EFDA-JET-PR(12)57
Modelling of Pellet Particle Ablation and Deposition: The Hydrogen Pellet Injection Code HPI2
The processes of pellet particle ablation and deposition considering the B-induced ExB drift of the ionised ablated pellet particle cloudlets, i.e. the plasmoids, are reviewed and summarised in a first-principles based model for the determination of the pellet deposition profile. Motivated by clear experimental evidence for a significant ExB drift displacement of the pellet particles in tokamak plasmas as for instance at JET, particular emphasis is placed on the characterisation and model representation of physical phenomena that can influence the plasmoid drift and homogenisation dynamics, such as Alfvén wave propagation, external and internal short-circuit currents. Numerous related aspects that are currently under discussion are analytically and numerically examined, and the model equations are modified and complemented accordingly. The model has been implemented in a new simulation program called HPI2 for the calculation of hydrogen pellet material deposition in magnetically confined plasmas, e.g. in tokamaks, stellarators and reversed field pinch machines (RFPs). The program can consider various second-order effects like e.g. plasma pre-cooling, enhanced ExB drift damping in proximity of rational flux surfaces, or the rocket-like acceleration of the pellet due to inhomogeneous ablation. Results of a first validation are presented, and exemplary simulation cases for ITER-relevant plasmas are shown and interpreted. According to the model predictions, the ExB drift will play a crucial role in ITER to achieve a level of pellet particle penetration that is sufficient for fuelling purposes.