Studies on 13C Deposition in ASDEX Upgrade

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Studies on 13C Deposition in ASDEX Upgrade
E. Vainonen-Ahlgren1, J. Likonen1, T. Renvall1,
V. Rohde2, R. Neu2, M. Mayer2, R. Pugno2, K.
Krieger2 and the ASDEX Upgrade Team

• 1Technical Research Centre of Finland
• 2Max-Planck-Institut für Plasmaphysik, Germany

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Why did we do this?

• Carbon is considered as divertor target material
  for ITER (good neutrons and heat load resistance,
  low plasma energy loss due to impurities,
  thermodynamically efficient)
• Formation of aC-H layers takes place in tokamaks
  (mechanism is partly unclear)
• In/out assymetry of carbon deposition at the
  divertor
• gt

experimental investigation of material transport
in SOL and divertor deposition was performed
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How did we do this in practice?

• full poloidal set of marker tiles (3-7 µm of C
  on top of 100 nm Re)
• AUG IIb divertor, 13CH4 puffed from

• outer mid-plane, 13 bottom single null H-mode
  (ELM type I) shots, integrated puff time 37s,
  total amount of 13C injected 9x1021 atoms
• main plasma Ip1.0 MA, Bt-2.0T,
  ne8.5x1019m-3, Paux6.5MW
• RBS 1.6 2.5 MeV H beam, SIMS 5 keV O2 beam

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Some points to be kept in mind

• regardless of the only one puffing location,
  toroidal distribution of 13C can be considered
  symmetrical (earlier experiments by R. Neu and A.
  Kallenbach)
• results of the present study represent the
  effect of the main chamber only

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What experimental results did we obtain? (1 of 4)

• total amount of 13C measured was 1x1021 at. (vs.
  9x1021 at. puffed, i.e. 11)
• reason deposition of 13C on central column,
  protection limiter, top area (upper limiter and
  divertor) and underneath the roof baffle

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What experimental results did we obtain? (2 of 4)

• SIMS depth profiles of 13C normalised to 12C
  signal and natural 13C background subtracted.
  Presented profiles are for tiles 1B and 9A
• 13C at the surface region and decrease within
  the bulk

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What experimental results did we obtain? (3 of 4)

• strike points were at the centre in the inner
  divertor tile 4 and the outer divertor tile 1B
• 13C peaks below the strike point are shifted
  toward the roof baffle
• a peak at s1.15 m (top of 1B) might be
  attributed with shadowing by 1A

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What experimental results did we obtain? (4 of 4)

• High peak of 13C on 6A (top inner div.)
• no similar effect at the outer div.
• reason edge SOL particles 13C travels along
  the fieldlines
• small bump of 13C on 9A due to redeposition of
  eroded material from 1B

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What have we learned? (i.e. conclusions)

• Transport by the SOL plasma (and the influence of
  the main chamber only) might be the reason for
• quite high deposition at the top of the inner
  divertor
• smaller total 13C deposition at the inner
  divertor compared with the one at the outer
  divertor by a factor of 1.5

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Long term data

• different sputtering rates
• plasma deposited film 2.50 nm/s
• original Diarc film 0.99 nm/s

SIMS spectrum at s1.51 m (tile 3)
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Long Term Data

• areas with both original and deposited films
  present
• erosion observed on tiles 4 (concave area), 9B
  and 1A

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SIMS RBS

• general trend is similar
• difference at tiles 4 (concave area), 9A and 1A

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We are grateful to

• Association Euratom-Tekes
• DIARC-Technology Inc.