Viewing and Metrology measurements using the prototype In-Vessel Viewing System on a full-scale ITER Divertor IVT and damaged tungsten monoblocks

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. Following the construction and validation of a full-scale prototype of the measurement probe compatible with the final harsh environment against generic test targets in 2023, recent advancements have showcased its application on real, damaged ITER tungsten monoblock targets, including measurements on a full-scale divertor inner-vertical target (IVT). These tests have successfully validated performance of the IVVS at ITER-relevant viewing angles, distances, and focal parameters, over ITER-specific geometries, and at full cable/fiber length, confirming its suitability for in-vessel use.

The system clearly detected geometrical features such as tile gaps & edges, with the metrology channel providing precise range measurements with precision on a planar areas of 0.1 mm from 0.5-10m and angles from 0-60 degrees. Over the full IVT geometry dimensional errors are <1 mm. Viewing measurements provided high contrast images with spatial resolution limited by sampling density. The viewing channel was able to identify damage caused by heat treatment, even when the surface changes were sub-10 micron in dimension.

The metrology performance was further tested against a set of damaged tungsten monoblocks, ranging from surface roughening with no volumetric change to full melting and reshaping of the tungsten. Accurate assessment of the melting/erosion/deposition was demonstrated for damage meeting certain conditions. These findings further validate the IVVS's suitability to monitoring the condition of the ITER first wall.