This title appears in the Scientific Report :
2019
Material erosion and deposition on the divertor and vessel walls of W7-X
Material erosion and deposition on the divertor and vessel walls of W7-X
Material erosion and deposition on the divertor and vessel walls of W7-XM. Mayera,*, M. Baldena, S. Brezinsekc, V.V. Burwitza, C.P. Dhardb, A. Dudekb, G.Ehrkeb, R. Guimarãesd, S. Kloseb, R. Königb, M. Krauseb, R. Laubeb, M. Lauxb, A.Manharda, D. Naujoksb, R. Neua, J.Oelmannc, C. Rusete, T.S. Silvad,...
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Personal Name(s): | Mayer, M. (Corresponding author) |
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Balden, M. / Brezinsek, S. / Burwitz, V. V. / Dhard, C. P. / Dudek, A. / Ehrke, G. / Guimarães, R. / Klose, S. / König, R. / Krause, M. / Laube, R. / Laux, M. / Manhard, A. / Naujoks, D. / Neu, R. / Oelmann, J. / Ruset, C. / Silva, T. S. | |
Contributing Institute: |
Plasmaphysik; IEK-4 |
Imprint: |
2019
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Conference: | 17th International Conference on Plasma-Facing Materials and Components for Fusion Applications, Eindhoven (the Netherlands), 2019-05-21 - 2019-05-24 |
Document Type: |
Abstract |
Research Program: |
Plasma-Wall-Interaction |
Publikationsportal JuSER |
Material erosion and deposition on the divertor and vessel walls of W7-XM. Mayera,*, M. Baldena, S. Brezinsekc, V.V. Burwitza, C.P. Dhardb, A. Dudekb, G.Ehrkeb, R. Guimarãesd, S. Kloseb, R. Königb, M. Krauseb, R. Laubeb, M. Lauxb, A.Manharda, D. Naujoksb, R. Neua, J.Oelmannc, C. Rusete, T.S. Silvad, and W7-X TeamaMax-Planck-Institut für Plasmaphysik, Garching, GermanybMax-Planck-Institut für Plasmaphysik, Greifswald, GermanycForschungszentrum Jülich GmbH, Jülich, GermanydUniversity of São Paulo, São Paulo, BrazileNational Institute for Laser, Plasma and Radiation Physics, Bucharest, RomaniaWendelstein 7-X (W7-X) is foreseen to demonstrate the benefits of optimized stellarators at parametersapproaching those of a fusion power plant. Operation phase 1.2a (OP1.2a)in the second half of 2017was the first operation phase with an uncooled but otherwise complete divertor made from fine grain graphite(test divertor unit, TDU) havingthe same geometry as the water-cooled steady-state carbon-fibre-compositedivertor foreseen for operation in the early 2020’s. Erosion and deposition processes on divertor tiles were investigated using specially developed carbon marker coatingswith a thickness of 5 –10μm on a 200nm thick Mo interlayer, which allows separating the marker layer from the carbon bulkfor depth profilingmethods. The thicknesses of the carbon markerlayerswere measured on 132 divertor tiles at 16 different toroidal positions using elastic backscattering of 2.5MeV protons before and after OP1.2a. The surface morphology was investigated using scanning electron microscopy and focused ion beam cross-sectioning. Erosion and deposition processes at the vessel walls were studied using long term samples consisting of Si wafers or thin Ni or a-C:H layerson Si.The divertor operated nominally at room temperature,but with surfaceheating up to 800°C by plasma impact. The carbon markers were substantially eroded at the divertor strike point locations. In areas with maximum erosion the whole carbon marker and even the underlying Mo layer were completely eroded. Eroded surfaces were notably smoothed. This very high erosion was probably due to physical sputtering and chemical erosion by carbon and oxygen ions, which were the main plasma impuritiesduring OP1.2a. Oxygen originated mainly from release of water molecules.Only very small, if any, deposition of carbon and no detectable deposition of metal impurities were observed on the whole divertor surface and in remote divertor areas: The eroded carbon therefore was not redeposited in the divertor region but was transported out of the divertor area and was either redeposited at the vessel walls,inside pump ducts, or was pumped outas CO, CO2, or CH4. This is a profound difference to divertors in tokamaks, where eroded material is typically redeposited in remote divertor areas or in the inner divertor.*Corresponding author:tel.: +49 89 3299 1639, e-mail: matej.mayer@ipp.mpg.de |