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Title: RECONNECTION OF QUASI-SINGULAR CURRENT SHEETS: THE ''IDEAL'' TEARING MODE

A strong indication that fast reconnection regimes exist within resistive magnetohydrodynamics was given by the proof that the Sweet-Parker current sheet, maintained by a flow field with an appropriate inflow-outflow structure, could be unstable to a reconnecting instability which grows without bound as the Lundquist number, S, tends to infinity. The requirement of a minimum value for S in order for the plasmoid instability to kick in does little to resolve the paradoxical nature of the result. Here we argue against the realizability of Sweet-Parker current sheets in astrophysical plasmas with very large S by showing that an ''ideal'' tearing mode takes over before current sheets reach such a thickness. While the Sweet-Parker current sheet thickness scales as ∼S {sup –1/2}, the tearing mode becomes effectively ideal when a current sheet collapses to a thickness of the order of ∼S {sup –1/3}, up to 100 times thicker than S {sup –1/2}, when (as happens in many astrophysical environments) S is as large as 10{sup 12}. Such a sheet, while still diffusing over a very long time, is unstable to a tearing mode with multiple x-points: here we detail the characteristics of the instability and discuss how it may help solve themore » flare trigger problem and effectively initiate the turbulent disruption of the sheet.« less
Authors:
 [1] ;  [2]
  1. Dipartimento di Fisica e Astronomia, Università degli Studi, Firenze (Italy)
  2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
Publication Date:
OSTI Identifier:
22364057
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; ELECTRIC CURRENTS; MAGNETIC RECONNECTION; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA DISRUPTION; SOLAR FLARES; SUN; TEARING INSTABILITY