DIFFER
DIFFER Publication

Impact of carbon and tungsten as divertor materials on the scrape-off layer conditions in JET

Author
Abstract

The impact of carbon and beryllium/tungsten as plasma-facing components on plasma radiation, divertor power and particle fluxes, and plasma and neutral conditions in the divertors has been assessed in JET both experimentally and by edge fluid code simulations for plasmas in low-confinement mode. In high-recycling conditions the studies show a 30% reduction in total radiation in the scrape-off (SOL) layer when replacing carbon (JET-C) with beryllium in the main chamber and tungsten in the divertor (JET-ILW). Correspondingly, at the low-field side (LFS) divertor plate a two-fold increase in power conducted to the plate and a two-fold increase in electron temperature at the strike point were measured. In low-recycling conditions the SOL was found to be nearly identical for both materials' configurations. Saturation and rollover of the ion currents to both low- and high-field side (HFS) plates was measured to occur at 30% higher upstream densities and radiated power fraction in JET-ILW. Past saturation, it was possible to reduce the ion currents to the LFS targets by a factor of 2 and to continue operating in stable, detached conditions in JET-ILW; in JET-C the reduction was limited to 50%. These observations are in qualitative agreement with predictions from the fluid edge code package EDGE2D/EIRENE, for which a 30% reduction of the total radiated power is also yielded when switching from C to Be/W. For matching upstream parameters the magnitude of predicted radiation is, however, 50% to 100% lower than measured, independent of the materials' configuration. Inclusion of deuterium molecules and molecular ions, and temperature and density dependent rates in EIRENE reproduced the experimentally observed rollover of the ion current to the LFS plate, via reducing the electron temperature at the plate.

Year of Publication
2013
Journal
Nuclear Fusion
Volume
53
Number
9
Issue
9
Number of Pages
093016
URL
http://www.euro-fusionscipub.org/wp-content/uploads/2014/11/EFDP12047.pdf
DOI
10.1088/0029-5515/53/9/093016
PId
e6475d91c3e0170859510179c3cf0128
Alternate Journal
Nucl. Fusion
Label
OA
Journal Article
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