Modelling of the propagation of a large negative hydrogen beam

Negative ion-based Neutral Beam Injectors (N-NBI) are one of the plasma heating methods envisaged for the ITER tokamak. The heating power is deposited by a highly energetic neutral beam, which is obtained by neutralising a precursor negative ion beam. The propagation of the latter is guaranteed by positive charges produced by the interaction between the beam and the background neutral gas: positive ions allow to compensate the negative space charge of the beam ions to prevent the beam from diverging due to mutual charge repulsion. The aim of this thesis is the numerical investigation of the negative ion beam propagation, with a view to provide a deeper understanding of the involved physical processes. The results of these analyses will be exploited to reproduce synthetic measurements of beam diagnostics such as beam tomography and beam emission spectroscopy, in such a way as to benchmark the results against the experimental findings obtained during the 2021 SPIDER experimental campaign and also to better identify the phenomena underlying specific features of the experimental results, ultimately aiming at providing additional knowledge about the beam propagation in view of the future experimental campaigns.