In recent years the concept of Lagrangian Coherent Structures (LCS), borrowed from the study of Dynamical Systems, has been successfully used in the context of transport processes in complex fluid flows. Their importance stems from the fact that they separate the flow domain into macro regions inside which fast mixing phenomena take place. Over a finite time interval these macro-regions do not exchange fluid elements and thus act as transport barriers.
LCSs have been shown to provide a very effective tool that has been applied to the description of transport processes in a wide range of conditions^1: the pollutant transport on the ocean surface, blood flow, the spreading of plankton blooms, turbulent combustion, atmospheric dataset analysis, solar photospheric flows, saturation of a nonlinear dynamo, etc.
In this presentation I will show how the concept of Lagrangian Coherent Structures can be applied to magnetic field configurations^2 in order to separate regions where field lines have different kinds of behaviour: periodic, quasi-periodic or chaotic. I will then relate his behaviour to the plasma particle transport in a magnetized plasma in the presence of magnetic field line reconnection.
^1 T. Peacock, G. Haller. “Lagrangian coherent structures: The hidden skeleton of fluid flows” Physics Today, 66, 41 (2013), G. Haller, F.J. Beron-Vera, "Coherent Lagrangian vortices: the black holes of turbulence", J. Fluid Mech., 731, R4, (2013).
^2 M.V. Falessi, F. Pegoraro, T.J. Schep, “Lagrangian coherent structures and plasma transport processes”, Journal of Plasma Physics, 81, 495810505 (2015).