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(EXP4/25) The Control of Divertor Carbon Erosion/Redeposition in the DIII-D Tokamak

D. G. Whyte1), W. P. West2), C. P. C. Wong2), R. Bastasz3), J. N. Brooks4), W. R. Wampler3), N. H. Brooks2), J. W. Davis5), R. Doerner1), A. A. Haasz5), R. C. Isler6), G. L. Jackson2), R. G. Macaulay-Newcombe5), M. R. Wade6)
 
1) Fusion Energy Research Program, University of California, San Diego, La Jolla, California USA
2) General Atomics, P.O. Box 85608, San Diego, California 92186-5608 USA
3) Sandia National Laboratories, Albuquerque, New Mexico & Livermore, California USA
4) Argonne National Laboratory, Argonne, Illinois USA
5) University of Toronto Institute for Aerospace Studies, Toronto Canada
6) Oak Ridge National Laboratory, Oak Ridge, Tennessee USA

Abstract.  The DIII-D tokamak has demonstrated an operational scenario where the graphite-covered divertor is free of net erosion. Reduction of divertor carbon erosion is accomplished using a low temperature (detached) divertor plasma that eliminates physical sputtering. Likewise, the carbon source rate arising from chemical erosion is found to be very low in the detached divertor. Near strikepoint regions, the rate of carbon deposition is $ \sim$ 3 cm/burn-year, with a corresponding hydrogenic codeposition rate > 1kg/m2/burn-year; rates both problematic for steady-state fusion reactors. The carbon net deposition rate in the divertor is consistent with carbon arriving from the core plasma region. Carbon influx from the main wall is measured to be relatively large in the high-density detached regime and is of sufficient magnitude to account for the deposition rate in the divertor. Divertor redeposition is therefore determined by non-divertor erosion and transport. Despite the success in reducing divertor erosion on DIII-D with detachment, no significant reduction is found in the core plasma carbon density, illustrating the importance of non-divertor erosion and the complex coupling between erosion/redeposition and impurity plasma transport.

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IAEA 2001