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Progress in ITER relevant exhaust physics at JET

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.

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Progress in ITER relevant exhaust physics at JET

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  1. Progress in ITER relevant exhaust physics at JET Presented byR. A. PittsCRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederationon behalf of JET Task Force E and JET EFDA Contributors49th Annual Meeting of the APS-DPP, Orlando, Florida, US, 12-16 November 2007

  2. with thanks to many co-authors A. Alonso1, P. Andrew2, G. Arnoux3, S. Brezinsek4, M. Beurskens5, J. P. Coad5, T. Eich6, G. Esser4, W. Fundamenski5, A. Huber4, S. Grünhagen7, B. Gulejova8, S. Jachmich9, M. Jakubowski10, A. Kirschner4, S. Knipe5, A. Kreter4, T. Loarer3, J. Likonen11, A. Loarte12, E. de la Luna1, J. Marki8, M. Maslov8, G. F. Matthews5, V. Philipps4, M. Rubel13, E. Solano1, M. F. Stamp5, J. D. Strachan14, D. Tskhakaya15, A. Widdowson5 and JET EFDA Contributors* 1Associacion Euratom/CIEMAT para Fusion, Madrid, Spain 2ITER Organization, Cadarache, France, 3Association EURATOM-CEA, DSM-DRFC, CEA Cadarache, 13108 Saint Paul lez Durance, France 4Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Jülich, Germany 5Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK 6Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, D-85748 Garching, Germany 7FZ Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany 8CRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation 9LPP, ERM/KMS, Association Euratom-Belgian State, B-1000, Brussels, Belgium 10Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Germany 11VTT Technical research Centre of Finland, Association EURATOM-Tekes, Finland 12EFDA-Close Support Unit, Garching, Boltzmannstrasse 2, D-85748 Garching bei München, Germany 13Association EURATOM-VR, Fusion Plasma Physics, Stockholm, Sweden 14PPPL Princeton University, Princeton, NJ 0854, USA 15University 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)

  3. 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. Tritium retention

  5. A major worry for ITER … 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 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 JET has performed dedicated gas balance expts. in sets of repeated, identical discharges 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).

  6. Particle balance procedure Repeat sets of identical discharges (no intershot conditioning): L-mode, H-mode (Type III, I) Regenerate cryopumps before and after expt.  collect total pumped gas with ~1.2% accuracy Calibrated particle injection:Gas, NBI, …. Wall retention – short (dynamic) and long term Divertor cryopump 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. Example: Type I ELMing H-mode Fluxes (1021 elec/s) @16sRetention ~ 51021Ds-1Short term = 2.21021Ds 1(44%)Long term = 2.81021Ds-1 (56%) ne~0.7nGW Injected Pumped Retained Long term retention estimate (from overall gas balance) Time (s) @20sRetention ~ 31021Ds-1Long term retention totally dominates after ~6s heating #69260 – 5 repeat shots T. Loarer et al., EPS 2007 PTOT (MW) Da(in) Da (out) Time (s) Ip = 2.0 MA, Bj = 2.0 TDWELM ~100 kJNBI+ICRH, fELM ~ 60 HzCryopumps: divertor+1NBI

  8. Particle Balance summary • 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1022D • Independent of discharge type, ELM energy, quantity of injected particles

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

  10. Post-mortem analysis (II) 0.02 D/C ratios: Campaigns C5-C14, 2001-2004 0.14 Total D inner: 30 gTotal D outer: 13 g(from Nuclear Reaction Analysis) 0.42 0.11 0.15 0.91 0.25 0.17 0.08 0.12 0.79 J. Likonen, J. P. Coad, M. Rubel, to be submitted to PSI 2008

  11. T-retention summary D, C Post-mortem analysis:total D-retention (inner + outer divertor): 43 gTotal D inlet: 1800 gFuel retention: 2.4%Gas balance: long term retention in the range 10 - 20% Discrepancy in range 4 – 8Effects 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 13C puffing experiments

  12. 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 Explains high deposition rates on water-cooled louvres during 1997 JET DT experiments  high T-retention A. Kreter, H. G. Esser et al., submitted to PRL

  13. ELMs

  14. The problem with ELMs Important also in preparation for JET ITER-like wall and improved understanding of ELM SOL physics 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 JET Type I ELMs can approach 1 MJ  study the effects on first wall surfaces and edge plasma This implies an ELM energy loss, DWELM~ 1 MJ ~0.3% of stored energy in ITER QDT = 10 burning plasma! This is lower than any ELM energy so far achieved  mitigation strategies required. BUT …

  15. Large ELMs with low fueling #70226 – no gas fuelling Da (inner) PTOT(MW) WDIA(MJ) Te,ped (keV) ne,ped(1019m-3) H98Y Zeff(Brems) Time (s) Mostly NBI Vertical targets, MarkIIHD div.Specific JET sessionIp = 3.0MA, Bj = 3.0T, gas scanq95 ~ 3.1, d95 ~ 0.25Input energy ~195 MJEnergy Tile 3,7: 24.6, 70.1 MJ R. A. Pitts et al., ITPA, Garching, 2007

  16. Large ELMs with low fueling #70226 – no gas fuelling Da (inner) PTOT(MW) WDIA(MJ) Te,ped (keV) ne,ped(1019m-3) H98Y Zeff(Brems) Time (s) ITER Lowest fuelling cases at ITER relevant n*ped WELM/Wped ~ 0.2 for largest ELMs R. A. Pitts et al., ITPA, Garching, 2007

  17. Target surface temperatures ~600ºC ~200ºC #70228 – no gas fuelling Target surface temperatures from tangential view. Time resolution insufficient for power flux analysis Da (inner) #70228 Inner Outer Total wetted area ~1.0 m2 (cf. ITER ~ 3.5 m2) Tmax inner (ºC) Inter-ELM power loads higher at outer than inner as usualClear affect of surface layers on inner target (none on outer)Large ELMs: DTsurf (inner) ~ 600ºCDTsurf (outer) ~ 200ºCTsurf far from bulk sublimation Tmax outer (ºC) Time (s) J. Marki, T. Eich

  18. Radiation during large ELMs 0.85 MJ 1.29 MJ 1.08 MJ 0.58 MJ #70225, low fuelling A. Huber et al., EPS 2007 Da(inner) WDIA (MJ) PRAD (MW) Erad (MJ) Strong in-out asymmetry in ELM induced radiation for high DWELM  probably due to layers on inner targets and preferential inboard deposition of ELM energy Time (s)

  19. In-out ELM radiation asymmetry DERAD/DWELM ~ 0.5 if DWELM 0.6 MJ Evidence for a break at largerDWELM > ~ For DWELM 0.6 MJ radiation “spills over” separatrix – in-out radiation asymmetry reduced < ~ First ELM spikeonly Up to 70% DWELM radiated WELM = 0.45 MJ WELM = 0.85 MJ R. A. Pitts, ITPA 2007, A. Huber et al., EPS 2007

  20. Main wall ELM filaments ELM exposure superimposed on ambient background Difference frame: ELM – previous ELM-free frames #66515 DWELM ~ 200 kJt = 7.6 sExp. time 300 msFrame 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 W. Fundamenski, M. Jakubowski, ITPA Garching May 2007, P. Andrew et al., EPS 2007

  21. Filament footprint field aligned Df = 22o,35o 68193, 57 s Filament IR footprint in main chamber closely aligned to pre-ELM field linesMode number (in this case) n ~360/Dj = 11-16. More cases  n = 10 - 50 Field aligned filaments also seen at upper dump plates: crude mode analysis gives n ~ 5 - 20

  22. How much ELM energy to walls? Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally Make energy balance for a single outboard poloidal limiter during H-mode phase, assume:Only ELMs can deposit energy on limitersNo energy to upper dump platesNo energy deposited in compound phasesSame energy on 16 limiters 68193, 57 s

  23. How much ELM energy to walls? 17.405 s 20.016 s #70226 Da (inner) Temp. (ºC) 13 12 11 Energy per tile (kJ) ∑Etile (15 tiles) Time (s) Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally Make energy balance for a single outboard poloidal limiter during H-mode phase, assume:Only ELMs can deposit energy on limitersNo energy to upper dump platesNo energy deposited in compound phasesSame energy on 16 limiters 68193, 57 s

  24. Wall loading and ELM size Ip = 3.0 MA, Bj = 3.0 T, gas scan. Separatrix-midplane outer wall gap fixed at ~5.0 cm. DWELM estimated for first ELM peak only 68193, 57 s Larger ELMs deposit more energy on outboard main chamber surfaces. How does this compare with theory?

  25. Compare with filament model > ~  W/W0 = 9.4% at limiter radius, cf. Experiment = 8.8%Excellent agreement given inherent approximations ELMs with <DWELM> 500 kJ deposit ~10% of their energy on the main chamber limiters (for separatrix-wall gap ~ 5 cm) Assume mid-pedestal paramsTe,0 = Ti,0 ~ 800 eVne,0 ~ 3.01019 m-3Dped ~ 4 cmvELM = 600 ms-1 Filament parallel energy loss model(W. Fundamenski, R. A. Pitts, PPCF 48 (2006) 109)

  26. 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 QDT = 10 pulse expecting to use ~50g T at 20% retention, 1 kg in-vessel mobilisable T-limit reached in ~100 pulses!

  27. Conclusions (II) • Large ELMs • JET can access ELM conditions which match new ITER specifications (DWELM ~ 1 MJ) in pulses at Ip = 3.0 MA with upstream lp ~ 5 mm and divertor wetted area ~1.0 m2 • 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 DTsurf provoked by largest ELMs relatively modest (~ few 100 ºC) • ELM filaments seen clearly at main chamber limiters but only carry ~10% of DWELM for largest ELMs (<DWELM> > 0.5 MJ with fixed wall gap (~5 cm).

  28. Reserve slides

  29. Example: L-mode Fluxes (1021 elec/s) #70534 @15sRetention = 6.31021Ds-1Short term = 4.561021Ds-1 (72%)Long term = 1.741021Ds-1 (28%) ne~0.4nGW Injected T. Loarer et al., EPS 2007 Pumped PTOT (MW) Retained Da(in) Da (out) Long term retention Time (s) Time (s) @25sRetention = 4.681021Ds-1Short term = 2.941021Ds-1 (63%)Long term = 1.741021Ds-1 (37%) Ip = 2.0 MA, Bj = 2.0 TICRH only (~1.2 MW)Divertor cryopump only

  30. Large ELMs with low fueling #70226 – no gas fuelling Da (inner) PTOT(MW) WDIA(MJ) Te,ped (keV) ne,ped(1019m-3) H98Y Zeff(Brems) Time (s) Large ELMs have large drop in Te,ped New data populate scaling beyond DTe,ELM/Te,ped = 0.4 R. A. Pitts et al., ITPA, Garching, 2007

  31. Filaments in fast visible light 1 2 3 6 5 4 Courtesy of J. A. Alonso, CIEMAT #70228 Da (inner)divertor WDIA(MJ) Time (s) Frame time 33 ms, main chamber view – filament-wall interaction seen during divertor Da rise. DWELM = 804 kJDERAD = 537 kJ

  32. Parallel ELM transport T, n tELM = 200 ms Post ELM 150 ms dR 2L|| = 80 m Nparticles = 0.8 – 5.0  106, Ncells = 6000High resolution, low noiseTped = 0.5 – 5 keVnped = 0.15 – 15  1019 m-3DWELM = 0.025 – 2.5 MJ 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 tELM with specified Tped, nped DWELM ~ tELM3npedTped2pLpolRdR Plasma expelled into 1D SOL with cosine distribution centred on midpoint between targets.B = const., inclined targets (~5º) D. Tskhakaya et al., EPS 2007

  33. Test case: PIC vs. expt. PIC ONLY D. Tskhakaya Example: DWELM = 400 kJ Tped = 1.5 keVnped = 51019 m-3 tELM Clear separation of electron (~2 ms) and ion (~100 ms) transit times Assumed “ELM duration” 200 ms te ti

  34. Test case: PIC vs. expt. PIC + EXPT. IR data obtained at outer target (no layers) from coherent average of 20 similar ELMs with <DWELM> ~ 310 ± 66 kJ Time resolution artifically enhanced to 50 ms Good agreement in shape of pulse rise Width a question of time and shape of ELM pedestal loss PIC overestimates expt. by ~ factor 5 D. Tskhakaya, T. Eich, R. A. Pitts Factor ~2 due to known in-out ELM loading asymmetryFactor ~2 due to 1D nature of PICReasonable agreement given how DWELM specified in the code

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