Transport processes characterizing the Quasi-­Single-­Helicity states in RFX-­mod

The fluid-dynamical approach developed in Refs. [1, 2] and based on the behavior of the Finite Time Lyapunov Exponent (FTLE) field, associated to the magnetic configuration is applied to investigate a real situation [3]. We consider the magnetic field characterizing the emergence of self-organized quasi-helical states [4], predicted by magnetohydrodynamic (MHD) simulations [5] and observed in high current experiments in the reversed field pinch configurations. The associated FTLE field shows the presence of ridges, that can be recognized as Lagrangian Coherent Structures (LCSs) for the magnetic field. These structures actually limit the field lines motion and provide a chaos healing e?ect, by influencing the transport properties of the system.