Search NASA⌕ Search

SEARCH · Search NASA

Results for “PROTON DENSITY”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Initial Explorer 45 substorm observations and electric field considerations

Description of initial Explorer 45 substorm observations of particle distributions near the equator at altitudes from 5 to 5.5 earth radii. These initial results pertain to the evening sector and to a substorm occurring on Dec. 12, 1971. Fluxes, spectra, and energy densities are presented for 1- to 300-keV protons and 1.5- to 560-keV electrons. Arrival time dispersion effects are shown for electrons. These data are compared with the plasma cloud concepts and electric field model used by DeForest and McIlwain (1971) and McIlwain (1972) to explain particle observations at geosynchronous orbit.

Williams, D. J.↗
NASA NTRS1974

The lower ionosphere of Venus

Galactic cosmic ray bombardment provides a permanent background ionosphere in planetary atmospheres. A transport technique is used to compute the cosmic ray ionization rate profile in a model of the Venusian atmosphere at altitudes between 55 and 100 km. These ionization rates are then applied to a model of ion chemistry to predict equilibrium electron and ion density profiles. Ionization rates for typical solar flare proton events are available from earlier calculations and have been included.

Dubach, J.↗
NASA NTRS1974

Absorption of trapped particles by Jupiter's moons

Inclusion of absorption effects of the four innermost moons in the radial transport equations for electrons and protons in Jupiter's magnetosphere. It is found that the phase space density n at 2 Jupiter radii for electrons with equatorial pitch angles less than 69 deg is reduced by a factor of 42,000 when lunar absorption is included in the calculation. For protons with equatorial pitch angles less than 69 deg the corresponding reduction factor is 2,300,000. The effect of the satellites becomes progressively weaker for both electrons and protons as equatorial pitch angles of 90 deg are approached, because the likelihood of impacting a satellite becomes progressively smaller. The large density decreases found at the orbits of Io, Europa, and Ganymede result in corresponding particle flux decreases that should be observed by spacecraft making particle measurements in Jupiter's magnetosphere. The characteristic signature of satellite absorption should be a downward-pointing vertex in the flux versus radius curve at the L value corresponding to each satellite.

Hess, W. N.↗
NASA NTRS1979

Plasma injection and diamagnetism

A detailed study of the diamagnetic properties of magnetospheric plasma injected at synchronous altitudes is presented. Defining the magnetic induction field B = H + 4piM, the magnetization M is computed from the plasma distribution functions and it is shown that the diamagnetic contribution of the particles having energies of 100 eV to 81 eV can completely account for observed changes in the magnetic induction energy density. Computation of the resulting magnetic field H indicates that the current system in the magnetosphere is complex. Significant changes in H have been observed in a few minutes time scale. Studies of the particle density at various magnetic moments show that both protons and electrons together or individually act to cause the diamagnetic variations in B.

Gurgiolo, C.↗
NASA NTRS1979

In situ identification of various ionic species in Jupiter's magnetosphere

Continuing analysis of the Voyager 1 in situ measurements of the plasma (10-5,950 V) near Jupiter has revealed the existence of further atomic and molecular ions as minor constituents of the plasma. Ions with mass per charge values of 1, 8, 10-2/3, 16, 23, 32, 64, about 104, and about 160 were identified within 20 Jovian radii of Jupiter in the dayside magnetosphere. Wherever both protons and heavy ions were detected, the mass density was dominated by the heavy ions by a factor of about 100. The plasma ions moved with a common component of velocity which is not always the value expected geometrically from co-rotation. The ions with mass per charge values equal to or larger than 64 were probably molecular ions.

Sullivan, J. D.↗
NASA NTRS1994

A survey of bidirectional greater than or equal to MeV ion flows during the Helios 1 and Helios 2 mission: Observations from the Goddard Space Flight Center instruments

A survey is made of 1.1-2.1 MeV and 3-21 MeV bidirectional ion flows (BIFs) in the solar wind at 0.3-1.0 AU observed by the Goddard Space Flight Center instruments on the Helios 1 and Helios 2 spacecraft during the spacecraft mission in 1974-1984 and 1979-1980, respectively. Some 774 events have been identified Helios 1, and 223 at Helios 2, with mean durations of approximately 2.5 hr at each spacecraft. BIFs were observed for approximately 1%-3% of the observation time during solar minimum conditions in 1975-1977 and for approximately 10%-14% in 1980-1981 around solar maximum. These occurrence rates are similar to those of approximately 1 MeV BIFs observed at the Interplanetary Monitoring Platform 8 and International Sun Earth Explorers (ISEE) 3 spacecraft, and of bidirectional electron heat fluxes at ISEE 3. Solar wind plasma parameters during BIFs were similar to those found generally during the Helios missions, though BIFs have a greater tendency to be associated with cool, low-beta plasma, moderately enhanced and low-variance magnetic fields, both less than 300 km/s and greater than 750 km/s solar wind. Solar wind features associated with the greater than 4 hr duration BIFs include clear plasma shock-driver signatures: approximately 36% of the events; postshock plasma, not associated with shock-driver signatures: approximately 13%; noncompressive density enhancements: approximately 22% (half associated with plasma proton temperature depression); high-speed streams not associated with shocks: approximately 10%; corotating interaction regions: approximately 5%; immediately upstream of shocks: approximately 5%. Around 8% were associated with other solar wind structures, while approximately 4% showed no associated structure. BIFs were present in several of the shock drivers associated with coronal mass ejections (CMEs) observed by the Solwind coronagraph during intervals when Helios 1 was off the limbs of the Sun, showing directly the association of some BIFs with CMEs. some BIFs with CMEs.

Richardson, I. G.↗
NASA NTRS1994

Cosmic bullets as particle accelerators and radio sources

We have simulated in two dimensions the dynamical evolution of dense gas clouds(`cosmic bullets') moving supersonically through a uniform low-density medium. The diffusive shock acceleration of relativistic protons (cosmic rays) and their dynamical feedback on the background flow are included by the two-fluid model for this process. The acceleration of relativistic electrons is approximated by a test-particle model, and a passive magnetic field is followed by a simple advection scheme. Strong bow shocks, with Mach numbers similar to that of a bullet's motion, are the most important particle accelerators in the flow, while tail shocks and shocks inside the bullets do not play generally significant roles in this regard. For our simulation parameters, approximately greater than 10% of the initial bullet kinetic energy is converted to a combination of internal energy of gas and cosmic-ray protons by the time the bullets begin to be disrupted. Characteristically, the cosmic rays gain several percent of the available kinetic energy. Bullet destruction on timescales only a little larger than the ram pressure bullet crushing time begins in response to Kelvin-Helmholtz and especially to Rayleigh-Taylor instabilities along the forward bullet surface. For dense bullets this happens before the bullet is stopped by ram pressure. According to our simple model for synchrotron emission from relativistic electrons accelerated and transported within the flows, that emission increases rapidly as the bullet begins to fragment, when it is strongly dominated by field enhancement in sheared flows. Synchrotron emission from the acceleration region within the bow shock is, by contrast, much weaker.

Jones, T. W.↗
NASA NTRS2003

Modeling the Extended Neutral Atmosphere and Plasma Environment near Saturn

In the three years of this study we have published five papers in refereed journals. We have first examined satellite sources and their contribution to the observed neutral cloud. Based on the total calculated satellite sources and the spatial distribution of sputtered H20, we concluded that they cannot produce observed OH cloud. The E-ring contribution has been also studied in detail.In order to produce observed OH cloud we suggested that the E-ring might be the dominant source in inner Saturnian magnetosphere. We proposed a possible resupply mechanism which is needed to keep both E-ring and OH cloud in the present state: collisions between E-ring grains and remains of a disrupted satellite near Enceladus Lagrangian points. In this scenario a large amount of material, ranging from a few micrometers to hundred of meters, which is optically invisible at present, is likely to exist there. The fourth paper compares the magnetosheaths of the outer planets. A surprising result is that the hot proton component comprises about 40% of the total density, much larger than predicted by shock theory. Gas dynamic models of the boundaries show that the magnetospheres of Jupiter and Saturn are flattened at the poles. The last paper was published in GRL and is the first based of the model of neutrals developed as a main goal of this grant and which is now operational.This Monte Carlo collision code self- consistently determines the neutral distribution. from the rings and satellites until they are lost by ionization, by collisions with rings, moons, or Saturn, or by escape from Saturn. Our model is unique in that it includes the effects of plasma chemistry and both plasma-neutral and neutral neutral collisions to determine the dynamical evolution of the water group neutrals in Saturn's magnetosphere. The lifetimes of the neutrals against loss to photoionization, charge exchange, electron dissociation and electron impact dissociation are based on the model given by (Richardson et al. 1998) and vary with position in the magnetosphere. The dominant neutral dissociation channels H20->OH+H, H20-> O+H2, and OH->O+H2 are considered.

Richardson, John D.↗
NASA NTRS2005

Improved Anode for a Direct Methanol Fuel Cell

A modified chemical composition has been devised to improve the performance of the anode of a direct methanol fuel cell. The main feature of the modified composition is the incorporation of hydrous ruthenium oxide into the anode structure. This modification can reduce the internal electrical resistance of the cell and increase the degree of utilization of the anode catalyst. As a result, a higher anode current density can be sustained with a smaller amount of anode catalyst. These improvements can translate into a smaller fuel-cell system and higher efficiency of conversion. Some background information is helpful for understanding the benefit afforded by the addition of hydrous ruthenium oxide. The anode of a direct methanol fuel cell sustains the electro-oxidation of methanol to carbon dioxide in the reaction CH3OH + H2O--->CO2 + 6H(+) + 6e(-). An electrocatalyst is needed to enable this reaction to occur. The catalyst that offers the highest activity is an alloy of approximately equal numbers of atoms of the noble metals platinum and ruthenium. The anode is made of a composite material that includes high-surface-area Pt/Ru alloy particles and a proton-conducting ionomeric material. This composite is usually deposited onto a polymer-electrolyte (proton-conducting) membrane and onto an anode gas-diffusion/current-collector sheet that is subsequently bonded to the proton-conducting membrane by hot pressing. Heretofore, the areal density of noble-metal catalyst typically needed for high performance has been about 8 mg/cm2. However, not all of the catalyst has been utilized in the catalyzed electro-oxidation reaction. Increasing the degree of utilization of the catalyst would make it possible to improve the performance of the cell for a given catalyst loading and/or reduce the catalyst loading (thereby reducing the cost of the cell). The use of carbon and possibly other electronic conductors in the catalyst layer has been proposed for increasing the utilization of the catalyst by increasing electrical connectivity between catalyst particles. However, the relatively low density of carbon results in thick catalyst layers that impede the mass transport of methanol to the catalytic sites. Also, the electrical conductivity of carbon is less than 1/300th of typical metals. Furthermore, the polymer-electrolyte membrane material is acidic and most metals are not chemically stable in contact with it. Finally, a material that conducts electrons (but not protons) does not contribute to the needed transport of protons produced in the electro-oxidation reaction.

Valdez, Thomas↗
NASA NTRS1985

The heating of the solar wind by the interstellar neutral gas

Solar wind heating by ionization and assimilation of the interstellar neutral wind is investigated using a numerical model of the interaction. The model is a time-dependent, one-dimensional, spherically symmetric, one-fluid code which includes mass, momentum, and energy sources due to the efficient incorporation of ionized interstellar hydrogen. Solar wind data at 1 AU from October 12, 1978 to February 25, 1980 were input to the inner boundary of the model and propagated out to 10 AU. Then, 52-day averages of proton temperature as functions of radius were produced for three values of the interstellar hydrogen density: 0.0, 0.03, and 0.1 per cu cm. It is concluded that, within the context of the model, the observations of solar wind proton temperatures at Voyager 1 and Pioneer 11 are consistent with heating of the solar wind by an interaction with inflowing interstellar neutral hydrogen. The density of this inflowing gas is near 0.03/cu cm.

Isenberg, P. A.↗
NASA NTRS1974

Thermal proton flow in the plasmasphere - The morning sector

Vertical profiles of electron density obtained in the vicinity of the plasmapause using the Alouette-2 topside sounder have been analyzed to assess the presence of H(+) flow in the topside ionosphere. The observations in the midnight sector show clearly the presence of the plasmapause - i.e., there is a sharp boundary separating the poleward regions of polar wind H(+) flow and the more gentle conditions of the plasmasphere where light ions are present in abundance. In contrast, in the sunlit morning sector upward H(+) flow is deduced to be present to invariant latitudes as low as 48 deg (L = 2.2) in the regions normally known to be well inside the plasmasphere. The upward H(+) flux is so large 300,000,00 ions per sq cm per sec that the plasmapause cannot be seen in the latitudinal electron density contours of the topside ionosphere.

Banks, P. M.↗
NASA NTRS1985

AMPTE/CCE energetic particle composition measurements during the September 4, 1984 magnetic storm

The results of measurements for the magnetic-storm period of September 4-7, 1984 from the medium-energy particle analyzer (MEPA) on the CCE spacecraft are presented. It is shown that within L-shells of about 2.5 to 5 in the dusk sector near the equatorial plane, the enhancement factor in the fluxes for the CNO group is greater than that of helium, which is greater than that of protons. The flux ratios of helium and CNO over all ions at the same total energy show considerable increases in the same L-shell ranges. For the particle population measured by MEPA, a local current-density enhancement of about 0.5 nA/sq m is found over the L range of 3.5 to 6 during the magnetic storm. It is found that the total current density is dominated by the pressure-gradient current of the protons.

Mcentire, R. W.↗
NASA NTRS1972

Stably trapped proton limits for Jupiter

A general introduction to pitch-angle diffusion for Earth and Jupiter magnetospheres is given. The instabilities which might limit the trapped fluxes in the earth magnetosphere are identified as the interchange or ballooning mode, electrostatic loss cone modes, and electromagnetic ion cyclotron wave. The instability theory of the ion cyclotron wave is discussed. This wave can be unstable only if protons can be in cyclotron resonance with the wave. The instability growth rate is proportional to the cyclotron frequency, the fractional number density of fast particles, and the anisotropy of the fast particle distribution. The critical proton energy is the lowest energy for which the stably trapped limit applies, and is calculated to be 150 MeV at L = 2 and for 10 ion pairs/cu cm. Particles above the critical threshold energy are considered and their stability limit is approximately 3 x 10 to the 10th power/sq cm/sec divided by L to the 4th power.

Kennel, C.↗
NASA NTRS1995

Fission foil measurements of neutron and proton fluences in the A0015 experiment

Results are given from sets of fission foil detectors (FFD's) (Ta-181, Bi-209, Th-232, U-238) which were included in the A0015 experiment to measure combined proton/neutron fluences. Use has been made of recent FFD high energy proton calibrations for improved accuracy of response. Comparisons of track density measurements have been made with the predictions of environmental modeling based on simple 1-D (slab) geometry. At 1 g/cm(exp 2) (trailing edge) the calculations were approximately 25 percent lower than measurements; at 13 g/cm(exp 2) (Earthside) calculations were more than a factor of 2 lower. A future 3-D modeling of the experiment is needed for a more meaningful comparison. Approximate mission proton doses and neutron dose equivalents were found. At Earthside (13 g/cm(exp 2) the dose was 171 rad and dose equivalent was 82 rem. At the trailing edge (1 g/cm(exp 2) dose was 315 rad and dose equivalent was 33 rem. The proton doses are less than expected from TLD doses by 16 percent and 37 percent, respectively. These differences can be explained by uncertainties in the proton and neutron spectra and in the method used to separate proton and neutron contributions to the measurements.

Frank, A. L.↗
NASA NTRS1992

Studies of the charging of a thin dust layer in a plasma

When an infinite plane layer of dust having a number-density profile normal to the plane is exposed to an ambient e(sup -), p(sup +) plasma, one can imagine the features of the charging process near the layer boundary. If the e(sup -), p(sup +) temperatures are equal, and the B field is normal to the dust layer, the controlling factor is the large electron relative to proton speeds. Since the collision rate between plasma particles of number density n and speed v and an uncharged dust grain of radius a is estimated as the product n v pi a(exp 2), electrons dominate the charging process. The outer edge of the layer charges negatively, setting up an electrical potential that inhibits penetration of electrons into the layer and at the same time accelerates protons inward. Interior to the outer negative region then, one would expect many energetic protons compared to a reduced number of electrons from the ambient plasma. Charge imbalances are bound to arise, but the details are not so easy to deduce from simple arguments. These details are the subject of the present study.

Peterson, Lennart R.↗
NASA NTRS1993

Radiation effects in heteroepitaxial InP solar cells

Heteroepitaxial InP solar cells, with GaAs substrates, were irradiated by 0.5 and 3 MeV protons and their performance, temperature dependency, and carrier removal rates determined as a function of fluence. The radiation resistance of the present cells was significantly greater than that of non-heteroepitaxial InP cells at both proton energies. A clear difference in the temperature dependency of V(sub oc), was observed between heteroepitaxial and homoepitaxial InP cells. The analytically predicted dependence of dV(sub oc)/dT on Voc was confirmed by the fluence dependence of these quantities. Carrier removal was observed to increase with decreasing proton energy. The results obtained for performance and temperature dependency were attributed to the high dislocation densities present in the heteroepitaxial cells while the energy dependence of carrier removal was attributed to the energy dependence of proton range.

Weinberg, I.↗
NASA NTRS1965

Plasma pressures in the magnetosphere

Plasma energy density estimation near equatorial magnetopause considering only solar wind protons and plasma effect on geomagnetic field

PLASMA SPECTRUM↗