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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Electron acceleration through two successive electron beam driven wakefield acceleration stages

Structure based wakefield acceleration may provide a viable approach for accelerating sufficiently large numbers of electrons and positrons at the high gradient needed to meet the luminosity, efficiency, and cost requirements of a future linear collider. An important step in proving its viability is the demonstration of acceleration in multiple stages. Here we show the results of the first experimental demonstration of staged two beam wakefield acceleration, conducted at the Argonne Wakefield Accelerator Facility (AWA), in which a 0.5 nC electron bunch gained equal amounts of energy in two stages (~2.4 MeV per stage, corresponding to an average acceleration gradient of ~70 MeV/m). Meanwhile 150MeV/m of acceleration in a single stage has been achieved. The demonstration experiment should be scalable to staged-acceleration at gradients of the order of 200 to 300 MeV/m. Furthermore, such a development would considerably reduce both the cost and footprint of both a future high-energy physics (HEP) collider, as well as future X-ray light sources.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Improved DC Gun and Insulator Assembly

Many user facilities such as synchrotron radiation light sources and free electron lasers rely on DC high voltage photoguns with internal field gradients as high as 10 to 15 MV/m. These high gradients often lead to field emission which poses serious problems for the photocathode used to generate the electron beam and the ceramic insulators used to bias the photocathode at high voltage. Ceramic insulators are difficult to manufacture, require long commissioning times, and have poor reliability, in part because energetic electrons bury themselves in the ceramic causing a buildup of charge and eventual puncture, and also because large diameter ceramics are difficult to braze reliably. The lifetimes of photo cathodes inside high current DC guns exhibiting field emission are limited to less than a hundred hours. Reducing the surface gradients on the metals reduces the field emission, which serves to maintain the required ultrahigh vacuum condition. A novel gun design with gradients around 5 MV/m and operating at 350 kV, a major improvement over existing designs, was proposed that allows for the in-situ replacement of photo cathodes in axially symmetric designs using inverted ceramics. In this project, the existing JLAB CEBAF asymmetric gun design with an inverted ceramic support was modeled and the beam dynamics characterized. An improved structure was designed that reduces the surface gradients and improves the beam optics. To minimize the surface gradients, a number of electrostatic gun designs were studied to determine the optimum configuration of the critical electrodes within the gun structure. Coating experiments were carried out to create a charge dissipative coating for cylindrical ceramics. The phase II proposal, which was not granted, included the design and fabrication of an axially symmetric DC Gun with an inverted ceramic that would operate with less than 5 MV/m at 350 kV and would be designed with an in-situ replaceable photo-cathode.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

A fast chopper for medium energy beams

The key elements have been constructed for a fast chopper system capable of removing single 2.5 MeV proton bunches spaced at 325 MHz. The average chopping rate is ~ 1 MHz. The components include a pulse delaying microstrip structure for deflecting the beam, high voltage (1.2 kV) fast (ns rise time) pulsers, and an associated wideband combiner. Various designs for the deflecting structures have been studied. Measurements of the microstrip structures' coverage factors and pulse shapes are presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

SU-E-T-547: A Method to Correlate Treatment Planning Issue with Clinical Analysis for Prostate Stereotactic Body Radiotherapy (SBRT)

Purpose: In this study, the algorithms and calculation setting effect and contribution weighing on prostate Volumetric Modulated Arc Therapy (VMAT) based SBRT were evaluated for clinical analysis. Methods: A low risk prostate patient under SBRT was selected for the treatment planning evaluation. The treatment target was divided into low dose prescription target volume (PTV) and high Dose PTV. Normal tissue constraints include urethra and femur head, and rectum was separated into anterior, lateral and posterior parts. By varying the constraint limit of treatment plan calculation setting and algorithms, the effect on dose coverage and normal tissue dose constraint parameter carried effective comparison for the nominal prescription and constraint. For each setting, their percentage differences to the nominal value were calculated with geometric mean and harmonic mean. Results: In the arbitrary prostate SBRT case, 14 variables were selected for this evaluation by using nominal prescription and constraint. Six VMAT planning settings were anisotropic analytic algorithm stereotactic beam with and without couch structure in grid size of 1mm and 2mm, non stereotactic beam, Acuros algorithm . Their geometry means of the variable sets for these plans were 112.3%, 111.9%, 112.09%, 111.75%, 111.28%, and 112.05%. And the corresponding harmonic means were 2.02%, 2.16%, 3.15%, 4.74%, 5.47% and 5.55%. Conclusions: In this study, the algorithm difference shows relatively larger harmonic mean between prostate SBRT VMAT plans. This study provides a methodology to find sensitive combined variables related to clinical analysis, and similar approach could be applied to the whole treatment procedure from simulation to treatment in radiotherapy for big clinical data analysis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Semiconductor Behavior and Room Temperature Ferromagnetism in e-Beam Evaporated Co/TiO{sub 2} Multilayer Thin Films

The Co/TiO{sub 2} multilayer thin films have been deposited by e-beam evaporation method on glass substrates in vacuum and annealed in air at 773 K for 1 h. The crystal structure, surface morphology, optical properties, electrical properties and magnetic properties of Co/TiO{sub 2} multilayer thin films have been systematically investigated. The results showed that the particle sizes were significantly reduced when the samples are annealed and the enlargement of particle size occurred when the samples thickness is increased. The spectroscopic analysis exhibited enhanced transmittance and higher optical band gap of annealed sample than the as-deposited one and it was decreased with sample thickness. The resistivity measurement confirmed resistivity decreament with temperature. Furthermore, by investigating the magnetic properties, room temperature ferromagnetism was observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

BEAM DYNAMICS STUDIES OF 499 MHz SUPERCONDUCTING RF-DIPOLE DEFLECTING CAVITY SYSTEM

A 499 MHz deflecting cavity has been designed as a three-way beam spreader to separate an electron beam into 3 beams. The rf tests carried out on the superconducting rf-dipole cavity have demonstrated that a transverse voltage of 4.2 MV can be achieved with a single cavity. This paper discusses the beam dynamics on a deflecting structure operating in continuous-wave mode with a relativistic beam. The study includes the analysis on emittance growth, energy spread, and change in bunch size including effects due to field non-uniformities.

De Silva, Payagalage Subashini↗
NASA NTRS1992

Microwave properties of peeled HEMT devices sapphire substrates

The focus of this research is to demonstrate the first full radio frequency characterization of high electron mobility transistor (HEMT) device parameters. The results of this research are used in the design of circuits with peeled HEMT devices, e.g. 10 GHz amplifiers. Devices were fabricated using two HEMT structures grown by molecular beam epitaxy methods. A 500 A AlAs release layer for 'peel off' was included under the active layers of the structure. The structures are a homogeneously doped Al(0.3)GA(0.7)As/GaAs and a delta doped square well Al(.23)Ga(.77)As/GaAs HEMT structure. Devices were fabricated using a mesa isolation process. Contacts were done by sequentially evaporating Au/Ge/Au/Ni/Au followed by rapid thermal anneal at 400 C for 15 seconds. Gates were wet etch recessed and 1 to 1.4 micron Ti/Au gate metal was deposited. Devices were peeled off the GaAs substrate using Apiezon wax to support the active layer and a HF:DI (1:10) solution to remove the AlAs separation layer. Devices were then attached to sapphire substrates using van der Waals bonding.

Young, Paul G.↗
DOE OSTI2016

Nanoforging Single Layer MoSe 2 Through Defect Engineering with Focused Helium Ion Beams

Development of devices and structures based on the layered 2D materials critically hinges on the capability to induce, control, and tailor the electronic, transport, and optoelectronic properties via defect engineering, much like doping strategies have enabled semiconductor electronics and forging enabled introduction of iron age. Here, we demonstrate the use of a scanning helium ion microscope (HIM) for tailoring the functionality of single layer MoSe 2 locally, and decipher associated mechanisms at atomic level. We demonstrate He + beam bombardment that locally creates vacancies, shifts the Fermi energy landscape and thereby increases the Young s modulus of elasticity. Furthermore, we observe for the first time, an increase in the B-exciton photoluminescence signal from the nanoforged regions at room temperature. In conclusion, the approach for precise defect engineering demonstrated here opens opportunities for creating functional 2D optoelectronic devices with a wide range of customizable properties that include operating in the visible region.

42 ENGINEERING↗
NASA NTRS2020

Beam Propagation Through Atmospheric Turbulence Using an Altitude-Dependent Structure Profile with Non-Uniformly Distributed Phase Screens

For free-space optical communication systems, numerical wave optics simulations provide a useful technique for modeling turbulence-induced beam degradation when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such applications we use a split-step method modeling the turbulence as a series of random phase screens using the Hufnagel-Valley turbulence profile. We employ a space-to-ground case study to examine the irradiance and phase statistics for uniformly and non-uniformly located screens and find better agreement with theory using a non-uniform discretization minimizing the contribution of each screen to the total scintillation. In this poster, we summarize the method and the results of the case study including a comparison to layered models used in astronomical imaging applications.

Chahine, Yousef K.↗
DOE OSTI2018

Micro- and macro-structural heterogeneities in 316L stainless steel prepared by electron-beam melting

Highlights: • Electron beam melting manufactured parts has a complicated thermal history. • The microstructure varies with the position in the sample. • Pronounced molybdenum segregation at the top disappears at the bottom. • Fast molybdenum diffusion in cell boundaries as well as grain boundaries. - Abstract: This is a study of the micro- and macrostructural variations in samples of stainless steel with the overall composition of the grade 316L, produced using electron beam melting. Electron beam melting is one of the processing methods under consideration for manufacturing some of the International Thermo- Nuclear Experimental Reactor In-Vessel components. Therefore further studies of the homogeneity of the material were conducted. Electron beam melting results in a complicated thermal history of the manufactured part giving a significant impact on the microstructure. A cellular structure that is often observed in samples prepared by selective laser melting was found in the top layers of the specimens. Further down, the structure changed until the cellular structure was almost non-existing, and the grain boundaries had become more pronounced. This revelation of a heterogeneous structure throughout the entire part is crucial for large-scale industrial applications like the Thermo- Nuclear Experimental Reactor to make sure that it is understood that the properties of the material might not be the same at every point, as well as to assure that the correct post-treatment is done. It is also exposed that a significant part of this change is due to molybdenum redistribution inside the sample when it diffuses from the cell boundaries into the cells, and into bigger agglomerates in the grain boundaries. This diffusion seems not to affect the microhardness of the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Empirically Derived Strength of Residential Roof Structures for Solar Installations

Engineering certification for the installation of solar photovoltaic (PV) modules on wood roofs is often denied because existing wood roofs do not meet structural design codes. This work is intended to show that many roofs are actually sufficiently strong given the conservatism in codes, documented allowable strengths, roof structure system effects, and beam composite action produced by joist-sheathing interaction. This report provides results from a testing program to provide actual load carrying capacity of residential rooftops. The results reveal that the actual load carrying capacity of structural members and systems tested are significantly stronger than allowable loads provided by the International Residential Code (IRC 2009) and the national structural code found in Minimum Design Loads for Buildings and Other Structures (ASCE 7-10). Engineering analysis of residential rooftops typically ignores the system affects and beam composite action in determining rooftop stresses given a potential PV installation. This extreme conservatism combined with conservatism in codes and published allowable stress values for roof building materials (NDS 2012) lead to the perception that well built homes may not have adequate load bearing capacity to enable a rooftop PV installation. However, based on the test results presented in this report of residential rooftop structural systems, the actual load bearing capacity is several times higher than published values (NDS 2012).

Dwyer, Stephen F.↗
DOE OSTI2014

Near- and far-field measurements of phase-ramped frequency selective surfaces at infrared wavelengths

Near- and far-field measurements of phase-ramped loop and patch structures are presented and compared to simulations. The far-field deflection measurements show that the phase-ramped structures can deflect a beam away from specular reflection, consistent with simulations. Scattering scanning near-field optical microscopy of the elements comprising the phase ramped structures reveals part of the underlying near-field phase contribution that dictates the far-field deflection, which correlates with the far-field phase behavior that was expected. These measurements provide insight into the resonances, coupling, and spatial phase variation among phase-ramped frequency selective surface (FSS) elements, which are important for the performance of FSS reflectarrays.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structure-phase states evolution in Al-Si alloy under electron-beam treatment and high-cycle fatigue

By methods of scanning and transmission electron diffraction microscopy the analysis of structure-phase states and defect substructure of silumin subjected to high-intensity electron beam irradiation in various regimes and subsequent fatigue loading up to failure was carried out. It is revealed that the sources of fatigue microcracks are silicon plates of micron and submicron size are not soluble in electron beam processing. The possible reasons of the silumin fatigue life increase under electron-beam treatment are discussed.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Scanning Light Sheet Would Measure Deflection Of Beam

Scanning-light-sheet apparatus designed to measure linear and angular displacement or deflection of structure. Intended specifically to measure deflection of beam-shaped truss structure. Includes conventional low-powered laser, lenses, mounts, single-axis optical scanner, several photodiodes, and electronic controller. Apparatus measures motion of structure and also used to determine positions, deflections, and velocities. Besides use in aerospace field, displacement measurements have many applications in construction-equipment and automotive industries.

Tcheng, Ping↗
DOE OSTI2014

Spatial shaping for generating arbitrary optical dipole traps for ultracold degenerate gases

We present two spatial-shaping approaches – phase and amplitude – for creating two-dimensional optical dipole potentials for ultracold neutral atoms. When combined with an attractive or repulsive Gaussian sheet formed by an astigmatically focused beam, atoms are trapped in three dimensions resulting in planar confinement with an arbitrary network of potentials – a free-space atom chip. The first approach utilizes an adaptation of the generalized phase-contrast technique to convert a phase structure embedded in a beam after traversing a phase mask, to an identical intensity profile in the image plane. Phase masks, and a requisite phase-contrast filter, can be chemically etched into optical material (e.g., fused silica) or implemented with spatial light modulators; etching provides the highest quality while spatial light modulators enable prototyping and realtime structure modification. This approach was demonstrated on an ensemble of thermal atoms. Amplitude shaping is possible when the potential structure is made as an opaque mask in the path of a dipole trap beam, followed by imaging the shadow onto the plane of the atoms. While much more lossy, this very simple and inexpensive approach can produce dipole potentials suitable for containing degenerate gases. High-quality amplitude masks can be produced with standard photolithography techniques. Amplitude shaping was demonstrated on a Bose-Einstein condensate.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1980

Post-buckling behavior of a beam-column on a nonlinear elastic foundation with a gap

The structural behavior of an elastic beam-column placed with a gap between two nonlinearity elastic layers each resting on a rigid foundation was examined. The beam-column was laterally supported at both ends and subjected to a uniform transverse load and axial compression. Its slenderness was such that the axial compressive force exceeds the amount that would be necessary to buckle it as a simple supported column. The elastic layers were represented by an elastic foundation with a strongly nonlinear specific reaction taken as a rapidly increasing function of the layer compression. The analytical model developed simulated the entire pattern of the deflection and stress state including layer and end support reactions, under gradually increasing axial force.

Kuznetsov, E. N.↗
NASA NTRS1981

Composite beam builder

The building block approach to large space structures is discussed, and the progress made in constructing aluminum beams is noted. It is pointed out that composites will also be required in space structures because they provide minimal distortion characteristics during thermal transients. A composite beam builder currently under development is discussed, with attention given to cap forming and the fastening of cross-braces. The various composite materials being considered are listed, along with certain of their properties. The need to develop continuous forming stock up to 300 m long is stressed.

Poveromo, L. M.↗