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

2. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 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 q div (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

3. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 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 (?)

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

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

6. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 6 Proposed ITER specifications (M. Sugihara/M. Shimada) Scenario 2 : unit ( MJ/m 2 ) Energy release at TQ(1/2-1/3)W peak W peak  E // near separatrix at outer midplane 200 - 70 400 - 200  E // near upper ceiling region (6 cm from 1 st separatrix) 20 - 50 60 - 100  E // near lower baffle region (6 cm from 1 st separatrix) 16 - 40 48 - 80  E // to divertor plate near 1 st separatrix 280 – 90 (out) 375 – 120 (in) 560 – 280 (out) 750 – 380 (in) =2.5 cm (left), 5 cm (right)Total energy deposition time duration = 3-9 ms Energy Fluxes during disruptions (III)

7. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 7 Energy release at TQW peak (325 MJ)  E // near separatrix at outer midplane 510 - 255  E // near upper ceiling region (5 cm from 1 st separatrix) 120 - 160  E // near lower baffle region (5 cm from 1 st separatrix) 95 - 130  E // to divertor plate near 1 st separatrix 730 – 365 (out) 375 – 120 (in) =2.5 cm (left), 5 cm (right)Total energy deposition time duration = 3-9 ms Proposed ITER specifications (M. Sugihara/M. Shimada) Scenario 4 : unit ( MJ/m 2 ) Energy Fluxes during disruptions (IV) Plasma shift caused by beta collapse does not cause IW contact in ITER unlike JET experiments (P. Andrew)

8. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 8 Energy Fluxes during VDEs (I) JET ITER Presently proposed ITER specifications based on JET based extrapolations  input from other tokamaks needed   W 2 = 20-55 MJ   2 =  JET /  L-mode JET (0.03-0.09)*  L-mode ITER   W 3 = W(  2 )-dW/dt| L-mode *  3

9. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 9 Downward VDE with fast CQ - EM load on BM / DIV by eddy (+halo) current - Heat load on lower Be wall & W baffle Upward VDE with fast CQ - EM load on BM by eddy (+halo) - Heat load on upper Be wall during VDE and TQ Energy Fluxes during VDEs (II)

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

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

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

13. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 13 P wall (MW/m 2 ) Power deposited on the Wall Poloidal distance along wall (m) Radiation peaking Radiation during current quench (II) JET (A. Huber) But deposited power on the wall has a peaking factor of only 2

14. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 14 Predicted runaway current10 (MA) Energy spectrum of electrons (E0 for exp(-E/E0))12.5 MeV Inclined angle1 - 1.5  Total energy deposition due to runaway current20 MJ Average energy density deposition1.5 MJ/m 2 Duration of the average energy density deposition100 ms Maximum energy density deposition (end of the plasma termination)25 MJ/m 2 Duration of the maximum energy deposition10 ms Number of eventEvery major disruption  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 Runaway electron fluxes on PFCs (I)

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

16. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 16 Runaway electron fluxes on PFCs (III)  Significant drift of runaways near upper X-point due to poloidal field null [f(E) = 1/E 0 exp(-E/E 0 ) with E 0 = 12.5 MeV]  Angle of impact of runaways on drift orbits at upper X-point < 1.5 o but impact direction mainly toroidal

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

18. Alberto Loarte 10 th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 18 Major disruptions during limiter phase : (M. Sugihara/M. Shimada) Ip (MA)4.56.5 W peak (MJ)  10  20 P  ; peak energy density (MJ/m 2 )  7.7  15 Most severe assumption : No broadening of deposition width (Kobayashi NF 07) 2 limiter case Energy Fluxes during disruptions (V) If there is no broadening energy fluxes on limiter for disruptions can be similar or larger than for the divertor disruptions in scenario 2