Abstract
The ITER divertor impurity monitor (DIM) is a diagnostic system that directly observes 200-1000 nm light emissions from nuclear fusion plasma. Because the DIM observes a wide range of light from infrared to ultraviolet using a single optical system, high optical performance, such as spatial resolution and aberration, is required for the DIM optical elements. The DIM must be highly robust against external environmental factors, such as temperature, humidity, vibration, and magnetic field. Components having high radiation resistance must be used because of the high radiation environment in ITER. In this study, DIM optical elements installed in the interspaces and the port cells are investigated because gamma ray irradiation can impact their optical performance. The irradiation experiments were performed at QST's gamma-ray irradiation facilities in Takasaki. The attenuation of transmittance due to gamma irradiation were evaluated for silica, fluorite, and LiCaAlF6 as the glass material in the spectrometers to be installed in the port cell. The influence of irradiation on silica polka dot beam splitters was found to be negligible; however, the transmittance of high OH concentration fibres for measuring UV light decreased significantly due to irradiation and will thus require countermeasures. The information necessary for proceeding with the ITER DIM design was obtained from these experimental results.
