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 profile and the penetration of the pellet in the plasma. Furthermore, this movement of the ablation cloud offers a new explanation for the often observed striations in the light emission. In contrast to the picture of the pellet periodically leaving the ablation cloud, the ablation cloud moves periodically away from the pellet.