CVD Diamond Disks for ITER ECH windows - dielectric loss characterization and optical inspection

Diamond disks with a diameter of 70 mm and a thickness of 1.11 mm will be installed into windows of the Electron Cyclotron Heating and Current Drive System (EC-HCD) of the fusion reactor ITER. The bare disks, manufactured by a microwave plasma assisted chemical vapor deposition process, need to ensure high mechanical stability, thermal conductivity and transmission of MW-class microwave beams. Factory acceptance tests of the disks produced by Diamond Materials include a check of dimensional properties and a determination of its dielectric loss. The loss characterization and the comparison with the respective specifications is performed at KIT using dedicated Fabry-Perot
resonators, that allow the measurement of the loss tangent at the disk centre and a mapping of it over the disk area. An optical inspection with a digital microscope completes the examination. More than 60 diamond disks need to be qualified prior to their integration into the window assemblies and the application in the ITER EC-system. The disk qualification activities are performed within a contract between F4E and KIT and the talk will present the current status. Part: KFM