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Plasmas as a Prototypical Complex System: Self-Organized Criticality as a Paradigm for Plasma Transport
David Newman, University of
Alaska-Fairbanks, Physics Department
In nature there are many systems which exhibit some form of
self-organization. Among these are forest fires, earthquakes, sandpiles,
maybe sunspots and even life itself. Investigations into the similarity
of the dynamics of such systems have been undertaken by using simple
cellular automata models. These models have produced some important
insight into the dynamics of such systems. Recently a Self-Organized
Criticality (SOC) model for turbulent transport in magnetically confined
plasmas has been proposed in order to explain some of the observed
features of the transport dynamics in these plasmas. This model is based
on the dynamics of a sandpile and has among others, the remarkable
feature that a sheared wind across the sandpile (or a flow across the
plasma) can fundamentally change the transport. The dynamics of the
model show some remarkably similar characteristics to the observed data
and suggest explanations for some puzzling aspects of the observations.
Adding new, physically realistic, dynamical transport mechanisms such as
classical diffusion to the SOC system have been found to lead to a new
set of dynamical regimes with evidence of critical transitions between
them. These regimes can then be explored in the plasma experiments. In
addition to the intrinsic novelty of the basic physics involved, these
observations can have interesting ramifications for the control of many
real systems. Some of these features of the SOC systems, from forest
fires to earthquakes, and the extension to the sandpile model for
turbulent transport will be discussed as well as their connection to
fusion plasmas. |