Speaker
Ibere Luiz Caldas
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1029.pdf
Manifold Tracing For Symplectic Maps Of Magnetic Field Lines
D. Ciro, I. L. Caldas
Institute of Physics, University of São Paulo, São Paulo, Brazil
Invariant manifolds of unstable closed magnetic field lines (periodic saddles), organize the
dynamics of chaotic field lines in magnetically confined plasmas. They are fundamental to
understanding the structure of the chaotic field lines and provide insight into the mechanisms
of transport at the plasma edge. In some situations, the geometry of the manifolds can be
estimated through the mapping of a large collection of orbits close to the periodic saddle.
However, without an ordering scheme and refinement this method is computationally
expensive and limited in resolution. Here, we apply a recently proposed approximation
technique [1], based on an intuitive geometrical decomposition of the manifolds in bare and
fine details, for tracing the invariant manifolds of the unstable periodic orbits of the Ullmann
Map, a symplectic map describing large aspect-ratio tokamaks perturbed by a magnetic
limiter. The manifold tangles obtained for remnant internal islands near the last closed
magnetic surface explain the field line stickiness and escape channels to the tokamak wall [2].
References
1- Efficient manifold tracing for planar maps. D. Ciro, T. Evans, I. L. Caldas. arXiv:1710.10140 (2018).
2- Escape patterns of chaotic magnetic field lines in a tokamak with reversed magnetic shear and an ergodic
limiter. T. Kroetz, M. Roberto, E. C. Silva, I. L. Caldas, R. L. Viana. Physics of Plasmas 15, 092310 (2008).
