1. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 1 Report on EU-PWI SEWG on Transient Loads Alberto Loarte European Fusion Development Agreement Close Support Unit - Garching Contributors to SEWG : CEA : F. Saint-Laurent CRPP : R. Pitts ENEA : G. Maddaluno IPP : G. Pautasso, A. Herrmann, T. Eich ITER : G. Federici, G. Strohmayer FZJ : K.H. Finken, M. Lehnen, J. Linke, T. Hirai FZK : I. Landman, S. Pestchanyi, B. Bazylev UKAEA : V. Riccardo, P. Andrew, W. Fundamenski, G. Counsell, A. Kirk

2. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 2 Outline 1. Summary of work in 2006 Effects of transient loads on materials Characterisation of ELM loads Characterisation of Disruption loads Disruption mitigation 2. Plans for 2007 3. Conclusions

3. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 3 Expected transient loads at ITER divertor/first wall are uncertain but have strong implications for PFC lifetime Expected loads in ITER transients (I) Raclette - G. Federici & G. Strohmayer Be

4. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 4 As guideline for experiments the following energy ranges and plasma impact energies have been defined Divertor target (CFC and W without/with Be coatings) Type I ELM : 0.5 – 4 MJ/m 2, t = 300-600 s, E e ~ E i ~ 3 – 5 keV Thermal quench : 2.0 – 13 MJ/m 2, t = 1-3 ms, E e ~ E i ~ 3 – 5 keV Main wall (Be) Type I ELM : 0.5 – 2 MJ/m 2, t = 300-600 s, E e ~ 100 eV, E i ~ 3 keV Thermal quench : 0.5 – 5 MJ/m 2, t = 1-3 ms, E e ~ E i ~ 3 – 5 keV Mitigated disruptions : 0.1 – 2.0 MJ/m 2, t = 0.2-1 ms, radiation Expected loads in ITER transients (II)

5. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 5 FZJ e-beam Judith facilities J. Linke T. Hirai

6. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 6 QSPA facility provides adequate pulse durations and energy densities. It is applied for erosion measurement in conditions relevant to ITER ELMs and disruptions Plasma flow Target Diagnostic windows Vacuum chamber 60 0 The diagram of QSPA facility View of QSPA facility Plasma parameters (ELMs +Disruptions): Heat load 0.5 – 2 MJ/m 2 / 8 – 10MJ/m 2 Pulse duration0.1 – 0.6 ms Plasma stream diameter 5 cm Magnetic field0 T Ion impact energy 0.1 keV Electron temperature< 10 eV Plasma density 10 22 m -3 / 10 22 m -3 Conditions for ITER ELMs & disruptions not easily reproducible in tokamaks QSPA reproduces : Energy density & Timescale with plasma pressure ~ 10 too high nT 3/2 | QSPA =nT 3/2 | ITER but T| ITER =10-100 x T| QSPA TRINITI facilities QSPA (I)

7. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 7 The energy density distribution on CFC surface,% The energy density distribution on W surface,% Typical energy density profile on CFC surface X,Y, cm 2 Energy densirt, MJ/m 2 X,Y, cm 2 Energy densirt, MJ/m 2 Typical energy density profile on W surface,% TRINITI facilities QSPA (II)

8. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 8 Typical micrographs of the tungsten droplets tracks Surface of the sample Plasma stream direction 3 ms after first shot Mass loss 67 mg/shot Surface of the sample Plasma stream direction 3 ms after 60 th shot Mass loss 2 mg/shot During the first shot droplets ejected mainly from the edges of the tiles. As a result of edge smoothing and bridging of gaps the droplet ejection was reduced and mass losses were decreased. TRINITI facilities QSPA (III)

9. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 9 TRINITI facilities QSPA (IV) W and CFC erosion at ~ 1.5 MJm -2 QSPA can reproduce plasma-interaction processes at ITER-like load levels : Melt layer displacement under plasma pressure Vapour shielding formation and effects on damage development Extrapolation to ITER requires modelling (Pressure too high, no magnetic field, etc.)

10. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 10 1.Under ITER-like heat loads erosion of CFC was determined mainly by the erosion of PAN-fibers: 2.Noticeable mass losses of a sample took place at an energy density of 1.4 MJ/m 2 3.Severe crack formation was observed at energy densities 0.7 MJ/m 2 (cracking of pitch fibre bundles) energy density / MJm -2 0.51.0 1.5 negligible erosion erosion starts at PFC corners PAN fibre erosion of flat surfaces after 100 shot significant PAN fibre erosion after 50 shots PAN fibre erosion after 10 shots CFC CFC results

11. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 11 1.Under ITER-like heat loads erosion of tungsten macrobrush was determined mainly by melt layer movement and droplets ejection: 2.Noticeable W erosion mainly due to droplet formation took place at w max = 1.6 MJ/m 2. The average erosion was approx. 0.06 μm/shot (1 μm/shot during the first shot, and then decreased to 0.03 μm/shot after 40th pulse). 3.Cracks formation was observed at energy densities 0.7 MJ/m 2. Metallographic sections show crack depths ranging from 50 to 500 µm. energy density / MJm -2 0.51.0 1.5 negligible erosion melting of tile edges melting of the full tile surface (no droplet ejection) droplet ejection and bridging of tiles after 50 shots W W results

12. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 12 ELMs in JET cause significant impurity influx (& deposition) particularly when ~ 1MJ ELMs is reached Impurity generation and deposition by ELMs can dominate in ITER even if target lifetime is OK 0.15 g-C/ELM 150 g-C per shot Determination of impurity influx and C-deposition during ELMs (W & C comparison) ELMs erosion/deposition and impurity influxes

13. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 13 Main plasma ELM energy loss W ELM correlated with n ped, T ped (, ) & transport loss mechanism Conduction Convection Convective ELMs obtained so far in regimes not compatible with ITER Q DT = 10 scenario i) q 95 ~ 3 (I p ~ 15 MA) but too high * (~ n/T 2 ) or ii) low * but q 95 > 4 (I p ~ 11 MA)

14. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 14 During ELM event energy flows to divertor target and main chamber PFCs e,i losses along B to divertor Inner divertor Outer divertor ASDEX Upgrade Herrmann e,i losses along B to divertor i losses across B to main wall v ELM ~ km/s ASDEX Upgrade Herrmann PPCF 2004 Kirk PPCF ELM power fluxes to PFCs (I)

15. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 15 Eich JNM 2005 Loarte PoP 2004 q ELM,div (t) more than 60% of W ELM,div arrives after q ELM,div max smaller T surf ELM Fundamenski PPCF 2006 Energy balance of ELM divertor power pulse in agreement with PIC simulations

16. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 16 Eich PSI 2006 ELM energy deposition at divertor in/out asymmetric asymmetry depends on B direction but extrapolation of observations to next step devices remains unclear In/out asymmetries of ELM divertor power fluxes

17. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 17 Formation and dynamics of ELM filaments and energy deposition at main chamber starts to be well diagnosed ELM energy fluxes to main chamber PFCs (I) V tor ~ 0 before filament leaves LCFS v r goes from 0 at LCFS to 1–3 km Filaments leave LCFS at different times MAST-Kirk Energy flux to the wall by individual filaments Herrmann-AUG Energy per filament < 2.5 % W ELM (MAST)

18. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 18 JET-IR Eich ELM energy deposition at main chamber given by competition of parallel and perpendicular transport (JET-Fundamenski + Pitts validated model) larger V ELM (M ELM ) larger W ELM wall ELM energy fluxes to main chamber PFCs (II) AUG-Kirk Correlation between v ELM and W ELM found experimentally : v ELM /c s ~ ( W ELM /W ped ) with > 1 (deduced from DIII-D, Loarte IAEA 2006) v ELM /c s ~ ( W ELM /W ped ) with = 1/2 (JET, Fundamenski PSI 2006) v ELM /c s ~ ( W ELM /W ped ) with = 0 (Kirk, AUG)

19. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 19 Riccardo NF 2005Riccardo NF 2005, Pautasso EPS 2004 H-L transition thermal quench Pre-disruption energy confinement degradation (I) W plasma at thermal quench usually much smaller than W plasma full-performance (except for VDEs and ideal- limits) caused by E deterioration Size scaling and/or disruption amelioration actions ? VDEs -limits (ITBs)

20. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 20 Pre-disruption energy confinement degradation (II) Does this hold across devices ? Confinement deterioration takes place in timescales ~ E except for fast H-L transition & growth/locking of modes but p does not change much Most disruptions largest divertor surface temperature rise is caused by power fluxes during thermal quench rather than pre-disruption events T ~ q div 1/2

21. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 21 Timescale of thermal quench power fluxes timescale of thermal quench fluxes increases with R but large disruption-to- disruption variability q t.q,div (t) more than 75% of W ELM,div arrives after q t.q.,div max smaller T surf t.q.

22. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 22 Footprint of thermal quench power fluxes Power flux during thermal quench broadens significantly (even after radiation correction) & can develop toroidal asymmetries ( ~ 2-3) A. Herrmann - ASDEX Upgrade G. Counsell - MAST

23. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 23 Power fluxes on PFCs during ITER ELMs & disruptions Extrapolation of power fluxes to PFCs based on experimental evidence & models toroidal symmetry assumed ITER PFCs lifetime can be evaluated from these loads tolerable W ELM & W t.q.

24. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 24 Material erosion by ELM/disruption transient loads - no vapour shielding & no redeposition (Raclette, Federici & Strohmayer) CFC target lifetime requires q ELMmax < 1.5-2.0 GWm -2 W ELM /W ped < 0.05 (convective ELMs) q Upper-Be ELM < 50 MWm -2 No Be melting Calculated ELM-driven/disruption erosion in ITER CFC target lifetime requires q dis,max < (2-4) GWm -2 W ped /W plasma full-performance < 0.4 (typical for JET ELMy H-modes) q Upper-Be ELM ~ 100-400 MWm -2 No Be melting for q experimental (t)

25. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 25 Massive gas injection systems available in ASDEX-Upgrade, JET, TEXTOR and TORE-Supra Disruption mitigation (I) G. Counsell - MAST F. Saint-Laurent – Tore Supra He injection in Tore-Supra very effective in suppressing e runaway generation in disruptions Time to t.q. depends on pressure but He penetration does not depend on pressure He injection does not suppress e runaways already produced M. Lehnen – TEXTOR no neutral penetration in MGI shots dynamics of disruption correlated with impurity mass Ar + D produces fast termination reduction of thermal loads and runaway suppression (pure Ar produces runaways)

26. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 26 ECRH has been used to suppress disruption by affecting evolution of MHD Disruption mitigation (II) Density limit G. Maddaluno – FTU Mo-injection G. Maddaluno – FTU ECRH power and localisation requires optimisation for different disruption type (central for DL and peripheral for Mo-injection)

27. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 27 Plans for 2007 (I) Proposed joint activities Comparison of models for material damage during ELMs and subsequent plasma evolution with existing experimental data (mainly from JET) : FZK, FZJ, JET, CSU Garching, IPP Analysis of pre-disruptive thermal confinement deterioration and associated power fluxes on PFCs for similar disruptive triggers (density limit, low q disruption, ideal limits, etc.) and pre-disruptive regimes (L-mode, H-mode, ITBs, …) : FZJ, CRPP, ENEA, UKAEA, CEA, IPP, JET, CRPP, CSU Garching Determination of spatial and temporal characteristics of power fluxes during disruption thermal quenches for comparable disruptions : FZJ, CRPP, ENEA, UKAEA, CEA, IPP, JET, CSU Garching

28. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 28 Plans for 2007 (II) Proposed joint activities Comparative studies for the optimisation of disruption mitigation by massive gas injection for runaway suppression and thermal load minimisation : FZJ, CEA, IPP, JET, CRPP, HAS, CSU Garching Determination of spatial and temporal characteristics of power/particle fluxes during ELMs for comparable plasma conditions : CRPP, UKAEA, IPP, JET, CSU Garching

29. Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 29 Conclusions Experiments and modelling of material damage under ITER-like transient loads are providing firm basis to determine maximum tolerable ELM/disruption loads for acceptable lifetime Coordinated experiments and data analysis on disruptions and ELMs are starting to provide a physics-based extrapolation of expected transient loads in ITER Further progress in 2007 expected in by coordinated experiments and data analysis Many EU devices are now equipped with systems for disruption mitigation by massive gas injection significant progress in 2007 expected in this area by inter-machine comparison