Diamond windows for microwave application: numerical analyses and characterization by microscope and Raman measurements

Electron cyclotron heating and current drive systems in nuclear fusion devices feature optical quality polycrystalline diamond windows for the transmission of microwave beams of 1 to 2 MW power. The windows consist of diamond disks of 1 to 2 mm thickness integrated into a metallic housing. Numerical analyses verify the performance of such windows with respect to temperature and stress limits. In this work, examples of analyses are provided with reference to a Brewster-angle window design featuring a first-of-its-kind manufactured diamond disk with 180 mm diameter. For the first time, instead of a single constant value, the entire map of the loss tangent measured over the disk has been given as input to the analysis. In addition, examples of microscope and Raman investigations of the disks are shown with reference to dark microfeatures and residual stresses generated by the chemical vapour deposition process.