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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Probing gravity and growth of structure with gravitational waves and galaxies’ peculiar velocity

The low-redshift velocity field is a unique probe of the growth of cosmic structure and gravity. Here, we propose to use distances from gravitational wave (GW) detections, in conjunction with the redshifts of their host galaxies from wide field spectroscopic surveys (e.g., DESI, 4MOST, TAIPAN), to measure peculiar motions within the local Universe. Such measurement has the potential to constrain the growth rate f σ 8 and test gravity through determination of the gravitational growth index γ , complementing constraints from other peculiar velocity measurements. We find that binary neutron star mergers with associated counterpart at z ≲ 0.2 that will be detected by the Einstein Telescope (ET) will be able to constrain f σ 8 to ~ 3 % precision after 10 years of operations when combined with galaxy overdensities from DESI and TAIPAN. If a larger network of third generation GW detectors is available (e.g., including the Cosmic Explorer), the same constraints can be reached over a shorter timescale ( ~ 5 years for a 3 detectors network). The same events (plus information from their hosts’ redshifts) can constrain γ to σ γ ≲ 0.04 . This constraint is precise enough to discern general relativity from other popular gravity models at 3 σ . This constraint is improved to σ γ ~ 0.02 – 0.03 when combined with galaxy overdensities. The potential of combining galaxies’ peculiar velocities with gravitational wave detections for cosmology highlights the need for extensive optical to near-infrared follow-up of nearby gravitational wave events, or exquisite GW localization, in the next decade.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Physics Goals of DWA Experiments at FACET-II

The dielectric wakefield acceleration (DWA) program at FACET produced a multitude of new physics results that range from GeV/m acceleration to the discovery of high field-induced conductivity in THz waves, and beyond, to a demonstration of positron-driven wakes. Here we review the rich program now developing in the DWA experiments at FACET-II. With increases in beam quality, a key feature of this program is extended interaction lengths, near 0.5 m, permitting GeV-class acceleration. Detailed physics studies in this context include beam breakup and its control through the exploitation of DWA structure symmetry. The next step in understanding DWA limits requires the exploration of new materials with low loss tangent, large bandgap, and improved thermal characteristics. Advanced structures with photonic features for mode confinement and exclusion of the field from the dielectric, as well as quasi-optical handling of coherent Cerenkov signals is discussed. Use of DWA for laser-based injection and advanced temporal diagnostics is examined.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Self-consistent interaction of linear gravitational and electromagnetic waves in non-magnetized plasma

Here, this paper explores the hybridization of linear metric perturbations with linear electromagnetic (EM) perturbations in non-magnetized plasma for a general background metric. The local wave properties are derived from first principles for inhomogeneous plasma, without assuming any symmetries of the background metric. First, we derive the effective (“oscillation-center”) Hamiltonian that governs the average dynamics of plasma particles in a prescribed quasimonochromatic wave that involves metric perturbations and EM fields simultaneously. Then, using this Hamiltonian, we derive the backreaction of plasma particles on the wave itself and obtain gauge-invariant equations that describe the resulting self-consistent gravito-electromagnetic (GEM) waves in a plasma. The transverse tensor modes of gravitational waves are found to have no interaction with the plasma and the EM modes in the geometrical-optics limit. However, for $longitudinal$ GEM modes with large values of the refraction index, the interplay between gravitational and EM interactions in plasma can have a strong effect. In particular, the dispersion relation of the Jeans mode is significantly affected by electrostatic interactions. As a spin-off, our calculation also provides an alternative resolution of the so-called Jeans swindle.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Variational Monte Carlo Calculations of A ≤ 4 Nuclei with an Artificial Neural-Network Correlator Ansatz

Here, the complexity of many-body quantum wave functions is a central aspect of several fields of physics and chemistry where nonperturbative interactions are prominent. Artificial neural networks (ANNs) have proven to be a flexible tool to approximate quantum many-body states in condensed matter and chemistry problems. In this work we introduce a neural-network quantum state ansatz to model the ground-state wave function of light nuclei, and approximately solve the nuclear many-body Schrodinger equation. Using efficient stochastic sampling and optimization schemes, our approach extends pioneering applications of ANNs in the field, which present exponentially scaling algorithmic complexity. We compute the binding energies and point-nucleon densities of A ≤ 4 nuclei as emerging from a leading-order pionless effective field theory Hamiltonian. We successfully benchmark the ANN wave function against more conventional parametrizations based on two- and three-body Jastrow functions, and virtually exact Green's function Monte Carlo results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

A 3D Full Stress Tensor Model for Oklahoma

Abstract The stress tensor is an important property for upper crustal studies such as those that involve pore fluids and earthquake hazards. At tectonic plate scale, plate boundary forces and mantle convection are the primary drivers of the stress field. In many local settings (10–100 s of km and <10 km depth) in tectonic plate interiors, we can simplify by assuming a constant background stress field that is perturbed by local heterogeneity in density and elasticity. Local stress orientation and sometimes magnitude can be estimated from earthquake and borehole‐based observations when available. Modeling of the local stress field often involves interpolating sparse observations. We present a new method to estimate the 3D stress field in the upper crust and demonstrate it for Oklahoma. We created a 3D material model by inverting multiple types of geophysical observations simultaneously. Integrating surface‐wave dispersion, local travel times and gravity observations produces a model of P‐wave velocity, S‐wave velocity, and density. The stress field can then be modeled using finite element simulations. The simulations are performed using our simplified view of the local stress field as the sum of a constant background stress field that is perturbed by local density and elasticity heterogeneity and gravitational body forces. An orientation of N82°E, for the maximum compressive tectonic force, best agrees with previously observed stress orientations and faulting types in Oklahoma. The gravitational contribution of the horizontal stress field has a magnitude comparable to the tectonic contribution for the upper 5 km of the subsurface.

58 GEOSCIENCES↗
DOE OSTI2020

Lower Hybrid Waves at the Magnetosheath Separatrix Region

Lower hybrid waves are investigated at the magnetosheath separatrix region in asymmetric guide field reconnection by using the Magnetospheric Multiscale (MMS) mission. Three of the four MMS spacecraft observe clear wave activities around the lower hybrid frequency across the magnetosheath separatrix, where a density gradient is present. The observed waves are consistent with generation by the lower hybrid drift instability. The characteristic properties of these waves include the following: (1) the waves propagate toward the x-line in the spacecraft frame due to the large out-of-plane magnetic field, which is in the same direction of the diamagnetic drift of the x-line; (2) the wave potential is about 20% of the electron temperature. Furthermore, these drift waves effectively produce cross-field particle diffusion, enabling the transport of magnetosheath electrons into the exhaust region. At last, we suggest that the lower hybrid waves at the magnetosheath separatrix region represent some unique features of asymmetric guide field reconnection, which is different from that widely observed at the magnetospheric side of magnetopause reconnection.

58 GEOSCIENCES↗
DOE OSTI2025

Nonunitary Variational Quantum Eigensolver with the Localized Active Space Method and Cost Mitigation

Accurately describing strongly correlated systems with affordable quantum resources remains a central challenge for quantum chemistry applications on near and intermediate term quantum computers. The localized active space self-consistent field (LASSCF) approximates the complete active space self-consistent field (CASSCF) by generating active space-based wave functions within specific fragments while treating interfragment correlation with mean-field approach, hence is computationally less expensive. Hardware-efficient ansatzes (HEA) offer affordable and shallower circuits, yet they often fail to capture the necessary correlation. Previously, Jastrow-factor-inspired nonunitary qubit operators were proposed to use with HEA for variational quantum eigensolver (VQE) calculations (so-called nuVQE), as they do not increase circuit depths and recover correlation beyond the mean-field level for Hartree–Fock initial states. Here, in this study, we explore running nuVQE with LASSCF as the initial state. The method, named LAS-nuVQE, is shown to recover interfragment correlations, reach chemical accuracy with a small number of gates (<70) in both H 4 and square cyclobutadiene (C 4 H 4 ), and produces more accurate energetics than its HEA counterparts at all circuit depths. To further address the inherent symmetry-breaking in HEA, we implemented spin-constrained LAS-nuVQE to extend the capabilities of HEA further and show spin-pure results for square cyclobutadiene. We also mitigate the increased measurement overhead of nuVQE via Pauli grouping and shot-frugal sampling, reducing measurement costs by up to 2 orders of magnitude compared to ungrouped operator, and show that one can achieve better accuracy with a small number of shots (10 3–4 ) per one expectation value calculation compared to noiseless simulations with one or two orders of magnitude more shots. Finally, wall clock time estimates show that, with our measurement mitigation protocols, nuVQE becomes a cheaper and more accurate alternative than vanilla VQE with HEA. Taken together, these developments illustrate a practical pathway toward performing multireference chemical simulations with accuracy and affordable resources on today’s quantum hardware, achieving both accuracy and affordability in challenging correlated systems.

Wang, Qiaohong [Univ. of Chicago, IL (United State↗
DOE OSTI2020

Coexistence of antiferromagnetism and topological superconductivity on the honeycomb lattice Hubbard model

In this report, motivated by the recent numerical simulations for doped t-J model on the honeycomb lattice, we study superconductivity of singlet and triplet pairing on the honeycomb lattice Hubbard model. We show that a superconducting state with coexisting spin-singlet and spin-triplet pairings is induced by the antiferromagnetic order near half filling. The superconducting state we obtain has a topological phase transition that separates a topologically trivial state and a nontrivial state with Chern number two. Possible experimental realization of such a topological superconductivity is also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nonlinear self-focusing in strongly magnetized pair plasma

An intense radiation field can modify plasma properties and the corresponding refractive index and lead to nonlinear propagation effects such as self-focusing. In this work, we estimate the corresponding effects in pair plasmas for circularly polarized waves, in both unmagnetized and strongly magnetically dominated cases. First, in the unmagnetized pair plasma the ponderomotive force does not lead to charge separation but to density depletion. Second, for astrophysically relevant plasmas of pulsar magnetospheres [and possible loci of fast radio bursts (FRBs)], where the cyclotron frequency $ω_B$ dominates over the plasma frequency $ω_p$ and the frequency of the electromagnetic wave $ω_B \gg ω_p, ω$, we show that (i) there is virtually no nonlinearity due to changing effective mass in the field of the wave; (ii) the ponderomotive force is $F^{(B)}_p = –m_ec^2/4B^2_0∇E^2$, which is reduced by a factor $(ω/ω_B)^2$ if compared to the unmagnetized case ($B_0$ is the external magnetic field and $\textit{E}$ is the electric field of the wave); and (iii) for a radiation beam propagating along a constant magnetic field in the pair plasma with density $n_±$, the ponderomotive force leads to the appearance of circular currents that lead to a decrease of the field within the beam by a factor $ΔB/B_0 = 2πn_±m_ec^2E^2 /B^4_0$. Applications to the physics of FRBs are discussed; we conclude that for the parameters of FRBs, the dominant magnetic field completely suppresses nonlinear self-focusing or filamentation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Effect of optical field ionisation on the generation of wake fields by femtosecond laser pulses in an inhomogeneous plasma

We consider the interaction of a high-intensity short laser pulse with an argon gas during optical field ionisation. Modelling in a three-dimensional cylindrical symmetric geometry is performed at various moderately relativistic intensities and positions of the focal plane of the laser beam in the case of both optical gas ionisation and a pre-ionised plasma. The influence of the processes occurring during optical field ionisation of the gas on the generation of wake waves is investigated, and the conditions are found under which intense wake fields are produced in a plasma formed from an inhomogeneous argon gas jet. The possibility of using a gas with a large number of electrons on the outer shell (argon) to excite intense wake waves and accelerate electrons is demonstrated. Despite significant ionisation refraction of the laser pulse on a radially inhomogeneous density profile of plasma electrons formed during optical field ionisation, the region of the parameters of the laser pulse and the gas target is determined at which ionisation refraction leads to the excitation of an intense wake wave. It is found that in a pre-ionised plasma a wake wave is not generated even at the same laser radiation intensity. (paper)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Selection rules and dynamic magnetoelectric effect of the spin waves in multiferroic Bi Fe O 3

Here, we report the magnetic-field dependence of the THz absorption and nonreciprocal directional dichroism spectra of BiFeO 3 measured on the three principal crystal cuts for fields applied along the three principal directions of each cut. From the systematic study of the light polarization dependence, we deduced the optical selection rules of the spin-wave excitations. Our THz data, combined with small-angle neutron scattering results showed that (i) an in-plane magnetic field rotates the q vectors of the cycloids perpendicular to the magnetic field and (ii) the selection rules are mostly determined by the orientation of the q vector with respect to the electromagnetic fields. We observed a magnetic field history-dependent change in the strength and the frequency of the spin-wave modes, which we attributed to the change of the orientation and the length of the cycloidal q vector, respectively. Finally, we compared our experimental data with the results of linear spin-wave theory that reproduces the magnetic-field dependence of the spin-wave frequencies and most of the selection rules, from which we identified the spin-polarization coupling terms relevant for the optical magnetoelectric effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

High-fidelity retrieval from instantaneous line-of-sight returns of nacelle-mounted lidar including supervised machine learning

Abstract. Wind turbine applications that leverage nacelle-mounted Doppler lidar are hampered by several sources of uncertainty in the lidar measurement, affecting both bias and random errors. Two problems encountered especially for nacelle-mounted lidar are solid interference due to intersection of the line of sight with solid objects behind, within, or in front of the measurement volume and spectral noise due primarily to limited photon capture. These two uncertainties, especially that due to solid interference, can be reduced with high-fidelity retrieval techniques (i.e., including both quality assurance/quality control and subsequent parameter estimation). Our work compares three such techniques, including conventional thresholding, advanced filtering, and a novel application of supervised machine learning with ensemble neural networks, based on their ability to reduce uncertainty introduced by the two observed nonideal spectral features while keeping data availability high. The approach leverages data from a field experiment involving a continuous-wave (CW) SpinnerLidar from the Technical University of Denmark (DTU) that provided scans of a wide range of flows both unwaked and waked by a field turbine. Independent measurements from an adjacent meteorological tower within the sampling volume permit experimental validation of the instantaneous velocity uncertainty remaining after retrieval that stems from solid interference and strong spectral noise, which is a validation that has not been performed previously. All three methods perform similarly for non-interfered returns, but the advanced filtering and machine learning techniques perform better when solid interference is present, which allows them to produce overall standard deviations of error between 0.2 and 0.3 m s−1, or a 1 %–22 % improvement versus the conventional thresholding technique, over the rotor height for the unwaked cases. Between the two improved techniques, the advanced filtering produces 3.5 % higher overall data availability, while the machine learning offers a faster runtime (i.e., ∼ 1 s to evaluate) that is therefore more commensurate with the requirements of real-time turbine control. The retrieval techniques are described in terms of application to CW lidar, though they are also relevant to pulsed lidar. Previous work by the authors (Brown and Herges, 2020) explored a novel attempt to quantify uncertainty in the output of a high-fidelity lidar retrieval technique using simulated lidar returns; this article provides true uncertainty quantification versus independent measurement and does so for three techniques rather than one.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Guided plasma jets directed onto wet surfaces: angular dependence and control

The optimal use of atmospheric pressure plasma jets (APPJs) for treatment of surfaces—inorganic, organic and liquid—depends on being able to control the flow of plasma-generated reactive species onto the surface. The typical APPJ is a rare gas mixture (RGM) flowed through a tube to which voltage is applied, producing an RGM plasma plume that extends into the ambient air. The RGM plasma plume is guided by a surrounding shroud of air due to the higher electric field required for an ionization wave (IW) to propagate into the air. Additionally, the mixing of the ambient air with the RGM plasma plume then determines the production of reactive oxygen and nitrogen species (RONS). The APPJ is usually oriented perpendicular to the surface being treated. However, the angle of the APPJ with respect to the surface may be a method to control the production of reactive species to the surface due to the change in APPJ propagation properties and the resulting gas dynamics. In this paper, we discuss results from computational and experimental investigations addressing two points—propagation of IWs in APPJs with and without a guiding gas shroud as a function of angle of the APPJ with respect to the surface; and the use of this angle to control plasma activation of thin water layers. We found that APPJs propagating out of the plasma tube into a same-gas environment lack any of the directional properties of shroud-guided jets, and largely follow electric field lines as the angle of the plasma tube is changed. Guided APPJs propagate coaxially with the tube as the angle is changed, and turn perpendicularly towards the surface only a few mm above the surface. The angle of the APPJ produces different gas dynamic distributions, which enable some degree of control over the content of RONS transferred to thin water layers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Spin waves excitation at micron-sized, anisotropy modified regions in amorphous Fe 80 B 20 stripes: Local properties and inter-regions coupling

We report on the measurement of the local magnetization dynamics occurring, at units of GHz, in large aspect ratio stripes lithographed from reduced damping amorphous Fe 80 B 20 films. The stripes were submitted to local anisotropy modifications by micrometric beam synchrotron X-ray irradiation. Our results include data on the dispersion relationships and group velocities corresponding to spin waves excited at both the non-irradiated and the irradiated regions. Whereas in the former case we observed standing spin waves with transverse-to-the stripe axis wave vector, in the latter one, for which the wave vector of the spin waves was parallel-to-the stripe axis, propagating spin waves were excited. In both regions, we measured the effective propagation distance of the spin waves, which resulted to be independent of the wave vector orientation. In the spin waves excited at the irradiated region, we also measured the decay time and effective damping coefficient, which was in good agreement with previously reported values obtained from FMR measurements in amorphous Fe 80 B 20 continuous films. We show that the interaction of the non-irradiated and irradiated zones results, at the stripe transverse saturation remanence and under an exciting field frequency of 4 GHz, in the introduction of a π phase shift between the standing spin waves excited at both sides of the irradiated region. This result opens the possibility of using the local, transverse to the stripe axis, magnetic anisotropy easy axis induced by the X-ray irradiation as a crucial constituent of a zero-applied field spin wave phase-shifter.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Enhanced tuneable rotatory power in a rotating plasma

We report that the gyrotropic properties of a rotating magnetized plasma are derived analytically. Mechanical rotation leads to a new cutoff for wave propagation along the magnetic field, and polarization rotation above this cutoff is the sum of the classical magneto-optical Faraday effect and the mechanico-optical polarization drag. Exploiting the very large effective group index near the cutoff, we expose here that polarization drag can be 10 4 larger than Faraday rotation at GHz frequency. The rotation leads to weak absorption while allowing direct frequency control, demonstrating the unique potential of rotating plasmas for nonreciprocal elements. The very large rotation frequency of a dense non-neutral plasma could enable unprecedented gyrotropy in the THz regime.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Designed Spin‐Texture‐Lattice to Control Anisotropic Magnon Transport in Antiferromagnets

Abstract Spin waves in magnetic materials are promising information carriers for future computing technologies due to their ultra‐low energy dissipation and long coherence length. Antiferromagnets are strong candidate materials due, in part, to their stability to external fields and larger group velocities. Multiferroic antiferromagnets, such as BiFeO 3 (BFO), have an additional degree of freedom stemming from magnetoelectric coupling, allowing for control of the magnetic structure, and thus spin waves, with the electric field. Unfortunately, spin‐wave propagation in BFO is not well understood due to the complexity of the magnetic structure. In this work, long‐range spin transport is explored within an epitaxially engineered, electrically tunable, 1D magnonic crystal. A striking anisotropy is discovered in the spin transport parallel and perpendicular to the 1D crystal axis. Multiscale theory and simulation suggest that this preferential magnon conduction emerges from a combination of a population imbalance in its dispersion, as well as anisotropic structural scattering. This work provides a pathway to electrically reconfigurable magnonic crystals in antiferromagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Modeling the pseudogap metallic state in cuprates: Quantum disordered pair density wave

We present a way to quantum-disorder a pair density wave and propose it to be a candidate of the effective low-energy description of the pseudogap metal which may reveal itself in a sufficiently high magnetic field that suppresses the d-wave pairing. The ground state we construct is a small-pocket Fermi liquid with a bosonic Mott insulator in the density-wave-enlarged unit cell. At low energy, the charge density is mainly carried by charge 2e bosons, which develop a small insulating gap. As an intermediate step, we discuss the quantum disordering of a fully gapped superconductor and its excitation spectrum. A simplified 1D model, which we solve numerically, is used to illustrate the introduced concepts. Here, we discuss a number of experimental consequences. The interplay between the electron and the small-gap boson results in a step-function background in the electron spectral function which may be consistent with existing angle-resolved photoemission spectroscopy data. Optical excitation across the boson gap can explain the onset and the magnitude of the mid infrared absorption reported long ago.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Floquet stability analyses of stratified oscillating boundary layers on adiabatic slopes

The presence of a no-slip, impermeable, adiabatic, sloped boundary in an otherwise quiescent, stably stratified, Boussinesq flow generates baroclinic vorticity within a diffusive boundary layer. Such conditions are typical of the oscillating boundary layers on adiabatic abyssal slopes, sloped lake bathymetry and sloped coastal bathymetry in the absence of high-wavenumber internal waves, mean flows, far-field turbulence on larger scales, and resonant tidal–bathymetric interaction. We investigate the linear stability of the oscillating flow within non-dimensional parameter space typical of the $M_2$ tide and hydraulically smooth, middle-latitude abyssal slopes through Floquet linear stability analysis. The flow dynamics depends on three non-dimensional variables: the Reynolds number for Stokes’ second problem, the Prandtl number, and a frequency ratio that accounts for the resonance conditions ($C$, criticality) of the buoyant restoring force and the tidal forcing. The Floquet analysis results suggest that oscillating laminar boundary layers on adiabatic abyssal slopes are increasingly unstable as Reynolds number, criticality parameter and/or spanwise disturbance wavenumber are increased. We also show that the two-dimensional Floquet linear instability necessarily generates three-dimensional baroclinic vorticity, which suggests that the evolution of the gravitational instabilities may be nonlinear as $t→∞$.

42 ENGINEERING↗