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Plasma Theory and Modelling Group

plasmas, fluids — complex physical systems

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Turbulence and coherent structures in driven systems

A complex physical system is a non-equilibrium, open system driven, as a consequence of the throughput of energy and matter with associated net entropy outflow and via nonlinear processes, into various forms of self-organisation, typically on multiple scales. On the coarsest scale, dissipative systems can be described by a finite number (hopefully small) of time-dependent macroscopic parameters obeying low-dimensional dynamics. At the next level a fluid description is appropriate for describing long-wavelength, low-frequency waves, instabilities, coherent structures and turbulence. Shorter-scale, higher-frequency phenomena require the particle nature of matter to be taken into account through kinetic theory and nonequilibrium statistical mechanics.

The energy released by fusion reactions in the sun not only provides the high-grade radiant energy that drives the self-organising, life-supporting environment of the earth, but also causes more violent events that give rise to "space weather". There is a worldwide research and development program for producing power from fusion, a far more benign source than fission. As in the sun, this is complicated by turbulence. Understanding, predicting and controlling these processes is essential to our long-term future on this planet and requires a multi-disciplinary complex systems approach.

From the theoretical point of view there are close analogies between magnetically confined plasmas and planetary atmospheres, where the Coriolis force plays the role of the magnetic field. The work of the group focusses on developing a fundamental understanding of the complex physics of plasmas and fluids with applications to such fields as fusion power and atmospheric dynamics.

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Movie showing time evolution of vorticity in a simulation of quasi-two-dimensional resistive drift wave turbulence, modelled by the Hasegawa-Wakatani equation. In the modified Hasegawa-Wakatani model, this isotropic turbulence condenses into zonal flows, causing a "Dimits shift" --- an increase in the threshold for turbulence: Bifurcation in electrostatic resistive drift wave turbulence   R. Numata, R. Ball, and R.L. Dewar   Phys. Plasmas 14, 102312-1--8 (2007)   E-print arXiv:0708.4317v1

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Turbulence: Simulation of temperature-gradient-driven plasma turbulence in a fusion experiment. (Courtesy Peter Beyer, Université de Provence. Requires QuickTime plug-in.)	Coherent structure: A large low-pressure system off Australia’s southern coast on 20 February 2002.