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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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NASA NTRS2019

New Evidence for Third Harmonic Electromagnetic Radiation in Interplanetary Type III Solar Radio Bursts

This article provides new evidence for a third harmonic component in the electromagnetic radiation generated by interplanetary type III solar radio bursts observed locally near 1 AU. This evidence comes mainly from the analysis of the low-frequency radio emissions observed by the Wind spacecraft. The analysis examines, at high-time and high-frequency resolution, the local type III radiation that is occasionally observed at Wind. The associated Langmuir waves and energetic electron beams, as well as simultaneous observations from the Solar Terrestrial Relations Observatory (STEREO) and Ulysses spacecraft where possible, are used to confirm the local nature of the observed radiation and to help identify the solar origin. We find that the detection of a third harmonic component in the local type III radiation near 1 AU is exceedingly rare. However, our analyses indicate that, in addition to the more commonly observed second harmonic component, a third harmonic component is sometimes conspicuously evident in the local type III radiation. We find that the third harmonic component, when observed, is less intense than the second harmonic component, with the intensity ratio varying between 0.3 and 0.7. Sometimes the third harmonic component is expected to be detected, but it is not observed.

Interplanetary↗
NASA NTRS1978

Mechanisms and sites for astrophysical gamma ray line production

The production of gamma ray lines and estimates of line fluxes resulting from nuclear deexcitations, positron annihilation, and electron capture at various astrophysical sites are discussed. Supernova and nova explosions synthesize long-lived radioactive isotopes and eject them into space where they produce observable gamma ray lines by decaying into excited levels of daughter nuclei or by emitting positrons. Energetic charged particles in the interstellar medium, in supernova remants, in solar or stellar flares, and possibly in the vicinity of compact objects, produce gamma-ray lines by inelastic collisions which either excite nuclear levels or produce positrons and neutrons. Energetic particles can result from acceleration in time-varying magnetic fields (solar flares) or from gravitational accretion onto neutron stars and black holes. Electromagnetic processes in the strong magnetic fields of pulsars can produce positron-electron pairs, with line emission resulting from positron annihilation. Deexcitations of quantized states in strong magnetic fields can also produce lines.

Ramaty, R.↗
NASA NTRS2020

Small Electron Events Observed by Parker Solar Probe/IS⨀IS During Encounter 2

The current understanding of the characteristics of solar and inner heliospheric electron events is inferred almost entirely from observations made by spacecraft located at 1 astronomical unit (AU). Previous observations within 1 AU of the Sun, by the Helios spacecraft at ~0.3-1 AU, indicate the presence of electron events that are not detected at 1 AU or may have merged during transport from the Sun. Parker Solar Probe's close proximity to the Sun at perihelion provides an opportunity to make the closest measurements yet of energetic electron events. We present an overview of measurements of electrons with energies between ~17 keV and ~1 MeV made by the Parker Solar Probe Integrated Science Investigation of the Sun (IS⨀IS) instrument suite during Encounter 2 (2019 March 31-April 10 with perihelion of ~ 0:17 AU), including several small electron events. We examine these events in the context of the electromagnetic and solar wind environment measured by the FIELDS and SWEAP instruments on Parker Solar Probe. We find most of these electron enhancements to be associated with type III radio emissions that reach the local plasma frequency and one enhancement that appears to be primarily associated with abrupt changes in the local magnetic field. Together, these associations suggest that these are indeed the first measurements of energetic electron events within 0.2 AU.

Sun flares↗
NASA NTRS1966

Enhanced fluctuations in plasmas.

Enhanced plasma fluctuations produced by suprathermal electron effect on emission and scattering of electromagnetic waves, noting analogy with corona plasma

PLASMA-ELECTROMAGNETIC INTERACTION↗
NASA NTRS1989

Correlated plasma wave, magnetic field, and energetic ion observations in the ion pickup region of Comet Giacobini-Zinner

Relationships between simultaneous plasma wave, magnetic field, and energetic heavy ion data obtained by the International Cometary Explorer (ICE) spacecraft in the large-scale solar wind particle pickup region surrounding Comet Giacobini-Zinner are examined. In particular, consideration is given to the conditions under which electrostatic emissions at frequencies of a few kilohertz and electromagnetic waves at a few tens of hertz are observed. It is shown that the data are consistent with the view that the kilohertz electrostatic emissions result from a beam-type instability excited by the pickup photoelectron population when the angle alpha between the magnetic field and the plasma velocity vectors is not too large. The data also suggest that the few tens of hertz electromagnetic waves may be excited by a ring-type instability associated with the pickup ion population, which occurs when the magnetic field is near to orthogonality with the flow.

Richardson, I. G.↗
NASA NTRS2016

Scientific Considerations for Future Spectroscopic Measurements from Space of Activity on the Sun

High-resolution UV and X-ray spectroscopy are important to understanding the origin and evolution of magnetic energy release in the solar atmosphere, as well as the subsequent evolution of heated plasma and accelerated particles. Electromagnetic radiation is observed from plasma heated to temperatures ranging from about 10 k K to above 10 MK, from accelerated electrons emitting photons primarily at X-ray energies, and from ions emitting in gamma rays. These observations require space-based instruments sensitive to emissions at wavelengths shorter than the near UV. This article reviews some recent observations with emphasis on solar eruptive events, the models that describe them, and the measurements they indicate are needed for substantial progress in the future. Specific examples are discussed demonstrating that imaging spectroscopy with a cadence of seconds or better is needed to follow, understand, and predict the evolution of solar activity. Critical to substantial progress is the combination of a judicious choice of UV, EUV, and soft X-ray imaging spectroscopy sensitive to the evolution of this thermal plasma combined with hard X-ray imaging spectroscopy sensitive to suprathermal electrons. The major challenge will be to conceive instruments that, within the bounds of possible technologies and funding, have the flexibility and field of view to obtain spectroscopic observations where and when events occur while providing an optimum balance of dynamic range, spectral resolution and range, and spatial resolution.

Holman, Gordon D.↗
NASA NTRS1985

Definition of the cusp

The history of the dayside or polar cusp is reviewed briefly, beginning with the work of Chapman and Ferraro, Axford and Hines, and Dungey. Solar wind plasma comes down the cusp to low altitudes; the remarkably broad area over which this penetration occurs prompted the use of the term cleft, apparently at the foot of the entry layer inside the magnetopause. The consensus of discussion at the workshop was that cusp should refer mainly to the narrow feature in the magnetic profile. Cleft would refer to the broader region defined by the solar wind plasma (perhaps somewhat modified by acceleration or retardation processes); distinctive features observable in the ionosphere or on the ground are photo-emission, enhanced plasma density and temperature, plasma convection, electromagnetic waves, and turbulence.

Heikkila, W. J.↗
NASA NTRS2012

Solar Eruptive Events

It s long been known that the Sun plays host to the most energetic explosions in the solar system. But key insights into the forms that energy takes have only recently become available. Solar flares have been phenomena of both academic and practical interest since their discovery in 1859. From the academic point of view, they are the nearest events for studying the explosive release of energy in astrophysical magnetized plasmas. From the practical point of view, they disrupt communication channels on Earth, from telegraph communications in 1859 to radio and television signals today. Flares also wreak havoc on the electrical power grid, satellite operations, and GPS signals, and energetic charged particles and radiation are dangerous to passengers on high-altitude polar flights and to astronauts. Flares are not the only explosive phenomena on the Sun. More difficult to observe but equally energetic are the large coronal mass ejections (CMEs), the ejection of up to ten billion tons of magnetized plasma into the solar wind at speeds that can exceed 1000 km/s. CMEs are primarily observed from the side, with coronagraphs that block out the bright disk of the Sun and lower solar atmosphere so that light scattered from the ejected mass can be seen. Major geomagnetic storms are now known to arise from the interaction of CMEs with Earth's magnetosphere. Solar flares are observed without CMEs, and CMEs are observed without flares. The two phenomena often occur together, however, and almost always do in the case of large flares and fast CMEs. The term solar eruptive event refers to the combination of a flare and a CME. Solar eruptive events generate a lot of heat: They can heat plasma to temperatures as high at 50 million Kelvin, producing radiation across the electromagnetic spectrum. But that s not all. A fascinating aspect of solar eruptive events is the acceleration of electrons and ions to suprathermal often relativistic energies. The accelerated particles are primarily observed through their emissions in the higher energy x-ray, gamma-ray, and rf regimes. The radio and x-ray emissions are both from mildly relativistic electrons with energies of tens of keV and above. Gamma-ray line emission comes indirectly from accelerated protons and heavier ions with MeV and higher energies. The difficulty in collecting spatially and spectrally resolved x-ray and gamma-ray data has long been a barrier to learning about the accelerated particles. Considerable progress has been made in the last decade in understanding the relationship between the flare, the CME, energy release, and particle acceleration. But many new questions have also arisen. In this article, I describe those new insights and our evolving understanding of solar eruptive events.

Holman, Gordon D.↗
NASA NTRS1998

Constraints on Nonlinear and Stochastic Growth Theories for Type 3 Solar Radio Bursts from the Corona to 1 AU

Existing, competing theories for coronal and interplanetary type III solar radio bursts appeal to one or more of modulational instability, electrostatic (ES) decay processes, or stochastic growth physics to preserve the electron beam, limit the levels of Langmuir-like waves driven by the beam, and produce wave spectra capable of coupling nonlinearly to generate the observed radio emission. Theoretical constraints exist on the wavenumbers and relative sizes of the wave bandwidth and nonlinear growth rate for which Langmuir waves are subject to modulational instability and the parametric and random phase versions of ES decay. A constraint also exists on whether stochastic growth theory (SGT) is appropriate. These constraints are evaluated here using the beam, plasma, and wave properties (1) observed in specific interplanetary type III sources, (2) predicted nominally for the corona, and (3) predicted at heliocentric distances greater than a few solar radii by power-law models based on interplanetary observations. It is found that the Langmuir waves driven directly by the beam have wavenumbers that are almost always too large for modulational instability but are appropriate to ES decay. Even for waves scattered to lower wavenumbers (by ES decay, for instance), the wave bandwidths are predicted to be too large and the nonlinear growth rates too small for modulational instability to occur for the specific interplanetary events studied or the great majority of Langmuir wave packets in type III sources at arbitrary heliocentric distances. Possible exceptions are for very rare, unusually intense, narrowband wave packets, predominantly close to the Sun, and for the front portion of very fast beams traveling through unusually dilute, cold solar wind plasmas. Similar arguments demonstrate that the ES decay should proceed almost always as a random phase process rather than a parametric process, with similar exceptions. These results imply that it is extremely rare for modulational instability or parametric decay to proceed in type III sources at any heliocentric distance: theories for type III bursts based on modulational instability or parametric decay are therefore not viable in general. In contrast, the constraint on SGT can be satisfied and random phase ES decay can proceed at all heliocentric distances under almost all circumstances. (The contrary circumstances involve unusually slow, broad beams moving through unusually hot regions of the Corona.) The analyses presented here strongly justify extending the existing SGT-based model for interplanetary type III bursts (which includes SGT physics, random phase ES decay, and specific electromagnetic emission mechanisms) into a general theory for type III bursts from the corona to beyond 1 AU. This extended theory enjoys strong theoretical support, explains the characteristics of specific interplanetary type III bursts very well, and can account for the detailed dynamic spectra of type III bursts from the lower corona and solar wind.

Cairns, Iver H.↗
NASA NTRS2004

Electromagnetic Formation Flight (EMFF) for Sparse Aperture Arrays

Traditional methods of actuating spacecraft in sparse aperture arrays use propellant as a reaction mass. For formation flying systems, propellant becomes a critical consumable which can be quickly exhausted while maintaining relative orientation. Additional problems posed by propellant include optical contamination, plume impingement, thermal emission, and vibration excitation. For these missions where control of relative degrees of freedom is important, we consider using a system of electromagnets, in concert with reaction wheels, to replace the consumables. Electromagnetic Formation Flight sparse apertures, powered by solar energy, are designed differently from traditional propulsion systems, which are based on V. This paper investigates the design of sparse apertures both inside and outside the Earth's gravity field.

Kwon, Daniel W.↗
NASA NTRS1991

Neutrino-heated stars and broad-line emission from active galactic nuclei

Nonthermal radiation from active galactic nuclei indicates the presence of highly relativistic particles. The interaction of these high-energy particles with matter and photons gives rise to a flux of high-energy neutrinos. In this paper, the influence of the expected high neutrino fluxes on the structure and evolution of single, main-sequence stars is investigated. Sequences of models of neutrino-heated stars in thermal equilibrium are presented for masses 0.25, 0.5, 0.8, and 1.0 solar mass. In addition, a set of evolutionary sequences for mass 0.5 solar mass have been computed for different assumed values for the incident neutrino energy flux. It is found that winds driven by the heating due to high-energy particles and hard electromagnetic radiation of the outer layers of neutrino-bloated stars may satisfy the requirements of the model of Kazanas (1989) for the broad-line emission clouds in active galactic nuclei.

Macdonald, James↗
NASA NTRS1974

Solar flux and its variations

Current knowledge of the electromagnetic solar spectrum and radiant energy output for conditions of quiet and active sun is summarized. Discussed are temporal behavior and occurrence of solar phenomena such as active regions, calcium plages and flares, X-rays, UV and other energetic emissions, and their relationships to 11- and 22-year solar cycles.

Smith, E. V. P.↗
NASA NTRS1984

Radio Science

Radio science experiments use electromagnetic waves to probe or study the solar system. Three major research areas were identified within this discipline: radio astronomy, radar astronomy, and celestial mechanics. Radio astronomy (or radiometry) is the detection and measurement of naturally produced radio frequency emissions. Sources include surfaces, atmospheres, rings, and plasmas. Radar astronomy is the observation of man-made signals after their interaction with a target. Both imaging and non-imaging results. Celestial mechanics includes all studies related to the motions of (and gravity fields of) bodies within the solar system. These should not be considered rigid separations, but aid in the discussion of the data sets.

Source record↗
NASA NTRS1981

Emissivities of strong ultraviolet lines

Using atomic data published during the last few years for Li to Mg sequence ions, we have carried out multilevel calculations over a range of electron pressures to obtain absolute intensities for spectral lines in the UV and EUV regions of the electromagnetic spectrum. Both the pressure dependence of the ionization balance and the dependence of line emissivities on the populations of metastable levels are taken into account. These line emissivities may be used to obtain plane-parallel model atmospheres for different solar transition region structures, and in general for other late-type stars which have observable lines over a wide range of excitation potentials.

Raymond, J. C.↗
NASA NTRS1974

Non-relativistic solar electrons

Summary of both the direct spacecraft observations of nonrelativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the sun and in the interplanetary medium. These observations bear on three physical processes basic to energetic particle phenomena: (1) the acceleration of particles in tenuous plasmas; (2) the propagation of energetic charged particles in a disordered magnetic field, and (3) the interaction of energetic charged particles with tenuous plasmas to produce electromagnetic radiation. Because these electrons are frequently accelerated and emitted by the sun, mostly in small and relatively simple flares, it is possible to define a detailed physical picture of these processes. In many small solar flares nonrelativistic electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. Nonrelativistic electrons exhibit a wide variety of propagation modes in the interplanetary medium, ranging from diffusive to essentially scatter-free. This variability in the propagation may be explained in terms of the distribution of interplanetary magnetic field fluctuations.

Lin, R. P.↗
NASA NTRS1993

The FNAS Gamma Ray Observatory

Highly stressed and nonpotential magnetic fields in solar active region are believed to be the site and source of M or X class flares which release as much as 10(exp 32) ergs in a periods of 10 to 1000 s with intense emission detected over most of the electromagnetic spectrum. Such M or X class flares are the most likely gamma-ray emission candidates since sheared magnetic field is the means of energy storage for flare events. We have studied the correlation between 'nonpotentiality' parameters such as 'shear angle' and maximum magnetic field strength with the occurrences gamma-ray events. Also the angle of deviation of the magnetic field from the line of sight was studied since the bremsstrahlung gamma-ray beam produced by relativistic ions and electrons is highly directional in the forward direction and required non-vertical field-lines for the detection of the disk-center events.

Emslie, A. Gordon↗
NASA NTRS1992

Numerical simulations of bursty radio emissions from planetary magnetospheres

One-dimensional electromagnetic particle simulations are used to investigate the characteristics of radiation from electron beams with a large temperature anisotropy, in order to identify the origin of the smooth and bursty radio emissions from Uranus and Neptune observed by the Voyager spacecraft. It is shown that these electron beams, which would typically originate from the sporadic or impulsive injections of energetic electrons, can generate electromagnetic radiation which should be able to escape into the solar wind despite the growth of the electrostatic instability. The amount of radiation with frequencies above the local x mode cutoff increases with the beam speed. It is also proposed that some of the radiation generated below the local x mode cutoff may also be able to escape the plasma and be detected remotely via mode conversion between regions where field-aligned currents produce local perturbations in the magnetic field.

Winglee, R. M.↗
NASA NTRS2017

Swift and NuSTAR Observations of GW170817: Detection of a Blue Kilonova

With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counter part of the binary neutron star merger GW170817.The bright, rapidly fading UV emission indicates a high mass (0.03 solar masses) wind-driven outflow with moderate electron fraction (Ye ≈ 0.27). Combined with the x-ray limits, we favor an observer viewing angle of ≈30° away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultra relativistic, highly collimated ejecta (a gamma-ray burst afterglow).

Evans, P. A.↗