Physics – Plasma Physics
Scientific paper
May 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000rmxac...9..344h&link_type=abstract
Astrophysical Plasmas: Codes, Models, and Observations, Proceedings of the conference held in Mexico City, October 25-29, 1999,
Physics
Plasma Physics
Scientific paper
During the past two decades, non-linear dynamics and out of equilibrium thermodynamics have developed along with plasma physics, providing qualitatively new approaches to complex problems. It is thus widely accepted nowadays, for instance, that non-equilibrium may be a source of order in dissipative systems, allowing the emergence of self-organization. Evidence of self-organization has actually been observed in laboratory magnetically confined systems, and probably in ball lightnings. The basis of this research was actually established in the context of astrophysical plasmas by Chandrasekhar and Woltjer in the fifties. Most plasma systems are forced and dissipative systems far from equilibrium, which share some essential features with other complex non-linear systems that show spatial and temporal coherence. When the system, which may be described by dissipative non-linear partial differential equations, relaxes towards such a self-organized state, it takes advantage of instabilities that lead it, for instance, to a minimum energy state, under certain constraints that prevent it from falling into a trivial unconfined state. Such constraints appear as quadratic or higher order quantities, which are conserved in the absence of dissipation. The relevant feature is that, in the presence of dissipation, one of these quantities decays faster than the others. In general, it remains to be clarified which is the relevant variational principle underlying the relaxation mechanisms described above. Some alternative possibilities that have been explored beyond the simple minimization of energy are the maximization of entropy, minimization of energy dissipation rate, or of entropy production. All these approaches imply the existence of approximate conservation laws for a dissipative system, so that dynamic evolution is sustained long enough, before the plasma is driven by dissipation into an uninteresting uniform state.
Herrera-Velázquez J.
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