scholarly journals Dynamic mitigation of the tearing mode instability in a collisionless current sheet

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yan-Jun Gu ◽  
Shigeo Kawata ◽  
Sergei V. Bulanov
Keyword(s):  
Current Sheet ◽  
Small Amplitude ◽  
Electron Current ◽  
Tearing Mode ◽  
Mode Instability ◽  
Feed Forward Control ◽  
Collisionless Plasmas ◽  
Instability Growth ◽  
Field Lines ◽  
The Magnetic Field

AbstractDynamic mitigation for the tearing mode instability in the current sheet in collisionless plasmas is demonstrated by applying a wobbling electron current beam. The initial small amplitude modulations imposed on the current sheet induce the electric current filamentation and the reconnection of the magnetic field lines. When the wobbling or oscillatory motion is added from the electron beam having a form of a thin layer moving along the current sheet, the perturbation phase is mixed and consequently the instability growth is saturated remarkably, like in the case of the feed-forward control.

scholarly journals Dynamic Mitigation of Tearing Mode Instability in Current Sheet in Collisionless Plasma

2021 ◽  
Author(s):  
Yan-Jun Gu ◽  
Shigeo Kawata ◽  
Sergei Bulanov
Keyword(s):  
Current Sheet ◽  
Small Amplitude ◽  
Collisionless Plasma ◽  
Electron Current ◽  
Tearing Mode ◽  
Mode Instability ◽  
Feed Forward Control ◽  
Instability Growth ◽  
Field Lines ◽  
The Magnetic Field

Abstract Dynamic mitigation for the tearing mode instability in the current sheet in collisionless plasma is demonstrated by applying a wobbling electron current beam. The initial small amplitude modulations imposed on the current sheet induce the electric current filamentation and the reconnection of the magnetic field lines. When the wobbling or oscillation motion is added from the electron beam having a form of a thin layer moving along the current sheet, the perturbation phase is mixed and consequently the instability growth is saturated remarkably, like in the case of the feed-forward control.

scholarly journals Probing Current Sheet Instabilities from Flare Ribbon Dynamics

2021 ◽  
Vol 922 (2) ◽  
pp. 117
Author(s):  
Ryan J. French ◽  
Sarah A. Matthews ◽  
I. Jonathan Rae ◽  
Andrew W. Smith
Keyword(s):  
Solar Flare ◽  
Current Sheet ◽  
Solar Flares ◽  
Spatial Scales ◽  
Tearing Mode ◽  
Scale Growth ◽  
Mode Instability ◽  
Field Lines ◽  
Flare Ribbon ◽  
High Cadence

Abstract The presence of current sheet instabilities, such as the tearing mode instability, are needed to account for the observed rate of energy release in solar flares. Insights into these current sheet dynamics can be revealed by the behavior of flare ribbon substructure, as magnetic reconnection accelerates particles down newly reconnected field lines into the chromosphere to mark the flare footpoints. Behavior in the ribbons can therefore be used to probe processes occurring in the current sheet. In this study, we use high-cadence (1.7 s) IRIS Slit Jaw Imager observations to probe for the growth and evolution of key spatial scales along the flare ribbons—resulting from dynamics across the current sheet of a small solar flare on 2016 December 6. Combining analyses of spatial scale growth with Si iv nonthermal velocities, we piece together a timeline of flare onset for this confined event, and provide evidence of the tearing mode instability triggering a cascade and inverse cascade toward a power spectrum consistent with plasma turbulence.

scholarly journals Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy

2004 ◽  
Vol 11 (5/6) ◽  
pp. 579-587 ◽  
Author(s):  
L. M. Zelenyi ◽  
H. V. Malova ◽  
V. Yu. Popov ◽  
D. Delcourt ◽  
A. S. Sharma
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Plasma Pressure ◽  
Quasi Equilibrium ◽  
Electrostatic Effects ◽  
Current Sheets ◽  
Thin Current Sheet ◽  
Field Lines ◽  
The Magnetic Field

Abstract. Thin current sheets represent important and puzzling sites of magnetic energy storage and subsequent fast release. Such structures are observed in planetary magnetospheres, solar atmosphere and are expected to be widespread in nature. The thin current sheet structure resembles a collapsing MHD solution with a plane singularity. Being potential sites of effective energy accumulation, these structures have received a good deal of attention during the last decade, especially after the launch of the multiprobe CLUSTER mission which is capable of resolving their 3D features. Many theoretical models of thin current sheet dynamics, including the well-known current sheet bifurcation, have been developed recently. A self-consistent 1D analytical model of thin current sheets in which the tension of the magnetic field lines is balanced by the ion inertia rather than by the plasma pressure gradients was developed earlier. The influence of the anisotropic electron population and of the corresponding electrostatic field that acts to restore quasi-neutrality of the plasma is taken into account. It is assumed that the electron motion is fluid-like in the direction perpendicular to the magnetic field and fast enough to support quasi-equilibrium Boltzmann distribution along the field lines. Electrostatic effects lead to an interesting feature of the current density profile inside the current sheet, i.e. a narrow sharp peak of electron current in the very center of the sheet due to fast curvature drift of the particles in this region. The corresponding magnetic field profile becomes much steeper near the neutral plane although the total cross-tail current is in all cases dominated by the ion contribution. The dependence of electrostatic effects on the ion to electron temperature ratio, the curvature of the magnetic field lines, and the average electron magnetic moment is also analyzed. The implications of these effects on the fine structure of thin current sheets and their potential impact on substorm dynamics are presented.

Resistive tearing-mode instability in a magnetic-field-reversing current sheet with coplanar viscous stagnation-point flow

1996 ◽  
Vol 56 (2) ◽  
pp. 265-284 ◽  
Author(s):  
Justin T. C. Ip ◽  
Bengt U. Ö. Sonnerup
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Stagnation Point ◽  
Linear Growth ◽  
Field Configuration ◽  
Stagnation Point Flow ◽  
Magnetic Islands ◽  
Tearing Mode ◽  
Mode Instability ◽  
Simulation Results

The tearing-mode instability of a magnetic-field-reversing current sheet in the presence of coplanar incompressible stagnation-point flow is examined. The unperturbed equilibrium state is an exact solution of the steady-state, dissipative, incompressible magnetohydrodynamic equations; thus the analysis is valid even for small viscous and resistive Lundquist numbers Sν and Sη. The instability problem has no known analytical solution; for this reason, it is studied numerically by use of a finite-element method. Simulation results indicate stability for sufficiently small values of Sν or Sη and instability for large values. The boundary separating stable and unstable regions in the (Sν, Sη) plane is located. In the unstable regime, the simulation results show formation and subsequent convection of magnetic islands along the current sheet at about 80% of the unperturbed outflow flow speed, on average. Stretching and pinching of convecting magnetic islands are also observed. The results show the occurrence of multiple X-line reconnection at the centre of the current sheet (x = 0). Small-scale structures of vorticity and current density near the X-point reconnection sites are found to be qualitatively consistent with results obtained by Matthaeus. Normalized global linear growth rates are found to obey the approximate power law, within the ranges 20 ≦ Sν ≦ 70 and 200 ≦ Sη 1000. At least for Sν ≦ 1000, the number of magnetic islands is found to be nearly independent of Sν indicating the existence of a narrow band of dominant wavelengths in this range. The stretching of magnetic islands, which is present in this coplanar flow and field configuration, but not in the perpendicular flow and field configuration examined by Phan and Sonnerup, causes a substantial decrease in linear growth rate relative to that obtained by those authors. The stability curves obtained are qualitatively similar in both analyses, but the stable region is much larger for coplanar flow and field. Unlike most simulations of the tearing mode, no symmetry conditions are imposed on the perturbations; nevertheless, they develop in a symmetric manner.

scholarly journals 3D reconnection due to oblique modes: a simulation of Harris current sheets

2000 ◽  
Vol 7 (3/4) ◽  
pp. 151-158 ◽  
Author(s):  
G. Lapenta ◽  
J. U. Brackbill
Keyword(s):  
Current Sheet ◽  
Growth Rates ◽  
Sheet Thickness ◽  
Helical Structure ◽  
Three Dimensions ◽  
Linear Stage ◽  
Tearing Mode ◽  
Kink Mode ◽  
Non Linear ◽  
Field Lines

Abstract. Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.

Characteristics and variability of Titan's magnetic environment

2008 ◽  
Vol 367 (1889) ◽  
pp. 789-798 ◽  
Author(s):  
César L Bertucci
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Current Sheet ◽  
Radial Component ◽  
Wind Pressure ◽  
Rotation Direction ◽  
Background Magnetic Field ◽  
Solar Wind Pressure ◽  
Field Lines ◽  
The Magnetic Field

The structure and variability of Saturn's magnetic field in the vicinity of Titan's orbit is studied. In the dawn magnetosphere, the magnetic field presents a significant radial component directed towards Saturn, suggesting that Titan is usually located below the planet's warped and dynamic magnetodisc. Also, a non-negligible component along the co-rotation direction suggests that Saturn's magnetic field lines close to the magnetodisc are being swept back from their respective magnetic meridians. In the noon sector, Titan seems to be closer to the magnetodisc central current sheet, as the field lines in this region seem to be more dipolar. The distance between the central current sheet and Titan depends mainly on the solar wind pressure. Also, δ | B |/| B |∼0.5 amplitude waveforms at periods close to Saturn's kilometric radiation period are present in the background magnetic field. This modulation in the field is ubiquitous in Saturn's magnetosphere and associated with the presence of a rotating asymmetry in the planet's magnetic field.

scholarly journals Effect of guide field on three-dimensional electron shear flow instabilities in electron current sheets

2015 ◽  
Vol 81 (6) ◽  
Author(s):  
Neeraj Jain ◽  
Jörg Büchner
Keyword(s):  
Shear Flow ◽  
Current Sheet ◽  
Three Dimensional ◽  
Sheet Thickness ◽  
Electron Current ◽  
Tearing Mode ◽  
Current Sheets ◽  
Tearing Modes ◽  
Guide Field ◽  
Half Thickness

We examine, in the limit of electron plasma ${\it\beta}_{e}\ll 1$, the effect of an external guide field and current sheet thickness on the growth rates and nature of three-dimensional (3-D) unstable modes of an electron current sheet driven by electron shear flow. The growth rate of the fastest growing mode drops rapidly with current sheet thickness but increases slowly with the strength of the guide field. The fastest growing mode is tearing type only for thin current sheets (half-thickness ${\approx}d_{e}$, where $d_{e}=c/{\it\omega}_{pe}$ is the electron inertial length) and zero guide field. For finite guide field or thicker current sheets, the fastest growing mode is a non-tearing type. However, growth rates of the fastest 2-D tearing and 3-D non-tearing modes are comparable for thin current sheets ($d_{e}<\text{half thickness}<2\,d_{e}$) and small guide field (of the order of the asymptotic value of the component of magnetic field supporting the electron current sheet). It is shown that the general mode resonance conditions for tearing modes depend on the effective dissipation mechanism. The usual tearing mode resonance condition ($\boldsymbol{k}\boldsymbol{\cdot }\boldsymbol{B}_{0}=0$, $\boldsymbol{k}$ is the wavevector and $\boldsymbol{B}_{0}$ is the equilibrium magnetic field) can be recovered from the general resonance conditions in the limit of weak dissipation. The conditions (relating current sheet thickness, strength of the guide field and wavenumbers) for the non-existence of tearing mode are obtained from the general mode resonance conditions. We discuss the role of electron shear flow instabilities in magnetic reconnection.

scholarly journals The structure and dynamics of a large-scale plasmoid generated by fast reconnection in the geomagnetic tail

2011 ◽  
Vol 29 (1) ◽  
pp. 147-156 ◽  
Author(s):  
M. Ugai
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Large Scale ◽  
Field Component ◽  
The North ◽  
Reconnection Region ◽  
Field Lines ◽  
The Magnetic Field ◽  
East West ◽  
Fast Reconnection

Abstract. As a sequence of Ugai (2010b), the present paper studies in detail the structure and dynamics of large-scale (principal) plasmoid, generated by the fast reconnection evolution in a sheared current sheet with no initial northward field component. The overall plasmoid domain is divided into the plasmoid reconnection region P and the plasmoid core region C. In the region P, the magnetized plasma with reconnected field lines are accumulated, whereas in the region C, the plasma, which was intially embedded in the current sheet and has been ejected away by the reconnection jet, is compressed and accumulated. In the presence of the sheared magnetic field in the east-west direction in the current sheet, the upper and lower parts of the reconnection region P are inversely shifted in the east-west directions. Accordingly, the plasmoid core region C with the accumulated sheared field lines is bent in the north-south direction just ahead of the plasmoid center x=XC, causing the magnetic field component in the north-south direction, whose sign is always opposite to that of the reconnected field lines. Therefore, independently of the sign of the initial sheared field, the magnetic field component Bz in the north-south direction has the definite bipolar profile around XC along the x-axis. At x=XC, the sheared field component has the peak value, and as the sheared fields accumulated in the region C become larger, the bipolar field profile becomes more distinct.

scholarly journals Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

2015 ◽  
Vol 33 (12) ◽  
pp. 1485-1493 ◽  
Author(s):  
V. A. Sergeev ◽  
I. A. Chernyaev ◽  
V. Angelopoulos ◽  
N. Y. Ganushkina
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Time History ◽  
Resonant Scattering ◽  
Curvature Radius ◽  
Local Data ◽  
Adaptive Models ◽  
Data Adaptive ◽  
Field Lines ◽  
The Magnetic Field

Abstract. Data from a cluster of three THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft during February–March 2009 frequently provide an opportunity to construct local data-adaptive magnetospheric models, which are suitable for the accurate mapping along the magnetic field lines at distances of 6–9 Re in the nightside magnetosphere. This allows us to map the isotropy boundaries (IBs) of 30 and 80 keV protons observed by low-altitude NOAA POES (Polar Orbiting Environmental Satellites) to the equatorial magnetosphere (to find the projected isotropy boundary, PIB) and study the magnetospheric conditions, particularly to evaluate the ratio KIB (Rc/rc; the magnetic field curvature radius to the particle gyroradius) in the neutral sheet at that point. Special care is taken to control the factors which influence the accuracy of the adaptive models and mapping. Data indicate that better accuracy of an adaptive model is achieved when the PIB distance from the closest spacecraft is as small as 1–2 Re. For this group of most accurate predictions, the spread of KIB values is still large (from 4 to 32), with the median value KIB ~13 being larger than the critical value Kcr ~ 8 expected at the inner boundary of nonadiabatic angular scattering in the current sheet. It appears that two different mechanisms may contribute to form the isotropy boundary. The group with K ~ [4,12] is most likely formed by current sheet scattering, whereas the group having KIB ~ [12,32] could be formed by the resonant scattering of low-energy protons by the electromagnetic ion-cyclotron (EMIC) waves. The energy dependence of the upper K limit and close proximity of the latter event to the plasmapause locations support this conclusion. We also discuss other reasons why the K ~ 8 criterion for isotropization may fail to work, as well as a possible relationship between the two scattering mechanisms.

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

&lt;p&gt;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&amp;#8217;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.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document