Magnetic confinement fusion-Experimental physics: Reversed field pinches

Significant advances have been achieved in recent years in Reversed Field Pinch (RFP) physics, both from the experimental and the theoretical point of view. The main theoretical advances are based on fully 3D nonlinear visco-resistive MHD simulations, which gained a deeper understanding of the RFP's magnetic self-organization. Improved confinement regimes have been explored with two different approaches in the RFP. The first is associated with the spontaneous topological bifurcation from a cylindrical to a helical magnetic equilibrium. Such equilibria are favored by high plasma current levels and are associated with the emergence of partially conserved magnetic flux surfaces, resulting in the onset of a transport barrier. A fundamental role in determining the improvement of the experimental results is played by advanced active feedback control systems for the control of MHD instabilities. The second approach is based on active control of the current profile, which can induce significant enhancements of the confinement properties. High confinement of fast particles has been also observed in RFP plasmas.