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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Scientific visualization tools for the ISTP project: Mission planning, data analysis and model interpretation

Visualization tools are being developed to meet the challenges of mission planning and data analysis presented by the International Solar-Terrestrial Physics (ISTP) program. ISTP encompasses a large number of spacecraft, multiple ground-based observatories, and several theoretical investigations, with the goal of understanding the global behavior of the solar wind/magnetosphere/ionosphere system. The tools include three-dimensional displays of key boundaries in geospace along with spacecraft trajectories, which can be animated and synchronized to universal time. Magnetic field models and MHD simulation results can be invoked to reveal the magnetic topology or to identify magnetic conjunctions between spacecraft and/or ground-based facilities. Simultaneous displays of satellite trajectories, spacecraft-borne observations, and model predictions are available to facilitate data processing and interpretation efforts. The current status of these tools is described, and their implementation at the ISTP Science Planning and Operations Facility and distribution to the entire ISTP community are discussed.

Peredo, M.↗
NASA NTRS1992

Analysis, modelling and simulation of the large-angle magnetic suspension test fixture

The large-angle magnetic suspension test fixture (LAMSTF) research project is described which is based on a sophisticated finite element computer program, VF/GFUN, for calculating magnetic fields. The LAMSTF design includes eddy current paths the effect of which on system dynamics is being studied to modify the system dynamic model and the digital controller. Linearized equations of motions have been developed for system modelling and analysis of controllers.

Britcher, Colin P.↗
NASA NTRS2005

A Mechanism for the Loading-Unloading Substorm Cycle Missing in MHD Global Magnetospheric Simulation Models

Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.

Klimas, A. J.↗
NASA NTRS2003

FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identi@ the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral Snapshot (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data were used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and/or a long-system particle in cell simulation to model the magnetically connected region between the two satellites. Results from the study indicate that there are three main drivers of auroral acceleration: (1) field-aligned currents that lead to quasistatic parallel potential drops (parallel electric fields), (2) earthward flow of high-energy plasma beams from the magnetotail into the auroral zone that lead to quasistatic parallel potential drops, and (3) large-amplitude Alfven waves that propagate into the auroral region from the magnetotail. The events examined thus far confm the previously established invariant latitudinal dependence of the drivers and show a strong dependence on magnetic activity. Alfven waves tend to occur primarily at the poleward edge of the auroral region during more magnetically active times and are correlated with intense electron precipitation. At lower latitudes away from the poleward edge of the auroral zone is the primary field-aligned current region which results in the classical field- aligned acceleration associated with the auroral zone (electrons earthward and ion beams tailward). During times of high magnetic activity, high-energy ion beams originating from the magnetotail are observed within, and overlapping, the regions of primary and return field-aligned current. Along the field lines where the high-energy magnetotail ion beams are located, field-aligned acceleration can occur in the auroral zone leading to precipitating electrons and upwelling ionospheric ion beams. Field-aligned currents are present during both quiet and active times, while the Alfven waves and magnetotail ion beams were observed only during more magnetically active events.

Schriver, D.↗
NASA NTRS2002

FAST/Polar Conjunction Study of Field-Aligned Auroral Acceleration and Corresponding Magnetotail Drivers

The discrete aurora results when energized electrons bombard the Earth's atmosphere at high latitudes. This paper examines the physical processes that can cause field-aligned acceleration of plasma particles in the auroral region. A data and theoretical study has been carried out to examine the acceleration mechanisms that operate in the auroral zone and to identity the magnetospheric drivers of these acceleration mechanisms. The observations used in the study were collected by the Fast Auroral SnapshoT (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. During these events FAST was in the middle of the auroral zone and Polar was above the auroral zone in the near-Earth plasma sheet. Polar data was used to determine the conditions in the magnetotail at the time field-aligned acceleration was measured by FAST in the auroral zone. For each of the magnetotail drivers identified in the data study, the physics of field-aligned acceleration in the auroral region was examined using existing theoretical efforts and a long-system particle-in-cell simulation to model the magnetically connected region between the two satellites.

Schriver, D.↗
NASA NTRS2002

Self-Consistent Magnetosphere-Ionosphere Coupling: Theoretical Studies

A self-consistent ring current (RC) model has been developed that couples electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self-consistent magnetosphere- ionosphere coupling loop. First, in addition to the RC ions, we solve an electron kinetic equation in our model. Second, using the relation of Galand and Richmond [2001], we calculate the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our code. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has has been comprehensively studied, and compare our results with different theoretical approaches. The self-consistent inclusion of the hot electrons and, their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self-consistent results) is evident in the inner magnetosphere. This changes the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells.

Khazanov, G. V.↗
NASA NTRS2002

Self-Consistent Magnetosphere-Ionosphere Coupling

A self-consistent ring current (RC) model has been developed that couples electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self-consistent magnetosphere-ionosphere coupling loop. First, in addition to the RC ions, we have solved an electron kinetic equation in our model. Second, using the relation of Galand and Richmond, we have calculated the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our model. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has been comprehensively studied by Fok et al., and have compared our results with different theoretical approaches. The self-consistent inclusion of the hot electrons and their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self-consistent results) is evident in the inner magnetosphere. These effects change the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells.

Six, N. Frank↗
NASA NTRS2017

Parsec-Scale Obscuring Accretion Disk with Large-Scale Magnetic Field in AGNs

A magnetic field dragged from the galactic disk, along with inflowing gas, can provide vertical support to the geometrically and optically thick pc (parsec) -scale torus in AGNs (Active Galactic Nuclei). Using the Soloviev solution initially developed for Tokamaks, we derive an analytical model for a rotating torus that is supported and confined by a magnetic field. We further perform three-dimensional magneto-hydrodynamic simulations of X-ray irradiated, pc-scale, magnetized tori. We follow the time evolution and compare models that adopt initial conditions derived from our analytic model with simulations in which the initial magnetic flux is entirely contained within the gas torus. Numerical simulations demonstrate that the initial conditions based on the analytic solution produce a longer-lived torus that produces obscuration that is generally consistent with observed constraints.

galaxies↗
NASA NTRS2010

Simulation and 'TWINS Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 is the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly -80nT at 7:00 and 10:00 UT. During the main phase and at the peak of the storm, TWINS 1 and 2 were near apogee and moving from pre-dawn to post-dawn local time. The energetic neutral atom (ENA) imagers on the 2 spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the ENA emissions was seen in the midnight-to-dawn local-time sector. The development of this storm has been simulated using the Comprehensive Ring Current Model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in-situ ion data from THEMIS satellites. Simulation with static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always eastward than those in the observed TWINS images. On the other hand, simulation with a dynamic magnetic field gives better spatial agreements with both ENA and insitu particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, Mei-Ching↗
NASA NTRS2011

Simulation and Twins Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 was at the time the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly .80 nT at 0700 and 1000 UT. During the main phase, and at the peak of the storm, TWINS 1 and 2 were near apogee and moving between predawn and postdawn local time. The energetic neutral atom (ENA) imagers on the two spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the high-altitude ENA emissions was seen in the midnight-to-dawn local time sector. The development of this storm has been simulated using the comprehensive ring current model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in situ ion data from a THEMIS satellite. Simulation with a static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always more eastward than those in the observed TWINS images. On the other hand, the simulation with a dynamic magnetic field gives better spatial agreement with both ENA and in situ particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, M.-C.↗
NASA NTRS1988

Numerical simulation of mass injection for the formation of prominence magnetic field configurations. II - Symmetric injection

A two-dimensional MHD model simulating the formation of Kippenhahn-Schluter (1957) quiescent prominence (QP) magnetic field configurations is used to explore symmetric mass injection into a dipole magnetic field. An optimum magnetic field strength for QP formation by mass injection is obtained. It is found that a weaker magnetic field strength is more favorable for the condensation of the injected plasma but that a stronger field is more favorable for supporting the condensed plasma against gravity.

An, C.-H.↗
NASA NTRS2013

Jovian Plasmas Torus Interaction with Europa. Plasma Wake Structure and Effect of Inductive Magnetic Field: 3D Hybrid Kinetic Simulation

The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa (Cassidy et al., 2007; Shematovich et al., 2005). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with Oþ þ and Sþ þ background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population (Cassidy et al., 2007). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europa's atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive magnetic dipole and low oceanic shell conductivity).

Jovian magnetosphere↗
NASA NTRS2008

How Ionospheric Ions Populate the Magnetosphere during a Magnetic Storm

Ionospheric oxygen ions have been observed throughout the magnetosphere, from the plasma sheet to the ring current region. I t has been found that the O+ /H+ density ratio in the magnetosphere increases with geomagnetic activity and varies with storm phases. During the magnetic storm in late September to earIy October 2002, Cluster was orbiting in the plasma sheet and ring current regions. At prestorm time, Cluster observed high H+ density and low O+ density in the plasma sheet and lobes. During the storm main phase, 0+ density has increased by 10 times over the pre-storm level. Strong field-aligned beams of O+ were observed in the lobes. O+ fluxes were significantly reduced in the central plasma sheet during the storm recovery. However, 0+ was still evident on the boundaries of the plasma sheet and in the lobes. In order to interpret the Cluster observations and to understand how O+ ions populate the magnetosphere during a magnetic storm, we model the storm in early October 2002 using our global ion kinetic simulation (GIK). We use the LFN global simulation model to produce electric and magnetic fields in the outer magnetosphere, the Strangeway outflow scaling with Delcourt ion trajectories to include ionospheric outflows, and the Fok inner magnetospheric model for the plasmaspheric and ring current response to all particle populations. We find that the observed composition features are qualitatively reproduced by the simulations, with some quantitative differences that point to future improvements in the models.

Fok, Mei-Ching↗
NASA NTRS2007

A Three-Dimensional MHD Simulation of the Solar Wind for a Tilted-Dipole Magnetic Field on the Sun

Using a three-dimensional MHD model, we simulate the global steady-state structure of the solar corona and solar wind for a dipole magnetic field on the Sun inclined by 30 degrees to the solar rotation axis. This represents the solar conditions typical for a declining phase of solar cycle. The computations can extend from the coronal base out to 100-AU and at large heliospheric distances includes the effects of interstellar neutral hydrogen and their interaction with solar wind protons. The simulations can model the formation of corotating interaction regions and the heliospheric current sheet. The simulations are also capable of describing very strong rarefaction regions that include embedded sub-Alfvenic regions that form on the trailing edge of a fast flows.

Goldstein, Melvyn L.↗
NASA NTRS1982

The effect of corotating interaction regions on the propagation of relativistic cosmic rays in the heliosphere

This paper questions the validity of modulation theories that ignore the presence of large regions of enhanced magnetic field in the heliosphere. The scatter-free and diffusive motion of relativistic cosmic rays is simulated in models of the heliospheric magnetic field, which include compressed field structures representing the corotating interaction regions that are believed to be present in the interplanetary medium throughout most of the solar cycle. It is found that the strong field gradients associated with these regions greatly perturb the drift pattern anticipated for simple Parkerian fields, and thus the expected streaming of cosmic rays from over the poles or along the current sheet, during consecutive solar cycles, no longer holds.

Thomas, B. T.↗
NASA NTRS1992

Lunar magnetic fields - Implications for utilization and resource extraction

Numerical simulations are used to show that solar wind ion deflection by strong lunar magnetic anomalies can produce local increases, as well as decreases, in the implantation rate of solar wind hydrogen. Model simulations suggest that the ability of magnetic anomalies to shield the surface from incident ions increases with the angle of incidence and therefore for most particle sources, with selenographic latitude. The possibility that relatively strong anomalies can provide significant protection of materials and men against major solar flare particle events is found to be unlikely.

Hood, Lon L.↗
NASA NTRS1985

Node-avoiding Levy flight - A numerical test of the epsilon expansion

A study is conducted of an extension of Levy flight to include self-repulsion in the path of the walk. The extension is called node-avoiding Levy flight and its equivalence to the n approaches 0 limit of a statistical mechanical model for a magnetic system with long-range interactions between the spins is shown. By use of this equivalence it is possible to make a detailed comparison beween the results of the epsilon expansion for the magnetic model, a Monte Carlo simulation of the Levy flight model, and the results of a Flory-type argument. This is the first comparison of the epsilon expansion for epsilon much less than 1 with a numerical simulation for any model. Some speculations are made on applications of the model of node-avoiding Levy flight.

Halley, J. W.↗