Stress Testing and Shoring Up Bank Capital (open access)

Stress Testing and Shoring Up Bank Capital

June report of the U.S. Congressional Oversight Panel describing their activities and findings regarding the stress testing of banks by federal banking regulators to examine the ability of banks to continue operations in a weaker than expected economic environment.
Date: June 9, 2009
Creator: United States. Congressional Oversight Panel.
Object Type: Report
System: The UNT Digital Library
Estimating Groundwater Concentrations from Mass Releases to the Aquifer at Integrated Disposal Facility and Tank Farm Locations Within the Central Plateau of the Hanford Site (open access)

Estimating Groundwater Concentrations from Mass Releases to the Aquifer at Integrated Disposal Facility and Tank Farm Locations Within the Central Plateau of the Hanford Site

This report summarizes groundwater-related numerical calculations that will support groundwater flow and transport analyses associated with the scheduled 2005 performance assessment of the Integrated Disposal Facility (IDF) at the Hanford Site. The report also provides potential supporting information to other ongoing Hanford Site risk analyses associated with the closure of single-shell tank farms and related actions. The IDF 2005 performance assessment analysis is using well intercept factors (WIFs), as outlined in the 2001 performance assessment of the IDF. The flow and transport analyses applied to these calculations use both a site-wide regional-scale model and a local-scale model of the area near the IDF. The regional-scale model is used to evaluate flow conditions, groundwater transport, and impacts from the IDF in the central part of the Hanford Site, at the core zone boundary around the 200 East and 200 West Areas, and along the Columbia River. The local-scale model is used to evaluate impacts from transport of contaminants to a hypothetical well 100 m downgradient from the IDF boundaries. Analyses similar to the regional-scale analysis of IDF releases are also provided at individual tank farm areas as additional information. To gain insight on how the WIF approach compares with other approaches …
Date: June 9, 2005
Creator: Bergeron, Marcel P. & Freeman, Eugene J.
Object Type: Report
System: The UNT Digital Library
Nuclear fusion driven by coulomb explosions of deuterium clusters (open access)

Nuclear fusion driven by coulomb explosions of deuterium clusters

We have examined the interaction of deuterium clusters with high intensity, ultrafast laser radiation. Upon irradiation a hot plasma is created with a sufficient temperature to produce nuclear fusion. We have seen that larger clusters produce more fusion neutrons than smaller clusters, consistent with a Coulomb explosion model. Fusion yield is currently limited by propagation effects. Using inter ferometric imaging we have examined the laser propagation and found that the laser energy is absorbed before it penetrates to the center (highest density region) of the gas jet.
Date: June 9, 2000
Creator: Zweiback, J.; Smith, R. A.; Cowan, T. E.; Hays, G.; Hartley, J.; Howell, R. et al.
Object Type: Article
System: The UNT Digital Library
Level Densities and Radiative Strength Functions in 170,171Yb (open access)

Level Densities and Radiative Strength Functions in 170,171Yb

Level densities and radiative strength functions in {sup 171}Yb and{sup 170}Yb nuclei have been measured with the {sup 171}Yb({sup 3}He, {sup 3}He{prime}{gamma}){sup 171}Yb and {sup 171}Yb({sup 3}He,{alpha}{gamma}){sup 170}Yb reactions. A simultaneous determination of the nuclear level density and the radiative strength function was made. The present data adds to and is consistent with previous results for several other rare earth nuclei. The method will be briefly reviewed and the result from the analysis will be presented. The radiative strength function for {sup 171}Yb is compared to previously published work.
Date: June 9, 2003
Creator: Agvaanluvsan, U.; Schiller, A.; Becker, J. A.; Berstein, L. A.; Guttormsen, M.; Mitchell, G. E. et al.
Object Type: Report
System: The UNT Digital Library
Fast Neutral Pressure Gauges in NSTX (open access)

Fast Neutral Pressure Gauges in NSTX

None
Date: June 9, 2004
Creator: Raman, R; Kugel, H; Gernhardt, R; Provost, T; Jarboe, T & Soukhanovskii, V
Object Type: Article
System: The UNT Digital Library
Expansion and Improvement of the NCSP Nuclear Criticality Safety Bibliographic Database (open access)

Expansion and Improvement of the NCSP Nuclear Criticality Safety Bibliographic Database

None
Date: June 9, 2004
Creator: Koponen, B L & Huang, S T
Object Type: Article
System: The UNT Digital Library
Real-Time Characterization of Virulence Factor Expression in Yersinia pestis Using a Green Fluorescent Protein Reporter System (open access)

Real-Time Characterization of Virulence Factor Expression in Yersinia pestis Using a Green Fluorescent Protein Reporter System

A real-time reporter system was developed to monitor the thermal induction of virulence factors in Yersinia pestis. The reporter system consists of a plasmid in Y. pestis in which the expression of green fluorescent protein (GFP) is under the control of the promoters for six virulence factors, yopE, sycE, yopK, yopT, yscN, and lcrE/yopN, which are all components of the Type III secretion virulence mechanism of Y. pestis. Induction of the expression of these genes in vivo was determined by the increase in fluorescence intensity of GFP in real time. Basal expression levels observed for the Y. pestis promoters, expressed as percentages of the positive control with GFP under the control of the lac promoter, were: yopE (15%), sycE (15%), yopK (13%), yopT (4%), lcrE (3.3%) and yscN (0.8%). The yopE reporter showed the strongest gene induction following temperature transition from 26 C to 37 C. The induction levels of the other virulence factors, expressed as percentages of yopE induction, were: yopK (57%), sycE (9%), yscN (3%), lcrE (3%), and yopT (2%). The thermal induction of each of these promoter fusions was repressed by calcium, and the ratios of the initial rates of thermal induction without calcium supplementation compared to …
Date: June 9, 2004
Creator: Forde, C.; Rocco, J.; Fitch, J. P. & McCutchen-Maloney, S.
Object Type: Article
System: The UNT Digital Library
The Early Days of Lattice Gauge Theory (open access)

The Early Days of Lattice Gauge Theory

I discuss some of the historical circumstances that drove us to use the lattice as a non-perturbative regulator. This approach has had immense success, convincingly demonstrating quark confinement and obtaining crucial properties of the strong interactions from first principles. I wrap up with some challenges for the future.
Date: June 9, 2003
Creator: Creutz, M.
Object Type: Article
System: The UNT Digital Library
Applications of X-Ray Lasers Utilizing Plasmas that are only a Few Times Ionised (open access)

Applications of X-Ray Lasers Utilizing Plasmas that are only a Few Times Ionised

With the advent of tabletop X-ray lasers that operate at high repetition rate more emphasis is being put on finding useful applications for these lasers. The 14.7 nm Ni-like Pd X-ray laser at Lawrence Livermore National Laboratory is being used to do many interferometer experiments. As detailed quantitative comparisons are done between experiments and code simulations it is clear that some of the assumptions used to analyze the experiments need to be modified as one explores plasmas that are only a few times ionized. In the case of aluminium plasmas that have been analyzed with interferometers there has been some unusual behavior where the fringe lines bend the wrong way. In this work we will discuss how the index of refraction for aluminium is far more complicated than generally assumed because there are significant contributions to the index from the continuum and line structure of the bound electrons that can dominate the free electron contribution and even cause the index to be greater than one. We will also discuss some potential applications of the high repetition rate Ne-like Ar X-ray laser at 46.9 nm. In particular we will present modeling that shows how the Ar laser could be used to …
Date: June 9, 2004
Creator: Nilsen, Joseph & Scofield, James H
Object Type: Article
System: The UNT Digital Library
Experimental Confirmation of CH Mandrel Removal from Be Shells (open access)

Experimental Confirmation of CH Mandrel Removal from Be Shells

Sputtered Be shells are made by sputter deposition of Be, with a radially graded Cu dopant as necessary, onto plastic mandrels supplied by General Atomics. Although the plastic mandrel may not be a design issue, it is a fielding issue because at cryo temperatures the plastic shrinks more than the Be and delaminates. We described in previous memos a proposed method for thermally removing the plastic by burning it in air at elevated temperature. A key aspect to this process is getting air in and out of the shell through the small diameter hole that must be laser drilled in the capsule wall to serve as a fill hole for the fuel. Because the hole is quite small, gas flow through the orifice must be forced, and an external pressure variation was suggested to do this. Further calculations showed that since the volume of the capsule is quite small and the amount of plastic in the shell by comparison is large, the ''pumping'' of air in and out of the shell must occur at least once per minute in order to supply enough O{sub 2} to completely burn the plastic to CO{sub 2} and H{sub 2}O in a reasonable time. …
Date: June 9, 2004
Creator: Cook, B; Letts, S & Buckley, S
Object Type: Report
System: The UNT Digital Library
Cleanliness improvements of NIF (National Ignition Facility) amplifiers as compared to previous large-scale lasers (open access)

Cleanliness improvements of NIF (National Ignition Facility) amplifiers as compared to previous large-scale lasers

Prior to the recent commissioning of the first NIF (National Ignition Facility) beamline, full-scale laser-amplifier-glass cleanliness experiments were performed. Aerosol measurements and obscuration data acquired using a modified flatbed scanner compare favorably to historical large-scale lasers and indicate that NIF is the cleanest large-scale laser built to date.
Date: June 9, 2004
Creator: Honig, J.
Object Type: Article
System: The UNT Digital Library
Science Based Stockpile Stewardship and RIA (open access)

Science Based Stockpile Stewardship and RIA

One aspect of Science Based Stockpile Stewardship (SBSS) is to improve the quality of neutron cross section data for certain isotopes. The isotopes of interest are used to monitor neutron and charged particle fluxes in environments of brief, intense neutron fluxes. The accuracy of flux determination is dependent on the accuracy of cross section data for the stable isotopes loaded into the system and the unstable isotopes produced when the neutrons are incident on the monitor. For isotopes with a half-life greater than one day it is possible, given the production rates of RIA, to make radioactive targets for neutron irradiation. This would require the ability to harvest isotopes at RIA, an onsite radiochemistry facility for processing the harvested material into a target, and an onsite neutron source facility. The radiochemistry facility will need to handle activity levels on the order of 100's of Curie's while the neutron source facility will need to provide high intensity ''monoenergetic'' neutrons from 10's keV to 20 MeV. For isotopes with a half-life much less than one day, only indirect methods can be used to get information on the neutron cross sections because of the lack of a target. Both experimental techniques will be …
Date: June 9, 2003
Creator: Ahle, L. E.; Bernstein, L. A.; Hausmann, M. & Vieira, D. J.
Object Type: Report
System: The UNT Digital Library
Perchlorate and Nitrate Remediation Efficiency and Microbial Diversity in a Containerized Wetland Bioreactor (open access)

Perchlorate and Nitrate Remediation Efficiency and Microbial Diversity in a Containerized Wetland Bioreactor

We have developed a method to remove perchlorate (14 to 27 {micro}g/L) and nitrate (48 mg/L) from contaminated groundwater using a wetland bioreactor. The bioreactor has operated continuously in a remote field location for more than two years with a stable ecosystem of indigenous organisms. This study assesses the bioreactor for long-term perchlorate and nitrate remediation by evaluating influent and effluent groundwater for reduction-oxidation conditions and nitrate and perchlorate concentrations. Total community DNA was extracted and purified from 10-g sediment samples retrieved from vertical coring of the bioreactor during winter. Analysis by denaturing gradient gel electrophoresis of short, 16S rDNA, polymerase-chain-reaction products was used to identify dominant microorganisms. Bacteria genera identified were closely affiliated with bacteria widely distributed in soils, mud layers, and fresh water. Of the 17 dominant bands sequenced, most were gram negative and capable of aerobic or anaerobic respiration with nitrate as the terminal electron acceptor (Pseudomonas, Acinetobacter, Halomonas, and Nitrospira). Several identified genera (Rhizobium, Acinetobactor, and Xanthomonas) are capable of fixing atmospheric nitrogen into a combined form (ammonia) usable by host plants. Isolates were identified from the Proteobacteria class, known for the ability to reduce perchlorate. Initial bacterial assessments of sediments confirm the prevalence of facultative …
Date: June 9, 2004
Creator: Daily, Bill, Jr.; Dibley, Valerie; Pinkart, Holly & Legler, Tina
Object Type: Article
System: The UNT Digital Library
Potential National Security Applications of Nuclear Resonance Fluorescence Methods (open access)

Potential National Security Applications of Nuclear Resonance Fluorescence Methods

The objective of this report is to document the initial investigation into the possible research issues related to the development of NRF-based national security applications. The report discusses several potential applications ranging from measuring uranium enrichment in UF6 canisters to characterization of gas samples. While these applications are varied, there are only a few research issues that need to be addressed to understand the limitation of NRF in solving these problems. These research issues range from source and detector development to measuring small samples. The next effort is to determine how best to answer the research issues, followed by a prioritization of those questions to ensure that the most important are addressed. These issues will be addressed through either analytical calculations, computer simulations, analysis of previous data or collection of new measurements. It will also be beneficial to conduct a thorough examination of a couple of the more promising applications in order to develop concrete examples of how NRF may be applied in specific situations. The goals are to develop an understanding of whether the application of NRF is limited by technology or physics in addressing national security applications, to gain a motivation to explore those possible applications, and to …
Date: June 9, 2009
Creator: Warren, Glen A.; Peplowski, Patrick N. & Caggiano, Joseph A.
Object Type: Report
System: The UNT Digital Library
Experiments in Molecular Optics - Final Rerport (open access)

Experiments in Molecular Optics - Final Rerport

A combined experimental and theoretical study of the manipulation of molecules with laser light is reported. It is shown that the dipole force produced by the electric field of a focused laser may be used to deflect, align, and orient molecules in a collision free environment. The feasibility of applying these techniques to nanolithography is explored, and a scheme for orienting molecules in space is developed.
Date: June 9, 2009
Creator: Gordon, Robert J.
Object Type: Report
System: The UNT Digital Library
Electrostatic Dust Detector with Improved Sensitivity (open access)

Electrostatic Dust Detector with Improved Sensitivity

Methods to measure the inventory of dust particles and to remove dust if it approaches safety limits will be required in next-step tokamaks such as ITER. An electrostatic dust detector, based on a fine grid of interlocking circuit traces, biased to 30 or 50 V, has been developed for the detection of dust on remote surfaces in air and vacuum environments. Gaining operational experience of dust detection on surfaces in tokamaks is important, however the level of dust generated in contemporary short-pulse tokamaks is comparatively low and high sensitivity is necessary to measure dust on a shot-by-shot basis. We report on modifications in the detection electronics that have increased the sensitivity of the electrostatic dust detector by a factor of up to 120, - a level suitable for measurements on contemporary tokamaks.
Date: June 9, 2008
Creator: D.P. Boyle, C.H. Skinner, and A. L. Roquemore
Object Type: Report
System: The UNT Digital Library
MADmap: A Massively Parallel Maximum-Likelihood Cosmic Microwave Background Map-Maker (open access)

MADmap: A Massively Parallel Maximum-Likelihood Cosmic Microwave Background Map-Maker

MADmap is a software application used to produce maximum-likelihood images of the sky from time-ordered data which include correlated noise, such as those gathered by Cosmic Microwave Background (CMB) experiments. It works efficiently on platforms ranging from small workstations to the most massively parallel supercomputers. Map-making is a critical step in the analysis of all CMB data sets, and the maximum-likelihood approach is the most accurate and widely applicable algorithm; however, it is a computationally challenging task. This challenge will only increase with the next generation of ground-based, balloon-borne and satellite CMB polarization experiments. The faintness of the B-mode signal that these experiments seek to measure requires them to gather enormous data sets. MADmap is already being run on up to O(1011) time samples, O(108) pixels and O(104) cores, with ongoing work to scale to the next generation of data sets and supercomputers. We describe MADmap's algorithm based around a preconditioned conjugate gradient solver, fast Fourier transforms and sparse matrix operations. We highlight MADmap's ability to address problems typically encountered in the analysis of realistic CMB data sets and describe its application to simulations of the Planck and EBEX experiments. The massively parallel and distributed implementation is detailed and scaling …
Date: June 9, 2009
Creator: Cantalupo, Christopher; Borrill, Julian; Jaffe, Andrew; Kisner, Theodore & Stompor, Radoslaw
Object Type: Article
System: The UNT Digital Library
Mode Conversion of Langmuir to Electromagnetic Waves with Parallel Inhomogeneity in the Solar Wind and the Corona (open access)

Mode Conversion of Langmuir to Electromagnetic Waves with Parallel Inhomogeneity in the Solar Wind and the Corona

Linear mode conversion of Langmuir waves to radiation near the plasma frequency at density gradients is potentially relevant to multiple solar radio emissions, ionospheric radar experiments, laboratory plasma devices, and pulsars. Here we study mode conversion in warm magnetized plasmas using a numerical electron fluid simulation code with the density gradient parallel to the ambient magnetic field B0 for a range of incident Langmuir wavevectors. Our results include: (1) Both o- and x-mode waves are produced for Ω ∝ (ωL)1/3(ωc/ω) somewhat less than 1, contrary to previous ideas. Only o mode is produced for Ω and somewhat greater than 1.5. Here ωc is the (angular) electron cyclotron frequency, ω the angular wave frequency, and L the length scale of the (linear) density gradient. (2) In the unmagnetized limit, equal amounts of o- and x-mode radiation are produced. (3) The mode conversion window narrows as Ω increases. (4) As Ω increases the total electromagnetic field changes from linear to circular polarization, with the o- and x- mode signals remaining circularly polarized. (5) The conversion efficiency to the x mode decreases monotonically as Ω increases while the o-mode conversion efficiency oscillates due to an interference phenomenon between incoming and reflected Langmuir/z modes. …
Date: June 9, 2008
Creator: Eun-Hwa Kim, Iver H. Cairns, and Peter A. Robinson
Object Type: Report
System: The UNT Digital Library
Use of Yb(III) Centered Near Infra-Red (NIR) Luminescence to Determine the Hydration State of a 3,2-HOPO based MRI-Contrast Agent (open access)

Use of Yb(III) Centered Near Infra-Red (NIR) Luminescence to Determine the Hydration State of a 3,2-HOPO based MRI-Contrast Agent

It has been more than a decade since the first reports of [Gd(Tren-Me-3,2-HOPO)(H{sub 2}O){sub 2}] as a potential new class of magnetic resonance imaging contrast agent (MRI-CA). The defining feature of these 1-methyl-3-hydroxypyridin-2-one (Me-3,2-HOPO) based compounds has been the use of a hexadentate ligand design, and hence an increase in the number of metal bound water molecules, without sacrificing complex stability compared to the typically octadentate contrast agents used commercially. Since that time, significant advances in the properties of these chelates have been steadily reported, including improvements in relaxivity, incorporation into macromolecular architectures and, recently, the first direct verification of solution structure using the discovery of Eu(III) centered luminescence with the isomeric 1-hydroxypyridin-2-one (1,2-HOPO) chelate as a sensitizing chromophore. Nonetheless, it has remained frustrating that direct measurements of the inner sphere hydration state, q, using luminescence techniques with the parent Me-3,2-HOPO compounds have remained elusive, even when direct laser excitation of weakly absorbing f-f transitions were employed (eg. for Eu(III) complexes). This failing can likely be traced to the presence of a low lying LMCT state which efficiently quenches metal based emission. Instead, estimates of the q and hence solution structure have relied on the fitting of relaxivity data to …
Date: June 9, 2008
Creator: Moore, Evan G.; Seitz, Michael & Raymond, Kenneth N.
Object Type: Article
System: The UNT Digital Library
In-situ post-deposition thermal annealing of co-evaporated Cu(InGa)Se2 thin films deposited at low temperatures (open access)

In-situ post-deposition thermal annealing of co-evaporated Cu(InGa)Se2 thin films deposited at low temperatures

The effects of deposition temperature and in-situ post-deposition annealing on the microstructure of coevaporated Cu(InGa)Se2 thin films and on the performance of the resulting solar cell devices have been characterized. Films were deposited at substrate temperatures of 150°C, 300°C and 400°C. Films were also deposited at these temperatures and then annealed in-situ at 550°C for 10 minutes. In as -deposited films without annealing, additional XRD reflections that may be due to a polytypic modification of the chalcopyrite phase were observed. Films deposited at 150°C were Se-rich. Post-deposition annealing caused microstructural changes in all films and improved the resulting solar cells. Only films deposited at 400°C, however, yielded high-efficiency devices after post-deposition annealing that were equivalent to devices made from films grown at 550°C. Films originally deposited at 300°C yielded devices after post-deposition annealing with VOC close to that of devices made from films grown at 550°C, despite smaller grain size.
Date: June 9, 2009
Creator: Wilson, James D.; McCandless, Brian E.; Birkmire, Robert W. & Shafarman, William N.
Object Type: Article
System: The UNT Digital Library
Improvement of Anadromous Fish Habitat and Passage in Omak Creek, 2008 Annual Report : February 1, 2008 to January 31, 2009. (open access)

Improvement of Anadromous Fish Habitat and Passage in Omak Creek, 2008 Annual Report : February 1, 2008 to January 31, 2009.

During the 2008 season, projects completed under BPA project 2000-100-00 included installation of riparian fencing, maintenance of existing riparian fencing, monitoring of at-risk culverts and installation of riparian vegetation along impacted sections of Omak Creek. Redd and snorkel surveys were conducted in Omak Creek to determine steelhead production. Canopy closure surveys were conducted to monitor riparian vegetation recovery after exclusion of cattle since 2000 from a study area commonly known as the Moomaw property. Additional redd and fry surveys were conducted above Mission Falls and in the lower portion of Stapaloop Creek to try and determine whether there has been successful passage at Mission Falls. Monitoring adult steelhead trying to navigate the falls resulted in the discovery of shallow pool depth at an upper pool that is preventing many fish from successfully navigating the entire falls. The Omak Creek Habitat and Passage Project has worked with NRCS to obtain additional funds to implement projects in 2009 that will address passage at Mission Falls, culvert replacement, as well as additional riparian planting. The Omak Creek Technical Advisory Group (TAG) is currently revising the Omak Creek Watershed Assessment. In addition, the group is revising strategy to focus efforts in targeted areas to …
Date: June 9, 2009
Creator: Dasher, Rhonda & Fisher, Christopher
Object Type: Report
System: The UNT Digital Library
Optimization of interdigitated back contact silicon heterojunction solar cells by two-dimensional numerical simulation (open access)

Optimization of interdigitated back contact silicon heterojunction solar cells by two-dimensional numerical simulation

In this paper, two-dimensional (2D) simulation of interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells is presented using Sentaurus Device, a software package of Synopsys TCAD. A model is established incorporating a distribution of trap states of amorphous-silicon material and thermionic emission across the amorphous-silicon / crystalline-silicon heterointerface. The 2D nature of IBC-SHJ device is evaluated and current density-voltage (J-V) curves are generated. Optimization of IBC-SHJ solar cells is then discussed through simulation. It is shown that the open circuit voltage (VOC) and short circuit current density (JSC) of IBC-SHJ solar cells increase with decreasing front surface recombination velocity. The JSC improves further with the increase of relative coverage of p-type emitter contacts, which is explained by the simulated and measured position dependent laser beam induced current (LBIC) line scan. The S-shaped J-V curves with low fill factor (FF) observed in experiments are also simulated, and three methods to improve FF by modifying the intrinsic a-Si buffer layer are suggested: (i) decreased thickness, (ii) increased conductivity, and (iii) reduced band gap. With all these optimizations, an efficiency of 26% for IBC-SHJ solar cells is potentially achievable.
Date: June 9, 2009
Creator: Lu, Meijun; Das, Ujjwal; Bowden, Stuart; Hegedus, Steven & Birmire, Robert
Object Type: Article
System: The UNT Digital Library
Optical and quantum efficiency analysis of (Ag,Cu)(In,Ga)Se2 absorber layers (open access)

Optical and quantum efficiency analysis of (Ag,Cu)(In,Ga)Se2 absorber layers

(Ag,Cu)(In,Ga)Se2 thin films have been deposited by elemental co-evaporation over a wide range of compositions and their optical properties characterized by transmission and reflection measurements and by relative shift analysis of quantum efficiency device measurements. The optical bandgaps were determined by performing linear fits of (αhν)2 vs. hν, and the quantum efficiency bandgaps were determined by relative shift analysis of device curves with fixed Ga/(In+Ga) composition, but varying Ag/(Cu+Ag) composition. The determined experimental optical bandgap ranges of the Ga/(In+Ga) = 0.31, 0.52, and 0.82 groups, with Ag/(Cu+Ag) ranging from 0 to 1, were 1.19-1.45 eV, 1.32-1.56 eV, and 1.52-1.76 eV, respectively. The optical bowing parameter of the different Ga/(In+Ga) groups was also determined.
Date: June 9, 2009
Creator: Boyle, Jonathan; Hanket, Gregory & Shafarman, William
Object Type: Article
System: The UNT Digital Library
Mass changes in NSTX Surface Layers with Li Conditioning as Measured by Quartz Microbalances (open access)

Mass changes in NSTX Surface Layers with Li Conditioning as Measured by Quartz Microbalances

Dynamic retention, lithium deposition, and the stability of thick deposited layers were measured by three quartz crystal microbalances (QMB) deployed in plasma shadowed areas at the upper and lower divertor and outboard midplane in the National Spherical Torus Experiment (NSTX). Deposition of 185 {micro}/g/cm{sup 2} over 3 months in 2007 was measured by a QMB at the lower divertor while a QMB on the upper divertor, that was shadowed from the evaporator, received an order of magnitude less deposition. During helium glow discharge conditioning both neutral gas collisions and the ionization and subsequent drift of Li{sup +} interrupted the lithium deposition on the lower divertor. We present calculations of the relevant mean free paths. Occasionally strong variations in the QMB frequency were observed of thick lithium films suggesting relaxation of mechanical stress and/or flaking or peeling of the deposited layers.
Date: June 9, 2008
Creator: C.H. Skinner, H.W. Kugel, A. L. Roquemore, PS. Krstic and A. Beste
Object Type: Article
System: The UNT Digital Library