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Alberto Loarte European Fusion Development Agreement Close Support Unit – Garching

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

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Alberto Loarte European Fusion Development Agreement Close Support Unit – Garching

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  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. Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 1

  2. Fluxes to limiter during Ramp-up/down (I) ITER PID only specifies Pmaxlimiters = 15 MW (max 9 MW on one limiter) • Reference ITER ramp-up(/down) has long limiter phases up to Ip = 7 MA (10 MA) in which plasma is limited by two limiters 180o apart (power loads & erosion) • 2 limiter configuration and qlim = 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 • PSOL for all ITER reference scenarios (ramp up/down with heating) • Scaling of SOL transport with Ip and R (JET extrapolation for Kobayashi NF 2007) Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 2

  3. Fluxes to main wall and divertor during diverted operation (I) ITER power and power fluxes estimated with B2-Eirene for a range of burn conditions (mainly QDT = 10) to maintain detachment but weak physics basis for SOL transport and main chamber fluxes • near SOL transport  lp = 5 mm (close to most pessimistic scalings 4 mm) for Ip = 15 MA (6 mm for scenario 3 (hybrid) and 8 mm for scenario 4 (ITB) if lp ~ Ip-1)  qII = 570 – 760 MWm-2 for PSOL = 100 MW (typical for scenarios 1 & 2) H-mode scenarios 1 & 2 Dwall = 5–20 cm  qIIwall < 0.04 MWm-2 lIB L-mode scenarios 1& 2 (PSOL=35 MW, lL=2 lH) & Dwall=5–20 cm qIIwall < 1.0 MWm-2 IIB 0.5o < a < 15o  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 lp Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 3

  4. Fluxes to main wall and divertor during diverted operation (II) Particle flux to ITER main wall expected to be > 1023 s-1 (> 1% of Gdiv) Lipschultz “Scarce” data & ITER B2-Eirene modelling : • n (Dsep ~ 5 cm) = 0.4 - 1.0 1019 m-3 • vSOL = 30 – 100 ms-1 • TSOL = 10 – 20 eV • lSOL = 4.5 – 21 cm • qII < few MW II B on (outer) first wall  local particle & power fluxes on edges and edges of ports ? • qperp < 0.3 MW m-2 < OK for FW panels Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 4

  5. Fluxes associated with heating systems and steady-state non-toroidal asymmetries w/o convection • NBI shine-through limit ne > 3.7 1019 m-3 (30% nGW) 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) P//=88kW P//=94kW (/20MW) • Integrated losses : typically 100kW for 20MW injected (low density case) • Localised peak at 10MW/m2; average ~2.5MW/m2 • 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! Q//=0.4|VRF|necs with convection Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 5

  6. Plasma Position and Shape Control In transient events 1 cm SOL field line touches first wall for 1 s If plasma in H-mode then depending on location of contact  plasma stays in H-mode or H  L transition sin a = 1-8 10-2 sin a = 1.5-2.5 10-1 in “minor disruptions” separatrix can touch dome for ~ 1 s qII in,dome ~ 380 - 570 MWm-2 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 6

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

  8. Fluxes to divertor during ELMs (II) Loarte, PPCF’03 DWELM < 30 MJ Eich application of Fundamenski PPCF’06 tdown,ELM = 1-2 trise,ELM Eich, PIPB’07 trise,ELM = 200-500 ms Adiv,ELM = 4 m-2 Broadening < 1.5 Eich, PIPB’07 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 8

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

  10. Fluxes to divertor during ELMs (III) Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 10

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

  12. Herrmann-AUG 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 ~ Llim/LSOL ? • qII in filament estimated with model by Fundamenski  required input to model : • nfil, Tfil, <vELM/cs,ped> & distance from sep @ filament detachment • Outstanding issues : • Relation VELM & DWELM vELM/cs,ped = 10-2DWELM/Wped or 1.5 10-3 (DWELM/Wped)0.5 • nfil, Tfil Rfil at instant of detachment & tELMWall (~ tELMdiv ?) • GwallELM sputtering Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 12

  13. Fluxes to main wall and divertor during Disruption thermal quench (I) PID specifications generally in line with current evidence from disruption loads but need to be refined to incorporate latest findings on divertor/wall loads • 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 ? Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 13

  14. Fluxes to main wall and divertor during Disruption thermal quench (II) • Plasma energy at t.q. typically less than 40% expected from H98 = 1 (Size scaling ?) • Dedicated experiments at JET in 2006/2007 show that Wt.q. < 0.4 W (Type I H-mode) for density limits, radiative limits and NTM driven disruption t.q. timescale has large scatter associated with MHD activity but similar to ELMs large amount of energy reaches PFCs after qmax JET-Riccardo NF’05 MAST-Counsell Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 14

  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 JET-Paley-PhD Thesis ‘07 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) Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 15

  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 ? JET Pulse No. 69816 ITB grad-P disruption PICRH (X 10 MW) PNBI (X 10 MW) Prad (X 100 MW) Wdia (MJ) Ip (MA) n = 1 (a.u.) n = 2 (a.u.) Mode-lock (a.u.) Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 16

  17. Disruptions in limiter phase Not considered in PID but potentially serious because of lack of broadening of power footprint for limiter disruptions (lt.q. < 1.5 ls.s.) TEXTOR-Finken NF 1992 Janos-TFTR-JNM 1992 Disruptive-normal discharge Normal discharge For lp > 2 cm  Aeff,limiters = 2.5 m2 (H. Pacher) • EOL-ramp-up : Ip = 7 MA, if Pinp = 5 MW  Wplasma (ITER-89) = 15 MJ • BOL-ramp-down : Ip = 10 MA, if Pinp = 7 MW  Wplasma (ITER-89) = 24 MJ Disruptions during limiter phases may cause loads > 6 – 10 MJm-2 with tt.q. ~ 1 ms Major issue for power fluxes during VDEs  needs to be confirmed Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 17

  18. Energy Fluxes to main wall and divertor PFCs during VDEs (I) Large discrepancy between PID specifications and new proposed specifications in Sugihara NF ‘07 e ~ 134 MJm-2s-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) • DWplasma (30-50 % of Wplasma) deposited on wall in Dt < tL-mode with lp ~ 1 cm • Plasma is in contact with wall in limiter L-mode PSOL = 100 MW + dW/dt • Plasma disrupts in limiters configuration when q ~ 1.5-2 with Wplasma > 100 MJ Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 18

  19. Energy Fluxes to main wall and divertor PFCs during Marfes (I) PID specifications for Marfe loads in ITER (physics model ?) Three types of “Marfes” expected in ITER (L-mode Plasma) : • Inner-wall Marfe  Potentially steady-state Prad < PSOL (100 MW) (<0.15MWm-2>) • X-point Marfe  Potentially steady-state Prad < PSOL (100 MW) (<0.15MWm-2>) • Pre-thermal quench divertor Marfe  short-lived (< 0.1 s in JET and AUG) period in which ~ 0.25 of Wplasma (H98 = 1) can be radiated  Prad ~ 900 MW (<1.3 MWm-2>) • Pre-thermal quench limiter Marfe  short-lived (< 0.1 s in JET) period in which a fraction (?) of Wplasma (H89 =1) can be radiated  Prad < 240 MW (<0.35 MWm-2>) • 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 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 19

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

  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 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 21

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

  23. Plasma Position and Shape Control (I) 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 SOB Minor disruption Appendix E qII 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 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 23

  24. a Energy Fluxes to main wall and divertor PFCs during current quench Most tokamaks find that close to 100 % of magnetic energy at t.q. is radiated with the exception of Alcator C-mod (< 25%) Wmag = ½ Lp Ip2 After t.q.  bp= 0 (0.2-pre), li~ 0.5 (0.85-pre), Ip <18 MA (15 MA-pre) Wmag < 1.85 GJ Most of Wmag V.V. and in-vessel conducting structures  Wc.q.PFCs < 315 MJ For fastest timescale of c.q. in ITER ~ 16 ms (exponential) 36 ms (linear) qradmax < 80 MWm-2 critical assumptions : Wc.q.PFCs < 315 MJ, 100% radiation & peaking factor < 1.4 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 24

  25. Energy Fluxes to main wall and divertor PFCs during mitigated disruptions 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 • Sugihara NF’07 assumes qrad = 0.5 – 1.0 GWm-2 in 1 ms • Estimates from Whyte for ITER predict <qrad> ~ 4 GW/m2 for Dtrad < 200 ms Whyte PRL’02 Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 25

  26. Runaway electron fluxes on PFCs (I) 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 ? Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 26

  27. Runaway electron fluxes on PFCs (II) • Runaway electrons are not generated if q95 < 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 qedge = 3, 2 touches the wall • Runaway beam has a peaked current profile ar.e. ~ 0.25 aplasma and is vertically unstable • Runaway impact point determined by vertical instability of column and narrow e-folding length (~ few mm)  Aeff ~ 0.5 m2 (if toroidally symmetric) • Runaways are lost in bursts of ~ 100 ms over ~ 5-10 ms timescales (JET and JT-60U) • Unclear whether all these facts are taken into account in present PID specifications or not Alberto Loarte 9th ITPA Divertor and SOL Physics Meeting IPP-Garching 7-10/5/2007 27

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