Deposition in JET divertor tiles has been observed to be
asymmetric; i.e. heavy deposition occurs in the SOL at
the inner divertor whereas there is little deposition at
the outer divertor. Heavy deposition at the inner
divertor has lead to flaking on the water-cooled louvres
and after the DTE1 tritium experiment at JET it was
observed that majority of the retained tritium is in the
flakes that have spallen from the louvres.
Erosion/deposition issues have thus a great impact on the
tritium retention and lifetime of first wall components
in present and future fusion devices.
The asymmetry in the deposition implies a drift in the
SOL. To investigate material transport and SOL flows
observed at JET, 13CH4 and SiH4 were injected into the
plasma boundary in the last day of discharges prior to
the JET 2001 shutdown. Methane was puffed at the top of
the vessel, and the silane at the outer divertor wall.
Silicon was observed spectroscopically as an impurity in
the plasma. A set of special tiles was installed in the
Mk IIGB divertor during the 1999 shutdown. The tiles were
coated with poloidal stripes of a boron doped carbon
layer on a rhenium interlayer. These tiles were removed
in the 2001 shutdown, and have been analysed in 2002 to
determine the erosion/deposition profile, and 13C and
28Si distribution over the entire divertor cross-section.
The analysis techniques used have been Secondary Ion Mass
Spectrometry (SIMS) and the Ion Beam Analysis (IBA)
methods Time of Flight Elastic Recoil Detection Analysis
(TOF-ERDA) and Rutherford backscattering (RBS).
13C could be found in large amounts on the surfaces of
the inner divertor tiles whereas in the outer divertor it
was hardly detected. Under the 13C layer a deuterium rich
carbon layer was found on the inner divertor tiles. Thick
deposits of beryllium were buried under the carbon layer.
Also the silicon distribution was recorded. The observed
13C and Si distributions are discussed in relation to the
position of strike point and the ion fluxes measured with
divertor Langmuir probes.
This work has been conducted under the European Fusion
Development Agreement and is partly funded by EURATOM.
|Title of host publication||22nd Symposium on Fusion Technology|
|Subtitle of host publication||Book of Abstracts|
|Place of Publication||Espoo|
|Publisher||VTT Technical Research Centre of Finland|
|Publication status||Published - 2002|
|Event||22nd Symposium on Fusion Technology - Helsinki, Finland|
Duration: 9 Sep 2002 → 13 Sep 2002
Conference number: 22
|Conference||22nd Symposium on Fusion Technology|
|Period||9/09/02 → 13/09/02|