Hannover 2016 – scientific programme

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P: Fachverband Plasmaphysik

P 5: Poster Session- Helmholtz Graduate School for Plasma Physics

P 5.22: Poster

Monday, February 29, 2016, 16:30–19:00, Empore Lichthof

Investigation of Cs dynamics in RF negative ion sources by means of numerical simulations and laser absorption spectroscopy. — •Alessandro Mimo, Christian Wimmer, Dirk Wünderlich, and Ursel Fantz — Max-Planck-Institut für Plasmaphysik, 85748 Garching

The Neutral Beam Injection systems at ITER are based on large and powerful RF sources for negative hydrogen and deuterium ions, in which the main mechanism of negative ion production is the conversion of atoms on low work function surfaces. In order to achieve a low work function of the conversion surface, caesium is evaporated into the source and its temporal and spatial dynamics, which is influenced by plasma parameters, can then affect the homogeneity and stability of the beam. Cesium redistribution is influenced by the plasma drift, due to the presence of the magnetic filter field in the source, which leads to a plasma asymmetry in the vertical direction. The Monte Carlo transport code CsFlow3D, which allows calculating caesium fluxes and coverage onto the source surfaces as well as caesium density along specific lines of sight, was used to investigate the effect of plasma asymmetry on cesium dynamics. The simulated caesium density is calculated for different plasma density profiles and can then be directly compared with the laser absorption spectroscopy experimental data obtained at the IPP prototype RF ion source.