Particle modelling of the hybrid negative ion source

In this paper we present results of different particle-based models of expansion and extraction regions for the ITER negative ion source. Results show the important role of electron-induced processes (eV excitation and dissociation) and gas-surface and plasma-surface interactions (atom recombinative desorption and ion neutralization) for the production of negative ion precursors. The spatial distribution of neutral and ionized caesium as well as the drag due to the deuterium flow and its re-evaporation from the plasma grid is calculated. The self-consistent two-dimensional electric field distribution in the extraction region allows a better understanding of the transport of surface-produced negative ions towards the orifice. The model delivers an extraction probability of less than 25%.