Numerical Study of Magnetic Topology and Test Particle Transport in the Reversed Field Pinch and in the Tokamak

The analysis and the numerical simulations described in this Thesis allow to better understand the confinement properties of toroidally confined plasmas dedicated to the research on controlled thermonuclear fusion. Two important configurations have been investigated: the Reversed Field Pinch (RFP) and the Tokamak. In the former we have focused our attention on advanced regimes recently discovered, named Quasi Single Helicity (QSH). The magnetic topology and the particle transport have been studied in these states both in the experiments RFX-mod (Padua, Italy) and MST (Madison,WI,USA). A new algorithm has been implemented in order to study the thermal particle transport in a helically deformed plasma, i.e. in the typical geometry of QSH states. The interaction between an high energy ion population and the perturbations of the plasma has been the other main topic of this Thesis. This has been analyzed in the tokamak experiment ASDEX-Upgrade (Garching, Germany) and in MST. The different properties of fast ions in the two toroidal configurations have been explained with an analytical model in terms of drift motion of particles in a non-uniform and curved magnetic field