(EX/P4-16) Localized Tungsten Deposition in Divertor Region in JT-60U

Y. Ueda1), M. Fukumoto1), J. Watanabe1), Y. Ohtsuka1), T. Arai2), N. Asakura2), Y. Nobuta2), M. Sato2), T. Nakano2), J. Yagyu2), K. Ochiai3), K. Takakura3), T. Tanabe4)
 
1) Graduate School of Engineering, Osaka University, Osaka, Japan
2) Japan Atomic Energy Agency, Mukouyama, Naka, Ibaraki-ken 311-0193, Japan
3) Japan Atomic Energy Agency, Tokai-mura, Naka, Ibaraki-ken 319-1195, Japan
4) Interdisciplinary Graduate School of Engineering Science, Kyusyu University, Hakozaki, Fukuoka 812-8581, Japan

Abstract.  Deposition profiles of tungsten released from the outer divertor were studied in JT-60U. A neutron activation method together with XPS and EDX was used for the first time to accurately measure deposited tungsten on the graphite tiles in tokamak devices. Surface density of tungsten in the thick carbon deposition layer can be measured by this method. In the experimental campaigns 2003-2004 (1st) and 2005-2006 (2nd) in JT-60U, 12 tungsten-coated CFC tiles (10 tiles for the 2nd campaign) were installed in the outer divertor (section P-8). This tile array covered about 1/21 toroidal length. In most discharges, W-tiles were faced with the outer SOL plasma. Although some of discharges (2-3% of total number) had outer strike points on the W-tiles, most of tungsten erosion took place without strike points on the W-tiles. It was observed that eroded tungsten was mainly deposited on the inner divertor (around inner strike points) and on the outer wing of the dome. Tungsten deposition on the dome tiles was found only near the top surface (within the depth of a few μm), while tungsten on the inner divertor tiles was codeposited with carbon to the depth up to about 60 μm. Toroidal distribution of the W deposition was significantly localized near the tungsten released position both on the outer wing and on the inner divertor. Toroidal localization of tungsten deposition was more pronounced on the outer wing than the inner divertor. These data suggested that inward drift in the divertor region played a significant role in tungsten transport in JT-60U. In addition, asymmetry of tungsten toroidal distribution on the outer wing suggested the effect of plasma flow along magnetic fields on the tungsten transport.

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