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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Radiative and continuum dampings of reversed shear Alfvén eigenmodes and perturbative analysis limitations for tokamaks

A careful theoretical analysis of the excitation of Alfvén eigenmodes (AEs), such as TAE (toroidicity-induced AE) and RSAE (reversed shear AE), by superalfvenic energetic particles is required for reliable predictions of energetic ion relaxation in present day fusion experiments. This includes the evaluation of different AE damping mechanisms including radiative and continuum dampings which are the focus of this study. A recent comprehensive benchmark of different eigenmode solvers including gyrokinetic, gyrofluid and hybrid magenetohydrodynamics (MHD) has shown that employed models may have deficiencies when addressing some of them (Taimourzadeh et al., Nucl. Fusion, vol. 59, 2019, 066006). Here, in this paper, we are studying the radiative and continuum dampings of RSAEs in details which were missing in hybrid NOVA/NOVA-C calculations to prepare a NOVA-C package with a substantial upgrade. Both dampings require the finite Larmor radius (FLR) corrections to AE mode structures to be accounted for. Accurately calculating different damping rates and understanding their parametric dependencies, we resolve the limitation coming out of the perturbative approach. In particular, here, the radiative damping is included perturbatively, whereas the continuum damping is computed non-perturbatively. Our comparison leads to the conclusion that the non-perturbative treatment of the unstable RSAE modes is needed to find the agreement with the gyrokinetic calculations. We expect that the RSAE mode structure modification plays a dominant role in determining the RSAE stability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys

Here, we report on the magnetic damping properties of polycrystalline Fe-V alloy thin films that are deposited at room temperature. By varying the concentration of V in the alloy, the saturation magnetization can be adjusted from that of Fe to near zero.We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%–20% V concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% V. The measured intrinsic damping has a minimum value of (1.53±0.08)×10 –3 , which is approximately a factor of 3 higher than our calculated value of 0.48×10 –3 . From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at V concentrations greater than approximately 35% V content.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanoscale imaging of Gilbert damping using signal amplitude mapping

Ferromagnetic resonance force microscopy (FMRFM) is a powerful scanned probe technique that uses sub-micrometer-scale, spatially localized standing spin wave modes (LMs) to perform local ferromagnetic resonance (FMR) measurements. In this work, we show the spatially resolved imaging of Gilbert damping in a ferromagnetic material (FM) using FMRFM. Typically damping is measured from the FMR linewidth. We demonstrate an approach to image the spatial variation of Gilbert damping utilizing the LM resonance peak height to measure the LM resonance cone angle. This approach enables determination of damping through field-swept FMRFM at a single excitation frequency. The extreme force sensitivity of similar to 2 fN at room temperature can resolve changes of Gilbert damping as small as ~2 x 10 -4 at 2GHz, corresponding to ~0.16Oe in FMR linewidth resolution. This high sensitivity, high spatial resolution, and single frequency imaging of Gilbert damping creates the opportunity to study spin interactions at the interface between an insulating FM and a small volume of nonmagnetic material such as atomically thin two-dimensional materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Overcoming the Damping–Elasticity Paradox via 3D‐Printed NiTiSn Nanocomposite

Abstract Developing high damping alloys (HDAs) with large elastic strain has attracted growing attention due to the increasing demand for energy absorption with overload reliability and reusability. However, damping capacity inherently conflicts with elasticity, because the former requires a liable movement of crystal defects while the latter opposite. To deal with the damping‐elasticity paradox, the advantage of pseudobinary eutectic reaction and rapid cooling of laser powder bed fusion is taken to fabricate a bulk NiTiSn nanocomposite with a two‐level hierarchical structure. The first‐level architecture is composed of martensitic NiTi nanolamellae and reinforced Ti 3 Sn nanolamellae. In addition to lattice strain matching and lamellar boundary strengthening, a novel mechanism of martensite reorientation mediated by reversible stress‐induced detwinning‐twinning is activated to generate large elastic strain. A high density of nanotwins and nanodomains within NiTi nanolamellae constitute the second‐level architecture, which provides pronounced internal friction for high damping capacity. As a result, our NiTiSn nanocomposite exhibits a record‐high integration of damping capacity (tanδ > 0.10) and elastic strain (exceeding 4.5%), as well as superb stability under cyclic overload. This research not only represents a major breakthrough in achieving HDAs with outstanding damping and elastic strain but also offers a novel paradigm for high‐performance functional and structural materials.

Chemistry↗
DOE OSTI2020

Wide-Area Measurement-Based Modal Decoupling for Power System Oscillation Damping

Inter-area oscillation modes usually fall within the same frequency range of 0.1 to 1.0 Hz; thus, power oscillation damping (POD) control methods should avoid unnecessary excitation of weakly damped modes. This paper presents a decoupled control strategy to damp inter-area oscillations in the power grid. Pure oscillation mode signals are extracted from wide-area measurements and used as feedback input for POD actuators such as power system stabilizers or high-voltage direct current transmission. The decoupled control strategy is able to increase the damping of the concerned oscillation modes without deteriorating others. This proposed strategy could be implemented independently, or serve as a complement and work along with conventional POD controllers to damp concerned inter-area modes. The proposed method has been tested on a modied MinniWECC system. Extensive results indicate that inter-area oscillations can be successfully and precisely damped using the proposed decoupled strategy.

Fan, Rui↗
DOE OSTI2022

Inviscid damping of an elliptical vortex subject to an external strain flow

Inviscid spatial Landau damping is studied experimentally for the case of oscillatory motion of a two-dimensional vortex about its elliptical equilibrium in the presence of an applied strain flow. Here, the experiments are performed using electron plasmas in a Penning–Malmberg trap. They exploit the isomorphism between the two-dimensional Euler equations for an ideal fluid and the drift-Poisson equations for the plasma, where plasma density is the analog of vorticity. Perturbed elliptical vortex states are created using E x B strain flows, which are generated by applying voltages to electrodes surrounding the plasma. Measurements of spatial Landau damping (also called critical-layer damping) are in agreement with previous studies in the absence of an applied strain, where the damping is due to a resonance between the local fluid motion and the vortex oscillations. Interestingly, the damping rate does not change significantly over a wide range of applied strain rates. This can be accurately predicted from the initial vorticity profile, even though the resonant frequency is reduced substantially due to the applied strain. For higher amplitude perturbations, nonlinear trapping oscillations also exhibit behavior similar to the strain-free case. In principle, higher-order effects of the applied strain, such as separatrix crossing of peripheral vorticity and interactions with harmonics of the fundamental resonance, are expected to change the damping rate. However, this occurs only for conditions that are not realized in the experiments described here. Vortex-in-cell simulations are used to investigate the possible roles of these effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Anharmonic phonon damping enhances the T c of BCS-type superconductors

In this study, a theory of superconductivity is presented where the effect of anharmonicity, as entailed in the acoustic, or optical, phonon damping, is explicitly considered in the pairing mechanism. The gap equation is solved including diffusive Akhiezer damping for longitudinal acoustic phonons or Klemens damping for optical phonons, with a damping coefficient which, in either case, can be directly related to the Grüneisen parameter and hence to the anharmonic coefficients in the interatomic potential. The results show that the increase of anharmonicity has a strikingly nonmonotonic effect on the critical temperature T c . The optimal damping coefficient yielding maximum T c is set by the velocity of the bosonic mediator. This theory may open up unprecedented opportunities for material design where T c may be tuned via the anharmonicity of the interatomic potential, and presents implications for the superconductivity in the recently discovered hydrides, where anharmonicity is very strong and for which the anharmonic damping is especially relevant.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Magnetostriction and temperature dependent Gilbert damping in boron doped Fe 80 ⁢Ga 20 thin films

Magnetic thin films with strong magnetoelastic coupling and low Gilbert damping are key materials for many magnetoelectric devices. Here, we investigated the effects of boron doping concentration on magnetostriction and temperature dependent Gilbert damping in magnetron sputtered (Fe 80 ⁢Ga 20 ) 1−𝑥 ⁢B 𝑥 films. A crystalline to amorphous structural transition was observed for a boron content near 8% and coincided with a decrease in coercivity from 76 Oe to 3 Oe. A 10% doping concentration is optimal for achieving both large magnetostriction of 48.8 ppm and low Gilbert damping of 6×10 −3 . The temperature dependence of the damping shows an increase at low temperatures with a peak around 40 K, and we associate the relative increase Δ⁢𝛼/𝛼 RT with magnetoelastic contributions to the damping, which has a maximum of 55.7% at 8% boron. An increase in the inhomogeneous linewidth broadening was observed in the structural transition regime at about 8% boron concentration. Furthermore, this study suggests that incorporation of glass forming elements, in this case boron, into Fe 80 ⁢Ga 20 is a practical pathway for simultaneously achieving enhanced magnetoelastic coupling and reduced Gilbert damping.

Cryogenics↗
DOE OSTI2022

Stability Evaluation for a Damped, Constrained-Motion Cutting Force Dynamometer

This paper describes the dynamic stability evaluation of a constrained-motion dynamometer (CMD) with passive damping. The CMD’s flexure-based design offers an alternative to traditional piezoelectric cutting force dynamometers, which can exhibit adverse effects of the complex structural dynamics on the measurement accuracy. In contrast, the CMD system’s structural dynamics are nominally single degree of freedom and are conveniently altered by material selection, flexure element geometry, and element arrangement. In this research, a passive damping approach is applied to increase the viscous damping ratio and, subsequently, the stability limit. Cutting tests were completed and the in situ CMD displacement and velocity signals were sampled at the spindle rotating frequency. The periodic sampling approach was used to determine if the milling response was synchronous with the spindle rotation (stable) or not (chatter) by constructing Poincaré maps for both experiment and prediction (time-domain simulation). It was found that the viscous damping coefficient was increased by 130% and the critical stability limit was increased from 4.3 mm (no damping) to 15.4 mm (with damping).

36 MATERIALS SCIENCE↗
DOE OSTI2024

Process damping identification using Bayesian learning and time domain simulation

Process damping can provide improved machining productivity by increasing the stability limit at low spindle speeds. However, existing methods for identifying process damping models experimentally require specialized setups and/or multiple cutting tests. While the phenomenon is well known, the modeling challenges limit pre-process parameter selection that leverages the potential increases in material removal rates. This paper proposes a physics-informed Bayesian method that can identify the cutting force and process damping models from a limited set of test cuts without requiring direct measurements of cutting force or vibration. The method uses time domain simulation to incorporate process damping and provide a basis for test selection. Here, new strategies for efficient sampling and dimensionality reduction are applied to lower computation time and minimize the effect of model error. The proposed method is demonstrated and the identified cutting and damping force coefficients are compared to values obtained using machining tests and least-squares fitting.

42 ENGINEERING↗
DOE OSTI2025

Chemical Interface Damping Revealed by Single-Particle Absorption Spectroscopy

Plasmon-induced interfacial charge separation is a promising way to efficiently extract energetic carriers through direct plasmon decay. This mechanism of charge transfer has been investigated by single-particle scattering spectroscopy, which measures the homogeneous plasmon line width. The line width is broadened by charge transfer, generally known as chemical interface damping. However, conflicting reports exist regarding the effect of chemical interface damping on the corresponding single-particle absorption spectrum, which is needed to accurately determine absolute light conversion efficiencies. This work aims to resolve this question by directly correlating absorption and scattering spectra of individual gold nanorods in the presence and absence of a charge-accepting interface. We find that for TiO 2 coated nanorods, the absorption line width is indeed broadened due to chemical interface damping but is overall narrower than the scattering line width. Here, chemical interface damping is furthermore found to increase with larger resonance energies. The observed differences in line widths between absorption and scattering are elucidated within the context of an analytically tractable model describing the lowest energy optically bright and higher-order optically dark plasmon modes of the nanorod, including bulk, radiative, and chemical interface damping effects. Taken together, these results establish that single-particle absorption spectroscopy is capable of revealing interfacial charge injection by direct plasmon decay.

absorption↗
DOE OSTI2020

The role of iron in magnetic damping of Mg(Al,Fe) 2 O 4 spinel ferrite thin films

© 2020 Author(s). We have investigated magnesium aluminum ferrite thin films with a range of iron concentrations and identified the optimal iron content to obtain high crystalline quality thin films with the low magnetic damping required for spin current-based applications. Epitaxial MgAl 2-x FexO4 films with 0.8 < x < 2.0 were grown by pulsed laser deposition on single crystal MgAl2O4 substrates and were characterized structurally and magnetically. We find that the x = 1.5 composition minimizes the room-temperature magnetic damping with a typical Gilbert damping parameter of α eff = 1.8 × 10-3. This minimized damping is governed by a competition between the more robust magnetic ordering with increased iron content, x, and the more defective structure due to larger film-substrate lattice mismatch with increased iron content. The temperature-dependent magnetization curves indicate that Tc is suppressed below room temperature for iron content x ≤ 1.2 and eventually suppressed entirely for x = 0.8. X-ray magnetic circular dichroism results indicate that for all x the magnetic moment is dominated by Fe 3 + cations distributed in a 60:40 ratio on the octahedral and tetrahedral sites, with minimal contribution from Fe 2 + cations. Films with x = 1.4-1.6 exhibit very strong ferromagnetic resonance and low Gilbert damping with α eff = (1.8-6) × 10-3, making them ideal candidates for microwave and spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Physics-informed KNN milling stability model with process damping effects

This paper describes a k-nearest neighbors, or KNN, model for milling stability including process damping effects. A physics-based, frequency domain milling stability solution is used to generate the training data, but does not incorporate process damping effects. The data set is then updated using limited tests to capture the process damping behavior. A “stair step” approach is used to select the test points, where a first spindle speed-axial depth combination is selected based on the physics-based stability map, subsequent tests are defined using the previous test result, and data points are updated by knowledge of process damping behavior and the test results. Furthermore, the KNN modeling approach demonstrates the ability to predict both stable and unstable results, including process damping behavior.

42 ENGINEERING↗
DOE OSTI2022

Damping inter-area oscillation using reinforcement learning controlled TCSC

Appropriate damping control of the inter-area oscillation would ensure the grid stability and maintain the tie-line power transfer capability. In this paper, we proposed a novel reinforcement learning (RL) based power oscillation damping (POD) controller that uses Thyristor Controlled Series Compensators (TCSC) to damp inter-area oscillations. By leveraging the unbiased gradient direction estimation of the natural evolution strategy (NES), we successfully regulated the power flows on the tie-lines and damped inter-area oscillations through dynamically modulating the inserted reactance of the TCSC. The proposed RL-based POD controller has been tested on both two-area four-machine system and North American Minni-WECC system. Extensive studies have demonstrated the excellent performance of the proposed RL-based TCSC POD controller in damping inter-area oscillations.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators

The linear collisionless damping of zonal flows is calculated for quasi-symmetric stellarator equilibria in flux-tube, flux-surface, and full-volume geometry. Equilibria are studied from the quasi-helical symmetry configuration of the Helically Symmetric eXperiment (HSX), a broken symmetry configuration of HSX, and the quasi-axial symmetry geometry of the National Compact Stellarator eXperiment (NCSX). Zonal flow oscillations and long-time damping affect the zonal flow evolution, and the zonal flow residual goes to zero for small radial wavenumber. The oscillation frequency and damping rate depend on the bounce-averaged radial particle drift in accordance with theory. While each flux tube on a flux surface is unique, several different flux tubes in HSX or NCSX can reproduce the zonal flow damping from a flux-surface calculation given an adequate parallel extent. The flux-surface or flux-tube calculations can accurately reproduce the full-volume long-time residual for moderate kx, but the oscillation and damping time scales are longer in local representations, particularly for small kx approaching the system size.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Viscoelastic Damping and Wave Cutoff of Titanium Alloy and Lattices

Here, the 3D-printed titanium alloy Ti5553 solid and octet truss lattice specimens are studied via resonant ultrasound spectroscopy, free decay of vibration and quasi-static methods to determine viscoelastic damping. Damping in solid alloy and a lattice is between 10 -4 and 10 -3 . Much of the damping at high sonic frequency is attributed to stress-induced heat flow between heterogeneities due to 3D printing. Pulsed wave ultrasound experiments disclose reverberation in the cell structure of the lattice. Continuous wave ultrasound experiments show that the transmissibility in the lattice rolls off beginning at about 50 kHz and becomes negligible above 110 kHz. By contrast, the polymer polymethyl methacrylate (PMMA), though it is viscoelastic, readily transmits waves up to 1 MHz. The cutoff frequency in the lattice is associated with the structure size, not intrinsic damping in the alloy. The octet truss lattice, in addition to providing good mechanical performance, is also an ultrasonic metamaterial.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Monodomain Liquid‐Crystal Elastomer Lattices for Broad Strain‐Rate Mechanical Damping

Designing structures that effectively dissipate energy across a broad range of mechanical loading rates, including those from compression, shock, and vibration, poses a significant engineering challenge. In this study, liquid‐crystal elastomers (LCEs), which possess anisotropic properties due to the alignment of their polymer backbone, are explored. As a result, LCEs exhibit a soft elastic response under mechanical loading, making them ideal for energy dissipation. Advances in additive manufacturing (AM) enable simple fabrication of foamlike dissipative structures with complex lattice geometries. Herein, direct ink write 3D printing, an extrusion AM method, is used to fabricate aligned, monodomain LCE lattice structures for broad strain‐rate mechanical damping. In this work, it is shown that these structures can dissipate strain energy in quasi‐static environments, comparable to traditional elastomeric lattices, and provide improved damping under high strain‐rate drop testing due to LCE soft elasticity. Additionally, under dynamic mechanical vibration, monodomain LCE lattices enhance damping at structural natural frequencies and provide high‐frequency attenuation. Finally, in these findings, a promising method is presented for fabricating mechanical damping devices that effectively dissipate energy across a broad range of loading rates.

3D printings↗
DOE OSTI2020

Increased damping through captured powder in additive manufacturing

This paper describes the retention of metal powder within additively manufactured structures to achieve increased damping. In this work, solid and hollow (powder filled) aluminum cylinders were fabricated in using laser powder bed fusion where the internal, captured powder in the hollow cylinders served as an energy dissipation mechanism. Impact testing was completed to compare the frequency response functions of three cylinder geometries: one solid cross-section and two hollow cross-sections with different inner diameters and, therefore, different powder volumes. Increased damping with larger inner diameter was observed. The damping was quantified using a structural damping model.

36 MATERIALS SCIENCE↗