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Title: Formation of current sheets in magnetic reconnection

An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ℓ along the lines, δ(ℓ)=δ(0)e{sup σ(ℓ)}. The non-ideal effects required to break magnetic field line connections scale as e{sup −σ}, so the breaking of connections is inevitable for σ sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j{sub ||}/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j{sub ||}/B occurs. Independent of the original spatial distribution of j{sub ||}/B, the evolution is into a sheet current, which is stretched by a factor e{sup σ} in width and contracted by a factor e{sup σ} in thickness with the current density j{sub ||} increasing as e{sup σ}. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of currentmore » flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not.« less
Authors:
 [1]
  1. Department of Applied Physics and Applied Mathematics Columbia University, New York, New York 10027 (United States)
Publication Date:
OSTI Identifier:
22299843
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 7; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COMPARATIVE EVALUATIONS; CURRENT DENSITY; CURRENTS; EQUILIBRIUM; MAGNETIC FIELDS; MAGNETIC RECONNECTION; PLASMA; RELAXATION; SPATIAL DISTRIBUTION; THICKNESS