scholarly journals ON THE EQUILIBRIUM CONFIGURATIONS OF AN INCOMPRESSIBLE FLUID WITH AXISYMMETRIC MOTIONS AND MAGNETIC FIELDS

1958 ◽  
Vol 44 (9) ◽  
pp. 842-847 ◽  
Author(s):  
S. Chandrasekhar
Keyword(s):  
Magnetic Fields ◽  
Incompressible Fluid ◽  
Equilibrium Configurations

On the possibility of magnetic fields and fluid flows parallel to the X-line in a re-connexion geometry

1974 ◽  
Vol 12 (2) ◽  
pp. 319-339 ◽  
Author(s):  
S. W. H. Cowley
Keyword(s):  
Magnetic Field ◽  
Fluid Flow ◽  
Magnetic Fields ◽  
Incompressible Fluid ◽  
Fluid Flows ◽  
The Other ◽  
Diffusion Region ◽  
Incompressible Fluid Flow ◽  
Common Line ◽  
Parallel Field

We consider the possibility of modifying the Sonnerup solution for incompressible fluid flow about an X-type re-connexion line, to include fields and flows parallel to the X line. We find that such fields and flows may change across the discontinuities of the Sonnerup solution. By considering the requirements imposed by a proper matching across the various regions of flow, and by the integral conservation properties of the diffusion region, we seek to find the restrictions that are imposed on this parallel field and flow, and on the arrangement of the discontinuity planes around the diffusion region. We find that four types of such arrangements are possible, each corresponding to a different set of restrictions on the parallel field and flow. In one case, where all the discontinuity planes intersect at a common line, the ‘ parallel’ parameters of the in-flow and out-flow regions may be arbitrarily and independently chosen. Of the remaining three cases, one contains solutions with uniform parallel fields ad flows, while the other two depend for their existence on large fluid flow or magnetic field shears across the two in-flow regions.

scholarly journals Stationary and axisymmetric configurations of compact stars with extremely strong and highly localized magnetic fields

2010 ◽  
Vol 6 (S274) ◽  
pp. 232-235
Author(s):  
Kotaro Fujisawa ◽  
Shin'ichiro Yoshida ◽  
Yoshiharu Eriguchi
Keyword(s):  
Magnetic Fields ◽  
Current Density ◽  
Compact Stars ◽  
Model Parameters ◽  
Flux Function ◽  
Narrow Region ◽  
Deep Interior ◽  
Equilibrium Configurations ◽  
Basic Equations ◽  
New Formulation

AbstractUsing a new formulation to compute structures of stationary and axisymmetric magnetized barotropic stars in Newtonian gravity, we have succeeded in obtaining numerically exact models of stars with extremely high interior magnetic fields. In this formulation, there appear four arbitrary functions of the magnetic flux function from the integrability conditions among the basic equations. Since in our new formulation these arbitrary functions appear in the expression of the current density, configurations with different current distributions can be specified by choosing the forms of the arbitrary functions.By choosing appropriate forms for the four arbitrary functions, we have solved many kinds of equilibrium configurations both with poloidal and toroidal magnetic fields. Among them, by choosing special form for the toroidal current density, we have been able to obtain magnetized stars which have extremely strong poloidal magnetic fields deep inside the core region near the symmetric axis. By adopting the appropriate model parameters for the neutron stars, the magnetic fields could be 1014 ~ 1015 G on the surfaces and be about 1017 G in the deep interior regions. For other model parameters appropriate for white dwarfs, the magnetic fields could be around 107 ~ 108 G (surface regions) and 109 ~ 1010 G (core regions). It is remarkable that the regions with very strong interior magnetic fields are confined to a very narrow region around the symmetric axis in the central part of the stars. The issues of stability of these configurations and of evolutionary paths to reach such configurations need to be investigated in the future work.

scholarly journals Convective mechanism of amplification and structuring of magnetic fields

2012 ◽  
Vol 8 (S294) ◽  
pp. 137-142
Author(s):  
A. V. Getling ◽  
V. V. Kolmychkov ◽  
O. S. Mazhorova
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Incompressible Fluid ◽  
Spatial Scales ◽  
Fluid Motion ◽  
Horizontal Layer ◽  
Field Lines ◽  
The Magnetic Field ◽  
Initial Magnetic Field ◽  
Peripheral Regions

AbstractMagnetoconvection in a horizontal layer of incompressible fluid is simulated numerically. The initial magnetic field is assumed to be uniform and horizontal. The interaction of quasi-ordered cellular convection with the magnetic field is shown to be able to produce bipolar (and also diverse more complex) configurations of a substantially amplified magnetic field. The operation of this mechanism, which can be regarded as a modification of the mechanism suggested by Tverskoi (1966), is controlled by the very topology of the cellular flow, should be manifest on various spatial scales, and does not require strong initial fields. Magnetic configurations develop both in the central parts of convection cells, where circulatory fluid motion “winds” magnetic field lines, and in the network formed by their peripheral regions due to the “sweeping” of magnetic field lines.

scholarly journals The source of magnetic fields in (neutron-) stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 61-74 ◽  
Author(s):  
Hendrik C. Spruit
Keyword(s):  
Magnetic Fields ◽  
Neutron Stars ◽  
Core Collapse ◽  
Magnetorotational Instability ◽  
Dynamo Action ◽  
Field Amplification ◽  
Equilibrium Configurations ◽  
Puzzling Problem ◽  
Collapse Process

AbstractSome arguments, none entirely conclusive, are reviewed about the origin of magnetic fields in neutron stars, with emphasis of processes during and following core collapse in supernovae. Possible origins of the magnetic fields of neutron stars include inheritance from the main sequence progenitor and dynamo action at some stage of evolution of progenitor. Inheritance is not sufficient to explain the fields of magnetars. Energetic considerations point to differential rotation in the final stages of core collapse process as the most likely source of field generation, at least for magnetars. A runaway phase of exponential growth is needed to achieve sufficient field amplification during relevant phase of core collapse; it can probably be provided by a some form of magnetorotational instability. Once formed in core collapse, the field is in danger of decaying again by magnetic instabilities. The evolution of a magnetic field in a newly formed neutron star is discussed, with emphasis on the existence of stable equilibrium configurations as end products of this evolution, and the role of magnetic helicity in their existence. A particularly puzzling problem is the large range of field strengths observed in neutron stars (as well as in A stars and white dwarfs). It implies that a single, deterministic process is insufficient to explain the origin of the magnetic fields in these stars.

scholarly journals 4. Non-stable magneto-hydrodynamical processes in stars

1958 ◽  
Vol 6 ◽  
pp. 33-45
Author(s):  
A. J. Kipper
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Incompressible Fluid ◽  
Viscous Liquid ◽  
Preceding Paper ◽  
Ideal Incompressible Fluid ◽  
Stellar Matter ◽  
Different Dimensions ◽  
The Stability ◽  
The Magnetic Field

1. The behaviour of the magnetic field of a star was investigated by Cowling, Lamb and Wrubel on the assumption of the star as a solid body and on the assumption that the field variations caused by the extinction do not create any motions of the stellar matter. The important results obtained make possible the interpretation of magneto-hydrodynamical processes in stars only quite roughly. When motions of stellar matter caused by the electromagnetic forces are taken into account new properties may be revealed and the non-stability of the magneto-hydrodynamical processes in stars established. Entangled magnetic fields are the general expression of non-stability.2. The mathematical criterion of a confused stellar magnetic field is given in the preceding paper from the magneto-hydrodynamical equations for an ideal incompressible fluid. The conception of a confused field as a superposition of various fields of different scales is introduced.3. It is known that the presence of a magnetic field causes an increase of the stability of hydrodynamical processes, as compared with processes in the absence of a magnetic field. It may most probably be concluded that the extent of confusion of a magnetic field is not the same, as it happens as a result of ordinary turbulent motions in a liquid. However, owing to magneto-hydrodynamical formulae, it may be stated in the present paper that if the field confusion is considered as a superposition of fields of different dimensions and not as a field of entangled magnetic lines, no stability of the above kind can be expected.4. The theory of a totally entangled magnetic field, as a field in a state of maximum confusion is examined. A very close similarity between a totally entangled magnetic field and the turbulent motion in a viscous liquid is established. The question of the time of extinction of a magnetic field of a star is discussed.Note. Sections 1, 2, 4 of the paper are based upon the results obtained by the author, reported by him at the 4th Cosmological Conference. Section 3 contains unpublished results.

Convection-region solutions for the re-connexion of anti-parallel magnetic fields of unequal magnitude in an incompressible plasma

1974 ◽  
Vol 12 (2) ◽  
pp. 341-352 ◽  
Author(s):  
S. W. H. Cowley
Keyword(s):  
Magnetic Fields ◽  
Incompressible Fluid ◽  
Unique Solution ◽  
Flow Direction ◽  
Neutral Line ◽  
Plasma Parameters ◽  
Flow Parameters ◽  
Flowing Plasma ◽  
Parallel Magnetic Fields

We consider the flow of a highly conducting incompressible fluid in the convection region surrounding an X-type neutral line. The Sonnerup solution is generalized to include cases in which the in-flowing anti-parallel magnetic fields are of unequal magnitude, and in which the plasmas of the two in-flow regions have unequal density. It is found that there exists no unique solution for a given set of in-flow plasma parameters, but that the out-flowing plasma may exit within a certain range of angles with respect to the in-flow direction, depending on in-flow parameters.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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