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Results for “MAGNETIC EQUATOR”

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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The possible role of meridional flows in suppressing magnetic buoyancy

The equation of motion for a toroidal flux ring in a stellar convective envelope is derived, and the equilibrium of such a ring is considered. Necessary conditions for the stability of toroidal flux rings are derived, and results of stability calculations for a particular model of the meridional flow are presented. The motions of the flux rings when the rings are far from their equilibrium position or when equilibrium does not exist are considered. The results confirm the linear stability analysis, and show that in the absence of stable equilibrium, the rings move toward the solar surface along a trajectory which is parallel to the rotation axis. It is expected that viscosity will tend to reduce the rotational velocity difference between the flux ring and its surroundings, thus reducing the Coriolis force and altering the equilibrium. The storage time of toroidal flux rings is estimated, and some implications for the sun are discussed.

Van Ballegooijen, A. A.↗
NASA NTRS1976

On the equation of state for an electron gas in an intense magnetic field

In this paper we derive the equation of state for a relativistic electron gas imbedded in a static homogeneous magnetic field of arbitrary strength. The derivation is based on the evaluation of the energy-momentum tensor and the use of Dirac's equation for such a problem. Contrary to a derivation presented several years ago, the present derivation is completely gauge-invariant. We also show how to recover, in an exact manner, the perfect gas law for the case of weak magnetic fields.

Canuto, V.↗
NASA NTRS1993

Computer code for scattering from impedance bodies of revolution. Part 3: Surface impedance with s and phi variation. Analytical and numerical results

The third phase of the development of the computer codes for scattering by coated bodies that has been part of an ongoing effort in the Electromagnetics Laboratory of the Electrical Engineering and Computer Science Department at the University of Illinois at Chicago is described. The work reported discusses the analytical and numerical results for the scattering of an obliquely incident plane wave by impedance bodies of revolution with phi variation of the surface impedance. Integral equation formulation of the problem is considered. All three types of integral equations, electric field, magnetic field, and combined field, are considered. These equations are solved numerically via the method of moments with parametric elements. Both TE and TM polarization of the incident plane wave are considered. The surface impedance is allowed to vary along both the profile of the scatterer and in the phi direction. Computer code developed for this purpose determines the electric surface current as well as the bistatic radar cross section. The results obtained with this code were validated by comparing the results with available results for specific scatterers such as the perfectly conducting sphere. Results for the cone-sphere and cone-cylinder-sphere for the case of an axially incident plane were validated by comparing the results with the results with those obtained in the first phase of this project. Results for body of revolution scatterers with an abrupt change in the surface impedance along both the profile of the scatterer and the phi direction are presented.

Uslenghi, Piergiorgio L. E.↗
NASA NTRS1985

Numerical simulations of large-scale solar magnetic fields

A transport equation which describes the evolution of the large-scale magnetic field of the sun was solved numerically. Data derived from solar magnetic observations are used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle. The objective is to assess the ability of the model to reproduce the observed evolution of the field patterns. Recent results from simulations of individual active regions over a few solar rotations and of the magnetic field of the sun over sunspot cycle 21 are discussed.

Devore, C. R.↗
NASA NTRS1989

Boundary-Value Problem For Magnetic-Cutoff Rigidities

Field equations yield overview of motions of many charged particles. Alternative approach developed for calculation of magnetic cutoff rigidities of electrically-charged particles in static magnetic field. New formulation involves partial differential field equation treated as boundary-value problem. Tracing of trajectories needed only to supply boundary conditions.

Edmonds, Larry D.↗
NASA NTRS1990

Formal mathematical solutions of the force-free equations, spontaneous discontinuities, and dissipation in large-scale magnetic fields

Direct integration of the force-free field equation del x B = alpha B, in the simple case of the local deformation of a laminar field, produces field configurations containing tangential discontinuities (current sheets). Whereas continuous solutions allow only restricted field topologies, the discontinuities provide the necessary release from those restrictions in more general topologies. Magnetic fields in nature are strongly deformed by convection, so as to contain significant internal discontinuities. The bipolar magnetic fields containing the active X-ray corona of the sun are a case in point. It appears that the dissipation caused by the discontinuities may be the primary heat source producing the X-ray corona.

Parker, E. N.↗
NASA NTRS1991

Viscosity and inertia in cosmic-ray transport - Effects of an average magnetic field

A generalized transport equation is introduced which describes the transport and propagation of cosmic rays in a magnetized, collisionless medium. The equation is valid if the cosmic-ray distribution function is nearly isotropic in momentum, if the ratio of fluid speed to fluid-flow particle speed is small, and if the ratio of collision time to time for change in the macroscopic flow is small. Five independent cosmic-ray viscosity coefficients are found, and the ralationship of this viscosity to particle orbits in a magnetic field is presented.

Williams, L. L.↗
NASA NTRS1974

First order latitude effects in the solar wind

The Weber-Davis model of the solar wind is generalized to include the effects of latitude. The principal assumptions of perfect electrical conductivity, rotational symmetry, a polytropic relation between pressure and density, and a flow aligned magnetic field in a system rotating with the Sun, are retained. The original three dimensional magnetohydrodynamic flow problem is reduced to a two dimensional hydrodynamic flow problem. The solution at 1 Au is most sensitive to a latitudinal dependence in the coronal boundary temperature and least sensitive to a latitudinal dependence in the magnetic field magnitude. A solution obtained for an approximate dipolar variation in the coronal magnetic field magnitude predicts that the latitudinal flow is initially toward the equator due to magnetic channeling; however, this effect is rapidly overcome and the latitudinal flow at 1 Au is toward the pole and not significantly different from the solution for constant boundary conditions.

Winge, C. R., Jr.↗
NASA NTRS1983

On the field configuration in magnetic clouds

Interplanetary magnetic clouds are represented by cylindrically symmetric equilibrium solutions of the MHD equations. The radial magnetic pressure gradient of the force free field is balanced by the curvature stress. The field inside is essentially parallel to the cylinder axis, far outside it is oriented in azimuthal direction. These configurations therefore differ from the nonselfconsistent model where the field lines are tightly wound even near the axis.

Goldstein, H.↗
NASA NTRS2009

Pair-Starved Pulsar Magnetospheres

We propose a simple analytic model for the innermost (within the light cylinder of canonical radius, approx. c/Omega) structure of open-magnetic-field lines of a rotating neutron star (NS) with relativistic outflow of charged particles (electrons/positrons) and arbitrary angle between the NS spin and magnetic axes. We present the self-consistent solution of Maxwell's equations for the magnetic field and electric current in the pair-starved regime where the density of electron-positron plasma generated above the pulsar polar cap is not sufficient to completely screen the accelerating electric field and thus establish thee E . B = 0 condition above the pair-formation front up to the very high altitudes within the light cylinder. The proposed mode1 may provide a theoretical framework for developing the refined model of the global pair-starved pulsar magnetosphere.

Muslimov, Alex G.↗
NASA NTRS1988

Dynamics of localized ion-acoustic waves in a magnetized plasma

The evolution of negative potential pulses in a magnetized plasma is studied. A three-dimensional nonlinear ion-acoustic wave equation, including nonstationary effects of reflected electrons, has been derived from the Poisson-Vlasov equations with uniform magnetic field. The studies show that a negative potential pulse can be enhanced by drifting electrons. The growing pulse develops asymmetrically with an oscillatory precursor and a local potential jump resembling the early phase of weak double layer formation.

Qian, S.↗
NASA NTRS1986

The physics of the cometary contact surface

The contact surface, which separates outflowing cometary plasma from solar wind controlled cometary plasma, is explained in terms of a balance between the magnetic pressure gradient force and ion-neutral drag. Giotto data indicate that the plasma pressure inside the contact surface cannot balance the sum of the external plasma and magnetic pressures, and therefore a Venus-like ionopause is not present at the contact surface. An expression for the magnetic field strength as a function of cometocentric distance is derived from the momentum equation. The theoretical magnetic field profile agrees quite well with the profile measured by the Giotto magnetometer in the vicinity of the contact surface.

Cravens, Thomas E.↗
NASA NTRS1988

Transport equations for low-energy solar particles in evolving interplanetary magnetic fields

Two new forms of a simplified Fokker-Planck equation are derived for the transport of low-energy solar energetic particles in an evolving interplanetary magnetic field, carried by a variable radial solar wind. An idealized solution suggests that the 'invariant' anisotropy direction reported by Allum et al. (1974) may be explained within the conventional theoretical framework. The equations may be used to relate studies of solar particle propagation to solar wind transients, and vice versa.

Ng, C. K.↗
NASA NTRS1992

FNAS: The magnetic configuration leading to solar flares

We present a method for solving plasma magnetohydrodynamic (MHD) problems arising from the interaction of plasmas with magnetic fields in stellar atmospheres. Our approach, in contrast to previous methods, is not based on solving equations for the magnetic field and plasma velocity but rather studies the evolution of the electric current and density (and the related gas pressure). We have applied the method to several studies involving linearized departures from static, current-free equilibria. The applications show explicit solutions for cases found in astrophysics and to problems encountered with earlier studies where the gas pressure was neglected. The method is particularly well suited for studying situations which involve a transition between high and low plasma-beta regions. It shows precisely how electric currents, and magnetic free-energy, build up in the plasma as a result of the slow stressing of a potential magnetic field configuration. The method also demonstrates how transverse-current waves, a mix of Alfven and magneto-acoustic modes, propagate in a low-beta plasma for any density stratification and background field geometry.

Fontenla, Juan M.↗