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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae

We examine the feasibility of detecting auroral emission from the potentially habitable exoplanet Proxima Centauri b. Detection of aurorae would yield an independent confirmation of the planet’s existence, constrain the presence and composition of its atmosphere, and determine the planet’s eccentricity and inclination, thereby breaking the mass-inclination degeneracy. If Proxima Centauri b is a terrestrial world with an Earth-like atmosphere and magnetic field, we estimate that the power at the 5577 Å O i auroral line is on the order of 0.1 TW under steady-state stellar wind, or ∼100× stronger than that on Earth. This corresponds to a planet–star contrast ratio of 10{sup −6}--10{sup −7} in a narrow band about the 5577 Å line, though higher contrast (10{sup −4}--10{sup −5}) may be possible during periods of strong magnetospheric disturbance (auroral power 1–10 TW). We searched the Proxima Centauri b HARPS data for the 5577 Å line and for other prominent oxygen and nitrogen lines, but find no signal, indicating that the O i auroral line contrast must be lower than 2×10{sup −2} (with power ≲3000 TW), consistent with our predictions. We find that observations of 0.1 TW auroral emission lines are likely infeasible with current and planned telescopes. However, future observations with a space-based coronagraphic telescope or a ground-based extremely large telescope (ELT) with a coronagraph could push sensitivity down to terawatt oxygen aurorae (contrast 7×10{sup −6}) with exposure times of ∼1 day. If a coronagraph design contrast of 10{sup −7} can be achieved with negligible instrumental noise, a future concept ELT could observe steady-state auroral emission in a few nights.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Global modeling of ULF waves at Mercury

Abstract ULF waves in the ion cyclotron frequency range waves are regularly observed at Mercury's magnetosphere. Although previous statistical studies have shown that ULF waves are primarily compressional near the equator and transverse with linear polarization at higher latitude, the underlying reason for this distribution of wave polarization has not been understood. In order to address this key question, we have developed a two‐dimensional, finite element code that solves the full wave equations in global magnetospheric geometry. Using this code, we show that (1) efficient mode conversion from the fast compressional waves to the ion‐ion hybrid resonance occurs at Mercury consistent with previous calculations; (2) such mode‐converted waves globally oscillate similar to field line resonance at Earth; and (3) compressional wave energy is primarily localized near the equator, while field‐aligned transverse, linearly polarized waves generated by mode conversion at the ion‐ion hybrid resonance radiate to higher latitude. Based on these wave solutions, we suggest that the strong transverse component of observed ULF waves at Mercury in high magnetic latitude can be explained as excitation of the field line resonant waves at the ion‐ion hybrid resonance.

Kim, Eun‐Hwa↗
DOE OSTI2018

A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares

Two scenarios have been proposed to account for sustained ≥30 MeV gamma-ray emission in solar flares: (1) prolonged particle acceleration/trapping involving large-scale magnetic loops at the flare site, and (2) precipitation of high-energy (>300 MeV) protons accelerated at coronal/interplanetary shock waves. To determine which of these scenarios is more likely, we examine the associated soft X-ray flares, coronal mass ejections (CMEs), and solar energetic proton events for (a) the long-duration gamma-ray flares (LDGRFs) observed by the Large Area Telescope on Fermi , and (b) delayed and/or spatially extended high-energy gamma-ray flares observed by the Gamma-ray Spectrometer on the Solar Maximum Mission , the Gamma-1 telescope on the Gamma satellite, and the Energetic Gamma-Ray Experiment Telescope on the Compton Gamma-Ray Observatory . For the Fermi data set of 11 LDGRFs with >100 MeV emission lasting for ≥~2 hr, we search for associations and reverse associations between LDGRFs, X-ray flares, CMEs, and SEPs, i.e., beginning with the gamma-ray flares and also, in turn, with X-class soft X-ray flares, fast (≥1500 km s -1 ) and wide CMEs, and intense (peak flux ≥2.67 × 10 -3 protons cm -2 s -1 sr -1 , with peak to background ratio >1.38) >300 MeV SEPs at 1 au. While LDGRFs tend to be associated with bright X-class flares, we find that only one-third of the X-class flares during the time of Fermi monitoring coincide with an LDGRF. However, nearly all fast, wide CMEs are associated with an LDGRF. These preliminary association analyses favor the proton precipitation scenario, however there is a prominent counter-example of a potentially magnetically well-connected solar eruption with >100 MeV emission for ~10 hr for which the near-Earth >300 MeV proton intensity did not rise above background.

58 GEOSCIENCES↗
DOE OSTI2023

Oblique propagation and temperature effects on the resonant right-hand ion beam instability

The resonant right-hand instability (RHI) is often the dominant mode driven by reflected ions upstream of Earth’s quasi-parallel bow shock. In the tradition of Peter Gary, this paper further explores the right-hand instability using numerical solutions of the plasma dispersion relation and non-linear kinetic simulations, with parameters inspired by observations from NASA’s Magnetospheric Multiscale (MMS) mission. Agreement is found between the ion distributions in the particle-in-cell simulations and Magnetospheric Multiscale spacecraft data, which show the gyrophase bunching characteristic of the instability. The non-linear structures created by right-hand instability tend to be stronger when the plasma beta is lower. These structures have sizes of around 100 to 200 ion inertial lengths perpendicular to the magnetic field, presenting planet-sized disturbances to the magnetosphere. 2d and 3D hybrid particle-in-cell simulations show that modes with a range of propagation angles oblique to the magnetic field are excited, providing a ground to understand previous statistical studies of observed foreshock waves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Near-earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L~5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ~40 s and a dispersionless injection of electrons up to ~3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.

58 GEOSCIENCES↗
DOE OSTI2017

Mass and energy transfer across the Earth's magnetopause caused by vortex-induced reconnection: Mass and energy transfer by K-H vortex

When the interplanetary magnetic field (IMF) is strongly northward, a boundary layer that contains a considerable amount of plasma of magnetosheath origin is often observed along and earthward of the low-latitude magnetopause. Such a pre-existing boundary layer, with a higher density than observed in the adjacent magnetosphere, reduces the local Alfvén speed and allows the Kelvin-Helmholtz instability (KHI) to grow more strongly. We employ a three-dimensional fully kinetic simulation to model an event observed by the Magnetospheric Multiscale (MMS) mission in which the spacecraft detected substantial KH waves between a pre-existing boundary layer and the magnetosheath during strong northward IMF. Initial results of this simulation [Nakamura et al., 2017] have successfully demonstrated ion-scale signatures of magnetic reconnection induced by the non-linearly developed KH vortex, which are quantitatively consistent with MMS observations. Furthermore, we quantify the simulated mass and energy transfer processes driven by this vortex-induced reconnection (VIR) and show that during this particular MMS event (i) mass enters a new mixing layer formed by the VIR more efficiently from the pre-existing boundary layer side than from the magnetosheath side, (ii) mixed plasmas within the new mixing layer convect tailward along the magnetopause at more than half the magnetosheath flow speed, and (iii) energy dissipation in localized VIR dissipation regions results in a strong parallel electron heating within the mixing layer. Finally, the quantitative agreements between the simulation and MMS observations allow new predictions that elucidate how the mass and energy transfer processes occur near the magnetopause during strong northward IMF.

58 GEOSCIENCES↗
DOE OSTI2017

Effects of electric field methods on modeling the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics

Here, we report a self-consistent electric field coupling between the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics represented in a kinetic ring current model. This implementation in the model features another self-consistency in addition to its already existing self-consistent magnetic field coupling with plasma. The model is therefore named as Ring current-Atmosphere interaction Model with Self-Consistent magnetic (B) and electric (E) fields, or RAM-SCB-E. With this new model, we explore, by comparing with previously employed empirical Weimer potential, the impact of using self-consistent electric fields on the modeling of storm time global electric potential distribution, plasma sheet particle injection, and the subauroral polarization streams (SAPS) which heavily rely on the coupled interplay between the inner magnetosphere and midlatitude ionosphere. We find the following phenomena in the self-consistent model: (1) The spatially localized enhancement of electric field is produced within 2.5 < L < 4 during geomagnetic active time in the dusk-premidnight sector, with a similar dynamic penetration as found in statistical observations. (2) The electric potential contours show more substantial skewing toward the postmidnight than the Weimer potential, suggesting the resistance on the particles from directly injecting toward the low-L region. (3) The proton flux indeed indicates that the plasma sheet inner boundary at the dusk-premidnight sector is located further away from the Earth than in the Weimer potential, and a “tongue” of low-energy protons extends eastward toward the dawn, leading to the Harang reversal. (4) SAPS are reproduced in the subauroral region, and their magnitude and latitudinal width are in reasonable agreement with data.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

The global context of the 14 November 2012 storm event

From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20–30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in-situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in-situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Three‐Dimensional Magnetic Reconnection Spreading in Current Sheets of Non‐Uniform Thickness

Abstract Magnetic reconnection in naturally occurring and laboratory settings often begins locally and elongates, or spreads, in the direction perpendicular to the plane of reconnection. Previous work has largely focused on current sheets with a uniform thickness, for which the predicted spreading speed for anti‐parallel reconnection is the local speed of the current carriers. We derive a scaling theory of three‐dimensional (3D) spreading of collisionless anti‐parallel reconnection in a current sheet with its thickness varying in the out‐of‐plane direction, both for spreading from a thinner to thicker region and a thicker to thinner region. We derive an expression for calculating the time it takes for spreading to occur for a current sheet with a given profile of its thickness. A key result is that when reconnection spreads from a thinner to a thicker region, the spreading speed in the thicker region is slower than both the Alfvén speed and the speed of the local current carriers by a factor of the ratio of thin to thick current sheet thicknesses. This is important because magnetospheric and solar observations have previously measured the spreading speed to be slower than previously predicted, so the present mechanism might explain this feature. We confirm the theory via a parametric study using 3D two‐fluid numerical simulations. We use the prediction to calculate the time scale for reconnection spreading in Earth's magnetotail during geomagnetic activity. The results are also potentially important for understanding reconnection spreading in solar flares and the dayside magnetopause of Earth and other planets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Drift turbulence, particle transport, and anomalous dissipation at the reconnecting magnetopause

Here, using fully kinetic 3D simulations, the reconnection dynamics of asymmetric current sheets are examined at the Earth's magnetopause. The plasma parameters are selected to model MMS magnetopause diffusion region crossings with guide fields of 0.1, 0.4, and 1 of the reconnecting magnetosheath field. In each case, strong drift-wave fluctuations are observed in the lower-hybrid frequency range at the steep density gradient across the magnetospheric separatrix. These fluctuations give rise to cross-field electron particle transport. In addition, this turbulent mixing leads to significantly enhanced electron parallel heating in comparison to 2D simulations. We study three different methods of quantifying the anomalous dissipation produced by the drift fluctuations, based on spatial averaging, temporal averaging, and temporal averaging followed by integrating along magnetic field lines. A comparison of different methods reveals complications in identifying and measuring the anomalous dissipation. Nevertheless, the anomalous dissipation from short wavelength drift fluctuations appears weak for each case, and the reconnection rates observed in 3D are nearly the same as in 2D models. Finally, the 3D simulations feature a number of interesting new features that are consistent with recent MMS observations, including cold beams of magnetosheath electrons that penetrate into the hotter magnetospheric inflow, the related observation of decreasing temperature in regions of increasing total density, and an effective turbulent diffusion coefficient that agrees with predictions from quasi-linear theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Multipoint Observations of Quasiperiodic Emission Intensification and Effects on Energetic Electron Precipitation

The two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 h. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. A Low-Earth-Orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. Finally, this scenario is quantitatively confirmed by our quasilinear diffusion simulation results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Active Experiments in Space: Past, Present, and Future

Between 1958 and 1962 the United States and the Soviet Union performed several nuclear detonation tests in the atmosphere, including the Starfish Prime event which involved a 1.4 Mt explosion at 400 km altitude over Johnston island on July 9, 1962 (Gombosi et al., 2017). These tests can be considered as the beginning of active experiments in space (i.e., experiments that deliberately perturb the local environment). They demonstrated the potential destructive power of high-altitude nuclear explosions, both in terms of the resulting electromagnetic pulse as well as for the creation of a potentially long-lasting artificial radiation belt from the radioactive fission debris. For instance,one of the unintended consequences of Starfish Prime was to cripple at least seven spacecraft in low-Earth orbit (LEO), about a third of the LEO spacecraft of the time (Gombosi et al., 2017).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Specification of the near-Earth space environment with SHIELDS

Here, predicting variations in the near-Earth space environment that can lead to spacecraft damage and failure is one example of “space weather” and a big space physics challenge. A project recently funded through the Los Alamos National Laboratory (LANL) Directed Research and Development (LDRD) program aims at developing a new capability to understand, model, and predict Space Hazards Induced near Earth by Large Dynamic Storms, the SHIELDS framework. The project goals are to understand the dynamics of the surface charging environment (SCE), the hot (keV) electrons representing the source and seed populations for the radiation belts, on both macro- and micro-scale. Important physics questions related to particle injection and acceleration associated with magnetospheric storms and substorms, as well as plasma waves, are investigated. These challenging problems are addressed using a team of world-class experts in the fields of space science and computational plasma physics, and state-of-the-art models and computational facilities. A full two-way coupling of physics-based models across multiple scales, including a global MHD (BATS-R-US) embedding a particle-in-cell (iPIC3D) and an inner magnetosphere (RAM-SCB) codes, is achieved. New data assimilation techniques employing in situ satellite data are developed; these provide an order of magnitude improvement in the accuracy in the simulation of the SCE. SHIELDS also includes a post-processing tool designed to calculate the surface charging for specific spacecraft geometry using the Curvilinear Particle-In-Cell (CPIC) code that can be used for reanalysis of satellite failures or for satellite design.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Experimental observations of detached bow shock formation in the interaction of a laser-produced plasma with a magnetized obstacle

The magnetic field produced by planets with active dynamos, like the Earth, can exert sufficient pressure to oppose supersonic stellar wind plasmas, leading to the formation of a standing bow shock upstream of the magnetopause, or pressure-balance surface. Scaled laboratory experiments studying the interaction of an inflowing solar wind analog with a strong, external magnetic field are a promising new way to study magnetospheric physics and to complement existing models, although reaching regimes favorable for magnetized shock formation is experimentally challenging. This paper presents experimental evidence of the formation of a magnetized bow shock in the interaction of a supersonic, super-Alfvenic plasma with a strongly magnetized obstacle at the OMEGA laser facility. The solar wind analog is generated by the collision and subsequent expansion of two counterpropagating, laser-driven plasma plumes. The magnetized obstacle is a thin wire, driven with strong electrical currents. Hydrodynamic simulations using the FLASH code predict that the colliding plasma source meets the criteria for bow shock formation. Spatially resolved, optical Thomson scattering measures the electron number density, and optical emission lines provide a measurement of the plasma temperature, from which we infer the presence of a fast magnetosonic shock far upstream of the obstacle. Proton images provide a measure of large-scale features in the magnetic field topology, and reconstructed path-integrated magnetic field maps from these images suggest the formation of a bow shock upstream of the wire and as a transient magnetopause. Finally, we compare features in the reconstructed fields to two-dimensional MHD simulations of the system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Experimental observations of detached bow shock formation in the interaction of a laser-produced plasma with a magnetized obstacle

The magnetic field produced by planets with active dynamos, like the Earth, can exert sufficient pressure to oppose supersonic stellar wind plasmas, leading to the formation of a standing bow shock upstream of the magnetopause, or pressure-balance surface. Scaled laboratory experiments studying the interaction of an inflowing solar wind analog with a strong, external magnetic field are a promising new way to study magnetospheric physics and to complement existing models, although reaching regimes favorable for magnetized shock formation is experimentally challenging. This paper presents experimental evidence of the formation of a magnetized bow shock in the interaction of a supersonic, super-Alfvenic plasma with a strongly magnetized obstacle at the OMEGA laser facility. The solar wind analog is generated by the collision and subsequent expansion of two counter- propagating, laser-driven plasma plumes. The magnetized obstacle is a thin wire, driven with strong electrical currents. Hydrodynamic simulations using the FLASH code predict that the colliding plasma source meets the criteria for bow shock formation. Spatially resolved, optical Thomson scat- tering measures the electron number density, and optical emission lines provide a measurement of the plasma temperature, from which we infer the presence of a fast magnetosonic shock far upstream of the obstacle. Proton images provide a measure of large-scale features in the magnetic field topology, and reconstructed path-integrated magnetic field maps from these images suggest the formation of a bow shock upstream of the wire and as a transient magnetopause. We compare features in the reconstructed fields to two-dimensional MHD simulations of the system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US–CRCM

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases ("dropouts") in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere–ionosphere (M–I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US–CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open–closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M–I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M–I coupling aspects that have not previously been investigated.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Lithosphere-Surfacesphere–Atmosphere-Ionosphere coupling model for Vrancea seismic zone in Romania

This paper presents a complex multidisciplinary approach concept to explain the nature of short-term earthquake precursors observed in land surface, atmosphere, ionosphere and magnetosphere for strong intermediate depth earthquakes recorded in Vrancea region in Romania. A developed Lithosphere-Surfacesphere-Atmosphere-Ionosphere (LSAI) coupling model can explain most of these presignals as a synergy between different anomalies of geophysical/geochemical parameters. These anomalies prior to medium to strong earthquakes are attributed to the thermodynamic, degassing and ionization processes in the Earth-Atmosphere system and micro-fracturing in the rocks especially along area’s active faults. The main outcome of this paper is an unified concept for systematic validation of different types of earthquake precursors of which Land Surface Temperature (LST), outgoing Long wave Radiation (OLR), Surface Latent Heat Flux (SLHF), Air Temperature (AT), radon gas concentration, ionospheric Total Electron Content (TEC) are the most reliable parameters within the chain of the processes described by LSAI model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗