Analysis of intra-ELM tungsten erosion during partially-detached plasma operation in DIII-D

Tungsten (W) is a favorable material for plasma-facing divertor components due to properties such as a high melting point, thermal conductivity & low sputtering yield, which will be necessary to tolerate the extreme heat & particle flux faced by the divertor. Edge-Localized Modes (ELMs) are predicted to be a significant cause of erosion in both current and future fusion devices. A technique known as detachment may be used to reduce particle & heat flux reaching the divertor target during ELMs. Detachment involves increasing divertor density to lower the divertor plasma temperature. However, ELMs may “burn through” the detachment front, leading to detrimental levels of W-erosion. This research examines trends in intra-ELM W-erosion during detached operation by focusing on data collected from the DIII-D Metal Rings Campaign, which tested two rows of toroidally-symmetric, W-coated tiles in the lower divertor. The erosion rate was quantified via high-resolution WI emission spectroscopy and the degree of detachment via Langmuir probe & line-averaged density measurements. The authors intend for this work to guide development of partially-detached scenarios that are robust against ELMs, thereby reducing erosion & long-term damage to divertor PFCs.