Fast backward drift of pellet ablatant in tokamak plasmas

Pellet ablation in the Rijnhuizen Tokamak Project has been studied with an array of 16 fibers viewing the pellet trajectory along very narrow lines of sight. Rapid backward drift of the ablation cloud away from the pellet was observed. This has implications for the determination of the fueling profi le and the penetration of the pellet in the plasma. Furthermore, this movem ent of the ablation cloud offers a new explanation for the often observed s triations in the light emission. In contrast to the picture of the pellet p eriodically leaving the ablation cloud, the ablation cloud moves periodical ly away from the pellet. [S0031-9007(99)08796-7].