HR: 1340h
AN: SM23A-0405    [Abstracts]
TI: Magnetic reconnection in current sheets : Phase transition-like behavior
AU: Khare, A
EM: akhare@physics.du.ac.in
AF: University of Delhi, Department of Physics and Astrophysics, Delhi, 110007 India
AU: * Sharma, A S
EM: ssh@astro.umd.edu
AF: University of Maryland, Department of Astronomy, College Park, MD 20742 United States
AB: The physical process underlying the evolution of many natural and laboratory plasmas is magnetic reconnection occurring in thin current sheets. The global reconfiguration following the reconnection leads to a sudden transition, e.g., the magnetospheric substorms, and such transitions exhibit phase transition-like behavior. A theoretical model of magnetic reconnection that highlights the nature of the associated transitions is developed. In MHD J_z = J_z(Ψ) (J_z is the axial current density and Ψ is the associated flux function) and any choice of J_z(Ψ) constitutes an equilibrium of the current sheet. In order to study different equilibria and possible transitions among them, an entropy measure is employed. The current sheet is discretized into a set of non-overlapping current rods, allowing the construction of a Lynden-Bell entropy measure. This measure is maximized subject to dynamical constraints and the solutions are characterized by Lagrange mulipliers, which in turn can be identified with the parameters of the system. As the parameters are varied, solutions show a bifurcation from 1D (un-reconnected) to 2D solutions with islands. In a region of the parameter space a sub-critical pitchfork bifurcation from 1D solution to a 2D solution with islands is obtained, and can be identified with a first order phase transition. Other parameter values yield a super-critical pitchfork bifurcation from 1D to 2D solution. This is characteristic of a second order phase transition and is associated with the multiscale behavior and power law distributions of the magnetosphere.
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2744 Magnetotail
DE: 2790 Substorms
DE: 4465 Phase transitions
DE: 7835 Magnetic reconnection (2723, 7526)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005