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 fusion plasmas is characterized by the emergence of self-organized quasi-helical states found both in magnetohydrodynamic (MHD) simulations and in high current experiments 1, 2, 3. Numerical modeling can reproduce with high fidelity the MHD dynamics of high current RFP experiments, which are characterized by the formation of helical states 4 . Such helical states are quasi-periodically interrupted by transient relaxation to 3D states associated with strong reconnection events. Seed helical perturbations at the magnetic boundary are predicted to affect the helicity and the intermittency of the emergent helical states and first experimental tests have indeed confirmed this capability. Of particular interest is the possibility to stimulate non-resonant helical states, which feature better topological properties with respect to magnetic chaos healing 5,6 . This opens a new path to configuration optimization. Simulation results and first experimental evidence of alternative helical states formation in RFX-mod will be presented, together with a discussion of the different magnetic topology properties and their impact on transport barrier formation.