A two-fluid study of oblique tearing modes in a force-free current sheet

Akçay, C.; Daughton, W.; Lukin, V. S.; Liu, Yi‐Hsin

doi:10.1063/1.4940945

Cited by 9 publications

(14 citation statements)

References 39 publications

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“…In a sheared magnetic field reconnection set-up, the strength of B y increases with distance from the midplane of the diffusion region, meaning that reconnection sites further from the centre should lead to greater obliqueness. While the generation of oblique current sheets and flux-tubes has been demonstrated in 3D PIC simulations with tearing-mode set-ups (Liu et al 2013;Akçay et al 2016), this study similarly demonstrates the oblique nature of vortex dynamics in 3D reconnection in an alternative reconnection set-up, i.e. X-point collapse.…”

Section: Introductionmentioning

confidence: 81%

“…As shown, there is a clear correspondence between the tilt of the vortex tubes and θ. Unlike in Baalrud et al (2012); Liu et al (2013) and Akçay et al (2016) where a tearing-mode set-up is used, it is not possible in X-point collapse to relate the locations of oblique structures to initial simulation parameters since X-point collpase is inherently time variant and the width and shape of the diffusion region is not fixed by the set-up. Furthermore, as there is no asymptotic magnetic field, there is no limit on the angle of obliqueness.…”

Section: Reconnection Dynamics In 3dmentioning

confidence: 99%

“…In this study the Q-value is used to show that vortical flows in 2.5D simulations correspond to 3D vortex tubes with structures that are not apparent from the 2.5D simulations. An additional possible feature, unique to 3D reconnection with a guide-field, is the generation of oblique modes as demonstrated in Liu et al (2013); Baalrud et al (2012) and Akçay et al (2016). In 2.5D simulations of magnetic reconnection, reconnection must occur at a magnetic X-point where it is possible for field-lines to change in topology.…”

Section: Introductionmentioning

confidence: 99%

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Role of electron inertia and reconnection dynamics in a stressedX-point collapse with a guide-field

Pahlen

Tsiklauri

2016

A&A

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Aims. In previous simulations of collisionless 2D magnetic reconnection it was consistently found that the term in the generalised Ohm's law that breaks the frozen-in condition is the divergence of the electron pressure tensor's non-gyrotropic components. The motivation for this study is to investigate the effect of the variation of the guide-field on the reconnection mechanism in simulations of X-point collapse, and the related changes in reconnection dynamics. Methods. A fully relativistic particle-in-cell (PIC) code was used to model X-point collapse with a guide-field in two and three spatial dimensions.Results. We show that in a 2D X-point collapse with a guide-field close to the strength of the in-plane field, the increased induced shear flows along the diffusion region lead to a new reconnection regime in which electron inertial terms play a dominant role at the X-point. This transition is marked by the emergence of a magnetic island -and hence a second reconnection site -as well as electron flow vortices moving along the current sheet. The reconnection electric field at the X-point is shown to exceed all lower guide-field cases for a brief period, indicating a strong burst in reconnection. By extending the simulation to three spatial dimensions it is shown that the locations of vortices along the current sheet (visualised by their Q-value) vary in the out-of-plane direction, producing tilted vortex tubes. The vortex tubes on opposite sides of the diffusion region are tilted in opposite directions, similarly to bifurcated current sheets in oblique tearing-mode reconnection. The tilt angles of vortex tubes were compared to a theoretical estimation and were found to be a good match. Particle velocity distribution functions for different guide-field runs, for 2.5D and 3D simulations, are analysed and compared.

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Section: Introductionmentioning

confidence: 81%

Section: Reconnection Dynamics In 3dmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Role of electron inertia and reconnection dynamics in a stressedX-point collapse with a guide-field

Pahlen

Tsiklauri

2016

A&A

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“…Cowley, Kulsrud and Hahm previously studied the influence of temperature gradients. 54 It is also interesting to note that for force-free equilibria, which do not have diamagnetic drifts, tearing modes have been observed to span the current sheet 39,53 The results of Eq. (22) in the absence of diamagnetic drift agree well with the predictions of the standard kinetic tearing mode theory of Drake and Lee 24 .…”

Section: A Growth Rate Profilesmentioning

confidence: 98%

Collisionless kinetic theory of oblique tearing instabilities

Bhattacharjee

Daughton

2018

Physics of Plasmas

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The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for a Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle (θ) with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes (θ = 0). We find that this stabilization is associated with the density-gradientdriven diamagnetic drift. The analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. A simple analytic estimate for the stability criterion is provided.

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“…[3][4][5][6][7][8][9][10][11][12][13][14][15]. Equations (1)- (3) imply that the current density is parallel to the magnetic field: j ¼ aðrÞB.…”

Section: Introductionmentioning

confidence: 99%

Force-free collisionless current sheet models with non-uniform temperature and density profiles

2017

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We present a class of one-dimensional, strictly neutral, Vlasov-Maxwell equilibrium distribution functions for force-free current sheets, with magnetic fields defined in terms of Jacobian elliptic functions, extending the results of Abraham-Shrauner [Phys. Plasmas 20, 102117 (2013)] to allow for non-uniform density and temperature profiles. To achieve this, we use an approach previously applied to the force-free Harris sheet by Kolotkov et al. [Phys. Plasmas 22, 112902 (2015)]. In one limit of the parameters, we recover the model of Kolotkov et al. [Phys. Plasmas 22, 112902 (2015)], while another limit gives a linear force-free field. We discuss conditions on the parameters such that the distribution functions are always positive and give expressions for the pressure, density, temperature, and bulk-flow velocities of the equilibrium, discussing the differences from previous models. We also present some illustrative plots of the distribution function in velocity space.

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A two-fluid study of oblique tearing modes in a force-free current sheet

Cited by 9 publications

References 39 publications

Role of electron inertia and reconnection dynamics in a stressedX-point collapse with a guide-field

Role of electron inertia and reconnection dynamics in a stressedX-point collapse with a guide-field

Collisionless kinetic theory of oblique tearing instabilities

Force-free collisionless current sheet models with non-uniform temperature and density profiles

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