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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Tensile stress effect on epitaxial BiFeO 3 thin film grown on KTaO 3

Comprehensive crystal structural study is performed for BiFeO 3 (BFO) film grown on KTaO 3 (KTO) substrate using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Nano beam electron diffraction (NBED) combined with structure factor calculation and high resolution TEM images clearly reveal that the crystal structure within BFO thin film is rhombohedral BFO, i.e., bulk BFO phase. Epitaxial relationship found by NBED indicates the BFO film grows in a manner that minimizes lattice mismatch with KTO. It further suggests BFO film is under slight biaxial tensile stress (~0.35%) along in-plane direction. XRD reveals BFO lattice is under compressive stress (~1.6%), along out-of-plane direction as a result of the biaxial tensile stress applied along in-plane direction. This leads to Poisson’s ratio of ~0.68. In addition, we demonstrate (1) why hexagonal notation rather than pseudocubic one is required for accurate BFO phase evaluation and (2) a new XRD method that shows how rhombohedral BFO can readily be identified among other phases by measuring a rhombohedral specific Bragg’s peak.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Report on study of accelerating structures for muons in the velocity range of β=v/c=0.08-0.3 for J-PARC (g-2)/EDM experiment

We explored three types of structures for muon acceleration in the beam velocity range β = 0.08-0.3. Somewhat surprisingly, the venerable DTL looks like the best option based on its low maximal field, reasonable efficiency, and simplicity. It also provides the largest flexibility of the beam focusing options. The accelerating gradient for the DTL is the highest of the considered designs, and can be further increased if needed. The IH-APF structure, the baseline choice, is very attractive due its efficiency and potentially lower fabrication cost. However, detailed EM analysis indicated some reasons for concern, mainly related to the high maximal electric fields. We suggested to change the cavity design to CH type, which leads to a novel type of structure, CH-APF. Dr. M. Otani produced the CST model of CH-APF, and preliminary results of its EM analysis are encouraging. Unfortunately, the fabrication of CH-APF structure is likely more complicated than for IH-APF.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Optical and Structural Properties of Microcrystalline GaN on an Amorphous Substrate Prepared by a Combination of Molecular Beam Epitaxy and Metal-Organic Chemical Vapor Deposition

Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

14 SOLAR ENERGY↗
DOE OSTI2015

Long range surface plasmon resonance with ultra-high penetration depth for self-referenced sensing and ultra-low detection limit using diverging beam approach

Using an insulator-metal-insulator structure with dielectric having refractive index (RI) larger than the analyte, long range surface plasmon (SP) resonance exhibiting ultra-high penetration depth is demonstrated for sensing applications of large bioentities at wavelengths in the visible range. Based on the diverging beam approach in Kretschmann-Raether configuration, one of the SP resonances is shown to shift in response to changes in the analyte RI while the other is fixed; thus, it can be used as a built in reference. The combination of the high sensitivity, high penetration depth and self-reference using the diverging beam approach in which a dark line is detected of the high sensitivity, high penetration depth, self-reference, and the diverging beam approach in which a dark line is detected using large number of camera pixels with a smart algorithm for sub-pixel resolution, a sensor with ultra-low detection limit is demonstrated suitable for large bioentities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1971

Buckling analysis for axially compressed flat plates, structural sections, and stiffened plates reinforced with laminated composites

A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked plate and beam elements. Plates are idealized as multilayered orthotropic elements. Structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply-supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections, and stiffened plates is investigated. Buckling loads are the lowest of all possible general and local failure modes, and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections, and stiffened plates including boron-reinforced structures are discussed. In general correlations are reasonably good.

Viswanathan, A. V.↗
DOE OSTI2015

SU-E-T-166: Characterization of Efficiency and Plan Quality for the FFF Beams On Various Anatomical Sites

Purpose: To characterize efficiency and plan quality for the FFF beams for various sites. Methods: 5 brain, Head and Neck, prostate, lung and liver cancer patients IMRT plans (25 total) were generated on either Prowess 4.6 or Eclipse 13.5 using the same dose constraints for each treatment site. Step and shoot with static gantry IMRT was used for treatment delivery. PTV coverage, critical structure doses, MUs, number of segments and beam on times were compared. Results: The average PTV size was 29.0, 34.9, 89.2, 257.6, 289.2 cm3 for liver, lung, prostate, head and neck and brain respectively.All plans were normalized such that 95% of the PTV volume would receive at least 95% of prescribed dose. All doses to the critical structures for both the FFF and flat beam met the targeted dose constraints.For plans with field sizes < 10 cm, the number of segments and MUs required to achieve the same plan quality were similar. For these small field sizes with large dose per fraction, an increase in efficiency up to 58.8% is seen.Plans with field sizes > 10 cm, required 10% – 20% more segments and MUs for the FFF beam to achieve the same plan quality as the flat beam. Despite this, for fraction sizes less than 2.5 Gy the FFF beam is still approximately 13.9% more efficient in terms of delivery time. Conclusion: For the various treatment sites studied here, plans generated with the FFF beam were dosimetrically similar to those generated with a flattened beam. Despite the greater number of MUs and segments required to achieve the same plan quality as the flat beam for some plans, the FFF beam is still more efficient compared to the flat beam.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Plasma shape control by pulsed solenoid on laser ion source

A Laser ion source (LIS) provides high current heavy ion beams with a very simple mechanical structure. Plasma is produced by a pulsed laser ablation of a solid state target and ions are extracted by an electric field. It was difficult to manipulate the beam parameters of a LIS, since the plasma condition could only be adjusted by the laser irradiation condition. To enhance flexibility of LIS operation, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The experimentally obtained current profile was satisfactorily controlled by the pulsed magnetic field. Thus, this approach may also be useful to reduce beam emittance of a LIS.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Understanding the crack formation of graphite particles in cycled commercial lithium-ion batteries by focused ion beam - scanning electron microscopy

Here in this paper, the structure degradation of commercial Lithium-ion battery (LIB) graphite anodes with different cycling numbers and charge rates was investigated by focused ion beam (FIB) and scanning electron microscopy (SEM). The cross-section image of graphite anode by FIB milling shows that cracks, resulted in the volume expansion of graphite electrode during long-term cycling, were formed in parallel with the current collector. The crack occurs in the bulk of graphite particles near the lithium insertion surface, which might derive from the stress induced during lithiation and de-lithiation cycles. Subsequently, crack takes place along grain boundaries of the polycrystalline graphite, but only in the direction parallel with the current collector. Furthermore, fast charge graphite electrodes are more prone to form cracks since the tensile strength of graphite is more likely to be surpassed at higher charge rates. Therefore, for LIBs long-term or high charge rate applications, the tensile strength of graphite anode should be taken into account.

25 ENERGY STORAGE↗
NASA NTRS1990

InAs/Ga(1-x)In(x)Sb superlattices for infrared detector applications

The successful growth of InAs/Ga(1-x)In(x)Sb superlattices and their optical and structural characterization is discussed. Samples were grown by molecular beam epitaxy at fairly low substrate temperatures (less than 400 C). Structural quality was assessed by reflection high energy electron difrraction, transmission electron microscopy, and x ray diffraction. Excellent structures were achieved for growth on thick, strain relaxed GaSb buffer layers on GaAs substrates, despite a residual threading dislocation density of 10(exp 9)cm(exp -2) originating at the GaSb/GaAs interface. Despite a lattice mismatch of 1.7 percent, InAs/Ga(0.75)In(0.25)Sb superlattices are observed to be free of misfit dislocations at the thicknesses examined here, owing to the close lattice match between the superlattice and GaSb, which evenly distributes compressive and tensile stresses between the InAs and Ga(0.75)In(0.25)Sb layers. Photoluminescence and photoconductivity measurements indicate that the energy gaps of the strain-layer superlattices are smaller than those of InAs/GaSb superlattices with the same layer thicknesses, and are in agreement with the theoretical predictions of Smith and Mailhiot. Energy gaps of 80 to 250 meV (15 to 5 microns) have been measured for InAs/Ga(0.75)In(0.25)Sb superlattices with 45 to 25 A/25 A layer thickness. Results demonstrate that far-infrared cutoff wavelengths are compatible with the thin superlattice layers required for strong optical absorption in type-II superlattices.

Miles, Richard H.↗
NASA NTRS1991

Simulation of deep one- and two-dimensional redshift surveys

It is shown that slice or pencil-beam redshift surveys of galaxies can be simulated in a box with nonequal sides. This method saves a lot of computer time and memory while providing essentially the same results as from whole-cube simulations. A 2457.6/h Mpc-long rod (out to a redshift z = 0.58 in two opposite directions) is simulated using the standard biased cold dark matter model as an example to mimic the recent deep pencil-beam surveys by Broadhurst et al. (1990). The structures (spikes) seen in these simulated samples occur when the narrow pencil-beam pierces walls, filaments, and clusters appearing randomly along the line-of-sight. A statistical test for goodness of fit to a periodic lattice has been applied to the observations and the simulations. It is found that the statistical significance level (P = 15.4 percent) is not strong enough to reject the null hypothesis that the observations and the simulations were drawn at random from the same set.

Park, Changbom↗
DOE OSTI2019

Phase Space Dynamics of a Plasma Wakefield Dechirper for Energy Spread Reduction

Plasma-based accelerators have made impressive progress in recent years. However, the beam energy spread obtained in these accelerators is still at the ~1% level, nearly one order of magnitude larger than what is needed for challenging applications like coherent light sources or colliders. In plasma accelerators, the beam energy spread is mainly dominated by its energy chirp (longitudinally correlated energy spread). Furthermore, we demonstrate that when an initially chirped electron beam from a linac with a proper current profile is sent through a low-density plasma structure, the self-wake of the beam can significantly reduce its energy chirp and the overall energy spread. The resolution-limited energy spectrum measurements show at least a threefold reduction of the beam energy spread from 1.28% to 0.41% FWHM with a dechirping strength of ~1 (MV/m)/(mm pC). Refined time-resolved phase space measurements, combined with high-fidelity three-dimensional particle-in-cell simulations, further indicate the real energy spread after the dechirper is only about 0.13% (FWHM), a factor of 10 reduction of the initial energy spread.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Femtosecond Compression Dynamics and Timing Jitter Suppression in a THz-driven Electron Bunch Compressor

Herein we present the first demonstration of THz driven bunch compression and timing stabilization of a relativistic electron beam. Quasi-single-cycle strong field THz radiation is used in a shorted parallel-plate structure to compress a few-fC beam with 2.5 MeV kinetic energy by a factor of 2.7, producing a 39 fs rms bunch length and a reduction in timing jitter by more than a factor of 2 to 31 fs rms. This THz driven technique offers a significant improvement to beam performance for applications like ultrafast electron diffraction, providing a critical step towards unprecedented timing resolution in ultrafast sciences, and other accelerator applications using femtosecond-scale electron beams.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

FLUKA Analysis of Linac Fault Study Dose Rates

The planned Linac Fault Study was conducted on December 5 and 6, 2013 according to the Fault Study Procedure. Beam energy out the end of the Linac was typically 200 MeV, except for the LB-B1 Fault study that used 100 MeV beam out of the 4 th accelerator cavity (ACC4, also called and labeled as 4 th accelerating structure, AS4). The Linac fault study where beam was steered into the 4 th accelerator cavity (upstream) had beam energy of 150 MeV, since the last cavity was not traversed. Table I describes the list of the Beam Loss Fault Studies generated for verification of the Linac tunnel bulk and Linac supplemental shield effectiveness. The beam charge for the loss locations was typically measured at the LB-IT1 integrating current monitor after the ACC4 cavity, between LB-Q1 and LB-Q2. If beam was transported to the dumps a Faraday cup (LB-DU1 or LBDU2) monitor will yield the transported current to the dump, with the difference between LB-IT1 and LB-DU1 yielding the charge lost ahead of the dump. For beam miss-steered or intercepted ahead of the dumps the transport efficiency is zero. For the ACC4 beam loss fault the assumed current was the LB-ITI value before the miss-steering. For most of the faults the LB-ITI current was reading ~13.4 nC and the pulse rate was 1Hz, for 13.4 nC/s beam current.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Surface hardening alloy VT6 of electric explosion and by electron beam

The aim is to study the phase composition, structure and properties of the surface layer of the VT6 titanium alloy, subjected to combined treatment, consisting of alloying by the plasma of an electric explosion of a graphite fiber with a charge of the SiC powder and subsequent exposure by a high-intense electron beam. As a result of such treatment, a multiphase surface layer with a submicron and nanosize structure forms with the microhardness manifold exceeding its value in the sample volume are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Design of flexible proton beam imaging energy spectrometers (PROBIES)

A simple repeating step-filtered structure has been designed and deployed for the detection of MeV-energy proton beams produced from high-intensity short-pulse laser-driven experiments. Due to the diagnostic's ability to recover energy-resolved images of proton beams, it is called the proton beam imager and energy spectrometer (or PROBIES). The flexible design has two useful applications. First, it can be fielded in a configuration with a scintillator and imaging setup in order to collect proton beam information in high-repetition rate experiments. Here we show a configuration that collects the equivalent of a nine-film radiochromic film (RCF) stack, and a technique for using a neural network (NN) to rapidly analyze the images on millisecond time-scales. Second, when using RCF stacks as the detector, the energy resolution capability is greatly increased compared to traditional RCF stacks, while simultaneously reducing the total number of films required to make each measurement. We demonstrate a configuration that provides up to 90 spatially- and energy-resolved datapoints using just ten films. Both designs presented here can be easily customized for anticipated experimental outputs and manufactured at low cost. Such designs allow for rapid prototyping using modern high-accuracy 3D printers or on-demand computer numerical control machining to reduce the reliance on time-consuming film media, analysis, or bulky electro-magnetically dispersing spectrometers. The analysis of data is discussed and a methodology for constructing a NN that is capable of rapidly analyzing data on-the-fly with greater than 95% accuracy is presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Shared Research Facilities: A Key Source of U.S. Scientific and Industrial Leadership

By the 1970s, it had become clear that X-ray and neutron beams could provide insights into the structure and properties of materials that were not obtainable in any other way. It was also clear that the cost and scale of the facilities required to produce such beams were beyond the reach of individual scientists or even major universities. So forty years ago, the Basic Energy Sciences (BES) office of DOE began to build dedicated facilities that could be used—shared—by many researchers. The result has been spectacular discoveries and insights into materials important for all forms of energy production and for national security, as well as insights into complex biological molecules and new drugs important for human health.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1994

The application of the Wigner Distribution to wave type identification in finite length beams

The object of the research described in this paper was to develop a means of identifying the wave-types propagating between two points in a finite length beam. It is known that different structural wave-types possess different dispersion relations: i.e., that their group speeds and the frequency dependence of their group speeds differ. As a result of those distinct dispersion relationships, different wave-types may be associated with characteristic features when structural responses are examined in the time frequency domain. Previously, the time-frequency character of analytically generated structural responses of both single element and multi-element structures were examined by using the Wigner Distribution (WD) along with filtering techniques that were designed to detect the wave-types present in the responses. In the work to be described here, the measure time-frequency response of finite length beam is examined using the WD and filtering procedures. This paper is organized as follows. First the concept of time-frequency analysis of structural responses is explained. The WD is then introduced along with a description of the implementation of a discrete version. The time-frequency filtering techniques are then presented and explained. The results of applying the WD and the filtering techniques to the analysis of a transient response is then presented.

Wahl, T. J.↗
NASA NTRS1972

Buckling analysis for structural sections and stiffened plates reinforced with laminated composites.

A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked flat plate and beam elements. Plates are idealized as multilayered orthotropic elements; structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections and stiffened plates is investigated. Buckling loads are found as the lowest of all possible general and local failure modes and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections and stiffened plates including boron-reinforced structures are discussed. In general, correlations are reasonably good.

Viswanathan, A. V.↗