Numerical investigation of Ne pellet formation for EAST shattered pellet injection system

Plasma disruptions can cause rapid loss of thermal and magnetic energy, significantly damaging tokamak devices. To mitigate the deleterious effects resulting from disruptions, shattered pellet injection (SPI) is widely adopted as a mitigation method. In this study, a numerical model utilizing the modified frosting model based on the Euler multi-phase flow method has been successfully established for Ne pellet in-situ formation, providing a reference for the design and experimental tests of SPI systems. Within this model, the process of Ne pellet formation is numerically investigated using a mass transfer model implemented as a user defined function in FLUENT. Moreover, the formation process of Ne pellets with the sizes of 5 × 15 mm (D × L) under a cold head temperature of 10 K and operating pressure of 60 mbar is simulated. The findings reveal that a Ne pellet with a weight of 0.175 g and density of 0.74 g/cm3 can be formed in 300 s. Evidently, the simulation and experimental outcomes present good agreement, with a 7 % discrepancy in the formation duration and 28 % deviation in density, indicating the model's capability to accurately describe the Ne pellet formation process. This study also reveals that the solid Ne can grow rapidly during the initial 100 s of pellet formation owing to the low temperature of the tube wall. Furthermore, the model is employed to simulate pellet formation under varying cold head temperatures. The results reveal that the durations in which the pellets attain the same weight also decrease with the decrease of the cold head temperature, whereas the average density almost remains unchanged.