T.Eich 1 / 26 rehearsal for PFMC, Jülich ELM divertor heat loads in JET- ILW and full-W ASDEX Upgrade T.Eich, R.Scannel, B.Sieglin, G.Arnoux, S.Devaux, I.Balboa, A.Scarabosio, M.Leyland, S.Brezinsek, G.F.Matthews, S.Jachmich, H.Thomsen, A.Herrmann, P.DeMarne, M.Beurskens, W.Fundamenski, G.Huysmans PFMC Jülich Germany,

T.Eich 2 / 26 rehearsal for PFMC, Jülich Outline Combining type-I ELM heat load from various experimental campaigns in JET and ASDEX Upgrade (both C and W) The story so far: Results from JET and AUG ‘carbon’ operation Comparison of ‘W’ and ‘C’ ELM heat loads A pedestal pressure based ELM divertor heat load scaling Outlook & Summary and Conclusions Not covered: Access to small ELM regimes

T.Eich 3 / 26 rehearsal for PFMC, Jülich ELMs: transient heat loads The transient heat flux factor has a simple relation to Energy (E), depositon Area (A dep ) and characteristic time scale (t c ): Mitigation of transient events needs to reduce either the energy, increase the area or the characteristic time scale heat flux factor J. Linke 0.5MJ/m 2

T.Eich 4 / 26 rehearsal for PFMC, Jülich Time scales: initial comparison of W and C Comparison of ELM power fluxes by IR derived from CFC and W surfaces in JET-C gave fair agreement #74380 ELM outer divertor target energy ~ 0.35 of ELM loss energy (same for W and C) Reference case CFC W

T.Eich 5 / 26 rehearsal for PFMC, Jülich ELM time scales in ‘Carbon’ ITER assumes : ELM decay time : 500us ELM rise time: 200us This temporal shape was used for material studies L c (m)T e (eV)q95c s (km/s)L c / c s AUG us JET us ITER us Temporal shape and time scales of ELM heat fluxes in JET and ITER are expected to be similar, since they scale with τ II = L c /c s t rise (μs) τ || =L c / c s (μs) 4401 ELMs, 25 discharges Triniti Plasma Gun (normalized) Measured ELM power load (JET) (us) (MW),(MW/m2)

T.Eich 6 / 26 rehearsal for PFMC, Jülich Relaxation of a Maxwell distribution T.Eich at al, JNM 2009 W.Fundamenski, PPCF 2006 ELM energy release time into the SOL, τ MHD << τ II ELM duration time x 2.4 ELM rise time A.Kirk, PPCF 2006 ASDEX Upgrade

T.Eich 7 / 26 rehearsal for PFMC, Jülich ELM time scales by AXUV studies Near target ELM induced radation (low density) shows also fair agreement and is in line with Maxwellian velocity full-W ASDEX Upgrade operation

T.Eich 8 / 26 rehearsal for PFMC, Jülich ELM heat loads in ripple experiments Natural ELMs Vertical ‘kicks’  For TF ripple studies, an increase of ELM frequencies is found (22Hz, 30Hz, 52Hz)  ELM peak heat fluxes are not reduced JET-C  BT =0.08%  BT =0.5%  BT =0.75% 22Hz 30Hz 50Hz E ELM (kJ)

T.Eich 9 / 26 rehearsal for PFMC, Jülich Divertor peak heat flux vs E ELM ELM wetted area increases with ELM loss energy peak heat flux (MWm -2 ) E ELM (kJ) Wetted area (m 2 ) JET: 2.5MA/2.5T ELM frequency (Hz) B=2.2 T, 2 MA, (q 95 ~3.6) δ av =0.45, P NBI =10-14 MW

T.Eich 10 / 26 rehearsal for PFMC, Jülich ELM wetted area Observed trend: ELM wetted area increases with ELM loss size, result seen in JET, DIII-D and ASDEX Upgrade H.Thomsen et al, NF (2011) M.Jakubowski et al, Nucl.Fusion (2009) JET DIII-D ITER: For minimum sized ELMs broadening (λ q,ELM =5mm) λ q,ELM = 20mm λ q,ELM = 5mm JET-ILW

T.Eich 11 / 26 rehearsal for PFMC, Jülich ELM ergodisation & filaments: complex deposition pattern No obvious differences found between W and C operation w.r.t. ELM ergodisation or filamentary substructure However, detailed studies are in progress,aiming at –(quasi-) toroidal mode numbers –energy distribution beweetn (radially moving) filaments and parallel losses due to ergodization of field lines Δt = -215 µs Δt = -129 µs Δt = -43 µs Δt = 43 µs Δt = 129 µs Δt = 215 µs JET-C JOREK (ITER) 4.0MJ (cond.) 1.6MJ (conv.)

T.Eich 12 / 26 rehearsal for PFMC, Jülich Tolerable ELM size in ITER A ELM = 2 π R div * λ ELM * f x = 0.90m 2 (λ ELM =5mm, f x =6.5, R div,inner =4.4m) No Radiation, 100% in deposited in divertor, In/Out Asymmetry 2:1 (favouring the inner) Result: E tol = 0.5MJ/m 2 * 1.5 * 0.90m 2 = 0.7MJ As A ELM increases with ELM loss, how scales effectively the ELM energy density?

T.Eich 13 / 26 rehearsal for PFMC, Jülich Comparing W- and C- ELMs NB: Experimental execution of discharges of JET-ILW and JET-C (slightly) different for dedicated ELM heat load studies Shaping, Triangularity, strike lines on target: identical Larger NBI heating power required for similar pedestal n e, T e B t / I p scan executed first at identical P NBI for C/W and with much increased P NBI for W (up to 26MW) H98y about 1 for best discharges in JET-ILW P NBI <13MW P NBI >20MW

T.Eich 14 / 26 rehearsal for PFMC, Jülich W versus C: time scales (1) Type-I ELMs in JET- ILW do not follow the simple scaling found for JET-C Interpretation: ELM energy release time (ELM MHD time?) is larger than parallel transport time JET-ILW JET-C τ MHD << τ II ? τ MHD >= τ II

T.Eich 15 / 26 rehearsal for PFMC, Jülich W versus C: time scales (2) Also the temporal shape of the ELM power fluxes approaches the shape observed for type-I ELMs in JET-C when τ II is shortest in DB Reminder: τ II ≈ T e -0.5 Same holds true for type-I ELMs full-W ASDEX Upgrade operation with good confinement (e.g. with N 2 seeding) JET-ILW JET-C

T.Eich 16 / 26 rehearsal for PFMC, Jülich example plots A couple of examples showing the increase of the ELM power deposition length, W-ELMs appear to be stretched for low T e JET-ILW full-W ASDEX Upgrade (2.0 & 2.4MA) / 2.5T P NI = 9MW, T e,ped = 480 eV P NI =10MW, T e,ped = 600 eV P NI =22MW, T e,ped = 1100eV JPN JPN Plot needed JPN 82630

T.Eich 17 / 26 rehearsal for PFMC, Jülich H98y vs time scales In summary we find, for good confinement conditions (at high pedestal temperature) there is almost no difference between W- ELMs and C-Elms w.r.t time scales Such ‘good’ conditions are achieved in JET-ILW at higher heating power or with e.g. N 2 seeding (In line with ASDEX Upgrade N 2 seeded experiments (t.b.c.))

T.Eich 18 / 26 rehearsal for PFMC, Jülich A note on ‘long’ ELMs ‘Longish’ time scales for pedestal collapse are observed e.g. by Thomson-Scattering or ECE measurements confirming previous assumption of τ MHD >= τ II Such conditions were rarely observed in JET-C, but e.g. in Helium discharges For conditions with ‘good’ confinement and high pedestal temperatures, short time scales are recovered (for AUG, PC: A.Burckhardt) Private communication, JET: L.Frassinetti, D.Dodt & AUG: A.Burckhardt

T.Eich 19 / 26 rehearsal for PFMC, Jülich JET-C ILW (no seeding) ILW with N 2 seeding  t≈ ms  t≈2-3ms  t≈10ms  t≈1ms  Behaviour relatively similar for each ELM  Time interval to reach the minimum:  t≈ ms  Two different behaviours  Time interval to reach the minimum:  t fast ≈2-3ms  t slow ≈10ms  Behaviour relatively similar for each ELM  Time interval to reach the minimum:  t≈1ms at  pol = at  pol = Duration of T e,ped drop: 0.3-3ms Courtesy of L.Frassinetti

T.Eich 20 / 26 rehearsal for PFMC, Jülich TIME SCALES: DISTRIBUTIONS Ip  2.5MA only ILW w/o N2 JET-C ILW with N2 Shots considered: Ip=2.5MA and Pnet≈15-19MW  5 CFC plasmas  6 ILW plasmas (not seeded)  11 ILW shots (with N2 seeding) - 6 with Wth comparable to CFC - 5 with low Wth W th (MJ) CFC ILW (not seeded) ILW (seeded) with high Wth ILW (seeded) with low Wth  CFC and ILW (not seeded) have clearly two different time scales  CFC and seeded ILW are comparable if the stored energy is similar  Seeded ILW are comparable to not seeded ILW if the stored energy is low  The ELM time scale seems to be related more to the stored energy than to the wall

T.Eich 21 / 26 rehearsal for PFMC, Jülich Definition of ELM energy fluency The ELM energy fluency is the peak of the time integrated heat flux profile (energy / area) ε max inter-ELM for reference (5ms) Typical numbers for large ELMs at JET: 150 kJ/m 2

T.Eich 22 / 26 rehearsal for PFMC, Jülich W/C: ELM energy fluency A jump ahead: Attempt to scale or order the ELM energy fluency NB: Data are mapped to parallel field lines in order to compare the different divertor geometries JET-C : ε target x 20 = ε II JET-ILW: ε target x 12 = ε II Important conclusion: Though distributed on a longer time scale, deposited energy / area is the same (!)

T.Eich 23 / 26 rehearsal for PFMC, Jülich W/C: ELM energy fluency Regression result for JET-C and JET-ILW ELM energy fluency (combined DB) Worth notifying: Very weak dependency on the relative ELM loss size (!) v*v* E ELM /W plasma (%)

T.Eich 24 / 26 rehearsal for PFMC, Jülich Only JET-ILW data Result for JET-ILW only: Almost linear to the pedestal pressure B.Sieglin

T.Eich 25 / 26 rehearsal for PFMC, Jülich Outlook The ultimate goal of this study is to provide a Multi-Machine Scaling for ELM energy fluency and the power deposition ELM time scales by combining JET, DIII-D and ASDEX Upgrade divertor ELM heat load data The next step is the inclusion of ASDEX Upgrade data and to provide (i) major R scaling (ii) extrapolation to ITER and (iii) case to compare with ELM models and ELM modelling (JOREK) For this endeavour we have run test pulses in GLADIS with JET lamellae, W-coated CFC target and AUG Div-III solid W target plates, in order to cross check JET and ASDEX Upgrade heat load data Latter experiments in GLADIS are presented in the poster of Bernd Böswirth (Date, Poster ID)

T.Eich 26 / 26 rehearsal for PFMC, Jülich Summary & Conclusions Pedestal top pressure and temperature is reduced for the reference pulses with same I p / B tor and heating power in JET-ILW At identical pedestal top densities and temperatures, ELM heat load time scales in JET-ILW and full-W AUG w.r.t ‘carbon’ similar ELM peak energy fluency (J/m 2 ) for JET-C and JET-ILW at given pedestal top pressure is very similar Simple regression reveals weak dependency of divertor peak energy fluency on relative ELM loss for JET data base Latter explains the observed absence of a mitigation of divertor peak heat fluxes with increased ELM frequencies at constant pressure, e.g. by kicks, in ripple discharges, ELM pellet pacing or simple gas puffing However, exceptions are e.g. B-coils in AUG or pellets in DIII-D

T.Eich 27 / 26 rehearsal for PFMC, Jülich Back Up (GLADIS) Results from GLADIS (B.Böswirth & B.Sieglin) α=333 kW/K/m 2

T.Eich 28 / 26 rehearsal for PFMC, Jülich EFCC & kicks for ELM mitigation n e,ped (10 19 m -3 )  rot (krad/sec) (pedestal) W thermal (MJ) T e,ped (keV)  f ELMs up ~3 (in this example)  ELM size reduced Δ W ELM by a factor of ~2.5  W~10% kicks EFCCs ~15 Hz 45 Hz+/ Hz+/ Time (sec) Courtesy of E. de la Luna  δ av =0.45, 2.2T/2.0MA (q 95 =3.6)  Moderate reduction in W th <10%  n e reduction (edge & core) ~ 30% : slightly higher for kicks (higher f ELM )  T e,ped, (and T i,ped ) up by ~ 25% Details:

T.Eich 29 / 26 rehearsal for PFMC, Jülich ε ELM versus p ped,e Assessing ELM mitigation techniques:

T.Eich 30 / 26 rehearsal for PFMC, Jülich To Do, Improvements Suttrop: AUG B-coils Jachmich: EFCC Results Power versus time for AUG

T.Eich 31 / 26 rehearsal for PFMC, Jülich ELM Heat Load Good agreement of ILW data with free streaming approach No dependence on relative ELM size