A comparative study of tungsten erosion-redeposition in divertor sheaths versus RF sheaths on WEST

Tungsten (W) is currently the material of choice for divertors and RF limiters in ITER and next-generation tokamaks. Therefore, it is crucial to have a detailed understanding of the erosion-redeposition behavior of W in close proximity to these plasma-facing components. In order to achieve this goal, we conducted a comparative computational analysis of the two regions that are most affected by impurity production, namely the divertor and the RF limiters. The calculations were performed based on the conditions observed in the WEST full-tungsten tokamak. The study was carried out in two parts: (1) we analyzed the emission and multi-step ionization of tungsten in the plasma; and (2) focused on the collisional transport within the SOL. The structure of the thermal sheaths and RF sheaths was determined using the hPIC2 code. The RustBCA code was used to model the W emission distributions on both the divertor and limiter walls. We also considered the collisional forces that regulate tungsten transport away from the surfaces. One of the key findings of this research was a comparative analysis of the distribution and percentage of prompt and nonlocal redeposition. Our analysis provides insights into the impurity screening efficiency, regulated by the different types of plasma sheaths.