Development of W Coatings for Fusion Applications
The paper gives a short overview on tungsten (W) coatings deposited by various methods on carbon materials (carbon fibre composite - CFC and Fine Grain Graphite - FGG). Vacuum Plasma Spray (VPS), Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) techniques are analyzed in respect with the characteristics and performances of the W coatings. A particular attention is paid to the Combined Magnetron Sputtering and Ion Implantation (CMSII) technique, which was developed during the last 4 years from laboratory to industrial scale and it is successfully applied for W coating (10-15mm and 20-25mm) of more than 2,500 tiles for the ITER-like Wall project at JET and ASDEX Upgrade. This technique involves simultaneously magnetron sputtering and high energy (tens of keV) ion implantation. Due to the ion bombardment a stress relief occurs within the coating enabling its growth without delamination to a relatively large thickness. In addition, in order to adjust the thermal expansion mismatch between CFC and W, a Mo interlayer of 2-3mm is currently used. Experimentally, W/Mo coatings with a thickness up 50mm were produced and successfully tested in the GLADIS ion beam facility up to 23MW/m2.