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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

SU-E-T-108: Development of a Novel Clinical Neutron Dose Monitor for Proton Therapy Based On Twin TLD500 Chips in a Small PE Moderator

Purpose: In proton therapy, it could be desirable to measure out-of-field fast neutron doses at critical locations near and outside the patient body. Methods: The working principle of a novel clinical neutron dose monitor is verified by MCNPX simulation. The device is based on a small PE moderator of just 5.5cm side length for easy handling covered with a thermal neutron suppression layer. In the simulation, a polystyrene phantom is bombarded with a standard proton beam. The secondary thermal neutron flux produced inside the moderator by the impinging fast neutrons from the treatment volume is estimated by pairs of α-Al2O3:C (TLD500) chips which are evaluated offline after the treatment either by TL or OSL methods. The first chip is wrapped with 0.5mm natural Gadolinium foil converting the thermal neutrons to gammas via (n,γ) reaction. The second chip is wrapped with a dummy material. The chip centers have a distance of 2cm from each other. Results: The simulation shows that the difference of gamma doses in the TLD500 chips is correlated to the mean fast neutron dose delivered to the moderator material. Different outer shielding materials have been studied. 0.5mm Cadmium shielding is preferred for cost reasons and convenience. Replacement of PE moderator material by other materials like lead or iron at any place is unfavorable. The spatial orientation of the moderator cube is uncritical. Using variance reduction techniques like splitting/Russian roulette, the TLD500 gamma dose simulation give positive differences up to distances of 0.5m from the treatment volume. Conclusion: Applicability and basic layout of a novel clinical neutron dose monitor are demonstrated. The monitor measures PE neutron doses at locations outside the patient body up to distances of 0.5m from the treatment volume. Tissue neutron doses may be calculated using neutron kerma factors.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2018

PowerSystems.jl and PowerSimulations.jl [SWR-18-23]

Data structures in Julia to enable power systems analysis. Also, PowerSimulations.jl is a Julia package for power system modeling and simulation found at https://github.com/NREL/PowerSimulations.jl. The objectives of the package are: Provide a flexible modeling framework that can accommodate problems of different complexity and at different time-scales. Streamline the construction of large scale optimization problems to avoid repetition of work when adding/modifying model details. Exploit Julia's capabilities to improve computational performance of large scale power system simulations. The flexible modeling framework is enabled through a modular set of capabilities that enable scalable power system analysis and exploration of new analysis methods. The modularity of PowerSimulations results from the structure of the simulations enabled by the package: Simulations define a set of problems that can be solved using numerical techniques. Problems are generated by expressing model formulations against system data For example, an annual production cost modeling simulation can be created by formulating a unit commitment model against system data to assemble a set of 365 daily time-coupled scheduling problems.

Lara, Jose Daniel↗
DOE OSTI2018

A new method for analyzing and visualizing plasma simulations using a phase-space tessellation

We apply a novel phase-space interpolation technique referred to as the simplex-in-cell (SIC) method to analyze two- and three-dimensional particle-in-cell (PIC) simulations of electromagnetic plasmas. SIC relies on a discretization of the initial phase-space distribution function into simplices, which allows an approximation to the full, continuously defined distribution function to be constructed at any later time in the simulation. This allows densities, currents, and even full momentum distribution functions to be measured at any point in the simulation domain without averaging over control volumes. The SIC approach applies to any PIC simulation for which a tessellation of the initial particle distribution can be constructed. In this study, we use outputs from standard PIC simulations of the Weibel instability and compare physical quantities such as charge and current densities calculated in postprocessing using SIC and standard particle deposits. Using 2D simulations with 1–65 536 particles-per-cell, we find that SIC eliminates discrete particle noise and in some cases can reach a given noise level using ~1000 times fewer simulation particles than with standard particle deposition schemes. In regions of low density, such as between current filaments, SIC is able to capture small amplitude features even with fewer particles than gridpoints due to the deformable nature of the SIC volume elements. Here, by calculating momentum distributions, we show how SIC can capture low density tails in the spectrum using far fewer particles than are necessary for standard particle deposits. We calculate the charge density on spatial grids of increasing resolution to demonstrate the ability of SIC to reveal fine-scale details that are not accessible with standard particle deposits. Finally, we show how SIC can be extended to 3D and give an example of its use to calculate the charge density from 3D PIC simulations of the Weibel instability. These results motivate the future implementation of SIC directly in the simulation force calculation for a novel low-noise electromagnetic plasma simulation method.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Computed Tomography of Transverse Phase Space

Two computed tomography techniques are explored to reconstruct beam transverse phase space using both simulated beam and multi-wire profile data in the Fermilab Muon Test Area ("MTA") beamline. Both Filtered Back-Projection ("FBP") and Simultaneous Algebraic Reconstruction Technique ("SART") algorithms [2] are considered and compared. Errors and artifacts are compared as a function of each algorithm’s free parameters, and it is shown through simulation and MTA beamline profiles that SART is advantageous for reconstructions with limited profile data.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

CosmoGAN: creating high-fidelity weak lensing convergence maps using Generative Adversarial Networks

Abstract Inferring model parameters from experimental data is a grand challenge in many sciences, including cosmology. This often relies critically on high fidelity numerical simulations, which are prohibitively computationally expensive. The application of deep learning techniques to generative modeling is renewing interest in using high dimensional density estimators as computationally inexpensive emulators of fully-fledged simulations. These generative models have the potential to make a dramatic shift in the field of scientific simulations, but for that shift to happen we need to study the performance of such generators in the precision regime needed for science applications. To this end, in this work we apply Generative Adversarial Networks to the problem of generating weak lensing convergence maps. We show that our generator network produces maps that are described by, with high statistical confidence, the same summary statistics as the fully simulated maps.

Mustafa, Mustafa (ORCID:0000000291770283)↗
DOE OSTI2025

Machine Learning Techniques for Data Reduction of Climate Applications

Scientists conduct large-scale simulations to compute derived quantities-of-interest (QoI) from primary data. Often, QoI are linked to specific features, regions, or time intervals, such that data can be adaptively reduced without compromising the integrity of QoI. For many spatiotemporal applications, these QoI are binary in nature and represent presence or absence of a physical phenomenon. We present a pipelined compression approach that first uses neural-network-based techniques to derive regions where QoI are highly likely to be present. Then, we employ a Guaranteed Autoencoder (GAE) to compress data with differential error bounds. GAE uses QoI information to apply low-error compression to only these regions. This results in overall high compression ratios while still achieving downstream goals of simulation or data collections. Experimental results are presented for climate data generated from the E3SM Simulation model for downstream quantities such as tropical cyclone and atmospheric river detection and tracking. These results show that our approach is superior to comparable methods in the literature.

Li, Xiao [University of Florida]↗
DOE OSTI2019

Radiation-induced Swelling and Microcracking in SiC Cladding for LWRs

After the Fukushima accident in 2011, SiC has attracted considerable attention as a potential material for fuel cladding that can offer increased accident tolerance in light water reactors (LWRs) compared to zircaloy cladding. Existing measurements on nuclear grade SiC/SiC composites made of high-purity, stoichiometric SiC have already shown very good radiation tolerance in various harsh environments. However, there are a number of challenges that need to be addressed before SiC composites can be successfully used in LWR technologies. One of them is irradiation-induced swelling, which can lead to development of significant stresses in the matrix, followed by microcracking and subsequent release of fission products. Models of irradiation-induced swelling had been largely empirical and therefore they cannot be used to predict the microstructural dependence of microcracking. Existing models are also limited by the lack of understanding of defects that form due to irradiation in the range of temperatures relevant to fuel cladding in LWRs (<1000°C). Many of the defects in this regime of temperature are too small to be detected with traditional transmission electron microscopy (TEM) techniques. In fact the defects observed in traditional TEM account only for 10-45% of the swelling measured in irradiated SiC. Here, we developed a multi-scale simulation methodology combined with state of the art experimental imaging techniques based on aberration corrected scanning transmission electron microscopy (STEM) to provide a scientific basis for predictive models of radiation swelling and microcracking in SiC. Specifically, we have developed a phase field fracture model that predicts microcrack initiation and growth in polycrystalline SiC. The model accounts for single crystal anisotropy, including anisotropy in the elastic constants and anisotropic surface energy. It also considers the reduced fracture strength of grain boundaries. The model was implemented using the MARMOT mesoscale nuclear materials tool. We have parameterized the model for SiC using molecular dynamics simulation results. The model has been verified using single crystal, bicrystal, and polycrystal examples. Swelling model has also been developed based on cluster dynamics simulations of defect evolution in SiC. We found that point defects and small defect clusters have a significant contribution to swelling. This finding is important because point defects and very small defect clusters are not visible in experiments (e.g., in TEM). Combined modeling and experiments can bring critical insights into how swelling depends on irradiation conditions and the microstructure. In situ nanoindentation tests and ex situ nanoindentation tests were performed on assynthesized 3C-SiC and 3C-SiC irradiated under different radiation conditions. Without radiation, bend contour movement and residual bend contours after indentation demonstrate some room temperature plastic flow and residual plastic deformation. Plastic deformation recovery is also observed on unirradiated samples during unloading. Radiation-induced embrittlement is demonstrated by differences in crack geometry in in situ tests, and is consistent with ex situ test results. Failure by single, straight, cracks indicates decreased fracture toughness due to irradiation in 3C-SiC. Future work includes coupling of the swelling and fracture models and development of a master equation that can be used in the BISON code.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics

Multigrid methods can solve some classes of elliptic and parabolic equations to accuracy below the truncation error with a work-cost equivalent to a few residual calculations – so-called “textbook” multigrid efficiency. We investigate methods to solve the system of equations that arise in time dependent magnetohydrodynamics (MHD) simulations with textbook multigrid efficiency. We apply multigrid techniques such as geometric interpolation, full approximate storage, Gauss-Seidel smoothers, and defect correction for fully implicit, nonlinear, second-order finite volume discretizations of MHD. We apply these methods to a standard resistive MHD benchmark problem, the GEM reconnection problem, and add a strong magnetic guide field, which is a critical characteristic of magnetically confined fusion plasmas. We show that our multigrid methods can achieve near textbook efficiency on fully implicit resistive MHD simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Probing plasmons in three dimensions by combining complementary spectroscopies in a scanning transmission electron microscope

The nanoscale optical response of surface plasmons in three-dimensional metallic nanostructures plays an important role in many nanotechnology applications, where precise spatial and spectral characteristics of plasmonic elements control device performance. Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) within a scanning transmission electron microscope have proven to be valuable tools for studying plasmonics at the nanoscale. Each technique has been used separately, producing three-dimensional reconstructions through tomography, often aided by simulations for complete characterization. Here we demonstrate that the complementary nature of the two techniques, namely that EELS probes beam-induced electronic excitations while CL probes radiative decay, allows us to directly obtain a spatially- and spectrally-resolved picture of the plasmonic characteristics of nanostructures in three dimensions. Furthermore, the approach enables nanoparticle-by-nanoparticle plasmonic analysis in three dimensions to aid in the design of diverse nanoplasmonic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

CEBAF Upgrade Bunch Length Measurements

Many accelerators use short electron bunches and measuring the bunch length is important for efficient operations. CEBAF needs a suitable bunch length because bunches that are too long will result in beam interruption to the halls due to excessive energy spread and beam loss. In this work, bunch length is measured by invasive and non-invasive techniques at different beam energies. Two new measurement techniques have been commissioned; a harmonic cavity showed good results compared to expectations from simulation, and a real time interferometer is commissioned and first checkouts were performed. Three other techniques were used for measurements and comparison purposes without modifying the old procedures. Two of them can be used when the beam is not compressed longitudinally while the other one, the synchrotron light monitor, can be used with compressed or uncompressed beam.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Testing aspects of advanced coherent electron cooling technique

An advanced version of the Coherent-electron Cooling (CeC) based on the micro-bunching instability was proposed. This approach promises significant increase in the bandwidth of the CeC system and, therefore, significant shortening of cooling time in high-energy hadron colliders. In this paper we present our plans of simulating and testing the key aspects of this proposed technique using the set-up of the coherent-electron-cooling proof-of-principle experiment at BNL.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Four dimensional magnetic resonance imaging with retrospective k-space reordering: A feasibility study

Purpose: Current four dimensional magnetic resonance imaging (4D-MRI) techniques lack sufficient temporal/spatial resolution and consistent tumor contrast. To overcome these limitations, this study presents the development and initial evaluation of a new strategy for 4D-MRI which is based on retrospective k-space reordering. Methods: We simulated a k-space reordered 4D-MRI on a 4D digital extended cardiac-torso (XCAT) human phantom. A 2D echo planar imaging MRI sequence [frame rate (F) = 0.448 Hz; image resolution (R) = 256 × 256; number of k-space segments (N{sub KS}) = 4] with sequential image acquisition mode was assumed for the simulation. Image quality of the simulated “4D-MRI” acquired from the XCAT phantom was qualitatively evaluated, and tumor motion trajectories were compared to input signals. In particular, mean absolute amplitude differences (D) and cross correlation coefficients (CC) were calculated. Furthermore, to evaluate the data sufficient condition for the new 4D-MRI technique, a comprehensive simulation study was performed using 30 cancer patients’ respiratory profiles to study the relationships between data completeness (C{sub p}) and a number of impacting factors: the number of repeated scans (N{sub R}), number of slices (N{sub S}), number of respiratory phase bins (N{sub P}), N{sub KS}, F, R, and initial respiratory phase at image acquisition (P{sub 0}). As a proof-of-concept, we implemented the proposed k-space reordering 4D-MRI technique on a T2-weighted fast spin echo MR sequence and tested it on a healthy volunteer. Results: The simulated 4D-MRI acquired from the XCAT phantom matched closely to the original XCAT images. Tumor motion trajectories measured from the simulated 4D-MRI matched well with input signals (D = 0.83 and 0.83 mm, and CC = 0.998 and 0.992 in superior–inferior and anterior–posterior directions, respectively). The relationship between C{sub p} and N{sub R} was found best represented by an exponential function (C{sub P}=100(1−e{sup −0.18N{sub R}}), when N{sub S} = 30, N{sub P} = 6). At a C{sub P} value of 95%, the relative error in tumor volume was 0.66%, indicating that N{sub R} at a C{sub P} value of 95% (N{sub R,95%}) is sufficient. It was found that N{sub R,95%} is approximately linearly proportional to N{sub P} (r = 0.99), and nearly independent of all other factors. The 4D-MRI images of the healthy volunteer clearly demonstrated respiratory motion in the diaphragm region with minimal motion induced noise or aliasing. Conclusions: It is feasible to generate respiratory correlated 4D-MRI by retrospectively reordering k-space based on respiratory phase. This new technology may lead to the next generation 4D-MRI with high spatiotemporal resolution and optimal tumor contrast, holding great promises to improve the motion management in radiotherapy of mobile cancers.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Effects of Dark Matter Self-interactions on Sagittarius and its Stream

This work explores how assumptions regarding the particle-physics nature of dark matter can alter the evolution of the Sagittarius (Sgr) dwarf spheroidal galaxy and its expansive stellar stream. We run a large suite of N-body simulations to model the infall of a spherically symmetric Sgr-like dwarf, exploring how the presence of dark matter self-interactions impacts its evolution. For a scattering cross section of σ/m χ = 30 cm 2 g −1 (at orbital velocity scales), these interactions result in significantly less stellar mass and little to no dark matter bound to the progenitor at the present day. To isolate the cause of this mass loss, we introduce a novel technique for controlling which pairs of dark matter simulation particles can interact. This enables us to identify ram-pressure evaporation—the scattering of satellite and host dark matter particles—as the primary source of the enhanced mass loss. The rapid disintegration of the Sgr progenitor when self-interactions are allowed alters some key properties of the resulting stellar stream, most dramatically suppressing the presence of a “spur” on the apocenter of the trailing stream arm that correlates with the mass of the satellite at last pericenter. We demonstrate how the effects on the Sgr system scale with the particular choice of self-interaction cross section, which affects the degree of ram-pressure evaporation. These findings generalize beyond the Sgr system, underscoring that dwarf stellar streams and dwarf galaxies with close passages may serve as sensitive probes for dark matter self-interactions.

Milky Way dark matter halo↗
DOE OSTI2015

Reduced Order Model Implementation in the Risk-Informed Safety Margin Characterization Toolkit

The RISMC project aims to develop new advanced simulation-based tools to perform Probabilistic Risk Analysis (PRA) for the existing fleet of U.S. nuclear power plants (NPPs). These tools numerically model not only the thermo-hydraulic behavior of the reactor primary and secondary systems but also external events temporal evolution and components/system ageing. Thus, this is not only a multi-physics problem but also a multi-scale problem (both spatial, µm-mm-m, and temporal, ms-s-minutes-years). As part of the RISMC PRA approach, a large amount of computationally expensive simulation runs are required. An important aspect is that even though computational power is regularly growing, the overall computational cost of a RISMC analysis may be not viable for certain cases. A solution that is being evaluated is the use of reduce order modeling techniques. During the FY2015, we investigated and applied reduced order modeling techniques to decrease the RICM analysis computational cost by decreasing the number of simulations runs to perform and employ surrogate models instead of the actual simulation codes. This report focuses on the use of reduced order modeling techniques that can be applied to any RISMC analysis to generate, analyze and visualize data. In particular, we focus on surrogate models that approximate the simulation results but in a much faster time (µs instead of hours/days). We apply reduced order and surrogate modeling techniques to several RISMC types of analyses using RAVEN and RELAP-7 and show the advantages that can be gained.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus

Purpose: Given the radiation concerns inherent to the x-ray modalities, accurately estimating the radiation doses that patients receive during different imaging modalities is crucial. This study estimated organ doses, effective doses, and risk indices for the three clinical chest x-ray imaging techniques (chest radiography, tomosynthesis, and CT) using 59 anatomically variable voxelized phantoms and Monte Carlo simulation methods. Methods: A total of 59 computational anthropomorphic male and female extended cardiac-torso (XCAT) adult phantoms were used in this study. Organ doses and effective doses were estimated for a clinical radiography system with the capability of conducting chest radiography and tomosynthesis (Definium 8000, VolumeRAD, GE Healthcare) and a clinical CT system (LightSpeed VCT, GE Healthcare). A Monte Carlo dose simulation program (PENELOPE, version 2006, Universitat de Barcelona, Spain) was used to mimic these two clinical systems. The Duke University (Durham, NC) technique charts were used to determine the clinical techniques for the radiographic modalities. An exponential relationship between CTDI{sub vol} and patient diameter was used to determine the absolute dose values for CT. The simulations of the two clinical systems compute organ and tissue doses, which were then used to calculate effective dose and risk index. The calculation of the two dose metrics used the tissue weighting factors from ICRP Publication 103 and BEIR VII report. Results: The average effective dose of the chest posteroanterior examination was found to be 0.04 mSv, which was 1.3% that of the chest CT examination. The average effective dose of the chest tomosynthesis examination was found to be about ten times that of the chest posteroanterior examination and about 12% that of the chest CT examination. With increasing patient average chest diameter, both the effective dose and risk index for CT increased considerably in an exponential fashion, while these two dose metrics only increased slightly for radiographic modalities and for chest tomosynthesis. Effective and organ doses normalized to mAs all illustrated an exponential decrease with increasing patient size. As a surface organ, breast doses had less correlation with body size than that of lungs or liver. Conclusions: Patient body size has a much greater impact on radiation dose of chest CT examinations than chest radiography and tomosynthesis. The size of a patient should be considered when choosing the best thoracic imaging modality.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2019

EXPLORING THE STRUCTURE OF GLASS-FORMING LIQUIDS USING HIGH ENERGY X-RAY DIFFRACTION, CONTAINERLESS METHODOLOGY AND STATE-OF-THE-ART MOLECULAR DYNAMICS SIMULATION

High energy X-ray diffraction can be combined with containerless techniques to provide information on the atomic arrangements in glass-forming liquids in stable and metastable regimes. The high incident energies provide bulk diffraction data to high values of scattering vector which enables significantly more robust analysis of the local and medium-range order that influences important physical properties such as viscosity and crystal nucleation. These combined techniques have been applied to a range of oxide liquids. In this contribution we illustrate addition of further dimensions to phase space by controlling the partial pressure of oxygen that permits the study liquids containing iron. The advantages of rapid data acquisition are also demonstrated in a study of tellurite glass-forming systems where a transition from ergodic to non-ergodic regimes in the deeply supercooled liquid is shown. Finally we demonstrate how descriptions of the liquid structure can be developed by combining HEXRD with molecular dynamics simulations.

containerless techniques↗
DOE OSTI2020

SU(2) non-Abelian gauge field theory in one dimension on digital quantum computers

A dynamical quantum simulation of SU(2) non-Abelian gauge field theory on a digital quantum computer is presented here. This was enabled on current quantum hardware by introducing a mapping of the field onto a register of qubits that utilizes local gauge symmetry while preserving local constraints on the fields, reducing the dimensionality of the calculation. Controlled plaquette operators and gauge-variant completions in the unphysical part of the Hilbert space were designed and used to implement time evolution. The new techniques developed in this work generalize to quantum simulations of higher dimensional gauge field theories.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Dynamic Distribution Voltage Stability Control Using Distributed Energy Resources for Improved Resiliency

The main goal of this paper is to present the development and simulation of a new dynamic voltage stability control technique, with a focus on effective control and coordination of all available reactive power generation resources in a microgrid setting. Both power electronics and synchronous generator based distributed energy resources (DERs), and grid-supporting functions, are considered to accommodate a high penetration of diverse DERs and energy storage by using an enhanced microgrid voltage stabilizer. A systematic controller parameter synthesizing method is employed, and the overall dynamic voltage stability of the system is studied and evaluated with a time-domain dynamic simulation during emergency, hazard and disaster events. The results with the new approach show significant improvements and enhancements on the dynamic voltage profile of the distribution system, leading towards a more resilient grid system with high penetration of diverse DERs during emergency, hazard and disaster events.

Hatipoglu, Kenan↗