Prompt vs Local Redeposition: Model Refinement and Experimental Design for Understanding High-Z Net Erosion in Magnetic Confinement Fusion

The economic and engineering success of magnetic confinement fusion reactors significantly depends upon the optimization of plasma facing component (PFC) design. For high-Z PFCs, the critical engineering condition is minimal net erosion (i.e. gross erosion – redeposition). Here, we present a high-Z net erosion model discriminating three primary redeposition mechanisms: prompt (geometric-driven), local (sheath-driven), and far (scrape-off-layer-driven). Using these distinctions, we show modeling for high-Z net erosion in magnetic-confinement fusion over a matrix of key plasma parameters. With Sobol’ methods we assess the sensitivity of each mechanism and show that prompt-vs-local trade-off critically explains underprediction in redeposition losses of up to two orders of magnitude across magnetic-field-to-PFC pitch angles. Finally, we report a “design-of-experiment” study exploring the measurability of prompt vs local distinctions in current experimental facilities. We use a combination of synthetic diagnostics and plasma-parameter optimization to propose an isotopic method of measurement by exploiting robust in situ and ex situ techniques. In principle, this approach provides a ready path forward for improving and validating PFC models needed to target optimal regimes of PFC design in future reactors.