Speaker
Description
In nuclear fusion, the extreme conditions inside of tokamaks, such as the WEST tokamak expose the plasma-facing components (PFCs) to intense heat and particles fluxes up to 10 MW/m². The interaction between the plasma and the PFCs is responsible for the temperature rise of these components, which are actively cooled to dissipate heat. Therefore, real-time temperature monitoring of the components is required to prevent damage. Infrared (IR) thermography is commonly used for this purpose, relying on IR cameras equipped with narrow-band filters centered on a specific wavelength in the IR domain.
However, the use of actively cooled tungsten (W) components in WEST makes temperature monitoring challenging due to the low emissivity of W (ϵ = 0.1). Moreover, emissivity can vary within a single component due to deposition and erosion processes induced by plasma–wall interactions. These processes lead to changes in surface state. This necessitates a detailed understanding of how emissivity evolves inside the machine.
Previous studies have identified specific regions of strong erosion and deposition that result in significant emissivity variations. A decrease in emissivity from 0.12 down to 0.05 has been observed in highly eroded zones, while in deposition zones it increases up to 0.85 [1]. Although these studies provide valuable insights into emissivity variations, they focus exclusively on the wavelengths of the tokamak’s IR cameras, at 3.9 ± 0.250 µm. Note that this wavelength range is used not only because it provides a good signal-to-noise ratio, but also because it highlights various physical phenomena, such as hot spots etc.
The objective of this work is to extend the investigated spectral range to 2.5–15 µm at temperatures up to 400 °C. This will allow to study the evolution of PFC emissivity as a function of surface state and identify specific behaviours or features that could facilitate temperature measurements in the WEST tokamak.
To this end, a dedicated setup equipped with a Fourier-transform spectrophotometer has been developed for studying W PFCs extracted from WEST. After a brief presentation of this setup, the spectra obtained on eroded and redeposited areas will be shown and discussed. In parallel, a characterization of redeposited areas (roughness and chemical composition) has been conducted to correlate the surface state with the emissivity spectra.
[1] J. Gaspar et al., Nucl. Fusion 62 (2022) 096023