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At least 1,333 records · Page 74

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NASA NTRS1984

High-altitude observations of an intense inverted V event

Inverted-V events which generally occur in the pre-midnight sector over the auroral zone are frequently associated with reversals in the convection electric field. Such a reversal is observed by the University of Iowa quasispherical LEPEDEA on board ISEE 1 at an altitude of 13 RE on May 1, 1978. The bulk of the plasma shows a large shear over a five-minute interval. The associated change in the convection electric field is 5.1 mV/m. Large values of the field-aligned current are simultaneously detected. The potential structure appears to extend to the satellite location. Using a theoretical model, the field-aligned current due to the electric field discontinuity has been calculated. The magnitude of the parallel potential drop and width of the inverted-V region agree well with observation.

Huang, C. Y.↗

NASA NTRS1990

Ionospheric modification using relativistic electron beams

The recent development of comparatively small electron linear accelerators (linacs) now makes possible a new class of ionospheric modification experiments using beams of relativistic electrons. These experiments can potentially provide much new information about the interactions of natural relativistic electrons with other particles in the upper atmosphere, and it may also make possible new forms of ionization structures extending down from the lower ionosphere into the largely un-ionized upper atmosphere. The consequences of firing a pulsed 1 A, 5 Mev electron beam downwards into the upper atmosphere are investigated. If a small pitch angle with respect to the ambient geomagnetic field is selected, the beam produces a narrow column of substantial ionization extending down from the source altitude to altitudes of approximately 40 to 45 km. This column is immediately polarized by the natural middle atmosphere fair weather electric field and an increasingly large potential difference is established between the column and the surrounding atmosphere. In the regions between 40 to 60 km, this potential can amount to many tens of kilovolts and the associated electric field can be greater than the field required for breakdown and discharge. Under these conditions, it may be possible to initiate lightning discharges along the initial ionization channel. Filamentation may also occur at the lower end to drive further currents in the partially ionized gases of the stratosphere. Such discharges would derive their energy from the earth-ionosphere electrical system and would be sustained until plasma depletion and/or electric field reduction brought the discharge under control. It is likely that this artificially-triggered lightning would produce measurable low-frequency radiation.

Banks, Peter M.↗

NASA NTRS1998

Penetration Electric Fields and Inner Magnetosphere Dynamics: A Model and Data Comparison

Significant progress has been made on the analysis of the June, 1991 storm. We have completed the analysis of the CRRES and DMSP data sets. We have been able to follow the evolution during the storm of the inner edge of the electric field patterns in the dusk sector and its relation to electron boundaries, ion boundaries and the ring current. Whereas the CRRES data provide radial cuts out through the plasmasphere every I 0 hours, DMSP provides snapshots every orbit of the potential and particle boundaries. Electric field and energetic particle measurements from CRRES and ion drifts and energetic particle measurements from DMSP provide the principal data sets. The combined data set provides high resolution definition of the boundary motions over the phases of the storm. L shell differences between the DMSP and CRRES particle boundaries are easily explained by inflation of the dusk sector by the ring current. The electric field boundaries are typically associated with the ion boundary and the inner edge of the ring current except during rapid increases in the cross-polar cap potential. A significant fraction of the dusk cell potential is found inside the plasmasheet electron inner edge. Twice during the storm this potential exceeded 60 kV. A paper (copy attached) has been prepared (Burke et al., 1998) and submitted to JGR. An invited paper will be presented by Burke at the spring AGU meeting. An abstract has also been submitted to the COSPAR meeting for presentation by Maynard. New simulations have been carried out with the Rice Convection Model for the magnetic storm of June 4-5, 1991, and comparisons have been made with CRRES and DMSP data.

Maynard, Nelson C.↗

DOE OSTI2024

IMS Rapid Response 2024 Summary Report: A Machine Learning Potential for the Periodic Table

Stockpile stewardship and nuclear waste remediation are inherently chemically complex, involving practically the full diversity of the periodic table, but existing methods are too expensive or not functional for a large diversity of atom types. Overall, the field of machine learning interatomic potentials (MLIPs) has advanced dramatically in 2024 with large high-accuracy datasets existing for bulk, surface, and organic chemical systems and new online leaderboards for diverse chemistry. To participate in, and bring LANL interests into this ecosystem, here, we have built upon existing technologies created by LANL to create a framework capable of creating machine learning interatomic potentials (MLIPs) for over 90 atom types. Our results have created a massively diverse coordination complex training dataset more than 3 times the size of existing datasets, parallelized MLIP training over multiple GPUs, enabling the training of an MLIP spanning the periodic table at 20 times the speed of prior training on 32 GPUs. These advances are substantial towards creation on foundational MLIPs for LANL-specific application areas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1976

Representation of magnetic fields in space

Several mathematical methods which are available for the description of magnetic fields in space are reviewed. Examples of the application of such methods are given, with particular emphasis on work related to the geomagnetic field, and their individual properties and associated problems are described. The methods are grouped in five main classes: (1) methods based on the current density, (2) methods using the scalar magnetic potential, (3) toroidal and poloidal components of the field and spherical vector harmonics, (4) Euler potentials, and (5) local expansions of the field near a given reference point. Special attention is devoted to models of the magnetosphere, to the uniqueness of the scalar potential as derived from observed data, and to the L parameter.

Stern, D. P.↗

DOE OSTI2023

7.86 kV GaN-on-GaN PN power diode with BaTiO3 for electrical field management

Devices based on gallium nitride (GaN) have great potential for high power switching applications due to the high breakdown field and high electron mobility. In this work, we present a vertical GaN-on-GaN PN power diode using high dielectric constant material, BaTiO3, for electrical field management and high breakdown voltages, in together with an optimized guard-ring and field plate design. Numerical simulation shows that with high-k dielectrics implemented, the peak electrical field at the PN interface is mitigated from 3.5 to 3.1 MV/cm under a reverse bias of −9.05 kV. The device design with BaTiO3 shows a breakdown voltage of 9.65 kV or about 600 V improvement. The fabricated diodes with a 57 μm thick drift layer demonstrate a breakdown voltage of 7.86 kV on a bulk GaN substrate. The device has an on-resistance of 2.8 mΩ cm2 and a Baliga figure of merit of 22 GW/cm2.

Physics↗

NASA NTRS1974

The average auroral zone electric field

Four hundred and seventy-eight hours of electric field data obtained by the flight of 32 balloons between L = 5.4 and L = 8.2 have been averaged to determine mean properties of the auroral zone electric field. The results are understood in terms of a model in which the two-cell convection pattern is rotated about the sun-earth line by an amount that depends on the sign and magnitude of the y component of the interplanetary magnetic field. This model and the data suggest either that important parallel potential drops exist along auroral zone magnetic field lines or that simple conjugacy between the two hemispheres does not exist along such field lines.

Mozer, F. S.↗

NASA NTRS1985

Characterization of synthetic carrier ampholytes by repetitive scanning of the electric field during focusing

This paper reports the utilization of a potential gradient array detector for monitoring the dynamics of the electric field during isoelectric focusing. Transient and steady state electric field profiles are presented for synthetic carrier ampholyte mixtures with a wide (about 3-10) pH range. Two available commercial products (Ampholine and Pharmalyte) and a laboratory synthesized mixture (PEHA ampholytes) are compared. The formation of conductivity gaps and their migration toward the cathode in extended experiments (cathodic drift) can be visualized with this system.

Thormann, W.↗

NASA NTRS2019

Reassessment of Electromagnetic Core-Mantle Coupling and Its Implications to the Earth's Decadal Polar Motion

The observed Earth's polar motion on decadal time scales has long been conjectured to be excited by the exchange of equatorial angular momentum between the solid mantle and the fluid outer core, via the mechanism of electromagnetic (EM) core-mantle coupling. However, past estimations of the EM coupling torque from surface geomagnetic observations is too weak to account for the observed decadal polar motion. Our recent estimations from numerical geodynamo simulations have shown the opposite. In this paper, we re-examine in detail the EM coupling mechanism and the properties of the magnetic field in the electrically conducting lower mantle (characterized by a thin D″-layer at the base of the mantle). Our simulations find that the toroidal field in the D″-layer from the induction and convection of the toroidal field in the outer core could be potentially much stronger than that from the advection of the poloidal field in the outer core. The former, however, cannot be inferred from geomagnetic observations at the Earth's surface, and is missing in previous EM torque estimated from geomagnetic observations. Our deduction suggests further that this field could make the actual EM coupling torque sufficiently strong, at approximately 5 × 10(exp 19) Nm, to excite, and hence explain, the decadal polar motion to magnitude of approximately 10 mas.

Kuang, Weijia↗

DOE OSTI2024

Analytic bounds on late-time axion-scalar cosmologies

The cosmological dynamics of multiple scalar/pseudoscalar fields are difficult to solve, especially when the field-space metric is curved. This presents a challenge in determining whether a given model can support cosmic acceleration, without solving for the on-shell solution. In this work, we present bounds on late-time FLRW-cosmologies in classes of theories that involve arbitrary numbers of scalar and pseudoscalar fields coupled both kinetically (leading to a curved field space metric) and through scalar potentials. Such bounds are proven analytically, independently of initial conditions, with no approximation in the field equations and without referring to explicit solutions. Besides their broad applications to cosmological model building, our bounds can be applied to studying asymptotic cosmologies of certain classes of string compactifications.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Evolution of Urca Pairs in the Crusts of Highly Magnetized Neutron Stars

Abstract We report on the effects of strong magnetic fields on neutrino emission in the modified Urca process. We show that the effect of Landau levels on the various Urca pairs affects the neutrino emission spectrum and leads to an angular asymmetry in the neutrino emission. For low magnetic fields, the Landau levels have almost no effect on the cooling. However, as the field strength increases, the electron chemical potential increases resulting in a lower density at which Urca pairs can exist. For intermediate field strength, there is an interesting interference between the Landau level distribution and the Fermi distribution. For high enough field strength, the entire electron energy spectrum is eventually confined to a single Landau level producing dramatic spikes in the emission spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1978

Solving magnetostatic field problems with NASTRAN

Determining the three-dimensional magnetostatic field in current-induced situations has usually involved vector potentials, which can lead to excessive computational times. How such magnetic fields may be determined using scalar potentials is reviewed. It is shown how the heat transfer capability of NASTRAN level 17 was modified to take advantage of the new method.

Hurwitz, M. M.↗

DOE OSTI2022

Lower‐Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions

Abstract We investigate waves close to the lower‐hybrid frequency in 12 magnetotail reconnection electron diffusion region (EDR) events with guide field levels of near‐zero to 30%. In about half of the events, the wave vector has a small component along the current sheet normal, consistent with known lower‐hybrid drift wave properties, but the perpendicular magnetic field fluctuations can be comparable or greater than the parallel component, a feature unique to the waves inside and adjacent to EDRs. Another new wave property is that the wave vector has a significant component along the current sheet normal in some events and completely along the normal for one event. In 1/4 of the events, the term has a significant contribution to the wave electric field, possibly a feature of lower‐hybrid waves more likely to exist in the diffusion region than further away from the X‐line. Electron temperature variations are correlated with the wave potential, due to wave electric field acceleration and crossings at the corrugated separatrix region with different amounts of mixing between reconnection inflowing and outflowing populations. The latter also leads to the anti‐correlation between parallel and perpendicular temperature components. Using four‐spacecraft measurements, the magnetic field line twisting is demonstrated by the correlated fluctuations in and . The lower‐hybrid wave in the EDR of weak guide field reconnection may be generated near separatrices and penetrate to the mid‐plane or locally generated, and the latter possibility is beyond the prediction of previous reconnection simulations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Assessment of Enhanced Oil Recovery Using Carbon Dioxide in Michigan Basin Silurian Pinnacle Reefs

The Midwest Regional Carbon Sequestration Partnership (MRCSP) has incorporated the work of geologic research teams (Geoteams) in its regional characterization, project planning and carbon dioxide (CO 2 ) injection implementation work since the partnership was established by the U.S. Department of Energy (DOE) in 2003. Over this 16-year period, the cohort of Geoteams has grown from five to ten states and has contributed to the characterization of geologic sequestration opportunities, refinement of reservoir and seal data, and supported injection efforts through both predictive and post-injection assessments. The Michigan team at Western Michigan University has provided technical analysis and support of the enhanced oil recovery (EOR) using carbon dioxide (CO 2 ) in the Northern Michigan Silurian Pinnacle reefs. With Core Energy, LLC as the industry partner, this project has assessed the potential for EOR in known fields in the Michigan Pinnacle reefs and the capacity for CO2 storage in the reef reservoirs as they are depleted and after reservoir abandonment. This project managed by Core Energy, LLC, involves the only commercial CO 2 Enhanced Oil Recovery floods within the MRCSP region. The Silurian pinnacle reef trend shows significant potential for CO 2 -EOR: this play is relatively new, with approximately 60% of the wells in the largest Niagaran fields still accessible. Most wells have modern logs and there are many cores, core analyses, pressure tests and produced water analyses available for study from these fields. These carbonate reservoirs in Michigan have produced sufficient oil to warrant evaluation for additional recovery efforts. The role of the Michigan team was to collect and analyze all relevant data about reservoir properties, including lithologic and depositional characteristics of the reservoir formations and porosity and fluid flow properties through different compartments in the reservoir. The team has also developed models that represent the geological and physical characteristics of the reservoir and seal system.

01 COAL, LIGNITE, AND PEAT↗

NASA NTRS1989

A digitally controlled system for effecting and presenting a selected electrical resistance

A digitally controlled resistance generator is described, in which resistors having values selected according to an expression 2(sup N-1)(R), where N is equal to the number of terms in the expression, and R is equal to the lowest value of resistance, are electrically inserted into a resistive circuit in accordance with a parallel binary signal provided by an analog-to-digital converter or a programmable computer. This binary signal is coupled via optical isolators which, when activated by a logical 1, provides a negative potential to some or all of the gate inputs of the normally on field effect transistors which, when on, shorts out the associated resistor. This applied negative potential turns the field effect transistors off and electrically inserts the resistor coupled between the source terminal and the drain terminal of that field effect transistor into the resistive circuit between the terminals.

Fletcher, James C.↗

DOE OSTI2021

Electrothermoplasmonic Trapping and Dynamic Manipulation of Single Colloidal Nanodiamond

Low-power trapping of nanoscale objects can be achieved by using the enhanced fields near plasmonic nanoantennas. Unfortunately, in this approach the trap site is limited to the position of the plasmonic hotspots and continuous dynamic manipulation is not feasible. In this work, we report a low-frequency electrothermoplasmonic tweezer (LFET) that provides low-power, high-stability and continuous dynamic manipulation of a single nanodiamond. LFET harnesses the combined action of the laser illumination of a plasmonic nanopillar antenna array and low-frequency alternating current (ac) electric field to establish an electrohydrodynamic potential capable of the stable trapping and dynamic manipulation of single nanodiamonds. We experimentally demonstrate the fast transport, trapping, and dynamic manipulation of a single nanodiamond using a low-frequency ac field below 5 kHz and low-laser power of 1 mW. This nanotweezer platform for nanodiamond manipulation holds promise for the scalable assembly of single photon sources for quantum information processing and low noise quantum sensors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2022

Electrical Potential Investigation of Reversible Metastability and Irreversible Degradation of CdTe Solar Cells

In this paper, we report on the stability of CdTe devices with a structure of TCO/MZO/CdSeTe/CdTe/back-contact. The device showed reversible transitions between the light-soak state (LSS) with the best device efficiency and the dark-soak state (DSS) with an inferior efficiency. However, it showed an irreversible degradation state (DgS) driven by long-hour light soaking at an elevated temperature. We have investigated transitions between these three states from the perspective of the electric field by nm-resolution potential imaging across the devices using Kelvin probe force microscopy (KPFM). The results exhibit different anomalous electric field profiles. At the LSS, the electric field exhibits a main peak inside the CdSeTe layer instead of the MZO/CdSeTe heterointerface, illustrating a buried homojunction (BHJ) of the device. At the DSS, a large electric field peak at the MZO/CdSeTe interface was measured, which probably resulted in the inferior fill factor at the DSS. At the DgS, the electric field peak at the MZO/CdSeTe interface increased further and a third electric field was measured at the back contact of the device. Device modeling using COMSOL software, in alignment with both the electric field and device current-voltage curves, elucidates that a low n-doped CdSeTe in the region near the MZO/CdSeTe interface caused the BHJ in the LSS and a loss of MZO doping and/or increase of the conduction band offset spike due to long-term stress caused the increased electric field near the MZO/CdSeTe interface at the DgS.

CdTe solar cell↗

NASA NTRS1994

A spectral formalism for computing three-dimensional deformations due to surface loads. 1: Theory

We outline a complete spectral formalism for computing high spatial resolution three-dimensional deformations arising from the surface mass loading of a spherically symmetric planet. The main advantages of the formalism are that all surface mass loads are always described using a consistent mathematical representation and that calculations of deformation fields for various spatial resolutions can be performed by simpley altering the spherical harmonic degree truncation level of the procedure. The latter may be important when incorporating improved observational constraints on a particular surface mass load, when considering potential errors in the computed field associated with mass loading having a spatial scale unresolved by the observational constraints, or when treating a number of global surface mass loads constrained with different spatial resolutions. The advantages do not extend to traditional 'Green's function' approaches which involve surface element discretizations of the global mass loads. Another advantage of the spectral formalism, over the Green's function approach, is that a posteriori analyses of the computed deformation fields are easily performed. In developing the spectral formalism, we consider specific cases where the Earth's mantle is assumed to respond as an elastic, slightly anelastic, or linear viscoelastic medium. In the case of an elastic or slightly anelastic mantle rheology the spectral response equations incorporate frequency dependent Love numbers. The formalism can therefore be used, for example, to compute the potentially resonant deformational response associated with the free core nutation and Chandler wobble eigenfunctions. For completeness, the spectral response equations include both body forces, as arise from the gravitational attraction of the Sun and the Moon, and surface mass loads. In either case, and for both elastic and anelastic mantle rheologies, we outline a pseudo-spectral technique for computing the ocean adjustment associated with the total gravitational perturbation induced by the external forcing. Three-dimensional deformations computed using the usual Love number approach are generally referenced to an origin at the center of mass of the undeformed planet. We derive a spectral technique for transforming the results to an origin located at the center of mass of the deformed planet.

Mitrovica, J. X.↗