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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 1,693 records · Page 94

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NASA NTRS1985

Diurnal modulation of the quiet time penetrating electron flux

Three sounding rocket measurements of energetic electron precipitation in the 65 to 80 km altitude range above Siple Station, Antarctica suggest a possible diurnal modulation of the precipitation. Flights made on January 10 and 11, 1981, to investigate this possibility showed that no electrons were present after local noon, while a significant flux of penetrating electrons was observed the following day near local dawn, even though the level of magnetic activity was higher during the postnoon flight. A prevous flight from Siple Station also observed a large flux of penetrating electrons near local dawn. Calculations of electron drift trajectories in a model magnetic field indicate that moderate values of the convection electric field could cause significant local time variations in the penetrating electron flux at the western edge of the South Atlantic anomaly. These calculations indicate that Siple Station is shadowed by eastern Siberia when it is at local noon, but not when it is at local dawn.

Sheldon, W. R.↗

NASA NTRS1983

Stimulated Raman up-conversion of electromagnetic waves by a gyrating electron beam

A gyrating electron beam supports negative energy modes near the harmonics of electron-cyclotron frequency. An electromagnetic wave passing through such a beam parametrically up-converts into high-frequency electromagnetic modes separated from the pump frequency by the electron-cyclotron harmonics. The growth rate for this process varies directly as the oscillatory velocity of beam electrons caused by the pump and as square root of the beam density. It has a maximum at values of scattering angle close to 180 deg and is also implicitly dependent on the beam veocity and the cyclotron frequency of electrons. The effect of a cold electron component is to reduce the growth rate.

Sharma, O. P.↗

NASA NTRS1985

Enhanced growth of whistlers due to bunching of untrapped electrons

Man-made signals propagating in the whistler mode in the magnetoshere have been observed to be amplified and to trigger other VLF emissions in the absence of other detectable magnetospheric signals in ground-based recordings. The absence of other magnetospheric signals implies that the growth rate of the triggered wave is enhanced over background noise. It is shown that, for at least low amplitude triggering waves, the phase bunching of untrapped electrons can account for the observed enhanced growth. The phase bunching is initially produced by perturbations in the electron trajectories due to their interactions with the front of the wave. Due to the inhomogeneity of the geomagnetic field, the phase-bunched electrons are able to gyroresonantly interact with a later portion of the triggering wave. Because the electrons are phase bunched, the electrons can lose energy to the wave faster than phase-random electrons and are thereby able to produce enhanced growth. Plasma conditions for which this phase bunching is effective in producing enhanced growth are derived.

Winglee, R. M.↗

NASA NTRS1985

Solar He-3-rich events and nonrelativistic electron events - A new association

In 15 months of observation by the ISEE-e spacecraft, it was found that virtually all solar greater than or approximately equal to 1.3 MeV/nucleon He-3-rich events are associated with impulsive 2 to approximately 100 keV electron events, although many electron events were not accompanied by detectable He-3 increases. Both the He-3 and the electrons exhibit nearly scatter-free propagation in the interplanetary medium, and the times of onset and maximum for the He-3 and electron increases are closely related by velocity dispersion. The electron events and their related type III solar radio bursts provide, for the first time, identification of the flares which produce the He-3-rich events. He-3 appears to be accelerated at the flash phase of solar flares along with nonrelativistic electrons.

Reames, D. V.↗

NASA NTRS1986

Set-up and demonstration of a Low Energy Electron Magnetometer (LEEM)

Described are the design, construction and test results of a Low Energy Electron Magnetometer (LEEM). The electron source is a commercial electron gun capable of providing several microamperes of electron beam. These electrons, after acceleration through a selected potential difference of 100-300 volts, are sent through two 30 degree second-order focussing parallel plate electrostatic analyzers. The first analyzer acts as a monochromator located in the field-free space. It is capable of providing energy resolution of better than 10 to the -3 power. The second analyzer, located in the test field region, acts as the detector for electrons deflected by the test field. The entire magnetometer system is expected to have a resolution of 1 part in 1000 or better.

Rayborn, G. H.↗

NASA NTRS1986

Theoretical study of the electron temperature in the high-latitude ionosphere for solar maximum and winter conditions

The T(e) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, T(e) hot spots develop, and these hot spots show a marked UT variation, by as much as 2500 K. The dominant parameter controlling the T(e) variation above 200 km is the magnetospheric heat flux into the ionosphere, which is essentially unknown. For realistic values of the magnetospheric heat flux, the maximum electron temperature ranges from 5000 to 10,000 K at 800 km. A magnetospheric heat flux is particularly effective in enhancing trough electron temperatures. In general, the electron heat flux at high altitudes is uniquely related to the electron temperature and gradient, except on auroral field lines where thermoelectric heat flow is important.

Schunk, R. W.↗

NASA NTRS1987

Jovian electrons at 1 AU - 1978-1984

Data on Jovian electrons sensed with a spectrometer on board the ISEE spacecraft at 1 AU are studied in terms of intensity variations over time and shape and variations of the electron spectra with time. Design and performance features of the electron spectrometer are described. The analyses cover solar cycle modulation of intensity, the synodic intensity modulation, micromodulation over a period of days, and adiabatic deceleration of electrons propagating in the expanding solar wind. Emphasis is placed on the effects of maximum solar activity on Jovian electron emission and propagation, noting a confirmed 13 mos intensity variation in the Jovian electrons.

Moses, Dan↗

NASA NTRS1986

An electromagnetic/electrostatic dual cathode system for electron beam instruments

A method of providing cathode redundancy which consists of two fixed cathodes and uses electromagnetic and/or electrostatic fields to direct the electron beam to the electron optical axis is presented, with application to the cathode system of the Scanning Electron Microscope and Particle Analyzer proposed for NASA's Mariner Mark II Comet Rendezvous/Asteroid Flyby projected for the 1990s. The symmetric double deflection system chosen has the optical property that the image of the effective electron source is formed above the magnet assembly near the apparent position of the effective source, and it makes the transverse positions of the electron sources independent of the electron beam energy. Good performance of the system is found, with the sample imaging resolution being the same as for the single-axis cathode.

Bradley, J. G.↗

NASA NTRS1988

On the spectrum of the secondary auroral electrons

Results are presented from a statistical study of the spectral characteristics of the (power-law-portion) secondary electrons associated with inverted-V electron precipitation events (IVEs). A total of 106 IVEs observed at low altitudes (below 1000 km) by the DE 2 spacecraft are included in data base. Spectral parameters for the electrons between 20 eV and 100 eV are plotted against the different parameters pertaining to the locations of the IVEs and the primary beams to determine their empirical dependences. It is found that the differential spectrum of the secondary electrons can be modeled by a power law, J proportional to E exp -gamma, with an averaged gamma of 1.85. This spectral parameter is relatively insensitive to the variation of locations of the IVEs, but it depends on the primary beam parameters. These results are compared with predictions, and theories on the generation of the low-energy auroral power-law secondary electrons are assessed. The analysis shows that collisional processses are the dominant source of the secondary electrons.

Fung, S. F.↗

NASA NTRS1987

Bidirectional electron anisotropies in the distant tail - ISEE 3 observations of polar rain

A detailed observational treatment of bidirectional electrons (50 approx. 500 eV) in the distant magnetotail (or greater than or equal to 100 R sub E) is presented. It is found that electrons in this energy range commonly exhibit strong, field aligned anisotropies in the tail lobes. Because of large tail motions, the ISEE-3 data provide extensive sampling of both the north and south lobes in rapid succession, demonstrating directly the strong asymetries that exist between the north and south lobes at any one time. The bidirectional fluxes are found to occur predominantly in the lobe directy connected to the sunward IMF in the open magnetosphere model (north lobe for away sectors and south lobe for toward sectors). Electron anisotropy and magnetic field data are presented which show the transition from unidirectional (sheath) electron populations to bidirectional (lobe) populations. Taken together, the present evidence suggests that the bidirectional electrons that we observe in the distant tail are closely related to the Polar rain electrons observed previously at lower altitudes. Furthermore, these data provide strong evidence that the distant tail is comprised largely of open magnetic field lines in contra distinction to some recently advanced models.

Baker, D. N.↗

NASA NTRS1989

Reversal electron attachment ionizer for detection of trace species

An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of the electrons, such that the electrons possess zero kinetic energy at the point of reversal, may be used to produce both negative and positive ions. A sample gas is introduced at the point of electron reversal for low energy electron-(sample gas) molecule attachment with high efficiency. The attachment process produces negative ions from the sample gas, which includes species present in trace (minute) amounts. These ions are extracted efficiently and directed to a mass analyzer where they may be detected and identified. The generation and detection of positive ions is accomplished in a similar fashion with minimal adjustment to potentials applied to the apparatus.

Bernius, Mark T.↗

NASA NTRS1988

Theory of high-field electronic transport in bulk ZnS and ZnSe

This paper theoretically investigates the nature of electronic transport and the high-energy tails of the electron distribution functions in bulk ZnSe and ZnS as a function of the applied electric field were investigated using calculations based on an ensemble Monte Carlo model. The calculations include the full details of the first two conduction bands as well as the full-order treatment of the electron-phonon scattering mechanisms. Results of high-field electronic transport calculations show that the electron energy distribution function is significanty cooler in ZnS than in ZnSe at comparable electric field strengths. The cooler distribution in ZnS is due to the much greater electron scattering rate. Consequently, it is more difficult to achieve carrier heating to comparable energies in ZnS than in ZnSe.

Brennan, Kevin↗

NASA NTRS1988

An electrostatically and a magnetically confined electron gun lens system

Focal properties, electron trajectory calculations, and geometries are given for two electron 'gun' lens systems that have a variety of applications in, for example, electron-neutral and electron-ion scattering experiments. One nine-lens system utilizes only electrostatic confinement and is capable of focusing electrons onto a fixed target with extremely small divergence angles, over a range of final energies 1-790 eV. The second gun lens system is a simpler three-lens system suitable for use in a uniform, solenoidal magnetic field. While the focusing properties of such a magnetically confined lens systenm are simpler to deal with, the system does illustrate features of electron extraction and Brillouin flow that have not been suitably emphasized in the literature.

Bernius, Mark T.↗

NASA NTRS1989

Three-electron atoms from a Bethe-Salpeter equation approach

The two-electron Bethe-Salpeter equation is reviewed. The transition to a Hamiltonian form is discussed, and the criterion that the first-order energy shift vanish is used to determine the electron-electron potential that appears in the Hamiltonian. A similar program is carried through for the three-electron case. The fundamental idea of Feldman and Fulton is used for the transition to the Hamiltonian form, although some changes are necessary. The optimum two-electron interaction is the same as that in the two-electron case.

Mittleman, Marvin H.↗

NASA NTRS1989

Angular dependent transport of auroral electrons in the upper atmosphere

The transport of auroral electrons through the upper atmosphere is analyzed. The transport equation is solved using a discrete-ordinate method, including elastic and inelastic scattering of electrons (resulting in changes of pitch angle) and degradation in energy as the electrons penetrate into the atmosphere. The transport equation is solved numerically for the electron intensity as a function of altitude, pitch angle, and energy. In situ measurements of the pitch angle and energy distribution of precipitating electrons over an auroral arc provide boundary conditions for the calculation. Model calculations were carried out with various different phase functions for elastic and inelastic collisions to attempt changing the angular scattering, but the observed pitch angle distributions remain unexplained. It is suggested that mechanisms other than collisional scattering influence the angular distribution of auroral electrons at or below 300 km altitude in the low-energy domain.

Lummerzheim, D.↗

NASA NTRS1989

The behavior of beams of relativistic non-thermal electrons under the influence of collisions and synchrotron losses

For many astrophysical situations, such as in solar flares or cosmic gamma-ray bursts, continuum gamma rays with energies up to hundreds of MeV were observed, and can be interpreted to be due to bremsstrahlung radiation by relativistic electrons. The region of acceleration for these particles is not necessarily the same as the region in which the radiation is produced, and the effects of the transport of the electrons must be included in the general problem. Hence it is necessary to solve the kinetic equation for relativistic electrons, including all the interactions and loss mechanisms relevant at such energies. The resulting kinetic equation for non-thermal electrons, including the effects of Coulomb collisions and losses due to synchrotron emission, was solved analytically in some simple limiting cases, and numerically for the general cases including constant and varying background plasma density and magnetic field. New approximate analytic solutions are presented for collision dominated cases, for small pitch angles and all energies, synchrotron dominated cases, both steady-state and time dependent, for all pitch angles and energies, and for cases when both synchrotron and collisional energy losses are important, but for relativistic electrons. These analytic solutions are compared to the full numerical results in the proper limits. These results will be useful for calculation of spectra and angular distribution of the radiation (x rays, gamma-rays, and microwaves) emitted via synchrotron or bremsstrahlung processes by the electrons. These properties and their relevance to observations will be observed in subsequent papers.

Mctiernan, James M.↗

NASA NTRS1989

Simulation of radial expansion of an electron beam injected into a background plasma

A 2-D electrostatic particle code was used to study the beam radial expansion of a nonrelativistic electron beam injected from an isolated equipotential conductor into a background plasma. The simulations indicate that the beam radius is generally proportional to the beam electron gyroradius when the conductor is charged to a large potential. The simulations also suggest that the charge buildup at the beam stagnation point causes the beam radial expansion. From a survey of the simulation results, it is found that the ratio of the beam radius to the beam electron gyroradius increases with the square root of beam density and decreases inversely with beam injection velocity. This dependence is explained in terms of the ratio of the beam electron Debye length to the ambient electron Debye length. These results are most applicable to the SEPAC electron beam injection experiments from Spacelab 1, where high charging potential was observed.

Koga, J.↗

NASA NTRS1990

Scattering of positrons and electrons by alkali atoms

Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.

Stein, T. S.↗