The emissivity of W coatings deposited on carbon materials for fusion applications

Tungsten coatings deposited on carbon materials such as carbon fiber composite (CFC) or fine grain graphite are currently used in fusion devices as amour for plasma facing components (PFC). More than 4000 carbon tiles were W-coated by Combined Magnetron Sputtering and Ion Implantation technology for the ITER-like Wall at JET, ASDEX Upgrade and WEST tokamaks.The emissivity of W coatings is a key parameter required by protection systems of the W-coated PFC and also by the diagnostic tools in order to get correct values of temperature and heat loading. The emissivity of tungsten is rather well known, but the literature data refer to bulk tungsten or tungsten foils and not to coatings deposited on carbon materials. The emissivity was measured at the wavelengths of 1.064μm, 1.75μm, 3.75μm and 4.0μm.It was found that the structure of the substrate has a significant influence on the emissivity values. The temperature dependence of the emissivity in the range of 400°C–1200°C and the influence of the viewing angle were investigated as well. The results are given in a table for W coatings and for other materials of interest for fusion such as bulk W and bulk Be.