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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Electron kinetics in a high- Z plasmoid

The problem of the electron dynamics on a closed magnetic field line passing through a high-Z plasmoid is considered. The electron kinetic equation is integrated over bounce motion and pitch angle, reducing the independent variables to a single adiabatic invariant plus time. Integration of the full Landau self-collision operator is carried out exactly, resulting in a nonlinear integro-differential operator in the new invariant. Conservation laws and the H theorem of the integrated self-collision operator are proven. Numerical solutions of the integrated kinetic equation are obtained with a self-consistent quasineutral electric potential, given the initial condition of a cold plasmoid immersed in a hot ambient plasma. The fact that cold electrons are deeply trapped in a potential with a parabolic peak leads to exactly 3/4 the usual rate of collisional heating by the ambient plasma, independent of any other parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2008

3D PIC Simulation of the Magnetosphere during IMF Rotation from North to South: Signatures of Substorm Triggering in the Magnetotail

Three dimensional PIC simulations are performed in order to analyse the dynamics of the magnetotail as the interplanetary magnetic field (IMF) rotates from northward to southward direction. This dynamics reveals to be quite different within meridian/equatorial planes over two successive phases of this rotation. First, as IMF rotates from North to Dawn-Dusk direction, the X-Point (magnetic reconnection) evidenced in the magnetotail (meridian plane) is moving earthward (from x=-35 Re to x=-17.5 ) distance at which it stabilizes. This motion is coupled with the formation of "Crosstail-S" patterns (within the plane perpendicular to the Sun-Earth mine) through the neutral sheet in the nearby magnetotail. Second, as IMF rotates from dawn-dusk to South, the minimum B field region is expanding within the equatorial plane and forms a ring. This two-steps dynamics is analyzed in strong association with the cross field magnetotail current Jy, in order to recover the signatures of substorms triggering.

Nishikawa, Ken-Ichi↗
NASA NTRS1999

The Effects of Magnetic Anomalies Discovered at Mars on the Structure of the Martian Ionosphere and the Solar Wind Interaction as Follows from Radio Occultation Experiments

The electron density distribution in the ionosphere of nonmagnetic (or weakly magnetized) planet depends not only on the solar ultraviolet intensity, but also on the nature of the SW interaction with this planet. Two scenarios previously have been developed based on the observations of the bow shock crossings and on the electron density distribution within the ionosphere. According to one of them Mars has an intrinsic magnetosphere produced by a dipole magnetic field and the Martian ionosphere is protected from the SW flow except during "overpressure conditions, when the planetary magnetic field can not balance the SW dynamic pressure. In the second scenario the Martian intrinsic magnetic dipole field is so weak that Mars has mainly an induced magnetosphere and a Venus-like SW/ionosphere interaction. Today the possible existence of a sufficiently strong global magnetic field that participates in the SW/Mars interaction can no longer be supported. The results obtained by the Mars-Global-Surveyor (MGS) space-craft show the existence of highly variable, but also very localized magnetic fields of crustal origin at Mars as high as 400-1500 nT. The absence of the large-scale global magnetic field at Mars makes it similar to Venus, except for possible effects of the magnetic anomalies associated with the remnant crustal magnetization. However the previous results on the Martian ionosphere obtained mainly by the radio occultation methods show that there appears to be a permanent existence of a global horizontal magnetic field in the Martian ionosphere. Moreover the global induced magnetic field in the Venus ionosphere is not typical at the solar zenith angles explored by the radio occultation methods. Additional information is contained in the original extended abstract.

Ness, N. F.↗
DOE OSTI2023

NMR relaxometry characterization of water adsorption in corn stover anatomical fractions

Nuclear magnetic resonance (NMR) relaxometry is applied to provide direct measurement of water adsorption in anatomical fractions of corn stover. NMR transverse T 2 relaxation time distribution measurements indicate multiple water populations, which vary with anatomical fraction and water adsorption. Measured T 2 data are used to calculate thermodynamic properties of Brunauer-Emmet-Teller adsorption theory using a model to estimate mono and bilayer relaxation. T 2 data are used directly to determine rotational diffusion correlation times indicating adsorption interaction strength. T 1 -T 2 longitudinal-transverse relaxation time correlation measurements quantify differences in the molecular level structural order of the adsorbate surface water as a function of water activity, i.e. relative humidity or water vapor partial pressure. The T 1 /T 2 ratio provides a measure of the surface energy related to the adsorption strength and surface diffusive mobility of the water adsorbate and differentiates the anatomical fractions. Furthermore, the results indicate that direct measurement of NMR relaxation times can be used to characterize corn stover biomass water adsorption, data relevant to processing and handling considerations.

09 BIOMASS FUELS↗
DOE OSTI2022

A resistive MHD model and simulation on plasma flow evolution in the presence of resonant magnetic perturbation in a tokamak

Nonaxisymmetric magnetic fields such as the intrinsic error field and the externally applied resonant magnetic perturbation (RMP) in a tokamak are known to influence the plasma momentum transport and flow evolution through plasma response, which itself strongly depends on the plasma flow as well. The nonlinear interaction between plasma response and flow has been previously modeled in the conventional error field theory with the “no-slip” condition, which has been recently extended to allow the “free-slip” condition. In this work, we further target this specific process and numerically simulate the nonlinear plasma response and flow evolution in the presence of a single-helicity RMP in a circular-shaped model tokamak configuration, based on the full resistive MHD model in the initial-value code NIMROD. Time evolution of the parallel (to k) flow or “slip frequency” profile and its asymptotic steady state obtained from the NIMROD simulations are compared with both conventional and extended nonlinear response theories. Here, k is the wave vector of the propagating island. Good agreement with the extended theory with free-slip condition has been achieved for the parallel flow profile evolution in response to RMP in all resistive regimes, whereas the difference from the conventional theory with the no-slip condition tends to diminish as the plasma resistivity approaches zero.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Metal-insulator and magnetic phase diagram of Ca 2 RuO 4 from auxiliary field quantum Monte Carlo and dynamical mean field theory

Layered perovskite ruthenium oxides exhibit a striking series of metal-insulator and magnetic-nonmagnetic phase transitions easily tuned by temperature, pressure, epitaxy, and nonlinear drive. In this work, we combine results from two complementary state-of-the-art many-body methods, auxiliary field quantum Monte Carlo and dynamical mean field theory, to determine the low-temperature phase diagram of Ca 2 RuO 4 . Both methods predict a low-temperature, pressure-driven metal-insulator transition accompanied by a ferromagnetic-antiferromagnetic transition. Further, the properties of the ferromagnetic state vary nonmonotonically with pressure and are dominated by the ruthenium $d_{xy}$ orbital, while the properties of the antiferromagnetic state are dominated by the $d_{xz}$ and $d_{yz}$ orbitals. Differences in the details of the predictions of the two methods are analyzed. This work is theoretically important as it presents the first application of the auxiliary field quantum Monte Carlo method to an orbitally degenerate system with both Mott and Hunds physics and provides an important comparison of the dynamical mean field and auxiliary field quantum Monte Carlo methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Shifting Valencies and Magnetic Responses in La-Based High-Entropy Oxide Perovskite Thin Films with Variable Mn Presence

Chemical disorder in compositionally complex perovskite oxides generates a broad distribution of exchange pathways and spin states, but the microscopic origin and spatial homogeneity of the resulting magnetic phases remain debated. Here, we tune the Mn fraction (x = 0.2–0.6) in epitaxial La(Cr, Mn, Fe, Co, Ni)O3 thin films and resolve the coupled evolution of valence, spin state, and magnetism using element-specific x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD). Mn enrichment drives an internal redistribution of charge, in which Mn evolves toward a Mn3+-rich mixed valence, while Co converts from predominantly Co3+ to high-spin Co2+. This valence/spin-state coupling amplifies the Mn- and Co-derived ferromagnetic response by nearly an order of magnitude while increasing the magnetic onset temperature to at least 250 K, whereas Fe and Cr remain essentially trivalent with weak dichroism. Depth-resolved low-energy muon spin spectroscopy (LE-μSR) shows magnetic homogeneity through the film thickness, with a secondary relaxation maximum near 25 K indicating a low-temperature dynamical crossover consistent with frustrated magnetism in a strongly disordered spin lattice.

Miertschin, Duncan [Baylor University]↗
DOE OSTI2022

Tunable Magnetic Labyrinth for Abrikosov Vortices

We study Abrikosov vortex dynamics in a superconducting layer covered with an array of T- and I-shaped magnetically soft permalloy elements. Application of the in-plane field H // polarizes thin permalloy bars forming the array and creates a periodic network of mutually perpendicular lines of the attractive or repulsive magnetic potential for vortices along the bar edges, which can be easily tuned by the rotation of H // . Magneto-optical imaging of the vortex trajectories confirms that such a reconfigurable magnetic potential dominates the vortex motion in a wide temperature range and can be a useful tool for manipulating vortices in fluxonic devices for low-loss microelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

In-situ monitoring of atomically dispersed Pt sites supported on OMS-2 during CO 2 activation

Atomically dispersed catalysts have drawn great interest lately, as they showcase a high density of active sites, selectivity, and high turnover frequencies in oxidation chemistry due to labile oxygen activation. In contrast, the applications of these catalysts have lagged in reduction reactions due to the ambiguity caused by the sintering and restructuring of active sites. To bridge this gap, the evolution of Pt 4+ isomorphically substituted into an octahedral molecular sieve structure (OMS-2) under reductive conditions was correlatively characterized using multiple in-situ analytical techniques such as ambient pressure X-ray photoelectron spectroscopy, environmental transmission electron microscopy, and solid-state nuclear magnetic resonance. The surface dynamics of the Pt single atoms were revealed during the Reverse Water Gas Shift (RWGS) reaction, where the active sites were identified as two-coordinated platinum single atoms. Under reaction, we show nonbinding atoms adjacent to the single atoms restructured the motif of the single atoms to Pt 2+ via ion mobility of potassium, increasing the activation energy by 25.6 kJ/mol. Here, this work also highlights the potential for increased stability of the single atom sites via isomorphic substitution of the metal oxide support, since the Pt-OMS-2 catalyst retained activity for about 33 h before deactivation, after which nanoparticles were observed in TEM images. This work offers a new perspective in single atom synthesis using the metal oxide as the host for the single atom site, instead of adatoms on the surface

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Early MRI Blood Volume Changes in Constrictor Muscles Correlate With Postradiation Dysphagia

Predicting individual patient sensitivity to radiation therapy (RT) for tumor control or normal tissue toxicity is necessary to individualize treatment planning. In head and neck cancer, radiation doses are limited by many nearby critical structures, including structures involved in swallowing. Previous efforts showed that imaging parameters correlate with RT dose; here, we investigate the role of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) blood volume (BV) changes in predicting dysphagia.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2024

Comparison of methods for the NMR measurement of motionally averaged dipolar couplings

Motionally averaged dipolar couplings are an important tool for understanding the complex dynamics of catalysts, polymers, and biomolecules. While there is a plethora of solid-state NMR pulse sequences available for their measurement, in can be difficult to gauge the methods’ strengths and weaknesses. In particular, there has not been a comprehensive comparison of their performance in natural abundance samples, where 1H homonuclear dipolar couplings are important and the use of large MAS rotors may be required for sensitivity reasons. In this work, we directly compared some of the more common methods for measuring C–H dipolar couplings in natural abundance samples using L-alanine (L-Ala) and the N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLF) tripeptide as model systems. Here, we evaluated their performance in terms of accuracy, resolution, sensitivity, and ease of implementation. We found that, despite the presence of 1H homonuclear dipolar interactions, all methods, with the exception of REDOR, were able to yield the reasonable dipolar coupling strengths for both mobile and static moieties. Of these methods, PDLF provides the most convenient workflow and precision at the expense of low sensitivity. In low-sensitivity cases, MAS-PISEMA and DIPSHIFT appear to be the better options.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

High-Field Magnetoelectric and Spin-Phonon Coupling in Multiferroic (NH 4 ) 2 [FeCl 5 ·(H 2 O)]

We combine high field polarization, magneto-infrared spectroscopy, and lattice dynamics calculations with prior magnetization to explore the properties of (NH 4 ) 2 [FeCl 5 ·(H 2 O)]-a type II molecular multiferroic in which the mixing between charge, structure, and magnetism is controlled by intermolecular hydrogen and halogen bonds. Electric polarization is sensitive to the series of field-induced spin reorientations, increasing linearly with the field and reaching a maximum before collapsing to zero across the quasi-collinear to collinear-sinusoidal reorientation due to the restoration of inversion symmetry. Magnetoelectric coupling is on the order of 1.2 ps/m for the P∥c, H∥c configuration between 5 and 25 T at 1.5 K. In this range, the coupling takes place via an orbital hybridization mechanism. Other forms of mixing are active in (NH 4 ) 2 [FeCl 5 ·(H 2 O)] as well. Magneto-infrared spectroscopy reveals that all of the vibrational modes below 600 cm –1 are sensitive to the field-induced transition to the fully saturated magnetic state at 30 T. We analyze these local lattice distortions and use frequency shifts to extract spin-phonon coupling constants for the Fe–O stretch, Fe–OH 2 rock, and NH 4 + libration. Inspection also reveals subtle symmetry breaking of the ammonium counterions across the ferroelectric transition. Here, the coexistence of such varied mixing processes in a platform with intermolecular hydrogen- and halogen-bonding opens the door to greater understanding of multiferroics and magnetoelectrics governed by through-space interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Variable-Temperature Scattering and Spectroscopy Characterizations for Temperature-Dependent Solution Assembly of PffBT4T-Based Conjugated Polymers

The solution structure of conjugated polymers (CPs) from which the films are cast is critical for tailoring the thin-film morphology thus device performance. Here, we used multimodal variable-temperature scattering and spectroscopy tools to fully quantify the solution assembly of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'''-dialkyl-2,2';5',2'';5'',2'''-quaterthiophen-5,5'''-diyl)] (PffBT4T) polymers with varying side-chain lengths at different assembly temperatures. The conformational and aggregation behaviors for PffBT4T-based CPs were found to be very sensitive to both temperature and side chain length using ultraviolet–visible (UV–vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). We found that with slightly increasing side chain length from 2-octyldodecyl (C8C12) to 2-nonyltridecyl (C9C13), PffBT4T-based CPs show a significant decrease in aggregation-to-dissolved chain transition temperature (10 °C), degree of aggregation, enthalpy change of aggregation, and size of the aggregates in solution. At room temperature, PffBT4T polymer strongly aggregated to form fabric structure with the film thickness of a few nanometers in thickness and hundreds of nanometers in length, as probed by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and dynamic light scattering (DLS). At the elevated temperature above the aggregation-to-dissolved chain transition temperature, PffBT4T is fully dissolved and adopts a semiflexible coil conformation with the persistence length of 3.1 nm for PffBT4T-C8C12 and a slightly increased persistence length of 3.4 nm for PffBT4T-C9C13, according to temperature-dependent SANS measurements. Longer side chains of PffBT4T-C9C13 also lead to less aggregation enthalpy gain compared with PffBT4T-C8C12. This work provides a solution structure manipulating strategy of CPs and thus will inspire the molecular design and processing protocols of CPs toward higher performance electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Solar Energetic Proton Access to the Inner Magnetosphere During the September 7–8, 2017 Event

Here, the access of solar energetic protons into the inner magnetosphere on September 7–8, 2017 is investigated by following reversed proton trajectories to compute the proton cutoff energy using the Dartmouth geomagnetic cutoff code (Kress et al., 2010, https://doi.org/10.1029/2009sw000488). The cutoff energies for protons coming from the west and east direction, the minimum and maximum cutoff energy respectively, are calculated every 5 min along the orbit of Van Allen Probes using TS07 and the Lyon-Fedder-Mobarry (LFM) MHD magnetic field model. The result shows that the cutoff energy increases significantly as the radial distance decreases, and that the cutoff energy decreases with the building up of the ring current during magnetic storms. Solar wind dynamic pressure also affects cutoff suppression (Kress et al., 2004, https://doi.org/10.1029/2003gl018599). The LFM-RCM model shows stronger suppression of cutoff energy than TS07 during strong solar wind driving conditions. The simulation result is compared with proton flux measurements, showing consistent variation of the cutoff location during the September 7–8, 2017 geomagnetic storm.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet C 9 H 18 N 2 CuBr 4

Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances. Here, we present a comprehensive study of the effect of hydrostatic pressure on the magnetic structure and spin dynamics of the spin-1/2 ladder compound C 9 H 18 N 2 CuBr 4 . Single-crystal heat capacity and neutron diffraction measurements reveal that the Néel-ordered phase breaks down beyond a critical pressure of Pc~1.0 GPa through a continuous quantum phase transition. Estimates of the critical exponents suggest that this transition may fall outside the traditional Landau paradigm. The inelastic neutron scattering spectra at 1.3 GPa are characterized by two well-separated gapped modes, including one continuum-like and another resolution-limited excitation in distinct scattering channels, which further indicates an exotic quantum-disordered phase above Pc.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d

Recent developments and tools integrated into the TAPaS code are presented, enabling realistic scenario simulations of particle dynamics within experimental tokamak magnetic equilibria. In particular, the enhanced capabilities of TAPaS enable seamless coupling with external simulations, provided the metric and equilibrium magnetic field of the external code are known. Coupling TAPaS with the gyro-fluid code FAR3d, the transport and losses of energetic particles in the presence Alfvén eigenmodes (AEs) in DIII-D plasma discharge #159243 were investigated. Detailed analyses of prompt losses with and without collisions were performed. Then, further analysis was performed in the presence of electromagnetic perturbations resulting from AEs activity. The results indicate that, for the energies and the initial conditions considered here, the presence of AEs enhances the particle losses.

Alfven eigenmodes↗
DOE OSTI2024

Invariant regimes of Spencer scaling law for magnetic compression of rotating FRC plasma

Abstract The scaling laws for the magnetic compression of a toroidally rotating field reversed configuration (FRC) have been investigated in this work. The magnetohydrodynamics (MHD) simulations of the magnetic compression on rotating FRCs employing the NIMROD code (Sovinec et al 2004 J. Comput. Phys. 195 355), are compared with the Spencer’s one-dimensional (1D) theory (Spencer et al 1983 Phys. Fluids 26 1564) for a wide range of initial flow speeds and profiles. The toroidal flow can influence the scalings directly through the alteration of the compressional work as also evidenced in the 1D adiabatic model, and indirectly by reshaping the initial equilibrium. However, in comparison to the static initial FRC equilibrium cases, the pressure and the radius scalings remain invariant for the magnetic compression ratio B w 2 / B w 1 up to 6 in presence of the initial equilibrium flow, suggesting a broader applicable regime of the Spencer scaling law for FRC magnetic compression. The invariant scaling has been proven a natural consequence of the conservation of angular momentum of both fluid and magnetic field during the dynamic compression process.

Ma, Yiming↗