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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Progress of Divertor Heat and Particle Flux Control in EAST for Advanced Steady-State Operation in the Last 10 Years

Active control of the excessively high heat and particle fluxes on the divertor target plates is of fundamental importance to the steady state operation of tokamaks, especially for fusion reactors. A series of experiments have been carried out on this critical issue to relieve the plasma-wall interactions in the experimental advanced superconducting tokamak (EAST) in the last ten years, not only contributing to the long pulse operation of EAST itself, but also providing physical understandings and potential techniques to the next-generation devices like ITER. Here we have characterized the power deposition pattern and broadened the divertor footprint width effectively. The plasma-wetted area is actively handled using either 3-dimentional edge magnetic topology or advanced plasma equilibrium, thereby peak heat flux around the strike point is reduced. Active control of detachment or radiation compatible with core plasma performance has progressed significantly in very recent years, with a series of active feedback control modules developed and utilized successfully, based on the divertor physics advances with both experiments and simulation. The upper divertor of EAST was upgraded from graphite to active water-cooling ITER-like tungsten in 2014, exhibiting much enhanced heat removal capability. As for the particle exhaust including both fueling and impurity particles, in addition to wall conditioning and impurity source control, the efficiency of particle flux exhaust is optimized by making full use of the divertor closure and the plasma drifts in both scrape-off layer and divertor volume. These heat and particle exhaust advances contribute greatly to a series of EAST achievements like H-mode operation over 100 s. A brief near-term plan on the integrated control of divertor plasma-wall interactions in long-time scale will also be introduced, aiming to provide favorable divertor operation solution for ITER and CFETR.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Response of the Verwey transition in magnetite to controlled point-like disorder induced by 2.5 MeV electron irradiation

Controlled point-like disorder induced by low temperature 2.5 MeV electron irradiation was used to probe the nature of the Verwey transition in magnetite, Fe 3 O 4 . Two large single crystals, one with optimal transition temperature, T V ≈ 121 K, and another with T V ≈ 109 K, as well as magnetite magnetosome nanocrystals harvested from the lysed cells of the marine magnetotactic vibrio Magnetovibrio blakemorei strain MV-1, T V ≈ 110 K, were examined. Temperature-dependent resistivity is consistent with the semiconductor-to-semiconductor (insulator) sharp, step-like Verwey transition from a state with a small bandgap of around 60 meV to a state with a large bandgap of about 300 meV. The irradiation causes an up-shift of the resistivity curves above the transition without transition smearing or broadening. It also causes an apparent down-shift of the resistivity maximum at high temperatures. In the lower crystal, the electron irradiation drives the transition temperature into a “forbidden” interval of T V , believed to separate the first order from the second order phase transition. Contrary to this belief, the transition itself remains sharp and hysteretic without a significant change in the hysteresis width indicating the strong 1st order character of the Verwey transition for all TV values. The separate 2nd order - looking transition is likely due to sample inhomogeneities. Here we conclude that the sudden change of the bandgap accompanied (or driven) by the monoclinic distortion and the change of magnetic anisotropy is the reason for the Verwey transition in magnetite and the effect of additional disorder is mostly in the smearing of the sharp gap edges near the Fermi level.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electrostatically controlled spin polarization in Graphene-CrSBr magnetic proximity heterostructures

Abstract The magnetic proximity effect can induce a spin dependent exchange shift in the band structure of graphene. This produces a magnetization and a spin polarization of the electron/hole carriers in this material, paving the way for its use as an active component in spintronics devices. The electrostatic control of this spin polarization in graphene has however never been demonstrated so far. We show that interfacing graphene with the van der Waals antiferromagnet CrSBr results in an unconventional manifestation of the quantum Hall effect, which can be attributed to the presence of counterflowing spin-polarized edge channels originating from the spin-dependent exchange shift in graphene. We extract an exchange shift ranging from 27 – 32 meV, and show that it also produces an electrostatically tunable spin polarization of the electron/hole carriers in graphene ranging from − 50% to + 69% in the absence of a magnetic field. This proof of principle provides a starting point for the use of graphene as an electrostatically tunable source of spin current and could allow this system to generate a large magnetoresistance in gate tunable spin valve devices.

Science & Technology - Other Topics↗
DOE OSTI2025

Cyclically symmetric radially self-similar phononic pseudocrystal isolator for broadband, ultrasonic vibration bandstop filtering

A 2D phononic pseudocrystal isolator exhibiting cyclic symmetry and radial self-similarity is measured and demonstrated to block a wide range of ultrasonic vibration. Measurements of longitudinal and shear wave blocking effects are made and compared with computational results. The use of the bandgap edge ratio is recommended for quantifying suppression in very-wide-bandgap materials. In conclusion, the upper-to-lower suppression edge frequency ratios of 3–4 are remarkably large for shear waves and even larger for longitudinal waves upper-to-lower suppression ratio (13 at 5 dB), such that 92.5% of frequencies in that range experience ≥ 5 dB of suppression.

Acoustic metamaterial↗
DOE OSTI2025

Fractional magnetic charges and channeling of Faraday lines by disclinations in artificial spin ice

We have studied the magnetic moments of artificial spin ice arrays of nanomagnets in both undistorted square arrays and in arrays with a topological defect induced by a single disclination. We confirm that the disclination induces global, macroscopic changes in the low-energy collective states of the nanomagnet moment configuration. Specifically, the disclination leads to Faraday lines of effective magnetic flux that run from the center all the way to the edge of the arrays. Moreover, the geometric deformation, induced by the topological defect, curves the geometry such that these Faraday lines are channeled preferentially by the arrays’ curved geometry. Our results demonstrate how the intentional combination of topology and geometry can be designed to control magnetic charges and the flow of local magnetization and thus manipulate associated collective excitations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Projecting end-of-century climate extremes and their impacts on the hydrology of a representative California watershed

Abstract. In California, it is essential to understand the evolution of water resources in response to a changing climate to sustain its economy and agriculture and to build resilient communities. Although extreme conditions have characterized the historical hydroclimate of California, climate change will likely intensify hydroclimatic extremes by the end of the century (EoC). However, few studies have investigated the impacts of EoC extremes on watershed hydrology. We use cutting-edge global climate and integrated hydrologic models to simulate EoC extremes and their effects on the water-energy balance. We assess the impacts of projected driest, median, and wettest water years under Representative Concentration Pathway (RCP) 8.5 on the hydrodynamics of the Cosumnes River basin. Substantial changes to annual average temperature (>+2.5 ∘C) and precipitation (>+38 %) will characterize the EoC extreme water years compared to their historical counterparts. A shift in the dominant form of precipitation, mostly in the form of rain, is projected to fall earlier. These changes reduce snowpack by more than 90 %, increase peak surface water and groundwater storages up to 75 % and 23 %, respectively, and drive the timing of peak storage to occur earlier in the year. Because EoC temperatures and soil moisture are high, both potential and actual evapotranspiration (ET) increase. The latter, along with the lack of snowmelt in the warm EoC, causes surface water and groundwater storages to significantly decrease in summer, with groundwater showing the highest rates of decrease. These changes result in more ephemeral EoC streams with more focused flow and increased storage in the mainstem of the river network during the summer.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Modelling of electrostatic ion-scale turbulence in divertor tokamaks with the gyrokinetic code $\mathrm{COGENT}$

Here, continuum gyrokinetic simulations of electrostatic ion scale turbulence are presented for the case of a diverted (single-null) tokamak geometry. The simulation model, implemented in the finite-volume code COGENT, solves the long-wavelength limit of the full-F gyrokinetic equation for ion species coupled to a vorticity equation for electrostatic potential variations, where a fluid model is used for an electron response. The model describes the ion scale ion temperature gradient (ITG) and resistive drift modes as well as neoclassical ion physics effects. Different turbulence regimes are observed depending on the plasma profiles, and the roles of a self-consistent background electric field and an X-point geometry are explored. In particular, increasing the pedestal density gradient and the corresponding radial electric field is demonstrated to suppress the ITG turbulence, whereas the same edge plasma background can still be destabilized by the resistive modes when the plasma resistivity is increased. The effects of X-point geometry are assessed by comparing cross-separatrix simulations with counterpart calculations performed for a toroidal annulus geometry. For the simulation parameters considered, similar global behaviour is observed in both cases, whereas strong local suppression of turbulence fluctuations is demonstrated near the X-point for the case of a single-null geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Multi-scale Interaction Mechanism for Edge-Localized-Mode Suppression in the Tokamak Edge

A central challenge in fusion energy is reconciling the high-confinement mode required for reactor performance with the intense intermittent relaxation events it produces, known as edge-localized modes. These instabilities arise in the steep pressure pedestal at the plasma edge when magnetohydrodynamic thresholds are crossed, inflicting damaging heat loads on reactor components. Here, we show that multiscale interactions between microscopic turbulence and macroscopic magnetohydrodynamic modes provide encouraging prospects for self-organized edge-localized modes regulation. Using direct quantitative measurements of multiscale modes, eddy dynamics, and turbulent flux, we show that small-scale electron drift wave turbulence actively scatters the large-scale peeling-ballooning modes. This scattering decorrelates the pressure and velocity fields of the instability, so arresting its growth. Our modeling and theoretical analysis confirm this suppression mechanism is effective even when conventional linear stability thresholds are exceeded. This work establishes a nonlinear principle for edge-localized modes stability, revealing how ambient micro-turbulence can be leveraged to maintain a macro-stable, high-performance pedestal for future fusion reactors.

experimental nuclear physics↗
DOE OSTI2021

L-H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations

The L–H transition power threshold PLH is observed to increase with applied n = 3 resonant magnetic perturbations (RMP) in ITER-similar-shape plasmas with balanced neutral beam torque injection in DIII-D. The increase is most pronounced with added electron–cyclotron heating: PLH increases with decreasing edge plasma collisionality as PLH/PLH-08 ~ (ν*)−0.5, where PLH-08 is the 2008 ITPA multi-machine power threshold scaling. This result raises concerns for H-mode access at low edge collisionality in ITER, where RMP may have to be applied before the L–H transition to safely suppress the first edge-localized mode. Non-axisymmetric modifications with RMP include a simultaneous reduction of the radial electric field (Er) well depth and E × B shear. This can be attributed to increasing edge toroidal co-current rotation, and is consistent with substantially increased local long-wavelength turbulence (measured via beam emission spectroscopy). At high RMP perturbation strength the edge electric field Er reverses sign locally (becomes positive), with changes in dominant turbulence modes. Edge magnetic stochasticity provides an attractive explanation of the observed modifications, and the observed changes in toroidal rotation and Er are consistent with a simple fluid model describing radial electron current flow along stochastic fieldlines. The observed collisionality dependence of the L-mode edge electric field with applied RMP is also qualitatively consistent with this model. Reflectometry data indicate a significant reduction of the normalized L-mode radial density gradient a/Ln at high RMP field with simultaneous increase in radial particle flux and electron thermal flux from power balance analysis. We conjecture that the increase of PLH with RMP results from the combined effects of reduced E × B flow shear (increasing turbulent transport levels) and toroidal/poloidal flow modulation due to edge stochasticity. Initial experiments indicate that non-resonant n = 3 magnetic perturbations lead only to relatively small changes in Er, E × B shear and fluctuation characteristics, and have less impact on the L–H transition power threshold. This motivates further exploration of the RMP spectrum dependence of PLH for possible mitigation of the observed threshold increase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Deciphering helix assembly in the heliconical nematic phase via tender resonant X-ray scattering

Being a link between a uniaxial nematic and a chiral nematic, the twist bend nematic (N TB ) has been an intriguing topic for research over the last decade as a key to understanding chirality generation. Accurate description and understanding of resonance effects in helical structures provide crucial knowledge on the phase behavior beyond positional ordering. We examined the manifestation of resonance effects in N TB via tender resonant X-ray scattering (TReXS) at the sulfur K-edge. For the first time we demonstrate quantitatively that the energy dependence of the scattering peak in the N TB phase follows the energy dependence of the complex refractive indices measured by X-ray absorption. Furthermore, taking advantage of molecular energy calculation, we decipher the distinct helical pitch variation trend for symmetric/asymmetric dimers from the perspective of hybridization and reveal the strong effect of substituting oxygen for sulfur atoms on the helical pitch and the thermal helix extension.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Direct observation of distinct bulk and edge nonequilibrium spin accumulation in ultrathin MoTe 2

Low-symmetry two-dimensional (2D) topological materials such as MoTe 2 host efficient charge-to-spin conversion (CSC) mechanisms that can be harnessed for novel electronic and spintronic devices. However, the nature of the various CSC mechanisms and their correlation with underlying crystal symmetries remain unsettled. In this work, we use local spin-sensitive electrochemical potential measurements to directly probe the spatially dependent nonequilibrium spin accumulation in MoTe 2 flakes down to four atomic layers. We are able to clearly disentangle contributions originating from the spin Hall and Rashba-Edelstein effects and uncover an abundance of unconventional spin polarizations that develop uniquely in the sample bulk and edges with decreasing thickness. Using ab-initio calculations, we construct a unified understanding of all the observed CSC components in relation to the material dimensionality and stacking arrangement. Our findings not only illuminate previous CSC results on MoTe 2 but also have important ramifications for future devices that can exploit the local and layer-dependent spin properties of this 2D topological material.

Science & Technology - Other Topics↗
DOE OSTI2023

BeyondPlanck X. Bandpass and beam leakage corrections

We discuss the treatment of bandpass and beam leakage corrections in the Bayesian BeyondPlanck CMB analysis pipeline as applied to the Planck LFI measurements. As a preparatory step, we first apply three corrections to the nominal LFI bandpass profiles including removal of a known systematic effect in the ground measuring equipment at 61 GHz; smoothing of standing wave ripples; and edge regularization. The main net impact of these modifications is an overall shift in the 70 GHz bandpass of +0.6 GHz; we argue that any analysis of LFI data products, either from Planck or BeyondPlanck, should use these new bandpasses. In addition, we fit a single free bandpass parameter for each radiometer of the form Δ i = Δ 0 + $δ$ i , where Δ 0 represents an absolute frequency shift per frequency band and $δ$i is a relative shift per detector. The absolute correction is only fitted at 30 GHz with a full $\chi$ 2 -based likelihood, resulting in a correction of Δ 30 = 0.24 ± 0.03 GHz. The relative corrections are fitted using a spurious map approach, fundamentally similar to the method pioneered by the WMAP team, but without introducing many additional degrees of freedom. All bandpass parameters are sampled using a standard Metropolis sampler within the main BeyondPlanck Gibbs chain, and bandpass uncertainties are thus propagated to all other data products in the analysis. In total, we find that our bandpass model significantly reduces leakage effects. For beam leakage corrections, we adopt the official Planck LFI beam estimates without additional degrees of freedom, and only marginalize over the underlying sky model. We note that this is the first-time leakage from beam mismatch has been included for Planck LFI maps.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

A Multi-Objective Approach for Optimizing Edge-Based Resource Allocation Using TOPSIS

Existing approaches for allocating resources on edge environments are inefficient and lack the support of heterogeneous edge devices, which in turn fail to optimize the dependency on cloud infrastructures or datacenters. To this extent, we propose in this paper OpERA, a multi-layered edge-based resource allocation optimization framework that supports heterogeneous and seamless execution of offloadable tasks across edge, fog, and cloud computing layers and architectures. By capturing offloadable task requirements, OpERA is capable of identifying suitable resources within nearby edge or fog layers, thus optimizing the execution process. Throughout the paper, we present results which show the effectiveness of our proposed optimization strategy in terms of reducing costs, minimizing energy consumption, and promoting other residual gains in terms of processing computations, network bandwidth, and task execution time. We also demonstrate that by optimizing resource allocation in computation offloading, it is then possible to increase the likelihood of successful task offloading, particularly for computationally intensive tasks that are becoming integral as part of many IoT applications such robotic surgery, autonomous driving, smart city monitoring device grids, and deep learning tasks. The evaluation of our OpERA optimization algorithm reveals that the TOPSIS MCDM technique effectively identifies optimal compute resources for processing offloadable tasks, with a 96% success rate. Moreover, the results from our experiments with a diverse range of use cases show that our OpERA optimization strategy can effectively reduce energy consumption by up to 88%, and operational costs by 76%, by identifying relevant compute resources.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Probing Distinctive Redox Mechanism in Ni-Rich Cathode Via Real-Time Quick X-Ray Absorption Spectroscopy

X-ray radiation damage on the measuring system has been a critical issue regularly for a long-time exposure to X-ray beam during the in operando characterizations, which is particularly severe when the applied X-ray energy is near the absorption edges (M, L, K, etc.) of the interest element. Here, to minimize the negative effects raised by beam radiation, we employ quick X-ray absorption spectroscopy (QXAS) to study the electrochemical reaction mechanism of a Ni-rich layered structure cathode for lithium-ion batteries. With the advanced QXAS technique, the electronic structure and local coordination environment of the transition metals (TMs) are monitored in-operando with limited radiation damage. Compared to the conventional step-mode X-ray absorption spectroscopy, the QXAS can provide more reliable oxidation state change and more detailed local structure evolutions surrounding TMs (Ni and Co) in Ni-rich layered oxides. By leveraging these advantages of QXAS, we demonstrated that the Ni dominates the electrochemical process with the Co being almost electrochemically inactive. Reversible Ni ions movement between TMs sites and Li sites is also revealed by the time-resolved QXAS technique.

25 ENERGY STORAGE↗
DOE OSTI2025

Angular-spectral filtering of recoil protons for optimization of fast neutron imaging employing proton converters

Fast neutron imaging is an important capability for diverse applications such as inertial confinement fusion diagnostics, cargo security, nuclear nonproliferation and arms control, and industrial inspection. Traditional phosphor image plates can be enhanced for fast neutron imaging using hydrogenous plastic converters which allow fast neutrons to scatter off hydrogen nuclei to produce energetic protons that can be recorded by the image plate. However, protons emitted by image plates are not constrained in their emission angle, which contributes to the blur of the resulting image. Here, we investigate two methods that can alter the spatial extent of converted protons that deposit energy in the image plate: reducing the converter thickness, and introducing a proton filter between the plastic converter and image plate to reduce the contribution of lower-energy, off-axis protons to the image. Here we determine the optimal plastic converter thickness for maximizing the signal intensity to be 2–3 mm through Monte Carlo simulations, and we benchmark this result against experimental measurements with a deuterium-tritium (DT) neutron generator. Next, we evaluate the image smearing and signal loss for various converters to show that solely reducing the converter thickness has the expected effect of reducing the blur from proton image smearing of the sharpness of an edge recorded on the image plate at the cost of reducing the signal intensity. The use of a proton filter is shown to achieve a similar improvement of edge sharpness as reducing the converter thickness while also sacrificing the signal intensity. We conclude that the use of proton energy filtering can improve the sharpness of fast neutron images in situations where the converter thickness cannot be reduced below some practical minimum. For more intense neutron sources, the signal intensity is of less concern, and optimizing the resolution of the image plate and therefore of the imaging system could have greater value. In these applications, proton filters may allow for improved fast neutron imaging measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Metal Sulfide Ion Exchangers: High Acid Stability of Na 2 x Mg 2 y – x Sn 4– y S 8 (NMS) and Topotactic Conversion to 2D Solid Acids with Semiconducting Character

Metal sulfide ion exchange materials (MSIEs) are of interest for nuclear waste remediation applications. Here, we report the high stability of two structurally related metal sulfide ion exchange materials, Na 2x Mg 2y–x Sn 4–y S 8 (Mg-NMS) and Na 2 SnS 3 (Na-NMS), in strongly acid media, in addition to the preparation of Na 2x Ni 2y–x Sn 4–y S 8 (Ni-NMS). Their formation progress during synthesis is studied with in-situ methods, with the target phases appearing in <15 min, reaction completion in <12 h, and high yields (75–80%). Upon contact with nitric or hydrochloric acid, these materials topotactically exchange Na + for H + , proceeding in a stepwise protonation pathway for Na 5.33 Sn 2.67 S 8 . Na-NMS is stable in 2 M HNO 3 and Mg-NMS is stable in 4 M HNO 3 for up to 4 h, while both NMS materials are stable in 6 M HCl for up to 4 days. However, the treatment of Mg-NMS and Na-NMS with 2–6 M H 2 SO 4 reveals a much slower protonation process since after 4 h of contact both NMS and HMS are present in the solution. The resultant protonated materials, H 2x Mg 2y–x Sn 4–y S 8 and H 4x [(H y Na y–1 ) 1.33x Sn 4––1.33x ]S 8 , are themselves solid acids and readily react with and intercalate a variety of organic amines, where the band gap of the resultant adduct is influenced by amine choice and can be tuned within the range of 1.88(5)–2.27(5) eV. The work function energy values for all materials were extracted from photoemission yield spectroscopy in air (PYSA) measurements and range from 5.47 (2) to 5.76 (2) eV, and the relative band alignments of the materials are discussed. DFT calculations suggest that the electronic structure of Na 2 MgSn 3 S 8 and H 2 MgSn 3 S 8 makes them indirect gap semiconductors with multi-valley band edges, with carriers confined to the [MgSn 3 S 8 ] 2– layers. Light electron effective masses indicate high electron mobilities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Incorporating the Nanoscale Encapsulation Concept from Liquid Electrolytes into Solid-State Lithium–Sulfur Batteries

Solid-state Li–S batteries are attractive due to their high energy density and safety. However, it is unclear whether the concepts from liquid electrolytes are applicable in the solid state to improve battery performance. Here, we demonstrate that the nanoscale encapsulation concept based on Li 2 S@TiS 2 core–shell particles, originally developed in liquid electrolytes, is effective in solid polymer electrolytes. Using in situ optical cell and sulfur K-edge X-ray absorption, we find that polysulfides form and are well-trapped inside individual particles by the nanoscale TiS 2 encapsulation. We see that this TiS 2 encapsulation layer also functions to catalyze the oxidation reaction of Li 2 S to sulfur, even in solid-state electrolytes, proven by both experiments and density functional theory calculations. A high cell-level specific energy of 427 W·h·kg –1 is achieved by integrating the Li 2 S@TiS 2 cathode with a poly(ethylene oxide)-based electrolyte and a lithium metal anode. This study points to the fruitful direction of borrowing concepts from liquid electrolytes into solid-state batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Atomic-Scale Dynamic Mechanisms of Embedded MoS 2 Wires

Nanowires composed of a 1:1 stoichiometry of transition metals and chalcogen ions can be fabricated from two-dimensional transition metal dichalcogenides (TMDs) by using electron beam irradiation. Wires fabricated through in situ experiments can be geometrically connected to TMD sheets in various ways, and their physical properties can vary accordingly. Understanding the structural transformation caused by electron beams is critical for designing wire-sheet structures for nanoelectronics. In this study, we report the behavior of nanowires formed inside a monolayer MoS 2 sheet by combining phase-contrast images and large-scale atomistic modeling. Here we investigate the effect of vacancies on the dynamic evolution of wires, such as rotations with different edge structures and breaking, by considering the interactions between MoS wires and MoS 2 nanosheets. The obtained insights can be applied to other monolayer TMDs to guide the behavior of TMD wires and fabricate favorable geometries for various applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗