Outline of the ITER Design/Assumptions

1. ITER Issue CardSTART-UP-1. Limitations to plasma start-up and optimize shaping flexibility for ITER Scenarios G. Federici, A.Loarte, H. D. Pacher, G. W. Pacher, A. Kukuskhin, T. Luce, A. Sips, A. Leonard, R. Stambaugh, C. Kessel Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 1

2. Outline of the ITER Design/Assumptions • Plasma breakdown and ramp-up and ramp-down in ITER is carried out in limiter configuration • To ease maintenance limiters are positioned in main horizontal ports • Be is chosen as limiter PFC  2 limiters are required for sufficient power handling limiter  X-point (6.5 MA) X-point  limiter (9.5 MA) Ramp-up scenario designed for fast current penetration Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 2

3. Psol = 6 MW Psol = 3 MW Psol = 2MW Psol = 3MW Psol = 2 MW Psol = 1MW Issue • We know now that : • Despite complex connection length pattern power load on limiters is reasonably well described by simple exponential decay • For reference ITER start-up scenario 2 with <ne>/nGW ~ 0.2  qlimiter,max ~ 3 MWm-2 in ramp-up • There is little margin in changing ne in ramp-up (radiative collapse) and limited capability for additional heating during ramp-up • Relative alignment of limiters is difficult to between than few mm • Early X-point transition at 3.5 MA but can lead to loss of half of flat top length Flexibility of ramp-up scenarios in ITER is limited by PFCs power handling and flux consumption  unreasonable limits to scenario development Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 3

4. Actions • Review/complete calculations of limiter power loading in present ITER ramp- up/ramp-down scenarios • Develop scenarios/analyse heating requirements for qmin > 1 operation • Study alternative limiter configuration  more limiters/different PFM/poloidal limiters with limited power handling (~ 0.5-1.0 MWm-2 ) located at inner or outer wall, etc. • Investigate early X-point formation (~ 3MA or lower) from outer limiter and from inner wall, divertor dome and implications for PF system Benefits to ITER : Larger device flexibility to explore different q profiles. If breakdown from inner wall is adopted there could be a gain in Volt-seconds. If early X-point transition achieved  large control of ramp-up conditions by heating/fuelling/pumping Implications in Cost and Schedule : Depending on outcome port limiters could be eliminated with a corresponding saving. This would be probably offset by a more expensive PF system Risks : More delicate PF system (if NbSn needed) and weakness of poloidal limiters to transient (~ s) plasma contact Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 4