In-vessel viewing system prototype performance measurements and simulation of measurement quality across the ITER in-vessel components

The In-Vessel Viewing and Metrology System (IVVS) is a fundamental tool for the ITER machine operations, tasked with inspection of plasma facing surfaces (PFS) of in-vessel components for both damage and erosion. The IVVS design has evolved to include a hybrid viewing and metrology system, using Frequency Modulated (FM) lidar for absolute distance measurements, and amplitude modulated (AM) lidar for surface viewing A fullscale prototype has been built, and has produced line-of-sight range precision of < 2 mu m in the optimum scenario. Error analysis indicates that 3D precision from 2 to 400 mu m should be available over surfaces from 0.5 to 10 m with 0-70 degrees incidence angles, exceeding the ITER requirements. Performance was found to be highly sensitive to received power and surface reflectivity. To parameterize the reflectivity, the Bidirectional Reflectance Distribution Function (BRDF) of a divertor monoblock prototype was measured and an analytic BRDF model was developed. An IVVS simulator was developed and used both to analyse the in-vessel geometry and to predict the coverage of the PFS. We have shown that 85% of the PFS area can be covered if the IVVS meets performance requirements up to incidence angles of 65 degrees and distances of 8 m.