Los Alamos, NM, United States
Los Alamos, NM, United States
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Kutsaev S.V.,Argonne National Laboratory | Kutsaev S.V.,TechSource, Inc. | Mustapha B.,Argonne National Laboratory | Mustapha B.,TechSource, Inc. | And 10 more authors.
Physical Review Special Topics - Accelerators and Beams | Year: 2014

We have developed a new design for a 176 MHz cw radio-frequency quadrupole (RFQ) for the SARAF upgrade project. At this frequency, the proposed design is a conventional four-vane structure. The main design goals are to provide the highest possible shunt impedance while limiting the required rf power to about 120 kW for reliable cw operation, and the length to about 4 meters. If built as designed, the proposed RFQ will be the first four-vane cw RFQ built as a single cavity (no resonant coupling required) that does not require π-mode stabilizing loops or dipole rods. For this, we rely on very detailed 3D simulations of all aspects of the structure and the level of machining precision achieved on the recently developed ATLAS upgrade RFQ. A full 3D model of the structure including vane modulation was developed. The design was optimized using electromagnetic and multiphysics simulations. Following the choice of the vane type and geometry, the vane undercuts were optimized to produce a flat field along the structure. The final design has good mode separation and should not need dipole rods if built as designed, but their effect was studied in the case of manufacturing errors. The tuners were also designed and optimized to tune the main mode without affecting the field flatness. Following the electromagnetic (EM) design optimization, a multiphysics engineering analysis of the structure was performed. The multiphysics analysis is a coupled electromagnetic, thermal and mechanical analysis. The cooling channels, including their paths and sizes, were optimized based on the limiting temperature and deformation requirements. The frequency sensitivity to the RFQ body and vane cooling water temperatures was carefully studied in order to use it for frequency fine-tuning. Finally, an inductive rf power coupler design based on the ATLAS RFQ coupler was developed and simulated. The EM design optimization was performed using cst Microwave Studio and the results were verified using both hfss and ansys. The engineering analysis was performed using hfss and ansys and most of the results were verified using the newly developed cst Multiphysics package. © 2014 Published by the American Physical Society.

Prettyman T.H.,Planetary Science Institute | Feldman W.C.,Planetary Science Institute | McSween Jr. H.Y.,University of Tennessee at Knoxville | Dingler R.D.,Los Alamos National Laboratory | And 7 more authors.
Space Science Reviews | Year: 2011

The NASA Dawn Mission will determine the surface composition of 4 Vesta and 1 Ceres, providing constraints on their formation and thermal evolution. The payload includes a Gamma Ray and Neutron Detector (GRaND), which will map the surface elemental composition at regional spatial scales. Target elements include the constituents of silicate and oxide minerals, ices, and the products of volcanic exhalation and aqueous alteration. At Vesta, GRaND will map the mixing ratio of end-members of the howardite, diogenite, and eucrite (HED) meteorites, determine relative proportions of plagioclase and mafic minerals, and search for compositions not well sampled by the meteorite collection. The large south polar impact basin may provide an opportunity to determine the composition of Vesta's mantle and lower crust. At Ceres, GRaND will provide chemical information needed to test different models of Ceres' origin and thermal and aqueous evolution. GRaND is also sensitive to hydrogen layering and can determine the equivalent H 2O/OH content of near-surface hydrous minerals as well as the depth and water abundance of an ice table, which may provide information about the state of water in the interior of Ceres. Here, we document the design and performance of GRaND with sufficient detail to interpret flight data archived in the Planetary Data System, including two new sensor designs: an array of CdZnTe semiconductors for gamma ray spectroscopy, and a loaded-plastic phosphor sandwich for neutron spectroscopy. An overview of operations and a description of data acquired from launch up to Vesta approach is provided, including annealing of the CdZnTe sensors to remove radiation damage accrued during cruise. The instrument is calibrated using data acquired on the ground and in flight during a close flyby of Mars. Results of Mars flyby show that GRaND has ample sensitivity to meet science objectives at Vesta and Ceres. Strategies for data analysis are described and prospective results for Vesta are presented for different operational scenarios and compositional models. © Springer Science+Business Media B.V. 2011.

Bruckner J.,Max Planck Institute for Chemistry | Reedy R.C.,Planetary Science Institute | Englert P.A.J.,University of Hawaii at Manoa | Drake D.M.,TechSource, Inc.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2011

To simulate planetary gamma-ray spectroscopy, gamma rays were measured during a series of five irradiations of up to 30-ton thick targets with protons beams of 1.5 and 2.5 GeV. The targets were steel (iron), basalt with structural steel, basalt with added S and Cl, and basalt with added H, S, and Cl. The pulsed proton beam was carefully monitored and counted. Spectra were collected with both proton beam on and beam off and with a lead shield both between the target and the germanium detector and with the lead shield removed. This set of four spectra was used to determine the fluxes of prompt gamma rays emitted from the target. Over 200 discrete gamma-ray lines per irradiation were observed and identified. Counting results for the more intense gamma rays were compiled, and gamma-ray fluxes determined for about 25 gamma rays of interest to planetary gamma-ray spectroscopy. The ratios of thermal and fast neutron induced gamma-ray fluxes between irradiations were similar. Thus the relative gamma-ray fluxes can be used in testing model calculations and interpreting planetary gamma-ray spectra. © 2011 Elsevier B.V. All rights reserved.

Prettyman T.H.,Planetary Science Institute | Mittlefehldt D.W.,NASA | Yamashita N.,Planetary Science Institute | Beck A.W.,Smithsonian Institution | And 16 more authors.
Meteoritics and Planetary Science | Year: 2013

Global maps of the macroscopic thermal neutron absorption cross section of Vesta's regolith by the Gamma Ray and Neutron Detector (GRaND) on board the NASA Dawn spacecraft provide constraints on the abundance and distribution of Fe, Ca, Al, Mg, and other rock-forming elements. From a circular, polar low-altitude mapping orbit, GRaND sampled the regolith to decimeter depths with a spatial resolution of about 300 km. At this spatial scale, the variation in neutron absorption is about seven times lower than that of the Moon. The observed variation is consistent with the range of absorption for howardite whole-rock compositions, which further supports the connection between Vesta and the howardite, eucrite, and diogenite meteorites. We find a strong correlation between neutron absorption and the percentage of eucritic materials in howardites and polymict breccias, which enables petrologic mapping of Vesta's surface. The distribution of basaltic eucrite and diogenite determined from neutron absorption measurements is qualitatively similar to that indicated by visible and near infrared spectroscopy. The Rheasilvia basin and ejecta blanket has relatively low absorption, consistent with Mg-rich orthopyroxene. Based on a combination of Fe and neutron absorption measurements, olivine-rich lithologies are not detected on the spatial scales sampled by GRaND. The sensitivity of GRaND to the presence of mantle material is described and implications for the absence of an olivine signature are discussed. High absorption values found in Vesta's "dark" hemisphere, where exogenic hydrogen has accumulated, indicate that this region is richer in basaltic eucrite, representative of Vesta's ancient upper crust. © The Meteoritical Society, 2013.

Hendricks J.S.,TechSource, Inc. | Hendricks J.S.,Los Alamos National Laboratory | Hendricks J.S.,Brookhaven National Laboratory | Quiter B.J.,University of California at Berkeley | Quiter B.J.,Lawrence Berkeley National Laboratory
Nuclear Technology | Year: 2011

The angular distribution of scattered photons is incorrect in MCNPX and MCNP5 because the incoherent and coherent form factors are obsolete. The obsolete data affect all photon transport problems with E > 74 keV. Elastic backscatter for E > 105 keVis completely missing. Consequently, a new ACE-format photoatomic data library, tentatively named MCPLIB05 and referred to herein as MCPLIBOST, has been developed for MCNP/X. Data in MCPLIB05T other than form factors are identical to that in its predecessor photoatomic library, MCPLIB04. The new form factor data in MCPLIB05T come directly from ENDF/B-VI1(rev. O) andare in a format incompatible with older versions of MCNP/X. Consequently, a new version of MCNP/X has been developed to identify and use the new MCPLIB05T data and yet retain backward compatibility, including tracking, when MCPLIB04 is used. The NJOY nuclear data processing system is undergoing development to enable future generations of photoatomic data libraries with modern form factor data in the new format.

Prettyman T.H.,Planetary Science Institute | Yamashita N.,Planetary Science Institute | Reedy R.C.,Planetary Science Institute | McSween H.Y.,University of Tennessee at Knoxville | And 3 more authors.
Icarus | Year: 2015

The globally-averaged concentrations of radioelements K and Th within Vesta's regolith are determined from gamma ray spectra acquired by Dawn's Gamma Ray and Neutron Detector (GRaND). Spectra measured by GRaND's bismuth germanate (BGO) scintillator, while in close proximity to Vesta, are analyzed. Improvements in data reduction and analysis methods enable detection and quantification of K and Th. Ample precision is achieved using the entire data set acquired by Dawn during 5 months of low-altitude operations. A simple, analytic model, which can be applied to measurements of Vesta and Ceres, is used to determine radioelement concentrations from measured counting rates. Systematic errors in the analysis are evaluated using simulated gamma ray spectra for representative vestan meteorite compositions. Concentrations of K and Th within Vesta's global regolith, measured by GRaND, are consistent with eucrite-rich howardite, and are distinct from most achondrites, all chondrites, and Mars meteorites. The K/Th ratio of Vesta (900. ±. 400) is similar to the average ratio for howardite (approximately 1200). These radioelement data, along with major element ratios determined by nuclear spectroscopy, strongly support the hypothesis that Vesta is the parent body of the HEDs. The depletion of moderately-volatile elements implied by the measured K/Th ratio is consistent with early accretion of Vesta from a hot, incompletely condensed solar nebula and/or, less likely, subsequent removal of volatiles by energetic collisions or degassing of magmas. © 2015 The Authors.

Hardgrove C.,University of Tennessee at Knoxville | Moersch J.,TechSource, Inc. | Drake D.,TechSource, Inc.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

The Dynamic Albedo of Neutrons (DAN) experiment, part of the scientific payload of the Mars Science Laboratory (MSL) rover mission, will have the ability to assess both the abundance and the burial depth of subsurface hydrogen as the rover traverses the Martian surface. DAN will employ a method of measuring neutron fluxes called neutron die-away that has not been used in previous planetary exploration missions. This method requires the use of a pulsed neutron generator that supplements neutrons produced via spallation in the subsurface by the cosmic ray background. It is well established in neutron remote sensing that low-energy (thermal) neutrons are sensitive not only to hydrogen content, but also to the macroscopic absorption cross-section of near-surface materials. To better understand the results that will be forthcoming from DAN, we model the effects of varying abundances of high absorption cross-section elements that are likely to be found on the Martian surface (Cl, Fe) on neutron die-away measurements made from a rover platform. Previously, the Mars Exploration Rovers (MER) Spirit and Opportunity found that elevated abundances of these two elements are commonly associated with locales that have experienced some form of aqueous activity in the past, even though hydrogen-rich materials are not necessarily still present. By modeling a suite of H and Cl compositions, we demonstrate that (for abundance ranges reasonable for Mars) both the elements will significantly affect DAN thermal neutron count rates. Additionally, we show that the timing of thermal neutron arrivals at the detector can be used together with the thermal neutron count rates to independently determine the abundances of hydrogen and high neutron absorption cross-section elements (the most important being Cl). Epithermal neutron die-away curves may also be used to separate these two components. We model neutron scattering in actual Martian compositions that were determined by the MER Alpha Proton X-Ray Spectrometer (APXS), as examples of local geochemical anomalies that DAN would be sensitive to if they were present at the MSL landing site. These MER targets, named Eileen Dean, Jack Russell, and Kenosha Comets, all have unusually high or low Cl or Fe abundances as a result of geochemical interactions involving water. Using these examples we demonstrate that DAN can be used not only to assess the amount of present-day hydrogen in the near-surface but also to identify locations that may preserve a geochemical record of past aqueous processes. © 2011 Elsevier B.V. All rights reserved.

Ion exchange resin macroporous beads for the highly selective extraction of univalent anions from aqueous solutions. A specific example is the removal of dicyanoaurate and dicyanoargentate from cyanide leach solutions and tailings. The beads have a maximum number of ligands specific for the desired univalent anion, while maintaining sufficient separation to minimize binding of polyvalent ions. The beads are prepared using a functionalized monomer with the use of a specifically tuned coordinator. The beads can be used as a sensor for detecting the amount of anions captured when interrogated by an appropriate light source.

Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase I | Award Amount: 99.96K | Year: 2013

This Small Business Innovative Research Phase 1 proposal requests $100,000 support for TechSource to identify and document feasible technology options to replace the White Sands Fast Burst Reactor (FBR); reference Army Topic Number A12-088,"Alternative Source for Neutron Generation. The U.S. Army requires a neutron generator to replace the FBR highly enriched uranium (HEU) based technology with a Low Enriched Uranium (LEU) technology that produces a radiation environment for nuclear survivability testing while reducing life-cycle costs, and increasing reliability and availability requirements. There is no obvious, low risk, economical approach to a HEU to LEU transition. TechSource will analyze the extensive body of knowledge in this area. We then will apply innovations to existing technologies and extend national lab research of critical experiments facilities, conversion of HEU reactors to LEU reactors, and application of accelerator technologies to enhance neutron environments. Our principal investigator (Ms. Charlene Cappiello) has recent, relevant, and firsthand knowledge and experience in radiation testing and experimentation environments. Our subject matter experts also have the firsthand, related science and technology knowledge experience needed to efficiently produce the most comprehensive analysis of what is feasible and provide the data for the required program and business case decision.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.71K | Year: 2010

Electron cloud effects, especially electron cloud driven beam instabilities, are critical technical risks for the next generation of high intensity proton rings and for upgrades to existing machines. Significant changes and improvements to the simulation codes for electron cloud generation are needed to accurately and reliably model electron cloud buildup in the high intensity proton accumulator rings that drive the DOE supported spallation neutron sources. Comparisons of simulation results with the extensive electron cloud measurements from the Los Alamos proton storage ring (PSR) have pointed to crucial areas for improvement of the widely used POSINST code. Changes to the code will be developed with the goal of obtaining more accurate and reliable modeling that provides better agreement with experimental results, especially with data from PSR. Commercial Applications and Other Benefits: Commercial applications for the codes produced for this project are limited but we anticipate that some accelerator laboratories may be interested in having us utilize the simulation tools for electron cloud issues at their facilities. The results of this project will directly benefit the understanding and mitigation of electron cloud effects at high-intensity, long-bunch proton rings such as the proton drivers for Oak Ridge Spallation Neutron Source and the Los Alamos Proton Storage Ring.

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