Tungsten and Beryllium Armour Development for the JET ITER-like Wall Project
The operational behaviour and the interplay of the ITER plasma facing material choice has never been investigated in a tokamak experiment. This motivated the ITER-like Wall Project at JET in which the present main chamber CFC tiles will be exchanged with Be tiles and in parallel a fully tungsten-clad divertor will be prepared. Among the scientific objectives of the ITER-like Wall project are general questions of plasma operation with a low melting Be wall, compatibility of all envisaged ITER scenarios with a W divertor, tritium retention and removal and mixed materials effects, erosion behaviour and lifetime investigations. Three R&D programs were initiated: Be coatings on inconel as well as Be erosion markers are developed for the first wall of the main chamber. This work is done by the Romanian Euratom association under the coordination of the Swedish Royal Institute of Technology. Forschungszentrum Jülich, Germany, developed a conceptual design for a bulk W horizontal target plate, based on an assembly of tungsten lamellae. For all other divertor parts five Euratom Fusion Associations performed R&D to provide the technology to coat the 2-directional CFC material used at JET with thin tungsten coatings. High heat flux screening and cyclic loading tests carried out on the Be coatings on Inconel showed excellent performance, above the required power and energy density. For the bulk W, a design was developed to minimise electromagnetic forces. The design consists of stacks of W lamellae of 6mm width that are insulated in toroidal direction. High heat flux tests of a test module were performed on the electron beam facility JUDITH at Forschungszentrum Julich at an absorbed power density up to 9MW/m2 for more than 150 pulses and finally with increasing power loads leading to surface temperatures in excess of 30000C. No macroscopic failure occurred during the test while SEM showed the development of microcracks on the loaded surface. The W coated CFC tiles were subjected to heat loads with power densities ranging up to 23.5MW/m2. In a second step, a selection of coatings was exposed to cyclic heat loading for 200 pulses at 10.5MW/2. All coatings developed cracks perpendicular to the CFC fibres due to the stronger contraction of the coating upon cool-down after the heat pulses.