1. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 1/15 Prediction of wall fluxes and implications for ITER limiters Max-Planck-Institut für Plasmaphysik Arne Kallenbach, ASDEX Upgrade Team

2. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 2/15 Topics of this talk: guidelines on load specifications  steady state particle main chamber fluxes from spectroscopy  estimates of connected power fluxes and decay lengths  contribution due to ELMs (enhancement factor)

3. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 3/15 Current ITER Guidelines (PID V3.0): Only radiation and CX load to first wall, 0.5 MW/m 2 diffusive transport between ELMs blobby transport between ELMs (radial outward convection) ELM SOL transport (like large blobs) - parallel drift towards high-field side - strong recycling around inner X-point additional players in particle transport: transport and drifts lead to parallel heat fluxes in far SOL

4. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 4/15 Main chamber spectroscopy at ASDEX Upgrade Ralph Dux

5. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 5/15 Innner and outer wall plasma-surface interaction in AUG from CII spectroscopy: very sensitive on in-out alignment  inner heat shield major recycling region except plasma close to outer limiter  lower inner wall flux dominated from inner divertor  upper inner wall flux has radial e-folding length ~ 2-3 cm R lim 8 m 2 0.3 m 2

6. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 6/15 How to estimate the stationary power flows on the limiters 1)estimate the total radial ion outflux* 2)estimate the deposited energy per electron-ion pair 3)estimate the effective wetted area or peak load and decay length  limiter power flux density average value from different models, be conservative and use upper end *IO calculates in terms of parallel power fluxes and decay lengths

7. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 7/15 AUG edge density profiles from Li-beam H-mode recycling rises Radial SOL particle flux in ITER ansatz with effective D:  = D dn/dr D = 3 m 2 /s this value typical for SOL wing in many devices dn/dr = 2  10 19 m -3 / 0.05 m  = 1.2  10 21 m -2 s -1 total main chamber ion influx: multiply  with 1/3 of plasma surface area F ITER = 680 m 2  1/3   ~ 3  10 23 s -1 1) Total radial ion wall flux in ITER [i] scaling like diffusive transport Transport balloons around outer midplane: conservative, can be larger

8. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 8/15 3.2  10 23 s -1 1)Total radial ion wall flux in ITER [ii] some alternative ways of estimation a)Same flux density as in AUG discharge with high similar f Green, P/R, and absolute density, scaled with area b) Same flux density as in AUG discharge with high similar f Green, P/R 2 and absolute density, scaled with area  16 c) Same flux density as in JET discharge with high similar f Green, P/R 2 and absolute density, scaled with area ( best use 4 MA, 25 MW discharge) ITER: 100 MW/6 m, not possible in AUG, scale P 0.24 [NF 42 (2002) 1184] ITER: 100 MW/36 m 2, 7.5 MW in AUG, AUG # as above AUG 21015/17, 7.5 MW, n e =10 20 m -3,  =2  10 22 1/s, dr XP =3 cm 4.4  10 23 s -1 JET 70054, 3.5 MA, 24 MW, 1e20, midplane H  20  72 m 2   main =7.2  10 22 s -1 2.9  10 23 s -1 Over all, 3(1-5)  10 23 s -1 seems reasonable estimate

9. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 9/15 100 eV per e-i pair  1.6 MW 2)Energy per electron ion pair T e in the SOL wing of a high density H-mode discharge is typically 5-10 eV, T i tends to be moderately higher We assume for ITER Te= 10 eV, Ti= 20 eV standard model for sheath power deposition (negl. secondary el. emission) P= e  i (2T i + 3T e + E rec ) + e  e 2T e  100 e  per 1  10 23 part/s

10. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 10/15 ITER quick guess: 18 protruding ribs, height 5 m, 0.05 m wetted width  4.5 m 2 for HFS and LFS each (good alignment required !) 3) effective wetted area and resulting loads The wetted area depends on actual wall design ! wetted width depends on decay length in limiter shadow Of course, the upper X-point region takes more power and must be strengthened 3 10 23 ions/s  4.8 MW  charge exchange is expected to increase this number by 10-20 %  ELMs contribute to recycling fux by factor 1.5  radiation is expected to contribute < 0.2 MW/m 2  some contrib. by fast ion losses on LFS overall, expected peak loads about 1 MW/m 2 not problematic, but safely  1 MW/m 2 would allow to avoid active cooling

11. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 11/15 ELM contributions to average particle influxes: small for D, C, dominnat for W Outer limiter ELM-cycle averaged, D and C fluxes increased by ~ 1.5 but: 70 % of the W influx due to ELMs (increased yield) R. Dux

12. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 12/15 Decay length depends on connection length to limiters measurements in AUG limiter shadow by H.W. Müller Increasing the number of limiters can reduce the power load. However: the decay length shortens with reduced connection length and more precise alignment will be required

13. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 13/15 ITER expects negligible loads on inner wall - does the existence of a 2nd sep. shield the inner wall ? No ! further investigations needed on inner wall load close DN dRXP= 3 mm

14. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 14/15 Comparison to previous estimate based on JET-AUG Recycling scaling (Tarragona meeting, July 2005) new insight: predominantly HFS recycling  multiply with S/4 only: R tot = 10 24 s - 1 (n e,sol = 4.7 10 19) Strong dependence of total recycling on n e,line-av (power 4)  If pellets are needed to reach 10 20 m -3 in ITER, this number comes down: If ITER produces n e = 7.5 10 19 by recycling only, R tot = 3 10 23, n e,sol = 2.6 10 19

15. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 15/15 Conclusions  Main chamber recycling occurs predominantly on the high field side and on wall structures touching the innermost flux surfaces  Effect supposed to be connected to strong drifts towards HFS  Strong plasma wall interaction with the inner wall close to DN operation is not understood: fluxes close to the separatrix or ExB drifts around upper X-point ?  Expected total particle fluxes 3  2 10 23 part/s, power fluxes ~ 5 MW How will the ITER FW will look like ?

16. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 16/15 ELMs: Simple size scaling and effect to wall materials Size scaling based on empirical findings: natural type-I ELM size ~ 10 % of pedestal energy, 3.5 % of plasma energy ELMs carry 30 % of the power flux simple algebra: P ELM = 0.3 P loss = 0.3 W tot /  E = 0.035 f ELM W tot = f ELM W ELM  f ELM = 8.6/  E ITER Sc. 1: W tot = 353 MJ,  E =3.4 s AUG typ.: 0.8 MJ, 0.1 s  f ELM = 2.5 Hz, W ELM = 12 MJ 80 Hz, 28 kJ controlled ELMs: if f ELM is changed, W ELM scales ~ 1/f ELM ITER PID: uncontrolled ELMs f ELM = 1 Hz, W ELM = 15-20 MJ controlled ELMs f ELM = 5 Hz, W ELM = 3-4 MJ o.k.

17. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 17/15 ELMs: Simple size scaling and effect to wall materials Divertor peak power load: ITER PID assumed effective wetted divertor area of 7.5 m 2 ( w= 0.1 m along targets) resulting maximum loads were 2.7 MJ/m 2 (uncontr.), 0.5 MJ/m 2 (contr.) Material properties: melting/ablation limits: Be 20, W 60, CFC 60-70 [MJ m -2 s -0.5 ] example: ELM 1 MJ/m 2, 0.5 ms duration  45 MJ m -2 s -0.5 recent lab exps. (Russian-EU collab.) suggest limit below 0.7 MJ/m 2 both for W and CFC (fatigue, crack formation)  reduce peak load by factor 0.5 1556 K 3683 K 3640 K (subl.) the maximum allowed ELM was controlled to  4 MJ latest changes: no ELM power broadening p  5 mm (fact 2/3) in-out asymmetry 2:1 – (fact ¾), recover factor 2 safety margin 0.5  0.25 MJ/m 2 ?  maximum “ELM” ~ 1 MJ too pessimistic – ignores large p inner div

18. 10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008 Arne Kallenbach 18/15 Open points = possible AUG contributions 1) midplane inter-ELM power width midplane T e decay length scales ~ machine size A. Kallenbach et al., ITPA SOL&Div Topical Group, PSI 2004 expected power width 2/7  Te considerably broader widths observed in divertor (mapped to omp) good topic for future AUG / inter-machine exps (L. Horton) AUG: 1.3 mm omp