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At least 235 records · Page 13

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NASA NTRS1981

Structure of the low-latitude boundary layer

High temporal resolution observations of the frontside magnetopause and plasma boundary layer made with the fast plasma analyzer aboard the ISEE 1 and 2 spacecraft are reported. The data are found to be compatible with a boundary layer that is always attached to the magnetopause but where the layer thickness has a large-scale spatial modulation pattern which travels tailward past the spacecraft. Periods are included when the thickness is essentially zero and others when it is of the order of 1 earth radius. The duration of these periods is highly variable but is typically in the range of 2-5 min corresponding to a distance along the magnetopuase of approximately 3-8 earth radii. The observed boundary layer features include a steep density gradient at the magnetopause with an approximately constant boundary layer plasma density amounting to about 25% of the magnetosheath density, and a second abrupt density decrease at the inner edge of the layer.

Sckopke, N.↗

NASA NTRS1993

Broad-Band X-Ray Telescope spectroscopy of Xi Puppis

The Broad-Band X-Ray Telescope obtained moderate-resolution (about 90 eV) X-ray spectra of the O4 f star Xi Pup during the STS 35/Astro 1 mission in 1990 December. Despite the shortness of the observation (600 s), the data show a surprising amount of detail. We report the detection of an O absorption edge produced by ionized overlying wind material and K-shell line emission from Mg produced by a thermal plasma of temperature near 6 x 10 exp 6 K. The data are used to place constraints on the location, temperature, and amount of the X-ray-emitting gas, as well as the abundance and ionization of the wind material.

Corcoran, M. F.↗

NASA NTRS2009

The Invariant Twist of Magnetic Fields in the Relativistic Jets of Active Galactic Nuclei

The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of accretion disks in Active Galactic Nuclei (AGNs) by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with photons. While dynamo processes show no preference for the polarity of the (presumably random) seed field that they amplify, this alternative mechanism uniquely relates the polarity of the poloidal B field to the angular velocity of the accretion disk, resulting in a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry came about by chance being less than 1 %. This lends support to the hypothesis that the Universe is seeded by B fields that are generated in AGN via this mechanism

Contopoulos, Ioannis↗

NASA NTRS2014

Ionosphere Plasma State Determination in Low Earth Orbit from International Space Station Plasma Monitor

A plasma diagnostic package is deployed on the International Space Station (ISS). The system - a Floating Potential Measurement Unit (FPMU) - is used by NASA to monitor the electrical floating potential of the vehicle to assure astronaut safety during extravehicular activity. However, data from the unit also reflects the ionosphere state and seems to represent an unutilized scientific resource in the form of an archive of scientific plasma state data. The unit comprises a Floating Potential probe and two Langmuir probes. There is also an unused but active plasma impedance probe. The data, at one second cadence, are collected, typically for a two week period surrounding extravehicular activity events. Data is also collected any time a visiting vehicle docks with ISS and also when any large solar events occur. The telemetry system is unusual because the package is mounted on a television camera stanchion and its data is impressed on a video signal that is transmitted to the ground and streamed by internet to two off center laboratory locations. The data quality has in the past been challenged by weaknesses in the integrated ground station and distribution systems. These issues, since mid‐2010, have been largely resolved and the ground stations have been upgraded. Downstream data reduction has been developed using physics based modeling of the electron and ion collecting character in the plasma. Recursive algorithms determine plasma density and temperature from the raw Langmuir probe current voltage sweeps and this is made available in real time for situational awareness. The purpose of this paper is to describe and record the algorithm for data reduction and to show that the Floating probe and Langmuir probes are capable of providing long term plasma state measurement in the ionosphere. Geophysical features such as the Appleton anomaly and high latitude modulation at the edge of the Auroral zones are regularly observed in the nearly circular, 51 deg inclined, 400 km altitude ISS orbit. Evidence of waves in the ion collection current data is seen in geographic zones known to exhibit the spread‐F phenomenon. An anomaly in the current collection characteristic of the cylindrical probe appears also too be organized by the geomagnetic field.

Kramer, Leonard↗

NASA NTRS1982

Observations of structuring in the downstream region of a large spherical model in a laboratory simulated solar wind plasma

The effects of inserting a spherical conducting model, large in comparison with the Debye length, into a free streaming high-energy 1 kV) unmagnetized hydrogen plasma are investigated in order to measure energies and compositions directly relevant to solar wind and astrophysical plasma phenomena. Holding the incident plasma parameters constant, transverse profiles of the net Langmuir probe current are plotted at various locations downstream in the model wake and are divided into three regions (the shadow, transition, and boundary). Results attributable to the use of a high-energy plasma show that enhancements in the shadow exist at downstream locations where the Mach ratio is less than one, and turbulence exists in the transition region on the shadow edges and outside in the boundary region. In addition, a small current enhancement is found in the boundary and can be attributed to the plasma/model interaction. It is concluded that many similar features observed by spacecraft downstream from planetary bodies are relatively permanent and are due to the intrinsic nature of the interaction between the solar wind plasma and the obstacle.

Intriligator, D. S.↗

NASA NTRS2011

K-Shell Photoionization of Nickel Ions Using R-Matrix

We present R-matrix calculations of photoabsorption and photoionization cross sections across the K edge of the Li-like to Ca-like ions stages of Ni. Level-resolved, Breit-Pauli calculations were performed for the Li-like to Na-like stages. Term-resolved calculations, which include the mass-velocity and Darwin relativistic corrections, were performed for the Mg-like to Ca-like ion stages. This data set is extended up to Fe-like Ni using the distorted wave approximation as implemented by AUTOSTRUCTURE. The R-matrix calculations include the effects of radiative and Auger dampings by means of an optical potential. The damping processes affect the absorption resonances converging to the K thresholds causing them to display symmetric profiles of constant width that smear the otherwise sharp edge at the K-shell photoionization threshold. These data are important for the modeling of features found in photoionized plasmas.

Witthoeft, M. C.↗

NASA NTRS2016

MMS Observations of Ion-Scale Magnetic Island in the Magnetosheath Turbulent Plasma

In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 di, where di is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma..

Huang, S. Y.↗

NASA NTRS1986

Quiet time mass composition at near-geosynchronous altitudes

Mass composition data acquired from the near-geosynchronous SCATHA spacecraft during magnetically quiet times are analyzed. The time intervals over which data were included in the study span some four months in the spring and summer of 1979. This allows a reasonable coverage in both L shell and magnetic local time. At the higher L shells, L greater than 6.5, the mass composition data are consistent with sunward convection of plasma sheet particles. Protons and alpha particle fluxes peak near the 90 deg pitch angle. There is evidence that the alpha particle spatial distribution has a sharp inner edge near L = 6.5. At lower L values, the proton characteristics change. The density of protons above 1 keV decreases, while the lower-energy protons show an increase in density. The oxygen ions show a similar change, in that there is a large increase in the lower-energy oxygen ions from high L to low L, especially, in the dusk and midnight local time sectors. This suggests that the ionosphere may be continuously supplying plasma to the inner magnetosphere even during magnetically quiet times.

Strangeway, R. J.↗

NASA NTRS1986

Analysis and interpretation of the shocklike electrostatic noise observed during the AMPTE solar wind lithium releases

During the AMPTE (Active Magnetospheric Particle Tracer Explorers) solar wind lithium release on September 11, and again on September 20, 1984, an intense burst of electrostatic noise was observed near the upstream edge of the ion cloud. Comparisons with measurements by the IMP-6 and ISEE-1 spacecraft show that the spectrum and overall features of this noise are very similar to electrostatic noise observed at the Earth's bow shock. A stability analysis using realistic parameters shows that the electrostatic noise can be accounted for by an ion beam-plasma instability caused by the solar wind proton beam streaming through the nearly stationary lithium cloud. The growth rate of this instability is largest when the ion density and solar wind proton density are similar, which explains why the noise only occurs near the outer edge of the ion cloud. The similarity to the noise in the Earth's bow shock suggest that a shock may exist in the solar wind plasma flow upstream of the ion cloud. If the noise is associated with a shock, then it must be an electrostatic shock, since the ion cyclotron radii are too small for the existence of a MHD shock. Since the electrostatic instability occurs at phase velocities near the lithium thermal velocity, the electrostatic turbulence may play a role in heating the lithium ions and transferring momentum from the solar wind to the ion cloud.

Gurnett, D. A.↗

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

Spectral evidence for stirring scales and two-dimensional turbulence in the auroral ionosphere

Electric field power spectra from two auroral sounding rocket flights show evidence of a distinct scale size regime for injection of energy into the auroral oval. The signature of this process is a broad plateau in the spectrum, with power law dependences at both shorter and longer scale sizes. We argue that the spectral properties at high k are dominated by processes occurring near the edges of inverted-V electron precipitation regions (auroral arcs). We see no compelling reason to conclude that a linear local plasma instability is occurring but rather, that nonlinear mixing and forward cascade yield the observed velocity field. The spectra of simultaneously observed density irregularities are quite different from those of the electric field, implying that the plasma density does not behave as a passive scalar in the auroral zone during active conditions. At low-k values we show that the rocket spectra are consistent with the power spectra of magnetospheric electric fields measured by the DE, AE-C, and Hilat stallites.

Earle, G. D.↗

NASA NTRS1995

ROSAT observations of the unusual supernova remnant CTB 80 containing the pulsar PSR 1951 + 32

The unusal supernova remnant CTB, 80 containing the 39.5 ms pulsar PSR 1951 + 32, has been observed with the Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI) aboard ROSAT. The HRI image, centered on the pulsar, is composed of a bright compact core of approximately 1 arcminute radius containing the pulsar and a compact nebula, as well as a diffuse nebula extending approximately 5 arcminutes eastward of the pulsar. The PSPC allowed us to model the spectra of the point source, the compact nebula and the 5 arcminute diffuse nebula. For a power-law spectrum with photon index Gamma approximately 2 and an interstellar column density of N(sub H) approximately 3 x 10(exp 21)/cm(exp 21) the derived luminosities are approximately 2.3 x 10(exp 33) d(sub 2.5)(exp 2) ergs/s from the pointlike source, approximately 3.9 x 10(exp 33) d(sup 2.5)(exp 2) ergs/s from the compact nebula, and approximately 1.8 x 10(exp 33) d(sub 2.5)(exp 2) ergs/s from the 5 arcminutes diffuse nebula. In addition, the 2 deg diameter circular field of view of the PSPC reveals a hard emission feature southeast of the pulsar with a conical geometry extending out to the edge of the detector. The spectrum from this region is well described by a two-temperature Raymond-Smith thermal plasma with an average temperature of approximately 10(exp 7) K and a luminosity of approximately 10(exp 34)d(sub 2.5)(exp 2) ergs/s. Pulsations from the 39.5 ms puslar, PSR 1951 + 32, are detected at the 99% confidence level. The implied pulsed fration is approximately 35% with a complicated energy-dependent behavior. The compact core and the extended diffuse nebula can be explained as synchrotron radiation from the relativistic pulsar wind confined by the ram pressure of the surrounding inhomgeneous medium. The conelike feature detected southeast of PSR 1951 + 32 is consistent with emission from an optically thin SNR in the radiative cooling phase of its evolution.

Safi-Harb, Samar↗

NASA NTRS1986

Plasma waves observed by the IRM and UKS spacecraft during the AMPTE solar wind lithium releases - Overview

The wave measurements from the Ion Release Module and the United Kingdom Satellite in the diamagnetic cavity, the transition region, and the upstream region are examined. Solar wind conditions during the releases on September 11 and 20, 1984 are described. The quasi-static electric field, wideband, high-frequency waves, and medium and VLF waves observations are analyzed. The data reveal that extremely low levels of wave activity are observed in the boundary between the diamagnetic cavity and external magnetic field, medium and VLF waves in the ion acoustic electrostatic cyclotron harmonic modes are detected in the transition region from the diamagnetic cavity to the solar wind, and decay in the magnetic field strength and density, and an increase in the quasi-static electric field is seen in the upstream edge of the transition region. The emissions observed are related to the different phases of the Li cloud development and different spatial regimes of the Li plasma-solar wind interaction.

Haeusler, B.↗

NASA NTRS1993

LDEF Space Plasma-High Voltage Drainage Experiment post-flight results

The Space Plasma-High Voltage Drainage Experiment (SP-HVDE) was comprised of two identical experimental trays. With one tray located on the leading (ram facing, B10) edge and the other located on the trailing (wake facing, D4) edge of the Long Duration Exposure Facility (LDEF), it was possible to directly compare the effects of ram and wake spacecraft environments on charged dielectric materials. Six arrays of Kapton dielectric samples of 2 mil, 3 mil, and 5 mil thicknesses maintained at +/- 300, +/- 500, and +/- 1000 voltage bias formed the experimental matrix of each tray. In addition, each tray carried two solar cell strings, one biased at +300 volts and the other at -300 volts, to study current leakage from High Voltage Solar Arrays (HVSA). The SP-HVDE provides the first direct, long-term, in-flight measurements of average leakage current through dielectric materials under electric stress. The experiment also yields information on the long term stability of the bulk dielectric properties of such materials. Data and findings of the SP-HVDE are an extension of those from shorter term flight experiments such as the PIX-1 (Plasma Interaction Experiment) and PIX-2 and are therefore valuable in the design and evaluation of long-lived space systems with high voltage systems exposed to the low earth orbital environment. A summary of the SP-HVDE post flight analysis final report delivered to the LDEF Project Office under contract to the National Aeronautics and Space Administration is presented.

Yaung, J. Y.↗

NASA NTRS1993

Double layer propagation in experiments with electron beam injection

Electron beam injection into a plasma is investigated using the analytical inverted Bernstein-Green-Kruskal method. Particle number and momentum conservation laws are applied to evaluate the propagation velocity and potential drop on the leading edge of the beam. Electric potential is supposed to be monotonic, thus the leading front has a double-layer-like structure. For the case of cold particles, analytical expressions for the double layer velocity and potential drop are obtained. It is pointed out that double layer velocity differs from the initial electron speed: even for weak beams a noticeable deceleration takes place. Strong beams are found incapable of penetrating into plasma - their propagation velocity is very small. Ambient electrons undergo a considerable acceleration forming a return current which neutralizes the injector. Possible instability of the distribution functions is discussed.

Bruskin, L. G.↗

NASA NTRS1982

The fine structure of the front side magnetopause during two successive crossings

The magnetopause crossings of November 10, 1977, which are considered to be representative of a class of structures, are investigated, and a procedure is developed to derive approximate surface currents near the magnetopause from ISEE 1 magnetic field data by assuming a constant speed of the magnetopause along its normal for each crossing of the magnetopause layer. Changes in the magnetic field indicate that current sheets exist on each side of the magnetopause layer, which is characterized by an irregular magnetic field and a magnetosheath-like energy distribution. No boundary layer plasma is observed on the magnetospheric field lines inside the magnetopause, and electromagnetic energy is found to be dissipated at the two edges of the magnetopause layer where the current layers are observed.

Formisano, V.↗

NASA NTRS1990

Observations of filamentary field-aligned current coupling between the magnetospheric boundary layer and the ionosphere

A distinct class of dayside high-latitude magnetic pulsations can be identified from the spatial characteristics of the disturbance field. These pulsations exhibit traveling radial patterns such as would result from moving filaments of field-aligned current interacting with the ionosphere to produce cells of Hall current and vortexlike plasma flow. Time intervals containing a series of continuous multiple vortices are investigated here. The vortices occur on the boundary between sunward and antisunward ionospheric plasma convection. Low altitude DMSP satellite particle measurements indicate that the vortices are on magnetic field lines which map to the inner edge of the magnetospheric low latitude boundary layer. No repetitive solar wind disturbance (e.g., pressure variations) appears to be associated with the events, suggesting that the vortices are related to a local magnetospheric instability. No strong correlation between interplanetary field conditions and the detection of vortices is found.

Clauer, C. R.↗

NASA NTRS1997

Gravity Wave Seeding of Equatorial Plasma Bubbles

Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.

Singh, Sardul↗