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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The abundances of hydrogen, helium, oxygen, and iron accelerated in large solar particle events

Energy spectra measured in 10 large flares with the University of Maryland/Max-Planck-Institut sensors on ISEE I and Goddard Space Flight Center sensors on IMP 8 allowed us to determine the average H, He, O, and Fe abundances as functions of energy in the range of about 0.3-80 MeV/nucleon. Model fits to the spectra of individual events using the predictions of a steady state stochastic acceleration model with rigidity-dependent diffusion provided a means of interpolating small portions of the energy spectra not measured with the instrumentation. Particles with larger mass-to-charge ratios were relatively less abundant at higher energies in the flare-averaged composition. The Fe/O enhancement at low SEP energies was less than the Fe/O ratios observed in He-3-rich flares. Unlike the SEP composition averaged above 5 MeV/nucleon, the average SEP abundances above 0.3 MeV/nucleon were similar to the average solar wind.

Mazur, J. E.↗
NASA NTRS1992

Gamma-ray and X-ray time profiles expected from a trap-plus-precipitation model for the 7 June 1980 and 27 April 1981 solar flares

Hard X-ray and prompt gamma-ray line emissions are the most direct signatures of, respectively, electron and ion acceleration during solar flares. The peak time of the gamma-ray emission for some events is delayed with respect to the peak time of the hard X-ray flux. These delays are either interpreted as evidence of a two-step acceleration process or as the result of the partial trapping and/or propagation of the particles from the acceleration region to the emission sites. It was shown earlier that hard X-ray and prompt gamma-ray line delays can be qualitatively reproduced in the frame of the latter hypothesis with models describing the time-dependent transport of energetic electrons and ions between these two sites. Here we focus on the close examination of the temporal evolution of X-ray and gamma-ray fluxes for the 7 June 1980 and 27 April 1981 events which exhibit delays between X-ray and gamma-ray maxima. The parameters of the ambient medium and of the accelerated particles are deduced for the two events and it is shown that the relative timing of X-ray and gamma-ray emissions is quantitatively reproduced in the present context.

Hulot, E.↗
NASA NTRS1979

Observed distribution functions of H, He, C, O, and Fe in corotating energetic particle streams: Implications for interplanetary acceleration and propagation

Distribution functions for H, He, C, O, and Fe derived from our IMP 8 measurements of approximately 0.15 to approximately 8 MeV/nucleon particles in three corotating streams observed near earth are shown to have a simple exponential dependence on the particle speed. The e-folding speed, v sub o, is typically 0.01c, is found to be the same for the distribution functions of all elements examined, and varies little from one corotating event to the next. The relative abundances of energetic particles in these events resemble most closely the solar coronal composition and, thus, presumably that of the solar wind. These results may imply that the acceleration of these particles, which occurs in corotating interaction regions at several AU from the sun, is by a statistical process.

Gloeckler, G.↗
NASA NTRS1979

Observed distribution functions of H, He, C, O, and Fe in corotating energetic particle streams - Implications for interplanetary acceleration and propagation

Distribution functions for H, He, C, O, and Fe derived from our IMP 8 measurements of about 0.15 to 8 MeV per nucleon particles in three corotating streams observed near Earth are shown to have a simple exponential dependence on the particle speed. The e-folding speed, typically 0.01c, is found to be the same for the distribution functions of all elements examined, and varies little from one corotating event to the next. The relative abundances of energetic particles in these events resemble most closely the solar coronal composition and thus, presumably, that of the solar wind. These results may imply that acceleration of these particles, which occurs in corotating interaction regions at several AU from the sun, is by a statistical process.

Gloeckler, G.↗
NASA NTRS1980

The striated dust tail of Comet West 1976 VI as a particle fragmentation phenomenon

The motions of 16 striae in the dust tail of Comet West are studied. It is found that all 16 striae have originated from particle ejections, and that the particles responsible for the formation of a discrete striae must be emitted simultaneously, be subjected to the same repulsive acceleration in the tail, and break up simultaneously. A strong correlation is found between the ejection times and the times of known explosive events. The repulsive accelerations of particle fragments in the striae vary from 0.6 to 2.7 times the solar attraction, indicating submicron grains of strongly absorbing materials. The repulsive acceleration of parent particles range from 0.55 to 1.10, which is only slightly smaller than those of their fragments and suggests highly nonspherical shapes of parents. The mass of dust in an average striae is estimated to be one-billion grams. Rotational bursting is discussed as a possible fragmentation mechanism. The absence of measurable effects of the Lorentz force indicate an upper limit of a few volts for the electric charge of the fragments.

Sekanina, Z.↗
NASA NTRS1983

The composition, propagation and acceleration of energetic solar particles - A review of United States research 1979-1982

The present review has the objective to cover major developments in American research related to solar energetic particles, both observational and theoretical, taking into account the period from late 1978 to late 1982. It is pointed out that particular progress has been made in the area of solar energetic particle composition with respect to elemental, isotopic, and the distribution of charge states. This progress is primarily the result of improved instrumentation available at a time of higher solar activity. An important aspect of solar particle studies is to understand the propagation of particles from the vicinity of the sun through interplanetary space to wherever the observing instruments are located. Almost all mathematical models for the transport of solar cosmic rays are derived in some sense from the same general Boltzmann or Vlasov equations. Attention is also given to advances related to an understanding of coronal propagation, and acceleration and injection processes.

Mcguire, R. E.↗
NASA NTRS1999

Multi-Wavelength Analysis of the March 26, 1991: Solar Flare

We have engaged in detailed multi-wavelength analysis of the March 26, 1991, solar flare in order to develop a method of diagnostics of the physical processes responsible for the efficient acceleration of charged particles to high energies and also for diagnostics of the photospheric response to the injection of the accelerated particles. Consideration of this particular flare is of special interest because to date it is the only flare in which the gamma-ray emission with energies of 20-1000 MeV was registered throughout the entire development of the event in the optical, radio and soft x-ray bands. individual registration by the GAMMA-1 telescope of the energy and precise time for each registered gamma-ray photon allowed the maximum detailed investigation of the energy spectrum and flux evolution during the flare.

Kurt, V. G.↗
NASA NTRS1979

Electron calibration of instrumentation for low energy, high intensity particle measurements at Mercury

Unique identification of the high intensity, impulsively accelerated charged particle fluxes discovered during Mariner 10's first encounter with Mercury (March 1974) requires a detailed knowledge of the responses of the two University of Chicago charged particle telescopes to low energy fluxes over a wide dynamic range of flux levels. The results of detailed analyses show that these telescopes can separate and identify unambiguously the presence of electron and proton fluxes for a wide range of electron spectra and intensities in the relevant overall range of about 30 keV to 2 MeV.

Christon, S. P.↗
NASA NTRS1975

Differential spectra and phase space densities of trapped electrons at Jupiter

Using Pioneer 10 data, differential spectra and phase-space densities have been constructed for trapped electrons at Jupiter. These quantities should assist in calculating synchrotron radiation from these particles and in evaluating the diffusion mechanisms that accelerate the particles. Absorption by the moons Io and Europa is evident, and injection by Io is demonstrated by a density peak in phase space, which demands a local source. There is also a rapid decrease in density between the moons, which could call for either a local loss mechanism or nonlocal losses fed by diffusion.

Mcilwain, C. E.↗
NASA NTRS1991

Consequences of wave-particle interactions on chaotic acceleration

The recent model of Ashour-Abdalla et al. (1991) has proposed that the earth's plasma sheet can be formed by chaotic acceleration in a magnetotail-like field configuration. The ion velocity distributions created by chaotic acceleration have unstable features and represent robust free energy sources for kinetic plasma waves that can modify the original distributions. In the plasma sheet boundary layer, field-aligned ion beamlets are formed which drive a host of instabilities creating a broadbanded noise spectrum and cause thermal spreading of the beamlets. In addition, there is strong heating of any cold background plasma that may be present. In the central plasma sheet, ion antiloss cone distributions are created which are unstable to very low frequency waves that saturate by filling the antiloss cone.

Schriver, David↗
NASA NTRS1979

Observations of energetic particles in the near and far interplanetary medium

Recent experimental results suggest that acceleration of particles to energies as high as 30 MeV/nucleon is commonplace in the interplanetary medium beyond several AU, and that most of the less than approximately 10 MeV/nucleon particles observed near earth, especially at solar minimum, are predominantly interplanetary in origin. Experimental observations of the anomalous 'cosmic-ray' component and of corotating particle streams are reviewed, with emphasis on the composition of these interplanetary particles. These direct observations, although still rudimentary, are already providing constraints necessary for developing realistic theoretical descriptions of interplanetary acceleration mechanisms and should thus help in understanding similar processes in other astrophysical objects.

Gloeckler, G.↗
NASA NTRS1979

Initial observations of low energy charged particles near the earth's bow shock on ISEE-1

Initial measurements from the ULECA sensor of the Max-Planck-Institut/University of Maryland experiment on ISEE 1 are reported. ULECA is an electrostatic deflection - total energy sensor consisting of a collimator, a deflection analyzer, and an array of solid-state detectors. The position of a given detector, which determines the energy per charge of an incident particle, together with the measured energy, determines the particle's charge state. It is found that a rich variety of phenomena are operative in the transthermal energy regime (about 10 keV/Q to 100 keV/Q) covered by ULECA. Specifically, observations are presented of locally accelerated protons, alpha particles, and heavier ions in the magnetosheath and upstream of earth's bow shock. Preliminary analysis indicates that the behavior of these locally accelerated particles is most similar at the same energy per charge.

Ipavich, F. M.↗
NASA NTRS1974

A new component of cosmic rays of unknown origin at a few MeV per nucleon

Recently discovered anomalies in the abundances and energy spectra of quiet time, extraterrestrial hydrogen, helium, carbon, nitrogen, and oxygen require serious revisions of origin theories to account for this new component of cosmic radiation. Abnormally large O/C and N/C ratios, long term intensity variations with time, and radial gradient measurements indicate a non-solar origin for these 2 to 30 MeV/nucleon particles. Ideas suggested to explain these measurements range from acceleration of galactic source material having an unusual composition to local acceleration of particles within the solar cavity. Observations are at present insufficient to choose between these alternate origin models.

Gloecker, G.↗
NASA NTRS1981

Measurements of bow shock particles far upstream from the earth

Electrons and ions moving upstream frequently appear at distances up to 240 earth radii from earth at times when the direction of the interplanetary magnetic field allows their propagation from the bow shock. Strong asymmetries in the ion angular pitch angle distribution are often observed, a consequence of the sharp gradient in guiding center density and very weak scattering. The gradient is due to the restricted spatial region over which these particles are accelerated. The solar wind electric field acts on these particles and produces striking effects in both the ion angular distributions and the ion energy spectra. The frequent occurrence of these effects implies that the source region of the diffuse ions at the bow shock is not more than a few tens of thousands of km.

Anderson, K. A.↗
NASA NTRS2006

Dynamic Theory of Relativistic Electrons Stochastic Heating by Whistler Mode Waves with Application to the Earth Magnetosphere

In the Hamiltonian approach an electron motion in a coherent packet of the whistler mode waves propagating along the direction of an ambient magnetic field is studied. The physical processes by which these particles are accelerated to high energy are established. Equations governing a particle motion by group symmetries of the problem were transformed in to a closed pair of nonlinear difference equations. The solutions of these equations have shown there exists the energetic threshold below that the electron motion is regular, and when the initial energy is above the threshold an electron moves stochastically. It is proved that the upper boundary of particle stochastic heating is conditioned by intrinsic property of the particle chaotic motion. Particle energy spectra and pitch angle electron scattering are described by the Fokker-Planck-Kolmogorov equations. It is shown that significant pitch angle diffusion occurs for the Earth radiation belt electrons with energies from a few keV up to a few MeV.

Khazanov, G. V.↗