Design consideration of an x-ray imaging crystal spectrometer for China Fusion Engineering Test Reactor

The x-ray imaging crystal spectrometer (XICS) is proposed as the principal method of diagnostics for plasma ion temperature and rotation for the China Fusion Engineering Test Reactor (CFETR) for its simplicity in implementation and no reliance on neutral beams. For D-T experiments with the electron temperature as high as 35-40 keV at the core region, highly charged high-Z ions can serve as the diagnostic ions for the XICS. For the CFETR, Xe⁴⁴⁺, Xe⁵¹⁺, and W⁶⁴⁺ are selected as the impurity ions. Appropriate crystal parameters are selected, as well as the preliminary layout for the spectrometer. We estimated the general performance of the spectrometer, including the emissivity of the impurities, the spatial resolution of the x-ray detector, and the expected count rate of line emissions. For the application in the fusion reactor environment, the effect of neutron irradiation on the crystal is briefly discussed.