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Ray tracing analysis of stray light for charge exchange recombination spectroscopy on ITER

Charge exchange recombination spectroscopy (CXRS) provides basic measurements in ITER such as the ion temperature, plasma rotation, and the impurity and helium content. One of the issues concerning all spectroscopic measurements in ITER is the influence of the reflection of light in a vacuum vessel, since ITER will have a full metallic wall, which has higher optical reflectance than a carbon wall. The noise level can be enhanced and the signal can be disturbed by the reflection. In this study, the influences of the light reflection on the CXRS measurement have been investigated using a ray tracing simulation. Influences of the reflection of the active CXRS signal, the light emission from the divertor and scrape off layer, and bremsstrahlung are quantitatively shown in typical discharge scenario cases.