scholarly journals Kinetic simulations of the coupling between current instabilities and reconnection in thin current sheets

2000 ◽  
Vol 7 (3/4) ◽  
pp. 141-150 ◽  
Author(s):  
T. Wiegelmann ◽  
J. Büchner
Keyword(s):  
Magnetic Reconnection ◽  
Current Flow ◽  
Flow Direction ◽  
Substantial Contribution ◽  
Tearing Mode ◽  
Tearing Modes ◽  
Tearing Instability ◽  
Instability Modes ◽  
Thin Current Sheet ◽  
Spatial Dimensions

Abstract. We investigate the coupling between current and tearing instability modes of a thin current sheet using the particle code GISMO. We identify pure tearing modes (kx≠ 0), instabilities in the current flow direction (ky≠ 0) and general 3D reconnection modes (kx≠ 0 and ky≠ 0). Our results give evidence that the coupling between tearing modes and current instabilities plays an important role for spontaneous magnetic reconnection. These modes give a substantial contribution to magnetic reconnection, additional to the well known 2D tearing mode. When allowing reconnection to occur in three spatial dimensions, a configuration, which was initially invariant in the current How direction, develops into a configuration with no invariant direction.

scholarly journals Nonlinear Mode Coupling of Resistive Instability and the Flares of February 4 and 6, 1986

1993 ◽  
Vol 141 ◽  
pp. 401-403
Author(s):  
X.H. Deng ◽  
S. Wang
Keyword(s):  
Solar Flare ◽  
Magnetic Reconnection ◽  
Mode Coupling ◽  
Anomalous Resistivity ◽  
Nonlinear Coupling ◽  
Tearing Mode ◽  
Tearing Modes ◽  
Tearing Instability ◽  
Nonlinear Mode ◽  
Nonlinear Mode Coupling

AbstractIn this paper, we propose a mechanism of solar flare based on the 3-D nonlinear mode coupling of resistive tearing instability. The results show that the nonlinear coupling of tearing modes leads the rapid destabilization of some high modes. Furthermore, tearing mode turbulence is formed and anomalous resistivity is produced, which in turn, quickens the development of tearing instability and accelerate the magnetic reconnection process. It is suggested that the fast magnetic reconnection as a mechanism of solar flare may be associated with this self-excited process caused by the nonlinear mode coupling of tearing instability in the solar corona. Using our model, we successfully explain all the main typical characters of the flares of February 4 and 6, 1986.

Forced reconnexion by fast magnetosonic waves in a current sheet with stagnation-point flows

1983 ◽  
Vol 30 (1) ◽  
pp. 109-124 ◽  
Author(s):  
Jun-Ichi Sakai
Keyword(s):  
Current Sheet ◽  
Stagnation Point ◽  
Solar Flares ◽  
Ponderomotive Force ◽  
Magnetosonic Wave ◽  
Fast Wave ◽  
Tearing Mode ◽  
Tearing Modes ◽  
Tearing Instability ◽  
A Current

Forced reconnexion due to tearing modes driven by fast magnetosonic waves in a current sheet with stagnation-point flows is discussed. The current sheet with stagnation-point flows which is weakly unstable against tearing modes can be strongly destabilized by vortex motions due to the ponderomotive force of the fast magnetosonic wave. This forced tearing instability can be driven when the incident fast magnetosonic wave intensity, I, exceeds a critical value given by where is the Alfvén velocity, vg the group velocity of the fast wave, vo the background inflow velocity, l the thickness of the current sheet and k the wavenumber of the forced tearing mode. The growth rate is estimated. Applications to solar flares and magnetopause reconnexion processes are briefly discussed.

Tearing instability inside a 2D current sheet with a normal magnetic field

2021 ◽  
Author(s):  
Chen Shi ◽  
Anton Artemyev ◽  
Marco Velli ◽  
Anna Tenerani
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Normal Component ◽  
Field Energy ◽  
Tearing Mode ◽  
Magnetic Field Energy ◽  
Tearing Instability ◽  
The Magnetic Field ◽  
Normal Magnetic Field

<p>Magnetic reconnection converts the magnetic field energy into thermal and kinetic energies of the plasma. This process usually happens at extremely fast speed and is therefore believed to be a fundamental mechanism to explain various explosive phenomena such as coronal mass ejections and planetary magnetospheric storms. How magnetic reconnection is triggered from the large magnetohydrodynamic (MHD) scales remains an open question, with some theoretical and numerical studies showing the tearing instability to be involved. Observations in the Earth’s magnetotail and near the magnetopause show that a finite normal magnetic field is usually present inside the reconnecting current sheet. Besides, such a normal field may also exist in the solar corona. However, how this normal magnetic field modifies the tearing instability is not thoroughly studied. Here we discuss the linear tearing instability inside a two-dimensional current sheet with a normal component of magnetic field where the magnetic tension force is balanced by ion flows parallel and anti-parallel to the magnetic field. We solve the dispersion relation of the tearing mode with wave vector parallel to the reconnecting magnetic field. Our results confirm that the finite normal magnetic field stabilizes the tearing mode and makes the mode oscillatory instead of purely growing.</p>

A Numerical Investigation Into the Interaction Between Current Flow and Fuel Consumption in a Segmented-in-Series Tubular SOFC

2009 ◽  
Vol 6 (3) ◽  
Author(s):  
B. A. Haberman ◽  
A. J. Marquis
Keyword(s):  
Density Distribution ◽  
Fuel Consumption ◽  
Current Density ◽  
Current Flow ◽  
Flow Direction ◽  
Ionic Current ◽  
Leading Edge ◽  
Current Density Distribution ◽  
Fuel Flow ◽  
In Series

A typical segmented-in-series tubular solid oxide fuel cell (SOFC) consists of flattened ceramic support tubes with rows of electrochemical cells fabricated on their outer surfaces connected in series. It is desirable to design this type of SOFC to operate with a uniform electrolyte current density distribution to make the most efficient use of the available space and possibly to help minimize the onset of cell component degradation. Predicting the electrolyte current density distribution requires an understanding of the many physical and electrochemical processes occurring, and these are simulated using the newly developed SOHAB multiphysics computer code. Of particular interest is the interaction between the current flow within the cells and the consumption of fuel from an adjacent internal gas supply channel. Initial simulations showed that in the absence of fuel consumption, ionic current tends to concentrate near the leading edge of each electrolyte. Further simulations that included fuel consumption showed that the choice of fuel flow direction can have a strong effect on the current flow distribution. The electrolyte current density distribution is biased toward the upstream fuel flow direction because ionic current preferentially flows in regions rich in fuel. Thus the correct choice of fuel flow direction can lead to more uniform electrolyte current density distributions, and hence it is an important design consideration for tubular segmented-in-series SOFCs. Overall, it was found that the choice of fuel flow direction has a negligible effect on the output voltage of the fuel cells.

scholarly journals tDCS changes in motor excitability are specific to orientation of current flow

2017 ◽  
Author(s):  
Vishal Rawji ◽  
Matteo Ciocca ◽  
Andre Zacharia ◽  
David Soares ◽  
Dennis Truong ◽  
...  
Keyword(s):  
Animal Studies ◽  
Current Flow ◽  
Motor Evoked Potentials ◽  
Flow Direction ◽  
Brain Regions ◽  
Afferent Pathways ◽  
Flow Models ◽  
Cortical Columns ◽  
Local Fluctuations ◽  
Hand Region

Measurements and models of current flow in the brain during transcranial Direct Current Stimulation (tDCS) indicate stimulation of regions in-between electrodes. Moreover, the cephalic cortex result in local fluctuations in current flow intensity and direction, and animal studies suggest current flow direction relative to cortical columns determines response to tDCS. Here we test this idea by measuring changes in cortico-spinal excitability by Transcranial Magnetic Stimulation Motor Evoked Potentials (TMS-MEP), following tDCS applied with electrodes aligned orthogonal (across) or parallel to M1 in the central sulcus. Current flow models predicted that the orthogonal electrode montage produces consistently oriented current across the hand region of M1 that flows along cortical columns, while the parallel electrode montage produces none-uniform current directions across the M1 cortical surface. We find that orthogonal, but not parallel, orientated tDCS modulates TMS-MEPs. We also show modulation is sensitive to the orientation of the TMS coil (PA or AP), which is through to select different afferent pathways to M1. Our results are consistent with tDCS producing directionally specific neuromodulation in brain regions in-between electrodes, but shows nuanced changes in excitability that are presumably current direction relative to column and axon pathway specific. We suggest that the direction of current flow through cortical target regions should be considered for targeting and dose-control of tDCS.

Control of Heat and Mass Transfers Due to Tearing Mode-Based Magnetic Islands During Disruption Phase in IR-T1 Tokamak

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
R. Sadeghi ◽  
A. Salar Elahi ◽  
M. Ghoranneviss ◽  
M. K. Salem
Keyword(s):  
Energy Content ◽  
Singular Value ◽  
Mode Analysis ◽  
Magnetic Fluctuations ◽  
Magnetic Islands ◽  
Tearing Mode ◽  
Tearing Modes ◽  
Complete Disruption ◽  
Value Decomposition ◽  
Mass Transfers

A structural change of perturbed magnetic configurations (such as magnetic islands) during disruption phase in IR-T1 tokamak was studied. The singular value decomposition (SVD) mode analysis and the (m,n) modes identification were presented. We also presented the SVD technique to analyze the tokamak magnetic fluctuations, time evolution of magnetohydrodynamics (MHD) modes, spatial structure of each time vector, and the energy content of each modes. We also considered different scenarios for plasma from steady-state to predisruption, complete disruption, creation of tearing modes, and finally magnetic islands.

scholarly journals The non-modal onset of the tearing instability

2018 ◽  
Vol 84 (5) ◽  
Author(s):  
D. MacTaggart
Keyword(s):  
Initial Conditions ◽  
Linear Equations ◽  
Initial Perturbation ◽  
Transient Growth ◽  
Tearing Mode ◽  
Eigenvalue Spectrum ◽  
Tearing Instability ◽  
Set Up ◽  
Solution Behaviour ◽  
Physical Quantities

We investigate the onset of the classical magnetohydrodynamic (MHD) tearing instability (TI) and focus on non-modal (transient) growth rather than the tearing mode. With the help of pseudospectral theory, the operators of the linear equations are shown to be highly non-normal, resulting in the possibility of significant transient growth at the onset of the TI. This possibility increases as the Lundquist number$S$increases. In particular, we find evidence, numerically, that the maximum possible transient growth, measured in the$L_{2}$-norm, for the classical set-up of current sheets unstable to the TI, scales as$O(S^{1/4})$on time scales of$O(S^{1/4})$for$S\gg 1$. This behaviour is much faster than the time scale$O(S^{1/2})$when the solution behaviour is dominated by the tearing mode. The size of transient growth obtained is dependent on the form of the initial perturbation. Optimal initial conditions for the maximum possible transient growth are determined, which take the form of wave packets and can be thought of as noise concentrated at the current sheet. We also examine how the structure of the eigenvalue spectrum relates to physical quantities.

scholarly journals Onset of magnetic reconnection in a collisionless, high- plasma

2019 ◽  
Vol 85 (1) ◽  
Author(s):  
Andrew Alt ◽  
Matthew W. Kunz
Keyword(s):  
Magnetic Reconnection ◽  
Collisionless Plasma ◽  
High Plasma ◽  
Tearing Modes ◽  
Associated Production ◽  
Pressure Anisotropy ◽  
Low Threshold ◽  
Collisionless Reconnection ◽  
Field Lines ◽  
The Impact

In a magnetized, collisionless plasma, the magnetic moment of the constituent particles is an adiabatic invariant. An increase in the magnetic-field strength in such a plasma thus leads to an increase in the thermal pressure perpendicular to the field lines. Above a$\unicode[STIX]{x1D6FD}$-dependent threshold (where$\unicode[STIX]{x1D6FD}$is the ratio of thermal to magnetic pressure), this pressure anisotropy drives the mirror instability, producing strong distortions in the field lines on ion-Larmor scales. The impact of this instability on magnetic reconnection is investigated using a simple analytical model for the formation of a current sheet (CS) and the associated production of pressure anisotropy. The difficulty in maintaining an isotropic, Maxwellian particle distribution during the formation and subsequent thinning of a CS in a collisionless plasma, coupled with the low threshold for the mirror instability in a high-$\unicode[STIX]{x1D6FD}$plasma, imply that the geometry of reconnecting magnetic fields can differ radically from the standard Harris-sheet profile often used in simulations of collisionless reconnection. As a result, depending on the rate of CS formation and the initial CS thickness, tearing modes whose growth rates and wavenumbers are boosted by this difference may disrupt the mirror-infested CS before standard tearing modes can develop. A quantitative theory is developed to illustrate this process, which may find application in the tearing-mediated disruption of kinetic magnetorotational ‘channel’ modes.

The Tearing Mode Instability in a Partially Ionized Plasma

1979 ◽  
Vol 3 (6) ◽  
pp. 367-368 ◽  
Author(s):  
N. F. Cramer ◽  
I. J. Donnelly
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Solar Flare ◽  
Experimental Evidence ◽  
Energy Release ◽  
Release Mechanism ◽  
Tearing Mode ◽  
Mode Instability ◽  
Laboratory Plasma ◽  
Tearing Instability

The resistive tearing mode instability is a mechanism that in some cases will render unstable a magnetohydrodynamic equilibrium of a plasma that is ideally stable, i.e. stable if no dissipative oiesses are taken into account. There is much experimental evidence that this instability is the cause of the current disruptions observed in laboratory plasma devices (von Goeler et al. 1974). In the astrophysical context, the instability has been invoked in connection with the solar flare energy release mechanism (Coppi and Friedland 1971) and the problem of the disconnection of the protostar matter from the interstellar magnetic field during star formation (Mestel 1966). In the latter problem the tearing instability gives rise to a much smaller timescale for magnetic reconnection than does ordinary resistive diffusion.

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