Initial characterization of MPA CVD diamond to be investigated by fracture toughness measurements

Microwave Plasma Assisted (MPA) Chemical Vapour Deposition (CVD) optical quality polycrystalline diamond is used in shape of disks with thickness of 1 to 2 mm in window units for plasma heating and stabilization in nuclear fusion devices. Due to limited body of work in literature and the important safety role of the disks, fracture toughness measurements on this type of diamond are planned to check its resistance against crack propagation. In this work, the activities aiming to characterize the diamond samples prior to the experiments are discussed mainly with reference to X-ray diffraction, electron backscatter diffraction and loss tangent measurements. For in-depth understanding, thermal grade diamond has been also considered. It grows much faster than the optical grade and it has a greater density of microfeatures. In addition, the design and thermo-mechanical performance of a typical diamond window unit in nuclear fusion devices are presented.