NDLI: Experiences With Tungsten Plasma Facing Components in ASDEX Upgrade and JET

Content Provider	IEEE Xplore Digital Library
Author	Neu, R.L. Brezinsek, S. Beurskens, M. Bobkov, V. de Vries, P. Giroud, C. Joffrin, E. Kallenbach, A. Matthews, G.F. Mayoral, M.-L. Pautasso, G. Putterich, T. Ryter, F. Schweinzer, J.
Copyright Year	1973
Abstract	ASDEX Upgrade (AUG) has been converted to all W plasma facing components (PFCs) in 2007 and JET has implemented the ITER like wall (ILW) project (2011) using the same PFC configuration as ITER during its active phase, namely Be in the main chamber and tungsten in the divertor. As a result of the all metal PFCs in both devices much less surface conditioning is needed to arrive at reproducible wall conditions. Specifically, the Be PFCs of JET led to a very small low- Z content (reduction of C and O by at least a factor of 10), reducing the edge radiation in steady-state operation as well as during disruptions. Both devices successfully employ massive gas injection to mitigate disruption forces and power loads to PFCs by radiating up to 100% of the available energy. Hydrogen retention is strongly reduced (AUG: factor 5, JET: factor 10) and the remaining retention is still dominated by codeposition with residual C in AUG and intrinsic Be in JET. The very low edge and divertor radiation could be compensated by impurity seeding either by a single gas species (N₂) (AUG and JET) or by combining N₂ and Ar (AUG) injection for divertor and main chamber radiation, respectively. The W sputtering in the divertor increases when seeding small amounts of N₂, but decreases for higher fluxes due to the plasma cooling provided by the nitrogen radiation. The tungsten content is controlled by the source as well as by its edge and central transport. It could be kept sufficiently small by using a minimum gas fueling to reduce the W erosion and to diminish the W penetration. The control of the central W transport by central (wave) heating had been well established in AUG, however, in both devices the W content is increased during ICRH operation most probably due to increased W sputtering caused by rectified sheaths. The H-Mode threshold is reduced by 20%-30% in AUG and JET, but on average the confinement is lower in JET-ILW than with C PFCs. To date it is not yet clear, whether the reduced H-Mode confinement has to be attributed to the use of W PFCs, since such a clear trend as in JET was not found in AUG. The increase of confinement with N₂ seeding observed in both devices hints to the fact, that low- Z impurities like carbon or nitrogen play a beneficial role for the pedestal confinement.
Sponsorship	IEEE Nuclear and Plasma Sciences Society
Starting Page	552
Ending Page	562
Page Count	11
File Size	1507119
File Format	PDF
ISSN	00933813
Volume Number	42
Issue Number	3
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2014-01-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Plasmas Tungsten Carbon Discharges (electric) Heating Materials Antennas tungsten Plasma properties plasma transport processes tokamaks
Content Type	Text
Resource Type	Article
Subject	Nuclear and High Energy Physics Condensed Matter Physics

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