Reconnection processes in 3D MHD modeling of Reversed Field Pinch magnetic self-organization

Since the early 90ties, 3D nonlinear MHD studies have been developing a fundamental framework for the understanding of the Reversed Field Pinch (RFP) self-organization. The simple visco-resistive MHD approximation clearly shows that 3D reconnection processes strongly characterize the dynamics both in low and high dissipation regimes (Lundquist/Hartmann number). In fact, this is particularly evident during the so-called sawtoothing activity observed in both Multiple and Quasi Helical regimes where the natural kinking of the current carrying plasma column triggers nearly periodic relaxations associated with localized shrinking/collapse of the global magnetic field perturbation. In this presentation we will provide a survey of the typical magnetic reconnection manifestation in nonlinear visco-resistive MHD of the RFP and some comparison with the similar behavior in circular tokamak case. The main features are: magnetic into kinetic energy conversion (possibly providing ion heating), 3D current sheets formation and related flow patterns, mode phase locking, (toroidal collapse of the helix), excitation of Alfvén waves. The possibility to “tune” the sawtooth cycle by adopting suitable Resonant or Non resonant Magnetic Perturbation will be also presented.