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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure

Deep-ultraviolet (DUV) aluminum gallium nitride-based light-emitting diodes (LEDs) on transparent aluminum nitride (AlN) substrates with high light extraction efficiency and high power are proposed and demonstrated. The AlN bottom side surface configuration, which is composed of a hybrid structure of photonic crystals and subwavelength nanostructures, has been designed using finite-difference time-domain calculations to enhance light extraction. We have experimentally demonstrated an output power improvement of up to 196% as a result of the use of the embedded high-light-extraction hybrid nanophotonic structure. The DUV-LEDs produced have demonstrated output power as high as 90 mW in DC operation at a peak emission wavelength of 265 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Design and fabrication of a duoplasmatron extraction geometry and LEBT for the LANSCE H{sup +} RFQ project

The 750-keV H{sup +} Cockcroft-Walton at LANSCE will be replaced with a recently fabricated 4-rod Radio Frequency Quadrupole (RFQ) with injection energy of 35 keV. The existing duoplasmatron source extraction optics need to be modified to produce up to 35 mA of H{sup +} current with an emittance <0.02 π-cm-mrad (rms, norm) for injection into the RFQ. Parts for the new source have been fabricated and assembly is in process. We will use the existing duoplasmatron source with a newly designed extraction system and low energy beam transport (LEBT) for beam injection into the RFQ. In addition to source modifications, we need a new LEBT for transport and matching into the RFQ. The LEBT uses two magnetic solenoids with enough drift space between them to accommodate diagnostics and a beam deflector. The LEBT is designed to work over a range of space-charge neutralized currents and emittances. The LEBT is optimized in the sense that it minimizes the beam size in both solenoids for a point design of a given neutralized current and emittance. Special attention has been given to estimating emittance growth due to source extraction optics and solenoid aberrations. Examples of source-to-RFQ matching and emittance growth (due to both non-linear space charge and solenoid aberrations) are presented over a range of currents and emittances about the design point. A mechanical layout drawing will be presented along with the status of the source and LEBT, design, and fabrication.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Effect of plasma grid bias on extracted currents in the RF driven surface-plasma negative ion source

Extraction of negative ions from the large inductively driven surface-plasma negative ion source was studied. The dependencies of the extracted currents vs plasma grid (PG) bias potential were measured for two modifications of radio-frequency driver with and without Faraday screen, for different hydrogen feeds and for different levels of cesium conditioning. The maximal PG current was independent of driver modification and it was lower in the case of inhibited cesium. The maximal extracted negative ion current depends on the potential difference between the near-PG plasma and the PG bias potentials, while the absolute value of plasma potential in the driver and in the PG area is less important for the negative ion production. The last conclusion confirms the main mechanism of negative ion production through the surface conversion of fast atoms.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Upgrade of the beam extraction system of the GTS-LHC electron cyclotron resonance ion source at CERN

Linac3 is the first accelerator in the heavy ion injector chain of the Large Hadron Collider (LHC), providing multiply charged heavy ion beams for the CERN experimental program. The ion beams are produced with GTS-LHC, a 14.5 GHz electron cyclotron resonance ion source, operated in afterglow mode. Improvement of the GTS-LHC beam formation and beam transport along Linac3 is part of the upgrade program of the injector chain in preparation for the future high luminosity LHC. A mismatch between the ion beam properties in the ion source extraction region and the acceptance of the following Low Energy Beam Transport (LEBT) section has been identified as one of the factors limiting the Linac3 performance. The installation of a new focusing element, an einzel lens, into the GTS-LHC extraction region is foreseen as a part of the Linac3 upgrade, as well as a redesign of the first section of the LEBT. Details of the upgrade and results of a beam dynamics study of the extraction region and LEBT modifications will be presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Preliminary results concerning the simulation of beam profiles from extracted ion current distributions for mini-STRIKE

The Radio Frequency (RF) negative hydrogen ion source prototype has been chosen for the ITER neutral beam injectors due to its optimal performances and easier maintenance demonstrated at Max-Planck-Institut für Plasmaphysik, Garching in hydrogen and deuterium. One of the key information to better understand the operating behavior of the RF ion sources is the extracted negative ion current density distribution. This distribution—influenced by several factors like source geometry, particle drifts inside the source, cesium distribution, and layout of cesium ovens—is not straightforward to be evaluated. The main outcome of the present contribution is the development of a minimization method to estimate the extracted current distribution using the footprint of the beam recorded with mini-STRIKE (Short-Time Retractable Instrumented Kalorimeter). To accomplish this, a series of four computational models have been set up, where the output of a model is the input of the following one. These models compute the optics of the ion beam, evaluate the distribution of the heat deposited on the mini-STRIKE diagnostic calorimeter, and finally give an estimate of the temperature distribution on the back of mini-STRIKE. Several iterations with different extracted current profiles are necessary to give an estimate of the profile most compatible with the experimental data. A first test of the application of the method to the BAvarian Test Machine for Negative ions beam is given.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Effect of Coulomb collision on the negative ion extraction mechanism in negative ion sources

To improve the H{sup −} ion beam optics, it is necessary to understand the energy relaxation process of surface produced H{sup −} ions in the extraction region of Cs seeded H{sup −} ion sources. Coulomb collisions of charged particles have been introduced to the 2D3V-PIC (two dimension in real space and three dimension in velocity space particle-in-cell) model for the H{sup −} extraction by using the binary collision model. Due to Coulomb collision, the lower energy part of the ion energy distribution function of H{sup −} ions has been greatly increased. The mean kinetic energy of the surface produced H{sup −} ions has been reduced to 0.65 eV from 1.5 eV. It has been suggested that the beam optics of the extracted H{sup −} ion beam is strongly affected by the energy relaxation process due to Coulomb collision.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Regenerated silica gel as stationary phase on vacuum column chromatography to purify temulawak’s extracts

Commercial silica gel only used once by many researchers and affected high cost for purification process, also less support the green chemistry program. This research focused in regeneration silica gel that used purification of temulawak’s extracts (Curcuma xanthorrhiza Roxb) by vacuum column chromatography. Sample extracts (contains 10.1195±0.5971% of curcuminoids) was purified by vacuum column chromatography (pressure: 45 kPa, column: 100mm on length and 16mm on diameter). Ethanol 96% and acetone were compared as eluent. The amount of solvent and yield of curcuminoids used as indicator purification. The silica gel was regenerated with heating in 600°C for 8 hours The silica gels were analyzed by IR spectroscopy and X-ray diffraction. Furthermore, regenerated silica gel was used as the stationary phase in vacuum column chromatography under the same conditions with the previous purification. All the purification experiments were performed in three repetitions. Based on regression equation, y=0.132x+0.0011 (r{sup 2}=0.9997) the yield of curcuminoids on purified products using ethanol as the eluent was improved 4.26% (to 14.3724±0.5749%) and by acetone was improved 3,03% (to 13.1450 ±0.6318%). The IR spectrum of both silica gel showed the same vibration profile and also there were three crystallinity peaks missing on its X-ray diffraction. Regenerated silica gel has the same performance with new silica gel in purification of temulawak’s extract: by ethanol has increased 4.08% (14.1947±0.7415%) and 2.93% (13.0447±0.4822) by acetone. In addition, all purification products showed similar TLC profiles. Purification using regenerated silica gel as the adsorbent on vacuum column chromatography has exactly same potential with the new silica gel.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Enhancing the light extraction efficiency of AlGaN deep ultraviolet light emitting diodes by using nanowire structures

The performance of conventional AlGaN deep ultraviolet light emitting diodes has been limited by the extremely low light extraction efficiency (<10%), due to the unique transverse magnetic (TM) polarized light emission. Here, we show that, by exploiting the lateral side emission, the extraction efficiency of TM polarized light can be significantly enhanced in AlGaN nanowire structures. Using the three-dimensional finite-difference time domain simulation, we demonstrate that the nanowire structures can be designed to inhibit the emission of guided modes and redirect trapped light into radiated modes. A light extraction efficiency of more than 70% can, in principle, be achieved by carefully optimizing the nanowire size, nanowire spacing, and p-GaN thickness.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Demonstration of a Thermosyphon Thermal Valve for Controlled Extraction of Stored Solar Thermal Energy

For concentrated solar power (CSP) to be an effective replacement for power generation by fossil fuels, the thermal energy must be stored and then released for when demand exceeds production, such as during off-sun hours. Until now, there has been limited methods to reliably and efficiently release and control the extraction of thermal energy from a material containing stored sensible or latent heat. Due to their isothermal property, phase change materials (PCMs) storing latent heat are an ideal choice for storage, though it has proven challenging to reliably extract and utilize that heat. To solve this problem, the geometry of a thermosyphon was rearranged to create a thermal valve that is able to turn the flow of thermal energy from a PCM 'on' and 'off'. A stainless steel thermal valve using sodium as the working fluid was designed, fabricated, assessed, and found to effectively and selectively extract heat from a 577 degrees C molten aluminum PCM. It is expected that thermal valves will significantly contribute to more widespread implementation of CSP as a stored energy source from distributed generation to utility-scale power production.

14 SOLAR ENERGY↗
DOE OSTI2023

Utility of Shockley–Read–Hall analysis to extract defect properties from semiconductor minority carrier lifetime data

The semiconductor minority carrier lifetime contains information about several important material properties, including Shockley–Read–Hall defect levels/concentrations and radiative/Auger recombination rates, and the complex relationships between these parameters produce a non-trivial temperature-dependence of the measured lifetime. It is tempting to fit temperature-dependent lifetime data to extract the properties of the Shockley–Read–Hall recombination centers; however, without a priori knowledge of the distribution of the Shockley–Read–Hall states across the bandgap, this fit problem is under-constrained in most circumstances. Shockley–Read–Hall lifetime data are not well-suited for the extraction of Shockley–Read–Hall defect levels but can be used effectively to extract minority carrier recombination lifetimes. The minority carrier recombination lifetime is observed at temperatures below 100 K in a Si-doped n-type InGaAs/InAsSb superlattice, and deviation from its expected temperature-dependence indicates that the capture cross section of the defect associated with Si-doping has an activation energy of 1.5 meV or a characteristic temperature of 17 K. This lower temperature regime is also preferrable for the analysis of the physics of defect introduction with displacement-damage-generating particle irradiation.

Physics↗
DOE OSTI2016

Thermal stability study of a new guanidine suppressor for the next-generation caustic-side solvent extraction process

Cesium stripping performance of thermally stressed solvent degrades slowly over time in batch tests of the Next Generation Caustic-Side Solvent Extraction (NGS) process. NGS is currently used at pilot scale at the Savannah River Site for the selective removal of cesium from high-level salt waste. Recently a new guanidine, N,N',N" -tris(3,7-dimethyloctyl)guanidine (TiDG), was chosen for use as the suppressor, a lipophilic organic base needed for stripping, and the present study was undertaken to address the question of its stability. The NGS process solvent was evaluated for a period of three months under a variety of temperature and storage conditions. The performance of the solvent was tested at 30-day increments using a standard extraction, scrub, strip, and extraction (ES 2 S 3 E) sequence. Lastly, the results provide insight on the effects of storage and process conditions, the stripping behavior of TiDG, and the stability of the new solvent composition.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

An Advanced TALSPEAK Concept Using 2-Ethylhexylphosphonic Acid Mono-2-Ethylhexyl Ester as the Extractant

A method for separating the trivalent actinides and lanthanides is being developed using 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) as the extractant. The method is based on the preferential binding of the actinides in the aqueous phase by N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA), which serves to keep the actinides in the aqueous phase while the lanthanides are extracted into an organic phase containing HEH[EHP]. The process is very robust, showing little dependence upon the pH or the HEH[EHP], HEDTA, and citrate concentrations over the ranges that might be expected in a nuclear fuel recycling plant. Single-stage runs with a 2-cm centrifugal contactor indicate that modifications to the process chemistry may be needed to increase the extraction rate for Sm, Eu, and Gd. The hydraulic properties of the system are favorable to application in centrifugal contactors.

actinide separation↗
DOE OSTI2025

An Application of Molecular Recognition for the Efficient Removal of Cesium from Hanford Nuclear Waste by Modular Solvent Extraction

In this work, experimental results leading to flowsheet design are presented showing how a calixarene-crown ether based solvent-extraction process can meet the challenge of cesium removal from nuclear tank wastes stored at the US Department of Energy Hanford site. Cleanup of legacy Cold War nuclear waste stored in underground tanks represents one of the greatest environmental challenges facing the US Department of Energy in terms of risk, cost, and effectiveness of applicable science and technology. Planning for the cleanup at the Hanford Site calls for the removal of the radioactive fission product 137Cs from its alkaline salt waste, including the use of modular processes that can be deployed near the tank farms. To meet the resulting need for extremely high selectivity, the Next-Generation Caustic-Side Solvent Extraction (NG-CSSX) process employing a calix[4]arene-crown ether in modified kerosene has been adapted to remove sub-millimolar cesium in competition with molar sodium and potassium in a high-nitrate alkaline matrix. Potassium loading in the solvent was determined in extraction, scrubbing, and stripping, leading to an empirical model closely approximating cesium distribution ratios for a variety of Hanford waste types. Process chemistry has been developed based on this molecular-recognition approach, focusing on the competitive effect of potassium loading and the mitigating process modifications needed, including extending the scrub section. The result is a modular flowsheet design that can achieve cesium decontamination factors well in excess of 15,000 even for the worst-case Hanford waste.

Williams, Neil [ORNL] (ORCID:000000023159226X)↗
DOE OSTI2015

EXTRACTING PERIODIC TRANSIT SIGNALS FROM NOISY LIGHT CURVES USING FOURIER SERIES

We present a simple and powerful method for extracting transit signals associated with a known transiting planet from noisy light curves. Assuming the orbital period of the planet is known and the signal is periodic, we illustrate that systematic noise can be removed in Fourier space at all frequencies by only using data within a fixed time frame with a width equal to an integer number of orbital periods. This results in a reconstruction of the full transit signal, which on average is unbiased despite no prior knowledge of either the noise or the transit signal itself being used in the analysis. The method therefore has clear advantages over standard phase folding, which normally requires external input such as nearby stars or noise models for removing systematic components. In addition, we can extract the full orbital transit signal (360°) simultaneously, and Kepler-like data can be analyzed in just a few seconds. We illustrate the performance of our method by applying it to a dataset composed of light curves from Kepler with a fake injected signal emulating a planet with rings. For extracting periodic transit signals, our presented method is in general the optimal and least biased estimator and could therefore lead the way toward the first detections of, e.g., planet rings and exo-trojan asteroids.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Linearly supporting feature extraction for automated estimation of stellar atmospheric parameters

We describe a scheme to extract linearly supporting (LSU) features from stellar spectra to automatically estimate the atmospheric parameters T{sub eff}, log g, and [Fe/H]. “Linearly supporting” means that the atmospheric parameters can be accurately estimated from the extracted features through a linear model. The successive steps of the process are as follow: first, decompose the spectrum using a wavelet packet (WP) and represent it by the derived decomposition coefficients; second, detect representative spectral features from the decomposition coefficients using the proposed method Least Absolute Shrinkage and Selection Operator (LARS){sub bs}; third, estimate the atmospheric parameters T{sub eff}, log g, and [Fe/H] from the detected features using a linear regression method. One prominent characteristic of this scheme is its ability to evaluate quantitatively the contribution of each detected feature to the atmospheric parameter estimate and also to trace back the physical significance of that feature. This work also shows that the usefulness of a component depends on both the wavelength and frequency. The proposed scheme has been evaluated on both real spectra from the Sloan Digital Sky Survey (SDSS)/SEGUE and synthetic spectra calculated from Kurucz's NEWODF models. On real spectra, we extracted 23 features to estimate T{sub eff}, 62 features for log g, and 68 features for [Fe/H]. Test consistencies between our estimates and those provided by the Spectroscopic Parameter Pipeline of SDSS show that the mean absolute errors (MAEs) are 0.0062 dex for log T{sub eff} (83 K for T{sub eff}), 0.2345 dex for log g, and 0.1564 dex for [Fe/H]. For the synthetic spectra, the MAE test accuracies are 0.0022 dex for log T{sub eff} (32 K for T{sub eff}), 0.0337 dex for log g, and 0.0268 dex for [Fe/H].

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Nearly monoenergetic positive ion beam with self-neutralized space charge extracted from a pulsed plasma

Not provided.A nearly monoenergetic Ar + ion beam (100 eV peak energy, 3.5 eV full width at half maximum), with self-neutralized space charge, was extracted from a power modulated (pulsed) inductively coupled plasma (ICP), through a single grounded grid. The beam energy was set by applying a synchronous DC bias voltage to a boundary electrode in contact with the plasma, in the late afterglow of the power pulse. A retarding field energy analyzer and a movable Faraday cup were used to measure the ion energy distribution (IED) and the time resolved ion and electron current densities, as a function of position along the beam axis, to unravel the mechanism of self-neutralization of the space charge of the beam. When a +100 V DC bias was applied to the boundary electrode during the afterglow, a ~100 eV beam (ion density ~10 9 cm -3 ) emerged that was space-charge neutralized by periodic injection of electrons, mainly during the early afterglow, into the region downstream of the extraction grid. A background plasma (electron density ~10 10 cm -3 ) was formed by these electrons, in conjunction with relatively low-energy ions (1–10 eV) that flew out of the ICP when the DC bias was off, as well as formed by resonant charge exchange of the 100 eV beam ions with the background Ar in the downstream region near the extraction grid. The behavior of the beam IED as a function of pressure and power of the ICP as well as the timing of application of the DC bias voltage was also studied.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Extraction of ion beam from laser ion source for direct plasma injection scheme

Laser ion sources are expected to be used in various applications of heavy ion beam technology. The plasma direct injection scheme (DPIS) is a method in which ion beams extracted from a laser ion source are directly injected into a radio frequency quadrupole (RFQ) linear accelerator. In this study, a new shape of the plasma electrode with a concave surface for the DPIS was proposed to inject a converging beam to a cavity of RFQ accelerator. This approach allows the use of a large-diameter extraction electrode, which is not limited by the aperture of the RFQ electrode rods. The DPIS, using the concave surface electrode, was employed to accelerate C 6+ ion beams. The results indicated that both the beam current and the number of ions increased nearly twice with the proposed electrode shape compared to values obtained with the conventional electrode. This enhancement corresponded to the increased extraction area of the beam.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Extraction of P11 Resonance from pi-N Data and Its Stability

An important question about resonance extraction is how much resonance poles and residues extracted from data depend on a model used for the extraction, and on the precision of data. We address this question with the dynamical coupled-channel (DCC) model developed in Excited Baryon Analysis Center (EBAC) at JLab. We focus on the P11 pi-N scattering. We examine the model-dependence of the poles by varying parameters to a large extent within the EBAC-DCC model. We find that two poles associated with the Roper resonance are fairly stable against the variation. We also develop a model with a bare nucleon, thereby examining the stability of the Roper poles against different analytic structure of the P11 amplitude below pi-N threshold. We again find a good stability of the Roper poles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗