion of cellulose to glucose and cellobiose by 20 mg protein/ g cellulose GC220 enzyme was assessed over a period of 7 days. Each sample consisted of 60 g of slurry in 125-mL cylindrical bottles rotated on mechanized rollers at 4 rpm incubated at 48.5°C. Enzymatic hydrolysis of pretreated insoluble solids suspended in DI water and citrate buffer was performed in duplicate with and without mechanical size reduction. GC220 enzyme is most effective at a pH near 5, thus necessitating the buffer in the insoluble solids samples. Pretreated whole biomass slurries include soluble and insoluble solids and have a pH around 1.5 – 2.0. Ammonium hydroxide was mixed into the whole slurry samples to increase the pH before enzyme addition. Results showed that increasing extent of pretreatment predicts increasing digestibility of the pretreated insoluble biomass samples in both cases. Despite particle size reduction of 10-40%, there was little difference in conversion between the two different particle size distribution materials. The results indicate that pretreatment is effective and the well-established correlation between smaller particle size and high digestibility is not a simple causal relationship. In all cases, whole slurry is more difficult to break down with enzymes than insoluble solids suspended in the equivalent amount of water, but ultimately this challenge will need to be overcome to efficiently convert biomass to fuels. This series of experiments begins to show the effect that process-relevant conditions have on cellulose digestibility. Further investigation into these operations can lead to modifications and improvements that may help cellulosic ethanol become the liquid fuel of the future.

Monte Carlo Simulation of Neutron Background Sources in the Measurement of the 12C(α,γ)16O Reaction Rate

The 12C(α, γ)16O reaction rate strongly affects the relative abundances of chemical elements, as well as when core collapse supernovae occur. There have been several attempts to measure the reaction rate, but the Coulomb barrier between the carbon nucleus and the α-particle inhibits direct measurement at stellar energies. In a proposed experiment, a water-filled bubble chamber will be used to measure the reverse reaction rate. This technique will accurately measure the reaction rate closer to stellar energies than previous experiments have accomplished. A potential background source is photoneutrons from the γ-ray beam collimator entering the bubble chamber and generating a false signal. To minimize this effect, a Monte Carlo simulation has been performed to compare the number of photoneutrons created in lead, copper, and aluminum collimators. It was found that 30 cm of copper would be an effective beam collimator by stopping 99.8% of γ-rays and generating no photoneutrons. The simulation also compared the effectiveness of concrete, polyethylene, and water as neutron shields. These simulations show that polyethylene consistently stops the most neutrons at relevant energies. Further simulation will be required to evaluate shielding materials for cosmic ray neutrons, which can also generate false signals.

Crystallographic Characterization of GaN Nanowires by Raman Spectral Image Mapping

Obtaining structural information of nano structured materials often requires electron microscopy for suficient spatial and crystallographic resolution. This study uses Raman spectral imaging to extract information regarding crystalline orientation and structure by non-invasive means. Seeking a correlation between crystallographic facet and favored Raman mode, Gallium Nitride (GaN) nanowires were imaged by confocal Raman microscopy with a 532nm laser, and scanning electron microscopy. Raman spectral maps containing pixel-by-pixel spectra were acquired. Comparison to scanning electron microscope (SEM) images revealed that for regularly-shaped wires at least 230nm in width, the E2 mode is observed more strongly in the [1 1 2] and [-1 -1 2] "smooth" facets of the wire, while the A1(TO) mode is only observed in the [0 0 1] "rough" facet, suggesting a strong surface-structure dependence of Raman signal that can be exploited for imaging. Further experimentation on irregular and small wires that exhibit only the E2 peak, on other favored modes in GaN, and with other group III/V nitrides is recommended.

Simulation and Optimization of the HINS Ion Source Extraction System

The heart of the High Intensity Neutrino Source (HINS) linear accelerator (linac) is a magnetron-type, circular aperture H􀀀 source, which is currently being tested at Fermilab. Although this prototype already delivers the beam current and emittance required by the HINS project, an exploration of whether or not the performance of the source could be improved was undertaken. To this end, the extraction geometry of the source was simulated with SIMION 8.0 and Finite Element Method Magnetics. The effects of changing the angle of the extraction cone (cone angle), the size of the gap between the extraction cone and the source plate (extraction gap), and the aperture of the extraction cone (extraction aperture) were studied. These parameters were chosen because we thought that they would have the greatest impact on space charge effects, which is a major source of emittance growth in this ion source. Based on the results of these simulations, four different configurations were ultimately tested in the ion source. The simulations indicated that the final emittance of the source should be significantly decreased by utilizing geometry with a 45 degree cone angle, a 4 mm extraction gap with extraction voltage of 25000 V, and a 3 mm extraction aperture. Subsequent emittance measurements on the ion source have confirmed this result. This new geometry also allows the source to output a higher current beam with the same duty factor.