Magnetohydrodynamics modelling successfully predicts new helical states in reversed-field pinch fusion plasmas

Nonlinear fluid modelling predictions of qualitatively new self-organized helical states in the reversed-field pinch configuration are confirmed by experiments in the RFX-mod device. The new states are realized by using a seed edge magnetic field, which can impose its helical pitch to the whole plasma. In simulations, we show increased magnetic order and reduced transport of magnetic field lines in regimes with the twist of a non-resonant mode. We reveal the existence of Cantori, encompassing the region characterized by conserved magnetic surfaces, which act as barriers to transport of magnetic field lines. This opens a new research line for transport studies in hot magnetized plasmas and highlights a path towards reversed-field pinches with high confinement at high current.