Current singularities: Drivers of impulsive reconnection

Bhattacharjee, A.; Germaschewski, K.; Ng, C. S.

doi:10.1063/1.1872893

Cited by 72 publications

(101 citation statements)

References 32 publications

(51 reference statements)

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“…Currently with D. E. Shaw Research,LLC, New York, NY 10036. tween islands approach the ion kinetic scale. This regime is typically referred to as kinetic or fast reconnection since a variety of two-fluid and kinetic models predict rates that are weakly dependent on the system size and dis sipation mechanism [6,7] (the precise scalings are still a subject of controversy [8,9]). In neutral sheet geom etry, both two-fluid simulations [10,11] Recently, this transition between collisional and kinetic reconnection was proposed as the central mechanism in regulating coronal heating [13-15J.…”

Section: Transition From Collisional To Kinetic Reconnection In Largementioning

confidence: 99%

Transition from collisional to kinetic regimes in large-scale reconnection layers

et al. 2009

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Using first-principles fully kinetic simulations with a Fokker-Planck collision operator, it is demon strated that Sweet-Parker reco=ection layers are unstable to a chain of plasmoids (secondary is lands) for Lundquist numbers beyond S ;C; 1000. The instability is increasingly violent at higher Lundquist number, both in terms of the number of plasmoids produced and the super-Alfvenic growth rate. A dramatic enhancement in the reconnect ion rate is observed when the half-thickness of the current sheet between two plasmoids approaches the ion inertial length. During this transi tion, the reconnection electric field rapidly exceeds the runaway limit, resulting in the formation of electron-scale current layers that are unstable to the continual formation of new plasmoids.PACS numbers: 52.35. Vd, 52.35.Py, The conversion of magnetic energy into kinetic energy through the process of magnetic reconnect ion remains one of the most challenging and far reaching problems in plasma physics. One key issue is the scaling of the recon nection dynamics for applications where the system size is vastly larger than the kinetic scales. The magnetohy drodynamics (MHD) model should provide an accurate description of collisional reconnect ion where the resis tive layers are larger than the ion kinetic scale. tween islands approach the ion kinetic scale. This regime is typically referred to as kinetic or fast reconnection since a variety of two-fluid and kinetic models predict rates that are weakly dependent on the system size and dis sipation mechanism [6,7] (the precise scalings are still a subject of controversy [8,9]). In neutral sheet geom etry, both two-fluid simulations [10,11] and theory [12J predict an abrupt transition from the collisional to the kinetic regime when 8 sp ::; d i where d i is the ion inertial length. In this geometry, d i is comparable to the ion gy roradius, and in the kinetic regime d i is also compa.rable to the ion crossing orbit scale.Recently, this transition between collisional and kinetic reconnection was proposed as the central mechanism in regulating coronal heating [13-15J. However, these es timates were based on the assumption of a stable SP layer within the collisional regime. To properly describe the dynamics at high Lundquist number, it is crucial to consider how plasmoid formation ma.y influence the tran sition. To address this problem, this work employs fully kinetic particle-in-cell (PIC) simulations with a Monte Carlo treatment [16] of the Fokker-Planck collision op erator. For Lundquist numbers where the SP layers are stable 5 ;s 1000, this powerful first-principles approach has demonstrated a clear transition between the colli sional and kinetic regimes near the expected thresholdHere we demonstrate that SP layers are in creasingly unstable to plasmoid formation in large-scale systems. The observed growth rate is super-Alfvenic, al lowing the islands to grow to large amplitude before they are convected downstream. A dramatic enhancement in the reconnection rate is observed when the current...

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Section: Transition From Collisional To Kinetic Reconnection In Largementioning

confidence: 99%

Transition from collisional to kinetic regimes in large-scale reconnection layers

et al. 2009

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“…In the case of Hall-MHD several, apparently contradictory conclusions have been drawn in this regard [2][3][4] which, however, have recently been argued to be motivated by the differing formulations of the problem [5].…”

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Reconnection in semicollisional, low-β plasmas

Schmidt¹,

Günter²,

Lackner³

2009

Physics of Plasmas

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Reconnection of semi-collisional, low-β plasmas is studied numerically for two model problems using a two-field description of the plasma including electron pressure effects (and hence kinetic Alfvén-wave dynamics). The tearing unstable Harris-sheet, with the global parameters of the GEMchallenge case shows a linear growth of the peak reconnection rate with the drift parameter s ρ when this scale is significantly larger than the resistive skin depth, and the island is smaller than the Harris sheet current layer width. As exemplary for a driven, rather than a spontaneous reconnection situation we study as second model system two coalescing islands, starting from a non-equilibrium situation.The peak reconnection rate again increases initially linearly with s ρ but saturates and becomes s ρ independent for larger values. In this saturated regime, no flux pile-up occurs, and the reconnection is limited by the rate of approach of the two coalescing islands. The qualitative differences between spontaneous and driven reconnection cases, and their scaling behaviour are best understood by considering the reconnection rate as a triple product of outflow Mach number, outflow to inflow channel width ratio, and magnetic energy density at a height s ρ above the X point.

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“…The Magnetic Reconnection Code (MRC) is a suite of codes (Germaschewski et al 2006;Bhattacharjee et al 2005) that integrate various reduced and extended fluid models of plasma flows. In this paper, the 2D AMR version of the code integrating the equations of RMHD has been used.…”

Section: Finite Difference Methodsmentioning

confidence: 99%

“…Adaptive spectral element methods have the potential to do just that, providing spectral-like accuracy that can be applied efficiently to resolve isolated structures. In this paper, we concentrate on comparing the accuracy of incompressible simulation results from a spectral-elementYbased AMR code (SE; Rosenberg et al 2006Rosenberg et al , 2007 and a finite-differenceYbased AMR code (FD; Germaschewski et al 2006;Bhattacharjee et al 2005) on an astrophysical problem that requires high spatial resolution as well as high accuracy, the so-called MHD island coalescence instability (MICI) problem (Ng & Bhattacharjee 1998). In order to make meaningful comparisons, we let each code run on essentially the same nonuniform grid (i.e., with the total degrees of freedom in the problem fixed) that is refined a priori in regions of the grid where the current sheets will form during the MICI.…”

Section: Introductionmentioning

confidence: 99%

A Comparison of Spectral Element and Finite Difference Methods Using Statically Refined Nonconforming Grids for the MHD Island Coalescence Instability Problem

Rosenberg

Germaschewski

et al. 2008

ASTROPHYS J SUPPL S

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A recently developed spectral-element adaptive refinement incompressible magnetohydrodynamic (MHD) code is applied to simulate the problem of MHD island coalescence instability (MICI ) in two dimensions. MICI is a fundamental MHD process that can produce sharp current layers and subsequent reconnection and heating in a high-Lundquist number plasma such as the solar corona. Because of the formation of thin current layers, it is highly desirable to use adaptively or statically refined grids to resolve them and to maintain accuracy at the same time. The output of the spectral-element static adaptive refinement simulations are compared with simulations using a finite-difference method on the same refinement grids, and both methods are compared to pseudospectral simulations with uniform grids as baselines. It is shown that with the statically refined grids roughly scaling linearly with effective resolution, spectral element runs can maintain accuracy significantly higher than that of the finite-difference runs, in some cases achieving close to full spectral accuracy.

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Current singularities: Drivers of impulsive reconnection

Cited by 72 publications

References 32 publications

Transition from collisional to kinetic regimes in large-scale reconnection layers

Transition from collisional to kinetic regimes in large-scale reconnection layers

Reconnection in semicollisional, low-β plasmas

A Comparison of Spectral Element and Finite Difference Methods Using Statically Refined Nonconforming Grids for the MHD Island Coalescence Instability Problem

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