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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Electrons in the ionospheric source cone - Evidence for runaway electrons as carriers of downward Birkeland currents

Extremely intense field-aligned fluxes of low energy electrons have been observed with ISIS-2 streaming out of the ionosphere at auroral latitudes. Fluxes in excess of 10 billion per sq cm sec ster at energies below 500 eV with peak fluxes from 10 to 100 eV were detected at 1400 km. The electrons are very strongly field-aligned, having pitch angles confined within 10 deg of the magnetic field. Since they are so intense and so highly collimated they cannot be produced by atmospheric backscattering of a primary auroral beam. These electrons are sometimes associated with ionospheric ions that have been accelerated transverse to the magnetic field. They occur in regions of downward field-aligned current, and may thus be carriers of the current, thus far unidentified. It is suggested that they are runaway electrons from the ionosphere produced by a downward field-aligned component of the electric field.

Klumpar, D. M.↗
NASA NTRS1984

The production of ion conics by oblique double layers

Magnetized test ions are subjected to acceleration through a numerically simulated oblique double layer in order to determine whether they emerge with velocity vectors aligned with or oblique to the ambient magnetic field. A criterion for oblique alignment, depending on the double-layer parameters and on the external magnetization, is obtained. When it is applied to observed and theoretical auroral double layers, this criterion predicts that accelerated heavy ions will be substantially less magnetic field aligned than will accelerated hydrogen ions, thus suggesting auroral double layers as a source of high-energy ion conics. Test particle simulations are also used to investigate the perpendicular heating of ions at low altitudes by the electric fields associated with moving auroral arcs. The rapid motion of small-scale structures in the arcs is suggested as a source of low-energy conical ion distributions, and the slow drifts of the entire arc forms are inferred to heat ionospheric ions.

Borovsky, J. E.↗
NASA NTRS1995

Geometry of interplanetary magnetic clouds

Two dimensional magnetohydrodynamic simulations are presented of the distortion of a magnetic flux rope that is being accelerated through ambient solar wind plasma. The flux rope magnetic field has an axial component parallel to the solar wind field and an azimuthal component, which lies in the simulation plane. As the flux rope moves through the solar wind plasma, vortices form on its trailing edge and couple strongly to its interior. If the flux rope azimuthal field is weak, it deforms into an elongated banana-like shape a few Alfven transit times. A strong azimuthal field component tends to inhibit this distortion. If the flux rope is taken to model a magnetic cloud, it is suggested that the shape of the cloud at 1 AU is determined by its distortion in the inner solar wind. Distortion timescales beyond 1 AU are estimated as many days. It is estimated that effective drag coefficients somewhat greater than unity are appropriate for modelling flux rope propagation.

Cargill, P. J.↗
NASA NTRS1989

Generation of macroscopic magnetic-field-aligned electric fields by the convection surge ion acceleration mechanism

The 'convection surge' model for ion acceleration, designed by Mauk (1986) to explain the observed ion distributions and the field-aligned character of middle magnetospheric ion distributions during the expansion phase of a substorm, was extended to include the self-consistent generation of magnetic-field-aligned electric fields. Results from the modified model show that the convection surge mechanism leads to the generation of dynamical macroscopic magnetic field-aligned electric fields that begin their strongest developments very near the magnetic equator and then propagate to higher latitudes. Potential drops as high as 1 to 10 kV might be expected, depending on the mass species of the ions and on the electron temperatures. It is speculated that the convection surge mechanism could be a key player in the transient field-aligned electromagnetic processes observed to operate within the middle magnetosphere.

Mauk, B. H.↗
NASA NTRS1976

Low-energy particle events associated with sector boundaries

Onsets of some 40 to 45 low-energy proton events during the years 1957-1969 coincided in time with transits of well-defined sector boundaries across the earth. These events can be interpreted as long-lived proton streams filling up some of the magnetic sectors, indicating an acceleration of protons which is not associated with typical proton-producing flares. The sharp onsets of these particle streams, as well as a deficiency of flare-associated particle events shortly before the boundary transit, indicate that in some cases magnetic sector boundaries can inhibit transverse propagation of low-energy particles in the solar corona or in interplanetary space.

Svestka, Z.↗
NASA NTRS2017

Magnetospheric Multiscale Mission Observations of the Outer Electron Diffusion Region

This paper presents Magnetospheric Multiscale mission (MMS) observations of the exhaust region in the vicinity of the central reconnection site in Earth's magnetopause current sheet. High-time-resolution measurements of field and particle distributions enable us to explore the fine structure of the diffusion region near the X line. Ions are decoupled from the magnetic field throughout the entire current sheet crossing. Electron jets flow downstream from the X line at speeds greater than the E by B drift velocity. At or around the magnetospheric separatrix, large-amplitude electric fields containing field-aligned components accelerate electrons along the magnetic field toward the X line. Near the neutral sheet, crescent-shaped electron distributions appear coincident with (1) an out-of-plane electric field whose polarity is opposite to that of the reconnection electric field and (2) the energy transfer from bulk kinetic to field energy. The observations indicate that MMS passed through the edge of an elongated electron diffusion region (EDR) or the outer EDR in the exhaust region.

Hwang, K.-J.↗
NASA NTRS1989

Plasma flow processes within magnetic nozzle configurations

An attempt is made to separate the interactive processes occurring in electromagnetic devices and to examine the acceleration of ionized gas within magnetic fields which can guide it through an expansion process. The plasma was generated in a single turn coil 50 cm long with a radius of 5.25 cm which surrounded a quartz tube with an internal radius of 3.81 cm and a length of 100 cm. Choking was found to occur at both sonic and cusp velocities which were coincident in the present experiment.

York, Thomas M.↗
NASA NTRS1994

Pulsed acceleration in solar flares

We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which suppport the following tentative conclusions: (1) Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components ('statistical flare' produced by a fragmented primary energy release). (2) The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by phase locking with an MHD wave (oscillation) mode, if both periods are close to each other. (3) Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar.

Aschwanden, Markus J.↗
NASA NTRS1985

Ultra high energy gamma rays, cosmic rays and neutrinos from accreting degenerate stars

Super-Eddington accretion for a recently proposed unipolar induction model of cosmic ray acceleration in accreting binary star systems containing magnetic white dwarfs or neutron stars is considered. For sufficiently high accretion rates and low magnetic fields, the model can account for: (1) acceleration of cosmic ray nuclei up to energies of 10 to the 19th power eV; (2) production of more or less normal solar cosmic ray composition; (3) the bulk of cosmic rays observed with energies above 1 TeV, and probably even down to somewhat lower energies as well; and (4) possibly the observed antiproton cosmic ray flux. It can also account for the high ultra high energy (UHE) gamma ray flux observed from several accreting binary systems (including Cygnus X-3), while allowing the possibility of an even higher neutrino flux from these sources, with L sub nu/L sub gamma is approximately 100.

Brecher, K.↗
NASA NTRS2018

The Advanced Energetic Pair Telescope for Gamma-Ray Polarimetry

The Advanced Energetic Pair Telescope (AdEPT), a future NASA/GSFC MIDEX mission, is being developed to perform high-sensitivity medium-energy (5-200 MeV) astronomy and revolutionary gamma-ray polarization measurements. The enabling technology for AdEPT is the Three- Dimensional Track Imager (3-DTI), a large volume gaseous time projection chamber with 2- dimentional micro-well detector (MWD) readout. The low density and high spatial resolution of the 3-DTI allows AdEPT to achieve high angular resolution (~0.5 at 67.5 MeV) and, for the first time, exceptional gamma-ray polarization sensitivity. These capabilities enable a wide range of scientific discovery potential for AdEPT. The key science goals of the AdEPT mission include: 1) Explore fundamental processes of particle acceleration in active astrophysical objects, 2) Reveal the magnetic field configuration of the most energetic accelerators in the Universe, 3) Explore the origins and acceleration of cosmic rays and the Galactic MeV diffuse emission, 4) Search for dark matter in the Galactic center, and 5) Test relativity with polarization measurements. We report on the latest developments of the MWDs for the 3-DTI.

Hunter, Stanley D.↗
NASA NTRS1981

Linear theory of tearing in a high-beta plasma

The linear dispersion relation for a collisionless plasma in a sheared one-dimensional current sheet is calculated with reference to conditions in the daytime magnetopause. Calculations are extended to include plasmas with beta approximately equal to 1. It is found that the tearing mode eigenstructure and temporal growth rate are a sensitive function of the ratios l sub s/l sub G, l sub s/l sub T, and l sub s/l sub n, where l sub s is the shearing length of the magnetic field, l sub G is the gradient scale length, and l sub T is the temperature gradient scale length. In particular, if beta is approximately equal to 1, and l sub s is less than l sub G, l sub n, and l sub T, then the thickness of the layer over which particles are resonantly accelerated by the induction magnetic field is approximately rho, a thermal gyroradius. If the above conditions are not satisfied, plasma gradients may electrostatically stabilize the mode.

Quest, K. B.↗
NASA NTRS1993

Effects of a parallel electric field and the geomagnetic field in the topside ionosphere on auroral and photoelectron energy distributions

The consequences of electric field acceleration and an inhomogeneous magnetic field on auroral electron energy distributions in the topside ionosphere are investigated. The one-dimensional, steady state electron transport equation includes elastic and inelastic collisions, an inhomogeneous magnetic field, and a field-aligned electric field. The case of a self-consistent polarization electric field is considered first. The self-consistent field is derived by solving the continuity equation for all ions of importance, including diffusion of O(+) and H(+), and the electron and ion energy equations to derive the electron and ion temperatures. The system of coupled electron transport, continuity, and energy equations is solved numerically. Recognizing observations of parallel electric fields of larger magnitude than the baseline case of the polarization field, the effect of two model fields on the electron distribution function is investigated. In one case the field is increased from the polarization field magnitude at 300 km to a maximum at the upper boundary of 800 km, and in another case a uniform field is added to the polarization field. Substantial perturbations of the low energy portion of the electron flux are produced: an upward directed electric field accelerates the downward directed flux of low-energy secondary electrons and decelerates the upward directed component. Above about 400 km the inhomogeneous magnetic field produces anisotropies in the angular distribution of the electron flux. The effects of the perturbed energy distributions on auroral spectral emission features are noted.

Min, Q.-L.↗
NASA NTRS1993

Effects of a Parallel Electric Field and the Geomagnetic Field in the Topside Ionosphere on Auroral and Photoelectron Energy Distributions

The consequences of electric field acceleration and an inhomogencous magnetic field on auroral electron energy distributions in the topside ionosphere are investigated. The one- dimensional, steady state electron transport equation includes elastic and inelastic collisions, an inhomogencous magnetic field, and a field-aligned electric field. The case of a self-consistent polarization electric field is considered first. The self-consistent field is derived by solving the continuity equation for all ions of importance, including diffusion of 0(+) and H(+), and the electron and ion energy equations to derive the electron and ion temperatures. The system of coupled electron transport, continuity, and energy equations is solved numerically. Recognizing observations of parallel electric fields of larger magnitude than the baseline case of the polarization field, the effect of two model fields on the electron distribution function in investigated. In one case the field is increased from the polarization field magnitude at 300 km to a maximum at the upper boundary of 800 km, and in another case a uniform field is added to the polarization field. Substantial perturbations of the low energy portion of the electron flux are produced: an upward directed electric field accelerates the downward directed flux of low-energy secondary electrons and decelerates the upward directed component. Above about 400 km the inhomogencous magnetic field produces anisotropies in the angular distribution of the electron flux. The effects of the perturbed energy distributions on auroral spectral emission features are noted.

Min, Q.-L.↗
NASA NTRS1988

An imaging vector magnetograph for the next solar maximum

Measurements of the vector magnetic field in the solar atmosphere with high spatial and temporal resolution over a large field of view are critical to understanding the nature and evolution of currents in active regions. Such measurements, when combined with the thermal and nonthermal X-ray images from the upcoming Solar-A mission, will reveal the large-scale relationship between these currents and sites of heating and particle acceleration in flaring coronal magnetic flux tubes. The conceptual design of an imaging vector magnetograph that combines a modest solar telescope with a rotating quarter-wave plate, an acousto-optical tunable prefilter as a blocker for a servo-controlled Fabry-Perot etalon, CCD cameras, and a rapid digital tape recorder are described. Its high spatial resolution (1/2 arcsec pixel size) over a large field of view (4 x 5 arcmin) will be sufficient to significantly measure, for the first time, the magnetic energy dissipated in major solar flares. Its millisecond tunability and wide spectra range (5000 to 8000 A) enable nearly simultaneous vector magnetic field measurements in the gas-pressure-dominated photosphere and magnetically dominated chromosphere, as well as effective co-alignment with Solar-A's X-ray images.

Canfield, Richard C.↗
NASA NTRS1999

The Magnetospheric Multiscale Mission...Resolving Fundamental Processes in Space Plasmas

The Magnetospheric Multiscale (MMS) mission is a multiple-spacecraft Solar-Terrestrial Probe designed to study the microphysics of magnetic reconnection, charged particle acceleration, and turbulence in key boundary regions of Earth's magnetosphere. These three processes, which control the flow of energy, mass, and momentum within and across plasma boundaries, occur throughout the universe and are fundamental to our understanding of astrophysical and solar system plasmas. Only in Earth's magnetosphere, however, are they readily accessible for sustained study through in-situ measurement. MMS will employ five co-orbiting spacecraft identically instrumented to measure electric and magnetic fields, plasmas, and energetic particles. The initial parameters of the individual spacecraft orbits will be designed so that the spacecraft formation will evolve into a three-dimensional configuration near apogee, allowing MMS to differentiate between spatial and temporal effects and to determine the three dimensional geometry of plasma, field, and current structures. In order to sample all of the magnetospheric boundary regions, MMS will employ a unique four-phase orbital strategy involving carefully sequenced changes in the local time and radial distance of apogee and, in the third phase, a change in orbit inclination from 10 degrees to 90 degrees. The nominal mission operational lifetime is two years. Launch is currently scheduled for 2006.

Curtis, S.↗
NASA NTRS1983

Electron cyclotron wave acceleration outside a flaring loop

A model for the secondary acceleration of electrons outside a flaring loop is proposed. The results suggest that the narrow bandwidth radiation emitted by the unstable electron distribution inside a flaring loop can become the driver for secondary electron acceleration outside the loop. It is shown that a system of electrons gyrating about and streaming along an adiabatically spatially varying, static magnetic field can be efficiently accelerated to high energies by an electromagnetic wave propagating along and polarized transverse to the static magnetic field. The predictions from our model appear to be in general agreement with existing observations.

Sprangle, P.↗
NASA NTRS2016

Electron Energization and Structure of the Diffusion Region During Asymmetric Reconnection

Results from particle-in-cell simulations of reconnection with asymmetric upstream conditions are reported to elucidate electron energization and structure of the electron diffusion region (EDR). Acceleration of unmagnetized electrons results in discrete structures in the distribution functions and supports the intense current and perpendicular heating in the EDR. The accelerated electrons are cyclotron turned by the reconnected magnetic field to produce the outflow jets, and as such, the acceleration by the reconnection electric field is limited, leading to resistivity without particle-particle or particle-wave collisions. A map of electron distributions is constructed, and its spatial evolution is compared with quantities previously proposed to be EDR identifiers to enable effective identifications of the EDR in terrestrial magnetopause reconnection.

magnetic reconnection↗