Electron and local gas densities in diffuse interstellar clouds from measurements of Ca I absorption
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Federman, S. R.↗
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The Parallax of Pulsar 0950+08 and the Local Free Electron Density
A parallax of 7.9 + or - 0.8 mas for PSR 0950+08, corresponding to a distance of 130 + or - 15 pc is reported. The measured pulse dispersion of this pulsar implies an average free electron density of 0.023 + or 0.002/cu cm along the line of sight. This parallax measurement is subject to systematic errors and questions of interpretation which are not yet fully explored.
Gwinn, C. R.↗
Electronic structure of BaO/W cathode surfaces
The local electronic structure of the emissive layer of barium dispenser thermionic cathodes is investigated theoretically using the relativistic scattered-wave approach. The interaction of Ba and O with W, Os, and W-Os alloy surfaces is studied with atomic clusters modeling different absorption environments representative of B- and M-type cathodes. Ba is found to be strongly oxidized, while O and the metal substrate are in a reduced chemical state. The presence of O enhances the surface dipole and Ba binding energy relative to Ba on W. Model results for W-Os alloy substrates show only relatively small changes in Ba and O for identical geometries, but very large charge redistributions inside the substrate, which are attributed to the electronegativity difference between Os and W. If Os is present in the surface layer, the charge transfer from Ba to the substrate and the Ba binding energy increase relative to W. Explanations are offered for the improved electron emission from alloy surfaces and the different emission enhancement for different alloy substrates.
Muller, Wolfgang↗
Theoretical study of the low-lying electronic states of ZnO and ZnS
Theoretical spectroscopic constants and dipole moments are determined for the 1 Sigma(+), 1,3 Pi, and 3 Sigma(+) states of ZnO and ZnS, using extended Gaussian basis sets and incorporating correlation using both configuration-interaction and coupled pair (CPF) methods. Relativistic corrections (Darwin plus mass velocity), included using first-order perturbation theory, are relatively small. At the CPF level, both ZnO and ZnS have 1 Sigma(+) ground states, with the 3 Pi state lying 209 and 2075/cm higher, respectively. The 3 Sigma(+) state lies about 1.5 eV higher in ZnO and 2.1 eV higher in ZnS. The 1,3 Pi states are relatively close together since the exchange splitting is small with the sigma electron localized on Zn and the pi electron on oxygen (or sulfur).
Bauschlicher, C. W., Jr.↗
Interaction with the lower ionosphere of electromagnetic pulses from lightning - Heating, attachment, and ionization
A Boltzmann formulation of the electron distribution function and Maxwell's equations for the EM fields are used to simulate the interaction of lightning radiated EM pulses with the lower ionosphere. Ionization and dissociative attachment induced by the heated electrons cause significant changes in the local electron density, N(e). Due to 'slow' field changes of typical lightning EM pulses over time scales of tens of microsec, the distribution function follows the quasi-equilibrium solution of the Boltzmann equation in the altitude range of interest (70 to 100 km). The EM pulse is simulated as a planar 100 microsec long single period oscillation of a 10 kHz wave injected at 70 km. Under nighttime conditions, individual pulses of intensity 10-20 V/m (normalized to 100 km horizontal distance) produce changes in N(e) of 1-30 percent while a sequence of pulses leads to strong modification of N(e) at altitudes less than 95 km. The N(e) changes produce a 'sharpening' of the lower ionospheric boundary by causing a reduction in electron density at 75-85 km (due to attachment) and a substantial increase at 85-95 km (due to ionization) (e.g., the scale height decreases by a factor of about 2 at about 85 km for a single 20 V/m EM pulse). No substantial N(e) changes occur during daytime.
Taranenko, Y. N.↗
Electron velocity space hole modes
In space plasmas the local electron distribution is formed by ballistic motion from different source regions. Since electrons with positive and negative parallel (v-parallel) velocities have different sources and experience different interactions with the large-scale electromagnetic fields, the electron distribution function near v-parallel = 0 should possess considerable structure, including the possibility of velocity space holes, i.e., regions where the phase space density is zero, and sharp discontinuities. A particular hole distribution, which may occur upstream of slow shocks in the distant geomagnetic tail, is shown to support a nonstandard plasma wave mode with frequencies between the ion and electron plasma frequencies and parallel phase speed above the ion, but well below the electron, thermal speed. The hole mode can be destabilized by a positive slope in the low parallel velocity electron distribution, and the growth rate is strongly enhanced if the electron parallel temperature exceeds the perpendicular temperature; the mode can also be excited by a hot, fast ion beam. The hole modes exist only for a narrow range of propagation angles about the magnetic field direction.
Coroniti, Ferdinand V.↗
Physics-based Tests to Identify the Accuracy of Solar Wind Ion Measurements: A Case Study with the Wind Faraday Cups
We present techniques for comparing measurements of velocity, temperature, and density with constraints imposed by the plasma physics of magnetized bi-Maxwellian ions. Deviations from these physics-based constraints are interpreted as arising from measurement errors. Two million ion spectra from the Solar Wind Experiment Faraday Cup instruments on the Wind spacecraft are used as a case study. The accuracy of velocity measurements is determined by the fact that differential flow between hydrogen and helium should be aligned with the ambient magnetic field. Modeling the breakdown of field alignment suggests velocity uncertainties are less than 0.16% in magnitude and 3deg in direction. Temperature uncertainty is found by examining the distribution of observed temperature anisotropies in high-beta solar wind intervals where the firehose, mirror, and cyclotron microinstabilities should drive the distribution to isotropy. The presence of a finite anisotropy at high beta suggests overall temperature uncertainties of 8%. Hydrogen and helium number densities are compared with the electron density inferred from observations of the local electron plasma frequency as a function of solar wind speed and year. We find that after accounting for the contribution of minor ions, the results are consistent with a systematic offset between the two instruments of 34%. The temperature and density methods are sensitive to non-Maxwellian features such as heat flux and proton beams and as a result are more suited to slow solar wind where these features are rare. These procedures are of general use in identifying the accuracy of observations from any solar wind ion instrument.
Kasper, J. C.↗
Distorted Perovskites for High Voltage Dielectric Capacitors
There are several mechanisms which have been proposed for the existence of colossal dielectric constant in the class of perovskite calcium copper titanate (CaCu3Ti4O12 or CCTO) materials. Researches indicate that existence of twinning parallel to (100) (001) and (010) planes causes planar defects and causes changes in local electronic structure. This change can cause insulating barriers locally which contribute to the large dielectric values irrespective of processing. The combination of insulating barriers, defects and displacements caused by twinning have been attributed to the generation of large dielectric constant in CCTO. To examine some of these arguments some researchers replaced Ca with other elements and evaluated this concept. In this study we present the synthesis and characterization of Ga2/3Cu3Ti4O12-xNx (GCTON) material. This provides both distortion due to atomic size difference and defects due to insertion of nitrogen. The morphology of the compound was determined to show that processing has tremendous effect on the dielectric values. The resistivity of GCTON was several order higher than CCTO and dielectric constant was higher than 10,000.
Gill, Puneet↗
Plasma wave electric fields in the solar wind - Initial results from Helios 1
Plasma-wave measurements by Helios 1 show that the electric-field intensities in the solar wind are usually very low, much lower than those for comparable measurements near earth, where particles moving upstream from the bow shock often cause large disturbances in the solar wind. The most commonly occurring plasma wave detected by Helios is a sporadic emission at frequencies from about 1 to 10 kHz, between the electron and ion plasma frequencies. These waves are thought to be ion acoustic waves Doppler-shifted upward in frequency from below the ion plasma frequency. The maximum electric-field intensity of these waves is a few hundred microvolts per meter. At higher frequencies, from about 20 to 100 kHz, electron plasma oscillations are detected at frequencies near the local electron plasma frequency. These electron plasma oscillations are more intense, with field strengths sometimes as large as a few millivolts per meter, but occur very infrequently. Both the ion acoustic waves and the electron plasma oscillations show a tendency to occur at higher frequencies closer to the sun but no pronounced variation in intensity with radial distance from the sun. In four cases, electron plasma oscillations have been found in association with type III radio bursts.
Gurnett, D. A.↗
Electronics Manufacturer Provided With Testing and Evaluation Data Necessary to Obtain Additional Orders
A local electronics manufacturer, the Sterling Manufacturing Company, was presented with the opportunity to supply 30,000 automotive cellular antennas to a European subsidiary of a large U.S. auto manufacturer. Although the company built an antenna that they believed would meet the auto manufacturer's specifications, they were unable to conduct the necessary validation tests in-house. They decided to work with NASA Lewis Research Center's Space Electronics Division, which, as part of its technology development program, evaluates the performance of antennas in its Microwave Systems Lab to assess their capabilities for space communications applications. Data measured in Lewis' Microwave Systems Lab proved that Sterling's antenna performed better than specified by the auto manufacturer.
Source record↗
Plasma wave observations during electron beam experiments at high altitudes
Electron beam experiments on the nearly geosynchronous P78-2 satellite conducted in 1979 resulted in observations of intense radiation near the local electron gyrofrequency. These signals resembled naturally occurring f(ce) waves during the same period. The amplitude of the simulated waves depended upon beam parameters. During 50-eV beam operations, current levels of 10 microamps produced strong emissions. Current levels of 1 microamp and 100 microamps did not. These emissions correspond in time to previously reported observations of electron distributions, which suggest heating of the local thermal plasma. Sufficient power is in the observed emissions to explain some aspects of the heated electron distributions observed during the experiments.
Olsen, R. C.↗
The downshift of electron plasma oscillations in the electron foreshock region
Electron plasma oscillations in the earth's electron foreshock region are observed to shift above and below the local electron plasma frequency. As plasma oscillations shift downward from the plasma frequency, their bandwidth increases and their wavelength decreases. Observations of plasma oscillations well below the plasma frequency are correlated with times when ISEE 1 is far downstream of the electron foreshock boundary. Although wavelengths of plasma oscillations below the plasma frequency satisfy k x lambda-De approximately 1 the Doppler shift due to the motion of the solar wind is not sufficient to produce the observed frequency shifts. A beam-plasma interaction with beam velocities on the order of the electron thermal velocity is suggested as an explanation for plasma oscillations above and below the plasma frequency. Frequency, bandwidth, and wavelength changes predicted from the beam-plasma interaction are in good agreement with the observed characteristics of plasma oscillations in the foreshock region.
Fuselier, S. A.↗
Optical observations of the beam-plasma discharge phenomenon
Spectroscopic observations of optical emissions from the beam-plasma discharge (BPD) phenomenon were made with NASA's vacuum chamber facility, at the Johnson Space Center, configured to simulate the physical conditions of magnetospheric electron beam injection into the ionospheric/upper-atmospheric environment. Nonlinear N2 and N2(+) optical emission growth rates (with respect to incremental electron beam current values) were observed from the chamber gas during transition to the BPD state. For electron-beam currents (I) near the BPD transition value (I(sub c)), the band emissions from the chamber gas produced by relatively low energy (less than or equal to 50 eV) electrons interacting with N2 were anomalously more intense than those requiring higher energy (greater than 100 eV) electrons to excite them. For I more greater than I(sub c), the optical emissions increased linearly with I (as was the case for I less than I(sub c)) and their ratios decreased significantly from the peak values attained when I approximately equals I(sub c). These observations suggest that during BPD some of the energy of the primary electron beam is efficiently transferred, via wave-particle interactions, to local electrons produced through ionization of the chamber gas; the resulting suprathermal electrons provide an additional source of excitation for the relatively low energy states (A, B and C) of N2. Such nonlinear excitation of upper atmospheric gas may occur in certain auroral events wherein the current due to the precipitating electrons approaches a value close to I(sub c).
Sivjee, G. G.↗
A computerized data-reduction technique for Langmuir probe analysis of electron temperature variations in the exhaust of a magnetoplasmadynamic arc
Computerized data reduction techniques for obtaining local electron temperature variations in plasma beams produced by magnetoplasmadynamic accelerators
DATA REDUCTION↗
Plasma waves associated with the AMPTE artificial comet
Numerous plasma wave effects were detected by the AMPTE/IRM spacecraft during the artificial comet experiment on December 27, 1984. As the barium ion cloud produced by the explosion expanded over the spacecraft, emissions at the electron plasma frequency and ion plasma frequency provided a determination of the local electron density. The electron density in the diamagnetic cavity produced by the ion cloud reached a peak of more than 5 x 10 to the 5th per cu cm, then decayed smoothly as the cloud expanded, varying approximately as t exp-2. As the cloud began to move due to interactions with the solar wind, a region of compressed plasma was encountered on the upstream side of the diamagnetic cavity. The peak electron density in the compression region was about 1.5 x 10 to the 4th per cu cm. Later, a very intense (140 mVolt/m) broadband burst of electrostatic noise was encountered on the sunward side of the compression region. This noise has characteristics very similar to noise observed in the earth's bow shock, and is believed to be a shocklike interaction produced by an ion beam-plasma instability between the nearly stationary barium ions and the streaming solar wind protons.
Gurnett, D. A.↗
Anode power deposition in a MPD thruster with a magnetically annulled Hall parameter anode
Results from previous studies indicate that the anode fall increases monotonically with the electron Hall parameter. In an attempt to reduce the anode fall by decreasing the local electron Hall parameter, a proof-of-concept test was performed in which an array of 36 permanent magnets were imbedded within the anode of a high power quasi-steady MPD thruster to decrease the local azimuthal component of the induced magnetic field. The modified thruster was operated at power levels between 150 kW and 4 MW with Ar and He propellants. Terminal voltage, triple probe, floating probe, and magnetic probe measurements were made to characterize the performance of the thruster with new anode. Incorporation of the modified anode resulted in a reduction of the anode fall by up to 15 V with Ar and 20 V with He, which corresponded to decreased anode power fractions of 40 and 45 percent with Ar and He, respectively.
Gallimore, Alec D.↗
MMS Observations of Electrostatic Waves in an Oblique Shock Crossing
High-resolution particle and wave measurements taken during an oblique bow shock crossing by the Magnetospheric Multiscale (MMS) mission are analyzed. Two regions of differing magnetic behavior are identified within the shock, one with active magnetic fluctuations and one with laminar interplanetary magnetic field topology. A prominent reflected ion population is observed in both regions. The active magnetic region is characterized by large-amplitude (>100 mV/m) electrostatic solitary waves, electron Bernstein waves, and ion acoustic waves, along with intermittent current activity and localized electron heating. In the region of laminar magnetic field, ion acoustic waves are prominently observed. Solar wind ion deceleration is observed in both regions of active and laminar magnetic field. All observations suggest that solar wind deceleration can occur as a result of multiple independent processes, in this case current and ion-ion instabilities.
Goodrich, Katherine A.↗
Maven Observations of Electron-Induced Whistler Mode Waves in the Martian Magnetosphere
We report on narrowband electromagnetic waves at frequencies between the local electron cyclotron and lower hybrid frequencies observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft in the Martian induced magnetosphere. The peaked electric field wave spectra below the electron cyclotron frequency were first observed by Phobos-2 in the Martian magnetosphere, but the lack of magnetic field wave data prevented definitive identification of the wave mode and their generation mechanisms remain unclear. Analysis of electric and magnetic field wave spectra obtained by MAVEN demonstrates that the observed narrowband waves have properties consistent with the whistler mode. Linear growth rates computed from the measured electron velocity distributions suggest that these whistler mode waves can be generated by cyclotron resonance with anisotropic electrons. Large electron anisotropy in the Martian magnetosphere is caused by absorption of parallel electrons by the collisional atmosphere. The narrowband whistler mode waves and anisotropic electrons are observed on both open and closed field lines and have similar spatial distributions in MSO and planetary coordinates. Some of the waves on closed field lines exhibit complex frequency-time structures such as discrete elements of rising tones and two bands above and below half the electron cyclotron frequency. These MAVEN observations indicate that whistler mode waves driven by anisotropic electrons, which are commonly observed in intrinsic magnetospheres and at unmagnetized airless bodies, are also present at Mars. The wave-induced electron precipitation into the Martian atmosphere should be evaluated in future studies.
martian↗