scholarly journals Magnetohydrodynamic evolution of magnetic skeletons

2007 ◽  
Vol 463 (2080) ◽  
pp. 1097-1115 ◽  
Author(s):  
Andrew L Haynes ◽  
Clare E Parnell ◽  
Klaus Galsgaard ◽  
Eric R Priest
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Three Dimensional ◽  
Heating Process ◽  
Initial State ◽  
Fundamental Building Block ◽  
New Type ◽  
Field Lines ◽  
First Time ◽  
The Magnetic Field

The heating of the solar corona is probably due to reconnection of the highly complex magnetic field that threads throughout its volume. We have run a numerical experiment of an elementary interaction between the magnetic field of two photospheric sources in an overlying field that represents a fundamental building block of the coronal heating process. The key to explaining where, how and how much energy is released during such an interaction is to calculate the resulting evolution of the magnetic skeleton. A skeleton is essentially the web of magnetic flux surfaces (called separatrix surfaces) that separate the coronal volume into topologically distinct parts. For the first time, the skeleton of the magnetic field in a three-dimensional numerical magnetohydrodynamic experiment is calculated and carefully analysed, as are the ways in which it bifurcates into different topologies. A change in topology normally changes the number of magnetic reconnection sites. In our experiment, the magnetic field evolves through a total of six distinct topologies. Initially, no magnetic flux joins the two sources. Then, a new type of bifurcation, called a global double-separator bifurcation , takes place. This bifurcation is probably one of the main ways in which new separators are created in the corona (separators are field lines at which three-dimensional reconnection takes place). This is the first of five bifurcations in which the skeleton becomes progressively more complex before simplifying. Surprisingly, for such a simple initial state, at the peak of complexity there are five separators and eight flux domains present.

scholarly journals 2D and 3D turbulent magnetic reconnection

2009 ◽  
Vol 5 (H15) ◽  
pp. 434-435
Author(s):  
A. Lazarian ◽  
G. Kowal ◽  
E. Vishniac ◽  
K. Kulpa-Dubel ◽  
K. Otmianowska-Mazur
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Large Scale ◽  
Gamma Ray ◽  
Three Dimensional ◽  
Turnover Time ◽  
Turbulent Fluid ◽  
Astrophysical Objects ◽  
Field Lines ◽  
The Magnetic Field

AbstractA magnetic field embedded in a perfectly conducting fluid preserves its topology for all times. Although ionized astrophysical objects, like stars and galactic disks, are almost perfectly conducting, they show indications of changes in topology, magnetic reconnection, on dynamical time scales. Reconnection can be observed directly in the solar corona, but can also be inferred from the existence of large scale dynamo activity inside stellar interiors. Solar flares and gamma ray busts are usually associated with magnetic reconnection. Previous work has concentrated on showing how reconnection can be rapid in plasmas with very small collision rates. Here we present numerical evidence, based on three dimensional simulations, that reconnection in a turbulent fluid occurs at a speed comparable to the rms velocity of the turbulence, regardless of the value of the resistivity. In particular, this is true for turbulent pressures much weaker than the magnetic field pressure so that the magnetic field lines are only slightly bent by the turbulence. These results are consistent with the proposal by Lazarian & Vishniac (1999) that reconnection is controlled by the stochastic diffusion of magnetic field lines, which produces a broad outflow of plasma from the reconnection zone. This work implies that reconnection in a turbulent fluid typically takes place in approximately a single eddy turnover time, with broad implications for dynamo activity and particle acceleration throughout the universe. In contrast, the reconnection in 2D configurations in the presence of turbulence depends on resistivity, i.e. is slow.

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.

FERMION THRESHOLD ENERGY STATES

1992 ◽  
Vol 06 (24) ◽  
pp. 1531-1534
Author(s):  
CHANGHONG ZHU
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Three Dimensional ◽  
Threshold Energy ◽  
Index Theorem ◽  
Equation Of Motion ◽  
Field Configuration ◽  
Two Dimensional ◽  
Magnetic Field Configuration ◽  
The Magnetic Field

We show that for a three-dimensional non-relativistic spinor confined on a plane, the spin-up component obeys the same equation of motion as a two-dimensional spinor. Threshold energy solution is investigated when the electron is moving in the vortex field. It can be proved from the index theorem that the existence of the threshold states depends on the magnetic flux only, not on the magnetic field configuration.

scholarly journals Nd-Fe-B MAGNETS UNDER ELECTRON IRRADIATION WITH THE ENERGY OF 23 MeV

2020 ◽  
pp. 23-27
Author(s):  
V.A. Bovda ◽  
А.М. Bovda ◽  
I.S. Guk ◽  
A.N. Dovbnya ◽  
V.N. Lyashchenko ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Magnetic Flux ◽  
Electron Irradiation ◽  
Reference Sample ◽  
Absorbed Dose ◽  
Initial State ◽  
Magnetic Performance ◽  
And Control ◽  
The Magnetic Field

Four Nd-Fe-B magnets underwent irradiation under 23 MeV electron beam. Nd-Fe-B magnets were magnetized to the technical saturation in the magnetic field of 3.5 T before electron treatment. Two Nd-Fe-B samples (1 and 2) were exposed to the direct electron beam with the energy of 23 MeV. Sample 2 was shielded by tungsten converter. The thickness of the tungsten converter was 4.72 mm. The absorbed dose for the samples was 16 GRad. Sample 3 was subjected to bremsstrahlung of electron irradiation with the energy of 23 MeV. Sample 4 was used as a reference sample for calibration and control measurements. While magnetic flux of sample under direct electron beam of 23 MeV was changed significantly, sample 2 showed the change of magnetic flux to a less degree. Magnetic performance of sample 3 corresponded closely to the initial state.

scholarly journals Chromospheric observations and magnetic configuration of a supergranular structure

2018 ◽  
Vol 621 ◽  
pp. A1 ◽  
Author(s):  
Carolina Robustini ◽  
Sara Esteban Pozuelo ◽  
Jorrit Leenaarts ◽  
Jaime de la Cruz Rodríguez
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Velocity Distribution ◽  
Field Approximation ◽  
Weak Field ◽  
Line Of Sight ◽  
Weak Field Approximation ◽  
Field Lines ◽  
Unipolar Region ◽  
The Magnetic Field

Context.Unipolar magnetic regions are often associated with supergranular cells. The chromosphere above these regions is regulated by the magnetic field, but the field structure is poorly known. In unipolar regions, the fibrillar arrangement does not always coincide with magnetic field lines, and polarimetric observations are needed to establish the chromospheric magnetic topology.Aims.In an active region close to the limb, we observed a unipolar annular network of supergranular size. This supergranular structure harbours a radial distribution of the fibrils converging towards its centre. We aim to improve the description of this structure by determining the magnetic field configuration and the line-of-sight velocity distribution in both the photosphere and the chromosphere.Methods.We observed the supergranular structure at different heights by taking data in the Fe I6301–6302 Å, Hα, Ca II8542 Å, and the Ca IIH&K spectral lines with the CRisp Imaging SpectroPolarimeter (CRISP) and CHROMospheric Imaging Spectrometer (CHROMIS) at the Swedish 1-m Solar Telescope. We performed Milne-Eddington inversions of the spectropolarimetric data of Fe I6301–6302 Å and applied the weak field approximation to Ca II8542 Å data to retrieve the magnetic field in the photosphere and chromosphere. We used photospheric magnetograms of CRISP, Hinode Solar Optical Telescope spectropolarimeter, and Helioseismic and Magnetic Imager to calculate the magnetic flux. We investigated the velocity distribution using the line-of-sight velocities computed from the Milne-Eddington inversion and from the Doppler shift of theK3feature in the Ca IIK spectral line. To describe the typical spectral profiles characterising the chromosphere above the inner region of the supergranular structure, we performed aK-mean clustering of the spectra in Ca IIK.Results.The photospheric magnetic flux shows that the supergranular boundary has an excess of positive polarity and the whole structure is not balanced. The magnetic field vector at chromospheric heights, retrieved by the weak field approximation, indicates that the field lines within the supergranular cell tend to point inwards, and might form a canopy above the unipolar region. In the centre of the supergranular cell hosting the unipolar region, we observe a persistent chromospheric brightening coinciding with a strong gradient in the line-of-sight velocity.

scholarly journals Interaction Of A Stellar Magnetic Field With A Turbulent Accretion Disk

1997 ◽  
Vol 163 ◽  
pp. 205-209
Author(s):  
Anne Bardou ◽  
Jean Heyvaerts
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Accretion Disk ◽  
Central Object ◽  
Field Lines ◽  
The Magnetic Field

AbstractMagnetized objects surrounded by a turbulent and keplerian accretion disk are considered. In such systems, magnetic field lines are embedded into the disk. The magnetic field of the central object is assumed to be dipolar in the absence of the accretion disk. In the presence of a turbulent accretion disk, it is shown that the interaction with the disk stretches magnetic field lines along the disk and that most of the non-magnetospheric magnetic flux is expelled outside the disk.

Proton acceleration in three-dimensional non-null magnetic reconnection

2016 ◽  
Vol 82 (5) ◽  
Author(s):  
Z. Akbari ◽  
M. Hosseinpour ◽  
M. A. Mohammadi
Keyword(s):  
Magnetic Field ◽  
Energy Distribution ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Three Dimensional ◽  
Null Point ◽  
Proton Acceleration ◽  
Electric And Magnetic Fields ◽  
Field Lines ◽  
The Magnetic Field

In a three-dimensional non-null magnetic reconnection, the process of magnetic reconnection takes place in the absence of a null point where the magnetic field vanishes. By randomly injecting a population of 10 000 protons, the trajectory and energy distribution of accelerated protons are investigated in the presence of magnetic and electric fields of a particular model of non-null magnetic reconnection with the typical parameters for the solar corona. The results show that protons are accelerated along the magnetic field lines away from the non-null point only at azimuthal angles where the magnitude of the electric field is strongest and therefore particles obtain kinetic energies of the order of thousands of MeV and even higher. Moreover, the energy distribution of the population depends strongly on the amplitude of the electric and magnetic fields. Comparison shows that a non-null magnetic reconnection is more efficient in accelerating protons to very high GeV energies than a null-point reconnection.

Magnetic damping of jets and vortices

1995 ◽  
Vol 299 ◽  
pp. 153-186 ◽  
Author(s):  
P. A. Davidson
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Angular Momentum ◽  
Kinetic Energy ◽  
Lorentz Force ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Magnetic Damping ◽  
Field Lines ◽  
The Magnetic Field

It is well known that the imposition of a static magnetic field tends to suppress motion in an electrically conducting liquid. Here we look at the magnetic damping of liquid-mental flows where the Reynolds number is large and the magnetic Reynolds number is small. The magnetic field is taken as uniform and the fluid is either infinite in extent or else bounded by an electrically insulating surface S. Under these conditions, we find that three general principles govern the flow. First, the Lorentz force destroys kinetic energy but does not alter the net linear momentum of the fluid, nor does it change the component of angular momentum parallel to B. In certain flows, this implies that momentum, linear or angular, is conserved. Second, the Lorentz force guides the flow in such a way that the global Joule dissipation, D, decreases, and this decline in D is even more rapid than the corresponding fall in global kinetic energy, E. (Note that both D and E are quadratic in u). Third, this decline in relative dissipation, D / E, is essential to conserving momentum, and is achieved by propagating linear or angular momentum out along the magnetic field lines. In fact, this spreading of momentum along the B-lines is a diffusive process, familiar in the context of MHD turbulence. We illustrate these three principles with the aid of a number of specific examples. In increasing order of complexity we look at a spatially uniform jet evolving in time, a three-dimensional jet evolving in space, and an axisymmetric vortex evolving in both space and time. We start with a spatially uniform jet which is dissipated by the sudden application of a transverse magnetic field. This simple (perhaps even trivial) example provides a clear illustration of our three general principles. It also provides a useful stepping-stone to our second example of a steady three-dimensional jet evolving in space. Unlike the two-dimensional jets studied by previous investigators, a three-dimensional jet cannot be annihilated by magnetic braking. Rather, its cross-section deforms in such a way that the momentum flux of the jet is conserved, despite a continual decline in its energy flux. We conclude with a discussion of magnetic damping of axisymmetric vortices. As with the jet flows, the Lorentz force cannot destroy the motion, but rather rearranges the angular momentum of the flow so as to reduce the global kinetic energy. This process ceases, and the flow reaches a steady state, only when the angular momentum is uniform in the direction of the field lines. This is closely related to the tendency of magnetic fields to promote two-dimensional turbulence.

scholarly journals Design and Implementation of Three axis Fluxgate Magnetometer and its Applications

2020 ◽  
Vol 9 (4) ◽  
pp. 960-965
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Flux ◽  
7 Tesla ◽  
Scientific Instrument ◽  
Fluxgate Magnetometer ◽  
Design And Implementation ◽  
Field Lines ◽  
The Magnetic Field ◽  
Ring Core

A scientific instrument which measures the magnetic field strength and its direction is known as Magnetometer. In this article a three axis Fluxgate Magnetometer is constructed by using simple ring core and simple drive circuits instead of specialized components like Hall Effect sensors. This type of Fluxgate magnetometers is working on the principle of magnetic flux linking a coil depends on the orientation of the coil with respect to the earth’s magnetic field lines. Here the three single axis fluxgate magnetometers are designed and placed perpendicular to each other on a board. The circuit is designed to produce 100 KHz frequency and to measure the Magnetic field in the range up to 7 Tesla. The sensitivity is tested through an external electromagnet. The readings are obtained in LAB-VIEW platform and the three-axis data is displayed.

scholarly journals Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

2013 ◽  
Vol 8 (S300) ◽  
pp. 416-417
Author(s):  
G. Allen Gary ◽  
Qiang Hu ◽  
Jong Kwan Lee
Keyword(s):  
Magnetic Field ◽  
Coronal Loop ◽  
Field Model ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Magnetic Field Model ◽  
Free Parameters ◽  
Field Lines ◽  
Fitness Parameter ◽  
The Magnetic Field

AbstractThis article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into the three-dimensional coronal loops. The method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D pseudo-magnetic field lines for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop.

Sign in / Sign up

Export Citation Format

Share Document