Investigations on symmetrizing the plasma properties in the expansion region of a large RF ion source via magnetic fields

Le résumé fourni par la source

Abstract A 2D RF self-consistent fluid plasma model is employed on the BATMAN Upgrade source for negative hydrogen ions to investigate the plasma inhomogeneity. An external magnetic filter field is applied in the vicinity of the extraction system for the suppression of the electrons, inevitably co-extracted with the ions, and to cool down the plasma. An unwanted effect of the filter are × B drifts, resulting in a vertical plasma inhomogeneity and accumulation of a second maximum of the electron density and the plasma potential close to the extraction. This can affect the co-extracted electrons and limit the source performance. An additional magnetic field is applied to provide more homogeneous vertical plasma parameters. The secondary field is non-symmetric in vertical and axial directions and can be created by permanent magnets. The aim is to weaken the field in the region of the second maximum of the electron density and the plasma potential. The results show that the superposition of both magnetic fields reduces the plasma inhomogeneity in the vicinity of the extraction system and provides a better symmetry of the electron flux to the grid. Thus, the collected electron current within the RF period becomes uniform in a vertical direction with a bottom/top ratio from 1 to 0.5, while in the standard case is from 3 to 5.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.