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At least 685 records · Page 38
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NASA NTRS1972

Geomagnetic field distortions and their effects on radiation belt particles.

One of the quadrupole terms in the main geomagnetic field is found to contribute to a north-south 'shear distortion' of the particle-drift shells, whereas one of the octupole components causes a longitude-dependent radial deformation and associated 'drift-shell splitting.' The collective action of all higher multipoles on trapped-particle motion is then used to analyze the 'true' anomalies or distortions of the internal geomagnetic field that are independent of the quadrupole-related eccentricity of the main dipole. These 'true' anomalies must originate in upper-mantle or crustal perturbations that lie relatively near the earth's surface on both sides of the mid-Atlantic ridge; they influence trapped-particle drift shells only where the latter have their closest approach to the earth (South Atlantic and South African areas). The quadrupole and octupole perturbations, on the other hand, obviously originate deep in the earth's core. In the final part of this review, we discuss the effects of external magnetospheric currents. A time-dependent symmetric ring current causes drift shells to be displaced radially, with associated particle acceleration; magnetopause currents introduce a day-night asymmetry, causing shell splitting.

Roederer, J. G.↗
NASA NTRS1972

The flares of August 1972

Analysis is made of observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra. In each flare the observations fit a model of particle acceleration in the chromosphere with emission produced by impart and by heating by the energetic electrons and protons. The region showed twisted flux and high gradients from birth, and flares appear due to strong magnetic shears and gradients across the neutral line produced by sunspot motions. Post flare loops show a strong change from sheared, force-free fields parallel to potential-field-like loops, perpendicular to the neutral line above the surface.

Zirin, H.↗
NASA NTRS1972

Applied Superconductivity Conference, 5th, Annapolis, Md., May 1-3, 1972, Proceedings.

Recently developed practical applications of superconductivity are described in papers dealing with transportation and propulsion, power generation, power transmission, special-purpose magnets, superconducting materials, Josephson junctions, and microwave systems. Important topics considered include tracked magnetic-cushion vehicles, electrical machines, cryogenic underground power transmission systems, magnets for fusion reactors and particle accelerators, thin-film superconductors, effects of the structural characteristics of materials on transition temperatures, frequency measurement with Josephson devices, and superconducting scientific instruments. Individual items are announced in this issue.

Source record↗
NASA NTRS1973

Nuclear gamma rays from solar flares

Solar gamma ray line emission and the source of that emission at 0.5, 2.2, 4.4, and 6.1 MeV were reviewed and updated. Data were taken from OSO-7 observations of the August 4 and 7 solar flares. A comparison, made between predicted and observed emissions, show that the 0.5, 2.2, 4.4, and 6.1 MeV lines are produced by positron annihilation, deuterium deexcitation following neutron capture on hydrogen, and the deexcitation of the first nuclear levels of C-12 and O-16 respectively. Accelerated particle spectra at the sun independent of assumed interaction were determined.

Ramaty, R.↗
NASA NTRS1974

Effect of small flares in the neutral component of secondary cosmic radiation

The results are presented of an investigation of the effect of small flares, scale divisions 1 and 1(+), in the neutron component of secondary cosmic radiation from the data of neutron supermonitors at the stations of Kiev, Bukhta Tiksi, and Deep River. It is shown that flares of scale divisions 1 and 1(+) are accompanied by an effect in the neutron component amounting to about 0.4%. A mechanism is presented for calculating the outflow of particles accelerated in small flares, owing to diffusion across the magnetic field of a trap.

Bondarenko, V. I.↗
NASA NTRS1974

Solar Physics - Plasma Physics Workshop

A summary of the proceedings of a conference whose purpose was to explore plasma physics problems which arise in the study of solar physics is provided. Sessions were concerned with specific questions including the following: (1) whether the solar plasma is thermal or non-themal; (2) what spectroscopic data is required; (3) what types of magnetic field structures exist; (4) whether magnetohydrodynamic instabilities occur; (5) whether resistive or non-magnetohydrodynamic instabilities occur; (6) what mechanisms of particle acceleration have been proposed; and (7) what information is available concerning shock waves. Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments.

Baum, P. J.↗
NASA NTRS1973

Nightside energetic particle decreases at the synchronous orbit

More than 100 cases of major decreases of proton and electron fluxes at the synchronous orbit have been observed and interpreted as a movement of the energetic particle trapping boundary earthward of 6.6 earth radii before the substorm expansion phase. These events are observed only between 1700 and 0800 LT and are consistent with the existence of a westward magnetospheric electric field of a few tenths of a millivolt per meter before substorm expansion. Most substorm particle events seen on the nightside do not exhibit this behavior, presumably because the trapping boundary moves inside 6.6 earth radii only during major events. Such events show evidence of particle acceleration, which probably was concentrated at higher L values, near the instantaneous location of the trapping boundary.

Bogott, F. H.↗
NASA NTRS1973

Some physical parameters of micrometeoroids

Detailed morphological parameters (depth/diameter ratio, circularity index) of microcraters in the 0.2 to 100 micron diameter range were obtained via SEM techniques for three lunar glass surfaces. The depth/diameter ratios are typically 0.5 to 0.8 with a range of 0.3 to 1.3. The circularity index varies from 0.4 to 1.0 with a pronounced maximum at 0.7 to 0.9. These parameters are compared with microcraters produced in the laboratory via electrostatic particle accelerators. The following conclusions are drawn: The great majority of observed crater depths are compatible with micrometeoroid densities of 2 to 4 g/cu cm; crater depths are incompatible for projectile densities less than 1 g/cu cm and greater than 7 g/cu cm. The circularity index of microcrater pits indicates rather equidimensional, if not spherical, projectiles. Needles, platelets and other highly irregular shapes can be excluded. Less than 5% of all craters observed may offer different conclusions.

Brownlee, D. E.↗
NASA NTRS1974

Phase A conceptual design study of the Atmospheric, Magnetospheric and Plasmas in Space (AMPS) payload

The 12 month Phase A Conceptual Design Study of the Atmospheric, Magnetospheric and Plasmas in Space (AMPS) payload performed within the Program Development Directorate of the Marshall Space Flight Center is presented. The AMPS payload makes use of the Spacelab pressurized module and pallet, is launched by the space shuttle, and will have initial flight durations of 7 days. Scientific instruments including particle accelerators, high power transmitters, optical instruments, and chemical release devices are mounted externally on the Spacelab pallet and are controlled by the experimenters from within the pressurized module. The capability of real-time scientist interaction on-orbit with the experiment is a major characteristic of AMPS.

Source record↗
NASA NTRS1974

Magnetic fields in flares and active prominences. II - The field configuration in some active prominences

Study of the longitudinal magnetic field in a number of active limb prominences showing fields in excess of 30 G. The objects fall into three groups: surges, caps, and active-region prominences. There appears to be an upper limit of 150 to 200 G for the field strength in prominences. A model of surges is presented in which a presurge axisymmetric magnetic field is established by a line current in the corona. Particle acceleration in surges is observed, which indicates that V x B is not equal to zero in these objects during periods comparable to the Alfven transit time. The strong fields observed in caps seem to run between parts of active regions in accordance with Hale's law of sunspot group polarities.

Tandberg-Hanssen, E.↗
NASA NTRS1974

Solar flares

A review of the knowledge about solar flares which has been obtained through observations from the earth and from space by various methods. High-resolution cinematography is best carried out at H-alpha wavelengths to reveal the structure, time history, and location of flares. The classification flares in H alpha according to either physical or morphological criteria is discussed. The study of flare morphology, which shows where, when, and how flares occur, is important for evaluating theories of flares. Consideration is given to studies of flares by optical spectroscopy, radio emissions, and at X-ray and XUV wavelengths. Research has shown where and possibly why flares occur, but the physics of the instability involved, of the particle acceleration, and of the heating are still not understood.

Zirin, H.↗
NASA NTRS1975

Hard X-ray bursts from flare behind the solar limb

The determination of the location of the region of origin of hard X-rays is important in evaluating the importance of 10-100 keV electrons in solar flares and in understanding flare particle acceleration. At present only limb-occulted events are available to give some information on the height of X-ray emission. In fifteen months of OSO-7 operation, nine major soft X-ray events had no reported correlated H alpha flare. We examine the hard X-ray spectra of eight of these events with good candidate X-ray flare producing active regions making limb transit at the time of the soft X-ray bursts. All eight bursts had significant X-ray emission in the 30-44 keV range, but only one had flux at the 3 sigma level above 44 keV. The data are consistent with most X-ray emission occurring in the lower chromosphere, but some electron trapping at high altitudes is necessary to explain the small nonthermal fluxes observed.

Mckenzie, D. L.↗
NASA NTRS1975

Solar emissions associated with impulsive solar flare X-rays

The major characteristics of some of the flare emissions are identified. The time-intensity profile of solar flare emissions is presented, where impulsive X-rays, impulsive microwave, optical and EUV emissions are emitted during the impulsive (flash) phase of a solar flare. The energy emitted in various electromagnetic emissions during flares with an impulsive phase is reported along with estimates of the kinetic energy of the energetic electrons and the energy of the hot plasma. Although the magnitudes of the various flare emissions vary from one flare to another, the total kinetic energy of the nonthermal particles produced during the impulsive phase is a significant fraction of the total flare energy (thermal and nonthermal). The process responsible for particle acceleration in some flares is shown to have a relatively high efficiency.

Kane, S. R.↗
NASA NTRS1974

The flash phase of solar flares - Satellite observations of electrons

Satellite observations of solar electrons bearing on flare particle acceleration and the generation of radio and X-ray emission are reviewed. The observations support a two-stage acceleration process for electrons, one stage commonly occurring at the flare flash phase and accelerating electrons up to about 100 keV, and a second stage occurring only in large proton flares and accelerating electrons up to relativistic energies. The location of the acceleration region appears to be no lower than the lower corona. The accelerated non-relativistic electrons generate type III radio burst emission as they escape from the sun. Direct spacecraft observations of the type III emission generated near 1 AU and the energetic electrons, provide quantitative information on the characteristics of the electrons exciting type III emission, the production of plasma waves, and the conversion from plasma waves to electromagnetic radiation.

Lin, R. P.↗
NASA NTRS1975

Measurements on the development of cascades in a tungsten-scintillator ionization spectrometer

The response of a tungsten-scintillator ionization spectrometer to accelerated particle beams has been investigated. Results obtained from exposure of the approx. 1000 g/sq cm apparatus to 5, 10, and 15 GeV/c electrons and pions as well as to 2.1 GeV/nucleon C-12 and O-16 ions are presented. These results include cascade-development curves, fractions of the primary energy measured by the spectrometer, and resolutions of the apparatus for measuring the primary energies. For 15 GeV/c electrons, an average of about 82% of the incident energy is measured by the apparatus with resolution (normal standard deviation) of about 6%. For 15 GeV/c pions, an average of about 65% of the incident energy is measured with resolution of about 18%. The energy resolution improves with increasing energy and with increasing depth of the spectrometer.

Cheshire, D. L.↗
NASA NTRS1975

The 10 sheath-accelerated electrons and ions

A model is presented that suggests that plasma sheaths form between the ionospheric plasma moving with Io and the ambient plasma corotating with Jupiter. Potentials across these sheaths could be as high as 580 kV which is the motional emf across Io's ionosphere. Electrons and ions can be accelerated across these sheaths. The sheaths may exist at the top of the Io ionosphere with characteristic thicknesses of 1/4 kilometers. The model is consistent with the Pioneer observations of 0.15 MeV electrons at the inner edge of Io's L-shell and the enhanced number density of low-energy protons at the outer edge. Ion sputtering of the Io surface is discussed and may explain the presence of atomic hydrogen and sodium in the vicinity of Io. Also these accelerated particles may be important to the formation of the Io ionosphere. High electron flux which may lead to decametric radio emissions, Jovian atmospheric heating and optical and X-ray emissions is also discussed.

Shawhan, S. D.↗
NASA NTRS1976

The acceleration of energetic particles in the interplanetary medium by transit-time damping

Transit time damping is examined as a possible means for accelerating low energy particles in co-rotating streams and interstellar ions. Data show that: the protons in co-rotating streams may be accelerated by transient-time damping the small-scale variations in the field magnitude that are observed at a low level in the inner solar system. The interstellar ions may be accelerated by transit time damping large-scale field variations in the outer solar system.

Fisk, L. A.↗
NASA NTRS1976

Preliminary Results from the European Space Agency's COS-B satellite for gamma-ray astronomy

The COS-B satellite carries a single experiment, capable of detecting gamma rays with energies greater than 30 MeV. Its objectives are to study the spatial, energy, and time characteristics of high energy radiation of galactic and extragalactic origin. The capability to search for gamma ray pulsations is enhanced by the inclusion in the payload of a proportional counter sensitive to X-rays of 2-12 Kev. The experiment was calibrated using particle accelerators. The results of these measurements are presented and the performance of the system in orbit is discussed.

Swanenburg, B.↗