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Tungsten: an option for divertor and
main chamber plasma facing components
in future fusion devices |
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R. Neu, R. Dux, A. Kallenbach, T. P¨ utterich, M. Balden,
J.C. Fuchs, A. Herrmann, C.F. Maggi, M. O’Mullane,
R. Pugno, I. Radivojevic, V. Rohde, A.C.C. Sips, W. Suttrop,
A. Whiteford and the ASDEX Upgrade team |
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2005 |
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DOI |
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Resumo |
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The tungsten programme in ASDEX Upgrade is pursued towards a full high-Z device. The spectroscopic diagnostic
ofWhas been extended and refined and the cooling factor ofWhas been re-evaluated. TheWcoated surfaces now
represent a fraction of 65% of all plasma facing components (24.8m2). The only two major components that are
not yet coated are the strikepoint region of the lower divertor as well as the limiters at the low field side. While extending the W surfaces, the W concentration and the discharge behaviour have changed gradually pointing to
critical issues when operating with a W wall: anomalous transport in the plasma centre should not be too low,
otherwise neoclassical accumulation can occur. One very successful remedy is the addition of central RF heating at
the 20–30% level. Regimes with low ELM activity show increased impurity concentration over the whole plasma
radius. These discharges can be cured by increasing the ELM frequency through pellet ELM pacemaking or by
higher heating power. Moderate gas puffing also mitigates the impurity influx and penetration, however, at the
expense of lower confinement. The erosion yield at the low field side guard limiter can be as high as 10−3 and fast
particle losses from NBI were identified to contribute a significant part to the W sputtering. Discharges run in the
upper W coated divertor do not show higher W concentrations than comparable discharges in the lower C based
divertor. According to impurity transport calculations no strong high-Z accumulation is expected for the ITER
standard scenario as long as the anomalous transport is at least as high as the neoclassical one. |
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