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CCIC-03 - A few excerpts from…

CCIC-03 - A few excerpts from…. Edge Power Fluxes in ITER : Implications for TBM Alberto Loarte ITER Fusion Science and Technology Department with thanks to : M. Sugihara, R. Pitts, A. Kukushkin, M. Shimada, C. Lowry, R. Mitteau, M. Pick, C. Kessel, G. Saibene, A. Portone, …. Outline of Talk.

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CCIC-03 - A few excerpts from…

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  1. CCIC-03 - A few excerpts from… Edge Power Fluxes in ITER : Implications for TBMAlberto LoarteITER Fusion Science and Technology Departmentwith thanks to : M. Sugihara, R. Pitts, A. Kukushkin, M. Shimada, C. Lowry, R. Mitteau, M. Pick,C. Kessel, G. Saibene, A. Portone, ….

  2. Outline of Talk • Introduction • Expected power fluxes to TBM frame and TBM during steady-state phases (H(He), D and DT phases) • Expected power fluxes to TBM frame and TBM during transient phases (H(He), D, and DT phases) • Conclusions

  3. New ITER ramp-up/down plasma scenarios • Development of low li ramp-ups an control of VS during ramp down  heating during current ramp-up/down • Full-bore ramp-up with divertor configuration from Ip ~ 3.5 MA • Maintaining divertor configuration as long as possible in ramp-down 5 MW (10-30 s), 10 MW (30-50 s), 15 MW (50-75 s), 20 MW (75-100s) Wb saving : 25 (ICRH), 34 (ECRH), 39 (LHCD) C. Kessel A. Portone

  4. Assumptions for calculations of TBM power fluxes • Power fluxes to TBM depend on detailed first wall design and detailed specifications of plasmas in all phases of ITER scenarios not yet fully developed • Highest fluxes on TBMs when 2-port limiters are retracted  estimates performed for this case (need for 2-port limiters being re-evaluated as part of FW design) • Plasma regimes considered during ITER operation phases • 7.5 MA/2.65T L-mode with <ne> = 0.4 nGW and Pinp < 50 MW (H) • 7.5 MA/2.65T L-mode with <ne> = 0.4 nGW and Pinp < 50 MW (He, D) • 7.5 MA/2.65T Type I ELMy H-mode with <ne> = 0.85 nGW and Pinp = 73 MW (He, D) • 15 MA/5.3T L-mode with <ne> = 0.4 nGW and Pinp < 73 MW (H, He, D) • 15 MA/5.3T Type I ELMy H-mode <ne> = 0.85 nGW and Pinp < 50 MW (DT) • 9MA/5.3T advanced scenario with and Pinp < 60 MW (DT) • Power fluxes to TBM and TBM frame in shadow of blanket modules evaluated • Plasma fluxes parallel to B  fluxes on structures depend on geometry  examples given for fluxes on TBM recessed 5 cm from separatrix & 3o impact angle • Radiation and charge-exchange fluxes perpendicular to TBM • Plasma fluxes versus local separatrix position at TBM port (separatrix deviation by ripple < 12 mm  see J. Snipes’ presentation)

  5. Power fluxes to main wall in limiter phases • Limiter phases during ramp-up (5 MA) and ramp-down (7.5 MA) in ohmic or with low level of heating (PSOL (MW) < Ip (MA)) for FW design • Power width scaling from divertor (~18 limiter) L-mode discharges (IPB) a) <ne>/nGW = 0.2, b) qlim ~ 3.45*(15/Ip(MA))0.7, c) Plim(MW) = Ip (MA), d) Zeff = 1.0+1.1/<ne>(1019m-3) Main SOL Limiter Shadow lp in limiter shadow ~ mm Positioning frame and TBM few cm in limiter shadow decreases plasma power to negligible values

  6. Steady-state power fluxes to main wall during diverted phases (I) • Power fluxes to main wall between ELMs dominated by far-SOL turbulent transport and long tails in density profiles • Physics model to extrapolate far-SOL transport to ITER being developed  empirical extrapolation of measurements + B2-Eirene modelling Parameters at line contacting the wall from B2-Eirene simulations for QDT = 10 • Te,w = 10-20 eV, Ti,w/Te,w ~ 2 • nw = 0.5-1.5 1019m-3 • VSOL < 100 ms-1 lq-far SOL ,mp = LcvSOL/cs,w< 0.17 m (for 15 MA H-mode)

  7. Steady-state power fluxes to main wall during diverted phases (II) • Upper levels of power fluxes for other regimes based on empirical scalings of plasma parameters and from B2-Eirene results for QDT =10  further work is needed • Prad,bulk ~ <ne>2 • In far-SOL  Te ~ 10 -20 eV (Ti/Te ~ 2) • ln,H-mode (QDT= 10) = 2.5 – 6.5 cm • ln,L-mode = 2 ln,H-mode • ln ~ Ip-1 • ne,sep ~ 1/3 <ne> • lq far-SOL,mp < vSOL*Lc/Lc(q=3)*(mxx/mDT)1/2 ASDEX Upgrade Neuhauser PPCF 2005 H-mode (Type I)

  8. Steady-state power fluxes to main wall during diverted phases (III) • Plasma power parallel fluxes parallel to B near outer midplane wall in the range of 1-4 MWm-2 for all phases of operation (H  DD & He  DT) • Decay of power fluxes (IIB) in limiter shadow strongly dependent on dominant transport mechanism • lshadow < 1 cm for convective transport (lshadow ~ Llim/Lc) • lshadow ~ 2 - 5 cm for convective transport (lshadow ~ (Llim/Lc)1/2) Steady plasma power flux onto TBM negligible (5 cm, 3o) < 0.02 MWm-2 DRsep (1st field line conn to wall)

  9. ELM power fluxes to main wall during diverted phases trise • Divertor damage avoidance during ELMs  tolerable ELMs restricted in size • 15 MA QDT = 10  DWELM = 1 MJ & fELM = 20 - 40 Hz • 9 MA QDT = 5  DWELM = 2.4 MJ & fELM = 8 - 17 Hz • 7.5 MA H-mode  DWELM = 2.4 MJ & fELM = 5 - 10 Hz • Occasional uncontrolled ELMs : ~ 20 MJ (15 MA & QDT =10), ~ 7 MJ (9 MA & QDT = 5), ~ 4 MJ (7.5 MA & H-mode) • Controlled ELM power flux on TBM negligible (5 cm, 3o) • < 0.01 MWm-2 • Uncontrolled ELM damage to TBM unlikely (5 cm, 3o) • < 0.005 MJm-2 Controlled ELMs

  10. Power fluxes by charge-exchange • Charge-exchange fluxes estimated by B2-Eirene for QDT =10 and empirical scaling of total plasma outflux from nW and vSOL~ 1 order of magnitude uncertainty, with upper range in agreement with present experimental evidence • Charge-exchange power flux is maximum near the outer midplane • Charge-exchange atom flux ~ normal to wall  receding TBM does not change loads much • For QDT = 10  typical C-X atom energy in the range 1 - 1.6 keV (Tped ~5 keV)  beyond sputtering threshold (TBM erosion ?)

  11. Power fluxes by radiation • Maximum radiative loads in main chamber limited by to 60% Pinp for L-mode and by L-H transition power for high confinement regimes (70 MW (QDT = 10) , 50 MW (QDT = 5), 30 MW (D), 40 (He)) • Highest radiation loads during steady-state Marfes (assuming performance is maintained which is unlikely)  no any other additional power flux to the wall • Radiation peaking < 2 for normal conditions and < 3 for Marfes • Average radiation flux ~ normal to wall  receding TBM does not change loads much

  12. Power Fluxes during disruptions : Thermal quench (I) trise • Energy fluxes to first wall during disruption determined by : • Maximum plasma energy at thermal quench : 0.8 Wplasma for L-mode (typical 0.4), 0.5 Wplasma for H-mode (typical 0.25), Wplasma for advanced regimes • Broadening of the power flux footprint wrt full performance < 10 trise = 1.5 ms Maximum absolute fluxes Typical fluxes a factor of 2 lower for all regimes except 9MA advanced scenario high b disruptions Even worse case disruption loads are unlikely to damage TBM (5 cm, 3o) < 0.01 MJm-2

  13. Power Fluxes during disruptions : Current quench • Power fluxes during current quench dominated by plasma radiation of the plasma poloidal magnetic energy ~ 550 MJ (15 MA), 190 MJ (9 MA), 140 MJ (7.5 MA) • Shortest time duration of current quench [Ip/(dIp/dt)] ~ 16 ms  tEc.q. ~ 8 ms • Peaking of radiation during current quench < 3 • Average radiation flux ~ normal to wall  receding TBM does not help much Even high Ip cases with high peaking at TBM (unlikely) are not expected to cause significant Be melting  more detailed modelling for TBM could be done if needed

  14. Conclusions • Studies carried out following ITER Design review have lead to re-specification of power fluxes to ITER PFCs • The design of the first wall has been modified for power fluxes IIB leading to higher power fluxes in some areas (upper X-point during diverted operation, outer side during ramp-up/down, etc.) • Power fluxes to TBM frame and TBM following same methodology as FW fluxes have been derived for steady and transient phases of ITER discharges • Present recession of ~ 5 cm beyond separatrix position at TBM is sufficient to maintain plasma fluxes to very low values (avoidance of edges on TBM face is advisable) both for steady-state and transients • Main power fluxes loads are radiative and C-X (erosion ?) • Typical values of ~ 0.3 MWm-2

  15. SOL Profiles QDT = 10 B2-Eirene simulations for a large range of conditions B2-Eirene V. Kotov

  16. ELM control and material damage J. Linke Control of ELM fluxes to divertor from material damage and experimental measurements in tokamaks • Material damage to CFC and avoidance of edge melting in macrobrushes  for controlled ELMs Ediv < 0.5 MJm-2 • ELM experimental measurements Ediv < 0.5 MJm-2  DWELMcontrol < 1 MJ (x 20 smaller than uncontrolled) R. Dejarnac- PIC simulations 0.5 mm gap, T ~ 2.5 KeV A. Kukushkin et al.

  17. ELM power fluxes to main wall during diverted phases (IV) • Basic design criteria EII,ELM(DRsep = 5 cm) < 0.1 EII,ELM(DRsep = 0 cm) A. Kirk Calculated with Fundamenski PPCF’06 Pcontrolled-ELMwall < 0.1 PELM < 4 MW

  18. ELM power fluxes to main wall during diverted phases (V) • Filament impact leads to concentrated power deposition • Typical FWHM = 0.25-0.5 ELM filament spacing • Random impact reduces average ELM power flux by 1.7-3.1  ELM filament impact overlap leads higher heat flux than average JET- R. Pitts. PSI’08 • <q||,ELMupper-X>= 12-24 MWm-2 (Dt < 0.5 s with q||,ELMupper-X = 16-32 MWm-2)

  19. ELM power fluxes to main wall during diverted phases (I) • Divertor damage avoidance during ELMs  tolerable ELMs restricted in size • 15 MA QDT = 10  DWELM = 1 MJ & fELM = 20 - 40 Hz • 9 MA QDT = 5  DWELM = 2.4 MJ & fELM = 8 - 17 Hz • 7.5 MA H-mode  DWELM = 2.4 MJ & fELM = 5 - 10 Hz • Occasional uncontrolled ELMs : ~ 20 MJ (15 MA & QDT =10), ~ 7 MJ (9 MA & QDT = 5), ~ 4 MJ (7.5 MA & H-mode) • Determination of ELM fluxes to main wall main wall by “validated” models but uncertainties remain  allowance for these in specifications • Basic design criteria • EII,ELM(DRsep = 5 cm) < 0.1 EII,ELM(DRsep = 0 cm) • lELM = 2.5 – 9.0 cm

  20. ELM power fluxes to main wall during diverted phases (II) • Filament impact leads to concentrated power deposition • Typical FWHM = 0.25-0.5 ELM filament spacing • Random impact reduces average ELM power flux by 1.7-3.1  ELM filament impact overlap leads to higher heat flux than average but for short periods (0.5 s for 40 Hz) JET- R. Pitts. PSI’08

  21. ELM power fluxes to main wall during diverted phases (III) trise • ELM plasma power fluxes parallel to B near outer midplane wall ~ 6 MWm-2 for DT and ~ 2 MWm-2 for DD/He • Energy fluxes parallel to B for uncontrolled ELMs in limiter shadow can cause melting of exposed edges • Decay of ELM fluxes (parallel to B) in limiter shadow strongly dependent on dominant transport mechanism • lshadow < 2-5 mm for convective transport (lshadow ~ Llim/Lc) • lshadow ~ 1 - 2 cm for diffusive transport (lshadow ~ (Llim/Lc)1/2)

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