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P: Fachverband Plasmaphysik

P 28: Helmholtz Graduate School III

P 28.1: Vortrag

Donnerstag, 16. März 2017, 14:00–14:25, HS 1010

Modelling of Caesium redistribution in the RF negative hydrogen ion source ELISE — •Alessandro Mimo, Christian Wimmer, Dirk Wünderlich, and Ursel Fantz — Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany

The Neutral Beam Injection systems for ITER rely on large and powerful RF sources of negative hydrogen ions, which are mostly produced by conversion of neutral hydrogen atoms on a converter surface. The conversion efficiency is increased by evaporating Cs in the source, which provides a reduction of the converter surface work function. Experiments have shown that a sufficient flux of Cs onto the converter surface during the beam pulse needs to be provided in order to avoid a reduction of the performance. The dynamics of Cs redistribution in negative ion sources was modeled by means of the Monte Carlo transport code CsFlow3D, which calculates the time evolution of Cs fluxes and coverage onto the source surfaces. Preliminary simulations have shown that the Cs dynamics is influenced by the location of the Cs evaporation nozzle and the amount of Cs present inside the source. This work focuses on the application of the code to the large ion source ELISE, half of the ITER NBI source size. Results of Cs redistribution simulations for different operational parameters, such as the Cs evaporation rate, the duty cycle and the duration of the beam pulse (from ten seconds up to one hour) will be presented and compared with experimental measurements. The results will help to improve the Cs management and to reduce the Cs consumption which is, in particular, of high relevance for a NBI system for DEMO.