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Local deposition of 13C tracer at the JET MkII-SRP outer divertor

Local deposition of 13C tracer at the JET MkII-SRP outer divertor. J Paul Coad Hydrogen Workshop, Salamanca, 2-3 June 2008. Local deposition of 13 C tracer at the JET MkII-SRP outer divertor

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Local deposition of 13C tracer at the JET MkII-SRP outer divertor

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  1. Local deposition of 13C tracer at the JET MkII-SRP outer divertor J Paul Coad Hydrogen Workshop, Salamanca, 2-3 June 2008

  2. Local deposition of 13C tracer at the JET MkII-SRP outer divertor • J. P. Coada, , L. K. Aho-Mantilab, M. I. Airilab, D. E. Holec, J. Likonend, A. Widdowsona and JET- EFDA Contributors[1] • JET-EFDA Culham Science Centre OX14 3DB, Abingdon, UK • aUKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, U.K. • bAssociation EURATOM-Tekes, Helsinki University of Technology TKK, PO Box 4100, 02015, TKK, Espoo, Finland • d Dept. of Engineering and Design, University of Sussex, Brighton, BN1 9QH, East Sussex, UK • eAssociation EURATOM-Tekes, VTT, PO Box 1000, 02044 VTT, Espoo, Finland • Introduction • 13C puffing experiment in 2004 • Local deposition near the puffing port • General considerations of shadowing in the JET divertor • Mk I divertor 1994-5 • Mk II divertors 1995 - present time • Conclusions [1]See the Appendix of M.L. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu) IAEA, (2006)

  3. 13C-methane puffing experiment in 2004 • 31 similar pulses on last day of operation • ELMy H-mode discharges:- BT 1.2T, IP 1.2 MA, ~7.5 MW additional heating • Total of 4.3 1023 molecules 13C-methane puffed in outer divertor from 48 locations • Approximate line of W-stripe is shown as white dashes

  4. Field line plot showing strike points and SOL region for the 13C-puffing experiment • Occasional sweeps of strike-point position for Langmuir probe data • Collector probe on reciprocating probe in SOL at top of machine

  5. Amounts of 13C measured on divertor tiles by SIMS and IBA Note: Measurements have been extrapolated, assuming toroidal symmetry Tile 13C amount(%) 1 2.2% 3 0.7% 4 3.2% SRP 1.8% 6 2.5% 7 15.4% 8 0.9% Total 27.0% Tile 1 Tile 3 Tile 4 Tile 8 Tile 7 Tile6 SRP Shadowing edge

  6. Modelling of SIMS and IBA data J Strachan et al

  7. G7B 8 7 6 5 4 3 2 1a 1 0a

  8. Total number deposited 13C in this area is ~215 x1018 atoms Tungsten stripe 13C injection 20mm Cores cut for SIMS analysis Deposition in shadow on tile 14OW G7B

  9. Be 13C 11063 11041 11047 O 12C 20mm

  10. 13C deposition on 2ON G7A

  11. D and 13C concentrations Count rate Distance on tile (poloidally), mm Ion Beam Analysis (Nuclear Reaction Analysis) data across tile depend on where line is relative to injection point

  12. 12C and 13C concentrations Count rate Distance on tile (poloidally), mm IBA data show film in shadowed region is almost pure 13C (plus a lot of H)

  13. Deposition at the JET Mk I divertor JET MkI divertor operated 1994-5, first with C, then Be tiles Pairs of tiles were mounted on water-cooled poloidal bars, 196 bars toroidally. There was a gap between each bar. Tiles were in a “roof-top” arrangement

  14. Cross-section of tiles of the JET Mk I divertor, and deposition at the outer strike zone • Exposed part of each tile in strike zone eroded • local re-deposition in the shadowed area

  15. Subsequent JET divertors have used large format tiles mounted to solid carriers, in turn mounted on a water-cooled support structure Pumping is only through the corners of the divertor, heavy deposition in these regions No significant deposition in areas shadowed toroidally on tiles

  16. Tritium remaining in the JET vessel after DTE1 in 1997 Collected from the louvres and divertor floor Rest of T assumed to be in flakes at bottom of vessel R-D Penzhorn, N Bekris, FZK, Karlsruhe

  17. G7B 8 7 6 5 4 3 2 1a 1 0a

  18. Tile 3, exposed 1998-2001 Region of tile shadowed by adjacent tile

  19. JET septum 1998-2001 Almost complete separation of inner and outer divertor, somewhat analogous to ITER

  20. Campaign averaged strikepoint position Source 0.8 mm 2.5 mm 15 mm Long term analysis in collaboration with TF FT Hydrocarbon migration in JET Recent analysis of septum shows low deposition ! Fit to sticking monitors:99% with sticking 0.9<1% with very low sticking Migration to ITER pump ducts may not be large Mayer, Rubel, Coad

  21. Conclusions • Thick deposits of 13C-H found in shadowed zone where puffed methane enters divertor • Overall 13C balance only marginally improved • Pattern of deposition in JET may be influenced by particle flow • Septum/PFR data in JET are encouraging for ITER dome, BUT this may be totally misleading

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