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Presented by Gerard van Rooij

Tungsten divertor erosion in all metal devices: lessons from the ITER-like wall of JET and the all tungsten ASDEX Upgrade. Presented by Gerard van Rooij Dutch Institute For Fundamental Energy Research, Assoc. EURATOM-FOM, The Netherlands PSI-20, Aachen, May 2012.

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Presented by Gerard van Rooij

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  1. Tungsten divertor erosion in all metal devices: lessons from the ITER-like wall of JET and the all tungsten ASDEX Upgrade Presented by Gerard van Rooij Dutch Institute For Fundamental Energy Research, Assoc. EURATOM-FOM, The Netherlands PSI-20, Aachen, May 2012

  2. with thanks to co-authors J.W. Coenen1, L. Aho-Mantila2, S. Brezinsek1, M. Clever1, R. Dux3, M. Groth4, K. Krieger3, S. Marsen3, G.F. Matthews5, A. Meigs5, R. Neu3, S. Potzel3, T. Pütterich3, J. Rapp6, M.F. Stamp5, the ASDEX Upgrade Team3 and JET-EFDA Contributors** JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon, UK 1Institute of Energy and Climate Research, ForschungszentrumJülich, Assoc EURATOM-FZJ, Jülich, Germany* 2VTT, P.O. Box 1000, FI-02044 VTT, Finland 3Max-Planck-Institut fürPlasmaphysik, Association EURATOM-IPP, Germany 4Aalto University, Association EURATOM-Tekes, Espoo, Finland 5Culham Centre for Fusion Energy, EURATOM-CCFE Association, Abingdon, UK 6Oak Ridge National Laboratory, Oak Ridge, USA *Partner in the Trilateral Euregio Cluster **See App. of F. Romanelli et al., Proceedings of the 23rd IAEA Fusion Energy Conf. 2010, Daejeon, Korea

  3. The questions • W impurity in plasma core leads to radiative cooling of plasma  must be controlled • ITER-Like Wall: highest W sputtering in outer divertor • This work: • What is the tungsten source in the outer divertorand by what is it determined: JET (& ASDEX Upgrade) • as a first step towards: • Divertor screening – how much comes out and how much is retained W?

  4. The ingredients • What is the tungsten source in the outer divertor and by what is it determined: • Identity and concentration of impurities (sputtering by hydrogen ions is insignificant) • Energy of impinging particles: • charge state, i.e. Te and transport • sheath acceleration, i.e. Te (and Ti)

  5. Outline • Approach to quantify W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species – compare JET & ASDEX-Upgrade • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering – compare JET & ASDEX-Upgrade • How to control sputtering • Conclusions

  6. Approach to quantify W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering • How to control sputtering • Conclusions

  7. W source from spectroscopy Divertor plasma • Integrating over line of sight: • and also S′ ne, Teincrease W+ * W+ Hn e.g. 400.9 nm S B W* W Imp X Y W target

  8. S/XB from experimental data base • Previously (e.g. ASDEX Upgrade) constant S/XB = 20 was commonly used • This work uses multi-machine fit for S/XB (Te) M. Laengner, this conference

  9. Direct imaging divertor spectrometer system New los (orange) and old (blue) Design covers full outer divertor target plate (360 mm = 20 ROI) MeigsHTPD andthisconference

  10. Example W I measurement in L-mode Three heating steps intensity profile of W I (400.9 nm) versus time spatial resolution ~1.8 cm time resolution ~40 ms sawteeth

  11. Te and G: probes or spectroscopy • Spectroscopy on Balmer epsilon G • (nearby W I 400.9 nm) • Probes  Te, G • In both cases correlation of local flux densities as well profile integrated G’s agree!

  12. Approach to quantifying W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering • How to control sputtering • Conclusions

  13. Investigate Yeffective(Te) • #82195: 1 MW NBI • Ramping divertor fuelling • Increases divertor ne • decreases Te • Increases G • Z-eff (i.e. impurity influx) changes with 10% • Tungsten erosion drops • Similar experiment with steps in density

  14. Be content sufficient for Yeff(Te) • Be fraction on basis of spectroscopy: 0.5% !! • Be fraction on basis of Z-eff: 3% • C fraction on basis of spectroscopy: 0.05% !! • Be charge state not evident, but at least 2+ • coronal equilibrium Be Be+ Be2+ Be3+ Be4+ • Thus beryllium sputtering dominates over carbon and oxygen!

  15. Compared with ASDEX Upgrade 4.0% C4+ 2.0% C4+ 1.0% C4+ 0.5% Be4+ 0.5% Be2+ 0.1% Be4+ ASDEX Upgrade JET, density steps JET, density ramp ASDEX Upgrade data: Dux et al., J Nucl Mat 390–391 (2009) 858

  16. Approach to quantifying W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering • How to control sputtering • Conclusions

  17. Zeff scan & Te oscillations (sawteeth) impurity content varies 3 MW 1 MW 2 MW ne = 1.6·1019 m-3 2.0·1019 m-3 2.8·1019 m-3 Te oscillations dominate Te (eV) Experimental approach: 3 steps in heating power for three densities t (s)

  18. Correlate instantaneous Yeff and Te WI 400.9 (ph/s·cm2·sr) WI 400.8 nm, PMT, raw WI 400.8 nm, PMT, smoothed Te from Langmuir probes 15.0 15.2 15.4 15.6 15.8 16.0

  19. W I measurement

  20. Zeffnotonly parameter forYeff 3 MW ICRH 2 MW ICRH 1 MW ICRH Effect of steps in power in line with Be impurity variation Sputtering yield ~quadruples in each density step ne = 1.6·1019 m-3 3 MW ICRH 2 MW ICRH 1 MW ICRH ne = 2.0·1019 m-3 0.5% Be2+ 3 MW ICRH 2 MW ICRH 1 MW ICRH ne = 2.8·1019 m-3 1 MW NBI ramp Be fraction doubles in each step 1 MW 2 MW 3 MW • Density determines: • impurity content / charge state • CX D-atoms •  D. Harting, this conference ne = 1.6·1019 m-3 2.0·1019 m-3 2.8·1019 m-3

  21. Approach to quantifying W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering • How to control sputtering • Conclusions

  22. Signature of prompt redeposition?  B Divertor plasma W+ Hn e.g. 364 nm S′ rL B ′ ne, Teincrease lion W+ * W+ W0 X′ Hn e.g. 400.9 nm S B W* W Imp X Y W target

  23. Where to expect changes?

  24. Suitable lines in UV

  25. WII / WI changes observed! 1.41019 m-3, 50 eV: 41018 m-3, 50 eV: Factor 2 change indicates >50% redeposition Textorsameresultatsame Te and ne S. Brezinsek et al., Phys. Scr. T145 (2011) 014016.

  26. Approach to quantifying W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering • How to control sputtering • Conclusions

  27. H-mode sputtering dominated by ELM 13 MW NBI, ne =7.5·1019 m-3, 10 Hz ELMs • Striking constancy of He

  28. JET and ASDEX Upgrade H-mode sputtering compared JET: 13 MW NBI, ne =7.5·1019 m-3, 10 Hz ELMs average between ELMs • Factor 6 between inter- and intra-ELM sputtering  • Similar ratio for JET Te=20 eV and AUG Te=6 eV ASDEX: Dux et al., J Nucl Mat 390–391 (2009) 858

  29. Approach to quantifying W erosion • L-Mode divertor tungsten sputtering • Identification of the main sputtering species • Effect of varying the beryllium concentration • Diagnosing prompt redeposition • H-mode divertor tungsten sputtering: inter- versus intra-ELM sputtering • How to control sputtering • Conclusions

  30. ImpurityseedingtodecreaseTdiv Increasing N • Trade off betweenincreasingimpurityconcentrationanddecreasingTdiv • Possible in L-modeand in-between ELMs. • ELMs, however, will burnthrough Increasing N L. Aho-Mantila, this conference

  31. Conclusions • Beryllium main sputtering particle, carbon order of magnitude less • Effective erosion yields of typically 10-4 in L-mode order of magnitude lower compared to intra-ELM sputtering in ASDEX Upgrade • Intra-ELM sputtering dominates, in given example by factor 5 • Total W source between 2·1018 and 3·1019 /s have been observed for the outer divertor • For the first time effect of prompt deposition observed in tungsten divertor spectroscopy • N2 seeding effectively suppresses sputtering

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