1. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 1 ITER Design Review Activities on Steady State and Transient Power Loads in ITER Alberto Loarte European Fusion Development Agreement Close Support Unit – Garching Acknowledgements : EU-PWI TF, ITPA Divertor & SOL Group, ITER and many others

2. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 2 Requirement to maintain l i 10 MW Analysis of port limiter for ITER (Kobayashi NF 2007) shows : for I p < 6.5 MA q lim max (MWm -2 ) ~ P SOL (MW) Stable ramp-up P tot /P rad ~ 0.3 + P tot > 11-14 MW P SOL > 8-10 MW q lim max > 8-10 (MWm -2 ) Ramp-up/down Phase

3. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 3 New proposed scenario to full bore ramp-up with short ohmic phase (P SOL < 3 MW), early X-point formation & heating Ramp-down in X-point configuration Full bore plasma : large plasma near first wall but low P SOL New Proposed Ramp-up/down Phase

4. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 4 All divertor tomakaks measure plasma particle fluxes (II B) to the main wall Extrapolated plasma flux to the main wall in ITER 1.0 - 5.0 10 23 s -1 (1-5 % of div ) Q DT = 10 steady plasma loads (I) Lipschultz IAEA 2000 Lipschultz

5. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 5 Plasma fluxes predominantly on outer side of first wall Corresponding maximum IIB power densities up to : 5 MWm -2 (Upper X- point) to 1 MWm -2 near outer midplane and 0.4 MWm -2 near inner midplane Q DT = 10 steady plasma loads (II) LaBombard NF 2004

6. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 6 C-X particle fluxes vary along wall but C-X power fluxes change only by ~2 C-X particle flux ~ 2 Ion flux 0.2-1.0 10 24 s -1 = 0.02-0.1 MWm -2 Q DT = 10 steady C-X and radiation loads P edge > 1.3 P L-H P rad < 0.12 MW m -2

7. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 7 Time scale of divertor ELM energy flux rise correlated with ion transport time Eich JNM 2005 PIPB 2007 Divertor ELM power fluxes : timescales Plasma conditions affect ELM IR ~ II relation (pre-ELM divertor plasma, W ELM, etc.) JET-Eich-JNM 2003 rise,ELM = 200-500 s

8. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 8 q ELM (t) Large proportion of W ELM arrives after IR smaller T surf for given W ELM down,ELM = 1-2 rise,ELM

9. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 9 Divertor Area for ELM power Fluxes (I) A div,ELM ~ 3.5 m -2 Broadening ~ 1 Eich, PIPB07 E in,ELM /E out,ELM = 1-2

10. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 10 Divertor Area for ELM power Fluxes (II) TPF div,ELM ~ 1.0 Divertor ELM load near separatrix ~ toroidally symmetric but strong in/out asymmetries Eich, PRL4 Loarte, PPCF03 from Leonard JNM97 DIII-D

11. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 11 Tolerable ELM size QSPA experiments on NB31 targets show energy density / MJm -2 0.51.0 1.5 negligible erosion erosion starts at PFC corners PAN fibre erosion of flat surfaces after 100 shot significant PAN fibre erosion after 50 shots PAN fibre erosion after 10 shots Tolerable ELM energy density 0.5 MJm -2 + no broadening + 2:1 in/out asymmetry W ELM ~ 1MJ

12. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 12 Part of W ELM is reaches the main wall PFCs energy flow along filaments Fluxes to main wall during ELMs AUG- Herrmann –PPCF06 highest q wall ELM by filament impact (A. Herrmann, AUG) Example (JET-P. Andrew EPS)

13. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 13 Model of II vs. I B transport during ELMs in agreement with experimental findings: ELM T i > T e far from separatrix (Langmuir Probes + Retarding Field Analyser) Deficit of divertor ELM energy for large ELMs (v r /c s ~( W ELM / W ped ) 0.5 + Radiation) ELM fluxes to Main wall fluxes R Fundamenski - PPCF 2006 R JET- Pitts IAEA 2006 & Fundamenski JNM 2007

14. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 14 ELM fluxes to Main wall in ITER (I) ELM power fluxes to PFCs in ITER evaluated by models/empirical extrapolation (input) : W ELM filaments / W ELM, R ELM, V r ELM vs. W ELM (n ped, T ped ), IR ( II ) Controlled ELM W ELM =1MJ f ELM =20-40 Hz Uncontrolled ELM W ELM =20MJ f ELM =1-2 Hz

15. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 15 ELM fluxes to Main wall in ITER (II) Average ELM power fluxes to PFCs require knowledge of filament dynamics

16. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 16 Energy Fluxes to main wall and divertor PFCs during Marfes Pre-disruptive Marfes occur when plasma is already in L-mode In steady state P rad = P inp = 70 -150 MW = 0.1-0.2 MWm -2 Timescale for transient Marfes ~ 0.01-0.1 s (no clear size dependence) Poloidal peaking < 3

17. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 17 Energy Fluxes during disruptions (I) Energy degradation before thermal quench for resistive MHD disruptions Large broadening of footprint for diverted discharges but small for limiter discharges

18. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 18 Energy Fluxes during disruptions (II) Timescale (~ R) but large variability (1.0-3.0 ms for ITER) Longer timescales in decay phase (> 2 rise phase) Toroidal asymmetries (~2) seen in some cases but poor documentation/statistics Systematic study of in/out asymmetries required

19. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 19 Proposed ITER specifications (M. Sugihara/M. Shimada) Scenario 2 : unit ( MJ/m 2 ) Energy release at TQ(1/2-1/3)W peak W peak E // near separatrix at outer midplane 200 - 70 400 - 200 E // near upper ceiling region (6 cm from 1 st separatrix) 20 - 50 60 - 100 E // near lower baffle region (6 cm from 1 st separatrix) 16 - 40 48 - 80 E // to divertor plate near 1 st separatrix 280 – 90 (out) 375 – 120 (in) 560 – 280 (out) 750 – 380 (in) =2.5 cm (left), 5 cm (right)Energy deposition time duration = 3-9 ms Energy Fluxes during disruptions (III)

20. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 20 Energy release at TQW peak (325 MJ) E // near separatrix at outer midplane 510 - 255 E // near upper ceiling region (5 cm from 1 st separatrix) 120 - 160 E // near lower baffle region (5 cm from 1 st separatrix) 95 - 130 E // to divertor plate near 1 st separatrix 730 – 365 (out) 375 – 120 (in) =2.5 cm (left), 5 cm (right)Energy deposition time duration = 3-9 ms Proposed ITER specifications (M. Sugihara/M. Shimada) Scenario 4 : unit ( MJ/m 2 ) Energy Fluxes during disruptions (IV)

21. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 21 Major disruptions during limiter phase : (M. Sugihara/M. Shimada) Ip (MA)4.56.5 W peak (MJ) 10 20 P ; peak energy density (MJ/m 2 ) 7.7 15 Most severe assumption : No broadening of deposition width (Kobayashi NF 07) 2 limiter case Energy Fluxes during disruptions (V) If there is no broadening energy fluxes on limiter for disruptions can be similar or larger than for the divertor disruptions in scenario 2

22. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 22 Energy Fluxes during disruptions (VI) JET ITER Presently proposed ITER specifications based on JET based extrapolations input from other tokamaks is required W 2 = 20-55 MJ 2 = JET / L-mode JET (0.03-0.09)* L-mode ITER W 3 = W( 2 )-dW/dt| L-mode * 3

23. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 23 Downward VDE with fast CQ - EM load on BM / DIV by eddy (+halo) current - Heat load on lower Be wall & W baffle Upward VDE with fast CQ - EM load on BM by eddy (+halo) - Heat load on upper Be wall during VDE and TQ Energy Fluxes during disruptions (VII)

24. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 24 Fast H-L transition ( loss in 1-2 s IW contact for up to ~ 5s) can lead to large loads on the inner wall Confinement transients

25. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 25 Predicted runaway current10 (MA) Energy spectrum of electrons (E0 for exp(-E/E0))12.5 MeV Inclined angle1 - 1.5 Total energy deposition due to runaway current20 MJ Average energy density deposition1.5 MJ/m 2 Duration of the average energy density deposition100 ms Maximum energy density deposition (end of the plasma termination)25 MJ/m 2 Duration of the maximum energy deposition10 ms Number of eventEvery major disruption These specifications are generally reasonable but physics basis is weak (very poor experimental input) Largest concern energy load by drifted electrons due to formation of X-point Runaway electron fluxes on PFCs (I)

26. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 26 Runaway generation mechanisms for ITER like disruptions conditions studied in detail but runaway losses and dynamics are worse known Runaway electron fluxes on PFCs (I)

27. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 27 Current profile during runaway discharge peaks (seen at JET) X-point formation in Scenario 2 Runaway electron fluxes on PFCs (II) Smith PoP 2006 EFIT reconstruction by S. Gerasimov

28. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 28 Runaway electron fluxes on PFCs (III) Significant drift of runaways near upper X-point due to poloidal field null [f(E) = 1/E 0 exp(-E/E 0 ) with E 0 = 12.5 MeV] Angle of impact of runaways on drift orbits at upper X-point < 1.5 o but impact direction mainly toroidal

29. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 29 Conclusions PID specifications for PFC loads in ITER considered for revision following ITER Design Review Process New specifications will be used for modification to existing design reasonable range and upper boundaries for loads have to be provided Input and constructive criticisms from EU-PWI TF and ITPA are gratefully acknowledged