Experimental analysis of MHD instability in a wide range of plasma equilibria for magnetic fusion confinement in RFX-mod

Toroidal magnetic configurations for fusion confinement can be classified according to the ratio between the magnetic pressure supplied by external coils and that produced by the plasma current itself, i.e. the self-confinement by pinch effect, associated to the toroidal and magnetic field components, Bz and B?, respectively. Thanks to its flexibility and unique control capability, the RFX-mod device can be operated in a wide range of experimental conditions. In particular, Reversed-Field Pinch (RFP), Tokamak and the full range of magnetic configurations in between the two, the ultra-low q, have been produced in the last years. The magneto-hydrodynamic (MHD) stability properties of the various plasmas are here studied thanks to a complex system of high-frequency and spatially resolved magnetic probes located inside the vacuum vessel of the RFX-mod device. In particular, an analysis of plasma instabilities and their characterization in terms of Fourier harmonics are performed, highlighting the role of the leading control parameter, the safety factor q, which gives the magnetic field line pitch as a function of plasma minor radius (q = rBz/RB? ). where r is the radial coordinate and R is the plasma major radius), whose value was spanned almost continuously from 4 (Tokamak) to negative values (RFP). The experimental results are compared to the predictions of dedicated 3D nonlinear visco-resistive MHD simulations.