Plasma–surface interaction, scrape-off layer and divertor physics: implications for ITER

TLDR

Recent SOL and divertor studies compare experimental data across devices, highlighting implications for ITER. Near‑separatrix investigations link profile–turbulence relationships to parallel power‑flow scaling. The review shows that enhanced low‑field side radial transport drives inboard parallel flows, medium‑n ELMs deposit 10–20 % of their energy in the far SOL, divertor loads are reduced while main chamber loads rise, massive gas puffing mitigates PFC heat, tritium retention on tile sides requires periodic cleanup, mixed materials lower melting temperatures and sputtering, and improved divertor modelling now better matches experiments and predicts ITER performance.

Abstract

Recent research in scrape-off layer (SOL) and divertor physics is reviewed; new and existing data from a variety of experiments have been used to make cross-experiment comparisons with implications for further research and ITER. Studies of the region near the separatrix have addressed the relationship of profiles to turbulence as well as the scaling of the parallel power flow. Enhanced low-field side radial transport is implicated as driving parallel flows to the inboard side. The medium-n nature of edge localized modes (ELMs) has been elucidated and new measurements have determined that they carry ∼10–20% of the ELM energy to the far SOL with implications for ITER limiters and the upper divertor. The predicted divertor power loads for ITER disruptions are reduced while those to main chamber plasma facing components (PFCs) increase. Disruption mitigation through massive gas puffing is successful at reducing PFC heat loads. New estimates of ITER tritium retention have shown tile sides to play a significant role; tritium cleanup may be necessary every few days to weeks. ITER's use of mixed materials gives rise to a reduction of surface melting temperatures and chemical sputtering. Advances in modelling of the ITER divertor and flows have enhanced the capability to match experimental data and predict ITER performance.