• Energy Research

Divertor tiles removed after the second JET ITER-Like Wall campaign 2013-2014 (ILW-2) were studied using Secondary Ion Mass Spectrometry (SIMS). Measurements show that the thickest beryllium (Be) dominated deposition layers are located at the upper part of the inner divertor and are up to ~40µm thick at the lower part of Tile 0 exposed in 2011-2014. The highest deuterium (D) amounts (>8 · 1018 at./cm²), in contrast, were found on the upper part of Tile 1 (2013-2014), where the Be deposits are ~10µm thick. D was mainly retained in the near-surface layer of the Be deposits but also deeper in tungsten (W) and molybdenum (Mo) layers of the marker coated tiles, especially at W-Mo layer interfaces. D retention for the ILW-2 divertor tiles is higher than for the first campaign 2011-2012 (ILW-1) and probable reasons for the difference are that SIMS measurements for the ILW-2 samples were done deeper than for the ILW-1 samples, some of the tiles were exposed during both ILW-1 and ILW-2 and therefore had a longer exposure time, and the differences between ILW-1 and ILW-2 campaigns e.g. in strike point distributions and injected powers.

The work presented draws on new analysis of components removed following the second JET ITER-like wall campaign 2013–14 concentrating on the upper inner divertor, inner and outer divertor corners, life- time issues relating to tungsten coatings on JET carbon fibre composite divertor tiles and dust/particulate generation. The results show that the upper inner divertor remains the region of highest deposition in the JET-ILW. Variations in plasma configurations between the first and second campaign have altered ma- terial migration to the corners of the inner and outer divertor. Net deposition is shown to be beneficial in the sense that it reduces W coating erosion, covers small areas of exposed carbon surfaces and even encapsulates particles. EURATOM 633053 RCUK Energy Programme EP/I501045

Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement HH(98, y2) 0.95. Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.