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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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NASA NTRS1978

The polarization of second harmonic plasma emission

It is shown that second-harmonic plasma emission is partially polarized in the sense of the ordinary mode of magnetoionic theory only when the Langmuir waves are confined to a small range of angles (less than 30 deg) to the magnetic-field lines. Consequently, Suzuki and Sheridan's (1977) observations of the polarization of harmonic Type III emission implies that (at least in the cases reported) the Langmuir waves must be nearly one-dimensional. For a nearly one-dimensional distribution, the degree of polarization and the frequency of observation should be related to the magnetic field. For the observed polarization of Type III bursts, the implied magnetic-field strengths are strong enough for induced scattering to cause the Langmuir waves to become nearly one-dimensional, which is consistent with the observed sense of polarization. In other applications of harmonic plasma emission where the Langmuir waves might be isotropic or in a loss-cone distribution, polarization in the sense of the extraordinary mode is predicted.

Melrose, D. B.↗

NASA NTRS1994

Waves in Space Plasmas (WISP)

Activities under this project have included participation in the Waves in Space Plasmas (WISP) program, a study of the data processing requirements for WISP, and theoretical studies of radio sounding, ducting, and magnetoionic theory. An analysis of radio sounding in the magnetosphere was prepared.

Calvert, Wynne↗

NASA NTRS1972

Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I.

A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.

Canuto, V.↗

NASA NTRS1990

Relaxation of the loss-cone by quasi-linear diffusion of the electron-cyclotron maser instability in the solar corona

A self-consistent numeric two-dimensional code using kinetic-wave particle equations has been developed and applied to the maser dynamics of the solar corona. Time histories generated by the code reveal details of the evolution of the linear phase, the saturation and subsequent relaxation of the loss cone. Quantitative values are obtained for the saturation time, the amount of the converted free energy, the critical wave energy level for onset of maser diffusion, the velocity and pitch angle range of the resonant particles, and the relative importance of the different magnetoionic modes and harmonics. A wide range of initial conditions is covered by varying the loss-cone distribution and the ambient cold plasma parameters.

Aschwanden, Markus J.↗

NASA NTRS1990

Faraday rotation measure variations in the Cygnus region and the spectrum of interstellar plasma turbulence

Linear polarization observations were made of eight double-lobed radio galaxies viewed through the galactic plane in the Cygnus region. These observations have been used to determine intra- and intersource rotation measure differences; in some cases, unambiguous rotation measures have been extracted. The rotation measures are dominated by foreground magnetoionic material. The differences in rotation measure between pairs of sources correlate with angular separation for separations from 10 arcsec to 1.5 deg. These rotation measure fluctuations are consistent with a model in which the electron density varies on roughly 0.1-200 pc scales. The amplitudes of these variations are, in turn, consistent with those electron density variations that cause diffractive interstellar scattering on scales less than 10 to the 11th cm.

Lazio, T. Joseph↗

NASA NTRS1989

Impulsive solar wind-driven emission from Uranus

Several days prior to the Voyager spacecraft encounter with Uranus, the plasma wave and radio astronomy receivers detected extraordinarily narrowband bursty signals, the first indication of any radio emission from the planet. The characteristics of these signals were so unusual that their identity as a natural planetary emission was questioned at first. Subsequent analysis has shown, however, that the n bursts are modulated at the 17.24-hour Uranus rotation period and are, therefore, planetary in origin. It is shown, in addition, that the typical bandwidth and time scale for the bursts are about 5 kHz and 250 ms, respectively. The phase of the rotation modulation suggests a probable source for these events in the vicinity of the north (weak) magnetic pole. The waves are right-hand polarized and are therefore emitted in the extraordinary magnetoionic mode if the emission in fact originates above the north magnetic pole.

Desch, M. D.↗