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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Physical conditions in the solar atmosphere above an active region

From a series of EUV spectra obtained at several heights above the limb in a solar active region, the volume emission measure is derived as a function of the electron temperature in the temperature range 70,000-1,500,000 K and the electron density at two locations. The emission measure from the coronal material (temperature greater than 700,000 K) is nearly the same everywhere and represents most of the material in the line of sight, while the emission measure from the transition region material (temperature between 70,000 and 250,000 K) fluctuates by two orders of magnitude from position to position above the active region. This is in agreement with the picture of this active region as consisting of a number of well-defined loops or lower portions of loops at transition region temperatures that are inhomogeneously distributed in much larger and more diffuse loop structures at coronal temperatures. The coronal data are in reasonable agreement with simple coronal models. Emission measures near 1,000,000 K evaluated using different ions differ by a factor of 4, suggesting difficulties with the atomic physics data.

Mariska, J. T.↗
DOE OSTI2022

Magnetic reconnection in the era of exascale computing and multiscale experiments

Astrophysical plasmas have the remarkable ability to preserve magnetic topology, which inevitably gives rise to the accumulation of magnetic energy within stressed regions including current sheets. This stored energy is often released explosively through the process of magnetic reconnection, which produces a reconfiguration of the magnetic field, along with high-speed flows, thermal heating and nonthermal particle acceleration. Either collisional or kinetic dissipation mechanisms are required to overcome the topological constraints, both of which have been predicted by theory and validated with in situ spacecraft observations or laboratory experiments. However, major challenges remain in understanding magnetic reconnection in large systems, such as the solar corona, where the collisionality is weak and the kinetic scales are vanishingly small in comparison with macroscopic scales. The plasmoid instability or formation of multiple plasmoids in long, reconnecting current sheets is one possible multiscale solution for bridging this vast range of scales, and new laboratory experiments are poised to study these regimes. In conjunction with these efforts, we anticipate that the coming era of exascale computing, together with the next generation of observational capabilities, will enable new progress on a range of challenging problems, including the energy build-up and onset of reconnection, partially ionized regimes, the influence of magnetic turbulence and particle acceleration.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2003

Structure and Dynamics of the Quiet Solar Chromosphere

For the meeting of the AAS/SPD in Albuquerque, NM, I organized a Topical Session of the AAS on Structure and Dynamics of Chromospheres. The grant support was used to bring to the US two of the speakers from abroad. I had invited them for presentations at the Session: Dr. Klaus Wilhelm, the former PI of the SUMER instrument on SOHO, from the Max-Planck Institut in Lindau, Germany, and Dr. Sirajul Hasan, from the Indian Institute of Astrophysics in Bangalore, India. Both speakers preceded their trip to the AAS meeting with a stay at the Smithsonian Astrophysical Observatory, where they interacted with members of the Solar and Stellar Physics division. The highlights of the visits were the talks at the AAS/SPD meeting, in which six invited speakers told the audience of astronomers about current problems in solar physics and their relation to stellar problems. An important result of the visits is a paper by Dr. Wilhelm and me on 'Observations of the upper solar chromosphere with SUMER on SOHO', which has been submitted to Astronomy and Astrophysics for publication.

Kalkofen, Wolfgang↗
DOE OSTI2015

Laboratory Study of the Equilibrium and Eruption of Line-Tied Magnetic Flux Ropes in the Solar Corona

Ideal magnetohydrodynamic (MHD) instabilities such as the kink instability and the torus instability are leading candidates to explain the sudden onset of eruptive events in the solar corona. These instabilities act on line-tied magnetic flux ropes--long-lived arched structures anchored to the solar surface. In spite of substantial observational and numerical research, however, the role of these instabilities in the corona remains a subject of intense debate. For this thesis, we have constructed and operated a new line-tied flux rope experiment that permits for the first time the study of both the kink and torus instabilities in the laboratory. This experiment has the following key features: (1) the arched flux rope is line-tied to two conducting footpoints; (2) the system is magnetically dominated (low-beta) with significant stored energy; (3) the system is driven quasi-statically, producing a long-lived equilibrium; and (4) the flux rope is generated within a potential (vacuum) magnetic field arcade whose decay index--the predicted torus instability control parameter--can be externally controlled. The flux ropes are diagnosed using a two-dimensional in situ magnetic probe array whose cross-section covers a substantial portion of the plasma. The central result of this thesis is that toroidal field forces, which are traditionally neglected in the analysis of coronal flux ropes, are identified for the first time as an essential contributor to both the equilibrium and the stability of line-tied flux ropes. Most importantly, experimental measurements show that a tension force derived from a self-generated paramagnetic toroidal field exerts a restoring force on the line-tied plasma and suppresses eruptive behavior in a significant portion of the parameter space. This suppression extends to regimes that are both kink and torus unstable. We find that, in order to explain the measured tension force, low aspect ratio and line-tying effects must be considered. Finally, flux rope eruptions are observed in these experiments, but only in regimes with sufficiently low external toroidal field where the tension force is reduced. These results constitute a new condition for the prediction of line-tied magnetic flux rope eruptions: that of low external toroidal field.

Magnetic Fields↗
DOE OSTI2011

DERIVING THE PHYSICAL PARAMETERS OF A SOLAR EJECTION WITH AN ISOTROPIC MAGNETOHYDRODYNAMIC EVOLUTIONARY MODEL

The time-space evolution of a {approx}50 Degree-Sign wide coronal mass ejection (CME) on 2007 May 21 is followed remotely with the Solar Terrestrial Relations Observatory heliospheric imager HI-1, and measured in situ near Venus by the MESSENGER and Venus-Express spacecraft. The paper compares the observations of the CME structure with a simple, analytical magnetohydrodynamic force-free solution. It corresponds to a self-similar evolution, which gives a consistent picture of the main spatial-temporal features for both remote and in situ observations. Our main findings are (1) the self-similar evolution allows us to map the CME bright front into about 1/3 of the whole interplanetary counterpart of the coronal mass ejection (ICME, i.e., corresponding to the in situ observed passage of the plasma and magnetic field structure), in good quantitative agreement with the imaging measurements, (2) the cavity following the CME front maps into the rest of the ICME structure, 80% or more of which is consistent with a force free, cylindrically shaped flux rope, and (3) time and space conditions constrain the translational speed of the FR center to 301 km s{sup -1}, and the expansion speed of the FR core to 26 km s{sup -1}. A careful determination of the ICME cross-section and volume allows us to calculate the mass of the CME bright region (4.3 {+-} 1.1 10{sup 14} g) from the in situ measurements of the proton number density, which we assume to be uniform inside the bright region, of excellent agreement with the value estimated from the SECCHI HI-1 observations for the same structure. We provide model estimates for several global parameters including FR helicity ({approx}2 Multiplication-Sign 10{sup 26} Weber{sup 2}).

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Air Force/Ion Physics hardened lithium doped solar cell development

Introduction of lithium by ion implantation eliminates reproducibility and surface problem deficiencies of other introduction techniques. Implantation has been demonstrated to make possible a degree of control over the cell lithium content which has not previously been available. Front barrier development remains to be completed. Successful development of the barrier will make available the freedom to select optimum lithium concentration throughout the cell, including in the vicinity of the junction.

Kirkpatrick, A.↗
NASA NTRS1973

Radio physics of the outer solar system.

The remote sensing of low frequency nonthermal radio emission is the astronomy of field and particle phenomena. Observations conducted from space lead to information about the composition and dynamic processes occurring in planetary magnetospheres as well as within the interplanetary and interstellar medium. The potential of this technique is demonstrated by considering observations obtained from earth orbit missions.

Stone, R. G.↗
NASA NTRS1977

Morphology and physical parameters of a solar flare

The chromospheric and coronal morphology of the flare of June 15, 1973, (1B/M3) in NOAA active region 131 (McMath 12379) is discussed, and results of quantitative analysis of Skylab soft X-ray observations of the event are presented. H-alpha and white-light observations reveal evidence of emerging flux near the site of the H-alpha flare onset. Preflare and early flare filament activity and its spatial and temporal correlation with the flare are discussed. Spatially resolved soft X-rays are compared with H-alpha and magnetic-field measurements. Full-disk high-temporal-resolution soft X-ray flux measurements and time profiles of the resultant temperature and density calculations are also presented which yield a peak temperature of about 14.2 million K and a peak electron density of approximately 3.5 deg 10 to the -10th power per cu cm and show a preflash-phase temperature rise to about 9 million K. The peak values should be compared with the respective values of approximately 25 million K and 4.5 by 10 to the -10th power per cu cm deduced from the spatially resolved data.

Smith, J. B., Jr.↗
NASA NTRS1978

Physics of the primitive solar nebula and of giant gaseous protoplanets

It has been proposed that the supernova responsible for injecting Al-26 into the early solar system was in fact responsible for triggering the collapse of an interstellar cloud in order to produce a system of stars, one of which would be the solar system. Details concerning the mechanism involved in such a process are discussed. Attention is given to the evolution of the primitive solar nebula, the instabilities in the primitive solar nebula, and the giant gaseous protoplanets. The principal conclusion to be drawn from the material presented is that the primitive solar nebula was a rather chaotic place, highly turbulent, with the multiple formation of giant gaseous protoplanets.

Cameron, A. G. W.↗
NASA NTRS1992

1991 Urey Prize Lecture: Physical evolution in the solar system - Present observations as a key to the past

The present evaluation of the use of new observational methods for exploring solar system evolutionary processes gives attention to illustrative cases from the constraining of near-earth asteroid sources and the discovery of main-belt asteroid fragments which indicate Vesta to be a source of basaltic achondrite meteorites. The coupling of observational constraints with numerical models clarifies cratering and collisional evolution for both main-belt and Trojan asteroids.

Binzel, Richard P.↗
NASA NTRS2001

Our Sun IV: The Standard Model and Helioseismology: Consequences of Uncertainties in Input Physics and in Observed Solar Parameters

Helioseismic frequency observations provide an extremely accurate window into the solar interior; frequencies from the Michaelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft, enable the adiabatic sound speed and adiabatic index to be inferred with an accuracy of a few parts in 10(exp 4) and the density with an accuracy of a few parts in 10(exp 3). This has become a Serious challenge to theoretical models of the Sun. Therefore, we have undertaken a self-consistent, systematic study of the sources of uncertainties in the standard solar models. We found that the largest effect on the interior structure arises from the observational uncertainties in the photospheric abundances of the elements, which affect the sound speed profile at the level of 3 parts in 10(exp 3). The estimated 4% uncertainty in the OPAL opacities could lead to effects of 1 part in 10(exp 3); the approximately 5%, uncertainty in the basic pp nuclear reaction rate would have a similar effect, as would uncertainties of approximately 15% in the diffusion constants for the gravitational settling of helium. The approximately 50% uncertainties in diffusion constants for the heavier elements would have nearly as large an effect. Different observational methods for determining the solar radius yield results differing by as much as 7 parts in 10(exp 4); we found that this leads to uncertainties of a few parts in 10(exp 3) in the sound speed int the solar convective envelope, but has negligible effect on the interior. Our reference standard solar model yielded a convective envelope position of 0.7135 solar radius, in excellent agreement with the observed value of 0.713 +/- 0.001 solar radius and was significantly affected only by Z/X, the pp rate, and the uncertainties in helium diffusion constants. Our reference model also yielded envelope helium abundance of 0.2424, in good agreement with the approximate range of 0.24 to 0.25 inferred from helioseismic observations; only extreme Z/X values yielded envelope helium abundance outside this range. We found that other current uncertainties, namely, in the solar age and luminosity, in nuclear rates other than the pp reaction, in the low-temperature molecular opacities, and in the low-density equation of state, have no significant effect on the quantities that can be inferred from helioseismic observations. The predicted pre-main-sequence lithium depletion is uncertain by a factor of 2. The predicted neutrino capture rate is uncertain by approximately 30% for the Cl-27 experiment and by approximately 3% for Ga-71 experiments, while the B-8 neutrino flux is uncertain by approximately 30%.

Boothroyd, Arnold I.↗
NASA NTRS2022

Dependence of Energetic Storm Particle Heavy Ion Peak Intensities and Spectra on Source CME Longitude and Speed

We examine variations in energetic storm particle (ESP) heavy ion peak intensities and energy spectra at CME-driven interplanetary shocks. We focus on their dependence with heliolongitude relative to the source region of their associated CMEs, and with CME speed, for events observed in Solar Cycle 24 at the STEREO-A, STEREO-B, and/or ACE spacecraft. We find that observations of ESP events at 1 au are organized by longitude relative to their CME solar source. The ESP event longitude distribution also showed organization with CME speed. The near-Sun CME speeds (V i ) for these events ranged from ∼560 to 2650 km s −1 while the average CME transit speeds to 1 au were significantly slower. The angular width of the events had a clear threshold at V i of ∼1300 km s −1 , above which events showed significantly larger angular extension compared to events with speeds below. High-speed events also showed larger heavy ion peak intensities near the nose of the shock compared to the flanks while their spectral index was smaller near the nose and larger near the flanks. This organization for events with V i < 1300 km s −1 was not as clear. These ESP events were observed over a narrower range of longitudes though the heavy ion peak intensities still appeared largest near the nose of the shock. Their heavy ion spectra showed no clear organization with longitude. These observations highlight the impact of spacecraft position relative to the CME source longitude and Vi on the properties of ESP events at 1 au.

Solar energetic particles↗
DOE OSTI2011

Solar neutrino experiments: Status and prospects

Solar neutrino experiments were originally conceived as a way to demonstrate that nuclear reactions are responsible for energy generation in stars. When solar neutrinos were first detected the measured flux was much less than what solar models predicted. The Solar Neutrino Problem thus came to be and it persisted for over thirty years. It is now known that the deficit in solar neutrinos (of electron neutrino flavour) was due to neutrino oscillations and that matter effects are important. Solar neutrino experiments played a key part in these discoveries and in recent developments in neutrino physics. This report summarizes Pontecorvo Neutrino Physics School lectures that explored the physics of solar neutrinos and the experiments that detected them. The lectures also included a look forward to future solar neutrino experiments and their physics goals and these are also discussed here.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1995

SPDE: Solar Plasma Diagnostic Experiment

The physics of the Solar corona is studied through the use of high resolution soft x-ray spectroscopy and high resolution ultraviolet imagery. The investigation includes the development and application of a flight instrument, first flown in May, 1992 on NASA sounding rocket 36.048. A second flight, NASA founding rocket 36.123, took place on 25 April 1994. Both flights were successful in recording new observations relevant to the investigation. The effort in this contract covers completion of the modifications to the existing rocket payload, its reflight, and the preliminary day reduction and analysis. Experience gained from flight 36.048 led us to plan several payload design modifications. These were made to improve the sensitivity balance between the UV and EUV spectrographs, to improve the scattered light rejection in the spectrographs, to protect the visible light rejection filter for the Normal Incidence X-ray Imager instrument (NIXI), and to prepare one new multilayer mirror coating to the NIXI. We also investigated the addition of a brassboard CCD camera to the payload to test it as a possible replacement for the Eastman type 101-07 film used by the SPDE instruments. This camera was included in the experimeter's data package for the Project Initiation Conference for the flight of NASA Mission 36.123, held in January, 1994, but for programmatic reasons was deleted from the final payload configuration. The payload was shipped to the White Sands Missile Range on schedule in early April. The launch and successful recovery took place on 25 April, in coordination with the Yohkoh satellite and a supporting ground-based observing campaign.

Bruner, Marilyn E.↗