Increasing the lifetime of W coated CFC, graphite and CuCrZr tiles for long time exploitation as Plasma Facing Components for WEST project
Partners
- National Institute for Lasers Plasma and Radiation Physics, Plasma Physics and Nuclear Fusion Dept. (Project responsible Dr. Eduard GRIGORE)
- Institut de Recherche sur la Fusion par confinement Magnétique, IRFM (Project responsible Dr. Caroline HERNANDEZ)
Objective
Within the framework of this project we proposed to extend the lifetime of W coated Plasma Facing Components (PFC) designed to WEST project. The WEST (Tungsten Environment in Steady state Tokamak) project is aimed to study and to supply technological solutions for ITER (International Thermonuclear Experimental Reactor). In this respect the WEST project intends to transform the Tore Supra tokamak into a platform for testing the ITER technologies especially by transforming the actual divertor into an actively cooling divertor similar to ITER. The materials used within the project will be similar to the ones that will be used at ITER.
Our goal is to develop and test different methods to refurbish the W coatings deposited on substrates similar to those used in WEST reactor. In this respect Combined Magnetron Sputtering and Ion Implantation (CMSII) technique will be used to coat with W, samples made of materials similar to those used in Tore Supra reactor: N11 Carbon Fibre Composite (CFC), Fine Grain Graphite (FGG) and CuCrZr alloy. The coatings (mono-layer or multilayers) will be applied on both actively cooled and inertial components.
The project will have four parts.
I. The first part is dedicated to the deposition of W coatings on samples made of N11 CFC, FGG and CuCrZr alloy, materials used in the structure of the WEST reactor. The deposition will be performed by INFLPR (Romanian partner in the project). Selection of coatings layout will be done together with IRFM (French partner in the project). At this stage a complete characterization of the coatings and an evaluation in terms of the resistance to high heat fluxes will be made (Milestone 1). The characterization of the coating before High Heat Flux Tests (HHFT) will give an “initial state” for each coating. That will be considered as a reference to achieve for the third part of the project.
II. After the HHFT and the identification of the failure mechanisms under thermal loading/stress and the definition of an (un)acceptable limit for each coating, the second part of the project will focus on the removal of damaged areas (Milestone 2). Different removal methods (milling, sand blasting etc.) will be tested.
III. The third part of the project will be focused on the re-deposition of new coatings on substrate materials recovered by method selected in second part of the project. The same three types of substrate materials (N11 CFC, Graphite and CuCrZr alloy) will be used for this new re-deposition.
IV. The last part of this project will be focused on the validation of the removal and deposition processes on real prototypes with complex geometry (rounded edges and gaps). After removing the W coating, a complete analyze will be performed (on the surface and on the gaps) to assess the cleaning process and verify the absence of residues in the gaps. Then, a re-deposition of new coating will be performed and characterized.
In the first phase of the project the following objectives were addressed:
- Synthesis of W coating on WEST materials substrates
- Investigations of physical and chemical characteristics of deposited layers
- Adhesion assessment of W coatings deposited on WEST substrate materials
Results
In the first part of the project W, coatings with thickness of 14.5 µm have been obtained. The coatings have been deposited on substrates similar to materials used in the WEST project namely: Carbon Fibre Composite (CFC type N11), Fine Grain Graphite (FGG) and CuCrZr alloy. Scanning Electron Microscopy (SEM) investigations revealed a columnar structure of the coatings (Fig. 1) and confirmed the coating thickness determined by Glow Discharge Optical Emission Spectrometry (GDOES) analysis.
SEM images of a W coatings deposited on CFC N11 substrate and on FGG substrate respectively
Further works
The research will continues with the investigations on the behavior of W coated N11 and FGG to HHF tests.
The coatings will be subjected to a testing program consisting in heating-cooling cycles at temperatures above 1000 0C. The pulse lenght will be
420 seconds, similar from temporal point of view, to ITER pulse. After HHF program a coating removal technology will
be established and then this technology will be validated.