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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The dynamo dilemma

The recent determination that the angular velocity Omega of the sun declines downward through the convective zone raises serious questions about the nature of the solar dynamo. The principal qualitative features of the sun are the azimuthal fields that migrate toward the equator in association with an oscillating poloidal field which reverses at about the time of maximum appearance of bipolar magnetic regions. If Omega decreases downward, or is negligible, the horizontal gradient in Omega produces a dynamo with some of these essential characteristics. There is reason to think that the dynamo is confined to the lower half of the convective zone, where alpha has the opposite sign from the usual (alpha of greater than 0 in the northern hemisphere) producing equatorward migration but reversing the sign of the associated poloidal field. Meridional circulation may play an essential role in shaping the dynamo. At the present time it is essential to measure Omega accurately and determine the nature of the meridional circulation.

Parker, E. N.↗
NASA NTRS1977

Radio-emitting electrons and cosmic ray confinement

Evidence from radio data obtained at frequencies of 10 to 8000 MHz for steepening of the observed background-radio-continuum spectra in the directions of the galactic Anticenter (A) and Halo Minimum (H) is used to deduce quantitative information on the variation of the magnetic field with distance from the galactic plane. The radio data are analyzed in the framework of the cosmic-ray diffusion model developed by Bulanov and Dogel (1975), and some inferences are drawn regarding the injection spectrum of cosmic-ray electrons as well as their propagation in the Galaxy. The results indicate that: (1) radio-spectrum steepening is centered around 200 MHz in the direction of H and around 330 MHz in the direction of A, implying a lower mean magnetic field toward H and supporting the existence of a radio halo; (2) an injection electron spectrum with a single power law up to the lowest energies cannot explain the radio observations satisfactorily in terms of the diffusion model; and (3) the observed spectral steepening can be satisfactorily understood as being due partly to the deviation from a power-law injection spectrum below a few GeV and partly to the first break arising from electron energy losses in approximately the same energy region.

Badhwar, G. D.↗
NASA NTRS1972

Quantum limit studies in single crystal and pyrolytic graphite

The occupied regions of momentum space in graphite are confined to elongated volumes near the hexagonal Brillouin zone edges. The elongation is along the hexagonal axis (c-axis), so that cross sectional areas perpendicular to that axis are very small. When magnetic fields are applied parallel to the c-axis, only the n = 0 Landau levels remain below the Fermi energy for fields above 7 tesla. The energy bands in graphite can be described by a set of seven parameters (including the Fermi energy as a parameter). In a quantizing magnetic field the Landau levels are described by a secular equation determined by diagonalizing the Hamiltonian. A major feature for the levels along the Brillouin zone edge is that the n = 0 Landau level for electrons is independent of magnetic field, while that for holes is field-dependent.

Woollam, J. A.↗
NASA NTRS1974

Evidence of a primordial solar wind

A model is reviewed which requires a T Tauri 'wind' and at the same time encompasses certain early-object stellar features. The theory rests on electromagnetic induction driven by the 'wind'. Plasma confinement of the induced field prohibits a scattered field, and all energy loss is via ohmic heating in the scatterer (i.e., planetary objects). Two modes, one caused by the interplanetary electric field (transverse magnetic) and the other by time variations in the interplanetary magnetic field (transverse electric) are present. Parent body melting, lunar surface melting, and a primordial magnetic field are components of the proposed model.

Sonett, C. P.↗
NASA NTRS1981

A nonthermal ion layer with high anisotropies at the plasmasheet boundary during substorm recovery

The energy spectra and anisotropies of protons and alpha particles are investigated at the plasmasheet boundary during the recovery phase of geomagnetic substorms using the Max Planck Institut/University of Maryland sensor system on the ISEE-1 satellite. The observations are found to reveal the presence of a thin nonthermal layer of approximately 60 keV/charge protons and alpha particles at the plasmasheet boundary, the particles streaming highly collimated in earthward direction. It is pointed out that the alpha particle layer is confined within the proton layer. It is thought that the principal features of the layers can be explained in terms of an acceleration model proposed by Speiser (1965) for the environment of a magnetic neutral line.

Moebius, E.↗
NASA NTRS1984

Magnetic field observations of evolved stars

A search has been made for Zeeman broadening in high resolution spectra of eight G and K type, evolved stars which have active chromospheres and coronae. No Zeeman broadening was found. It is likely that the fraction of the stellar surface that contains magnetic fields is similar in active giants and dwarfs, based on their comparable chromospheric line strengths and plage surface brightnesses (deduced from Mg II/C IV ratios) and on their comparable requirements for coronal confinement. Thus, since Zeeman broadening is detectable on active dwarfs, the nondetections of Zeeman broadening on these evolved stars are probably due to systematically lower field strengths. That the lower field strengths do not result in lower chromospheric surface brightnesses on giants is consistent with the theoretial 'slow mode' MHD wave generation rates of Ulmschneider and Stein (1982). The low field strengths can be explained by requiring that the fields be in equipartition with either the thermal or turbulent energy densities, both of which are reduced in late-type evolved stars compared with the sun.

Marcy, G. W.↗
NASA NTRS1987

Influence of collective effects on lifetimes of condensed excited states

The possibility that collective effects may dramatically influence autoionization-limited lifetimes of condensed excited states is investigated in the context of a two-band model of an insulator in a strong magnetic field. Two different mechanisms for suppressing autoionization are discussed which may prevent the potentially catastrophic destruction of the excited state. Under appropriate circumstances, the residual low-density Auger electrons may be confined in a superconducting state and paired by excitonic fluctuations in the conduction band.

Zmuidzinas, Jonas Stasys↗
NASA NTRS1992

Field quantization and squeezed states generation in resonators with time-dependent parameters

The problem of electromagnetic field quantization is usually considered in textbooks under the assumption that the field occupies some empty box. The case when a nonuniform time-dependent dielectric medium is confined in some space region with time-dependent boundaries is studied. The basis of the subsequent consideration is the system of Maxwell's equations in linear passive time-dependent dielectric and magnetic medium without sources.

Dodonov, V. V.↗
NASA NTRS2001

Onset of the Magnetic Explosion in Solar Flames and Coronal Mass Ejections

We present observations of the magnetic field configuration and its transformation in six solar eruptive events that show good agreement with the standard bipolar model for eruptive flares. The observations are X-ray images from the Yohkoh soft X-ray telescope (SXT) and magnetograms from Kitt Peak National Solar Observatory, interpreted together with the 1-8 Angstrom X-ray flux observed by Geostationary Operational Environmental Satellites (GOES). The observations yield the following interpretations: (1) Each event is a magnetic explosion that occurs in an initially closed single bipole in which the core field is sheared and twisted in the shape of a sigmoid, having an oppositely curved elbow on each end. The arms of the opposite elbows are sheared past each other so that they overlap and are crossed low above the neutral line in the middle of the bipole. The elbows and arms seen in the SXT images are illuminated strands of the sigmoidal core field, which is a continuum of sheared/twisted field that fills these strands as well as the space between and around them; (2) Although four of the explosions are ejective (appearing to blow open the bipole) and two are confined (appearing to be arrested within the closed bipole), all six begin the same way. In the SXT images, the explosion begins with brightening and expansion of the two elbows together with the appearance of short bright sheared loops low over the neutral line under the crossed arms and, rising up from the crossed arms, long strands connecting the far ends of the elbows; and (3) All six events are single-bipole events in that during the onset and early development of the explosion they show no evidence for reconnection between the exploding bipole and any surrounding magnetic fields. We conclude that in each of our events the magnetic explosion was unleashed by runaway tether-cutting via implosive/explosive reconnection in the middle of the sigmoid, as in the standard model. The similarity of the onsets of the two confined explosions to the onsets of the four ejective explosions and their agreement with the model indicate that runaway reconnection inside a sheared core field can begin whether or not a separate system of overlying fields, or the structure of the bipole itself, allows the explosion to be ejective. Because this internal reconnection apparently begins at the very start of the sigmoid eruption and grows in step with the explosion, we infer that this reconnection is essential for the onset and growth of the magnetic explosion in eruptive flares and coronal mass ejections.

Moore, Ronald L.↗
NASA NTRS1979

Jupiter's magnetosphere and radiation belts

Radioastronomy and Pioneer data reveal the Jovian magnetosphere as a rotating magnetized source of relativistic particles and radio emission, comparable to astrophysical cosmic ray and radio sources, such as pulsars. According to Pioneer data, the magnetic field in the outer magnetosphere is radially extended into a highly time variable disk-shaped configuration which differs fundamentally from the earth's magnetosphere. The outer disk region, and the energetic particles confined in it, are modulated by Jupiter's 10 hr rotation period. The entire outer magnetosphere appears to change drastically on time scales of a few days to a week. In addition to its known modulation of the Jovian decametric radio bursts, Io was found to absorb some radiation belt particles and to accelerate others, and most importantly, to be a source of neutral atoms, and by inference, a heavy ion plasma which may significantly affect the hydrodynamic flow in the magnetosphere. Another important Pioneer finding is that the Jovian outer magnetosphere generates, or permits to escape, fluxes of relativistic electrons of such intensities that Jupiter may be regarded as the dominant source of 1 to 30 MeV cosmic ray electrons in the heliosphere.

Kennel, C. F.↗
NASA NTRS1984

Cosmic ray propagation in the local superbubble

It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.

Steitmatter, R. E.↗
NASA NTRS1985

Cosmic ray propagation in the local superbubble

It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x 10 to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.

Streitmatter, R. E.↗
NASA NTRS1998

The Sun and the Solar Wind Close to the Sun

One of the benefits from the Ulysses, SOHO, and YOHKOH missions has been a strong stimulus to better understand the magnetohydrodynamic processes involved in coronal expansion. Three topics for which this has been especially true are described here. These are: (i) The observed constancy of the radial interplanetary magnetic field strength (as mapped to constant radius). (ii) The geometric spreading of coronal plumes and coronal holes, and the fate of plumes. (iii) The plasma Beta in streamers and the physics of streamer confinement.

Suess, Steven T.↗
NASA NTRS1974

Quantum limit studies in single-crystal and pyrolytic graphite

The occupied regions of momentum space in graphite are confined to very elongated volumes near the hexagonal Brillouin zone edges. The elongation is along the hexagonal axis (c axis) so that cross-sectional areas perpendicular to that axis are very small. Hence, when magnetic fields are applied parallel to the c axis only the n = 0 Landau levels remain below the Fermi energy for fields above 7 T (Woollam, 1971). The energy bands in graphite can be described by a set of seven parameters (McClure, 1971) (including the Fermi energy as a parameter). In a quantizing magnetic field the Landau levels are described by a secular equation determined by diagonalizing the Hamiltonian (McClure, 1960). A major unusual feature for the levels along the Brillouin zone edge is that the n = 0 Landau level for electrons is independent of magnetic field, while that for holes is field dependent.

Woollam, J. A.↗
NASA NTRS1977

Optimization of confinement in a toroidal plasma subject to strong radial electric fields

The toroidal ring of plasma contained in the NASA Lewis Bumpy Torus facility may be biased to positive or negative potentials approaching 50 kV by applying dc voltages of the respective polarity to 12 or fewer midplane electrode rings. The radial electric fields, which are responsible for raising the ions to high energies by E x B/B-squared drift, then point out of or into the plasma. A preliminary report is given on the identification and optimization of independent variables which affect the ion density and confinement time in the Bumpy Torus plasma. The independent variables include the polarity, position, and number of the midplane electrode rings, the method of gas injection, and the polarity and strength of a weak vertical magnetic field. Some characteristic data taken under conditions where most of the independent variables were optimized are presented. The highest value of the electron number density on the plasma axis is 3.2 trillion per cu cm, the highest ion heating efficiency is 47%, and the longest particle containment time is 2.0 msec.

Roth, J. R.↗
NASA NTRS1992

Simultaneous equatorial measurements of waves and precipitating electrons in the outer radiation belt

Simultaneous wave and precipitating electron measurements near the equator in the outer radiation belt have been made from the CRRES satellite. The electron data of principal concern here were acquired in and about the loss cone with narrow angular resolution spectrometers covering the energy range 340 eV to 5 MeV. The wave data included electric field measurements spanning frequencies from 5 Hz to 400 kHz and magnetic field measurements from 5 Hz to 10 kHz. This paper presents examples in which the variations in electron fluxes in the loss cone and the wave intensities were correlated. These variations in electron flux were confined to pitch angles less than about 30 deg. The association between the flux enhancements and the waves is consistent with wave-induced pitch angle diffusion processes.

Imhof, W. L.↗
NASA NTRS1977

Optimization of confinement in a toroidal plasma subject to strong radial electric fields

A preliminary report on the identification and optimization of independent variables which affect the ion density and confinement time in a bumpy torus plasma is presented. The independent variables include the polarity, position, and number of the midplane electrode rings, the method of gas injection, and the polarity and strength of a weak vertical magnetic field. Some characteristic data taken under condition when most of the independent variables were optimized are presented. The highest value of the electron number density on the plasma axis is 3.2 x 10 to the 12th power/cc, the highest ion heating efficiency is 47 percent, and the longest particle containment time is 2.0 milliseconds.

Roth, J. R.↗
NASA NTRS2000

Gasdynamic Mirror Fusion Propulsion Experiment

A gasdynamic mirror (GDM) fusion propulsion experiment is currently being constructed at the NASA Marshall Space Flight Center (MSFC) to test the feasibility of this particular type of fusion device. Because of the open magnetic field line configuration of mirror fusion devices, they are particularly well suited for propulsion system applications since they allow for the easy ejection of thrust producing plasma. Currently, the MSFC GDM is constructed in three segments. The vacuum chamber mirror segment, the plasma injector mirror segment, and the main plasma chamber segment. Enough magnets are currently available to construct up to three main plasma chamber segments. The mirror segments are also segmented such that they can be expanded to accommodate new end plugging strategies with out requiring the disassembly of the entire mirror segment. The plasma for the experiment is generated in a microwave cavity located between the main magnets and the mirror magnets. Ion heating is accomplished through ambipolar diffusion. The objective of the experiment is to investigate the stability characteristics of the gasdynamic mirror and to map a region of parameter space within which the plasma can be confined in a stable steady state configuration. The mirror ratio, plasma density, and plasma "b" will be varied over a range of values and measurements subsequently taken to determine the degree of plasma stability.

Emrich, Bill↗