Nonlinear 3D MHD modelling of the Alfvén waves in Tokamak and RFP Ohmic plasmas

We focus on the 3D nonlinear magnetohydrodynamics model applied to the numerical study of the Alfvén waves in Tokamak and RFP configurations. The main aim is the characterization and interpretation of Alfvén waves spectra and their excitation mechanism based on periodic magnetic reconnection events in Tokamak and RFP configurations. This is achieved after a thorough analysis of simpler cases, which provided renewed occasion for numerical code benchmarking. The main results obtained are the prediction by nonlinear MHD simulations of excitation of Alvén eigenmodes related to the magnetic reconnection events, togheter with a possible explanation of the physical origin of the experimentally observed Alfvén waves during Ohmic discharges in a number of present day RFP and Tokamak experiments. A possible theoretical identification as Alfvén eigenmodes of the coherent peaks experimentally observed in the power spectrum of the magnetic fluctuations at the plasma edge of RFX-mod, the biggest RFP experiment in the world, located in Padova,was achieved as well.