Nonlinear electron-magnetohydrodynamic simulations of three dimensional current shear instability

The dissipation mechanism by which the magnetic field reconnects in the presence of an external (guide) magnetic field in the direction of the main current is not well understood. In thin electron current sheets (half thickness close to an electron inertial length) formed in collisionless magnetic reconnection, electron shear flow instabilities are potential candidates for providing an anomalous dissipation mechanism which can break the frozen-in condition of the magnetic field affecting the structure and rate of reconnection. We present the results of investigations of the evolution of electron shear flow instabilities, from linear to nonlinear state, in guide field magnetic reconnection. The properties of the plasma turbulence resulting from the growth of the instability and their dependence on the strength of the guide field are studied. For this sake, we utilize three dimensional electron-magnetohydrodynamic simulations of electron current sheets. We show that, unlike the case of current sheets selfconsistently embedded in anti-parallel magnetic fields, the evolution of thin electron current sheets in the presence of a finite external guide field (equal to the asymptotic value of the reconnecting magnetic field or larger) is dominated by high wave number non-tearing mode instabilities. The latter cause the development of, first, a wavy structure of the current sheet. The turbulence, developed later, consists of current filaments and electron flow vortices. As a result of the nonlinear evolution of the instability, the current sheet broadens simultaneously with its flattening in the central region mimicking a viscous-like turbulent dissipation. Later, the flattened current sheet bifurcates. During the time of the bifurcation, the rate of the change of the mean electron flow velocity is proportional to the magnitude of the flow velocity, suggesting a resistive-like dissipation. The turbulence energy cascades to shorter wavelengths preferentially in the direction perpendicular to the guide magnetic field.The degree of anisotropy of the turbulence was found to increase with the increasing strength of the guide field.

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“…approximation have been reported earlier [15][16][17][18][19][20][21] . In EMHD the electron flow carries the current.…”

Section: Investigations Of Linear and Nonlinear Electron Shear Flow Isupporting

confidence: 71%

Nonlinear evolution of electron shear flow instabilities in the presence of an external guide magnetic field

2017

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“…Linear and nonlinear studies of electron shear flow instabilities in EMHD approximation have earlier been performed. [29][30][31][32][33][34][35] These instabilities have also been referred as current driven sausage and kink instabilities because, in EMHD, electron flow is equivalent to current. 30,32,33 Comparison of growth rates of 2-D instabilities in the plane containing directions of flow and shear (termed pure sausage mode) was made with the 2-D instabilities in the plane perpendicular to the sausage plane (termed pure kink mode).…”

Section: Introductionmentioning

confidence: 98%

Three dimensional instabilities of an electron scale current sheet in collisionless magnetic reconnection

Jain

Büchner

2014

Physics of Plasmas

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In collisionless magnetic reconnection, electron current sheets (ECS) with thickness of the order of an electron inertial length form embedded inside ion current sheets with thickness of the order of an ion inertial length. These ECS's are susceptible to a variety of instabilities which have the potential to affect the reconnection rate and/or the structure of reconnection. We carry out a three dimensional linear eigen mode stability analysis of electron shear flow driven instabilities of an electron scale current sheet using an electron-magnetohydrodynamic plasma model. The linear growth rate of the fastest unstable mode was found to drop with the thickness of the ECS. We show how the nature of the instability depends on the thickness of the ECS. As long as the half-thickness of the ECS is close to the electron inertial length, the fastest instability is that of a translational symmetric two-dimensional (no variations along flow direction) tearing mode. For an ECS half thickness sufficiently larger or smaller than the electron inertial length, the fastest mode is not a tearing mode any more and may have finite variations along the flow direction. Therefore, the generation of plasmoids in a nonlinear evolution of ECS is likely only when the half-thickness is close to an electron inertial length.

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“…However, recent experiments have shown that for sharp overdense plasmas (with an interface with a scale length \ $ light vacuum wavelength) which naturally result when the pulses are so short that CPA (Mourou 1997) leads to relativistic intensities, standard resonance absorption was replaced by Brunel mechanism which converted light energy into relativistic electron beams with energy of the order of few MeV. The subsequent propagation of relativistic beams into overdense plasmas has led to some very novel physics and resulted in a very fruitful collaboration between our group at IPR (led by Amita Das) and experimental groups at TIFR (GRK) and Osaka (KaT) (Sandhu et al 2002;Kahaly et al 2008;Mondal et al 2012;Das and Kaw 2001;Jain et al 2003;Sandhu et al 2005;Saxena et al 2006Saxena et al , 2007Jain et al 2007Jain et al , 2012Kahaly et al 2009;Yadav et al 2008Yadav et al , 2009Yadav and Das 2010;Gaur et al 2009;Sundar et al 2011). I shall also briefly summarize this work, in which I have actively participated, during the past decade or more.…”

Section: Early History Of Conceptual Advances In Laser-plasma Interacmentioning

confidence: 99%

Nonlinear laser–plasma interactions

Kaw

2017

Rev. Mod. Plasma Phys.

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Soon after lasers were invented, there was tremendous curiosity on the nonlinear phenomena which would result in their interaction with a fully ionized plasma. Apart from the basic interest, it was realized that it could be used for the achievement of nuclear fusion in the laboratory. This led us to a paper on the propagation of a laser beam into an inhomogeneous fusion plasma, where it was first demonstrated that light would go up to the critical layer (where the frequency matches the plasma frequency) and get reflected from there with a reflection coefficient of order unity. The reflection coefficient was determined by collisional effects. Since the wave was expected to slow down to near zero group speed at the reflection point, the dominant collision frequency determining the reflection coefficient was the collision frequency at the reflection point. It turned out that the absorption of light was rather small for fusion temperatures. This placed a premium on investigation of nonlinear phenomena which might contribute to the absorption and penetration of the light into high-density plasma. An early investigation showed that electron jitter with respect to ions would be responsible for the excitation of decay instabilities which convert light waves into electrostatic plasma waves and ion waves near the critical frequency. These electrostatic waves would then get absorbed into the plasma even in the collisionless case and lead to plasma heating which is nonlinear. Detailed estimates of this heating were made. Similar nonlinear processes which could lead to stimulated scattering of light in the underdense region ðx [ x p Þ were investigated together with a number of other workers. All these nonlinear processes need a critical threshold power for excitation. Another important process which was discovered around the same time had to do with filamentation and trapping of light when certain thresholds were exceeded. All of this work has been extensively verified in laser plasma experiments and have become the backbone of our present understanding of how lasers nonlinearly interact with fully ionized fusion plasmas. A review of this early work will be presented. We shall also present a review of our involvement in the recent work on nonlinearpenetration of light into overdense plasmas with gradual and sharp interfaces.

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Nonlinear electron-magnetohydrodynamic simulations of three dimensional current shear instability

Cited by 9 publications

References 29 publications

Nonlinear evolution of electron shear flow instabilities in the presence of an external guide magnetic field

Nonlinear evolution of electron shear flow instabilities in the presence of an external guide magnetic field

Three dimensional instabilities of an electron scale current sheet in collisionless magnetic reconnection

Nonlinear laser–plasma interactions

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