The Joint European Torus (JET) is the largest present-day tokamak. Its main plasma-facing components (PFC) are made of carbon. JET is also fully compatible with operation using a deuterium-tritium mixture and beryllium PFC, which are key features for a reactor-class device such as ITER. To achieve further progress in controlled fusion, the ITER-Like Wall Project at JET is under way in order to explore tokamak operation and plasma-wall interaction issues with a full metal wall: beryllium (Be) in the main chamber and tungsten (W) in the divertor.
The aim of this paper is to overview the scientific and technical issues related to the development of beryllium components of two major categories: (i) Be-coated inconel plates and (ii) bulk limiter tiles including so-called marker tiles designed for studies of Be erosion from the wall. The markers are composed of a layered structure: bulk beryllium block (15 x 30 cm) coated first with a thin high-Z metal film (interlayer) and then with several micrometers of a dense Be layer.
To ensure reliable performance of Be-coated components during tokamak operation, the first important step was the assessment of various beryllium deposition techniques to achieve high purity, thickness uniformity, vacuum compatibility and thermo-mechanical integrity of the coatings with the underlying substrate. Evaporation was selected for coating of the inconel plates and a thermionic vacuum arc method for the marker tiles.
The results of high-heat flux testing (HHF) and detailed characterisation of materials will be presented and discussed. The characterisation, before and after HHF, was carried out using a large set of material analysis methods from ultra-high resolution microscopy and surface sensitive electron spectroscopy to ion beam analysis and X-ray diffraction.
*See the Appendix to the paper of M.L. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Fusion Energy Conference, Chengdu, China 2006), IAEA, Vienna (2006).
|