O-36, p 1(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

Divertor heat load in ITER-like Divertor heat load in ITER-like advanced tokamak scenarios advanced tokamak scenarios

on JETon JETG.Arnoux1,(3), P.Andrew1, M.Beurskens1, S.Brezinsek2, C.D.Challis1,

P.DeVries1, W.Fundamenski1, E.Gauthier3, C.Giroud1, A.Huber2, S.Jachmich4, X.Litaudon3, R.A.Pitts5, F.Rimini3 and JET-EFDA collaborators*

1EURATOM/UKAEA Fusion Association, Culham Science Center, Abingdon, Oxon, OX14 3DB, UK2Institüt für Energieforschung – Plasmaphysik, Forschungzentrum Jülich, Trilateral Euregio Cluster, EURATOM-Assoziation, D-52425 Jülich, Germany3Association EURATOM-CEA, INRFM, CEA/Cadarache, F-13108 St Paul-Lez-Durance, France4Association “EURATOM-Belgian State” Laboratory for Plasma Physics Koninklijke Militaire scholl – Ecole Royale Militaire Renaissancelaan 20 Avenue de la renaissance, B-1000 Brussels Belgium 5Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (EPFL), CRPP, CH-1015 Lausanne, Switzerland

*See Appendix in M.L.Watkins et al., 21st IAEA Fusion Energy Conference, 2006, Chengdu, China

O-36, p 2(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

IntroductionIntroduction• Power balance

– Pin=Pcond+Prad

– Pin=Pdiv+Prad

– Pdiv=Pcond+(1-)Prad

• Heat load on divertor targets– Pdiv=Pin-Prad = Pin(1-frad)

• Prad∝ne2Zeff

– Density: ne

– Impurities: Zeff

Pin

Prad

P cond

High configuration

Outer target

Inner target

O-36, p 3(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

Heat load and the ITER-like wallHeat 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, frad: high density + extrinsic impurity seeding

• In ITER: steady-state Pdiv,pk≤10MW/m2

– Optimised divertor geometry (wetted area~4m2)

– Partially detached plasma (high ne)

– frad=75% probably using argon

• Pdiv must be assessed for the JET ITER-like wall (ILW)– Divertor tiles in CFC coated with tungsten: Tsurf<1600oC

– Tile 5 in tungsten: q⊥,pk<7.5MW/m2 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 18th PSI, Toledo, 26-30/05/2008

Scenarios in high Scenarios in high configurations configurations

AT

BL

Current

Non-inductive maximised

Inductive

Density

4<ne,av<5∙1019 m-3

0.6<ne,av/ne,gr<0.8

ne,av 10∙10≃ 19 m-3

ne,av/ne,gr≃1

Te at target

20<Te<40eV

Te≃10eV

Pin>16MW

O-36, p 5(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

Divertor heat load measurementDivertor heat load measurement

PFRPFR

PFR

SOLSOL

SOL

SOL• Space and time resolution– s=16mm (r≃4mm)– t=20ms (60s exposure)

• Time averaged profiles– Pin≃Cste

– frad≃Cste (inter-ELM)

– Strike point position

• THEODOR => heat load

• Correction factor from thermocouple

• Inner target– 1.3<EIR/ETC<2.0

• Outer target– 0.5<EIR/ETC<1.0

O-36, p 6(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

Heat load reduction on targetsHeat load reduction on targets

Neon seeding

18MW≤Pin≤24MW

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

RadiationRadiation

O-36, p 8(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

Peak heat load reductionPeak heat load reduction

Outer target: 10MW/m2

No clear dependence on injection location. Better cooling with N2?

At frad=50% same heat load for AT (seeded) and BL (higher density), but…

On inner target: 3MW/m2 => Tsurf=1600oC after… 50s

=> shorter pulses than 10s (Pin=24MW)

O-36, p 9(10) G. Arnoux 18th PSI, Toledo, 26-30/05/2008

Plasma contamination?Plasma contamination?

• Low density and high Prad => Higher Zeff (∝Prad/ne2)

• Higher W sputtering in ILW => Impurity accumulation in the core (ITB)?

• Increasing density (fgw>0.8?) => same heat load reduction but lower Zeff. (Zagorski et al.)

ne,av

fgw

Zeff

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

Summary and conclusionSummary 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 Pin=45MW (outer target)

• Heat load reduced at the level of baseline scenario with impurity seeding (same Prad) but high Zeff

• Will tungsten sputtering be a problem for core accumulation (ITB)?

• What is the net gain for divertor heat loads when increasing density and Pin?