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Extrapolation of RF-relevant ELM characteristics from JET to ITER Alberto Loarte

Extrapolation of RF-relevant ELM characteristics from JET to ITER Alberto Loarte. Outline. Review of material erosion by ELM-like loads, expected ELM power fluxes in ITER and requirements for ELM control

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Extrapolation of RF-relevant ELM characteristics from JET to ITER Alberto Loarte

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  1. Extrapolation of RF-relevant ELM characteristics from JET to ITERAlberto Loarte

  2. Outline • Review of material erosion by ELM-like loads, expected ELM power fluxes in ITER and requirements for ELM control • Expected ELM characteristics in ITER and “similar” experiments at JET  test of ILA for ITER • Other ITER ICRH-relevant pedestal issues to be considered for JET experiments  use of ILA for resolving ITER Physics questions

  3. CFC Erosion 0.65 MJm-2 CFC erosion caused by evaporation of material at high Tsurf and enhanced by 3-D effects N. Klimov + B. Bazylev + Federici • Real erosion threshold for NB31 CFC ~ 0.5-0.6 MJm-2 • Assume no ELM-caused erosion (beyond sputtering) up to ~ 0.6 MJm-2 dELM (mm) = 3.05 (EELM (MJm-2) – 0.6)2

  4. W erosion J. Linke 0.9 MJm-2 after 100 ELMs T. Hirai, J. Linke Damage threshold for W tentatively set ~ 0.5 MJm-2 • Local W erosion up to 1.0 MJm-2 dominated by edge melting and displacement along edges (30o in QSPA vs. ~ 3o in ITER). In QSPA Eedge/Eface ~ 2 • Net W erosion dominated by evaporation in absence droplet loss • W cracking from 0.2 MJm-2 but severity of problem increases beyond 0.7 MJm-2 and more when molten layer is formed  consequences for PFC and plasma unknown 1.0 MJm-2 before 0.5 MJm-2 R. Dejarnac- PIC simulations 0.5 mm gap, T ~ 2.5 KeV after 20 ELMs after 100 ELMs 1mm 1mm N. Klimov, T. Hirai, J. Linke Plasma impact direction

  5. Basis for definition of controlled ELMs in ITER (I) Time scale of divertor ELM energy flux rise correlated with ion transport time + sheath physics T. Eich – JNM 2007 T. Eich –PIPB 2007 trise,ELM = 200-500 ms Plasma conditions affect tELMIR ~ tII relation (pre-ELM divertor plasma, DWELM, etc.)

  6. Basis for definition of controlled ELMs in ITER (II) • Tolerable ELM energy density 0.5 MJm-2 + no broadening + 2:1 in/out asymmetry +toroidal symmetry •  DWELM ~ 1MJ • PELM ~ 0.2-0.4 Pedge • fELM ~ 20-40 Hz • 8000-16000 ELMs per QDT=10 shot uncontrolled ELMs controlled ELMs QDT =10 discharges in ITER will have ~ 104 controlled ELMs + few uncontrolled ELMs

  7. Expected ELM characteristics in ITER and basis for ILA experiments (I)  >ron all devices A. Kirk  r Data not incompatible with scaling with machine size

  8. Expected ELM characteristics in ITER and basis for ILA experiments (II) n = 20 Snyder NF’04 • HWFM poloidal extent typically ~ 25-50% distance between filaments • Expected values for ITER ITER (from Snyder results in NF’04) : • D distance between filaments (m) ~ 15/n •  full filament poloidal width (m) = (3.5-7)/n

  9. Expected ELM characteristics in ITER and basis for ILA experiments (III) JET-ILA experiments should demonstrate ELM resilience over a similar range of D/Hantenna and /Hantenna as expected in ITER (n = 10 – 40/50) ELM precursors depend on n*ped • ILA experiments (NBI dominated ?) expanding current range (Ip ~ 1.5 – 3.5 MA)

  10. Expected ELM characteristics in ITER and basis for ILA experiments (IV) • Precise value of energy flux on the wall depends on many parameters : plasma parameters at filament detachment, radial propagation velocities, losses IIB, duration of power pulse (losses IIB, filament dimension, propagation velocity) which are poorly known • Estimate for ITER based on simple model + uncertainties Fundamenski, Pitts PPCF’06

  11. Expected ELM characteristics in ITER and basis for ILA experiments (V) • Density and temperature in filaments near ITER ICRH antenna Loarte, ITER design review Fundamenski, Pitts PPCF’06 ELM nfil ~ 0.3  0.1 1020 m-3 (uncont.  controlled ELMs) Te,fil ~ 20  250 eV (uncont.  controlled ELMs) Te, far-SOL = 10-20 eV Ti,fil ~ 70  700 eV (uncont.  controlled ELMs) Ti, far-SOL = 20-40 eV

  12. Expected ELM characteristics in ITER and basis for ILA experiments (VI) A. Kirk Results of Monte Carlo simulation for an ITER equilibrium with a plasma wall gap of 6cm Assumed: filaments start with Ti= 1.5 keV and remain connected to the LCFS for 100 ms – followed by radial velocity of 0.5 or 1 kms-1 At time of separation 12 filaments each carry 2.5 % of total loss • Initial local perturbation caused by ELMs at wall typically is expected to have a timescale of ~ 100 – 200 ms • Post-ELM recycling ne increase can last ~ 10 times longer

  13. Expected ELM characteristics in ITER and basis for ILA experiments (VII) JET-ILA experiments should demonstrate ELM resilience over a similar range of nfil/nfar-SOL and Tfil/Tfar-SOL as expected in ITER JET  Ti (DRsep ~ 4 cm) ~ 0.2-0.5 Ti,ped • Experiments at Ip > 3.0 MA to match nped, Tped • ROG scans to vary nfilwall,Tfilwall/nped • Experiments at lower current Ip < 3.0 MA nfil, Tfil for controlled ELMs • ROG scans to vary nfilwall,Tfilwall/nped Resilience of ICRH coupling to (large) pellets needs to be demonstrated too !

  14. ICRH-relevant pedestal plasma issues for ITER (I) • Extrapolation of ELM and pedestal characteristics from present experiments to ITER based on NBI dominated H-modes • Significant contribution from ILA (PICRH ~ 10 MW) to ITER Physics Basis (no input torque, no particle fuelling)

  15. ICRH-relevant pedestal plasma issues for ITER (I) • Extrapolation of ELM and pedestal characteristics from present experiments to ITER based on NBI dominated H-modes • Significant contribution from ILA (PICRH ~ 10 MW) to ITER Physics Basis (no input torque, no particle fuelling, e-heating) • Role of toroidal rotation on pedestal plasma and ELM characteristics • Achievement of high densities and good confinement without NBI fuelling • Plasma performance with e-heating alone

  16. ICRH-relevant pedestal plasma issues for ITER (II) JT-60U and other devices report effects on ELMs and pedestal parameters caused by rotation but whether rotation/ripple/ion losses is unclear (NBI dominated plasmas)

  17. ICRH-relevant pedestal plasma issues for ITER (III) Previous experiments at JET did not show clear effects (but small ELMs to get good ICRH coupling)

  18. ICRH-relevant pedestal plasma issues for ITER (IV) • Gas fuelling in ITER • SOL plasma in ITER is dense and hot  thick to gas puff • Most of fuel gas ionised in far SOL and does not reach separatrix Typically < 10% of fuelled gas reaches separatrix (Ggas ~ Grecycling)

  19. ICRH-relevant pedestal plasma issues for ITER (V) • Core fuelling of ITER Typically GDT_p ~ 40% GDT_s ~ 5 Pa m3 s-1 missing ~ 50 Pa m3 s-1 by pellets

  20. ICRH-relevant pedestal plasma issues for ITER (VI) Possible ITER-relevant experiments at JET : • One-to-One comparison of NBI heated vs ICRH heated discharges at Padd ~10 MW with Ip ~ 2 MA • role of toroidal rotation on pedestal plasma and ELM characteristics • Achievement of high densities and good confinement without NBI fuelling (gas vs. pellet) • Plasma performance with e-heating alone and good e-i coupling at high <ne>

  21. ICRH-relevant pedestal plasma issues for ITER (VII) • One-to-One comparison of NBI dominated vs NBI/ICRH heated discharges at Padd ~ 20 MW with Ip > 3 MA • role of toroidal rotation on pedestal plasma and ELM characteristics • Achievement of high densities and good confinement with gas fuelling and pellet fuelling at ITER-like nped, Tped

  22. Conclusions • JET ILA antenna experiments can provide key input to the feasibility of ICRH heating of ITER H-mode plasmas • Key issues for ITER can be address by suitable set of plasma conditions at JET (Ip, <ne> and ROG) • If JET ILA performs and allows PICRH > 10 MW in JET H-mode plasmas over large range of conditions  key physics questions regarding pedestal, ELMs, fuelling, momentum and energy transport in ITER e-heated H-mode plasmas can be addressed in JET

  23. W = 0.25 <EELM> = 0.32 EELMmax W = 0.5 <EELM> = 0.59 EELMmax Expected ELM characteristics in ITER and basis for ILA experiments (VIIb) • Typical ELM power footprint FWHM/separation = 0.25-0.5 • ELMs impact randomly on the main wall  decreases of average heat load by ELMs • Periods with consecutive ELMs hitting the same place < 0.5 s

  24. Basis for definition of controlled ELMs in ITER (IIb) ELM losses show variability but dependence on plasma conditions remains to be studied JET- A. Loarte, APS 2003 JET- R. Pitts (large ELM experiments) Large ELMs Small ELMs Due to material erosion being a threshold effect  controlled ELMs need to be small on average but also highly reproducible If <DWELM> = 1.0 MJ & fELM = 20 Hz & 1% of ELMs at 2 MJ CFC divertor lifetime 400 QDT = 10 pulses

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