Investigation of cat's eye mirror with seven reflective surfaces for in-situ spectral calibration system on divertor impurity monitor for ITER

Abstract The divertor impurity influx monitor (DIM) for ITER is spectroscopic system to observe lights emitted from thermonuclear plasma from near ultra violet to infrared region. The spectral characteristics of the DIM system will change during operation due to the harsh environment, and then an in-situ spectral calibration system has been designed for the ITER divertor impurity monitor. A cat's eye mirror with seven reflective surfaces was suggested to apply the system, and then the validation was evaluated in the full-scale ITER DIM optical system. The returning ratios of the cat's eye mirror and micro retroreflector array in the full-scale system were observed using four visible lasers of different wavelengths. The cat's eye mirror is validated for the ITER DIM system, and the potential of improvement by reduction of the reflections were suggested.