R. A. Pitts et al th APS, Orlando, Florida, USA 12 November 2007 Progress in ITER relevant ELM exhaust physics at JET Presented by W.Fundamenski on behalf of JET Task Force E and JET EFDA Contributors Part of an invited talk by R. A. Pitts at the 49 th Annual Meeting of the APS-DPP, Orlando, Florida, US, November 2007

R. A. Pitts et al 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, Saint Paul lez Durance, France 4 Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D Jülich, Germany 5 Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK 6 Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, D Garching, Germany 7 FZ Karlsruhe, Postfach 3640, D 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 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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

R. A. Pitts et al 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/  = More cases  n = Field aligned filaments also seen at upper dump plates: crude mode analysis gives n ~ , 57 s

R. A. Pitts et al 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

R. A. Pitts et al 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 s 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 ∑E tile (15 tiles)

R. A. Pitts et al 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) 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)

R. A. Pitts et al 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  m -3  ped ~ 4 cm v ELM = 600 ms -1

R. A. Pitts et al th APS, Orlando, Florida, USA 12 November 2007 Conclusions –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). –Fraction of energy to the wall in good agreement with a parallel loss model of ELM filament evolution

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

R. A. Pitts et al 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

R. A. Pitts et al 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  W ELM = 804 kJ  E RAD = 537 kJ

R. A. Pitts et al 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  m -3  W ELM = – 2.5 MJ 2L || = 80 m dR

R. A. Pitts et al 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  m -3 ee ii  ELM D. Tskhakaya PIC ONLY

R. A. Pitts et al 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.