Diamond windows diagnostics for fusion reactors—Updates of the design

Abstract The future nuclear fusion power plants will require Electron Cyclotron Heating and Current Drive (ECH&CD) systems to heat up and stabilize the plasma inside the vacuum vessel. One of the key components of such systems is the Chemical Vapor Deposition (CVD) diamond window. The purpose of this device is to act as vacuum and tritium boundary while providing a high microwave transparency with minimal reflectivity. Although suited for high power microwave operation, the windows shall be internally monitored in order to properly ensure the ECH system efficiency and safety. In this paper, the latest assessment study on a set of diagnostics to be part of the window assembly is shown. The required diagnostics include arc and tritium detection, microwave stray radiation (perpendicular to the main beam and generated by cracks in the windows), pressure and disk temperature measurements. The devices must have a compact, simple and flexible layout, with a rugged design, to maximize serviceability and durability. When multiple options are possible for some of the diagnostic systems (e.g., scintillation devices vs solid state detectors for tritium detection), tradeoffs were assessed. To accommodate the diagnostics previously mentioned, a new design for the window housing was developed. As the design of the original diamond window assembly underwent further development since the beginning of this project, an update of the general layout was required. The new layout presented here integrates the updates of the windows assembly with those to the diagnostics. To validate the concepts, a test bench was developed to carry out measurements under conditions similar to the operative ones.