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Description
Tungsten coatings have received a great deal of attention as a technical solution for plasma facing components (PFC) in present-day tokamaks owing to their advantages over bulk tungsten, such as lower cost and weight. Nevertheless, tungsten (W) coatings are hard and fragile. Their lifetime is mainly limited by two degradation mechanisms occurring during the operation of the tokamak: erosion resulting from exposure to long plasma discharges and local damages caused by runaway electrons.
In this paper, an alternative solution to the current replacement of damaged PFCs is proposed. It consists of combining a stripping method and a physical vapor deposition (PVD) method for repairing their surface, with a particular interest for actively water-cooled components made of copper alloy.
First, the process of removing tungsten was investigated on CuCrZr samples coated with a 15µm layer of W using 3 carefully selected techniques: laser ablation, sandblasting and chemical attack. For each technique, etching properties were assessed by means of microscopic observations and topography analyses. The results presented here also highlight the issues related with controlling the etching depth and the treated surface area. The second part of the paper focuses on the fabrication of a new W coating layer by PVD. To ensure the performance of the coating after repair, the properties of the new W layer were characterized and compared to the one of the old coating.
In addition to establishing and validating a whole repair procedure for PFCs, this study will provide technical specifications to consider the integration of this technology on a robotic arm. A first application could be the in-situ repair of W coatings in WEST tokamak. From a technical point of view, the integration of different systems on a robotic arm might also be beneficial for ITER where maintenance and inspection will be carried out by robots.
