Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 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 2

Outline of the ITER Design/Assumptions

limiter X-point (6.5 MA)

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

handlingX-point limiter (9.5 MA)

Ramp-up scenario designed for fast current penetration

Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 3

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

Psol = 1MW

Psol = 3MW

Psol = 2 MW

Psol = 2MW

Psol = 6 MW

Psol = 3 MW

Alberto Loarte 7th ITPA Divertor Meeting – Toronto 6/9 – 11 – 2006 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