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Description
Accurate wall temperature monitoring is essential for the safe operation of magnetic confinement fusion devices like ITER, and is routinely performed using infrared (IR) thermography. However, the fully metallic nature of the ITER First Wall (FW) introduces strong reflective effects, where hot optics and thermal scene parasitic light and variable emissivity of surfaces can lead to significant errors in the temperature estimation [1]. Consequently, reliable modelling and interpretation of IR measurements requires detailed knowledge of the optical and emissive response of surfaces exposed to representative heat-flux conditions, obtained through systematic experimental characterization [2]. Moreover, previous studies have also demonstrated that the tungsten surface’s optical response, quantified through Bidirectional Reflectance Distribution Function (BRDF) and reflectivity measurements, are correlated with its topography [3].
In ITER, the FW will undergo Glow Discharge Boronization (GDB) using diborane (B2H6 or B2D6) gas mixed with He as a carrier gas. This process is intended to getter impurities and stabilize plasma operation by forming boron-based films on plasma-facing components [4]. However, boron film will alter the optical and emissive properties of the FW, affecting the accuracy of the IR-based temperature diagnostics.
This study aims to investigate the influence of boron film composition and thickness on the optical, emissive and morphological properties of ITER-relevant FW surfaces. Boron-containing coatings with a thickness of several tens to hundreds of nanometres with various compositions are deposited via magnetron sputtering. The resulting surfaces are characterized using a comprehensive set of characterization techniques, including emissivity measurements, scanning electron microscopy (SEM), confocal microscopy, X-ray photoelectron spectroscopy (XPS), BRDF measurement, and spectrophotometry.
By establishing quantitative correlations between emissivity, optical properties, and surface morphology, this work aims to provide a critical input for the calibration and accuracy of improvement of ITER’s IR thermographic diagnostic systems.
1. Le Bohec, M., Steiner, R., Natsume, H., Kajita, S., Yaala, M. B., Marot, L., Aumeunier, M. H. (2024). Relationship between topography and BRDF for tungsten surfaces in the visible-spectrum. Optik, 303, 171750.
2. Aumeunier, M. H., Gerardin, J., Talatizi, C., Le Bohec, M., Yaala, M. B., Marot, L., ... ASDEX-U team. (2021). IR-thermography in metallic-environments of WEST and ASDEX-U. Nuclear Materials and Energy, 26, 100879.
3. Retailleau, F., Aumenier, M. H., Marot, L. (2025). BRDF determination based on topography measurement and Monte Carlo ray-tracing. Optik, 172476.
4. Wauters, T., Hagelaar, G. J. M., Pitts, R. A. (2025). Modeling input to the ITER GDB system. Nuclear Materials and Energy, 42, 101891.