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Specification of ITER disruption/VDE Thermal Loads

Update on Thermal Loads during disruptions and VDEs A. Loarte with contributions from M. Sugihara , A. Herrmann, G. Arnoux, T. Eich, G. Counsell, G. Pautasso, V. Riccardo, etc. Specification of ITER disruption/VDE Thermal Loads.

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Specification of ITER disruption/VDE Thermal Loads

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  1. Update on Thermal Loads during disruptions and VDEsA. Loarte with contributions from M. Sugihara, A. Herrmann, G. Arnoux, T. Eich, G. Counsell, G. Pautasso, V. Riccardo, etc. Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 1

  2. Specification of ITER disruption/VDE Thermal Loads • New ITER specifications for disruptions and VDEs take into account latest physics findings • Pre-disruptive confinement degradation for H-mode disruptions • Footprint broadening at thermal quench • qdiv(t) at thermal quench • Radiation asymmetries in current quench • Plasma evolution to thermal quench in VDEs and broadening of footprint • Impact geometry of runaway electrons • etc. Some issues still poorly understood or restricted database : asymmetries, runaway power fluxes, thermal quench limiter disruptions ,etc.  Advice from ITPA required Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 2

  3. Energy Fluxes during disruptions (I) • Energy degradation before thermal quench for resistive MHD disruptions (not for ITBs) • Large broadening of footprint for diverted discharges but small for limiter discharges (?) Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 3

  4. Effect of background radiation A. Herrmann J. Paley, P. Andrew Energy to upper X-point(DRmp ~ 3.5 cm ) JET- G. Arnoux More systematic studies of power flux broadening required Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 4

  5. 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 Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 5

  6. Energy Fluxes during disruptions (III) Proposed ITER specifications (M. Sugihara/M. Shimada) Scenario 2 : unit (MJ/m2) =2.5 cm (left), 5 cm (right) Total energy deposition time duration = 3-9 ms Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 6

  7. Plasma shift caused by beta collapse does not cause IW contact in ITER unlike JET experiments (P. Andrew) Energy Fluxes during disruptions (IV) Proposed ITER specifications (M. Sugihara/M. Shimada) Scenario 4 : unit (MJ/m2) =2.5 cm (left), 5 cm (right) Total energy deposition time duration = 3-9 ms Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 7

  8. Energy Fluxes during VDEs (I) ITER JET Presently proposed ITER specifications based on JET based extrapolations  input from other tokamaks needed • DW2 = 20-55 MJ • t2 = tJET/tL-modeJET (0.03-0.09)*tL-modeITER • DW3 = W(t2)-dW/dt|L-mode*t3 Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 8

  9. Energy Fluxes during VDEs (II) Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 9

  10. JET-Arnoux ∫q(romp)dr Power width = qmax Energy Fluxes during VDEs (III) • Indications of broadening of power footprint at VDE thermal quench AUG-Herrmann Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 10

  11. JET-Paley-PhD Thesis 2006 JET-P. Andrew JNM 2007 Energy Fluxes during current quench (I) During current quench plasma magnetic energy is lost Part of Wmag transferred to conductors  Wohmic = Wmag-Wconductors  plasma heating JET-Pulse No. 69787 • Most tokamaks/disruptions Wohmic lost by Prad (except high Bf/high Z Alcator C-mod) Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 11

  12. Energy Fluxes during current quench (II) JET (A. Huber) #69787 During current quench the radiation distribution is poloidally asymmetric Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 12

  13. 3.5 3.0 t=66.869s t=66.861s 3.0 2.5 t=66.869s t=66.872s t=66.872s 2.5 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 0.0 0 2 4 6 8 10 Radiation during current quench (II) JET (A. Huber) Pwall(MW/m2) Power deposited on the Wall Radiation peaking But deposited power on the wall has a peaking factor of only 2 Poloidal distance along wall (m) Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 13

  14. Predicted runaway current 10 (MA) Energy spectrum of electrons (E0 for exp(-E/E0)) 12.5 MeV Inclined angle 1 - 1.5 Total energy deposition due to runaway current 20 MJ Average energy density deposition 1.5 MJ/m2 Duration of the average energy density deposition 100 ms Maximum energy density deposition (end of the plasma termination) 25 MJ/m2 Duration of the maximum energy deposition 10 ms Number of event Every major disruption Runaway electron fluxes on PFCs (I)  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 Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 14

  15. EFIT reconstruction by S. Gerasimov Runaway electron fluxes on PFCs (II) Current profile during runaway discharge peaks (seen at JET)  X-point formation in Scenario 2 Smith PoP 2006 Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 15

  16. Runaway electron fluxes on PFCs (III) • Significant drift of runaways near upper X-point due to poloidal field null [f(E) = 1/E0exp(-E/E0) with E0 = 12.5 MeV] • Angle of impact of runaways on drift orbits at upper X-point < 1.5o but impact direction mainly toroidal Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 16

  17. Conclusions • PID specifications for PFC loads during disruptions and VDEs in ITER being updated following ITER Design Review Process • Key issues for further refinement of disruption thermal quench loads are timescales, broadening, asymmetries and dependence on pre-disruptive plasma conditions • For current quench level  distribution of radiative and conducted loads to be studied systematically • Specifications for VDEs are now based on real H-mode plasma observations but more multi-machine data is required • Dedicated studies on runaway loads during disruptions are required to provide a firmer base of ITER specifications Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 17

  18. Energy Fluxes during disruptions (V) Major disruptions during limiter phase : (M. Sugihara/M. Shimada) (Kobayashi NF 07) 2 limiter case Most severe assumption : No broadening of deposition width If there is no broadening energy fluxes on limiter for disruptions can be similar or larger than for the divertor disruptions in scenario 2 Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 18

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