Kinetic Depletion Model and Toroidal Effects on Pellet Ablation

Introduction Understanding the mechanisms, which affect the pellet ablation in high temperature plasmas, is significant for development of fuelling and diagnostic systems for tokamaks and stellarators. Very special regimes of ablation are predicted theoretically and observed experimentally when pellets penetrate through regions with low shear value (the central zone or an island nearby a rational magnetic surface). So called self-limiting ablation is caused by the depletion effect [1,2]. Toriodal effects on ablation are also very significant and recently they initiated the program of high field side injection for improvement of the fueling efficiency [3]. This paper deals with a kinetic model for the depletion effect, which takes into account three-dimensional distribution of the ablation over the pellet surface. A new effect of the analysis presented is the deceleration of a pellet in low shear regions. Modification of the electron distribution function in toroidal configuration reduces the ablation rate for the high field side injection and increases it for the low field side compared to the case of linear magnetic field lines. The effect is evaluated quantitatively below.