Galactic Dynamics and Magnetic Field Amplification

1993 ◽  
pp. 395-401
Author(s):  
Harald Lesch
Keyword(s):  
Magnetic Field ◽  
Galactic Dynamics ◽  
Field Amplification

scholarly journals Magnetic field amplification in newly-born neutron stars

1996 ◽  
Vol 160 ◽  
pp. 435-436
Author(s):  
H.-J. Wiebicke ◽  
U. Geppert
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Gravitational Collapse ◽  
Dipole Field ◽  
Numerical Calculations ◽  
Selection Effects ◽  
Thermoelectric Effects ◽  
Field Amplification ◽  
Seed Field ◽  
Flux Conservation

AbstractWe present a scenario of magnetic field (MF) evolution of newly-born neutron stars (NSs). Numerical calculations show that in the hot phase of young NSs the MF can be amplified by thermoelectric effects, starting from a moderately strong seed-field. Therefore, there is no need to assume a 1012G dipole field immediately after the gravitational collapse of the supernova (SN) event. The widely accepted scenario for such a field to be produced by flux conservation during the collapse is critically discussed. Instead, it can be generated by amplification and selection effects in the first 104yrs, and by the subsequent fast ohmic decay of higher multipole components, when the NS cools down.

MAGNETIC FIELD AMPLIFICATION BY RELATIVISTIC SHOCKS IN AN INHOMOGENEOUS MEDIUM

2012 ◽  
Vol 08 ◽  
pp. 364-367
Author(s):  
YOSUKE MIZUNO ◽  
MARTIN POHL ◽  
JACEK NIEMIEC ◽  
BING ZHANG ◽  
KEN-ICHI NISHIKAWA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Inhomogeneous Medium ◽  
Magnetic Energy ◽  
Small Scale ◽  
Two Dimensional ◽  
Filamentary Structure ◽  
Field Amplification ◽  
Relativistic Shocks ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring in the postshock region. We also find that the amplitude of magnetic-field amplification depends on the direction of the mean preshock magnetic field.

scholarly journals Magnetic field amplification in cold dark matter anisotropic collapse

2003 ◽  
Vol 338 (3) ◽  
pp. 785-789 ◽  
Author(s):  
Marco Bruni ◽  
Roy Maartens ◽  
Christos G. Tsagas
Keyword(s):  
Magnetic Field ◽  
Dark Matter ◽  
Cold Dark Matter ◽  
Field Amplification

Magnetic Field Amplification by Shocks in Turbulent Fluids

2007 ◽  
Vol 663 (1) ◽  
pp. L41-L44 ◽  
Author(s):  
J. Giacalone ◽  
J. R. Jokipii
Keyword(s):  
Magnetic Field ◽  
Field Amplification ◽  
Turbulent Fluids

Analysis and Experimental Study of Magnetic-Field Amplification by a Double Coil

2017 ◽  
Vol 64 (4) ◽  
pp. 3216-3226 ◽  
Author(s):  
Ai-ichiro Sasaki ◽  
Olivier Ouellette ◽  
Maxime Beaudry-Marchand ◽  
Akihiko Hirata ◽  
Hiroki Morimura
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Field Amplification

scholarly journals Magnetic Field Amplification and Polar Jet Formation in Protostars

1987 ◽  
Vol 115 ◽  
pp. 384-384
Author(s):  
S. Hinata
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Kinetic Energy ◽  
Accretion Disk ◽  
Outer Edge ◽  
Moment Of Inertia ◽  
Simple Relationship ◽  
Field Amplification ◽  
Background Magnetic Field ◽  
The Moment

There is a simple relationship among moment of inertia I, rotational kinetic energy K, and momentum L given by (David Layzer, private communication), 2IK ≧ L. During the Hayashi phase a rotating protostar will amplify the trapped magnetic field by a dynamo-like process. Since the rotation is expected to be fast, many unstable modes will be excited and will grow exponentially in time until some nonlinear processes saturate the amplitude. However, it may happen that the reduction in rotational kinetic energy becomes so large that without increasing the moment of inertia the inequality given above may not be satisfied. The only way to increase the moment of inertia is to move the mass outward. This can be done by transferring the angular momentum outward through the magnetic field. So we will have a fast rotating mass shell at the outer edge of the star. Further transfer of angular momentum will push the shell against the accretion disk; the moving masses of the disk will divert the mass flow along the background magnetic field which extends perpendicular to the accretion disk. This results in the hollow cone jets from both poles because the outward motion is primarily on the equatorial plane.

Magnetic Field Enhancement with Soft Magnetic Flux Guides

2008 ◽  
Vol 587-588 ◽  
pp. 313-317
Author(s):  
D.C. Leitão ◽  
I.G. Trindade ◽  
R. Fermento ◽  
João P. Araújo ◽  
S. Cardoso ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Spin Valve ◽  
Field Enhancement ◽  
High Permeability ◽  
Soft Magnetic ◽  
Field Amplification ◽  
Close Proximity ◽  
Magnetic Field Enhancement ◽  
The Magnetic Field

In this work, a study of the sensitivity enhancement of spin valve sensors, when located in close proximity to magnetic flux guides, is presented. The magnetoresistance (MR) of spin-valve sensors, lithographically patterned into stripes with lateral dimensions, (length) l = 500 µm, (width) wsensor = 1, 2, 6 µm and placed near one/two Co93.5Zr2.8Nb3.7 (CZN) magnetic flux guide, is characterized at room temperature. CZN has a high permeability that together with a defined microstructured shape, is able to concentrate the magnetic flux in a small area, leading to an increase in sensor's sensitivity. The magnetic field amplification is estimated by comparison of sensor sensitivity with/without magnetic flux guides, in the linear operation range, and studied as a function of different parameters. Besides an enhancement in sensitivity, sensors also exhibit an important increase in the hard axis coercivity and a shift from MR(H=0) = 0.5, both attributed to the magnetic flux guides. Amplification factors of the order of 20 are observed..

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