(IT/1-4) Plasma-surface interaction, scrape-off layer and divertor physics: Implications for ITER

B. Lipschultz1), X. Bonnin2), A. Kukushkin3), A. Leonard4), J. Roth5), E. Tsitrone6), D. Whyte7), N. Asakura8), D. Coster5), G. Counsell9), R. Doerner10), R. Dux5), G. Federici3), M. Fenstermacher11), W. Fundamenski9), P. Ghendrih6), A. Herrmann5), J. Hu12), A. Kallenbach5), S. Krasheninnikov10), K. Krieger5), G. Kirnev13), A. Kreter14), V. Kurnaev15), B. LaBombard1), S. Lisgo16), A. Loarte17), T. Nakano8), R. Neu5), N. Ohno18), H. Pacher19), J. Paley9), Y. Pan20), G. Pautasso5), V. Philipps13), R. Pitts21), V. Riccardo9), V. Rohde5), D. Rudakov10), P. Stangeby16), S. Takamura18), T. Tanabe22), Y. Yang12), S. Zhu12)
1) Massachusetts Institute of Technology Plasma Science & Fusion Centre, Cambridge, United States of America
2) U. Paris, France,
3) ITER Team, Garching Germany,
4) General Atomics, San Diego CA USA,
5) MPI-IPP, Garching Germany,
6) CEA Cadarache, France,
7) U. Wisconsin Madison, WI, USA,
8) JAEA, Naka site, Japan,
9) UKAEA-Culham, UK,
10) UCSD, San Diego, CA, USA,
11) LLNL, Livermore, CA, USA,
12) ASIPP, Hefei, China,
13) Kurchatov Institute, Moscow, Russia,
14) FZ, Jülich, Germany,
15) MEPI, Moscow, Russia,
16) UTIAS, Toronto, Canada,
17) EFDA, IPP, Garching, Germany,
18) Nagoya U. Nagoya, Japan,
19) INRS-EMT, Varennes, Canada,
20) SWIPP, Chengdu, China,
21) EPFL, Lausanne, Switzerland,
22) Kyushu U. Kyushu, Japan

Abstract.  The work of the ITPA SOL/divertor group is reviewed and implications for ITER discussed. Studies of near SOL gradients have revealed a connection to underlying turbulence models. Analysis of a multi-machine database shows that parallel conduction gradients near the separatrix scale as major radius. New SOL measurements have implicated low-field side transport as driving parallel flows to the inboard side. The high-n nature of 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. Analysis of ELM measurements imply that the ELM continuously loses energy as it travels across the SOL – larger gaps should reduce surface loads. The predicted divertor power loads for ITER disruptions has been reduced as a result of finding that the divertor footprint broadens during the thermal quench and that the plasma can lose up to 80% of its thermal energy before the thermal quench (not true for VDEs or ITBs). On the other hand predictions of power loading to surfaces outside the divertor have increased. Disruption mitigation through massive gas puffing has been successful at reducing divertor heat loads but estimates of the effect on the main chamber walls indicate 10s of kG of Be could be melted/mitigation. Estimates of ITER tritium retention have reduced the amount retained/discharge although the uncertainties are large and tritium cleanup may be necessary every few days to weeks. Long-pulse studies have shown that the fraction of injected gas that can be recovered after a discharge decreases with discharge length. The retention rate on the sides of tiles appears to  1-3% of the ion flux to the front surface for C tiles and 100x less for Mo tiles. T removal techniques are being developed based on surface heating and surface ablation although ITER mixed materials will make T removal more difficult. The use of mixed materials gives rise to a number of potential processes – e.g. reduction of surface melting temperatures (formation of alloys) and reduction of chemical sputtering. Advances in modelling of the ITER divertor and flows have enhanced the capability to match experimental data and predict ITER performance.

Full paper and slides available (PDF)