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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Generation of attosecond gigawatt soft x-ray pulses through coherent Thomson backscattering

Collision between relativistic electron sheets and counterpropagating laser pulses is recognized as a promising way to produce intense attosecond x rays through coherent Thomson backscattering (TBS). In a double-layer scheme, the electrons in an ultrathin solid foil are first pushed out by an intense laser driver and then interact with the laser reflected off a second foil to form a high-density relativistic electron sheet with vanishing transverse momentum. However, the repulsion between these concentrated electrons can increase the thickness of the layer, reducing both its density and subsequently the coherent TBS. Here, we present a systematic study on the evolution of the flying electron layer and find that its resulting thickness is determined by the interplay between the intrinsic space-charge expansion and the velocity compression induced by the drive laser. How the laser driver, the target areal density, the reflector, and the collision laser intensity affect the properties of the produced x rays is explored. Multidimensional particle-in-cell simulations indicate that employing this scheme in the nonlinear regime has the potential to stably produce soft x rays with several gigawatt peak power in hundreds of terawatt ultrafast laser facilities. The pulse duration can be tuned to tens of attoseconds. Here, this compact and intense attosecond x-ray source may have broad applications in attosecond science.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Simulation of Rutherford backscattering spectrometry from arbitrary atom structures

Rutherford backscattering spectrometry in a channeling direction (RBS/C) is a powerful tool for analysis of the fraction of atoms displaced from their lattice positions. However, it is in many cases not straightforward to analyze what is the actual defect structure underlying the RBS/C signal. To reveal insights of RBS/C signals from arbitrarily complex defective atomic structures, we develop in this paper a method for simulating the RBS/C spectrum from a set of arbitrary read-in atom coordinates (obtained, e.g., from molecular dynamics simulations). We apply the developed method to simulate the RBS/C signals from Ni crystal structures containing randomly displaced atoms, Frenkel point defects, and extended defects, respectively. The RBS/C simulations show that, even for the same number of atoms in defects, the RBS/C signal is much stronger for the extended defects. Finally, comparison with experimental results shows that the disorder profile obtained from RBS/C signals in ion-irradiated Ni is due to a small fraction of extended defects rather than a large number of individual random atoms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Integrability Breaking from Backscattering

Herein we analyze the onset of diffusive hydrodynamics in the one-dimensional hard-rod gas subject to stochastic backscattering. While this perturbation breaks integrability and leads to a crossover from ballistic to diffusive transport, it preserves infinitely many conserved quantities corresponding to even moments of the velocity distribution of the gas. In the limit of small noise, we derive the exact expressions for the diffusion and structure factor matrices, and show that they generically have off diagonal components. We find that the particle density structure factor is non-Gaussian and singular near the origin, with a return probability showing logarithmic deviations from diffusion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Determination of α lamellae orientation in a β-Ti alloy using electron backscatter diffraction

The spatial orientation of α lamellae in a metastable β-Ti matrix of Timetal LCB (Ti–6.8 Mo–4.5 Fe–1.5 Al in wt%) was examined and the orientation of the hexagonal close-packed α lattice in the α lamella was determined. For this purpose, a combination of methods of small-angle X-ray scattering, scanning electron microscopy and electron backscatter diffraction was used. The habit planes of α laths are close to {111} β , which corresponds to (1$\bar3$20) α in the hexagonal coordinate system of the α phase. The longest α lamella direction lies approximately along one of the $\langle$110$\rangle$ β directions which are parallel to the specific habit plane. Taking into account the average lattice parameters of the β and α phases in aged conditions in Timetal LCB, it was possible to index all main axes and faces of an α lath not only in the cubic coordinate system of the parent β phase but also in the hexagonal system of the α phase.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electron backscatter diffraction of Nb 3 Sn coated niobium: Revealing structure as a function of depth

Over the last two decades, advances in Electron Backscatter Diffraction (EBSD) have moved the technique from a research tool to an essential characterization technique in many fields of material research. EBSD is the best suited technique for determining structure as a function of depth. This characterization is critically important, but has been previously absent from Nb 3 Sn efforts. While EBSD is the technique of choice, obtaining quality data can be difficult. Sample preparation in particular is non-trivial. Here we summarize the general principles of EBSD, discuss specific sample preparation techniques for Nb 3 Sn coated SRF cavity material, and give examples of how EBSD is being used to understand fundamental growth mechanisms for Nb 3 Sn coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Evaluation of the accuracy of stopping and range of ions in matter simulations through secondary ion mass spectrometry and Rutherford backscattering spectrometry for low energy heavy ion implantation

The freely available “Stopping and Range of Ions in Matter” (SRIM) code is used for evaluating ion beam ranges and depth profiles. We present secondary ion mass spectrometry and Rutherford backscattering experimental results of Si samples implanted with low energy Sb ions to evaluate the accuracy of SRIM simulations. We show that the SRIM simulation systematically overestimates the range by 2–6 nm and this overestimation increases for larger ion implantation energy. For the lowest energy implantation investigated, here we find up to a 25% error between the SRIM simulation and the measured range. Finally, the ion straggle shows excellent agreement between simulation and experimental results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Dose-to-water conversion for the backscatter-shielded EPID: A frame-based method to correct for EPID energy response to MLC transmitted radiation

Purpose: To develop a frame-by-frame correction for the energy response of amorphous silicon electronic portal imaging devices (a-Si EPIDs) to radiation that has transmitted through the multileaf collimator (MLC) and to integrate this correction into the backscatter shielded EPID (BSS-EPID) dose-to-water conversion model. Methods: Individual EPID frames were acquired using a Varian frame grabber and iTools acquisition software then processed using in-house software developed inMATLAB. For each EPID image frame, the region below the MLC leaves was identified and all pixels in this region were multiplied by a factor of 1.3 to correct for the under-response of the imager to MLC transmitted radiation. The corrected frames were then summed to form a corrected integrated EPID image. This correction was implemented as an initial step in the BSS-EPID dose-to-water conversion model which was then used to compute dose planes in a water phantom for 35 IMRT fields. The calculated dose planes, with and without the proposed MLC transmission correction, were compared to measurements in solid water using a two-dimensional diode array. Results: It was observed that the integration of the MLC transmission correction into the BSS-EPID dose model improved agreement between modeled and measured dose planes. In particular, the MLC correction produced higher pass rates for almost all Head and Neck fields tested, yielding an average pass rate of 99.8% for 2%/2 mm criteria. A two-sample independentt-test and fisher F-test were used to show that the MLC transmission correction resulted in a statistically significant reduction in the mean and the standard deviation of the gamma values, respectively, to give a more accurate and consistent dose-to-water conversion. Conclusions: The frame-by-frame MLC transmission response correction was shown to improve the accuracy and reduce the variability of the BSS-EPID dose-to-water conversion model. The correction may be applied as a preprocessing step in any pretreatment portal dosimetry calculation and has been shown to be beneficial for highly modulated IMRT fields.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

WE-EF-210-05: Diagnosis and Quantification of Liver Steatosis with Quantitative Ultrasound Backscatter Technique

Purpose: Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the United States, affects 30% of adult Americans and may progress to more serious diseases. Liver biopsy is the standard method for diagnosing NAFLD. MRI can accurately diagnose and quantify hepatic steatosis but is expensive. Sonography with qualitative interpretation by radiologists is lower cost, more accessible but less sensitive for detection. The objective of this study, using MRI proton density fat fraction (PDFF) as reference, is to assess the accuracy for diagnosing and quantifying steatosis with two quantitative US parameters-- backscatter coefficient (BSC) and attenuation coefficient (AC)--derived from RF signals using the calibration phantom technique. Methods: We performed a prospective, cross-sectional analysis of a cohort of adults (n=204) with NAFLD (MRI-PDFF≥5%) and without NAFLD (controls). Subjects underwent MRI-PDFF and BSC and AC US analyses of the liver on the same day. Patients were randomly assigned to training (n=102, mean age 51±17 years, mean body mass index 31±7 kg/m{sup 2}) and validation (n=102, mean age 49±17 years, body mass index 30±6 kg/m{sup 2}) groups; 69% of patients in each group had NAFLD. Results: BSC provided AUC 0.98 (95% CI 0.95–1.00, p<0.0001) for diagnosis of NAFLD; the optimal BSC cut-off provided sensitivity, specificity, positive and negative predictive values (PPV, NPV) of 87%, 91%, 95%, and 76%, respectively. AC provided AUC 0.89 (95% CI 0.81–0.96, p<0.0001) for diagnosis of steatosis; the optimal AC cut-off provided sensitivity, specificity, PPV, NPV of 80%, 84%, 92%, and 66%, respectively. BSC and AC both correlated significantly with MRI-PDFF (P<0.0001). Conclusion: QUS BSC and AC can accurately diagnose and quantify hepatic steatosis, using MRI-PDFF as reference. With further validation, QUS may emerge as an inexpensive, widely available tool for NAFLD assessment. General support: NIH R01 CA111289, K23 -DK090303, AmerGastroAssoc Found, TF Williams Scholarship, S3000 scanner loaned by Siemens, Sucampo, JA Hartford Found, Atlantic Philanthropies Amer Gastroenterological Assoc. Agencies had no role in design/conduct of study, collection, management, analysis or interpretation of the data; preparation, review, or approval of the manuscript.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Quantifying the Spectrum of Denial-of-Service Attacks through Internet Backscatter

Denial of Service (DoS) attacks are a major threat currently observable in computer networks and especially the Internet. In such an attack a malicious party tries to either break a service, running on a server, or exhaust the capacity or bandwidth of the victim to hinder customers to effectively use the service. Recent reports show that the total number of Distributed Denial of Service (DDoS) attacks is steadily growing with "mega-attacks" peaking at hundreds of gigabit/s (Gbps). In this paper, we will provide a quantification of DDoS attacks in size and duration beyond these outliers reported in the media. We find that these mega attacks do exist, but the bulk of attacks is in practice only a fraction of these frequently reported values. We further show that it is feasible to collect meaningful backscatter traces using surprisingly small telescopes, thereby enabling a broader audience to perform attack intelligence research.

Blenn, Norbert↗
DOE OSTI2025

Toward inverse backscatter absorption gas imaging: imaging a dry gas plume with ambient H 2 O absorption

This paper introduces inverse backscatter absorption gas imaging (iBAGI), a transparent gas imaging technique based on absorption spectroscopy of gases naturally present in ambient air being displaced by transparent gases. We demonstrate reconstruction of a 2-D image of a dry gas plume by measuring light of a raster-scanned diode laser tuned to an absorption line of atmospheric H 2 O. We quantify the performance depending on the distance to the backdrop and show that the key transmission metric is independent of absorption path length. We conclude with an outlook toward calibration-free, single-ended iBAGI using scattering from low-reflectivity backdrops.

Klug, Joseph C.↗
DOE OSTI2014

Final Technical Report "Study of Efficiency of Raman Backscattering Amplification in Plasma"

General : Our major scientific achievements in Raman Backscattering (RBS) amplification and compression of short laser pulses in plasma. The laser system based on RBS steps in where the current technology of chirped pulse amplification (CPA) (extremely successful in developing ultra-short and ultra-intense laser pulses in last 2 decades) becomes difficult and very expensive to apply. Good base for such RBS laser was created by our recent experiments, which were supported by GPS grants. The main objective of the present grant was: improvement efficiency of energy transfer from pump to seed. The results surpassed our expectations; we improved the efficiency of energy transfer from pump to seed by a factor of 6 compared to the best of our previous results and amplified seed pulse compressed down to about 50 fsec.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A Compact, Backscattering Deplolarization Cloud Spectrometer for Ice and Water Discrimination

This project was to develop a compact optical particle spectrometer, small enough for operation on UAVS, that measures the optical diameter of cloud hydrometeors and differentiates their water phase (liquid or solid). To reach this goal, a work plan was laid out that would complete three objectives: 1) Evaluation of designs for an optical particle spectrometer that measures the component of light backscattered at two polarization angles. 2) Testing of selected designs on an optical bench. 3) Construction and preliminary testing of a prototype instrument based on the selected, optimum design. A prototype instrument was developed and tested in an icing wind tunnel where the results showed good measurement of cloud droplets and ice particles.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Active Irradiation Testing of Temperature Sensing Capability of Clad Sapphire Optical Fibers with Type 2 Bragg Gratings using Optical Backscatter Reflectometry

This work investigated the temperature-sensing capabilities of Type II fiber Bragg gratings (FBGs) inscribed in sapphire optical fiber in the Ohio State University Research Reactor (OSURR). A Luna Innovations 4600 optical backscatter reflectometer (OBR) was used to interrogate FBGs in three sapphire optical fibers with an internal cladding that was developed by Ohio State. The sapphire fibers were fusion-spliced to silica lead fibers. In addition to the sapphire fibers, two silica fibers with the same Type II FBGs were included in the experiment as a reference. The fiber-based sensors were irradiated in the Central Irradiation Facility (CIF) of the OSURR for a total of 40 hours over 5 days at a reactor power of 450 kW, resulting in a total neutron fluence of approximately 2.5 × 10 18 n/cm 2 and a gamma dose of approximately 3.48 Grad. Two K-type thermocouples were included within the rig: one at the core centerline and the other 12 inches above the top of the core. The temperature was not actively controlled, but the thermocouples were used to provide a reference to which the fiber-based temperature measurements could be compared.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Improvements in the Sample Space for the Backscattering Silicon Spectrometer (BASIS)

The increase in neutron flux at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS), currently operating at 2.0 MW proton beam power, has created new opportunities for higher-throughput neutron scattering experiments while also increasing the importance of minimizing background scattering and optimizing sample-environment operations. To address these challenges on the Backscattering Silicon Spectrometer (BA-SIS), several upgrades were developed and evaluated, including boron carbide (B₄C) masking for flat-plate sample containers, multi-cell sample holders used with a vertically translating sample stick, and an automated helium pump and purge (HPP) system for closed-cycle refrigerators. Neutron diffraction measurements demonstrate that B₄C masks reduce background scattering by 49–67%, outperforming both borated aluminum and boron nitride masks while introducing no additional Bragg reflections within the instrument’s accessible Q-range. Commissioning tests of a double-cell flat-plate sample contain-er showed no measurable crosstalk between adjacent sample compartments and con-firmed stable thermal performance, enabling multiple samples to be measured without re-peated temperature cycling. In addition, the automated HPP system provided reproducible sample-space gas handling with approximately ±1 mbar precision while reducing the need for operator intervention and supporting remote operation. Together, these developments improve signal-to-noise performance, increase experimental throughput, and enhance operational efficiency at BASIS, supporting the instrument’s continued operation under higher neutron flux conditions.

Jalarvo, Niina [ORNL] (ORCID:0000000306446866)↗