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

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.

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

10.21203/rs.3.rs-242784/v1 ◽

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.

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

Journal of Plasma Physics ◽

10.1017/s0022377815001257 ◽

2015 ◽

Vol 81 (6) ◽

Cited By ~ 7

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.

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Probing Current Sheet Instabilities from Flare Ribbon Dynamics

The Astrophysical Journal ◽

10.3847/1538-4357/ac256f ◽

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.

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Cluster as current sheet surveyor in the magnetotail

Annales Geophysicae ◽

10.5194/angeo-31-1605-2013 ◽

2013 ◽

Vol 31 (9) ◽

pp. 1605-1610 ◽

Cited By ~ 8

Author(s):

Y. Narita ◽

R. Nakamura ◽

W. Baumjohann

Keyword(s):

Magnetic Field ◽

Current Sheet ◽

Time Series Data ◽

Sheet Thickness ◽

Dynamical Evolution ◽

Field Measurements ◽

Three Dimensions ◽

Series Data ◽

Time Step ◽

Analysis Technique

Abstract. A novel analysis technique is presented to estimate the current sheet thickness unambiguously and directly, without associating time series data with spatial structure. The technique is a combination of eigenvalue analysis and minimum variance estimator adapted to Harris current sheet geometry, and needs one-time, four-point magnetic field data as provided by the Cluster spacecraft. Two current sheet parameters, thickness and distance to the spacecraft, can be determined at each time step of the magnetic field measurements. An example is shown from a Cluster magnetotail crossing under quiet magnetospheric conditions, yielding the result that the current sheet thickness is on the scale of the proton gyroradius. The analysis technique can also be used to track the dynamical evolution of the current sheet structure in three dimensions.

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

Scientific Reports ◽

10.1038/s41598-021-91111-8 ◽

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.

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Optimal Perturbations of an Oceanic Vortex Lens

Fluids ◽

10.3390/fluids3030063 ◽

2018 ◽

Vol 3 (3) ◽

pp. 63 ◽

Cited By ~ 3

Author(s):

Thomas Meunier ◽

Claire Ménesguen ◽

Xavier Carton ◽

Sylvie Le Gentil ◽

Richard Schopp

Keyword(s):

Normal Mode ◽

Growth Rates ◽

Time Interval ◽

Time Intervals ◽

Horizontal Structure ◽

Azimuthal Wave ◽

Wave Numbers ◽

Non Linear ◽

Long Time ◽

Short Time

The stability properties of a vortex lens are studied in the quasi geostrophic (QG) framework using the generalized stability theory. Optimal perturbations are obtained using a tangent linear QG model and its adjoint. Their fine-scale spatial structures are studied in details. Growth rates of optimal perturbations are shown to be extremely sensitive to the time interval of optimization: The most unstable perturbations are found for time intervals of about 3 days, while the growth rates continuously decrease towards the most unstable normal mode, which is reached after about 170 days. The horizontal structure of the optimal perturbations consists of an intense counter-shear spiralling. It is also extremely sensitive to time interval: for short time intervals, the optimal perturbations are made of a broad spectrum of high azimuthal wave numbers. As the time interval increases, only low azimuthal wave numbers are found. The vertical structures of optimal perturbations exhibit strong layering associated with high vertical wave numbers whatever the time interval. However, the latter parameter plays an important role in the width of the vertical spectrum of the perturbation: short time interval perturbations have a narrow vertical spectrum while long time interval perturbations show a broad range of vertical scales. Optimal perturbations were set as initial perturbations of the vortex lens in a fully non linear QG model. It appears that for short time intervals, the perturbations decay after an initial transient growth, while for longer time intervals, the optimal perturbation keeps on growing, quickly leading to a non-linear regime or exciting lower azimuthal modes, consistent with normal mode instability. Very long time intervals simply behave like the most unstable normal mode. The possible impact of optimal perturbations on layering is also discussed.

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Beam instabilities in a magnetized pair plasma

Journal of Plasma Physics ◽

10.1017/s0022377899007837 ◽

1999 ◽

Vol 62 (1) ◽

pp. 65-86 ◽

Cited By ~ 11

Author(s):

MAXIM LYUTIKOV

Keyword(s):

Growth Rates ◽

Particle Interaction ◽

Kinetic Regime ◽

Pulsar Magnetosphere ◽

Pair Plasma ◽

Electron Positron ◽

Pulsar Radiation ◽

Radiation Generation ◽

Field Lines ◽

Beam Instabilities

Beam instabilities in the strongly magnetized electron–positron plasma of a pulsar magnetosphere are considered. We analyse the resonance conditions and estimate the growth rates of the Cherenkov and cyclotron instabilities of the ordinary (O), extraordinary (X) and Alfvén modes in two limiting regimes: kinetic and hydrodynamic. The importance of the different instabilities as a source of coherent pulsar radiation generation is then estimated, taking into account the angular dependence of the growth rates and the limitations on the length of the coherent wave–particle interaction imposed by the curvature of the magnetic field lines. We conclude that in the pulsar magnetosphere, Cherenkov-type instabilities occur in the hydrodynamic regime, while cyclotron-type instabilities occur in the kinetic regime. We argue that electromagnetic cyclotron-type instabilities on the X, O and probably Alfvén waves are more likely to develop in the pulsar magnetosphere.

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