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Material Erosion and Redeposition during the JET MkIIGB-SRP Divertor Campaign

Material Erosion and Redeposition during the JET MkIIGB-SRP Divertor Campaign. Trilateral Euregio Cluster. Forschungszentrum Jülich. A. Kirschner, V. Philipps, M. Balden, X. Bonnin, S. Brezinsek, J.P. Coad, D. Coster, S.K. Erents, H.G. Esser,

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Material Erosion and Redeposition during the JET MkIIGB-SRP Divertor Campaign

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  1. Material Erosion and Redeposition during the JET MkIIGB-SRP Divertor Campaign Trilateral Euregio Cluster Forschungszentrum Jülich A. Kirschner, V. Philipps, M. Balden, X. Bonnin, S. Brezinsek, J.P. Coad, D. Coster, S.K. Erents, H.G. Esser, W. Fundamenski, A. Huber, J. Likonen, H. Maier, G.F. Matthews, M. Mayer, R.A. Pitts, M. Rödig, M.J. Rubel, U. Samm, J.D. Strachan, M. Wischmeier, and JET-EFDA contributors 8 October 2006

  2. Outline  Motivation  Deposition on a quartz-microbalance  Erosion/deposition of a tungsten-stripe  13CH4 injection experiment  Conclusions A. Kirschner 2 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  3. Motivation (1) Wall erosion – Material migration – Re-deposition  Critical issues for ITER: - Lifetime of wall elements - Long-term tritium retention - Availability of ITER  Existing experiments necessary for extrapolations to ITER A. Kirschner 3 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  4. Motivation (2) net erosion • JET is currently the most ITER-relevant experiment with respect to: • size • magnetic field • high plasma current • Before upgrade to ITER-like wall: • Understanding of material migration in full-carbon surrounding A. Kirschner 4 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  5. The Quartz Micro Balance (QMB) inner divertor quartz monitor louver Principle: Resonance frequency of quartz changes with mass Thickness resolution: ~0.2 nm Shot-resolved measurement of deposition (erosion) at one specific location. A. Kirschner 5 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  6. QMB deposition in dependenceon strike point position z=-1.32m 1 z=-1.52m 3 z=-1.69m 4 z=-1.74m QMB C deposition [atoms/cm2s] base vertical tiles  H-mode  L-mode tile 3 tile 1 H.G. Esser et al., PSI 04 Largest deposition if strike point is on base plate A. Kirschner 6 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  7. Post-mortem analysis of QMB (1) Schematic horizontal cut of QMB-system across crystal • Quartz • (2) Electronic board (Al2O3) • (3) Lid of copper box • (4) Inner heat shield (stainless steel) • (5) Outer heat shield (stainless steel) • (6) Stainless steel ring with metal mesh A. Kirschner 7 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  8. Post-mortem analysis of QMB (2) Layer Thickness (SIMS) Deposition on quartz Average layer thickness on quartz: 1.85 µm ⇒ in accordance with total frequency shift: 9·1018 C atoms, layer density: ~1 g/cm3 A. Kirschner 8 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  9. Post-mortem analysis of QMB (3) Deposition on inner heat shield Significant deposition on inner heat shield: 6.2·1018 atoms (compared to 9·1018 on crystal) H.G. Esser et al., PSI 06 A. Kirschner 9 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  10. Tungsten stripe on one poloidal rowin the divertor W-stripe (on one poloidal row) SOL 1 8 PFR 7 3 SRP 6 4 W-stripe:  3 µm thickness  2 cm width - Study of erosion and deposition behaviour in the divertor - ITER-like wall project: assessment of required W-layer thickness for outer divertor A. Kirschner 10 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  11. Inner divertor:metallographic cross sections of W-stripe 1 W-layer 3 4 SRP Inner divertor is deposition-dominated Largest deposition on inclined part of tile 4  In total:540 g (3.2·1020 atoms) A. Kirschner 11 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  12. Outer divertor:ion beam analysis of W-stripe 8 7 6 M. Mayer et al., PSI 06 tile 7 Vertical tiles 7, 8 are erosion-dominated Largest erosion at position with highest fluence (tile 7)  Large erosion at apron of tile 8 A. Kirschner 12 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  13. Outer divertor:microscopic analysis of W-stripe SEM picture of tile 7  Non-uniform erosion on a scale-length of 10 – 30 µm  Possible explanation: surface roughness  Preferential erosion of hills, less erosion (or even deposition) in valleys C W 50 µm A. Kirschner 13 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  14. Outer divertor:ERO modelling of net erosion of W-stripe Modelled net erosion along tile 7  Using campaign- averaged plasma parameters C3+ - influx: 0.5%  Symmetry in toroidal direction Red: erosion due to background carbon Blue: erosion due to recycled physically sputtered carbon green: erosion due to recycled chemically eroded carbon  ~ 50% W-redeposition on stripe Erosion-dominated by background carbon Max. erosion ~ 7 µm bottom top A. Kirschner 14 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  15. Overall deposition in the divertor 1 8 7 3 6 4 SRP  Inner divertor tiles 1, 3, 4: 540 g (from metallographic cross-sections)  Outer divertor tile 6: 380 g (from metallographic cross-sections)  Inner louver region: 60 g (from QMB)  In total: 980 g or 5.9·1020 atoms/s Not included: SRP, gaps and main chamber ! Average deposition rate during MkIIGB-SRP is similar to previous campaigns (6.6·1020 in MkIIA and 3.5·1020 in MkIIGB) A. Kirschner 15 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  16. 13C marked methane injection 6.1% 2.7% 0.5% 10.9% 2.5% 3.8% J.P. Coad et al., PSI 06 •  Carried out at last shot day of the campaigns • 13CH4 injection into outer divertor during 32 identical discharges (ELMy H-mode, strike points on vertical tiles) • In total: 4.3·102313C atoms • No further plasma operation 1 8 13CH4 7 3 SRP 6 4 About 20% of injected 13C deposited at outer divertor tiles About 7% of injected 13C at inner divertor tiles 13C also detected on fast reciprocating probe at top of low field side transport around main plasma  Only small amount of 13C at shadowed areas A. Kirschner 16 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  17. 13C marked methane injection:EDGE2D modelling 8 1 13C 7 3 4 6 SRP J.D. Strachan et al., APS 06  NIMBUS code for neutrals, EDGE2D for ions SOL flow adjusted to measured data  No re-erosion of 13C 13C deposition along inner targets • Long-range 13C transport mainly in between ELMs • Most of 13C deposited on outer target (~90%) 13C deposition on inner target in SOL in good agreement with exp. A. Kirschner 17 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

  18. Conclusions - Inner divertor: everywhere deposition-dominated - Outer divertor: vertical tiles erosion-dominated, base plate: deposition - Tungsten stripe: at outer vertical tile heavy erosion ITER-like wall: 200 µm suggested - Material transport to remote areas mainly in specific magnetic configurations (strike point on base plate)  QMB, 13CH4 tracer injection - Estimated fuel retention rate : 2.7% (w/o gaps, SRP and main chamber ⇒ plus 50%) A. Kirschner 18 (18) 21st IAEA, Chengdu, China 16 – 21 Oct 2006

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