Engineering topics

Goldstein, M. L.

Publications and source records attributed to Goldstein, M. L..

At least 127 records · Page 7

NASA NTRS1979

Nonlinear stability of solar type III radio bursts. I - Theory

A theory of the excitation of solar type III bursts is presented. Electrons initially unstable to the linear bump-in-tail instability are shown to rapidly amplify Langmuir waves to energy densities characteristic of strong turbulence. The three-dimensional equations which describe the strong coupling (wave-wave) interactions are derived. For parameters characteristic of the interplanetary medium the equations reduce to one-dimension. In that case the oscillating two-stream instability (OTSI) is the dominant nonlinear instability. OTSI is stabilized through the production of nonlinear ion density fluctuations that efficiently scatter Langmuir waves out of resonance with the electron beam. An analytical model of the electron distribution function is also developed which is used to estimate the total energy losses suffered by the electron beam as it propagates from the solar corona to 1 AU and beyond.

Smith, R. A.↗

NASA NTRS1979

Microscale instabilities in stream interaction regions

The microstructure of solar wind stream interaction regions is considered theoretically with emphasis on the role of several electrostatic kinetic instabilities which may be important within the stream interface and the compression region. Inside of 1 AU, the interface is likely to be stable against the electrostatic streaming instabilities considered. Between 1 and 2 AU, the interface will excite the magnetized ion-ion instability. The compression region is also found to be unstable beyond 1 AU where the modified two-stream instability, beam-cyclotron instability, and ion-acoustic instability are important in determining the structure of the compressive pulses as they evolve into forward and reverse shocks. It is concluded that the modified two-stream instability and beam-cyclotron instability predominately play a role in heating the electrons to the threshold for the ion-acoustic instability. Various electrostatic plasma waves, ranging in frequency from the lower-hybrid to harmonics of the electron cyclotron frequency, would be produced by these instabilities. Their signature should also be seen by high time resolution measurements of the temperature of the various plasma species.

Eviatar, A.↗

NASA NTRS1979

An emission mechanism for the Io-independent Jovian decameter radiation

A theory of the Io-independent decameter radiation is developed. The radiation results from excitation of the electromagnetic loss-cone instability by keV electrons, stably trapped near L = 6. The radiation is excited in band III of the extraordinary mode. When the effects of refraction are estimated, it is shown that above 10 MHz radiation is beamed into the equatorial plane in a wide, but thin, conical sheet. When the instability analysis is coupled with one of the octopole models of the Jovian magnetic field, the maximum convective growth of the instability occurs in the directions of the non-Io A, B, and C sources. The shape of the peak radio flux frequency spectrum is found to be a consequence of the loss-cone shape of the electron distribution function.

Goldstein, M. L.↗

NASA NTRS1979

The mean free path of low rigidity cosmic rays

A simple heuristic argument is presented which suggests that the large rigidity independent mean free paths observed for low rigidity solar and galactic cosmic rays can be understood in terms of weak turbulence diffusion theory if one assumes that the interplanetary magnetic turbulence consists of a combination of Alfven waves propagating with constant field magnitude and a small (approximately 5-10%) admixture of compressive fluctuations.

Goldstein, M. L.↗

NASA NTRS1979

A beaming model of the Io-independent Jovian decameter radiation based on multipole models of the Jovian magnetic field

A geometrical model is presented in which the apparent source locations of the Io-independent decameter radiation are computed. The calculations assume that the radiation is produced by stably trapped electrons radiating near the local electron gyrofrequency and that the emission is then beamed onto a conical surface. The maximum occurrence probability of noise storms is associated with regions in the Jovian magnetosphere where the axis of the emission cone is most inclined toward the Jovian equatorial plane. The calculations utilize and compare two of the octopole spherical harmonic expansions of the Jovian magnetic field constructed from data accumulated by the fluxgate and vector helium magnetometers on board Pioneer 11.

Goldstein, M. L.↗

NASA NTRS1979

A theory of solar type 3 radio bursts

Energetic electrons propagating through the interplanetary medium are shown to excite the one dimensional oscillating two stream instability (OTSI). The OTSI is in turn stabilized by anomalous resistivity which completes the transfer of long wavelength Langmuir waves to short wavelengths, out of resonance with the electrons. The theory explains the small energy losses suffered by the electrons in propagating to 1 AU, the predominance of second harmonic radiation, and the observed correlation between radio and electron fluxes.

Goldstein, M. L.↗

NASA NTRS1979

A theory of solar type III radio bursts

A theory of type III bursts is reviewed. Energetic electrons propagating through the interplanetary medium are shown to excite the one dimensional oscillating two stream instability (OTSI). The OTSI is in turn stabilized by anomalous resistivity which completes the transfer of long wavelength Langmuir waves to short wavelengths, out of resonance with the electrons. The theory explains the small energy losses suffered by the electrons in propagating to 1 AU, the predominance of second harmonic radiation, and the observed correlation between radio and electron fluxes.

Goldstein, M. L.↗

NASA NTRS1978

Nonlinear stability of solar type 3 radio bursts. 2: Application to observations near 1 AU

A set of rate equations including strong turbulence effects and anomalous resitivity are solved using parmeters which model several solar type 3 bursts. Exciter distributions observed at 1 AU are excitation of the linear bump-in-tail instability, amplifying Langmuir waves above the threshold for the oscillating two stream instability (OTSI). The OTSI, and the attendant anomalous resistivity produce a rapid spectral transfer of Langmuir waves to short wavelengths, out of resonance with the electron exciter. Further energy loss of the beam is thus precluded. The various parameters needed to model the bursts are extrapolated inside 1 AU with similar results. Again, the OTSI is excited and decouples the electron beam from the Langmuir radiation. Reabsorption of the Langmuir waves by the beam is shown to be unimportant in all cases, even at 0.1 AU. The theory provides a natural explanation for the observed realationship between radio flux, and the electron flux.

Goldstein, M. L.↗

NASA NTRS1978

An emission mechanism for the Io-independent Jovian decameter radiation

A theory of the Io-independent decameter radiation is developed. The radiation results from excitation of the electromagnetic loss-cone instability by keV electrons, stably trapped near L = 6. The radiation is excited in Band 3 of the extraordinary mode. When the effects of refraction are estimated, it is shown that above 10 MHz radiation is beamed into the equatorial plane in a wide, but thin, conical sheet (Psi approximately equals 80 degrees). When the instability analysis is coupled with one of the octupole models of the Jovian magnetic field, the maximum convective growth of the instability occurs in the directions of the non-Io A, B, and C sources. The shape of the peak radio flux frequency spectrum is found to be a consequence of the loss cone shape of the electron distribution function.

Goldstein, M. L.↗

NASA NTRS1978

A beaming model of the Io-independent Jovian decameter radiation based on multipole models of the Jovian magnetic field

A geometrical model is presented in which the apparent source locations of the Io-independent decameter radiation are computed. The calculations assume that the radiation is produced by stably trapped electrons radiating near the electron gyrofrequency and that the emission is then beamed onto a conical surface. The maximum occurrence probability of noise storms is associated with regions in the Jovian magnetosphere where the axis of the emission cone is most inclined toward the Jovian equatorial plane. The calculations utilize and compare two of the octupole spherical harmonic expansions of the Jovian magnetic field constructed from data accumulated by the fluxgate and vector helium magnetometers on board Pioneer 11.

Goldstein, M. L.↗

NASA NTRS1978

An instability of finite amplitude circularly polarized Alfven waves

A demonstration is presented that a finite-amplitude circularly-polarized Alfven wave is generally unstable in a MHD fluid. The wave decays by a four-wave coupling process in which the daughter waves are forward propagating random density and magnetic fluctuations and a backward-propagating magnetic wave. For parameters typical of the solar corona and the solar wind (thermal to magnetic energy density ratios between 0.1 and 1, and values between 0.1 and 0.9 for the ratio of magnetic energy density of the initial Alfven wave to that of the background magnetic field), large decay rates are found.

Goldstein, M. L.↗

NASA NTRS1978

Nonlinear stability of solar type 3 radio bursts. 1: Theory

A theory of the excitation of solar type 3 bursts is presented. Electrons initially unstable to the linear bump-in-tail instability are shown to rapidly amplify Langmuir waves to energy densities characteristic of strong turbulence. The three-dimensional equations which describe the strong coupling (wave-wave) interactions are derived. For parameters characteristic of the interplanetary medium the equations reduce to one dimension. In this case, the oscillating two stream instability (OTSI) is the dominant nonlinear instability, and is stablized through the production of nonlinear ion density fluctuations that efficiently scatter Langmuir waves out of resonance with the electron beam. An analytical model of the electron distribution function is also developed which is used to estimate the total energy losses suffered by the electron beam as it propagates from the solar corona to 1 A.U. and beyond.

Smith, R. A.↗

NASA NTRS1977

Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients

In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.

Goldstein, M. L.↗

NASA NTRS1976

Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients

The propagation of charged particles through interstellar and interplanetary space has often been described as a random process in which the particles are scattered by ambient electromagnetic turbulence. In general, this changes both the magnitude and direction of the particles' momentum. Some situations for which scattering in direction (pitch angle) is of primary interest were studied. A perturbed orbit, resonant scattering theory for pitch-angle diffusion in magnetostatic turbulence was slightly generalized and then utilized to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field, Kappa. All divergences inherent in the quasilinear formalism when the power spectrum of the fluctuation field falls off as K to the minus Q power (Q less than 2) were removed. Various methods of computing Kappa were compared and limits on the validity of the theory discussed. For Q less than 1 or 2, the various methods give roughly comparable values of Kappa, but use of perturbed orbits systematically results in a somewhat smaller Kappa than can be obtained from quasilinear theory.

Goldstein, M. L.↗

NASA NTRS1976

A nonlinear theory of cosmic-ray pitch-angle diffusion in homogeneous magnetostatic turbulence

A plasma strong turbulence, weak coupling, theory is applied to the problem of cosmic-ray pitch-angle scattering in magnetostatic turbulence. The theory used is a rigorous generalization of Weinstock's 'resonance broadening' theory and contains no ad hoc approximations. A detailed calculation is presented for a model of 'slab' turbulence with an exponential correlation function. The results agree well with numerical simulations. The rigidity dependence of the pitch-angle scattering coefficient differs from that found by previous researchers. The differences result from an inadequate treatment of particle trajectories near 90 deg pitch angle in earlier work.

Goldstein, M. L.↗

NASA NTRS1976

On the theory of the type III burst exciter

In situ satellite observations of type III burst exciters at 1 AU show that the beam does not evolve into a plateau in velocity space, contrary to the prediction of quasilinear theory. The observations can be explained by a theory that includes mode coupling effects due to excitation of the parametric oscillating two-stream instability and its saturation by anomalous resistivity. The time evolution of the beam velocity distribution is included in the analysis.

Smith, R. A.↗

NASA NTRS1975

Lunar magnetism

It is shown, for a very simple model of the moon, that the existence of a primordial core magnetic field would give rise to a present day nonzero dipole external field. In the investigation a uniformly magnetized core embedded in a permeable mantle is considered. The significance of the obtained results for the conclusions reported by Runcorn (1975) is discussed. Comments provided by Runcorn to the discussion are also presented.

Goldstein, M. L.↗

NASA NTRS1975

Magnetostatic potential theory and the lunar magnetic dipole field

The lunar magnetic dipole moment is discussed. It is proposed that if a primordial core magnetic field existed, it would give rise to a present day nonzero external dipole magnetic field. This conclusion is based on the assumption that the lunar mantle is at least slightly ferromagnetic, and thus would maintain a permanent magnetization after the disappearance of the core magnetic field. Using a simple mathematical model of the moon, calculations are performed which support this hypothesis.

Goldstein, M. L.↗