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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Trigger, an active release experiment that stimulated auroral particle precipitation and wave emissions

The experimental design by which a cesium vapor cloud was suddenly released in order to stimulate auroral particle precipitation is described along with the general results obtained. A drastic increase of the field-aligned charged-particle flux was observed with subsequent particle bursts. It is suggested that low-energy acceleration was due to parallel electric fields created by an instability which was driven by field-aligned currents resulting from the plasma injection. Pitch angle scattering in the deep magnetosphere may account for particle precipitation continuing for 130 sec after release.

Holmgren, G.↗
NASA NTRS1973

Synchrotron sources. I - Extension of theory for small pitch angles.

Some of the features of synchrotron radiation are examined which occur when relativistic particles move at small pitch angles in a magnetic field. The emission from individual particles is computed. The general properties of the emission from distributions of particles with small pitch angles is discussed, and the emissivities and degrees of polarization for several specific source models are presented. For sources which mainly contain particles with small pitch angles, the degree of circular polarization will normally be high, whereas, if the magnetic field is somewhat irregular, the degree of linear polarization will be small. If the particle distribution also has a low-energy cutoff, the emissivity will vary linearly with frequency at low frequencies.

Epstein, R. I.↗
NASA NTRS1983

Coil planet centrifugation as a means for small particle separation

The coil planet centrifuge uses a centrifugal force field to provide separation of particles based on differences in sedimentation rates by flow through a rotating coiled tube. Three main separations are considered: (1) single phase fresh sheep and human erythrocytes, (2) single phase fixed heep and human erythrocytes, and (3) electrophoretically enhanced single phase fresh sheep and human erythrocytes.

Herrmann, F. T.↗
NASA NTRS1992

MHD turbulence, reconnection, and test-particle acceleration

We examine homogeneous MHD turbulence and turbulent magnetic reconnection as possible mechanisms for accelerating cosmic ray particles. Test particle calculations are performed using fields from MHD simulations, and initially Maxwellian particle distributions are shown to evolve into power-law distributions. Simple estimates for both the maximum energy attainable and the mean energies of the accelerated particles are fairly successful and are consistent with timescales for flares and cosmic rays.

Gray, Perry C.↗
NASA NTRS1998

Coulomb Crystallization of Charged Microspheres Levitated in a Gas Discharge Plasma

The technical topic of the project was the experimental observation of Coulomb crystallization of charged microspheres levitated in a gas discharge plasma. This suspension, sometimes termed a dusty plasma, is closely analogous to a colloidal suspension, except that it has a much faster time response, is more optically thin, and has no buoyancy forces to suspend the particles. The particles are levitated by electric fields. Through their collective Coulomb repulsions, the particles arrange themselves in a lattice with a crystalline symmetry, which undergoes an order-disorder phase transition analogous to melting when the effective temperature of the system is increased. Due to gravitational sedimentation, the particles form a thin layer in the laboratory, so that the experimental system is nearly 2D, whereas in future microgravity experiments they are expected to fill a larger volume and behave like a 3D solid or liquid. The particles are imaged using a video camera by illuminating them with a sheet of laser light. Because the suspension is optically thin, this imaging method will work as well in a 3D microgravity experiment as it does in a 2D laboratory system.

Goree, John↗
NASA NTRS2007

Modeling the Prodromal Effects and Performance Reduction of Astronauts from Exposure to Large Solar Particle Events

In space exploration outside the Earth's geomagnetic field, radiation exposure from solar particle events (SPE) presents a health concern for astronauts, that could impair their performance and result in possibility of failure of the mission. Acute risks are especially of concern during spacewalks on the lunar surface because of the rapid onset of SPE's and science goals that involve long distances to crew habitats. Thus assessing the potential of early radiation effect under such adverse conditions is of prime importance. Here we present a biologic based mathematical model which describes the dose and time-dependent early human responses to ionizing radiation. We examine the possible early effects on crew behind various shielding materials from exposure to some historical large SPEs on the lunar and Mars surfaces. The doses and dose rates were calculated using the BRYNTRN code (Kim, M.Y, Hu, X, and Cucinotta, F.A, Effect of Shielding Materials from SPEs on the Lunar and Mars Surface, AIAA Space 2005, paper number AIAA-2005-6653, Long Beach, CA, August 30-September 1, 2005) and the hazard of the early radiation effects and performance reduction were calculated using the RIPD code (Anno, G.H, McClellan, G.E., Dore, M.A, Protracted Radiation-Induced Performance Decrement, Volume 1 Model Development,1996, Defense Nuclear Agency: Alexandria VA). Based on model assumptions we show that exposure to these historical SPEs do cause early effects to crew members and impair their performance if effective shielding and medical countermeasure tactics are not provided. The calculations show multiple occurrence of large SPEs in a short period of time significantly increase the severity of early illness, however early death from failure of the hematopoietic system is very unlikely because of the dose-rate and dose heterogeneity of SPEs. Results from these types of calculations will be a guide in design of protection systems and medical response strategy for astronauts in case of exposure to high dose irradiation during future space missions.

Hu, S.↗
NASA NTRS2011

Modeling Acute Health Effects of Astronauts from Exposure to Large Solar Particle Events

In space exploration outside the Earth s geomagnetic field, radiation exposure from solar particle events (SPE) presents a health concern for astronauts, that could impair their performance and result in possible failure of the mission. Acute risks are of special concern during extra-vehicular activities because of the rapid onset of SPE. However, most SPEs will not lead to acute risks but can lead to mission disruption if accurate projection methods are not available. Acute Radiation Sickness (ARS) is a group of clinical syndromes developing acutely (within several seconds to 3 days) after high dose whole-body or significant partial-body ionizing radiation exposures. The manifestation of these syndromes reflects the disturbance of physiological processes of various cellular groups damaged by radiation. Hematopoietic cells, skin, epithelium, intestine, and vascular endothelium are among the most sensitive tissues of human body to ionizing radiation. Most ARS symptoms are directly related to these tissues and other systems (nervous, endocrine, and cardiovascular, etc.) with coupled regulations. Here we report the progress in bio-mathematical models to describe the dose and time-dependent early human responses to ionizing radiation. The responses include lymphocyte depression, granulocyte modulation, fatigue and weakness syndrome, and upper gastrointestinal distress. The modest dose and dose-rates of SPEs are predicted to lead to large sparing of ARS, however detailed experimental data on a range of proton dose-rates for organ doses from 0.5 to 2 Gy is needed to validate the models. We also report on the ARRBOD code that integrates the BRYNTRN and SUMDOSE codes, which are used to estimate the SPE organ doses for astronauts under various space travel scenarios, with our models of ARS. The more recent effort is to provide easy web access to space radiation risk assessment using the ARRBOD code.

Hu, Shaowen↗
NASA NTRS1984

Rocket observations of the ionosphere during the eclipse of 26 February 1979

Electron density profiles and energetic particle fluxes were determined from two rockets launched, respectively, at the beginning and end of totality during the solar eclipse of 26 February 1979. These, and one other rocket at the same time of day on 24 February 1979, were launched from near Red Lake, Ontario. The electron density profile from 24 February shows the electron density to be normal above 110 km, to rocket apogee. Below 110 km, the electron density is enhanced, by an order of magnitude in the D region, compared with data from Wallops Island at the same solar zenith angle (63 deg). The enhancement is qualitatively explained by the large flux of field aligned energetic particles observed on the same rocket. During totality (on 26 February) the electron density above 110 km to rocket apogee is reduced by a factor of about three. Below 110 km, the electron density is much greater than observed during previous eclipses. The particle flux measured on the 26 February was an order of magnitude less than that on the 24 February but showed greater variability, particularly at the higher energies (100 keV). A feature of the particle flux is that, for the two rockets that were separated horizontally by 38 km while above the absorbing region, the variations are uncorrelated.

Mcinerney, M. K.↗
NASA NTRS1972

Fermi acceleration of auroral particles.

Review of a number of nighttime acceleration mechanisms proposed in the literature for the role of producing the keV nighttime auroral-particle fluxes. Parallel electric fields are rejected for several reasons, but particularly because of the observed simultaneous precipitation of electrons and protons. Acceleration in the neutral sheet is inadequate for producing the particle energies, the observed field-aligned pitch-angle distribution at high latitudes, and the spectral hardening toward lower latitudes. Neutral point mechanisms, although often suggested in principle, have never been demonstrated satisfactorily in theory or in practice. Pitch-angle scattering from a trapped population produced by transverse adiabatic compression is also incapable of producing the field-aligned distribution. It is therefore suggested that longitudinal or Fermi acceleration, which results from the known magnetospheric convection, is the main nighttime auroral acceleration mechanism. The argument is supported by data obtained with the soft-particle spectrometer on Isis 1.

Sharber, J. R.↗
NASA NTRS2016

Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares

The mechanism that accelerates particles to the energies required to produce the observed high-energy impulsive emission in solar flares is not well understood. Drake et al. proposed a mechanism for accelerating electrons in contracting magnetic islands formed by kinetic reconnection in multi-layered current sheets (CSs). We apply these ideas to sunward-moving flux ropes (2.5D magnetic islands) formed during fast reconnection in a simulated eruptive flare. A simple analytic model is used to calculate the energy gain of particles orbiting the field lines of the contracting magnetic islands in our ultrahigh-resolution 2.5D numerical simulation. We find that the estimated energy gains in a single island range up to a factor of five. This is higher than that found by Drake et al. for islands in the terrestrial magnetosphere and at the heliopause, due to strong plasma compression that occurs at the flare CS. In order to increase their energy by two orders of magnitude and plausibly account for the observed high-energy flare emission, the electrons must visit multiple contracting islands. This mechanism should produce sporadic emission because island formation is intermittent. Moreover, a large number of particles could be accelerated in each magneto hydro dynamic-scale island, which may explain the inferred rates of energetic-electron production in flares. We conclude that island contraction in the flare CS is a promising candidate for electron acceleration in solar eruptions.

Guidoni, S. E.↗
NASA NTRS1979

The magnetic anomaly model of the Jovian magnetosphere - Predictions for Voyager

The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground-based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub-spacecraft System III longitude and the time, modulo 10 hours, of the first and subsequent magnetopause crossings.

Dessler, A. J.↗
NASA NTRS1976

Ion and electron pulses observed in the magnetotail and rapid annihilation of magnetic field lines

Hydrogen, helium, and CNO ion and electron pulses were detected in the magnetotail, and in the upstream region from the earth's bow shock. It was found that, in the magnetotail, ions appeared more frequently in the dusk than in the dawn quarter whereas the electron population had a reversed asymmetry. This spatial distribution - a polarization in the same direction as the electric field in the neutral sheet - suggests that these particles are accelerated by the electric field induced by a rapid annihilation of magnetic field lines. From the observed particle energies, the annihilation speed was estimated and found to be as high as 0.2 times the Alfven speed.

Fan, C. Y.↗
NASA NTRS1991

The 3-D description of vertical current sheets with application to solar flares

Following a brief review of the processes which have been suggested for explaining the occurrence of solar flares we suggest a new scenario which builds on the achievements of the previous suggestion that the current sheets, which develop naturally in 3-D cases with gravity from impacting independent magnetic structures (i.e., approaching current systems), do not consist of horizontal currents but are instead predominantly vertical current systems. This suggestion is based on the fact that as the subphotospheric sources of the magnetic field displace the upper photosphere and lower chromosphere regions, where plasma beta is near unity, will experience predominantly horizontal mass motions which will lead to a distorted 3-D configurations of the magnetic field having stored free energy. In our scenario, a vertically flowing current sheet separates the plasma regions associated with either of the subphotospheric sources. This reflects the balanced tension of the two stressed fields which twist around each other. This leads naturally to a metastable or unstable situation as the twisted field emerges into a low beta region where vertical motions are not inhibited by gravity. In our flare scenario the impulsive energy release occurs, initially, not by reconnection but mainly by the rapid change of the magnetic field which has become unstable. During the impulsive phase the field lines contort in such way as to realign the electric current sheet into a minimum energy horizontal flow. This contortion produces very large electric fields which will accelerate particles. As the current evolves to a horizontal configuration the magnetic field expands vertically, which can be accompanied by eruptions of material. The instability of a horizontal current is well known and causes the magnetic field to undergo a rapid outward expansion. In our scenario, fast reconnection is not necessary to trigger the flare, however, slow reconnection would occur continuously in the current layer at the locations of potential flaring. During the initial rearrangement of the field strong plasma turbulence develops. Following the impulsive phase, the final current sheet will experience faster reconnection which we believe responsible for the gradual phase of the flare. The reconnection will dissipate part of the current and will produce sustained and extended heating in the flare region and in the postflare loops.

Fontenla, Juan M.↗
NASA NTRS1993

The earth's magnetosphere under continued forcing - Substorm activity during the passage of an interplanetary magnetic cloud

Magnetic field and energetic particle observations from six spacecraft in the near-earth magnetotail are described and combined with ground magnetograms to document for the first time the magnetospheric substorm activity during a 30-hour long transit of an interplanetary cloud at 1 AU. During an earlier 11-hr interval when B(z) was continuously positive, the magnetosphere was quiescent, while in a later 18-hr interval when B(z) was uninterruptedly negative a large magnetic storm was set off. In the latter interval the substorm onsets recurred on average every 50 min. Their average recurrence frequency remained relatively undiminished even when the magnetic cloud B(z) and other measures of the interplanetary energy input decreased considerably. These results concur with current models of magnetospheric substorms based on deterministic nonlinear dynamics. The substorm onset occurred when the cloud's magnetic field had a persistent northward component but was predominantly westward pointing.

Farrugia, C. J.↗
NASA NTRS1984

Mapping the magnetosheath field between the magnetopause and the bow shock - Implications for magnetospheric particle leakage

An approximate picture of the volumes occupied by particles that originate in the vicinity of the magnetopause is obtained by mapping magnetosheath magnetic field lines which drape over the magnetopause through the bow shock. Subsets of these field lines that connect to potential sites of magnetic merging on the magnetopause are also traced in the event that the particle leakage occurs preferentially where normal components of the field are present across that boundary. The results of this modeling exercise suggest that energetic magnetospheric particles which are not scattered by magnetosheath magnetic fluctuations are likely to exit the magnetosheath in the region of the quasi-parallel shock.

Luhmann, J. G.↗
NASA NTRS1983

Interaction of ring current ions with the magnetopause

An analysis of phase space density observations of 30-130 keV ring current protons made during a magnetopause crossing of ISEE 1 indicates that the phase space densities of 30-65 keV protons within the magnetosphere are higher for particles streaming parallel to the field than antiparallel to the field. In the magnetosheath, phase space densities parallel to the field are higher than the densities of both outward- and inward-flowing particles parallel to the field within the magnetosphere. The observations are discussed in the terms of reflected and transmitted ring current protons' acceleration in the magneteopause current layer.

Scholer, M.↗