Comparative analysis between experimental measurements and simulated performances of an opto-mechanical model for the prototype In-Vessel Viewing System diagnostic

The In-Vessel Viewing and Metrology System (IVVS) is a diagnostic tool for the ITER project, designed to inspect plasma-facing surfaces within the tokamak. The specified resolutions for this diagnostic are 1mm for viewing and 0.1 mm for depth measurement for distances from the system from 0.5m to 10m. During ITER operations, the IVVS will be used to monitor more than 95% of the tokamak first wall surfaces for damage and erosion.

At Bertin Technologies, a new opto-mechanical hybrid design has been developped that allows both AM viewing and FM metrology LiDAR systems to be used simultaneously. This design has been manufactured, aligned, and tested by Bertin. The first results obtained with this fully integrated prototype have shown some limitations to reach the final performances. In particular, behaviour of the optical system when operating on targets at different distances from the optical focus created unexpected data loss and imaging artefacts.

A detailed simulated model based on the opto-mechanical optical model in FRED (PhotonEngineering) has been created allowing direct correlation between experimental measurements with the prototype and theoretical performances for various parameters. This optical model also integrates the possibility to use measured BRDF within the raytracing software to estimate the expected power feedback from several targets type and angles and replicates artifacts (Ring-like intensity artifacts, beam size impacts, etc.).

Finally, the goal of the model is to allow the upgrade of the system optical design to minimize the effect of working out-of-focus, thus confirming that the final performances achievable on any target to be seen at ITER-relevant viewing angles and distances are compliant with the needs.