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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 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Kinetic energy classification and smoothing for compact B-spline basis sets in quantum Monte Carlo

Quantum Monte Carlo calculations of defect properties of transition metal oxides have become feasible in recent years due to increases in computing power. As the system size has grown, availability of on-node memory has become a limiting factor. Saving memory while minimizing computational cost is now a priority. The main growth in memory demand stems from the B-spline representation of the single particle orbitals, especially for heavier elements such as transition metals where semi-core states are present. Despite the associated memory costs, splines are computationally efficient. In this paper, we explore alternatives to reduce the memory usage of splined orbitals without significantly affecting numerical fidelity or computational efficiency. We make use of the kinetic energy operator to both classify and smooth the occupied set of orbitals prior to splining. By using a partitioning scheme based on the per-orbital kinetic energy distributions, we show that memory savings of about 50% is possible for select transition metal oxide systems. Finally, for production supercells of practical interest, our scheme incurs a performance penalty of less than 5%.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

A compact multi-plane broadband (0.5-17 keV) spectrometer using a single acid phthalate crystal

Acid phthalate crystals such as KAP crystals are a method of choice to record x-ray spectra in the soft x-ray regime ( E ~ 1 keV) using the large (001) 2 d = 26.63 Å spacing. Reflection from many other planes is possible, and knowledge of the 2d spacing, reflectivity, and resolution for these reflections is necessary to evaluate whether they hinder or help the measurements. Burkhalter et al. [J. Appl. Phys., 52, 4379 (1981)] showed that the (013) reflection has efficiency comparable to the 2nd order reflection (002), and it can overlap the main first order reflection when the crystal bending axis ( b -axis) is contained in the dispersion plane, thus contaminating the main (001) measurement in a convex crystal geometry. We present a novel spectrograph concept that makes these asymmetric reflections helpful by setting the crystal b -axis perpendicular to the dispersion plane. In such an instance, asymmetric reflections do not overlap with the main (001) reflection and each reflection can be used as an independent spectrograph. In this work we demonstrate an achieved spectral range of 0.8-13 keV with a prototype setup. The detector measurements were reproduced with a 3D ray-tracing code.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Design of a compact hard x-ray split-delay system based on variable-gap channelcut crystals

Free Electron Lasers provide unique opportunities in investigating ultrafast atomic-scale dynamics using X-ray Pump X-ray Probe and two-pulse X-ray Speckle Visibility Spectroscopy techniques. However the performance of these techniques critically relies on maintaining the spatial overlap between the two beams at the sample location while adjusting the temporal separation between the two pulses. This presents major challenges for realizing hard X-ray split-delay optics, i.e an optical arrangement capable of generating two X-ray pulses separated in time from a single X-ray pulse. More specifically, it translates into nanoradian-scale angular precision requirements. We present here a hard X-ray split-delay optics concept using 4 channelcut crystals, where the beam path length difference can be adjusted by the linear translation of two crystals having non-parallel gaps. Having two Bragg reflections from the same monolithic crystal in the opposite direction cancels positioning errors from underlying stages. As a result, this concept has lower motion precision requirements on the hardware, and yet leads to significantly higher output beam angular stability. We present a case study for this concept that covers an energy range from 7 to 12 keV and provides a delay range from -3 to 10 ps at 9 keV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Multiple monoenergetic gamma radiography (MMGR) with a compact superconducting cyclotron

Smuggling of special nuclear materials and nuclear devices through borders and ports of entry constitutes a major risk to global security. Technologies are needed to reliably screen the flow of commerce for the presence of high-Z materials such as uranium and plutonium. Here, we present an experimental proof-of-concept of a technique that uses inelastic (p,p') nuclear reactions to generate monoenergetic photons, which provide means to measure the areal density and the effective-Z (Z eff ) of an object with an accuracy surpassing that achieved by current methods. We use an ION-12 SC superconducting 12 MeV proton cyclotron to produce 4.4, 6.1, 6.9, and 7.1 MeV photons from a variety of nuclear reactions. Using these photons in a transmission mode, we show that we are able to accurately reconstruct the areal densities and Zeff of a test object. This methodology could enable mobile applications to screen commercial cargoes with high material specificity, providing a means of distinguishing common cargo materials from high-Z materials that include uranium and plutonium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Compact, portable, laser induced fluorescence diagnostic for laboratory plasma sources

As diagnostic groups are increasingly called upon to participate in experimental campaigns at remote facilities, there is a need to develop portable versions of plasma diagnostic systems. One such diagnostic is laser induced fluorescence (LIF). Here, we describe a portable LIF apparatus that eliminates the need for an optical table, beam splitters, and an optical chopper. All of the light exiting the laser system is coupled through optical fibers to the experiment and housekeeping diagnostics. Here, the collected light is coupled through an optical fiber as well. A key feature is modulation of the tapered amplifier current instead of physical modulation of the laser output. Using this portable LIF system, measurements of ion temperature, ion flow, and relative metastable ion density are reported for two different remote experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Applications of machine learning to a compact magnetic spectrometer for high repetition rate, laser-driven particle acceleration

Accurately and rapidly diagnosing laser–plasma interactions is often difficult due to the time-intensive nature of the analysis and will only become more so with the rise of high repetition rate lasers and the desire to implement feedback on a commensurate timescale. Diagnostic analysis employing machine learning techniques can help address this problem while maintaining a high degree of accuracy. We report on the application of machine learning to the analysis of a scintillator-based electron spectrometer for experiments on high intensity, laser–plasma interactions at the Colorado State University Advanced Lasers and Extreme Photonics facility. Our approach utilizes a neural network trained on synthetic data and tested on experiments to extract the accelerated electron temperature. By leveraging transfer learning, we demonstrate an improvement in the neural network accuracy, decreasing the network error by 50%.

Swanson, K. K. (ORCID:0000000286880568)↗
DOE OSTI2023

Compact, portable, automatic sample changer stick for cryostats and closed-cycle refrigerators

Beamlines are facilities that produce and deliver highly focused and intense beams of radiation, typically x rays, synchrotron radiation, or neutrons, for scientific research purposes. Millions of dollars are spent annually to maintain and operate these scientific beamlines, oftentimes running continuously between cycles. To reduce human intervention and improve productivity, mechanical sample changers are often commissioned for use. Designing sample changers is difficult because mechanical parts can be bulky, expensive, and challenging to design for instruments with low volume access, high radiation, and cryogenic environments. We present a portable and inexpensive sample changer stick that can hold and manipulate up to four samples, specifically designed for use with cryogenic closed-cycle refrigerators. The sample changer stick enables rapid and efficient exchange of samples without manual intervention, and is compatible with standard sample mounts such as vanadium cans. The sample changer stick includes a motorized rotation and lancing mechanism, which enables the precise positioning of each sample in the neutron beam, while ensuring compatibility with the operating temperatures and vacuum conditions required for closed-cycle refrigerators. The design has been successfully tested at the VISION beamline at the Spallation Neutron Source. The mechanical action and software controls are detailed. Furthermore, the sample changer stick is a valuable tool for scientists working with cryogenic closed-cycle refrigerators.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Cryogen-free modular scanning tunneling microscope operating at 4-K in high magnetic field on a compact ultra-high vacuum platform

One of the daunting challenges in modern low temperature scanning tunneling microscopy (STM) is the difficulty of combining atomic resolution with cryogen-free cooling. Further functionality needs, such as ultra-high vacuum (UHV), high magnetic field (HF), and compatibility with μm-sized samples, pose additional challenges to an already ambitious build. We present the design, construction, and performance of a cryogen-free, UHV, low temperature, and high magnetic field system for modular STM operation. An internal vibration isolator reduces vibrations in this system, allowing for atomic resolution STM imaging while maintaining a low base temperature of ∼4 K and magnetic fields up to 9 T. Samples and tips can be conditioned in situ utilizing a heating stage, an ion sputtering gun, an e-beam evaporator, a tip treater, and sample exfoliation. In situ sample and tip exchange and alignment are performed in a connected UHV room temperature stage with optical access. Multisite operation without breaking vacuum is enabled by a unique quick-connect STM head design. A novel low-profile vertical transfer mechanism permits transferring the STM between room temperature and the low temperature cryostat.

Instruments & Instrumentation↗
DOE OSTI2025

A compact x-ray spectrometer for measurements of electron temperature distributions in inertial confinement fusion implosions at OMEGA

The Wedge Range Filter (WRF), commonly used for proton spectroscopy at the OMEGA Laser Facility and National Ignition Facility, is adapted to measure the x-ray continuum spectrum through transmission measurement using a continuous-gradient filter. Continuum x rays emitted from the hotspot of an implosion contain information about the plasma composition and electron temperature. The WRF data are leveraged to probe this distribution, specifically the electron temperature distribution. In this work, the data recorded with the WRF are forward modeled using a temperature distribution model folded with the WRF response function. An uncertainty analysis is conducted through a Bayesian regression algorithm using a Hamiltonian Monte Carlo sampler. This analysis enables the uncertainties in the instrument response to be folded into the uncertainty estimation of the electron temperature and absolute x-ray emission. Data analysis for a series of OMEGA implosions is presented and compared with radiation hydrodynamic simulations.

Lasers↗
DOE OSTI2025

Compact in situ probe for magnetotransport measurements of 2D materials under variable tensile strain

The recent development of freestanding oxide membranes has opened new opportunities for strain engineering of transition metal oxides beyond values accessible in bulk samples. While a number of studies have been performed with fixed strain, the ability to dynamically control the strain state during measurement would be greatly enabling. To this end, we present an in situ uniaxial strain probe optimized for transport measurements of tensile-strained 2D or quasi-2D materials down to 2 K. Utilizing a flexible polyimide substrate as the stress transfer medium, our platform simplifies the sample preparation process and allows precise alignment of strain fields relative to the crystalline axes. An in situ optical microscope monitors the macroscopic strain state operando and makes it possible to complete an entire magnetotransport study at cryogenic temperatures under continuous strain variations. We demonstrate the capabilities of the probe on a freestanding LaNiO 3 membrane, where we induce tensile strain up to 8% and observe a corresponding strong transport anisotropy. In view of the rapid developments in low-dimensional materials synthesis and the plethora of novel quantum phenomena they exhibit, this strain probe provides general instrumentation for examining and controlling these properties via strain.

2D materials↗
DOE OSTI2017

Quasi-regenerative mode locking in a compact all-polarisation-maintaining-fibre laser

A novel technique of mode locking in erbium-doped all-polarisation-maintaining-fibre laser has been developed and preliminary investigated. The proposed quasi-regenerative technique combines the advantages of conventional active mode locking (when an intracavity modulator is driven by an independent RF oscillator) and regenerative mode locking (when a modulator is driven by an intermode beat signal from the laser itself). This scheme is based on intracavity intensity modulation driven by an RF oscillator being phase-locked to the actual intermode frequency of the laser. It features also possibilities of operation at multiple frequencies and harmonic mode-locking operation. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Optimisation of the optical scheme of a compact double-pass Nd : YAG amplifier for range finding

It is shown that the use of misalignment and a divergent incident beam in a double-pass Nd : YAG amplifier of a master oscillator – amplifier system used in ranger finding makes it possible both to increase the output pulse energy and to improve the output beam quality. The misalignment suppresses the amplifier self-excitation caused by a finite contrast of the output polariser. The use of a divergent incident beam allows one to increase the efficiency of energy extraction from the amplifier and to decrease the vignetting effect. The experimental results agree with the results of numerical simulation. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Erbium – ytterbium codoped phosphate core/double silica clad composite optical fibres for compact amplifiers

We report a study of composite fibres as gain media of all-fibre amplifiers. A distinctive feature of the fibres is an erbium – ytterbium doped phosphate core in a double silica cladding. The high Yb{sup 3+} concentration (above 10{sup 21} cm{sup −3}) ensures effective pump absorption from the cladding at fibre lengths under 40 cm and effective erbium ion sensitisation. The silica cladding facilitates fusion splicing to standard fibres. The composite fibres offer a large gain coefficient: about 0.4 – 0.5 dB cm{sup −1} at a signal wavelength of 1550 nm. The maximum gain at a fibre length of just 36 cm and an input signal power of 0.37 mW at λ = 1550 nm is about 13.5 dB. Under such conditions, the amplified spontaneous emission level is lower than the input signal level by 10 dB. (optical fibres)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗