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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Two-scale Analysis of Solar Magnetic Helicity

We develop a two-scale formalism to determine global magnetic helicity spectra in systems where the local magnetic helicity has opposite signs on both sides of the equator, giving rise to cancellation with conventional methods. We verify this approach using first a synthetic one-dimensional magnetic field and then two-dimensional slices from a three-dimensional α effect-type dynamo-generated magnetic field, with forced turbulence of opposite helicity above and below the midplane of the domain. We then apply this formalism to global solar synoptic vector magnetograms. To improve the statistics, data from three consecutive Carrington rotations (2161–2163) are combined into a single map. We find that the spectral magnetic helicity representative of the northern hemisphere is negative at all wavenumbers and peaks at ≈0.06 Mm{sup −1} (scales around 100 Mm). There is no evidence of bihelical magnetic fields that are found in three-dimensional turbulence simulations of helicity-driven α effect-type dynamos.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2018

Acceleration Modes and Transitions in Pulsed Plasma Accelerators

Pulsed plasma accelerators typically operate by storing energy in a capacitor bank and then discharging this energy through a gas, ionizing and accelerating it through the Lorentz body force. Two plasma accelerator types employing this general scheme have typically been studied: the gas-fed pulsed plasma thruster and the quasi-steady magnetoplasmadynamic (MPD) accelerator. The gas-fed pulsed plasma accelerator is generally represented as a completely transient device discharging in approximately 1-10 microseconds. When the capacitor bank is discharged through the gas, a current sheet forms at the breech of the thruster and propagates forward under a j (current density) by B (magnetic field) body force, entraining propellant it encounters. This process is sometimes referred to as detonation-mode acceleration because the current sheet representation approximates that of a strong shock propagating through the gas. Acceleration of the initial current sheet ceases when either the current sheet reaches the end of the device and is ejected or when the current in the circuit reverses, striking a new current sheet at the breech and depriving the initial sheet of additional acceleration. In the quasi-steady MPD accelerator, the pulse is lengthened to approximately 1 millisecond or longer and maintained at an approximately constant level during discharge. The time over which the transient phenomena experienced during startup typically occur is short relative to the overall discharge time, which is now long enough for the plasma to assume a relatively steady-state configuration. The ionized gas flows through a stationary current channel in a manner that is sometimes referred to as the deflagration-mode of operation. The plasma experiences electromagnetic acceleration as it flows through the current channel towards the exit of the device. A device that had a short pulse length but appeared to operate in a plasma acceleration regime different from the gas-fed pulsed plasma accelerators was developed by Cheng, et al. The Coaxial High ENerGy (CHENG) thruster operated on the 10-microseconds timescales of pulsed plasma thrusters, but claimed high thrust density, high efficiency and low electrode erosion rates, which are more consistent with the deflagration mode of acceleration. Separate work on gas-fed pulsed plasma thrusters (PPTs) by Ziemer, et al. identified two separate regimes of performance. The regime at higher mass bits (termed Mode I in that work) possessed relatively constant thrust efficiency (ratio of jet kinetic energy to input electrical energy) as a function of mass bit. In the second regime at very low mass bits (termed Mode II), the efficiency increased with decreasing mass bit. Work by Poehlmann et al. and by Sitaraman and Raja sought to understand the performance of the CHENG thruster and the Mode I / Mode II performance in PPTs by modeling the acceleration using the Hugoniot Relation, with the detonation and deflagration modes representing two distinct sets of solutions to the relevant conservation laws. These works studied the proposal that, depending upon the values of the various controllable parameters, the accelerator would operate in either the detonation or deflagration mode. In the present work, we propose a variation on the explanation for the differences in performance between the various pulsed plasma accelerators. Instead of treating the accelerator as if it were only operating in one mode or the other during a pulse, we model the initial stage of the discharge in all cases as an accelerating current sheet (detonation mode). If the current sheet reaches the exit of the accelerator before the discharge is completed, the acceleration mode transitions to the deflagration mode type found in the quasi-steady MPD thrusters. This modeling method is used to demonstrate that standard gas-fed pulsed plasma accelerators, the CHENG thruster, and the quasi-steady MPD accelerator are variations of the same device, with the overall acceleration of the plasma depending upon the behavior of the plasma discharge during initial transient phase and the relative lengths of the detonation and deflagration modes of operation.

Polzin, Kurt A.↗
NASA NTRS1976

Numerical simulation of low gravity draining

A boundary value problem was solved numerically for a liquid that is assumed to be inviscid and incompressible, having a motion that is irrotational and axisymmetric, and having a constant (5 degrees) solid-liquid contact angle. The avoidance of excessive mesh distortion, encountered with strictly Lagrangian or Eulerian kinematics, was achieved by introducing an auxiliary kinematic velocity field along the free surface in order to vary the trajectories used in integrating the ordinary differential equations simulating the moving boundary. The computation of the velocity potential was based upon a nonuniform triangular mesh which was automatically revised to varying depths to accommodate the motion of the free surface. These methods permitted calculation of draining induced axisymmetric slosh through the many (or fractional) finite amplitude oscillations that can occur depending upon the balance of draining, gravitational, and surface tension forces. Velocity fields, evolution of the free surface with time, and liquid residual volumes were computed for three and one half decades of Weber number and for two Bond numbers, tank fill levels, and drain radii. Comparisons with experimental data are very satisfactory.

Bizzell, G. D.↗
NASA NTRS1978

Measurement and analysis of magnetic field variation during a class 2b flare

A digital analysis of high-time-resolution videomagnetograms taken during a class 2b flare that occurred at 60 deg east is reported. The data were obtained at the Big Bear Observatory and calibrated by a Mt. Wilson magnetogram. Changes of weak magnetic fields (less than 100 G) with an amplitude of 30% to 100% have been detected over 55% of the optical flare region, apparently taking place at the initial phase of the flare. Statistical considerations suggest a real flare association with most of these changes. H-alpha observations show that large changes took place over the footpoints of heavily inclined structures like penumbral fibrils, while smaller changes took place over the plage region. An apparent polarity reversal was found at the feet of erupted fibrils. Based on force-free field calculations these changes can be reasonably explained as a transformation of the current-carrying fields to potential fields which produced large changes in the field-line inclination and rotation.

Tanaka, K.↗
DOE OSTI2018

Ising-Type Single-Segment Ferromagnetic Nanowire with Core/Shell: the Dependences of the Angle, Temperature, and Geometry

The hysteresis properties of a nanostructure are affected by many factors, such as the material of the nanostructure, the shape and size of the nanostructure, the orientation of the magnetizing field. In the present study, the influence of angle, temperature, and geometry on an Ising-type single-segment ferromagnetic nanowire with core/shell are studied by the effective-field theory with correlations. The behavior of the coercivity is presented by means of phase diagrams in the seven different planes and detected the magnetic characteristics of the nanowire. We find that the magnetic hardness decreases as the angle and temperature increase. We also observe that hysteresis behaviors of ferromagnetic nanowire have strong dependence on interlayer length, shell length, and wire length.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1998

Computation of the Effects of Inhomogeneous Clouds on Retrieval of Remotely Sensed Properties

Current and future earth observation programs depend on satellite measurements of radiance to retrieve the properties of clouds on a global basis. At present, this retrieval is made assuming that the clouds in the instrument field of view are plane parallel and independent of adjacent pixels. While this assumption is known to be false except in very limited cases, its impact can be evaluated, and if possible corrected, based on emerging theoretical techniques. In this study, the Spherical Harmonic Discrete Ordinate Method (SHDOM, Evans, 1996) has been used to assess the sensitivity of the retrieval to a variety of cloud parameters. SHDOM allows the plane parallel assumption to be relaxed and makes 2D and even 3D radiative solutions practical. A previous study (Chambers et al., 1996) assessed the effect of horizontal inhomogeneity in 45 LANDSAT scenes of boundary layer clouds over ocean. The four scenes studied here represent overcast, broken, scattered and strongly thermally forced cloud fields and are used to perform sensitivity studies to a wider variety of parameters. Comparisons are made at three solar zenith angles (theta (sub 0) = 0, 49, and 63 degrees) to avoid ambiguity in the results due to solar zenith angle.

Chambers, Lin H.↗
DOE OSTI2016

ARCADE IMPLOSION CAUSED BY A FILAMENT ERUPTION IN A FLARE

Coronal implosions—the convergence motion of plasmas and entrained magnetic field in the corona due to a reduction in magnetic pressure—can help to locate and track sites of magnetic energy release or redistribution during solar flares and eruptions. We report here on the analysis of a well-observed implosion in the form of an arcade contraction associated with a filament eruption, during the C3.5 flare SOL2013-06-19T07:29. A sequence of events including the magnetic flux-rope instability and distortion, followed by a filament eruption and arcade implosion, lead us to conclude that the implosion arises from the transfer of magnetic energy from beneath the arcade as part of the global magnetic instability, rather than due to local magnetic energy dissipation in the flare. The observed net contraction of the imploding loops, which is found also in nonlinear force-free field extrapolations, reflects a permanent reduction of magnetic energy underneath the arcade. This event shows that, in addition to resulting in the expansion or eruption of an overlying field, flux-rope instability can also simultaneously implode an unopened field due to magnetic energy transfer. It demonstrates the “partial opening of the field” scenario, which is one of the ways in 3D to produce a magnetic eruption without violating the Aly–Sturrock hypothesis. In the framework of this observation, we also propose a unification of three main concepts for active region magnetic evolution, namely the metastable eruption model, the implosion conjecture, and the standard “CSHKP” flare model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Large-scale Plume in an X-class Solar Flare

Ever-increasing multi-frequency imaging of solar observations suggests that solar flares often involve more than one magnetic fluxtube. Some of the fluxtubes are closed, while others can contain open fields. The relative proportion of nonthermal electrons among those distinct loops is highly important for understanding energy release, particle acceleration, and transport. The access of nonthermal electrons to the open field is also important because the open field facilitates the solar energetic particle (SEP) escape from the flaring site, and thus controls the SEP fluxes in the solar system, both directly and as seed particles for further acceleration. The large-scale fluxtubes are often filled with a tenuous plasma, which is difficult to detect in either EUV or X-ray wavelengths; however, they can dominate at low radio frequencies, where a modest component of nonthermal electrons can render the source optically thick and, thus, bright enough to be observed. Here we report the detection of a large-scale “plume” at the impulsive phase of an X-class solar flare, SOL2001-08-25T16:23, using multi-frequency radio data from Owens Valley Solar Array. To quantify the flare’s spatial structure, we employ 3D modeling utilizing force-free-field extrapolations from the line of sight SOHO /MDI magnetograms with our modeling tool GX-Simulator. We found that a significant fraction of the nonthermal electrons that accelerated at the flare site low in the corona escapes to the plume, which contains both closed and open fields. We propose that the proportion between the closed and open fields at the plume is what determines the SEP population escaping into interplanetary space.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Phase-transition Theory of Kerr Black Holes in the Electromagnetic Field

For a Kerr black hole (KBH) with spin J and mass M in a steady electromagnetic field, a special Wald vacuum solution (WVS) has been found in the case of the no-source uniform field. For WVS, the Meissner effect (ME) occurs only in the the extreme KBH, where M{sup 2}/J = 1, in this case, the magnetic field is totally excluded from the event horizon (EH) of KBH. However, WVS does not consider the Hawking radiation (HR) but treats KBH as an absolutely black body. If HR is added , researchers believe that the condition is not so restricted and it is possible for ME to occur in the less-extreme case. How less is the “less-extreme case”? This paper tries to answer this question. Since the Hawking temperature T{sub H} of KBH defined by HR is proportional to the surface gravity κ at the EH, this question is actually about the so-called existence/non-existence of ME (ME/NME) or superconducting phase transition. In this paper, we study the connection between the superconductivity of KBH-EH and the existence of Weyl fermion. Using thermodynamic formulas and the KBH state equation, we prove that the inherent-parameter condition for ME to occur is M{sup 2}/J⩽ϵ{sub c}=1.5 in force-free fields whether it be in the simple axisymmetric vacuum zero source case or in the non-zero source case, which can be described by the nonlinear Grad–Shafranov equation. We suggest that this is a second-order phase transition and calculate the critical exponents δ = 1 and η = 1/2 for the specific heat diverging at constant J.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. III. Twist Number Method

We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twist multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Magnetic resonance force microscopy with a paramagnetic probe

Here, we consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2009

T-Rex: A Japanese Space Tether Experiment

Electrodynamic tether (EDT) thrusters work by virtue of the force a magnetic field exerts on a wire carrying an electrical current. The force, which acts on any charged particle moving through a magnetic field (including the electrons moving in a current-carrying wire), were concisely expressed by Lorentz in 1895 in an equation that now bears his name. The force acts in a direction perpendicular to both the direction of current flow and the magnetic field vector. Electric motors make use of this force: a wire loop in a magnetic field is made to rotate by the torque the Lorentz Force exerts on it due to an alternating current in the loop times so as to keep the torque acting in the same sense. The motion of the loop is transmitted to a shaft, thus providing work. Although the working principle of EDT thrusters is not new, its application to space transportation may be significant. In essence, an EDT thruster is just a clever way of getting an electrical current to flow in a long orbiting wire (the tether) so that the Earth s magnetic field will accelerate the wire and, consequently the payload attached to the wire. The direction of current flow in the tether, either toward or away from the Earth along the local vertical, determines whether the magnetic force will raise or lower the orbit. The bias voltage of a vertically deployed metal tether, which results just from its orbital motion (assumed eastward) through Earth s magnetic field, is positive with respect to the ambient plasma at the top and negative at the bottom. This polarization is due to the action of the Lorentz force on the electrons in the tether. Thus, the natural current flow is the result of negative electrons being attracted to the upper end and then returned to the plasma at the lower end. The magnetic force in this case has a component opposite to the direction of motion, and thus leads to a lowering of the orbit and eventually to re-entry. In this generator mode of operation the Lorentz Force serves both to drive the current and then to act on the current to decelerate the system. One of the most important features of tether thrusters is that they use renewable energy sources to drive the electrical current flow in either the orbit-raising or orbit-lowering modes. Sources inherent to Earth orbit are used. To raise the orbit, sunlight can be converted to the electrical energy required to drive the tether current. To lower the orbit, the orbital energy itself (supplied by the Earth-to-orbit launcher when it raises the system into orbit) is the energy source of the tether current via the action of the Lorentz Force. Electrodynamic tethers can be directly applied to a wide spectrum of uses in space. As a propulsion system, they include satellite de-orbit, transfer of a satellite from one orbit to another, altitude maintenance for large spacecraft such as the International Space Station, and since it works wherever there is a magnetic field and an ionosphere planetary exploration missions. An electrodynamic tether upper stage could be used as an Orbit Transfer Vehicle (OTV) to move payloads within low earth orbit. The OTV would rendezvous with the payload and launch vehicle, grapple the payload and maneuver it to a new orbital altitude or inclination without the use of boost propellant. The tug could then lower its orbit to rendezvous with the next payload and repeat the process. Conceivably, such a system could perform several orbital maneuvering assignments without resupply, making it relatively inexpensive to operate.

Johnson, Les↗
DOE OSTI2023

The confluence of machine learning and multiscale simulations

Multiscale modeling has a long history of use in structural biology, as computational biologists strive to overcome the time- and length-scale limits of atomistic molecular dynamics. Contemporary machine learning techniques, such as deep learning, have promoted advances in virtually every field of science and engineering and are revitalizing the traditional notions of multiscale modeling. Deep learning has found success in various approaches for distilling information from fine-scale models, such as building surrogate models and guiding the development of coarse-grained potentials. However, perhaps its most powerful use in multiscale modeling is in defining latent spaces that enable efficient exploration of conformational space. In conclusion, this confluence of machine learning and multiscale simulation with modern high-performance computing promises a new era of discovery and innovation in structural biology.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Non-kinematic Flux-transport Dynamos Including the Effects of Diffusivity Quenching

Turbulent magnetic diffusivity is quenched when strong magnetic fields suppress turbulent motion in a phenomenon known as diffusivity quenching. Diffusivity quenching can provide a mechanism for amplifying magnetic field and influencing global velocity fields through Lorentz force feedback. To investigate this effect, we conducted mean field flux-transport dynamo simulations that included the effects of diffusivity quenching in a non-kinematic regime. We found that toroidal magnetic field strength is amplified by up to approximately 1.5 times in the convection zone as a result of diffusivity quenching. This amplification is much weaker than that in kinematic cases as a result of Lorentz force feedback on the system’s differential rotation. While amplified toroidal fields lead to the suppression of equatorward meridional flow locally near the base of the convection zone, large-scale equatorward transport of magnetic flux via meridional flow, which is the essential process of the flux-transport dynamo, is sustainable in our calculations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

EUV emission, filament activation and magnetic fields in a slow-rise flare

Results are reported for observations and analysis of synoptic data on a 1B flare that occurred on January 19, 1972. The observations include large-scale H-alpha movies of the flare and pre-flare developments, OSO-7 satellite data on soft X-ray and EUV developments, magnetograms, and hard X-ray observations. Theoretical force-free magnetic field configurations are compared with structures seen in the soft X-ray, EUV, and H-alpha images, and the evolution of the flare is described. The energy available for the flare is estimated from the change of magnetic field inferred from the H-alpha filtergrams and from force-free field calculations. It is suggested that the flare originated in a twisted filament where it was compressed by emerging fields, and it is shown that the flare started below the corona and appeared to derive its energy from the magnetic fields in or near the filament.

Rust, D. M.↗
NASA NTRS1989

Steady state magnetic field configurations for the earth's magnetotail

A two-dimensional, force-balance magnetic field model is presented. The theoretical existence of a steady state magnetic field configuration that is force-balanced and consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD is demonstrated. A numerical solution is obtained for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The results are consistent with the convection time sequences reported by Erickson (1985).

Hau, L.-N.↗
DOE OSTI2025

Development and transferability of neural-network models for plasma-surface interactions

Plasma-surface interactions are increasingly critical to modern technologies; yet, accurate molecular dynamics simulations remain limited by the capabilities of interatomic potentials. Deep Potentials (DPs) promise to revolutionize the field by providing a systematic method for producing accurate interatomic potentials. The primary challenge of DP development is selecting a dataset, which efficiently spans the set of atomic environments one expects to encounter in the subsequent molecular dynamics simulations. The computational cost of density functional theory calculations, which are the typical basis for DP development, makes it impossible to directly verify the quality of a given DP. To address this challenge, we explore the development of a deep-learned interatomic potential, “DeepREBO,” trained to reproduce the behavior of the REBO2 empirical potential, enabling direct validation of training methodology and transferability. Using an active learning framework, we begin with a minimal dataset and iteratively expand it to train a Deep Potential-Smooth Edition model that faithfully reproduces REBO2 results for 25 eV hydrogen bombardment of diamond (001), a particularly challenging case. We show that small, carefully curated datasets can outperform large, unguided ones, with effective models requiring fewer than 15 000 snapshots. Subsequent transferability tests demonstrate that while DeepREBO generalizes well to diamond (111) surfaces, performance degrades for amorphous carbon or higher-energy impacts, highlighting the need for use-case-specific training data. We also evaluate methods to improve short-range repulsion. This study outlines best practices for training robust deep potentials and underscores the importance of dataset design for predictive plasma simulations.

Ab-initio molecular dynamics↗