1. Alberto Loarte 7 th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 1 ITER Issue Card PFC-4. Modification of geometry of the divertor PFCs and neutral by-pass leaks A. Loarte, T. Tanabe, H.D. Pacher, A. Kukushkin, G. Pacher

2. Alberto Loarte 7 th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 2 Outline of the ITER Design/Assumptions Divertor design in ITER optimised to meet various requirements and based on B2-Eirene modelling  W baffle for  R sep > 6 cm  Dome  eq  R sep = 1 cm  Separation between cassettes ~ 5 mm Aims of divertor design  Allow access to q div peak < 10 MWm -2 for conditions compatible with Q DT = 10  n He / < 6%  P main chamber /P div ~ 10 -4  P PFR above-dome / P PFR under-dome ~ 10 Key ingredients of the design : Dome & V-shape near strike point

3. Alberto Loarte 7 th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 3 Issue We know now that :  Under a given divertor leak rate main chamber pressure/plasma flux is determined by anomalous transport  Effect of septum in JET experiments is weak and only seen in one configuration  “Corner” or V-shape effect on detachment seen in JET and ASDEX-Upgrade but quantitative comparison with modelling remains outstanding  Modelling of plasma conditions in ITER requires inclusion of non-linear effects as proven by Alcator C-mod modelling  Geometry influence with non-linear effects weaker Issues  Requirements on divertor neutral leakage, helium pumping, detachment access, etc., and B2-Eirene modelling without non-linear effects have lead to a divertor design which has a restricted plasma configuration flexibility  Presence of dome may lead to hydrocarbon deposition in zones of difficult access  How long should be the CFC part of the target ?

4. Alberto Loarte 7 th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 4 Actions  Review critical effects that influence ITER divertor modelling results  Perform experimental/modelling quantitative assessment of above effects  Evaluate divertor performance with simplified geometry (i.e. without dome) with validated physics models  Evaluate trade-off between increased plasma configuration flexibility and other possible restrictions (reduction of detachment operation window, required pumping for He removal, …)  Evaluate pro’s and con’s of presence of dome with respect to hydrocarbon deposition/removal  Evaluate effect of increased cassette gap on divertor performance and perform optimisation (leak rate vs. feasibility of installation) Benefits to ITER : Larger device flexibility to explore magnetic configurations Implications in Cost and Schedule : Depending on outcome a simpler divertor would result on a cost saving and no impact on schedule Risks : Loss of diagnostics. Changes to detachment access and its compatibility with H-mode operation ?