1. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 1 Report on ITER Design Review Sub-group on : Heat and Particle Loads to in-vessel components associated with limiter and X-point operation, TF ripple, H&CD systems, ELMs, disruptions, VDEs, Marfes and runaway electrons in ITER Alberto Loarte European Fusion Development Agreement Close Support Unit – Garching Acknowledgements: A. Grosman, P. Stangeby, G. Saibene, R. Sartori, M. Sugihara, W. Fundamenski, T. Eich, P. Snyder, V. Riccardo, G. Counsell, R. Pitts, B. Lipschultz, P. Andrew, G. Pautasso, A. Leonard, G. Strohmayer, G. Federici, A. Kirk, J. Paley, M. Lehnen, B. Alper, C. Ingesson, etc.

2. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 2 ITER PID only specifies P max limiters = 15 MW (max 9 MW on one limiter) Fluxes to limiter during Ramp-up/down (I)  Reference ITER ramp-up(/down) has long limiter phases up to I p = 7 MA (10 MA) in which plasma is limited by two limiters 180 o apart (power loads & erosion)  2 limiter configuration and q lim = 5 lead to long connection lengths in SOL (>> 200 m) Magnetic shear + perpendicular transport  simple “single exponential” power decay length (Kobayashi, NF 2007) Main Uncertainties  P SOL for all ITER reference scenarios (ramp up/down with heating)  Scaling of SOL transport with I p and R (JET extrapolation for Kobayashi NF 2007)

3. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 3 ITER power and power fluxes estimated with B2-Eirene for a range of burn conditions (mainly Q DT = 10) to maintain detachment but weak physics basis for SOL transport and main chamber fluxes Fluxes to main wall and divertor during diverted operation (I)  near SOL transport  p = 5 mm (close to most pessimistic scalings 4 mm) for I p = 15 MA (6 mm for scenario 3 (hybrid) and 8 mm for scenario 4 (ITB) if p ~ I p -1 )  q II = 570 – 760 MWm -2 for P SOL = 100 MW (typical for scenarios 1 & 2) H-mode scenarios 1 & 2  wall = 5–20 cm  q II wall < 0.04 MWm -2 lIB L-mode scenarios 1& 2 (P SOL =35 MW, L =2 H ) &  wall =5–20 cm  q II wall < 1.0 MWm -2 IIB 0.5 o <  < 15 o  FW load < 0.5 MWm -2 fulfilled but loads on edges ? (2mm steps) and edges of ports ? Main uncertainties :  In/out divertor power asymmetry (ballooning transport)  Far SOL transport (wall fluxes)  Scaling of p

4. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 4 Particle flux to ITER main wall expected to be > 10 23 s -1 (> 1% of  div ) Fluxes to main wall and divertor during diverted operation (II) Lipschultz “Scarce” data & ITER B2-Eirene modelling :  n (  sep ~ 5 cm) = 0.4 - 1.0 10 19 m -3  v SOL = 30 – 100 ms -1  T SOL = 10 – 20 eV  SOL = 4.5 – 21 cm  q II < few MW II B on (outer) first wall  local particle & power fluxes on edges and edges of ports ?  q perp < 0.3 MW m -2 < OK for FW panels

5. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 5 w/o convection with convection P // =94kW (/20MW) P // =88kW Q // =0.4|V RF |n e c s Integrated losses : typically 100kW for 20MW injected (low density case) Localised peak at 10MW/m 2 ; average ~2.5MW/m 2 These results depend crucially on the density value in the first cm in front of the wall (far- SOL transport ?) Sheath rectification may reach 2-3 kV  Sputtering of surfaces! Fluxes associated with heating systems and steady-state non-toroidal asymmetries  NBI shine-through limit n e > 3.7 10 19 m -3 (30% n GW ) for 0.5 MWm -2 (edges ?) but no local ionisation or first orbit losses included  Ripple losses expected to to lead to less than 0.3 MWm -2 (3-D effects ?)  Effect of ELM RMP coils on power deposition assymetries ?  ICRH (and LH) can lead to large power fluxes on PFCs near and far field (not included in PID) EFDA Task TW6-TPHI-ICFS2 (L. Colas, CEA)

6. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 6 In transient events 1 cm SOL field line touches first wall for 1 s Plasma Position and Shape Control If plasma in H-mode then depending on location of contact  plasma stays in H-mode or H  L transition H-modeH  L 350 MJ  175 MJ q II contact-wall 77 – 102 MWm -2 p contact-wall 0.5 cm  t contact-wall 1 s q II L-H contact- wall > 105 - 140 MWm -2 p L-H 1.0 cm  p L-H < 1.7 s sin  = 1-8 10 -2 sin  = 1.5-2.5 10 -1 in “minor disruptions” separatrix can touch dome for ~ 1 s q II in,dome ~ 380 - 570 MWm -2

7. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 7 PID estimates of ELM loads for ITER carried out on simplified experimental basis Fluxes to main wall and divertor during ELMs (I) Specified loads are of the right magnitude but can be improved to include ELM physics understanding (time dependence, in/out asymmetries, relation “ ” vs  W ELM /W ped Sugihara, ITER_D_22JYYU, 2005 700-950 MWm -2 3.5-4.7 GWm -2

8. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 8 Fluxes to divertor during ELMs (II)  W ELM < 30 MJ A div,ELM = 4 m -2 Broadening < 1.5  rise,ELM = 200-500  s  down,ELM = 1-2  rise,ELM Loarte, PPCF’03 Eich, PIPB’07 Eich application of Fundamenski PPCF’06 Eich, PIPB’07

9. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 9 Fluxes to divertor during ELMs (III) TPF div,ELM < 1.5 E in,ELM /E out,ELM = 1-2 Divertor ELM load near separatrix ~ toroidally symmetric but strong in/out asymmetries Eich, PRL’4 Loarte, PPCF’03 from Leonard JNM’97 DIII-D Eich, JNM’07

10. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 10 Fluxes to divertor during ELMs (III)  W div,ELM 5 MJ 30 MJ E in max (MJ)< 3.3< 20 E out max (MJ)< 2.5< 15 E in min (MJ)< 2.5< 15 E out min (MJ)< 1.7< 10 q in max (GWm -2 )< 6.2< 37.5 q in min (GWm -2 )< 1.9< 11.3 q out max (GWm -2 )< 4.7< 28.1 q out min (GWm -2 )< 1.3< 7.6  rise max (  s) 500  rise min (  s) 200

11. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 11 Part of  W ELM is reaches the main wall PFCs  formation and ejection of filaments Fluxes to main wall during ELMs (I) Model of q II (t) for detached filaments developed by Fundamenski (PPCF’06) and validated with JET data (Pitts NF’06)  Application to ITER JET-Eich, PIPB’07 MAST- Kirk, EPS’06 AUG- Herrmann –PPCF’06 ?

12. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 12 q II in filament estimated with model by Fundamenski  required input to model :  n fil, T fil, & distance from sep @ filament detachment Fluxes to main wall during ELMs (II)  ELM fluxes to main wall (beyond second sep) only on outer wall  Power reaches the wall in filamentary structures (for ITER Snyder results in NF’04) : distance between filaments (m) = 15/n (if no break-up and all become unstable) filament poloidal width (m) = 3/n (rough estimate) Decay length of filaments in “limiter” shadow ~ L lim /L SOL ? Outstanding issues :  Relation V ELM &  W ELM  v ELM /c s,ped = 10 -2  W ELM /W ped or 1.5 10 -3 (  W ELM /W ped ) 0.5  n fil, T fil R fil at instant of detachment &  ELM Wall (~  ELM div ?)   wall ELM  sputtering Herrmann-AUG

13. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 13 PID specifications generally in line with current evidence from disruption loads but need to be refined to incorporate latest findings on divertor/wall loads Fluxes to main wall and divertor during Disruption thermal quench (I)  Classification of loads per disruption type (ideal MHD limits, etc.) and scenario  Disruptions in limiter phase are absent in specifications  Toroidal and in/out asymmetries ?  Radiation during thermal quench ?

14. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 14 Fluxes to main wall and divertor during Disruption thermal quench (II)  Plasma energy at t.q. typically less than 40% expected from H 98 = 1 (Size scaling ?)  Dedicated experiments at JET in 2006/2007 show that W t.q. < 0.4 W (Type I H-mode) for density limits, radiative limits and NTM driven disruption JET-Riccardo NF’05 MAST-Counsell t.q. timescale has large scatter associated with MHD activity but similar to ELMs large amount of energy reaches PFCs after q max

15. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 15 Fluxes to main wall and divertor during Disruption thermal quench (IV) Broadening of power width causes energy deposition IIB everywhere on PFCs (TPF < 2)  significant amount of energy deposited outside divertor Disruptions in divertor conditions triggered by ideal MHD limits and in limiter seem completely different many aspects (P. Andrew, PSI’06, Riccardo NF’05, Finken NF’92, Janos JNM’92, TFR JNM’82) JET-Paley-PhD Thesis ‘07

16. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 16 Fluxes to main wall and divertor during Disruption thermal quench (V) Ideal MHD limit disruptions can lead to large interactions with inner-wall or outer wall not seen in other disruption types  Not included in PID for scenario 4 (ITB)  implications for ITER ? P NBI (X 10 MW) P ICRH (X 10 MW) P rad (X 100 MW) JET Pulse No. 69816 ITB grad-P disruption W dia (MJ) I p (MA) Mode-lock (a.u.) n = 2 (a.u.) n = 1 (a.u.)

17. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 17 Disruptions in limiter phase Not considered in PID but potentially serious because of lack of broadening of power footprint for limiter disruptions ( t.q. < 1.5 s.s. )  EOL-ramp-up : I p = 7 MA, if P inp = 5 MW  W plasma (ITER-89) = 15 MJ  BOL-ramp-down : I p = 10 MA, if P inp = 7 MW  W plasma (ITER-89) = 24 MJ TEXTOR-Finken NF 1992 For p > 2 cm  A eff, limiters = 2.5 m 2 (H. Pacher) Disruptions during limiter phases may cause loads > 6 – 10 MJm -2 with  t.q. ~ 1 ms Major issue for power fluxes during VDEs  needs to be confirmed Janos-TFTR-JNM 1992 Normal discharge Disruptive-normal discharge

18. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 18 Large discrepancy between PID specifications and new proposed specifications in Sugihara NF ‘07 Energy Fluxes to main wall and divertor PFCs during VDEs (I)  ~ 134 MJm -2 s -1/2 Possible Realistic scenario  Plasma drifts towards wall in H-mode  At some point L-mode transition (H-modes with X-point behind target at JET)   W plasma (30-50 % of W plasma ) deposited on wall in  t <  L-mode with p ~ 1 cm  Plasma is in contact with wall in limiter L-mode P SOL = 100 MW + dW/dt  Plasma disrupts in limiters configuration when q ~ 1.5-2 with W plasma > 100 MJ

19. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 19 PID specifications for Marfe loads in ITER (physics model ?) Energy Fluxes to main wall and divertor PFCs during Marfes (I) Three types of “Marfes” expected in ITER (L-mode Plasma) :  Inner-wall Marfe  Potentially steady-state P rad )  X-point Marfe  Potentially steady-state P rad )  Pre-thermal quench divertor Marfe  short-lived ( )  Pre-thermal quench limiter Marfe  short-lived ( )  For all cases radiation peaks near X-point region or inner-wall Main issue is to determine realistic timescales and peaking factors of radiation on wall due to Marfe for ITER

20. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 20 Examples of Marfes at JET Energy Fluxes to main wall and divertor PFCs during Marfes (II) Steady-state limiter Marfe A. Loarte Memo to RI-mode working group’99 Transient limiter Marfe J. Wesson-Science of JET’99 ~ Steady-state X-point Marfe A. Huber-PSI’06

21. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 21 Conclusions  Many of the PID specifications for PFC loads in ITER are not far from expectations from latest experimental/model results  Other are in disagreement with present evidence and/or absent  A detailed review and update of PID specifications is needed & will be carried out as part of the design review  Contributions from ITPA groups and collaboration with ITER-IT will be essential to do this review Expected loads in ITER will determine fine details of PFC construction (edge shadowing, etc. ), overall PFC configuration & will have implications for the use of diiferent PFM in various areas of the device

22. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 22 Other transients following plasma disturbances and noise in feedback/measurement system Plasma Position and Shape Control (II)

23. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 23 Even if position control is recovered in 10s there are ~ 1s phases in which separatrix gets dangerously close to areas designed for low power loads Plasma Position and Shape Control (I) SOB Minor disruption Appendix E q II in,dome ~ 380 - 570 MWm -2 for ~ 1 s Control of plasma in ITER can lead to fluxes IIB on PFCs > 100 MWm -2 for timescales ~ 1s and possibly fast H-L transitions

24. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 24 Most tokamaks find that close to 100 % of magnetic energy at t.q. is radiated with the exception of Alcator C-mod (< 25%) Energy Fluxes to main wall and divertor PFCs during current quench W mag = ½ L p I p 2 After t.q.   p = 0 (0.2-pre), l i ~ 0.5 (0.85-pre), I p <18 MA (15 MA-pre)  W mag < 1.85 GJ a Most of W mag  V.V. and in-vessel conducting structures  W c.q. PFCs < 315 MJ For fastest timescale of c.q. in ITER ~ 16 ms (exponential) 36 ms (linear) q rad max < 80 MWm -2 critical assumptions : W c.q. PFCs < 315 MJ, 100% radiation & peaking factor < 1.4

25. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 25 Mitigation of disruptions by massive gas injection is a promising scheme but may lead to large fluxes on PFCs  specification of wall loads for ITER not yet in PID Energy Fluxes to main wall and divertor PFCs during mitigated disruptions  Sugihara NF’07 assumes q rad = 0.5 – 1.0 GWm -2 in 1 ms  Estimates from Whyte for ITER predict ~ 4 GW/m 2 for  t rad < 200  s Whyte PRL’02

26. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 26 Runaway generation mechanisms for ITER like disruptions conditions studied in detail but runaway losses and dynamics are worse known  specification of local loads for ITER ? Runaway electron fluxes on PFCs (I)

27. Alberto Loarte 9 th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 27 Runaway electron fluxes on PFCs (II)  Runaway electrons are not generated if q 95 < 2-2.5 before current quench (no r.e. in full VDEs but likely in disruptions)  Runaway electrons are lost to PFCs by MHD turbulence when q edge = 3, 2 touches the wall  Runaway beam has a peaked current profile a r.e. ~ 0.25 a plasma and is vertically unstable  Runaway impact point determined by vertical instability of column and narrow e-folding length (~ few mm)  A eff ~ 0.5 m 2 (if toroidally symmetric)  Runaways are lost in bursts of ~ 100  s over ~ 5-10 ms timescales (JET and JT-60U) Unclear whether all these facts are taken into account in present PID specifications or not