Within the international thermonuclear experimental reactor ITER, one of the most challenging components is the divertor, whose main function is to extract the power from the scrape-off layer of the plasma and to maintain plasma purity. The main parts of the divertor, i.e. the inner and outer vertical target and the dome liner, comprise various materials which form a composite that is highly resistant to cyclic thermo-mechanical loads.
In the first stage of ITER, the armour of the divertor will be made of carbon fibre reinforced carbon composite and tungsten, where both materials are joined to an actively cooled heat sink, consisting of precipitation hardened CuCrZr. In the later stages of ITER, the entire divertor surface will be covered by tungsten, representing a demand of more than 100 tons of tungsten. The first plasma in ITER has been scheduled for 2018, followed by an operating period of 12 years, where the divertor components will be replaced at least four times.
Furthermore, tungsten and tungsten alloys are presently considered as main candidate materials for helium cooled divertor designs for the next nuclear fusion reactor generation (DEMO). There are two types of applications for such materials, which impose quite different requirements on the properties:
(i) W as a plasma-facing armour or shield component material
(ii) W as a structural material
An armour material needs high cracking resistance under extreme thermal conditions whereas a structural material has to be ductile within the range of operation temperatures. Of course, both material types need to remain stable under high neutron irradiation. The first phase of operation in DEMO has been scheduled from 2033 to 2038. The tungsten material consumption strongly depends on the design, but will be at least more than the double of the amount needed in ITER.