O-36, p 1(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Divertor heat load in ITER-like advanced tokamak scenarios on JET G.Arnoux 1,(3), P.Andrew 1, M.Beurskens 1, S.Brezinsek 2, C.D.Challis 1, P.DeVries 1, W.Fundamenski 1, E.Gauthier 3, C.Giroud 1, A.Huber 2, S.Jachmich 4, X.Litaudon 3, R.A.Pitts 5, F.Rimini 3 and JET-EFDA collaborators* 1 EURATOM/UKAEA Fusion Association, Culham Science Center, Abingdon, Oxon, OX14 3DB, UK 2 Institüt für Energieforschung – Plasmaphysik, Forschungzentrum Jülich, Trilateral Euregio Cluster, EURATOM- Assoziation, D Jülich, Germany 3 Association EURATOM-CEA, INRFM, CEA/Cadarache, F St Paul-Lez-Durance, France 4 Association “EURATOM-Belgian State” Laboratory for Plasma Physics Koninklijke Militaire scholl – Ecole Royale Militaire Renaissancelaan 20 Avenue de la renaissance, B-1000 Brussels Belgium 5 Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (EPFL), CRPP, CH Lausanne, Switzerland *See Appendix in M.L.Watkins et al., 21 st IAEA Fusion Energy Conference, 2006, Chengdu, China

O-36, p 2(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008Introduction Power balance –P in =P cond +P rad –P in =P div +  P rad –P div =P cond +(1-  )P rad Heat load on divertor targets –P div =P in -  P rad = P in (1-  f rad ) P rad ∝n e 2 Z eff –Density: n e –Impurities: Z eff P in P rad P cond High  configuration Outer target Inner target

O-36, p 3(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Heat load and the ITER-like wall Steady-state heat loads onto the divertor must be controlled –Wetted area (target geometry and scrape-off layer transport) –Radiative fraction, f rad : high density + extrinsic impurity seeding In ITER: steady-state P div,pk ≤10MW/m 2 –Optimised divertor geometry (wetted area~4m 2 ) –Partially detached plasma (high n e ) –f rad =75% probably using argon P div must be assessed for the JET ITER-like wall (ILW) –Divertor tiles in CFC coated with tungsten: T surf <1600 o C –Tile 5 in tungsten: q ⊥, pk <7.5MW/m 2 for 10s (higher q ⊥, pk for shorter pulse) –Main chamber walls: beryllium (main radiator) Scenarios in high triangularity configuration compatible with ILW –Baseline scenario (BL): inductive current –Advanced tokamak scenario (AT): steady-state scenario Up to now, edge of plasmas in AT scenarios poorly documented

O-36, p 4(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Scenarios in high  configurations AT BL Current Non-inductive maximised Inductive Density 4<n e,av <5∙10 19 m <n e,av /n e,gr <0.8 n e,av ≃ 10∙10 19 m -3 n e,av /n e,gr ≃1 T e at target 20<T e <40eV T e ≃ 10eV P in >16MW

O-36, p 5(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Divertor heat load measurement PFR SOL Space and time resolution –  s=16mm (  r ≃ 4mm) –  t=20ms (60  s exposure) Time averaged profiles –P in ≃Cste –f rad ≃ Cste (inter-ELM) –Strike point position THEODOR => heat load Correction factor from thermocouple Inner target – 1.3<E IR /E TC <2.0 Outer target –0.5<E IR /E TC <1.0

O-36, p 6(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Heat load reduction on targets Neon seeding 18MW≤P in ≤24MW

O-36, p 7(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008Radiation

O-36, p 8(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Peak heat load reduction Outer target: 10MW/m 2 No clear dependence on injection location. Better cooling with N 2 ? At f rad =50% same heat load for AT (seeded) and BL (higher density), but… On inner target: 3MW/m 2 => T surf =1600 o C after… 50s => shorter pulses than 10s (P in =24MW)

O-36, p 9(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Plasma contamination? Low density and high P rad => Higher Z eff ( ∝P rad /n e 2 ) Higher W sputtering in ILW => Impurity accumulation in the core (ITB)? Increasing density (f gw >0.8?) => same heat load reduction but lower Z eff. (Zagorski et al.) n e,av f gw Z eff

O-36, p 10(10) G. Arnoux 18 th PSI, Toledo, 26-30/05/2008 Summary and conclusion First measurements of divertor heat load in AT scenario on JET (no ITB) AT scenario will be an issue in ILW for long pulse operation at P in =45MW (outer target) Heat load reduced at the level of baseline scenario with impurity seeding (same P rad ) but high Z eff Will tungsten sputtering be a problem for core accumulation (ITB)? What is the net gain for divertor heat loads when increasing density and P in ?