Sputtering Reduction Optimization via Volumetrically Complex Materials

Volumetrically complex materials (VCMs) have been experimentally proven to be up to ten times more robust in harsh plasma environments, with the implied potential to significantly increase the lifetime of confining surfaces for nuclear fusion, plasma electrodes, and space propulsion components. The objective of this effort is to use advanced ion-solid interaction simulation codes and fast gradient-based optimization algorithms to investigate optimal strategies to using volumetrically complex materials for plasma-facing environments.

In this work, high-fidelity ion-solid interaction simulation data were gathered from an experimentally validated ion-solid interaction code, TRI3DYN, and merged with an analytical sputtering model for volumetrically complex materials. Probability density functions (PDFs) of sputterant trajectory are determined for individual VCM ligaments, revealing the driving forces behind sputterant transport in micro-architectured materials. PDFs of a foam ligament with a circular cross section were calculated and found to vary in shape and backsputter fraction based on ion energy. These PDFs suggest that at energies up to 1 keV the high concentration of sputterant trajectories in off normal directions are favorable for trapping sputtered particles, as these regions of the PDF are readily captured by adjacent ligaments. The individual contributions of sputter yield from the ligament layers that comprise the VCM showed that the top layer in responsible for the majority of the back sputtered atoms, with subsequent layers contributing exponentially less.

Non-linear constrained optimization provides optimal designs of VCM geometry that reduce sputter yield on the order of 40%, subject to constraining the amount of forward-sputtered material passing through the VCM.