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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
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NASA NTRS1975

Adiabatic Hamiltonian of charged particle motion in a dipole field

The Hamiltonian for a dipole field is developed, and the result is expressed by an analytic approximation accurate to within about 1%. This allows extension of results derived for equatorial particles to particles with arbitrary pitch angles; in particular, it makes available even in the presence of electric fields orthogonal to the magnetic field a function K that is preserved by the bounce-averaged motion. This function provides at once the equations of drift paths in (alpha, beta) or of their projections onto the equatorial plane; the derivation of a pacing function that times the progress of particles along such drift paths is also described.

Chen, A. J.↗
NASA NTRS1975

Jupiter revisited - First results from the University of Chicago charged particle experiment on Pioneer 11

The data obtained by Pioneer 11 confirmed results from Pioneer 10 and provided new information for an understanding of the physics of the Jovian magnetosphere. Attention is given to the significance of Pioneer 11 data in relation to two fundamentally different models which have been proposed to account for the variations in the electron flux observed in Jupiter's outer magnetosphere. Proton flux characteristics are considered, taking into account the intensity profiles of energetic particles trapped in the dipole region of Jupiter's magnetic field.

Simpson, J. A.↗
NASA NTRS1975

On the distortion of the Jovian magnetic field R greater than about 40 Jovian radii as deduced from charged particle studies

The relationship between the rotation of Jupiter's magnetic field and time variations in the intensity of nearly 6 to 30 MeV electrons observed by Pioneer 10 in the outer regions of Jupiter's magnetosphere is considered. The 6-30 MeV electron flux showed regular intensity variations with a period of approximately 10 hours. The behavior of this energetic electron flux is found to be most consistent with confinement of particles to a magnetic equatorial plane which is considerably distorted from the shape expected for rigid corotation of the magnetic field with Jupiter. The distortion is likely to arise from stresses resulting from interaction of the magnetosphere with the solar wind and from inertial effects of the magnetospheric plasma.

Mckibben, R. B.↗
NASA NTRS1976

Trajectory Traces of Charged Particles in the Magnetosphere

The characteristic enhancements of ring current particles with energies of about 1 to 100 keV, associated with magnetospheric substorms, were observed by Explorer 45 around the plasmapause in the afternoon to midnight region, and showed the characteristic structure called a 'nose' in the proton spectrograms. The motion of these particles in the equatorial magnetosphere, under a recently proposed convection electric field and a dipole magnetic field is described. Approximate equations of a bounce period, a second adiabatic invariant, and a bounce-average azimuthal velocity are given with inaccuracies less than about 0.001 for all pitch angles. The complete set of flow patterns of 90 deg pitch angle particles is also presented by means of stagnation lines through which radial drifts and/or azimuthal drifts change their directions. The particle tracings in the magnetosphere give a basic concept to explain the observed nose characteristics.

Ejiri, M.↗
NASA NTRS1975

Charged particle propagation in strong disordered magnetic fields

The use of quasilinear theory in calculating particle trajectories in strong random fields is beset by a basic difficulty concerning the breakdown of the basic assumption of the theory. This assumption is that the random force acting on the particle becomes self-incoherent before it has changed the particle's trajectory in phase space, ie., its position or velocity, by a significant amount. The various time scales involved in this problem are defined and compared to determine in which regions the basic assumptions of quasilinear theory are violated. It is shown how nonlinear theories in general and the Partially Averaged Field theory (Jones et al. 1973) can partly alleviate these difficulties.

Jones, F. C.↗
NASA NTRS1975

The effect of adiabatic focusing upon charged particle propagation in random magnetic fields

This paper describes the effects of strong adiabatic focusing in terms of eigenfunctions of an operator which incorporates both scattering by random fields and focusing by a spatially inhomogeneous guiding field. It is found that focused transport differs from rectilinear transport in the following ways: (1) the coherent velocity toward stronger fields is larger than that toward weaker fields; (2) coherent effects are more prominent relative to diffusive effects when focusing is present; and (3) initial anisotropies at injection have a minimal influence upon rectilinear transport but they have a pronounced effect on focused transport. These features explain certain well-known discrepancies between the diffusive picture and the observed profiles of solar particle events. In particular, they explain the so-called scatter-free propagation of kilovolt flare electrons.

Earl, J. A.↗
NASA NTRS1976

Global characteristics of 0.2 to 26 keV charged particles at F region altitudes

Measurements have been made by the low energy electron experiment (LEE) on the Atmosphere Explorer-C satellite (AE-C) of electrons and protons in the energy range 0.2 to 26 keV. Data taken in the altitude range 250 to 300 km during the period 15 December 1973 to 25 May 1975 are analyzed. Measurements were made over a range of magnetic latitudes extending from the equator to 80 deg. The average electron flux at midlatitudes at night is found to be about (1-5) x 10 to the -4 ergs/sq cm/s, and increases by about an order of magnitude during the day. The upper limit for the nighttime and daytime proton energy flux is about 1 x 10 to the -4th ergs/sq cm/s. The total nighttime energy flux will result in a production rate of .3 to 10 ions/cu cm/s at the base of the F region and in the D region, respectively, and should constitute an important source of ionization in the nocturnal ionosphere.

Torr, D. G.↗
NASA NTRS1976

One-dimensional numerical study of charged particle trajectories in turbulent electrostatic wave fields

The paper describes a numerical simulation of electron trajectories in weak random electric fields under conditions that are approximately true for Langmuir waves whose wavelength is much longer than the Debye length. Two types of trajectory calculations were made: (1) the initial particle velocity was made equal to the mean phase velocity of the waves, or (2) it was equal to 0.7419 times the mean velocity of the waves, so that the initial velocity differed substantially from all phase velocities of the wave spectrum. When the autocorrelation time is much greater than the trapping time, the particle motion can change virtually instantaneously from one of three states - high-velocity, low-velocity, or trapped state - to another. The probability of instantaneous transition from a high- or low-velocity state becomes small when the difference between the particle velocity and the mean phase velocity of the waves becomes high in comparison to the trapping velocity. Diffusive motion becomes negligible under these conditions also.

Graham, K. N.↗
NASA NTRS1976

Magnetic shadowing of charged particles by an extended surface

The problem of particle shadowing by the lunar surface is examined. Shadow zones are obtained analytically for small-aperture detectors on an infinite flat surface and are shown to be in good agreement with those obtained by numerical trajectory tracing. The shadow zones cover about half of all possible external field orientations for a vertical detector, which may result in serious underestimations of the frequency of observation of a particular plasma region. Shadowing may cause wide variations between observed and actual pitch angle distributions even in the case of multiple- or large-aperture detectors. Since the particle flux can be considered approximately isotropic only for magnetic fields within 35 deg of the surface normal, the electron flux to the surface may be overestimated in current balance calculations ignoring the magnetic field direction. In addition, photoelectrons may be returned to the surface by the magnetic field.

Reiff, P. H.↗
NASA NTRS1976

Charged-particle absorption by Io

An idealized two-dimensional model of the distorted electric field configuration, in the limit of a perfectly conducting satellite or satellite ionosphere, has been constructed. This model has been used to trace the adiabatic guiding-center trajectories of energetic protons and electrons across Jupiter's magnetic-field lines, which are taken as rectilinear. The adiabatic trajectories of very low-energy particles (cold-plasma) are thus found to avoid the satellite and escape absorption. In the limit of very high particle energies the adiabatic trajectories are undistorted, and absorption proceeds as if Io were an insulator. The particle absorbing characteristics of an electrically conducting Jovian satellite are found to depend on both the species and the energy of the incident particle, and the satellite's particle-absorbing cross section differs systematically from its geometric cross section.

Schulz, M.↗
NASA NTRS1977

Charged-particle absorption by Io

The electrostatic field associated with the rotation of Jupiter, relative to the rest frame of Io, would be distorted if the satellite were an electrical conductor. An idealized two-dimensional model of the distorted electric-field configuration, in the limit of a perfectly conducting satellite or satellite ionosphere, has been constructed and used to trace the adiabatic guiding-center trajectories of energetic protons and electrons across Jupiter's magnetic field lines, which are taken as rectilinear. The adiabatic trajectories of very low-energy particles (cold plasma) are found to avoid the satellite and escape absorption. In the limit of very high particle energies, the adiabatic trajectories are undistorted, and absorption proceeds as if Io were an insulator. The interpolation between these limits is monotonic for protons, such that Io sweeps out a drift shell half as wide as the satellite for first invariants of the order of 1 GeV per gauss. The situation for electrons is more complicated, and no absorption from adiabatic trajectories is found at first invariants not exceeding 46 GeV per gauss. Electrons having first invariants of at least 50 GeV per gauss are typically swept out of drift shells wider than the satellite itself. However, electrons can impact only a portion of Io's exposed hemisphere for first invariants of 50-200 GeV per gauss. Thus, the particle-absorbing characteristics of an electrically conducting Jovian satellite are found to depend on both the species and the energy of the incident particle, and the satellite's particle-absorbing cross section differs systematically from its geometric cross section.

Schulz, M.↗
NASA NTRS1977

Interaction of large, high power systems with operational orbit charged particle environments

A potentially hazardous spacecraft environment interaction is discussed. The interaction of large high voltage systems with low energy (less than 50 eV) plasmas which can result in loss of power and/or arching was examined. The impact of this class of interactions where the ambient operation is most severe at low orbits where the ambient plasmas are densest. Results of experimental work and predictions of simple analytical models were presented and their implications for design of space systems were reviewed.

Purvis, C. K.↗
NASA NTRS1977

The Low Energy Charged Particle /LECP/ experiment on the Voyager spacecraft

The Low Energy Magnetosphere Particle Analyzer (LEMPA) and the Low Energy Particle Telescope (LEPT) on board the Voyager spacecraft are described. The LEMPA has an energy range of about 10 keV to greater than 11 MeV for electrons and about 15 keV to greater than 150 MeV for protons and heavier ions; the LEPT covers a range of about 0.05 to 40 MeV/nucleon with good energy and species resolution. The LEPT and LEMPA subsystems are mounted on a stepping platform which rotates at variable rate through eight angular sectors. Comprehensive measurements of particles in the Jovian, Saturnian, Uranian, and interplanetary environments are expected from the experiment.

Krimigis, S. M.↗
NASA NTRS1978

On the modulation of the Jovian decametric radiation by Io. I - Acceleration of charged particles

A steady-state analysis of the current circuit between Io and the Jovian ionosphere is performed, assuming that the current is carried by electrons accelerated through potential double layers in the Io flux tube. The circuit analysis indicates that electrons may be accelerated up to energies of several hundred keV. Several problems associated with the formation of double layers are also discussed. The parallel potential drops decouple the flux tube from the satellite's orbital motion.

Smith, R. A.↗