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 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 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.

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.

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.

scholarly journals A model of solar flares

1968 ◽  
Vol 35 ◽  
pp. 471-479 ◽  
Author(s):  
P. A. Sturrock
Keyword(s):  
Magnetic Field ◽  
Solar Flares ◽  
Transverse Dimension ◽  
Growth Time ◽  
Closed Field ◽  
Field Region ◽  
Tearing Mode ◽  
Magnetic Region ◽  
Field Lines ◽  
Photospheric Motion

A model of solar flares is proposed in which the preflare state comprises a bipolar magnetic-field structure associated with a bipolar photospheric magnetic region. At low heights, the magnetic-field lines are closed but, at sufficiently great heights, the lines are drawn out into an open structure comprising a bipolar flux tube containing a ‘neutral sheet’ or ‘sheet pinch’. Such a sheet pinch is probably related to a coronal streamer. The energy stored in the closed-field region is derived from photospheric motion whereas energy stored in the open-field region is derived from the non-thermal energy flux which heats the corona and drives the solar wind.The flare itself is identified with reconnection of magnetic field by the tearing-mode resistive instability. If the thickness of the sheet pinch is determined by resistive diffusion and a growth time of the bipolar region of order 1 day, the transverse dimension will be about 104 cm. The rise time of the tearing-mode instability is then a few seconds, compatible with the characteristic time of Type-III radio bursts. One can understand that the time-scale of the reconnection process is of order 102–103 sec if reconnection proceeds by the Petscheck mechanism, with the modification that resistive diffusion is replaced by the more rapid Bohm diffusion.The evolution of a flare, according to this model, appears to fit a number of the observational characteristics of flares.

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.

scholarly journals Anomalous-plasmoid-ejection-induced secondary magnetic reconnection: modeling solar flares and coronal mass ejections by laser–plasma experiments

2013 ◽  
Vol 1 (1) ◽  
pp. 11-16 ◽  
Author(s):  
Quanli Dong ◽  
Dawei Yuan ◽  
Shoujun Wang ◽  
Xun Liu ◽  
Yutong Li ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Coronal Mass Ejections ◽  
Solar Flares ◽  
Theoretical Models ◽  
High Energy ◽  
High Energy Density ◽  
Driving Mechanism ◽  
Secondary Current ◽  
Field Lines

AbstractThe driving mechanism of solar flares and coronal mass ejections is a topic of ongoing debate, apart from the consensus that magnetic reconnection plays a key role during the impulsive process. While present solar research mostly depends on observations and theoretical models, laboratory experiments based on high-energy density facilities provide the third method for quantitatively comparing astrophysical observations and models with data achieved in experimental settings. In this article, we show laboratory modeling of solar flares and coronal mass ejections by constructing the magnetic reconnection system with two mutually approaching laser-produced plasmas circumfused of self-generated megagauss magnetic fields. Due to the Euler similarity between the laboratory and solar plasma systems, the present experiments demonstrate the morphological reproduction of flares and coronal mass ejections in solar observations in a scaled sense, and confirm the theory and model predictions about the current-sheet-born anomalous plasmoid as the initial stage of coronal mass ejections, and the behavior of moving-away plasmoid stretching the primary reconnected field lines into a secondary current sheet conjoined with two bright ridges identified as solar flares.

scholarly journals On the Acceleration Processes in Solar Flares

1975 ◽  
Vol 68 ◽  
pp. 427-439
Author(s):  
Z. Švestka
Keyword(s):  
Solar Flares ◽  
Thermal Process ◽  
Second Step ◽  
Relativistic Electrons ◽  
Type Ii ◽  
Tearing Mode ◽  
Mode Instability ◽  
X Ray ◽  
Mev Protons ◽  
Microwave Bursts

The paper summarizes what we know about the acceleration processes on the Sun. Four different instabilities are distinguished: (1) One with purely thermal consequences giving rise to the origin of any flare. (2) A non-thermal process at the flash phase of flares giving rise to ∼ 100 keV electrons and protons, manifested through hard X-ray and impulsive microwave bursts (current interruption?). (3) An instability giving rise to streams of electrons, without accelerating protons, manifested by type III bursts (tearing-mode instability?). When (2) and (3) are linked, flare associated electron events in space are often recorded. (4) Finally an explosive instability produces a shock wave which manifests itself as a type II burst. This instability leads to a second-step acceleration of particles preaccelerated in (2) and gives origin to >10 MeV protons and relativistic electrons (probably stochastic acceleration).

scholarly journals Current Sheets in Solar Flares

1985 ◽  
Vol 107 ◽  
pp. 233-244
Author(s):  
E. R. Priest
Keyword(s):  
Numerical Simulations ◽  
Magnetic Reconnection ◽  
Solar Flares ◽  
Tearing Mode ◽  
Mode Instability ◽  
Current Sheets ◽  
Magnetic Arcade

Until recently magnetic reconnection in solar flares was discussed simplistically in terms of either a spontaneous tearing mode instability or a driven Petschek mode. Now the subtle relationship between these two extremes is much better understood. Current sheets may form and reconnection may be initiated in many different ways. There are also a variety of nonlinear pathways from a reconnection instability and several types of driven reconnection.In solar flares current sheets may be important as new flux emerges from below the photosphere and also as a magnetic arcade closes down after being blown open by an eruptive instability. Numerical simulations of these sheets will be described, including new features such as the presence of a fast shock in Petschek's mechanism and impulsive bursty reconnection due to secondary tearing and coalescence.

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