Geometry of magnetic field lines approaching a current sheet

2003 ◽  
Vol 69 (6) ◽  
pp. 541-550
Author(s):  
MANUEL NÚÑEZ
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Two Dimensions ◽  
Time Of Arrival ◽  
Positive Contribution ◽  
Neutral Sheet ◽  
Spatial Function ◽  
Field Lines ◽  
The Magnetic Field ◽  
A Current

The evolution of a magnetic field line in two dimensions near a neutral sheet is analysed. It is found that the general features of this evolution are rather independent of any particular model, provided that the magnetic field is small and the current density does not vanish. The time of arrival of a field line to the neutral sheet as well as its breaking and reconnection are proved to be finite and to satisfy a simple formula whose main parameter is the resistivity, which may be a spatial function. The shape of the evolving field lines satisfies a differential equation whose solution in some simple cases is shown to agree with certain classical reconnection configurations. Hyperresistivity is found to be more often a hindrance than a positive contribution to the reconnection process.

scholarly journals The development of magnetic field line wander by plasma turbulence

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Gregory G. Howes ◽  
Sofiane Bourouaine
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Large Scale ◽  
Magnetic Energy ◽  
Plasma Turbulence ◽  
Alfven Wave ◽  
Astrophysical Plasmas ◽  
Field Lines ◽  
The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

scholarly journals Quantitative estimations of the anomalous plasma diffusion in an active region

1968 ◽  
Vol 35 ◽  
pp. 131-133
Author(s):  
M. Kopecký ◽  
G. V. Kuklin
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Field Line ◽  
Solar Atmosphere ◽  
Plasma Diffusion ◽  
Field Lines ◽  
The Magnetic Field

In some recent papers the interdependence of the gas and magnetic-field motions in the solar atmosphere was considered. Some results indicate the occurrence of gas motion along the magnetic-field lines combined with motion of the field line, but sometimes we have to assume an obvious gas motion across the magnetic-field lines. As one of the possible mechanisms explaining this fact the anomalous plasma diffusion may be proposed.

scholarly journals Rotation of the magnetic field in Earth's magnetosheath by bulk magnetosheath plasma flow

2006 ◽  
Vol 24 (1) ◽  
pp. 339-354 ◽  
Author(s):  
M. Longmore ◽  
S. J. Schwartz ◽  
E. A. Lucek
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Plasma Flow ◽  
Mean Value ◽  
Flow Coupling ◽  
Parker Spiral ◽  
Magnetic Field Model ◽  
Field Lines ◽  
The Magnetic Field

Abstract. Orientations of the observed magnetic field in Earth's dayside magnetosheath are compared with the predicted field line-draping pattern from the Kobel and Flückiger static magnetic field model. A rotation of the overall magnetosheath draping pattern with respect to the model prediction is observed. For an earthward Parker spiral, the sense of the rotation is typically clockwise for northward IMF and anticlockwise for southward IMF. The rotation is consistent with an interpretation which considers the twisting of the magnetic field lines by the bulk plasma flow in the magnetosheath. Histogram distributions describing the differences between the observed and model magnetic field clock angles in the magnetosheath confirm the existence and sense of the rotation. A statistically significant mean value of the IMF rotation in the range 5°-30° is observed in all regions of the magnetosheath, for all IMF directions, although the associated standard deviation implies large uncertainty in the determination of an accurate value for the rotation. We discuss the role of field-flow coupling effects and dayside merging on field line draping in the magnetosheath in view of the evidence presented here and that which has previously been reported by Kaymaz et al. (1992).

Coherent Curvature Emission in Pulsar Magnetospheres: Non-dipolar Geometric Effects

1993 ◽  
Vol 10 (3) ◽  
pp. 258-262 ◽  
Author(s):  
Qinghuan Luo
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Rotation Period ◽  
Lorentz Factor ◽  
Maser Emission ◽  
Specific Geometry ◽  
Field Lines ◽  
First Time ◽  
The Magnetic Field ◽  
Geometric Effects

AbstractThe effects of the specific geometry of the magnetic field (such as field lines with torsion) on curvature emission and absorption in pulsar magnetospheres are discussed. Curvature maser emission can arise from two effects: the curvature drift, as has already been discussed in the literature, and field line torsion as discussed here in detail for the first time. Maser emission due to field line torsion can operate only when the Lorentz factor is larger than a certain value. However, when the Lorentz factor of electrons or positrons is sufficiently high, curvature masering is due to both curvature drift and magnetic field line torsion. The optical depth in the case of field line torsion is estimated. It is shown that if torsion is due to rotation, the resultant luminosity should be dependent on the rotation period in such a way that shorter periods correspond to larger luminosities.

scholarly journals Large polar caps for twisted magnetosphere of magnetars

2019 ◽  
Author(s):  
H Tong
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Energy Release ◽  
Open Field ◽  
Magnetic Energy ◽  
Hot Spot ◽  
Open Field Line ◽  
Field Lines ◽  
The Magnetic Field ◽  
Magnetic Energy Release

Abstract The magnetic field of magnetars may be twisted compared with that of normal pulsars. Previous works mainly discussed magnetic energy release in the closed field line regions of magnetars. For a twisted magnetic field, the field lines will inflate in the radial direction. Similar to normal pulsars, the idea of light cylinder radius is introduced. More field lines will cross the light cylinder and become open for a twisted magnetic field. Therefore, magnetars may have a large polar cap, which may correspond to the hot spot during outburst. Particle flow in the open field line regions will result in the untwisting of the magnetic field. Magnetic energy release in the open field line regions can be calculated. The model calculations can catch the general trend of magnetar outburst: decreasing X-ray luminosity, shrinking hot spot etc. For magnetic energy release in the open field line regions, the geometry will be the same for different outburst in one magnetar.

Prototypes of a Field Disruption Energy Harvester

2012 ◽  
Author(s):  
Karim El-Rayes ◽  
Ahmed Abdel-Aziz ◽  
Eihab M. Abdel-Rahman ◽  
Raafat Mansour ◽  
Ehab El-Saadany
Keyword(s):  
Magnetic Field ◽  
Energy Source ◽  
Energy Harvesting ◽  
Energy Harvester ◽  
Low Frequency ◽  
Center Frequency ◽  
Field Source ◽  
Field Lines ◽  
The Magnetic Field ◽  
A Current

Energy harvesting from vibrations offers a prevailing non-traditional energy source. We introduce a novel electromagnetic transduction mechanism that can be used to harvest low-frequency vibrations. The mechanism induces a current in a coil by disrupting the electromagnetic field around the coil. The harvester is composed of a coil wound around track and surrounded by a magnetic field. The coil and magnetic field source remain stationary while a ferromagnetic ball material moves freely along the track cutting the field lines, disrupting the magnetic field, and inducing current in the coil. We present a prototype and experiments validating our energy harvesting mechanism as well as a model for the energy harvester. We find that our harvester can generate as much as 2mV and 21 μW from base vibrations of 0.9g amplitude. Our harvester demonstrates low-frequency harvesting with a center frequency as low as 9.4 Hz and a 3db harvesting bandwidth as wide as 5.8 Hz.

scholarly journals A comparison between FUV remote sensing of magnetotail stretching and the T01 model during quiet conditions and growth phases

2007 ◽  
Vol 25 (1) ◽  
pp. 161-170 ◽  
Author(s):  
C. Blockx ◽  
J.-C. Gérard ◽  
V. Coumans ◽  
B. Hubert ◽  
M. Meurant
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Line ◽  
Time History ◽  
Field Configuration ◽  
Growth Phases ◽  
Theoretical Position ◽  
Proton Precipitation ◽  
Field Lines ◽  
The Magnetic Field

Abstract. In a previous study, Blockx et al. (2005) showed that the SI12 camera on board the IMAGE spacecraft is an excellent tool to remotely determine the position of the isotropy boundary (IB) in the ionosphere, and thus is able to provide a reasonable estimate of the amount of stretching of the magnetic field lines in the magetotail. By combining an empirical model of the magnetospheric configuration with Sergeev's criterion for non-adiabatic motion, it is also possible to obtain a theoretical position of IB in the ionosphere, for known conditions in the solar wind. Earlier studies have demonstrated the inadequacy of the Tsyganenko-1989 (T89) model to quantitatively reproduce the field line stretching, particularly during growth phases. In this study, we reexamine this question using the T01 model which considers the time history of the solar wind parameters. We compare the latitude of IB derived from SI12 global images near local midnight with that calculated from the T01 model and the Sergeev's criterion. Observational and theoretical results are found to frequently disagree. We use in situ measurements of the magnetic field with the GOES-8 satellite to discriminate which of the two components in the calculation of the theoretical position of the IB (the T01 model or Sergeev's criterion) induces the discrepancy. For very quiet magnetic conditions, we find that statistically the T01 model approximately predicts the correct location of the maximum proton precipitation. However, large discrepancies are observed in individual cases, as demonstrated by the large scatter of predicted latitudes. For larger values of the AE index, the model fails to predict the observed latitude of the maximum proton intensity, as a consequence of the lack of consideration of the cross-tail current component which produces a more elongated field configuration at the location of the proton injection along the field lines. We show that it is possible to match the observed location of the maximum proton precipitation by decreasing the current sheet half-thickness D parameter. We thus conclude that underestimation of the field line stretching leads to inadequately prediction of the boundary latitude of the non-adiabatic proton precipitation region.

scholarly journals Cosmic Magnetic Fields and Superconducting Strings

1990 ◽  
Vol 140 ◽  
pp. 507-512 ◽  
Author(s):  
Christopher Thompson
Keyword(s):  
Magnetic Field ◽  
Galaxy Formation ◽  
Large Scale ◽  
Cosmic Ray ◽  
String Model ◽  
Maximum Energy ◽  
Superconducting Loop ◽  
Field Lines ◽  
The Magnetic Field ◽  
A Current

A cosmic magnetic field may play a significant role in the formation of galaxies and large scale structure. In particular, a fossil field of present strength ~ 10−9 Gauss is an essential ingredient in the superconducting string model of galaxy formation (Ostriker, Thompson and Witten 1986 (OTW); Thompson 1988a). We discuss the mechanism by which a current is induced on a superconducting string, including recent work on the reconnection of magnetic field lines near the string (Kulsrud and Thompson 1989). A substantial amount of baryonic plasma is trapped on the magnetic field lines which close around the string. The current on a loop almost certainly does not undergo exponential dynamo amplification; an oscillating superconducting loop emits a relativistic MHD wind (Thompson 1988a). Decaying superconducting loops fill most of the intergalactic medium with a relativistic, magnetized fluid. In this model, the gas between galaxies is highly clumped and strongly magnetized, the field strength approaching 1 μG. The maximum energy of cosmic ray protons accelerated at string-driven shocks is ~ 1020 eV (Madau and Thompson 1989).

Peripheral Stochasticity in Tokamaks.The Martin-Taylor Revisited

1992 ◽  
Vol 47 (9) ◽  
pp. 941-944 ◽  
Author(s):  
R. L. Viana ◽  
I. L. Caldas
Keyword(s):  
Magnetic Field ◽  
Aspect Ratio ◽  
Theoretical Analysis ◽  
Field Line ◽  
Magnetic Field Line ◽  
Current Model ◽  
Large Aspect Ratio ◽  
Magnetic Surfaces ◽  
Field Lines ◽  
The Magnetic Field

Abstract We analyse the effect of an Ergodic Magnetic Limiter on the magnetic field line dynamics in the edge of a large aspect-ratio Tokamak. We model the limiter action as an impulsive perturbation and use a peaked-current model for the Tokamak equilibrium field. The theoretical analysis is made through the use of invariant flux functions describing magnetic surfaces. Results are compared with a numerical mapping of the field lines

A re-examination of the role of magnetic field lines in electromagnetic induction

1988 ◽  
Vol 66 (3) ◽  
pp. 245-248
Author(s):  
D. H. Boteler
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Field Line ◽  
Electric Fields ◽  
Electromagnetic Induction ◽  
Magnetic Reynolds Number ◽  
Unified View ◽  
Field Lines ◽  
The Magnetic Field

By adopting a view of magnetic fields, originally proposed by Faraday, in which the magnetic field changes by a movement of field lines, it is shown that a changing magnetic field can be described by the relation [Formula: see text] where v is the velocity of the magnetic field lines. These field-line velocities are shown to be the same as material velocities in conditions of infinite magnetic Reynolds number. The "moving field-line" view provides a phenomenological model of a changing magnetic field that is useful in electromagnetic induction studies. It also allows for a unified view of electromagnetic induction in which all induced electric fields can be explained by the v × B force alone.

Sign in / Sign up

Export Citation Format

Share Document