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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Investigations on the multiple-sector hard-copper X-band accelerating structures

The development of advanced, high gradient accelerating structures is one of the leading activity of the particle accelerator community. In the technological research of new construction methods for these devices, high-power testing is a critical step for the verification of their viability. Recent experiments showed that accelerating cavities made out of hard copper, fabricated without high-temperature processes, can achieve better performance as compared with soft copper ones. Recently, we have built cavities using Tungsten Inert Gas welding and the high-power experiments confirmed that this joining process is a robust and low-cost alternative to brazing or diffusion bonding. This is a good solution for high-gradient operation, with a gradient of about 150 MV/m in X-band, at a breakdown rate of 10 -3 /pulse/meter using a shaped RF pulse with a 150 ns flat part. We continue the design, construction and high power tests of three-cells standing-wave X-band accelerating cavities fabricated with a split-open geometry, made of hard copper and vacuum-sealed by welding. Our aim is the fabrication of accelerating structures made out of hard copper alloys by using innovative cost-effective technologies. Moreover, our method of multiple-sector structures opens the way to new technological approaches and design methods, for example providing the possibility of placing dampers of the parasitic higher-order modes. Such structures with dampers allow for acceleration of multi-bunch beams, both in standing and in travelling-wave accelerating modality. Here, this paper describes the design of two cavities made of multiple sectors that were fabricated at the Italian Institute for Nuclear Physics in Frascati, Italy (INFN-LNF), assembled by means of clamping and then joined with the Tungsten Inert Gas welding in order to preserve the hardness of the metal. These are three-cell standing-wave X-band accelerating cavities, to be operated in the π-mode. We report the low-power RF tests of the first one, made of two halves, and the RF design of the second one, made of four quadrants. Both structures were built for high-gradient tests at SLAC National Accelerator Laboratory.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Algorithm advances and applications of time‐dependent first‐principles simulations for ultrafast dynamics

Abstract Far from equilibrium phenomenon is a central theme of contemporary material research. Such phenomenon can exhibit itself in atomic structure and dynamics, but very often it also happens as non‐equilibrium phenomenon in the electronic structure. In ab initio material simulation, density functional theory (DFT) has played an essential role in studying electronic ground state problems. For excited states, besides many‐body perturbation theory, another powerful tool is the time dependent DFT (TDDFT) method. In particular, the real‐time TDDFT (rt‐TDDFT) method can be used to simulate many non‐equilibrium phenomena directly. Here we introduce our works on some algorithm advances based on our recently rt‐TDDFT method. This method uses the plane‐wave basis set, and significantly accelerates its efficiency by increasing the time step from 0.1–1 as in traditional methods to 0.2–0.5 fs. The noncollinear magnetic moments and spin–orbit coupling have also been included in our rt‐TDDFT method. Furthermore, a Boltzmann‐TDDFT algorithm has been developed to solve the hot carrier overheating problem in Ehrenfest dynamics, and a natural orbital branching algorithm has been developed to overcome the mean‐field approximation in Ehrenfest dynamics nuclear trajectory, thus allows stochastic multiple paths in chemical reactions. Utilizing these methods, we have studied the photoinduced ultrafast demagnetization, ultrafast phase transition, energy transfer between plasmon and hot carriers, as well as the high‐energy ion implantation and low‐energy atomic diffusion in semiconductors. We believe the tools as the ones introduced here can enable us to study a wide range of phenomena which are of great interest in modern day material research. This article is categorized under: Structure and Mechanism > Computational Materials Science Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory

Liu, Wen‐Hao↗
DOE OSTI2018

Angular streaking of betatron X-rays in a transverse density gradient laser-wakefield accelerator

In a plasma with a transverse density gradient, laser wavefront tilt develops gradually due to phase velocity differences in different plasma densities. The wavefront tilt leads to a parabolic trajectory of the plasma wakefield and hence the accelerated electron beam, which leads to an angular streaking of the emitted betatron radiation. In this way, the temporal evolution of the betatron X-ray spectra will be converted into angular “streak,” i.e., having a critical energy-angle correlation. An analytical model for the curved trajectory of a laser pulse in a transverse density gradient is presented. This gives the deflection angle of the electron beam and the betatron X-rays as a function of the plasma and laser parameters, and it was verified by particle-in-cell simulations. This angular streaking could be used as a single-shot diagnostic technique to reveal the temporal evolution of betatron X-ray spectra and hence the electron acceleration itself.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Democratizing uncertainty quantification

Uncertainty Quantification (UQ) is vital to safety-critical model-based analyses, but the widespread adoption of sophisticated UQ methods is limited by technical complexity. In this paper, we introduce UM-Bridge (the UQ and Modeling Bridge), a high-level abstraction and software protocol that facilitates universal interoperability of UQ software with simulation codes. It breaks down the technical complexity of advanced UQ applications and enables separation of concerns between experts. UM-Bridge democratizes UQ by allowing effective interdisciplinary collaboration, accelerating the development of advanced UQ methods, and making it easy to perform UQ analyses from prototype to High Performance Computing (HPC) scale. In addition, we present a library of ready-to-run UQ benchmark problems, all easily accessible through UM-Bridge. These benchmarks support UQ methodology research, enabling reproducible performance comparisons. We demonstrate UM-Bridge with several scientific applications, harnessing HPC resources even using UQ codes not designed with HPC support.

Benchmarks↗
DOE OSTI2024

A fast, matrix-based method to perform omnidirectional pressure integration

Abstract Experimentally-measured pressure fields play an important role in understanding many fluid dynamics problems. Unfortunately, pressure fields are difficult to measure directly with non-invasive, spatially resolved diagnostics, and calculations of pressure from velocity have proven sensitive to error in the data. Omnidirectional line integration methods are usually more accurate and robust to these effects as compared to implicit Poisson equations, but have seen slower uptake due to the higher computational and memory costs, particularly in 3D domains. This paper demonstrates how omnidirectional line integration approaches can be converted to a matrix inversion problem. This novel formulation uses an iterative approach so that the boundary conditions are updated each step, preserving the convergence behavior of omnidirectional schemes while also keeping the computational efficiency of Poisson solvers. This method is implemented in Matlab and also as a GPU-accelerated code in CUDA-C++. The behavior of the new method is demonstrated on 2D and 3D synthetic and experimental data. Three-dimensional grid sizes of up to 125 million grid points are tractable with this method, opening exciting opportunities to perform volumetric pressure field estimation from 3D PIV measurements.

42 ENGINEERING↗
DOE OSTI2021

Neutron generation using pyroelectric crystals

According to one embodiment, a method for producing a directed neutron beam includes producing a voltage of negative polarity of at least −100 keV on a surface of a deuterated or tritiated target in response to a temperature change of a pyroelectric crystal of less than about 40° C., the pyroelectric crystal having the deuterated or tritiated target coupled thereto, pulsing a deuterium ion source to produce a deuterium ion beam, accelerating the deuterium ion beam to the deuterated or tritiated target to produce a neutron beam, and directing the ion beam onto the deuterated or tritiated target to make neutrons using at least one of a voltage of the pyroelectric crystal, and a high gradient insulator (HGI) surrounding the pyroelectric crystal. The directionality of the neutron beam is controlled by changing the accelerating voltage of the system. Other methods are presented as well.

Tang, Vincent↗
NASA NTRS1990

An overlapped grid method for multigrid, finite volume/difference flow solvers: MaGGiE

The objective is to develop a domain decomposition method via overlapping/embedding the component grids, which is to be used by upwind, multi-grid, finite volume solution algorithms. A computer code, given the name MaGGiE (Multi-Geometry Grid Embedder) is developed to meet this objective. MaGGiE takes independently generated component grids as input, and automatically constructs the composite mesh and interpolation data, which can be used by the finite volume solution methods with or without multigrid convergence acceleration. Six demonstrative examples showing various aspects of the overlap technique are presented and discussed. These cases are used for developing the procedure for overlapping grids of different topologies, and to evaluate the grid connection and interpolation data for finite volume calculations on a composite mesh. Time fluxes are transferred between mesh interfaces using a trilinear interpolation procedure. Conservation losses are minimal at the interfaces using this method. The multi-grid solution algorithm, using the coaser grid connections, improves the convergence time history as compared to the solution on composite mesh without multi-gridding.

Baysal, Oktay↗
NASA NTRSDate not supplied

Real-Time State Estimation of Structural Modes for an Aeroelastic Wind Tunnel Model

A method is presented for estimating displacements, velocities, and accelerations of structural modes in generalized coordinates from measured sensor data in real time. Specifically, strain data from conventional strain gauges and fiber optic strain sensors (FOSS) were combined with the strain modes (obtained from a finite element model) in a least-squares estimator to produce structural mode displacement estimates and uncertainties. Likewise, accelerometer data were combined with displacement mode shapes in a second least-squares estimator to produce structural mode acceleration estimates. A Kalman filter was then used to refine the displacement estimates and obtain velocity estimates. The method was applied to the half-span wind tunnel test article used in the NASA-Boeing collaboration called the Integrated Adaptive Wing Technology Maturation (IAWTM) project. The technique was found to be useful for real-time control and system identification applications.

Jared A. Grauer↗
NASA NTRS2002

A methodology for modeling the mechanical interaction between a reaction wheel and a flexible structure

This paper presents a modeling methodology used to predict the performance of a flexible structure, such as a space telescope, in the presence of an on-board vibrational disturbance source, such as a reaction wheel assembly (RWA). Both decoupled and coupled analysis methods are presented. The decoupled method relies on blocked RWA disturbances, measured with the RWA hardmounted to a rigid surface. The coupled method corrects the blocked RWA disturbance boundary conditions using "force filters," which depend on estimates of the interface accelerances of the RWA and space-craft. Both methods were validated on the Micro-Precision Interferometer testbed at the Jet Propulsion Laboratory. Experimental results are encouraging, indicating that both methods provide sufficient accuracy compared to measured values; however, the coupled method provides the best results when the gyroscopic nature of the spinning RWA is captured in the RWA accelerance model. Additionally, the RWA disturbance cross spectral density terms are found to be influential.

vibration↗
NASA NTRS1978

Estimation of payload loads using rigid body interface accelerations

In the design/analysis process of a payload structural system, the accelerations at the payload/launch vehicle interface obtained from a system analysis using a rigid payload are often used as the input forcing function to the elastic payload to obtain structural design loads. Such an analysis is at best an approximation since the elastic coupling effects are neglected. This paper develops a method wherein the launch vehicle/rigid payload interface accelerations are modified to account for the payload elasticity. The advantage of the proposed method, which is exact to the extent that the physical system can be described by a truncated set of generalized coordinates, is that the complete design/analysis process can be performed within the organization responsible for the payload design. The method requires the updating of the system normal modes to account for payload changes, but does not require a complete transient solution using the composite system model. An application to a real complex structure, the Viking Spacecraft System, is given.

Chen, J. C.↗
DOE OSTI2023

Accelerated fission rate irradiation design, pre-irradiation characterization, and adaptation of conventional PIE methods for U-10Mo and U-17Mo

Metallic U alloys have high U density and thermal conductivity and thus have been explored since the beginning of nuclear power research. Alloys of U with modest amounts of Mo, such as U-10 wt % Mo (U-10Mo), are of particular interest because the γ-U crystal structure in this alloying addition shows prolonged stability in reactor service. Historically, radiation data on U-10Mo fuels were collected in Na fast reactors or lower temperature research reactor conditions, but little is known about irradiation behavior, particularly swelling and creep, at irradiation temperatures between 250 and 500°C. This work discusses the methodology and pre-irradiation characterization results from a U-Mo irradiation campaign performed in the High Flux Isotope Reactor at Oak Ridge National Laboratory. U-10Mo and U-17Mo samples irradiations are being completed at temperatures ranging from 250 to 500°C to three targeted fission densities between 2 × 10 20 and 1.5 × 10 21 fissions per cubic centimeter. Swelling measurement of the specimen sizes studied here required development and assessment of new methods for volume determination before and after irradiation. Laser profilometry and X-ray computation tomography (XCT) were used to provide preirradiation characterization of samples to determine the error and applicability of each to determine swelling following irradiation. These outcomes are contextualized through use of BISON simulations performed to assess the predicted expansion of U-Mo fuels subjected to the irradiation conditions of this work. Use of existing BISON fuel performance models predicted a maximum of 7% swelling under the irradiation conditions of this study. Pre-irradiation characterization revealed the as-cast U-Mo fuel samples were uniformly large-grained fully cubic U crystals with small U-C/N bearing precipitates and pores distributed throughout. Samples were found to contain a bulk porosity between .4 and 3% because of the casting process. Local porosity in areas far from large, interconnected pores was found by Slice-and-View to be under .2%. Nanometer-sized precipitates rich in C and N were identified in all samples, likely because of impurities during the fabrication process. Dendritic bands were also observed throughout the samples. These bands were characterized by variable Mo content that deviated from the overall Mo content by 2–3 wt %. No other microstructural features were correlated to these bands. Mechanical properties were found to be slightly strengthened compared to literature reports of bulk U-Mo fuels due to the nano-scale precipitates throughout the sample.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1982

Effect of Rayleigh accelerations applied to an initially moving fluid

The General Interpolant Method computer code was used to analyze two-dimensional unsteady thermal convection in circular cylinders under variable low-g conditions associated with space flight. When an acceleration vector was applied parallel to the thermal gradient, in the case of a fluid at rest, no convection resulted for the stable direction, and an instability led to Rayleigh convection for the opposite direction. However, when the acceleration had a component orthogonal to the gradient, convection resulted at any Rayleigh number. The effect on convection of both types of acceleration, applied concurrently or sequentially, was investigated, including the case when the resultant vector varied in direction with time. An analysis of experimental results shows that for space flight conditions, the Rayleigh accelerations induce significant, but not dominating, changes in the established convection even when the Rayleigh number is less than critical.

Dressler, R. F.↗
DOE OSTI2021

Machine-learning-accelerated multimodal characterization and multiobjective design optimization of natural porous materials

Natural porous materials such as nanoporous clays are used as green and low-cost adsorbents and catalysts. The key factors determining their performance in these applications are the pore morphology and surface activity, which are typically represented by properties such as specific surface area, pore volume, micropore content and pH. The latter may be modified and tuned to specific applications through material processing and/or chemical treatment. Characterization of the material, raw or processed, is typically performed experimentally, which can become costly especially in the context of tuning of the properties towards specific application requirements and needing numerous experiments. In this work, we present an application of tree-based machine learning methods trained on experimental datasets to accelerate the characterization of natural porous materials. The resulting models allow reliable prediction of the outcomes of experimental characterization of processed materials (R2 from 0.78 to 0.99) as well as identification of key factors contributing to those properties through feature importance analysis. Furthermore, the high throughput of the models enables exploration of processing parameter–property correlations and multiobjective optimization of prototype materials towards specific applications. We have applied these methodologies to pinpoint and rationalize optimal processing conditions for clays exploitable in acid catalysis. One of such identified materials was synthesized and tested revealing appreciable acid character improvement with respect to the pristine material. Specifically, it achieved 79% removal of chlorophyll-a in acid catalyzed degradation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Expanding the breeder’s toolbox for perennial grasses

With the increase in world energy demand and the environmental impacts associated with continued fossil fuel use, there is a great need for the development of alternative and sustainable fuel sources. Switchgrass ( Panicum virgatum L. ), a perennial grass native to North America, is poised to become one of the first dedicated biomass crops deployed on a large scale in the United States in large part due to its inherent high yield, adaptability and perennial nature. Current ‘cultivars’ of switchgrass are essentially undomesticated wild selections from natural populations. Thus, there is considerable potential for improvement of this emerging energy crop. Traditional breeding approaches in switchgrass have been hampered by its self-incompatibility and sensitivity to inbreeding, therefore there is a significant need to develop new tools for improved switchgrass breeding. The proposed research uses a systems biology approach to accelerate switchgrass breeding, to develop its biotechnological improvement through the generation of stress-tolerant varieties, and to establish ways to minimize the potential impact of transgenes on ecosystems. In this proposal, we will develop new breeding tools for perennial grasses and apply these tools toward improving switchgrass. Specifically, we will employ two complementary approaches to overcome the difficulty of breeding a large, polyploid, self-incompatible plant. The first approach will accelerate conventional breeding by developing a method to rapidly create doubled haploid (homozygous) lines for breeding. This approach is based on altering CENH3, a centromere-specific histone, leading to the production of haploid offspring when the centromere mutant is crossed to wild type plants. Subsequent genome doubling results in fully homozygous individuals and overcomes one of the major limitations in breeding self-incompatibile crops. These homozygous lines would allow switchgrass breeders to apply a variety of breeding approaches that have been previously impossible. The second approach is to develop tools and reagents to accelerate the biotechnological improvement of switchgrass including: modules for improved stress tolerance, a test bed to evaluate transgenes in a perennial model grass and a robust gene containment system. In order to maintain a favorable energy balance and avoid competition with food crops, dedicated biomass crops must be grown with minimal inputs (fertilizer and water) on marginal lands that are unsuited to the traditional high input agriculture necessary to produce food. Thus, abiotic stress tolerance and efficient water and nutrient use are of paramount importance. Considerable basic research has been directed at these areas and this knowledge has been used to develop transgenic approaches to greatly improve water and nutrient use efficiency. By applying these approaches to switchgrass we will rapidly increase drought tolerance and nutrient use efficiency. This approach can rapidly introduce these traits in different cultivars allowing breeders to add these traits to their elite germplasm. Since biotechnologically improved switchgrass must ultimately be grown in open fields, they must be designed to minimize the potential impact of the transgenes on non-target ecosystems. The best way to do this is to minimize gene flow from the transgenic plants. Thus, we will develop technology to introduce sterility into the transgenic plants. We will then combine this technology with the stress resistance modules to create switchgrass lines with enhanced resistance to abiotic stresses.

09 BIOMASS FUELS↗
DOE OSTI2018

Expanding the Breeder’s Toolbox for Perennial Grasses

With the increase in world energy demand and the environmental impacts associated with continued fossil fuel use, there is a great need for the development of alternative and sustainable fuel sources. Switchgrass (Panicum virgatum L.), a perennial grass native to North America, is poised to become one of the first dedicated biomass crops deployed on a large scale in the United States in large part due to its inherent high yield, adaptability and perennial nature. Current ‘cultivars’ of switchgrass are essentially undomesticated wild selections from natural populations. Thus, there is considerable potential for improvement of this emerging energy crop. Traditional breeding approaches in switchgrass have been hampered by its self-incompatibility and sensitivity to inbreeding, therefore there is a significant need to develop new tools for improved switchgrass breeding. The proposed research uses a systems biology approach to accelerate switchgrass breeding, to develop its biotechnological improvement through the generation of stress-tolerant varieties, and to establish ways to minimize the potential impact of transgenes on ecosystems. In this proposal, we will develop new breeding tools for perennial grasses and apply these tools toward improving switchgrass. Specifically, we will employ two complementary approaches to overcome the difficulty of breeding a large, polyploid, self-incompatible plant. The first approach will accelerate conventional breeding by developing a method to rapidly create doubled haploid (homozygous) lines for breeding. This approach is based on altering CENH3, a centromere-specific histone, leading to the production of haploid offspring when the centromere mutant is crossed to wild type plants. Subsequent genome doubling results in fully homozygous individuals and overcomes one of the major limitations in breeding self-incompatibile crops. These homozygous lines would allow switchgrass breeders to apply a variety of breeding approaches that have been previously impossible. The second approach is to develop tools and reagents to accelerate the biotechnological improvement of switchgrass including: modules for improved stress tolerance, a test bed to evaluate transgenes in a perennial model grass and a robust gene containment system. In order to maintain a favorable energy balance and avoid competition with food crops, dedicated biomass crops must be grown with minimal inputs (fertilizer and water) on marginal lands that are unsuited to the traditional high input agriculture necessary to produce food. Thus, abiotic stress tolerance and efficient water and nutrient use are of paramount importance. Considerable basic research has been directed at these areas and this knowledge has been used to develop transgenic approaches to greatly improve water and nutrient use efficiency. By applying these approaches to switchgrass we will rapidly increase drought tolerance and nutrient use efficiency. This approach can rapidly introduce these traits in different cultivars allowing breeders to add these traits to their elite germplasm. Since biotechnologically improved switchgrass must ultimately be grown in open fields, they must be designed to minimize the potential impact of the transgenes on non-target ecosystems. The best way to do this is to minimize gene flow from the transgenic plants. Thus, we will develop technology to introduce sterility into the transgenic plants. We will then combine this technology with the stress resistance modules to create switchgrass lines with enhanced resistance to abiotic stresses.

09 BIOMASS FUELS↗