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Abstract

A recurring problem in magnetic reconnection is the identification of the appropriate generalized Ohm's law. In weakly collisional plasmas with a strong magnetic guide field component, a fluid model may be adopted, where electron inertia and the electron pressure gradient play important roles. In the absence of collisions, electron inertia provides the mechanism for magnetic field-line breaking. Electron compressibility alters significantly the structure of the reconnection region and allows for faster reconnection rates, which are consistent with the fast relaxation times of sawtooth oscillations in tokamak plasmas. The Hall term may also become important when the guide field is weak.

The very possibility of non-linear, irreversible magnetic reconnection in the absence of dissipation is addressed. We show that in a collisionless plasma, magnetic islands can grow and reach a saturated state in a coarse-grained sense. Magnetic energy is transferred to kinetic energy in smaller and smaller spatial scale lengths through a phase mixing process. The same model is then applied to the interpretation of driven reconnection events in the vicinity of a magnetic X-line observed in the VTF experiment at MIT. The reconnection is driven by externally induced plasma flows in a background magnetic configuration that has a hyperbolic null in the reconnection plane and a magnetic guide field component perpendicular to that plane. Where the guide field is strong, assuming the external drive to be sufficiently weak for a linear approximation to hold, a dynamic evolution of the system is obtained which does not reach a stationary state.

Additional information

Authors: PORCELLI F, Burning Plasma Research Group, INFM and Department of Energetics, Politecnico di Torino (IT);BORGOGNO D, Burning Plasma Research Group, INFM and Department of Energetics, Politecnico di Torino (IT);GRASSO D, Burning Plasma Research Group, INFM and Department of Energetics, Politecnico di Torino (IT);CALIFANO F, Istituto Nazionale Fisica della Materia, Department of Physics, University of Pisa (IT);PEGORARO F, Istituto Nazionale Fisica della Materia, Department of Physics, University of Pisa (IT);OTTAVIANI M, Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion 44 (December 2002), pp.389-405
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://stacks.iop.org/0741-3335/44/389
Record Number: 200316022 / Last updated on: 2003-03-06
Category: PUBLICATION
Original language: en
Available languages: en