Month

Fast Neutron Damage Studies on NdFeB Materials (open access)

Fast Neutron Damage Studies on NdFeB Materials

Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) since both accelerator and detectors will be subjected to large fluences of hadrons, leptons and {gamma}'s over the life of the facility [1]. While the linacs will be superconducting, there are still many uses for NdFeB in the damping rings, injection and extraction lines and final focus. Our understanding of the situation for rare earth, permanent magnet materials was presented at PAC03 [2]. Our first measurements of fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD MNRC) were presented at EPAC04 [3]. We have extended the doses, included other manufacturer's samples, and measured induced radioactivities which are discussed in detail.
Date: May 17, 2005
Creator: Anderson, S.; Spencer, J.; Wolf, Z.; /SLAC; Baldwin, A.; Pellett, D. et al.
Object Type: Article
System: The UNT Digital Library
PEP-II Large Power Supplies Rebuild Program at SLAC (open access)

PEP-II Large Power Supplies Rebuild Program at SLAC

Seven large power supplies (LGPS) with output ratings from 72kW to 270kW power PEP-II quad magnets in the electron-positron collider region. These supplies have posed serious maintenance and reliability problems since they were installed in 1997, resulting in loss of accelerator availability. A redesign/rebuild program was undertaken by the SLAC Power Conversion Department. During the 2004 summer shutdown all the control circuits in these supplies were redesigned and replaced. A new PWM control board, programmable logic controller, and touch panel have been installed to improve LGPS reliability, and to make troubleshooting easier. In this paper we present the details of this rebuilding program and results.
Date: May 17, 2005
Creator: Bellomo, P.; Lipari, J. J.; de Lira, A. C. & Rafael, F. S.
Object Type: Article
System: The UNT Digital Library
Beam Dynamics Studies for a Laser Acceleration Experiment (open access)

Beam Dynamics Studies for a Laser Acceleration Experiment

The NLC Test Accelerator (NLCTA) at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun is being installed together with a large-angle extraction line at 60 MeV followed by a matching section, buncher and final focus for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range, high resolution spectrometer (HES) for electron bunch analysis. Another spectrometer at 6 MeV will be used for analysis of bunch charges up to 1 nC. Emittance compensating solenoids and the low energy spectrometer (LES) will be used to tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5{sup o} extraction line provide 1:1 phase space transfer without use of sextupoles for a large, 6D phase space volume and range of input conditions. Design techniques, tolerances, tuning sensitivities and orthogonal knobs are discussed.
Date: May 17, 2005
Creator: Colby, E.; Noble, R.; Palmer, D.; Siemann, R. & Spencer, J.
Object Type: Article
System: The UNT Digital Library
Defense: FY2006 Authorization and Appropriations (open access)

Defense: FY2006 Authorization and Appropriations

This report is a guide to one of the 13 regular appropriations bills that Congress considers each year. It is designed to supplement the information provided by the House and Senate Appropriations Subcommittees on Defense. It summarizes the status of the bill, its scope, major issues, funding levels, and related congressional activity, and is updated as events warrant. The report lists the key CRS staff relevant to the issues covered and related CRS products.
Date: May 17, 2005
Creator: Daggett, Stephen
Object Type: Report
System: The UNT Digital Library
Beam Position Monitoring using the HOM-Signals from a Damped and Detuned Accelerating Structure (open access)

Beam Position Monitoring using the HOM-Signals from a Damped and Detuned Accelerating Structure

The Next and Global Linear Collider (NLC/GLC) designs require precision alignment of the beam in the accelerator structures to reduce short range wakefields. The moderately damped and detuned structures themselves provide suitable higher order mode (HOM) signals to measure this alignment. The modes in the lowest dipole band, whose frequencies range from 14-16 GHz, provide the strongest signals. To determine the position resolution they provide, an NLC/GLC prototype structure that was installed in the ASSET facility of the SLAC Linac was instrumented to downmix and digitize these signals. The beam position within the structure was determined by simultaneously measuring the signals at three frequencies (14.3, 15, 15.7 GHz) corresponding to modes localized at the beginning, the middle and the end of the 60 cm long structure. A resolution of 1 micron was achieved even with 28 dB signal attenuation, which is better than the 5 micron resolution required for the NLC/GLC.
Date: May 17, 2005
Creator: Dobert, S; Adolphsen, C.; Jones, R.; Lewandowski, J.; Li, Z.; Pivi, M. et al.
Object Type: Article
System: The UNT Digital Library
High Gradient Performance of NLC/GLC X-band Accelerating Structures (open access)

High Gradient Performance of NLC/GLC X-band Accelerating Structures

During the past five years, there has been a concerted program at SLAC and KEK to develop accelerator structures that meet the high gradient (65 MV/m) performance requirements for the Next Linear Collider (NLC) and Global Linear Collider (GLC) initiatives. The design that resulted is a 60-cm-long, traveling-wave structure with low group velocity and 150 degree per cell phase advance. It has an average iris size that produces an acceptable short-range wakefield, and dipole mode damping and detuning that adequately suppresses the long-range wakefield. More than eight such structures have operated at a 60 Hz repetition rate over 1000 hours at 65 MV/m with 400 ns long pulses, and have reached breakdown rate levels below the limit for the linear collider. Moreover, the structures are robust in that the rates continue to decrease over time, and if the structures are briefly exposed to air, the rates recover to their low levels within a few days. This paper presents a summary of the results from this program, which effectively ended last August with the selection of ''cold'' technology for an International Linear Collider (ILC).
Date: May 17, 2005
Creator: Doebert, S.; Adolphsen, C.; Bowden, G.; Burke, D.; Chan, J.; Dolgashev, V. et al.
Object Type: Article
System: The UNT Digital Library
Results of a Search for Cold Flows of Dark Matter Axions (open access)

Results of a Search for Cold Flows of Dark Matter Axions

None
Date: May 17, 2005
Creator: Duffy, L.; Sikivie, P.; Tanner, D. B.; Asztalos, S.; Hagmann, C.; Kinion, D. et al.
Object Type: Article
System: The UNT Digital Library
Modeling Lost-Particle Backgrounds in PEP-II Using LPTURTLE (open access)

Modeling Lost-Particle Backgrounds in PEP-II Using LPTURTLE

Background studies during the design, construction, commissioning, operation and improvement of BaBar and PEP-II have been greatly influenced by results from a program referred to as LPTURTLE (Lost Particle TURTLE) which was originally conceived for the purpose of studying gas background for SLC. This venerable program is still in use today. We describe its use, capabilities and improvements and refer to current results now being applied to BaBar.
Date: May 17, 2005
Creator: Fieguth, T.; Barlow, R. & Kozanecki, W.
Object Type: Article
System: The UNT Digital Library
Diffraction Of Laser-Plasma-Generated Electron Pulses (open access)

Diffraction Of Laser-Plasma-Generated Electron Pulses

We report the observation of Debye-Scherrer diffraction using electron pulses emitted from a fs-laser plasma. Titanium sapphire laser pulses with 1.6 mJ/45 fs at 1 kHz are focused on a moving steel tape at close to normal incidence. The laser plasma generated ejects a large number of electrons in the direction of polarization, with a continuous energy spectrum extending up to 100 keV. Selecting an energy range of these electrons and scattering them on a thin aluminium sample generates a ''streaked'' diffraction pattern with unique features.
Date: May 17, 2005
Creator: Fill, E; Trushin, S & Tommasini, R
Object Type: Article
System: The UNT Digital Library
Improving CO2 Efficiency for Recovering Oil in Heterogeneous Reservoirs (open access)

Improving CO2 Efficiency for Recovering Oil in Heterogeneous Reservoirs

None
Date: May 17, 2005
Creator: Grigg, Reid B.; Svec, Robert K.; Zeng, Zheng Wen; Bai, Baiojun & Liu, Yi
Object Type: Report
System: The UNT Digital Library
Peak Stripping Methodology for Plutonium Analysis in the Presence of Neptunium (open access)

Peak Stripping Methodology for Plutonium Analysis in the Presence of Neptunium

Quantitative Plutonium analysis depends upon the accurate identification of the assay peak. The Np[Pa] equilibrium pair introduces interfering peaks in {sup 239}Pu, {sup 238}Pu, and {sup 235}U assay peak region. When an interfering peak is present, it negates the assay unless an appropriate technique can be developed to deal with the interference. Peak Stripping is one such technique. Peak stripping involves an algorithm to strip an entire peak from another, resulting in a spectrum that can then be analyzed for the isotope of interest. A simpler method is a ''pseudo-peak-stripping'' whereby the effects of the interfering peak are quantified and those effects are stripped from the assay data. In this case the integrated peak areas are analyzed and corrected. There are two methods presented in this paper. Both assimilate the integrated data for the assay peak regions (in this case {sup 238}Pu, {sup 239}Pu, and {sup 235}U) and for the Neptunium/Protactinium secular equilibrium pair (Np[Pa]). Using Np[Pa] assumes that the Protactinium has come to equilibrium with Neptunium. This requires only {approx}6 months from the time chemical purification. Therefore it is a valid assumption in most cases. A correction is then applied to the assay peak areas to ''strip'' the underlying …
Date: May 17, 2005
Creator: Hodge, Christ
Object Type: Report
System: The UNT Digital Library
Phenotype Array Analysis of Metabolic Differences in Yersinia pestis (open access)

Phenotype Array Analysis of Metabolic Differences in Yersinia pestis

None
Date: May 17, 2005
Creator: Holtz, A. & McCutchen-Maloney, S.
Object Type: Article
System: The UNT Digital Library
An Approach to Performance Prediction for Parallel Applications (open access)

An Approach to Performance Prediction for Parallel Applications

Accurately modeling and predicting performance for large-scale applications becomes increasingly difficult as system complexity scales dramatically. Analytic predictive models are useful, but are difficult to construct, usually limited in scope, and often fail to capture subtle interactions between architecture and software. In contrast, we employ multilayer neural networks trained on input data from executions on the target platform. This approach is useful for predicting many aspects of performance, and it captures full system complexity. Our models are developed automatically from the training input set, avoiding the difficult and potentially error-prone process required to develop analytic models. This study focuses on the high-performance, parallel application SMG2000, a much studied code whose variations in execution times are still not well understood. Our model predicts performance on two large-scale parallel platforms within 5%-7% error across a large, multi-dimensional parameter space.
Date: May 17, 2005
Creator: Ipek, E; de Supinski, B R; Schulz, M & McKee, S A
Object Type: Article
System: The UNT Digital Library
India: Chronology of Recent Events (open access)

India: Chronology of Recent Events

This report provides a reverse chronology of recent events involving India and India - U.S relations.
Date: May 17, 2005
Creator: Kronstadt, K. Alan
Object Type: Report
System: The UNT Digital Library
Production of High Harmonic X-ray Radiation from Non-linear Thomson Scattering at LLNL PLEIADES (open access)

Production of High Harmonic X-ray Radiation from Non-linear Thomson Scattering at LLNL PLEIADES

We describe an experiment for production of high harmonic x-ray radiation from Thomson backscattering of an ultra-short high power density laser by a relativistic electron beam at the PLEIADES facility at LLNL. In this scenario, electrons execute a ''figure-8'' motion under the influence of the high-intensity laser field, where the constant characterizing the field strength is expected to exceed unity: a{sub L} = eE{sub L}/m{sub e}cw{sub L} {ge} 1. With large a{sub L} this motion produces high harmonic x-ray radiation and significant broadening of the spectral peaks. This paper is intended to give a layout of the PLEIADES experiment, along with progress towards experimental goals.
Date: May 17, 2005
Creator: Lim, J; Doyuran, A; Frigola, P; Travish, G; Rosenzweig, J; Anderson, S et al.
Object Type: Article
System: The UNT Digital Library
The Workforce Investment Act of 1998 (WIA): Reauthorization of Job Training Programs (open access)

The Workforce Investment Act of 1998 (WIA): Reauthorization of Job Training Programs

This report focuses on Workforce Investment Systems, Title I of Workforce Investment Act of 1998.
Date: May 17, 2005
Creator: Lordeman, Ann
Object Type: Report
System: The UNT Digital Library
Nuclear Weapons: Comprehensive Test Ban Treaty (open access)

Nuclear Weapons: Comprehensive Test Ban Treaty

None
Date: May 17, 2005
Creator: Medalia, Jonathan
Object Type: Report
System: The UNT Digital Library
Federal Pell Grants: Implications of Increasing the Maximum Award (open access)

Federal Pell Grants: Implications of Increasing the Maximum Award

Every year the maximum Pell Grant award is established during the appropriations process. Debate often ensues during this process about the feasibility of increasing the maximum Pell award. As families continue to confront rising college prices, federal student aid in general, and Pell Grants specifically, become particularly important for needy students.
Date: May 17, 2005
Creator: Mercer, Charmaine
Object Type: Report
System: The UNT Digital Library
In Search of the True Temperature and Stress Intensity Factor Dependencies for PWSCC (open access)

In Search of the True Temperature and Stress Intensity Factor Dependencies for PWSCC

None
Date: May 17, 2005
Creator: Morton, D; Attanasio, S; Richey, E & Young, G
Object Type: Article
System: The UNT Digital Library
Final Report: Novel nanowires as probes of electron coherence and correlations in restricted geometries (DE-FG03-01ER45946) (open access)

Final Report: Novel nanowires as probes of electron coherence and correlations in restricted geometries (DE-FG03-01ER45946)

This is a final summary report of the research conducted under DE-FG03-01ER45946, which was a research program using metal nanostructures to examine quantum coherence of electrons in normal and ferromagnetic metals. This program was the PI's first federal research grant, and by augmenting with other funds (Packard Foundation), this grant supported two graduate students during its duration. In normal metal nanostructures, quantum coherence was assessed by two independent techniques: weak localization magnetoresistance, and time-dependent universal conductance fluctuations (TDUCF noise). This work found that, in AuPd nanowires, the coherence information inferred from these two techniques were quantitatively consistent, even in the presence of magnetic impurity and phonon scattering. This confirmed theoretical expectations. However, in Ag and Au wires, the two techniques disagree, with noise measurements indicating a lower coherence length at low temperatures than weak localization. We have a candidate explanation for this, and are finishing these experiments. This work shows that subtleties remain in our understanding of coherence processes even in normal metals, particularly those involving the tunneling two-level systems that produce low frequency noise; this has relevance for quantum information processing implementations using metal devices. We have also studied time-dependent universal conductance fluctuations in ferromagnetic metals for the first …
Date: May 17, 2005
Creator: Natelson, Douglas
Object Type: Report
System: The UNT Digital Library
Top Quark Pair Production at the Tevatron (open access)

Top Quark Pair Production at the Tevatron

The measurement of the top quark pair production crosssection inproton-antiproton collisions at 1.96 TeV is a test ofquantumchromodynamics and could potentially be sensitive to newphysics beyondthe standard model. I report on the latest t-tbarcross section resultsfrom the CDF and DZero experiments in various finalstate topologies whicharise from decays of top quark pairs.
Date: May 17, 2005
Creator: Nielsen, Jason
Object Type: Article
System: The UNT Digital Library
SCC Initiation Testing of Nickel-Based Alloys Using In-Situ Monitored Uniaxial Tensile Specimens (open access)

SCC Initiation Testing of Nickel-Based Alloys Using In-Situ Monitored Uniaxial Tensile Specimens

None
Date: May 17, 2005
Creator: Richey, E; Morton, D & Schurman, M
Object Type: Article
System: The UNT Digital Library
Depth profile of uncompensated spins in an exchange bias system (open access)

Depth profile of uncompensated spins in an exchange bias system

We have used the unique spatial sensitivity of polarized neutron and soft x-ray beams in reflection geometry to measure the depth dependence of magnetization across the interface between a ferromagnet and antiferromagnet. The new uncompensated magnetization near the interface responds to applied field, while the uncompensated spins in the antiferromagnetic bulk are pinned, thus providing a means to establish exchange bias.
Date: May 17, 2005
Creator: Roy, S.; Fitzsimmons, M.R.; Park, S.; Dorn, M.; Petracic, O.; Roshchin, Igor V. et al.
Object Type: Article
System: The UNT Digital Library
Analysis of Coupled Multiphase Fluid Flow, Heat Transfer and Mechanical Deformation at the Yucca Mountain Drift Scale Test (open access)

Analysis of Coupled Multiphase Fluid Flow, Heat Transfer and Mechanical Deformation at the Yucca Mountain Drift Scale Test

A numerical simulation of coupled multiphase fluid flow, heat transfer, and mechanical deformation was carried out to study coupled thermal-hydrological-mechanical (THM) processes at the Yucca Mountain Drift Scale Test (DST) and for validation of a coupled THM numerical simulator. The ability of the numerical simulator to model relevant coupled THM processes at the DST was evaluated by comparison of numerical results to in situ measurements of temperature, water saturation, displacement, and fracture permeability. Of particular relevance for coupled THM processes are thermally induced rock-mass stress and deformations, with associated changes in fracture aperture and fractured rock permeability. Thermally induced rock-mass deformation and accompanying changes in fracture permeability were reasonably well predicted using a continuum elastic model, although some individual measurements of displacement and permeability indicate inelastic mechanical responses. It is concluded that fracture closure/opening caused by a change in thermally induced normal stress across fractures is an important mechanism for changes in intrinsic fracture permeability at the DST, whereas fracture shear dilation appears to be less significant. Observed and predicted maximum permeability changes at the DST are within one order of magnitude. These data are important for bounding model predictions of potential changes in rock-mass permeability at a future repository …
Date: May 17, 2005
Creator: Rutqvist, J.; Tsang, C. F. & Tsang, Y.
Object Type: Report
System: The UNT Digital Library