Study of Viewing and Metrology performances on damaged plasma facing components and a full-scale ITER Divertor IVT using 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. Following the construction and validation of a full-scale prototype of the measurement probe compatible with the final harsh environment in 2023, recent progress has showcased its application on a full-scale divertor inner-vertical target (IVT) and on real, damaged tungsten Plasma Facing Unit (PFU) from CEA WEST that had been exposed to. The plasma-exposed WEST target showed various surface changes, currently being studied, and could have major implications for the ITER project or any tungsten-based tokamak.

The tests done by Bertin Technologies have successfully validated the 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. They have also shown the capabilities of the system to detect deposition on the WEST tungsten due to plasma environment interaction with real tiles.

On the IVT measurement campaign, the system clearly detected geometrical features such as tile gaps and edges, with the metrology channel providing precise range measurements with precision on 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.

Deposition on the WEST tungsten monoblocks is know to be <10 microns thick, below the metrology resolution of the IVVS's, however the viewing channel provided clear identification of deposition zones, showing the capability to detect and analyze surface changes. These findings further validate the IVVS's suitability for monitoring the condition of the ITER first wall.

A comparative study of the performances obtained on the different targets will demonstrate the preliminary capabilities of such a diagnostic. The design development and prototyping done by Bertin are key to confirming the system’s suitability for its final use.