Theoretical Physics Seminar:  

Apr 29, 2009 11:00 AM, Theoretical Physics Seminar Room, LC 3.17

Towards a model of a 3-D fusion plasma equilibria fully consistent with existence of field-line chaos

Speaker: McGann, Mathew

Abstract: The particles in a magnetically confined fusion plasma are (to a good approximation) confined to magnetic field lines, which spiral around within a toroidal volume. If the plasma is axisymmetric, the field lines lie within an infinite set of nested toroidal 'flux surfaces' and as a result the plasma tends to stay tied to the surfaces. If the toroidal plasma is geometrically deformed, flux surfaces begin to break up and, while some field lines still draw out a toroidal shape, other field lines wander chaotically within a toroidal volume, meaning the plasma tied to these field lines is no longer confined. Our group is developing a model which relaxes the plasma energy within potentially chaotic regions, using the surviving flux surfaces as separating barriers. Such a model is the first variational magnetohydrodynamic model to reconcile the coexistence of confinement and chaos in a way fully consistent with nonlinear Hamiltonian dynamics theory. This seminar will give an overview of both the theoretical and computational issues. In particular, the seminar will concentrate on the effort to determine which surfaces are most likely to survive the perturbations. The surface goes critical just as it is about be to be destroyed, it has a fractal structure but there is evidence that some field lines, ones that are in the same 'universality class' may approach the edge of chaos in the same way. Further, pressure discontinuities must exist across the surviving surfaces and this makes them less resistant to deformations, I'll also investigate how these two sources of chaos interact.

Contact: McGann, Mathew mmc105@rsphysse.anu.edu.au