Optimizing ITER Bolometer Cameras in View of Internal Reflections and Crosstalk Between Channels

Bolometer cameras in ITER (lat.: the way) are designed as pinhole and collimator cameras, optimizing the requirements from available physical space, constraints in design options and desired line-of-sight (LOS) distribution. While for both camera types of internal reflections can be significant and lead to an increase in the effective viewing cone, collimator cameras may also suffer from crosstalk of light between channels in case internal apertures are not optimized. The concepts and simulations employed to optimize bolometer collimator cameras are presented. They are based on geometrical considerations for choosing the number and distribution of internal apertures, using the desired viewing cones as input. In the second step, ray-tracing simulations based on the Raysect packages are applied to assess internal reflections as a function of wavelength in the range IR to X-rays for the chosen geometry as well as to assess the impact of choices for material and material finishings (e.g., roughness). Examples presented focus on port-mounted bolometer cameras. The results allow us to improve the geometrical description of bolometer cameras in the ITER database of synthetic diagnostics and thus support performance assessments and studies in the preparation of tomographic reconstructions of plasma radiation. For example, the calculated measurements for LOS assuming standard radiation distributions for ITER are presented.