Statistical properties of MHD fluctuations associated with high-speed streams from Helios-2 observations
(Previously announced in STAR as N82-18117)
Bavassano, B.↗
SEARCH · Engineering Papers
Results for “MHD”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Anisotropy in MHD turbulence due to a mean magnetic field
The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.
Shebalin, J. V.↗
Magnetohydrodynamics (MHD) Engineering Test Facility (ETF) 200 MWe power plant. Conceptual Design Engineering Report (CDER) supplement. Magnet system special investigations
The results of magnet system special investigations listed below are summarized: 4 Tesla Magnet Alternate Design Study; 6 Tesla Magnet Manufacturability Study. The conceptual design for a 4 Tesla superconducting magnet system for use with an alternate (supersonic) ETF power train is described, and estimated schedule and cost are identified. The magnet design is scaled from the ETF 6 T Tesla design. Results of a manufacturability study and a revised schedule and cost estimate for the ETF 6 T magnet are reported. Both investigations are extensions of the conceptual design of a 6 T magnet system performed earlier as a part of the overall MED-ETF conceptual design described in Conceptual Design Engineering Report (CDER) Vol. V, System Design Description (SDD) 503 dated September, 1981, DOE/NASA/0224-1; NASA CR-165/52.
Source record↗
Dynamic alignment and selective decay in MHD
Under some circumstances, incompressible magnetohydrodynamic turbulence will evolve toward a state in which the velocity fields and magnetic fields are aligned or anti-aligned. We propose a mechanism for this effect and illustrate with numerical computations. Under some other circumstances, the energy appears to decay selectively toward a minimum energy state in which the kinetic energy has disappeared. It has not been possible so far to identify a boundary in the phase space which divides the two regimes.
Matthaeus, W. H.↗
Non-planar MHD model for solar flare-generated disturbances in the heliospheric equatorial plane
An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is made for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the sun and 1 AU. The goal is to search for first-order global consequences rather than to make a parametric study. The analysis treats all three plasma velocity and magnetic field components in any convenient heliospheric plane of symmetry. The representative disturbance is examined for the canonical case in which the temporal and spatial changes in a homogeneous solar wind caused by a solar-flare-generated shock wave are described. All plasma and field parameters at three radial locations are examined. These are the central meridian and 33 deg W and 90 deg W of the flare's central meridian. It is found that the incorporation of a small meridional magnetic field in the ambient magnetic spiral field has negligible effect on the results. The magnetic field exhibits strong kinking within the interplanetary shocked flow, even reversed polarity that, coupled with low temperature and low density, suggests a plausible explanation for magnetic clouds' with accompanying double-streaming of electrons observed at directions approximately 90 deg to the heliocentric radius.
Wu, S. T.↗
Anisotropy in MHD turbulence due to a mean magnetic field
The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers. Previously announced in STAR as N83-12998
Shebalin, J. V.↗
MHD thermal instabilities in cool inhomogeneous atmospheres
The formation of a coronal state in a stellar atmosphere is investigated. A numerical code is used to study the effects of atmospheric gradients and finite loop dimension on the scale of unstable perturbations, solving for oscillatory perturbations as eigenfunctions of a boundary value problem. The atmosphere is considered as initially isothermal, with density and pressure having scale heights fixed by the hydrostatic equations. Joule mode instability is found to be an efficient mechanism for current filamentation and subsequent heating in initially cool atmospheres. This instability is mainly effective at the top of magnetic loops and is not suppressed by thermal conduction.
Bodo, G.↗
MHD Waves and Turbulence in the Sun and Interplanetary Medium
The existence, nature, and dynamics of magnetohydrodynamic waves and turbulence in the solar atmosphere and interplanetary medium are addressed. Remote sensing observations of global oscillations of the Sun and their possible interpretation in terms of waves or turbulence are considered. The region of solar wind acceleration as described by coronal imaging, resonance-line spectrometry, and radio techniques is discussed. Fluctuations and discontinuities in the interplanetary medium are considered using primary data collected by spaceborne magnetometers and plasma analyzers.
Source record↗
Transient flow analysis of the AEDC/HPDE MHD generator
Previously cited in issue 05, p. 686, Accession no. A83-16691
Wilson, D. R.↗
Oxidant system improvements for MHD energy conversion and industrial processes
Previously cited in issue 05, p. 686, Accession no. A83-16735
Juhasz, A. J.↗
Gyrating ions and large-amplitude monochromatic MHD waves upstream of the earth's bow shock
Episodes of nearly monochromatic, low-frequency (0.03 Hz) hydromagnetic waves are occasionally observed upstream of the earth's bow shock. High time resolution (3 s) measurements of two-dimensional ion distributions during two nearly monochromatic wave events reveal that the ion distributions asociated with these waves are 'gyrating ions.' Such distributions consists of suprathermal ions with parallel and perpendicular velocities confined to a fairly narrow range of (nonzero) values. The ions are also often confined to a fairly narrow range of gyrophase angle ('gyrophase bunched'). In one of the two cases, the observed frequency of the waves agrees quite well with the Doppler shifted resonance frequency of waves in right-hand resonance with the observed gyrating ions. In the second case, the observed frequency is lower than the predicted frequency by a factor of 1.5-2.
Thomsen, M. F.↗
The excitation of plasma waves by a current source moving in a magnetized plasma - The MHD approximation
Alfven waves are important in natural-space phenomena, and studies of these waves have been conducted by performing active experiments in space plasma. One method to study these waves involves the use of an electrodynamic tether. The electrodynamic tether consists of a subsatellite with a conducting outer surface connected to the Space Shuttle by an insulator-clad, conducting wire about 20 kilometers in length. The emf generated by the motion of the tether across the geomagnetic field will act to drive a current through the tethered system. It is pointed out that this current in the tether acts as a source for exciting the shear-Alfven wave. In the present investigation it is shown that fringing effects play a dominant role in determining the radiation pattern for currently envisioned deployments of the tether. The current paper is the first of three papers concerned with the excitation of low-frequency waves arising from a current source moving through a cold, magnetized plasma.
Rasmussen, C. E.↗
Dynamic alignment and selective decay in MHD
Under some circumstances, incompressible magnetohydrodynamic turbulence will evolve toward a state in which the velocity fields and magnetic fields are aligned or anti-aligned. We propose a mechanism for this effect and illustrate with numerical computations. Under some other circumstances, the energy appears to decay selectively toward a minimum energy state in which the kinetic energy has disappeared. It has not been possible so far to identify a boundary in the phase space which divides the two regimes.
Matthaeus, W. H.↗
Calibration of the kinematic method of studying solar wind disturbances on the basis of a one-dimensional MHD solution and a simulation study of the heliosphere disturbances between 22 November and 6 December 1977
Explore the source record for details and available documents.
Sun, W.↗
Auroral arc formation - Kinetic and MHD effects
Recent observations by the Dynamics Explorer satellites indicate that auroral field lines are not equipotentials. The field-aligned 'conductivity' is the same for up and downgoing currents and of the order of several 10 to the -8th to several 10 to the -9th/ohms sq m. This is not in agreement with models based on the resistance provided by the magnetic mirror force alone. It is suggested that the resistivity is due to damping of kinetic shear-Alfven wave packets. This damping may be nonlinear in nature or Landau damping. The properties of kinetic Alfven waves are reviewed.
Goertz, C. K.↗
Dispersive ducting of MHD waves in the plasma sheet - A source of Pi2 wave bursts
Fast magnetoacoustic waves can be ducted by plasma inhomogeneities such as the plasma sheet. As this ducting is dispersive an impulsive source will give rise to a well-defined, quasi-periodic wave packet with time-scales determined by the width of the inhomogeneity and characteristic speeds in the wave duct and surrounding medium. The duration of the wave packet depends upon the distance from the source. It is argued that an impulsive source in the plasma sheet at substorm onset will produce a wave packet near earth with characteristics similar to pi2 wave bursts and put this idea forward as a mechanism for the generation of pi2 pulsations.
Edwin, P. M.↗
Excitation of MHD waves upstream of Jupiter by energetic sulfur or oxygen ions
Large fluxes of heavy ions have been reported upstream of Jupiter's bow shock as Voyager 1 approached the planet (Zwickl et al., 1981; Krimigis et al., 1985). Enhanced low-frequency magnetic wave activity was also observed during the particle events. The fluctuations are left-handed, elliptically polarized in the plasma frame. The spectrum of these fluctuations contains a peak close to the Doppler-shifted resonance frequency of a sulfur or oxygen beam with streaming energy of approximately 30 keV. These fluctuations are also present in the spectrum of the magnitude of the field. It is concluded that the observations result from an instability driven by an energetic beam of either sulfur or oxygen. The wave observations can be described by a heavy ion distribution with both a streaming anisotropy and a temperature anisotropy. This class of heavy ion streaming instabilities may also play a role in wave-particle interactions in the vicinity of comets.
Goldstein, M. L.↗
Magnetohydrodynamic (MHD) analyses of various forms of activity and their propagation through helio spheric space
Theoretical and numerical modeling of solar activity and its effects on the solar atmosphere within the context of magnetohydrodynamics were examined. Specifically, the scientific objectives were concerned with the physical mechanisms for the flare energy build-up and subsequent release. In addition, transport of this energy to the corona and solar wind was also investigated. Well-posed, physically self-consistent, numerical simulation models that are based upon magnetohydrodynamics were sought. A systematic investigation of the basic processes that determine the macroscopic dynamic behavior of solar and heliospheric phenomena was conducted. A total of twenty-three articles were accepted and published in major journals. The major achievements are summarized.
Wu, S. T.↗