Fast ions losses during neutral beam injection in Tore-Supra

The Fokker-Planck calculation of the fast ions losses occurring during neutral beam injection (NBI), in Tore Supra tokamak, are presented. The sensitivity of these losses to various plasma parameters are tested and the most favourable heating scenarios are indicated. The Tore Supra NBI system is planned to provide a total power capability of 9 MW. The minimization of the ion losses is investigated. The effect of the plasma density and the displacements of the plasma column inside the vacuum vessel, are considered. The Fokker-PLanck calculations predict fast ions losses during NBI in Tore Supra. These losses are mainly due to beam ions on banana orbits with tips in the effective ripple zone. It is shown that the plasma position inside the vacuum vessel as well as density (average and profile) are sensible parameters. For smaller, inner wall limited plasmas (a=70cm) and for peaked density profiles, losses can be reduced to smaller values (25%). A vertical displacement of the plasma column in the opposite direction of the ion drift velocity can also improve fast ion confinement