Pellet source density in toroidal plasma configurations based on a 2D Gaussian deposition model

We develop a two-dimensional (2D) Gaussian deposition model to calculate the initial pellet deposition density immediately after pellet ablation, which is valid before the backward difference B-drift of the ablated material significantly shifts its location. A 2D Gaussian particle distribution is assumed in the ablation cloud cross-section. Applying this new model to a typical EAST plasma, and comparing it with the conventional point deposition model, it is found that the new model can resolve the tangential singularity problem encountered by the point deposition model. In addition, the model predicts that the initial pellet deposition density depends strongly on the ablation cloud radius as well as the form of the radial particle distribution in the ablation cloud with tangential injection. The backward difference B-drift is then introduced with the drift displacement estimated based on a scaling formula derived from HPI2 simulations. The model can provide a fast evaluation of pellet deposition density compared to the predictive HPI2 code at the expense of acceptable accuracy loss. This model could be a useful tool for physical studies relevant to pellet injection, such as pellet ELM triggering and particle and energy transport.