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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 199 records · Page 11
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NASA NTRS2000

The Observational Consequences of Proton-Generated Waves at Shocks

In the largest solar energetic particle (SEP) events, acceleration takes place at shock waves driven out from the Sun by fast coronal mass ejections. Protons streaming away from strong shocks generate Alfven waves that trap particles in the acceleration region, limiting outflowing intensities but increasing the efficiency of acceleration to higher energies. Early in the events, with the shock still near the Sun, intensities at 1 AU are bounded and spectra are flattened at low energies. Elements with different charge-to-mass ratios, Q/A, differentially probe the wave spectra near shocks, producing abundance ratios that vary in space and time. An initial rise in He/H, while Fe/O declines, is a typical symptom of the non-Kolmogorov wave spectra in the largest events. Strong wave generation can cause cross-field scattering near the shock and unusually rapid reduction in anisotropies even far from the shock. At the highest energies, shock spectra steepen to form a "knee." For protons, this spectral knee can vary from approx. 10 MeV to approx. 1 GeV depending on shock conditions for wave growth. In one case, the location of the knee scales approximately as Q/A in the energy/nucleon spectra of other species.

Reames, Donald V.↗
NASA NTRS1994

Particle acceleration by an interplanetary shock-pair seen at Ulysses at 3.15 AU

Observations from the HI-SCALE instrument on Ulysses of the ions and electrons associated with an interplanetary shock-pair at about 3.15 AU are presented. An empirical model is used to derive the evolution of the particle distribution in the solar wind frame. The forward shock is shown to be the primary source of ion acceleration, while the weaker and younger reverse shock is found to trap particles in its vicinity. There is also evidence of electron acceleration at the forward shock. We find evidence of multiple shock encounters for both ions and electrons.

Tappin, S. J.↗
NASA NTRS1983

Research in space physics at the University of Iowa, 1982

The energetic particles and the electric, magnetic, and electromagnetic fields associated with the Earth, the Sun, the Moon, the planets, comets, and the interplanetary medium are examined. Matters under current investigation are following: energetic particles trapped in the Earth's magnetic field, origin and propagation of very low frequency radio waves and electrostatic, the magnetospheres of Jupiter, Saturn and prospectively Uranus and Neptune, diffusion of energetic particles in Saturn's magnetosphere, radio emissions from Jupiter and Saturn, solar modulation and the heliocentric radial dependence of the intensity of galactic cosmic rays, interplanetary propagation and acceleration of energetic particles, the theory of wave phenomena in turbulent plasmas, and basic wave-particle-chemical processes in the ionospheric plasma.

Vanallen, J. A.↗
NASA NTRS1980

Some possible effects of Jupiter's rings on the Jovian inner plasmasphere

The ionospheric plasma density on magnetic field lines threading the Jovian rings which are located inside approximately 1.8 Jupiter radii on the jovigraphic equatorial plane is calculated by using a rotating ion exosphere model. It is found that the bulk of the ionospheric particles on these field lines are on ballistic trajectories. On field lines approximately symmetric with respect to the jovigraphic equator, the ring, which to a first approximation would absorb the population of trapped particles, consequently has little effect. On field lines which are made asymmetric by the higher-order multipoles of Jupiter's field and the tilt of the dipole axis, the rings may have a significant effect. It is suggested that better definition of the rings' atmospheric and ionospheric properties is required to model these localized effects. If the rings are found to be an important plasma source for the inner magnetosphere, the present exospheric model will have to be revised.

Luhmann, J. G.↗
NASA NTRS1978

Research in space physics at the University of Iowa

Specific fields of current investigation by satellite observation and ground-based radio-astronomical and optical techniques are discussed. Topics include: aspects of energetic particles trapped in the earth's magnetic field and transiently present in the outer magnetosphere and the solar, interplanetary, and terrestrial phenomena associated with them; plasma flows in the magnetosphere and the ionospheric effects of particle precipitation, with corresponding studies of the magnetosphere of Jupiter, Saturn, and possibly Uranus; the origin and propagation of very low frequency radio waves in the earth's magnetosphere and ionosphere; solar particle emissions and their interplanetary propagation and acceleration; solar modulation and the heliocentric radial dependence of the intensity of galactic cosmic rays; radio frequency emissions from the quintescent and flaring sun; shock waves in the interplanetary medium; radio emissions from Jupiter; and radio astronomy of pulsars, flare stars, and other stellar sources.

Vanallen, J. A.↗
NASA NTRS1988

Signatures of particle acceleration at SN1987a

Young SNRs may be bright sources of energetic photons and neutrinos generated by the collisions of particles accelerated within the remnant. Due to the large opacity of the shell at these early times, a photon signal may be suppressed; at later times, due to adiabatic losses of the magnetically-trapped particles in the expanding envelope, both neutron and neutrino signals will begin to decrease. There is therefore a window during which the secondary photon signal will be at its maximum. It is presently noted that if the observed decline of the optical light curve of SN1987a is due to Ni-56, Co-56 decay, this may place upper limits on such other sources of light as a central pulsar.

Gaisser, T. K.↗
NASA NTRS1984

Energetic particles in the inner magnetosphere of Saturn

Present knowledge of energetic particles in Saturn's inner magnetosphere (within about ten Saturn radii) is reviewed. Rings of particulate matter and the satellites inside 10 Saturn radii reduce the population of particles with energy above 0.5 MeV to values of the order 1000 times less than would otherwise be present. On the other hand, sputtering and outgassing of satellite surfaces injects gas into the system. All trapped particles lie outside the magnetic shell through the outer edge of Ring A. The radial distribution of very energetic protons with energies above tens of MeV exhibits three major peaks at 3.37, 2.68, and 2.44 Saturn radii, each of which is bounded by nearly complete voids associated with rings and satellites. The distribution of electrons with energies above 0.040 MeV extends throughout the magnetosphere with an internal boundary at the outer edge of Ring A and exhibits spectral features indicative of relatively unimpeded resonant diffusion across the orbits of satellites.

Van Allen, J. A.↗
NASA NTRS1993

DE 1 particle and wave observations in Auroral Kilometric Radiation (AKR) source regions

The high-altitude plasma instrument on board the DE 1 satellite was operating during several near crossings of the AKR source in the nightside auroral region. Observations of electron distributions indicate a region of perpendicular heating adjacent to, and within, the source region. Loss cones, trapped particles, beams, and electron conical distributions are also observed near and within the source region, which extends perpendicular to the magnetic field line for at least 20 km. Near the AKR source region wave-particle interactions appear to have modified the observed electron distributions. We compare the observations to those predicted by recently published numerical simulations.

Menietti, J. D.↗
NASA NTRS1992

Galactic cosmic ray exposure estimates for SAGE-3 mission in polar orbit

An analysis of the effects of galactic cosmic ray (GCR) exposures on charge-coupled devices (CCDs) was performed for the SAGE-III 5-year mission in sun-synchronous orbit between 1996 and 2001. A detailed environment model used in conjunction with a geomagnetic vertical cut-off code provides the predicted 5-year fluence of GCR ions. A computerized solid model of the spacecraft was used to define the effective shield thickness distribution around the CCD detector. The particle fluences at the detector location are calculated with the Langley heavy-ion transport code, and these fluences are used in conjunction with estimated nuclear stopping powers to evaluate dosimetric quantities related to the detector degradation. A previous study analyzing effects of trapped particle and solar flare protons indicated an approximate 20 percent reduction in detector sensitivity for the mission. The galactic cosmic ray contribution was thought to be relatively small and therefore was not previously analyzed. The present study provides quantification of the GCR effects, which are found to contribute less than 1 percent of the total environment degradation.

Nealy, John E.↗
NASA NTRS1990

Global magnetic anomaly and aurora of Neptune

The large offset and tilt of Neptune's dipole magnetic field combine to create a global magnetic anomaly, analogous to but much more important than earth's South Atlantic Anomaly. Energetic particle precipitation loss within the Neptune anomaly creates 'atmospheric drift shadows' within which particle fluxes are greatly reduced. The energetic particle dropout observed by Voyager near closest approach occurred near the predicted times when Voyager passed within the atmospheric drift shadow. Extremely soft, structured bursts of ions and electrons within the drift shadow may result from plasma wave-induced pitch angle scattering of trapped particles confined near the magnetic equator. The dropout does not necessarily imply that Voyager passed through an earth-like discrete auroral zone, as earlier reported. The ion and electron fluxes observed within the dropout period correspond to particles that must precipitate to Neptune's atmosphere within the anomaly region. This anomaly precipitation can account for a major portion of the ultraviolet emissions previously identified as Neptune aurora.

Cheng, Andrew F.↗
NASA NTRS1974

The average motion of a charged particle in a dipole field

The numerical representation of the average motion of a charged particle trapped in a geomagnetic field is developed. An assumption is made of the conservation of the first two adiabatic invariants where integration is along a field line between mirror points. The averaged motion also involved the parameters defining the magnetic field line to which the particle is attached. Methods involved in obtaining the motion in the equatorial plane of model magnetospheres are based on Hamiltonian functions. The restrictions imposed by the special nature of the dipole field are defined.

Chen, A. J.↗
NASA NTRS1972

Stability of a steady, large amplitude whistler wave.

Study of the behavior of weak electrostatic waves in a collisionless magnetoplasma supporting a steady large amplitude whistler wave. All waves are assumed to propagate parallel to a uniform background magnetic field B sub zero. In the presence of the whistler wave fields each particle executes an oscillatory motion parallel to B sub zero, in addition to a translation along B sub zero and transverse motions. This oscillation causes the Landau resonance to be replaced by a series of new resonances between particles and the electrostatic modes. A distribution function for the perturbed plasma is constructed by solving the Vlasov equation, linearized in the electrostatic wave amplitudes. A dispersion relation is obtained and solved approximately for the growth/damping rate of the perturbations. Growing electrostatic modes are found to be approximately uncoupled. Trapped particles have a strong influence on the stability of the system.

Palmadesso, P. J.↗
NASA NTRS1992

Three-dimensional shielding effects on charged particle fluences measured in the P0006 experiment in LDEF

The azimuthal and polar angle distribution of the galactic cosmic ray particles (mostly relativistic iron) was measured in the main stack and four side stacks of the P0006 experiment located on the west end of the LDEF satellite. A clear shadowing effect of the radiation shielding of the LDEF satellite is found. The total fluence of stopping protons (mostly primary, trapped particles) was measured as a function of the position in the main and side stacks of the P0006 experiment. Experimental results are compared with theoretical calculations and the effect of the strong location dependence of particle fluences is explained by the three dimensional shielding model of the P0006 stack. Through comparisons between experimental results and calculations, this work will lead to the refinement of the radiation environment computational models.

Csige, I.↗
NASA NTRS1983

Charged particle distributions in Jupiter's magnetosphere

In situ data from the Pioneer and Voyager spacecraft, supplemented by earth-based observations and theoretical considerations, are used as the basis for the present quantitative, compact model of the 1 eV-several MeV charged particle distribution in the Jovian magnetosphere. The thermal plasma parameters of convection speed, number density, and characteristic energy, are specified as functions of position for electrons and for the ion species H(+), O(+), O(2+), S(+), S(2+), S(3+), and Na(+). Major features of the magnetic field, thermal plasma, and trapped particle distributions, are modeled and results for each plasma region are compared with observed spectra. Comparisons show that the model represents the data to within a factor of 2 + or - 1, except where time variations are significant. Practical applications of the model to spacecraft near Jupiter are given.

Divine, N.↗
NASA NTRS1989

Access of energetic particles to storm time ring current through enhanced radial 'diffusion'

It is proposed that the transport of particles with energy of at least approximately 40 keV into the geomagnetic storm time ring current can result from enhanced stochastic radial transport driven by fluctuating electric fields during a storm's main phase. The effects of such electric fields are estimated by applying radial diffusion theory, assuming a preexisting trapped-particle population as the initial condition. The feasibility of explaining observed flux increases of particles of at least approximately 40 keV at no more than approximately 4 earth radii by enhanced radial 'diffusion' is then demonstrated. It is estimated that the at least approximately 40-keV portion of the storm time ring current at approximately 3 earth radii consists of about 50 percent preexisting and about 50 percent new particles. The formation of the storm time ring current is found to be perhaps explainable via a combination of direct radial transport at energies no greater than approximately 40 keV and 'diffusive' radial transport at higher energies.

Lyons, L. R.↗
NASA NTRS1997

Physics of Rotation Powered Pulsars and Their Nebulae

This letter is my progress report for the Astrophysics Theory grant. The first goal of the research supported by this grant is to produce a time dependent theory of the unsteady relativistic collisionless shock wave terminating the relativistic wind from a pulsar, and compare the predicted surface brightness fluctuations to Hubble Space Telescope observations of the wisps in the Crab Nebula. The second goal is to model the production of electron-positron pairs over the polar caps of rotation powered pulsars, and use the results to predict the heating of the surface due to particle trapping and bombardment of the atmosphere at the base of the polar field lines. We have succeeded in creating a one dimensional hybrid code, in which the electron-positron pairs incident on the shock structure are modeled as a relativistic, adiabatic, ideal MHD fluid, while the heavy ions are treated as particles using a particle-in-cell algorithm. The electromagnetic fields are evaluated from the currents and charge densities in the pairs and the ions, while the particles and the fluid accelerate in response to the computed self-consistent electromagnetic fields. The results are promising, in that the underlying ion cyclotron instability generates finite amplitude, propagating magnetosonic waves in the pairs, whose wavelengths and frequencies, when translated into physical units, are comparable to the observed running waves of brightness observed by HST near the Crab pulsar. The code is undergoing a number of tests, to assure us that this preliminary correspondence is not an artifact. In the coming year, the observational appearance of the models will be computed and compared to the HST observations of the Crab now in hand, and used to predict the HST results which will be obtained the year after next. WE also developed a one dimensional cascade theory for pair creation over pulsars' polar caps. A linear integral equation describing the synchrotron cascade has been derived and solved by iterative techniques, in the case when a high energy electron moving parallel to a star centered dipole magnetic field initiates the cascade through curvature gamma ray emission.

Arons, Jonathan↗
NASA NTRS1974

Electrons and protons accelerated in Mercury's magnetic field

Fluxes of protons with energies of about 550 kev and electrons with energies of about 300 kev which exceed approximately 10,000 and 100,000 per sq cm per sec, respectively, have been discovered in the magnetosphere of Mercury. Electron fluxes greater than 1000 per sq cm per sec are also observed in the outbound pass of the Mariner 10 spacecraft through the magnetosheath. The intensity vs time profiles of the particle fluxes in the magnetosphere appear with sudden onsets beginning at interplanetary background levels and persisting for times equivalent to their being distributed spatially over regions having a scale size comparable to the planetary radius. It is shown that the radiation events observed in the magnetosphere and magnetosheath are transient and are not interpretable in terms of stable trapped particle populations.

Simpson, J. A.↗
NASA NTRS1995

Acoustic Detection Of Loose Particles In Pressure Sensors

Particle-impact-noise-detector (PIND) apparatus used in conjunction with computer program analyzing output of apparatus to detect extraneous particles trapped in pressure sensors. PIND tester essentially shaker equipped with microphone measuring noise in pressure sensor or other object being shaken. Shaker applies controlled vibration. Output of microphone recorded and expressed in terms of voltage, yielding history of noise subsequently processed by computer program. Data taken at sampling rate sufficiently high to enable identification of all impacts of particles on sensor diaphragm and on inner surfaces of sensor cavities.

Kwok, Lloyd C.↗