Assessment of line of sight characteristics of ITER bolometer prototype collimators

This work outlines the present design status of developments on the optimization of line of sight (LOS) characteristics for the ITER bolometry collimators. The verification and measurement of the LOS of the bolometry is an important issue for a reliable operation of the tomographic reconstruction algorithms. Therefore the ITER Bolometer Robot Test Facility (IBOROB) is used as a diagnostic tool in order to analyze LOS geometry and assess the performance of different collimator prototypes. The LOS characteristics as a function of number of apertures are presented and the influence of a microwave filtering aperture was determined. The results of the improvement of stray light attenuation by application of the graphite based coating AQUADAG are evaluated as well and an overview about the current collimator design is given. This paper focuses on the most remarkable results, a way to further possible upgrades is outlined. However, some results are not in accordance with the ones predicted in theoretical calculations. Thus not all key parameters which influence the LOS could be clearly identified yet.