Magnetic chaos healing and transport barriers in new stimulated helical regimes of the Reversed Field Pinch

The reversed-field pinch configuration for the magnetic confinement of fusionplasmas is characterized by the emergence of self-organized quasi-helical states found both inmagnetohydrodynamic (MHD) simulations and in high current experiments 1, 2, 3. Numericalmodeling can reproduce with high fidelity the MHD dynamics of high current RFPexperiments, which are characterized by the formation of helical states 4. Such helical statesare quasi-periodically interrupted by transient relaxation to 3D states associated with strongreconnection events. Seed helical perturbations at the magnetic boundary are predicted toaffect the helicity and the intermittency of the emergent helical states and first experimentaltests have indeed confirmed this capability. Of particular interest is the possibility tostimulate non-resonant helical states, which feature better topological properties with respectto magnetic chaos healing 5,6. This opens a new path to configuration optimization.Simulation results and first experimental evidence of alternative helical states formation inRFX-mod will be presented, together with a discussion of the different magnetic topologyproperties and their impact on transport barrier formation.