Speaker
Description
Since the introduction of the new ITER baseline [1], significant efforts were made in selecting the Tungsten (W) based armour materials for the inertially cooled Temporary First Wall (TFW). The TFW provides an environment for ITER’s initial operation campaign “Start of Research Operations (SRO)” that is more forgiving to disruptions while mimicking the final actively cooled First Wall in terms of materials and geometry.
The TFW design considers a mixture of potential plasma-facing material types, including bulk W, W heavy alloy, and W coating on a stainless-steel substrate. While bulk W will be used in heavily loaded areas during thermal transients, alloys and coatings have been proposed for inboard, including start-up area and outboard TFW panels.
The W-coated tiles need to withstand steady heat fluxes of up to 0.4 MW.m-2. The operating temperatures are 100-300°C between discharges, 500-600°C for nominal conditions during discharges and up to 800°C as design temperature limit on locally loaded area [2].
In view of the testing of W coating technologies namely Vacuum Plasma Spray (VPS) and Physical Vapor Deposition (PVD) in tokamak conditions, three coated tiles were installed on two inner guard limiters in WEST and tested under successive limiter plasma discharges. These tiles were instrumented with thermocouples and the surface temperature is assessed with infrared thermography. In total, 24 limiter discharges of ~11-12 s duration each were performed on the ITER TFW tiles in WEST with a plasma current between 500 and 700 kA.
A model constrained by thermocouple measurements provides surface temperatures up to ~300°C during experiments while infrared thermography measurements are between ~400 and ~700°C. Visual inspections performed before and after the WEST experiments through a window reveal no evolution of the coating. The present study describes the outcome of the experiments with more refined data and the latest results from Langmuir probes and visible spectroscopy on the gross erosion of the different W coatings.
[1] R.A Pitts; A. Loarte; T. Wauters et al., “Plasma-wall interaction impact of the ITER re-baseline ☆,” vol. 42, no. December 2024, 2025, doi: 10.1016/j.nme.2024.101854.
[2] T. Hirai, Poster presentation at PFMC 2025 conference