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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 289 records · Page 16
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NASA NTRS1983

The hydrodynamics of magnetic nonequilibrium

Because the dynamical nonequilibrium of closely packed twisted flux tubes is essentially the problem of two-dimensional MHD turbulence, the extensive literature on two-dimensional turbulence represents the hydrodynamics of magnetic nonequilibrium. Many features of the turbulence can conversely be understood as a consequence of the dynamical nonequilibrium. Attention is presently given to the dynamics of the strong fluid jets, issuing from reconnection points, that are exhibited by numerical simulations of two-dimensional turbulence. Simple examples are given which show that the uniformity of jet width observed is a consequence of the form of the pressure of the magnetic fields between which the jets are confined. The general hydrodynamics of a layer of fluid confined by steady pressures is reducible to a quadrature, so that a variety of effects may be considered, including gravitation. The dissipation of the solar corona is discussed.

Parker, E. N.↗
NASA NTRS1994

Space Experiments with Particle Accelerators (SEPAC)

The scientific emphasis of this contract has been on the physics of beam ionosphere interactions, in particular, what are the plasma wave levels stimulated by the Space Experiments with Particle Accelerators (SEPAC) electron beam as it is ejected from the Electron Beam Accelerator (EBA) and passes into and through the ionosphere. There were two different phenomena expected. The first was generation of plasma waves by the interaction of the DC component of the beam with the plasma of the ionosphere, by wave particle interactions. The second was the generation of waves at the pulsing frequency of the beam (AC component). This is referred to as using the beam as a virtual antenna, because the beam of electrons is a coherent electrical current confined to move along the earth's magnetic field. As in a physical antenna, a conductor at a radio or TV station, the beam virtual antenna radiates electromagnetic waves at the frequency of the current variations. These two phenomena were investigated during the period of this contract.

Taylor, William W. L.↗
NASA NTRS1998

Global Distribution of Density Irregularities in the Equatorial Ionosphere

We analyzed measurements of ion number density made by the retarding potential analyzer aboard the Atmosphere Explorer-E (AE-E) satellite, which was in an approximately circular orbit at an altitude near 300 km in 1977 and later at an altitude near 400 km. Large-scale (greater than 60 km) density measurements in the high-altitude regions show large depletions of bubble-like structures which are confined to narrow local time longitude, and magnetic latitude ranges, while those in the low-altitude regions show relatively small depletions which are broadly distributed,in space. For this reason we considered the altitude regions below 300 km and above 350 km and investigated the global distribution of irregularities using the rms deviation delta N/N over a path length of 18 km as an indicator of overall irregularity intensity. Seasonal variations of irregularity occurrence probability are significant in the Pacific regions, while the occurrence probability is always high in die Atlantic-African regions and is always low in die Indian regions. We find that the high occurrence probability in the Pacific regions is associated with isolated bubble structures, while that near 0 deg longitude is produced by large depictions with bubble structures which are superimposed on a large-scale wave-like background. Considerations of longitude variations due to seeding mechanisms and due to F region winds and drifts are necessary to adequately explain the observations at low and high altitudes. Seeding effects are most obvious near 0 deg longitude, while the most easily observed effect of the F region is the suppression of irregularity growth by interhemispheric neutral winds.

Kil, Hyosub↗
NASA NTRS2003

Interplanetary Coronal Mass Ejections in the Near-Earth Solar Wind During 1996-2002

We summarize the occurrence of interplanetary coronal mass injections (ICMEs) in the near-Earth solar wind during 1996-2002, corresponding to the increasing and maximum phases of solar cycle 23. In particular, we give a detailed list of such events. This list, based on in-situ observations, is not confined to subsets of ICMEs, such as magnetic clouds or those preceded by halo CMEs observed by the SOHO/LASCO coronagraph, and provides an overview of 214 ICMEs in the near-Earth solar wind during this period. The ICME rate increases by about an order of magnitude from solar minimum to solar maximum (when the rate is approximately 3 ICMEs/solar rotation period). The rate also shows a temporary reduction during 1999, and another brief, deeper reduction in late 2000-early 2001, which only approximately track variations in the solar 10 cm flux. In addition, there are occasional periods of several rotations duration when the ICME rate is enhanced in association with high solar activity levels. We find an indication of a periodic variation in the ICME rate, with a prominent period of approximately 165 days similar to that previously reported in various solar phenomena. It is found that the fraction of ICMEs that are magnetic clouds has a solar cycle variation, the fraction being larger near solar minimum. For the subset of events that we could associate with a CME at the Sun, the transit speeds from the Sun to the Earth were highest after solar maximum.

Cane, H. V.↗
NASA NTRS1984

IUE observations of longitudinal and temporal variations in the Jovian auroral emission

The IUE's short wavelength spectrograph has been used to monitor the auroral emissions from Jupiter's northern hemisphere, yielding eight observations between January 1981 and January 1982 of H I Lyman-alpha and the H2 Lyman and Werner bands. Attention is given to an apparent periodic emission flux fluctuation, through detailed modeling of the emission geometry. Two possible auroral zones are defined at the north pole by mapping the magnetic field lines from the Io torus and the magnetotail onto the planet's atmosphere. The observed variation in flux with central meridian longitude is not consistent with a uniform brightness as a function of magnetic longitude in either auroral zone. The data can be fitted by confining the emissions to the region of the northern torus auroral zone, in qualitative agreement with the magnetic anomaly model. A similar emission from the magnetotail auroral zone cannot be ruled out.

Skinner, T. E.↗
NASA NTRS1987

Rapid temporal evolution of radiation from non-thermal electrons in solar flares

Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung x-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard x-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

Lu, Edward T.↗
NASA NTRS1988

Rapid temporal evolution of radiation from nonthermal electrons in solar flares

Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung X-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard X-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

Lu, Edward T.↗
NASA NTRS2010

Miniature Lightweight Ion Pump

This design offers a larger surface area for pumping of active gases and reduces the mass of the pump by eliminating the additional vacuum enclosure. There are three main components to this ion pump: the cathode and anode pumping elements assembly, the vacuum enclosure (made completely of titanium and used as the cathode and maintained at ground potential) containing the assembly, and the external magnet. These components are generally put in a noble diode (or differential) configuration of the ion pump technology. In the present state of the art, there are two cathodes, one made of titanium and the other of tantalum. The anodes are made up of an array of stainless steel cylinders positioned between the two cathodes. All the elements of the pump are in a vacuum enclosure. After the reduction of pressure in this enclosure to a few microns, a voltage is applied between the cathode and the anode elements. Electrons generated by the ionization are accelerated toward the anodes that are confined in the anode space by the axial magnetic field. For the generation of the axial field along the anode elements, the magnet is designed in a C-configuration and is fabricated from rare earth magnetic materials (Nd-B-Fe or Sm-Co) possessing high energy product values, and the yoke is fabricated from the high permeability material (Hiperco-50A composed of Fe-Co-V). The electrons in this region collide with the gas molecules and generate their positive ions. These ions are accelerated into the cathode and eject cathode material (Ti). The neutral atoms deposit on the anode surfaces. Because of the chemical activity of Ti, the atoms combine with chemically active gas molecules (e.g. N2, O2, etc.) and remove them. New layers of Ti are continually deposited, and the pumping of active gases is thus accomplished. Pumping of the inert gases is accomplished by their burial several atomic layers deep into the cathode. However, they tend to re-emit if the entrapping lattice atoms are sputtered away. For stable pumping of inert gases, one side of the cathode is made of Ta. Impaction on Ta produces energetic, neutral atoms that pump the inert gases on the anode structure at the peripheral areas of the cathodes (between anode rings). For inert gases stability, a post design has been implemented. Here, posts of cathode material (Ti) are mounted on the cathode. These protrude into the initial part of the anode elements. Materials sputtered from the posts condense on the anode assembly and on the cathode plane at higher rates than in the normal diodes due to enhanced sputtering at glancing angles from geometrical considerations. This increases pumping by burial. This post design has enhanced pumping rates for both active and inert gases, compared with conventional designs.

Sinha, Mahadeva P.↗
NASA NTRS1992

On the virial theorem for turbulent molecular clouds

An Eulerian, rather than Lagrangian, form of the virial theorem is derived for a turbulent, magnetized cloud embedded in a steady, turbulent, low-density intercloud medium. The role of turbulent pressure in cloud confinement is clarified, and it is shown that, in the absence of a magnetic field, a cloud can be at a somewhat lower pressure than the intercloud medium. Simple forms for the magnetic term in the virial equation are obtained. Radiation pressure is considered; its effects are relatively small under average conditions in the interstellar medium. Under typical conditions, external pressure and magnetic fields are shown to have a relatively small effect on virial estimates of the mass of self-gravitating clouds.

Mckee, Christopher F.↗
NASA NTRS1994

Galactic cosmic ray modulation and interplanetary medium perturbations due to a long-living active region during October 1989

During October 1989, three very energetic flares were ejected by the same active region at longitudes 9 deg E, 32 deg W, and 57 deg W, respectively. The shape of the galactic cosmic ray variations suggests the presence of large magnetic cloud structures (Nagashima et al., 1990) following the shock-associated perturbations. In spite of long data gaps the interplanetary observations at Interplanetary Monitoring Platform (IMP) 8 (near the Earth) and International Cometary Explorer (ICE)(approximately 1 AU, approximately 65 deg W) confirm this possibility for the event related to the 9 deg E flare; the principal axes analysis shows that the interplanetary magnetic field variations at both spacecraft locations are mainly confined on a meridian plane. This result suggests that the western longitudinal extension of this cloud is indeed very large (greater than or equal to 5 deg). The nonnegligible depression in the cosmic ray intensity observed inside the possible cloud related to the 57 deg W flare indicates that also the eastern extension could be very wide. The analysis of neutron monitor data shows clearly the cosmic ray trapping effect of magnetic clouds; this mechanism seems to be responsible for the enhanced diurnal effect often observed during the recovery phase of Forbush decreases. We give an interpretation for the anisotropic cosmic ray peak occurring in the third event, and, related to that, we suggest that the Forbush decrease modulated region at the Earth's orbit could be somewhat wider than the magnetic cloud, as already anticipated by Nagashima et al. (1990). By this analysis, based mainly on cosmic ray data, we show that it is possible to do reasonable inferences on the large-scale structure of flare-related interplanetary perturbations when interplanetary medium data are not completely present.

Bavassano, B.↗
NASA NTRS1976

The galactic distribution (in radius and Z) of interstellar molecular hydrogen

Observations of the galactic longitude and latitude distributions of gamma = 2.6 mm CO emission are presented. Analysis of this spectral line data yields the large scale distribution of molecular clouds in the galactic disk and their z-distribution out of the disk. Strong maxima in the number of molecular clouds occur in the galactic nucleus and at galactic radii 4-8 kpc. The peak at 4-8 kpc correlates well with a region of enhanced 100 Mev gamma ray emissivity. This correlation strongly supports the conclusion that the gamma rays are produced as a result of cosmic ray interactions in molecular H2 clouds rather than HI. One important implication of this is that the interstellar magnetic field lines to which cosmic rays are confined must therefore not be excluded from these dense clouds. The width of the cloud layer perpendicular to galactic plane between half density points is 105 + or - 15 pc near the 5.5 kpc peak. The total mass of molecular gas in the interior of the galaxy exceeds that of atomic hydrogen.

Scoville, N. Z.↗
NASA NTRS1983

A static model of chromospheric heating in solar flares

The response of the solar chromosphere to flare processes, namely nonthermal electrons, thermal conduction, and coronal pressure, is modeled. Finite difference methods employing linearization and iteration are used in obtaining simultaneous solutions to the equations of steady-state energy balance, hydrostatic equilibrium, radiative transfer, and atomic statistical equilibrium. The atmospheric response is assumed to be confined to one dimension by a strong vertical magnetic field. A solution is obtained to the radiative transfer equation for the most important optically thick transitions of hydrogen, magnesium, and calcium. The theoretical atmospheres discussed here are seen as elucidating the role of various physical processes in establishing the structure of flare chromospheres. At low coronal pressures, conduction is found to be more important than nonthermal electrons in establishing the position of the transition region. Only thermal conduction can adequately account for the chromospheric evaporation in compact flares. Of the mechanisms considered, only nonthermal electrons bring about significant heating below the flare transition region.

Ricchiazzi, P. J.↗
NASA NTRS1984

Study of alternate optical and fine guidance sensor designs for the space infrared telescope facility (SIRTF)

A unique optical design was developed that compensates for the coma degraded images caused by field chopping in SIRTF. The conic constants of a Cassegrain telescope were altered to compensate for the coma induced by the secondary mirror tilt. The modulation transfer function is essentially independent of secondary mirror tilt, and diffraction limited image quality is maintained over a several arcminute field during chopping. With an untilted secondary mirror, the coma compensated (CC) design has a smaller field than the unchopped Ritchey-Chretien design; but use of relay optics, such as the inverted Cassegrain design developed for the fine guidance sensor (FGS), can increase the CC telescope's field size. A reactionless secondary mirror chopper mechanism that uses superconducting magnets was studied. The heart producing elements are confined to a reaction plate that is not directly viewed by the IR focal plane. A design was also developed for a low moment of inertia, reticulated HIP beryllium secondary mirror consistent with blank fabrication technology and optical finishing requirements.

Wissinger, A.↗
NASA NTRS2003

Two-Pole Caustic Model for High-Energy Lightcurves of Pulsars

We present a new model of high-energy lightcurves from rotation powered pulsars. The key ingredient of the model is the gap region (i.e. the region where particle acceleration is taking place and high-energy photons originate) which satisfies the following assumptions: i) the gap region extends from each polar cap to the light cylinder; ii) the gap is thin and confined to the surface of last open magnetic-field lines; iii) photon emissivity is uniform within the gap region. The model lightcurves are dominated by strong peaks (either double or single) of caustic origin. Unlike in other pulsar models with caustic effects, the double peaks arise due to crossing two caustics, each of which is associated with a different magnetic pole. The generic features of the lightcurves are consistent with the observed characteristics of pulsar lightcurves: 1) the most natural (in terms of probability) shape consists of two peaks (separated by 0.4 to 0.5 in phase for large viewing angles); 2) the peaks possess well developed wings; 3) there is a bridge (inter-peak) emission component; 4) there is a non-vanishing off-pulse emission level; 5) the radio pulse occurs before the leading high-energy peak. The model is well suited for four gamma-ray pulsars - Crab, Vela, Geminga and B1951+32 - with double-peak lightcurves exhibiting the peak separation of 0.4 to 0.5 in phase. Hereby, we apply the model to the Vela pulsar. Moreover, we indicate the limitation of the model in accurate reproducing of the lightcurves with single pulses and narrowly separated (about 0.2 in phase) pulse peaks. We also discuss the optical polarization properties for the Crab pulsar in the context of the two-pole caustic model.

Dyks, J.↗
NASA NTRS2005

Reliability of Electronics for Cryogenic Space Applications Being Assessed

Many future NASA missions will require electronic parts and circuits that can operate reliably and efficiently in extreme temperature environments below typical device specification temperatures. These missions include the Mars Exploration Laboratory, the James Webb Space Telescope, the Europa Orbiter, surface rovers, and deep-space probes. In addition to NASA, the aerospace and commercial sectors require cryogenic electronics in applications that include advanced satellites, military hardware, medical instrumentation, magnetic levitation, superconducting energy management and distribution, particle confinement and acceleration, and arctic missions. Besides surviving hostile space environments, electronics capable of low-temperature operation would enhance circuit performance, improve system reliability, extend lifetime, and reduce development and launch costs. In addition, cryogenic electronics are expected to result in more efficient systems than those at room temperature.

Patterson, Richard L.↗
NASA NTRS2009

The Lower Solar Atmosphere During the WHI Campaign (20 Apr-16 May 2008)

The Whole Heliospheric Interval (WHI) period of 20 March - 16 April had a "quiet side" of the Sun, and an "active side," with three ARs. At least two of the ARs produced CMEs, but there were several events that may have been "confined eruptions" from these regions too. Examining the magnetic environment of the erupting regions gives insight into the onset and dynamics of the eruptions. Several of the CMEs can be traced back to likely disk sources, but several unmatched cases still remain. More work is needed to sort through these points.

Sterling, Alphonse↗
NASA NTRS2009

Saturn's Magnetosphere and Properties of Upstream Flow at Titan: Preliminary Results

Using Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) measurements, we present the ion fluid properties and its ion composition of the upstream flow for Titan's interaction with Saturn's magnetosphere. A 3D ion moments algorithm is used which is essentially model independent with only requirement is that ion flow is within the CAPS IMS 2(pi) steradian field-of-view (FOV) and that the ion 'velocity distribution function (VDF) be gyrotropic. These results cover the period from TA flyby (2004 day 300) to T22 flyby (2006 363). Cassini's in situ measurements of Saturn's magnetic field show it is stretched out into a magnetodisc configuration for Saturn Local Times (SLT) centered about midnight local time. Under those circumstances the field is confined near the equatorial plane with Titan either above or below the magnetosphere current sheet. Similar to Jupiter's outer magnetosphere where a magnetodisc configuration applies, one expects the heavy ions within Saturn's outer magnetosphere to be confined within a few degrees of the current sheet while at higher magnetic latitudes protons should dominate. We show that when Cassini is between dusk-midnight-dawn local time and spacecraft is not within the current sheet that light ions (H, 142) tend to dominate the ion composition for the upstream flow. If true, one may expect the interaction between Saturn's magnetosphere, locally devoid of heavy ions and Titan's upper atmosphere and exosphere to be significantly different from that for Voyager 1, TA and TB when heavy ions were present in the upstream flow. We also present observational evidence for Saturn's magnetosphere interaction with Titan's extended H and H2 corona which can extend approx. 1 Rs from Titan.

Sittler, E. C., Jr.↗