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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Generation of structured coherent extreme ultraviolet beams from an MgO crystal

Short wavelength high-harmonic sources are undergoing intense development for applications in spectroscopy and microscopy. Despite recent progress in peak and average power, spatial control over coherent extreme ultraviolet (XUV) beams remains a formidable challenge due to the lack of suitable optical elements for beam shaping and control. In this work, we demonstrate a robust and precise approach that structures XUV high-order harmonics in space as they are emitted from a nanostructured MgO crystal. Our demonstration paves the way for bridging the numerous applications of shaped light beams from the visible to the short wavelengths, with potential uses for applications in microscopy and nanoscale machining.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Reflection of light beams from a chirped dielectric plane-layered structure

The reflection of light beams with various widths of the angular spectrum from a chirped plane-layered dielectric structure is numerically studied. For wide beams, the total lateral shift of the reflected beam depends on the position of the photonic barrier inside the structure and the value of the Goos – Hänchen shift. For narrow beams, the region of the interaction with the structure increases, the profile broadens and the reflected beam wavefront becomes phase modulated. It is shown that the light reflected from a quasi-periodic structure with negative spatial dispersion undergoes focusing. (light beams)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1995

Compensation of Gravity-Induced Structural Deformations on a Beam- Waveguide Antenna Using a Deformable Mirror

At the NASA Deep Space Network (DSN) Goldstone Complex, a 34-meter- diameter beam-waveguide antenna, DSS-13, was constructed in 1988-1990 and has become an integral part of an advanced systems program and a test bed for technologies being developed to introduce Ka-band (32 GHz) frequencies into the DSN. A method for compensating the gravity- induced structural deformations in this large antenna is presented.

technologies DSN↗
DOE OSTI2015

Dynamic hysteretic sensing model of bending-mode Galfenol transducer

A dynamic hysteretic sensing model has been developed to predict the dynamic responses of the magnetic induction, the stress, and the output voltage for a bending-mode Galfenol unimorph transducer subjected simultaneously to acceleration and bias magnetic field. This model is obtained by coupling the hysteretic Armstrong model and the structural dynamic model of the Galfenol unimorph beam. The structural dynamic model of the beam is founded based on the Euler-Bernouli beam theory, the nonlinear constitutive equations, and the Faraday law of electromagnetic induction. Comparisons between the calculated and measured results show the model can describe dynamic nonlinear voltage characteristics of the device, and can predict hysteretic behaviors between the magnetic induction and the stress. Moreover, the model can effectively analyze the effects of the bias magnetic field, the acceleration amplitude, and frequency on the root mean square voltage of the device.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1978

Gamma ray facilities at the University of Maryland cyclotron

A special beam line was set up in a separate shielded experimental room to provide a low background station for gamma-ray measurements at the University of Maryland cyclotron. The transmitted beam leaving the target is gathered in by a magnetic quadrupole lens located 1.8 m further downstream and focused on a Faraday cup located on the far side of the 2.5 m thick concrete shielding wall of the experimental room. A software computer program permits timing information ot be obtained using the cyclotron beam fine structure as a time reference for the observed gamma-ray events. Measurements indicate a beam fine structure width of less than 1.2 nanoseconds repeated, for example, in the case of 140 MeV alpha particles every 90 nanoseconds. Twelve contiguous time channels of adjustable width may be set as desired with reference to the RF signal. This allows the creation of 12 separate 8192 channel analyzers.

Hornyak, W. F.↗
DOE OSTI2017

Generation of Ramped Current Profiles in Relativistic Electron Beams Using Wakefields in Dielectric Structures

We show that temporal pulse tailoring of charged-particle beams is essential to optimize efficiency in collinear wakefield acceleration schemes. In this Letter, we demonstrate a novel phase space manipulation method that employs a beam wakefield interaction in a dielectric structure, followed by bunch compression in a permanent magnet chicane, to longitudinally tailor the pulse shape of an electron beam. This compact, passive, approach was used to generate a nearly linearly ramped current profile in a relativistic electron beam experiment carried out at the Brookhaven National Laboratory Accelerator Test Facility. Here, we report on these experimental results including beam and wakefield diagnostics and pulse profile reconstruction techniques.

43 PARTICLE ACCELERATORS↗
NASA NTRS1988

Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

Benz, R. G., II↗
DOE OSTI2013

Effect of the annealing temperature on the low-temperature photoluminescence in Si:Er light-emitting structures grown by molecular-beam epitaxy

The photoluminescence spectra of light-emitting structures based on silicon doped with erbium during the course of molecular-beam epitaxy at a temperature of 500 Degree-Sign C are studied at 4.2 K on being annealed at 800-900 Degree-Sign C. Three sets of lines belonging to the emitting centers of erbium in silicon with a low oxygen-impurity concentration are revealed.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Design of titania nanotube structures by focused laser beam direct writing

In this work, we report on electrochemical fabrication of titania films consisting of nanotubes (NTs) and their treatment by focused laser beam. The results of sample characterization by optical and scanning electron microscopy, cathodoluminescence imaging, and Raman scattering scanning spectroscopy are compared to those inherent to specimens subjected to thermal treatment in a furnace. The obtained data demonstrate possibilities for controlling crystallographic structure of TiO{sub 2} NTs by focused laser beam direct writing. These findings open new prospects for the design and fabrication of spatial architectures based on titania nanotubes.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Molecular beam epitaxy of high structural quality Bi{sub 2}Se{sub 3} on lattice matched InP(111) substrates

Epitaxial layers of the topological insulator Bi{sub 2}Se{sub 3} have been grown by molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High resolution X-ray diffraction shows a significant improvement of Bi{sub 2}Se{sub 3} crystal quality compared to layers deposited on other substrates. The measured full width at half maximum of the rocking curve is {Delta}{omega}=13 arc sec, and the ({omega}-2{theta}) scans exhibit clear layer thickness fringes. Atomic force microscope images show triangular twin domains with sizes increasing with layer thickness. The structural quality of the domains is confirmed on the microscopic level by transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

We propose a new amplification regime based on a synchronous operation of four degenerate electromagnetic (EM) modes in a slow-wave structure and the electron beam, referred to as super synchronization. These four EM modes arise in a Fabry-Pérot cavity when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures based on synchronization with only a single EM mode. We demonstrate giant gain scaling with respect to the length of the slow-wave structure compared to conventional Pierce type single mode traveling wave tube amplifiers. We construct a coupled transmission line model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using the Pierce model generalized to multimode interaction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

Design procedures for fiber composite structural components: Rods, columns and beam columns

Step by step procedures are described which are used to design structural components (rods, columns, and beam columns) subjected to steady state mechanical loads and hydrothermal environments. Illustrative examples are presented for structural components designed for static tensile and compressive loads, and fatigue as well as for moisture and temperature effects. Each example is set up as a sample design illustrating the detailed steps that are used to design similar components.

Chamis, C. C.↗
DOE OSTI2013

pBEAM Documentation: Release 0.1.0

The Polynomial Beam Element Analysis Module (pBEAM) is a finite element code for beam-like structures. It was originally written to analyze tower/monopiles and rotor blades of wind turbines but can be used for any beam-like structure. This document discusses installation, usage, and documentation of the module.

17 WIND ENERGY↗
DOE OSTI2016

Hollow structure formation of intense ion beams with sharp edge in background plasmas

The transport of intense ion beams with sharp radial beam edge in plasmas has been studied with two-dimensional electromagnetic particle simulations. The initial solid beam evolves into a hollow beam due to the nonlinear sharp transverse force peak in the regions of beam edge. The magnitude and nonlinearity of this peak are enhanced as the ion beam travels further into the plasma, due to the self-consistent interactions between the beam ions and the plasma electrons. This structure formation is shown to be independent on the beam radius.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Ion-beam-induced magnetic and structural phase transformation of Ni-stabilized face-centered-cubic Fe films on Cu(100)

Metastable face-centered cubic (fcc) Fe/Cu(100) thin films are good candidates for ion-beam magnetic patterning due to their magnetic transformation upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni for stabilizing the fcc γ phase. The amount of Ni necessary to stabilize nonmagnetic, transformable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phase diagram revealing the transformable region is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Electronic structure, morphology and emission polarization of enhanced symmetry InAs quantum-dot-like structures grown on InP substrates by molecular beam epitaxy

The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As{sub 2} source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model and realistic system parameters. The results of calculations were compared to measured polarization-resolved photoluminescence data. On the basis of measured degree of linear polarization of the surface emission, the in-plane shape of the QDs has been assessed proving a substantial increase in lateral symmetry. This results in quantum-dot rather than quantum-dash like properties, consistent with expectations based on the growth conditions and the structural data.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Electric potential structures and propagation of electron beams injected from a spacecraft into a plasma

One-dimensional Vlasov simulations are used to study the propagation of electron beams injected from a spacecraft into an ambient plasma and the associated potential structures. It is shown that, for a given beam velocity, the propagation velocity and the potential structure depends on the beam density. In the case of moderate beams, a double layer forms near the beam head which propagates into the ambient plasma much more slowly than the initial beam velocity.

Singh, Nagendra↗