1. R. A. Pitts et al. 1 49 th APS, Orlando, Florida, USA 12 November 2007 Progress in ITER relevant exhaust physics at JET Presented by R. A. Pitts CRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation on behalf of JET Task Force E and JET EFDA Contributors 49 th Annual Meeting of the APS-DPP, Orlando, Florida, US, 12-16 November 2007

2. R. A. Pitts et al. 2 49 th APS, Orlando, Florida, USA 12 November 2007 A. Alonso 1, P. Andrew 2, G. Arnoux 3, S. Brezinsek 4, M. Beurskens 5, J. P. Coad 5, T. Eich 6, G. Esser 4, W. Fundamenski 5, A. Huber 4, S. Grünhagen 7, B. Gulejova 8, S. Jachmich 9, M. Jakubowski 10, A. Kirschner 4, S. Knipe 5, A. Kreter 4, T. Loarer 3, J. Likonen 11, A. Loarte 12, E. de la Luna 1, J. Marki 8, M. Maslov 8, G. F. Matthews 5, V. Philipps 4, M. Rubel 13, E. Solano 1, M. F. Stamp 5, J. D. Strachan 14, D. Tskhakaya 15, A. Widdowson 5 and JET EFDA Contributors * 1 Associacion Euratom/CIEMAT para Fusion, Madrid, Spain 2 ITER Organization, Cadarache, France, 3 Association EURATOM-CEA, DSM-DRFC, CEA Cadarache, 13108 Saint Paul lez Durance, France 4 Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Jülich, Germany 5 Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK 6 Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, D-85748 Garching, Germany 7 FZ Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany 8 CRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation 9 LPP, ERM/KMS, Association Euratom-Belgian State, B-1000, Brussels, Belgium 10 Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Germany 11 VTT Technical research Centre of Finland, Association EURATOM-Tekes, Finland 12 EFDA-Close Support Unit, Garching, Boltzmannstrasse 2, D-85748 Garching bei München, Germany 13 Association EURATOM-VR, Fusion Plasma Physics, Stockholm, Sweden 14 PPPL Princeton University, Princeton, NJ 0854, USA 15 University of Innsbruck, Institute for Theoretical Physics, Association EURATOM-ÖAW, A-6020 Innsbruck, Austria *See appendix of M. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu, 2006) IAEA Vienna (2006) with thanks to many co-authors

3. R. A. Pitts et al. 3 49 th APS, Orlando, Florida, USA 12 November 2007 Outline Long term Tritium retention –Gas balance and post-mortem analysis ELMs –Divertor induced radiation under large ELM impact –Filamentary structure and main wall interactions Conclusions

4. R. A. Pitts et al. 4 49 th APS, Orlando, Florida, USA 12 November 2007 Tritium retention

5. R. A. Pitts et al. 5 49 th APS, Orlando, Florida, USA 12 November 2007 A major worry for ITER … T-retention constitutes an outstanding problem for ITER operation A retention rate of 10% in ITER would lead to the in- vessel mobilisable T-limit (1 kg) being exceeded in ~200 pulses Retention rates of this order or higher are regularly found using gas balance in tokamaks Gas balance is difficult to make accurately and is strongly influenced by “history” (previous pulses). JET has performed dedicated gas balance expts. in sets of repeated, identical discharges Important aim is to provide best possible reference T-retention measurements in all-C JET before new Be-W ITER-like wall (ILW) expt. planned for 2010

6. R. A. Pitts et al. 6 49 th APS, Orlando, Florida, USA 12 November 2007 Particle balance procedure Wall retention – short (dynamic) and long term Calibrated particle injection: Gas, NBI, …. Divertor cryopump Regenerate cryopumps before and after expt.  collect total pumped gas with ~1.2% accuracy Repeat sets of identical discharges (no intershot conditioning): L-mode, H-mode (Type III, I) Injection = Short term ret. + Long term ret. + Pumped NB: Total recovered from cryo-regeneration = pumped+intershot outgassing over ~800s (assumed equal to short term retention)

7. R. A. Pitts et al. 7 49 th APS, Orlando, Florida, USA 12 November 2007 Example: Type I ELMing H-mode n e ~0.7n GW P TOT (MW) D   (in) D  (out) Time (s) Long term retention estimate (from overall gas balance) Time (s) Fluxes (10 21 elec/s) Injected Pumped Retained #69260 – 5 repeat shots @16s Retention ~ 5  10 21 Ds -1 Short term = 2.2  10 21 Ds 1 (44%) Long term = 2.8  10 21 Ds -1 (56%) @20s Retention ~ 3  10 21 Ds -1 Long term retention totally dominates after ~6s heating I p = 2.0 MA, B  = 2.0 T  W ELM ~100 kJ NBI+ICRH, f ELM ~ 60 Hz Cryopumps: divertor+1NBI T. Loarer et al., EPS 2007

8. R. A. Pitts et al. 8 49 th APS, Orlando, Florida, USA 12 November 2007 Particle Balance summary Pulse type Heating phase (s) Divertor phase (s) Injection (Ds -1 ) Long term retention (Ds -1 )  ret /  inj L-mode81126 ~1.8  10 22 1.74  10 21 ~10% Type III221350 ~0.6  10 22 1.31  10 21 ~20% Type I3250 ~1.7  10 22 2.83  10 21 ~17% Long term retention increases from L-mode to H-mode –Increased C erosion and transport due to increased recycling and effect of ELMs  enhanced C erosion  enhanced co-deposition and retention Recovery between pulses (short term retention) always constant within a factor ~2 – in the range 1-3  10 22 D –Independent of discharge type, ELM energy, quantity of injected particles

9. R. A. Pitts et al. 9 49 th APS, Orlando, Florida, USA 12 November 2007 J. Likonen, J. P. Coad, M. Rubel, to be submitted to PSI 2008 C-erosion/depostion: Campaigns C5-C14, 2001-2004 Divertor only – main chamber net erosion dominated 105g Louvre: 60g (from QMB) 233g 17g 99g 44g 67g 464g Erosion No clear erosion or deposition Negligible 83,000 s divertor plasma (23 hours) Total inner: 625 g Total outer: 507 g (  = 1.0 gcm -3 taken for deposit, toroidal symmetry assumed tile gaps ignored) Post-mortem analysis (I) 19g 24g Deposition

10. R. A. Pitts et al. 10 49 th APS, Orlando, Florida, USA 12 November 2007 J. Likonen, J. P. Coad, M. Rubel, to be submitted to PSI 2008 D/C ratios: Campaigns C5-C14, 2001-2004 0.910.25 0.15 0.11 0.42 0.02 0.12 Total D inner: 30 g Total D outer: 13 g (from Nuclear Reaction Analysis) Post-mortem analysis (II) 0.08 0.14 0.17 0.79

11. R. A. Pitts et al. 11 49 th APS, Orlando, Florida, USA 12 November 2007 T-retention summary Post-mortem analysis: total D-retention (inner + outer divertor): 43 g Total D inlet: 1800 g Fuel retention: 2.4% Gas balance: long term retention in the range 10 - 20% Discrepancy in range 4 – 8 Effects of long term outgassing, thermal release (plasma ops.), GDC, disruptions and because campaign averaged power generally very low (~ 4 MW) with variable plasma configs. Retention requires long range migration from net erosion to net co-deposition areas (e.g.): main chamber to divertor strike zones to PFR outer divertor to inner ELMs See poster GP8.00092 (Tuesday) by J. D. Strachan for more on C-migration based on JET 13 C puffing experiments D, C

12. R. A. Pitts et al. 12 49 th APS, Orlando, Florida, USA 12 November 2007 ELMs can move carbon Non-linear dependence of carbon erosion on ELM energy  thermal decomposition of surface layers and favourable geometry rapidly increases QMB deposition A. Kreter, H. G. Esser et al., submitted to PRL Explains high deposition rates on water-cooled louvres during 1997 JET DT experiments  high T-retention

13. R. A. Pitts et al. 13 49 th APS, Orlando, Florida, USA 12 November 2007 ELMs

14. R. A. Pitts et al. 14 49 th APS, Orlando, Florida, USA 12 November 2007 The problem with ELMs Material damage poses a limit on the maximum ELM size tolerable on ITER Current estimates indicate that ELM power fluxes (for CFC or W) must remain below ~0.5 MJm -2 at the ITER divertor targets This implies an ELM energy loss,  W ELM ~ 1 MJ  ~0.3% of stored energy in ITER Q DT = 10 burning plasma! This is lower than any ELM energy so far achieved  mitigation strategies required. BUT … JET Type I ELMs can approach 1 MJ  study the effects on first wall surfaces and edge plasma Important also in preparation for JET ITER-like wall and improved understanding of ELM SOL physics

15. R. A. Pitts et al. 15 49 th APS, Orlando, Florida, USA 12 November 2007 Large ELMs with low fueling Vertical targets, MarkIIHD div. Specific JET session I p = 3.0MA, B  = 3.0T, gas scan q 95 ~ 3.1,  95 ~ 0.25 Input energy ~195 MJ Energy Tile 3,7: 24.6, 70.1 MJ D  (inner) P TOT (MW) W DIA (MJ) T e,ped (keV) n e,ped (10 19 m -3 ) H 98Y Z eff (Brems) Time (s) #70226 – no gas fuelling R. A. Pitts et al., ITPA, Garching, 2007 Mostly NBI

16. R. A. Pitts et al. 16 49 th APS, Orlando, Florida, USA 12 November 2007 Large ELMs with low fueling Lowest fuelling cases at ITER relevant * ped W ELM /W ped ~ 0.2 for largest ELMs R. A. Pitts et al., ITPA, Garching, 2007 D  (inner) P TOT (MW) W DIA (MJ) T e,ped (keV) n e,ped (10 19 m -3 ) H 98Y Z eff (Brems) Time (s) #70226 – no gas fuelling ITER

17. R. A. Pitts et al. 17 49 th APS, Orlando, Florida, USA 12 November 2007 Target surface temperatures D  (inner) T max outer (ºC) Time (s) #70228 – no gas fuelling T max inner (ºC) Target surface temperatures from tangential view. Time resolution insufficient for power flux analysis Total wetted area ~1.0 m 2 (cf. ITER ~ 3.5 m 2 ) Inter-ELM power loads higher at outer than inner as usual Clear affect of surface layers on inner target (none on outer) Large ELMs:  T surf (inner) ~ 600ºC  T surf (outer) ~ 200ºC T surf far from bulk sublimation Inner Outer ~600ºC ~200ºC #70228 J. Marki, T. Eich

18. R. A. Pitts et al. 18 49 th APS, Orlando, Florida, USA 12 November 2007 Radiation during large ELMs Time (s) #70225, low fuelling D   (inner) W DIA (MJ) P RAD (MW)  E rad (MJ) 0.58 MJ 1.08 MJ 0.85 MJ 1.29 MJ Strong in-out asymmetry in ELM induced radiation for high  W ELM  probably due to layers on inner targets and preferential inboard deposition of ELM energy A. Huber et al., EPS 2007

19. R. A. Pitts et al. 19 49 th APS, Orlando, Florida, USA 12 November 2007 In-out ELM radiation asymmetry W ELM = 0.85 MJ W ELM = 0.45 MJ First ELM spike only For  W ELM 0.6 MJ radiation “spills over” separatrix – in-out radiation asymmetry reduced > ~  E RAD /  W ELM ~ 0.5 if  W ELM 0.6 MJ Evidence for a break at larger  W ELM < ~ R. A. Pitts, ITPA 2007, A. Huber et al., EPS 2007 Up to 70%  W ELM radiated

20. R. A. Pitts et al. 20 49 th APS, Orlando, Florida, USA 12 November 2007 Main wall ELM filaments W. Fundamenski, M. Jakubowski, ITPA Garching May 2007, P. Andrew et al., EPS 2007 #66515  W ELM ~ 200 kJ t = 7.6 s Exp. time 300  s Frame time 7.8 ms New wide angle IR camera diagnostic (E. Gauthier et al., CEA) using ITER-like front mirrors. 640x512 pixel FPA, max. full frame rate 100 Hz ELM exposure superimposed on ambient background Difference frame: ELM – previous ELM-free frames

21. R. A. Pitts et al. 21 49 th APS, Orlando, Florida, USA 12 November 2007 Filament footprint field aligned  = 22 o,35 o Filament IR footprint in main chamber closely aligned to pre-ELM field lines Mode number (in this case) n ~360/  = 11-16. More cases  n = 10 - 50 Field aligned filaments also seen at upper dump plates: crude mode analysis gives n ~ 5 - 20 68193, 57 s

22. R. A. Pitts et al. 22 49 th APS, Orlando, Florida, USA 12 November 2007 How much ELM energy to walls? Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally 68193, 57 s Make energy balance for a single outboard poloidal limiter during H-mode phase, assume: Only ELMs can deposit energy on limiters No energy to upper dump plates No energy deposited in compound phases Same energy on 16 limiters

23. R. A. Pitts et al. 23 49 th APS, Orlando, Florida, USA 12 November 2007 D  (inner) Time (s) Temp. (ºC) Energy per tile (kJ) #70226 How much ELM energy to walls? Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally 68193, 57 s 20.016 s 17.405 s 11 12 13 Make energy balance for a single outboard poloidal limiter during H-mode phase, assume: Only ELMs can deposit energy on limiters No energy to upper dump plates No energy deposited in compound phases Same energy on 16 limiters ∑E tile (15 tiles)

24. R. A. Pitts et al. 24 49 th APS, Orlando, Florida, USA 12 November 2007 Wall loading and ELM size 68193, 57 s Pulse No.  gas (10 22 e - /s) No. ELMs(MJ) (kJ) 702211.4713329.71.492245.3 702221.248723.91.022754.3 702230.895018.00.853604.7 702240.38168.340.715218.8 7022503014.91.374979.2 7022602412.71.4952811.8 I p = 3.0 MA, B  = 3.0 T, gas scan. Separatrix-midplane outer wall gap fixed at ~5.0 cm.  W ELM estimated for first ELM peak only Larger ELMs deposit more energy on outboard main chamber surfaces. How does this compare with theory? Pulse No.  gas (10 22 e - /s) No. ELMs(MJ) (kJ) 702211.4713329.71.492245.3 702221.248723.91.022754.3 702230.895018.00.853604.7 702240.38168.340.715218.8 7022503014.91.374979.2 7022602412.71.4952811.8

25. R. A. Pitts et al. 25 49 th APS, Orlando, Florida, USA 12 November 2007 Compare with filament model Filament parallel energy loss model (W. Fundamenski, R. A. Pitts, PPCF 48 (2006) 109)  W/W 0 = 9.4% at limiter radius, cf. Experiment = 8.8% Excellent agreement given inherent approximations  ELMs with 500 kJ deposit ~10% of their energy on the main chamber limiters (for separatrix-wall gap ~ 5 cm) > ~ Assume mid- pedestal params T e,0 = T i,0 ~ 800 eV n e,0 ~ 3.0  10 19 m -3  ped ~ 4 cm v ELM = 600 ms -1

26. R. A. Pitts et al. 26 49 th APS, Orlando, Florida, USA 12 November 2007 Conclusions (I) Long term Tritium retention –Dedicated gas balance: 10-20% increasing from L to H-mode –Post-mortem analysis: ~2.5% –Difference due to campaign averaging/conditioning cycles, low campaign averaged power –Majority of retention attributable to C migration to remote areas followed by co-deposition –ITER Q DT = 10 pulse expecting to use ~50g T  at 20% retention, 1 kg in-vessel mobilisable T-limit reached in ~100 pulses!

27. R. A. Pitts et al. 27 49 th APS, Orlando, Florida, USA 12 November 2007 Conclusions (II) Large ELMs –JET can access ELM conditions which match new ITER specifications (  W ELM ~ 1 MJ) in pulses at I p = 3.0 MA with upstream p ~ 5 mm and divertor wetted area ~1.0 m 2 –Strong in-out divertor radiation asymmetry – up to 70% of the ELM energy drop can be radiated, mostly in the divertor volume. –Evidence that thermal decomposition of inner divertor surface layers increases radiation but  T surf provoked by largest ELMs relatively modest (~ few 100 ºC ) –ELM filaments seen clearly at main chamber limiters but only carry ~10% of  W ELM for largest ELMs ( > 0.5 MJ with fixed wall gap (~5 cm).

28. R. A. Pitts et al. 28 49 th APS, Orlando, Florida, USA 12 November 2007 Reserve slides

29. R. A. Pitts et al. 29 49 th APS, Orlando, Florida, USA 12 November 2007 Example: L-mode n e ~0.4n GW P TOT (MW) D   (in) D  (out) Time (s) Injected Pumped Retained Long term retention Time (s) Fluxes (10 21 elec/s) #70534 @15s Retention = 6.3  10 21 Ds -1 Short term = 4.56  10 21 Ds -1 (72%) Long term = 1.74  10 21 Ds -1 (28%) @25s Retention = 4.68  10 21 Ds -1 Short term = 2.94  10 21 Ds -1 (63%) Long term = 1.74  10 21 Ds -1 (37%) I p = 2.0 MA, B  = 2.0 T ICRH only (~1.2 MW) Divertor cryopump only T. Loarer et al., EPS 2007

30. R. A. Pitts et al. 30 49 th APS, Orlando, Florida, USA 12 November 2007 Large ELMs with low fueling Large ELMs have large drop in T e,ped New data populate scaling beyond  T e,ELM /T e,ped = 0.4 R. A. Pitts et al., ITPA, Garching, 2007 D  (inner) P TOT (MW) W DIA (MJ) T e,ped (keV) n e,ped (10 19 m -3 ) H 98Y Z eff (Brems) Time (s) #70226 – no gas fuelling

31. R. A. Pitts et al. 31 49 th APS, Orlando, Florida, USA 12 November 2007 Filaments in fast visible light #70228 D  (inner) divertor W DIA (MJ) Time (s) Frame time 33  s, main chamber view – filament- wall interaction seen during divertor D  rise. Courtesy of J. A. Alonso, CIEMAT 123 654  W ELM = 804 kJ  E RAD = 537 kJ

32. R. A. Pitts et al. 32 49 th APS, Orlando, Florida, USA 12 November 2007 Parallel ELM transport Significant progress being made in realistic parallel transport modelling of ELM pulse with the BIT1 PIC code Treat ELM as a square wave pulse launched upstream over time  ELM with specified T ped, n ped  W ELM ~  ELM 3n ped T ped 2  L pol RdR Plasma expelled into 1D SOL with cosine distribution centred on midpoint between targets. B = const., inclined targets (~5 º ) D. Tskhakaya et al., EPS 2007  ELM = 200  s Post ELM 150  s T, n N particles = 0.8 – 5.0  106, N cells = 6000 High resolution, low noise T ped = 0.5 – 5 keV n ped = 0.15 – 15  10 19 m -3  W ELM = 0.025 – 2.5 MJ 2L || = 80 m dR

33. R. A. Pitts et al. 33 49 th APS, Orlando, Florida, USA 12 November 2007 Test case: PIC vs. expt. Clear separation of electron (~2  s) and ion (~100  s) transit times Assumed “ELM duration” 200  s Example:  W ELM = 400 kJ T ped = 1.5 keV n ped = 5  10 19 m -3 ee ii  ELM D. Tskhakaya PIC ONLY

34. R. A. Pitts et al. 34 49 th APS, Orlando, Florida, USA 12 November 2007 Test case: PIC vs. expt. D. Tskhakaya, T. Eich, R. A. Pitts IR data obtained at outer target (no layers) from coherent average of 20 similar ELMs with ~ 310 ± 66 kJ Time resolution artifically enhanced to 50  s Good agreement in shape of pulse rise Width a question of time and shape of ELM pedestal loss PIC overestimates expt. by ~ factor 5 Factor ~2 due to known in-out ELM loading asymmetry Factor ~2 due to 1D nature of PIC Reasonable agreement given how  W ELM specified in the code PIC + EXPT.