Emissivity Behavior of Materials Submitted to - Marseille, France - IUSTI CNRS UMR 7343

Description

Emissivity behavior of materials submitted to hostile conditions:

• Réf

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ABG-113103

• Sujet de Thèse 09/04/2023
• Autre financement public
• IUSTI CNRS UMR 7343
• Lieu de travail
• Marseille
• Provence-AlpesCôte d'Azur
• France
• Intitulé du sujet
• Emissivity behavior of materials submitted to hostile conditions
• Champs scientifiques
• Matériaux
• Energie
• Physique

Description du sujet:

• Infrared (IR) thermography is widely used in fusion research to study the heat load distribution on the plasma facing units (PFU) as well as ensuring their protections [1]. To these ends, assessing the emissivity of tungsten (W) components, as used for the ITER divertor, is necessary to derive accurate surface temperature from thermal radiation measured by infrared systems. The W emissivity is low and depends on various parameters as wavelength, temperature, and surface state such as its composition (oxidation, impurities) as well as its structure (roughness, cracks, deposited layers [2]). During plasma operation, the PFU surface state is expected to evolve as function of time because of the plasma wall interaction processes which are likely different from pulse to pulse. Consequently, this is strongly affecting the emissivity value and distribution [3]. As a first step, a dedicated setup was developed and applied to measure the emissivity of W samples representative of the WEST lower divertor, including samples with different damage levels generated by electron gun (microcracks and crack network) [4]. The experimental results showed, as expected, the dependencies with wavelength, temperature and surface state (roughness, cracks, pollution by impurities). For the same wavelength and temperature, the surface state showed a strong influence with a large increase of the emissivity with the micro cracks and crack network, by a factor up to 4. However, the samples used in this study did not see plasma operation that could have modified the surface state through plasma surface interaction (erosion, deposition and possible damages). As a second step, an insitu method was achieved to assess the emissivity evolution of the WEST divertor PFUs [5] during the first phase of WEST. The method is based on the measured infrared (IR) radiance, coming from isothermal PFUs at several temperature levels, to be compared with embedded thermal sensors before each pulse with the consideration of multiple reflections through photonic modelling. Based on this method an emissivity monitoring was performed during an experimental campaign of WEST. This monitoring has expectedly shown strong correlation of the emissivity distribution to the plasma operation, especially for the strike point location, plasma species and plasma current. Emissivity distribution from 0.12 to 0.65 was observed on a single PFU in few cm as well as emissivity variation at a day scale even in the main erosion area of the outer strike point (low field side). A third step relying on postmortem measurements started since the whole PFU divertor of WEST was removed from the machine to install the actively cooled ITERlike PFU. The objective of this third step is to accurately evaluate the emissivity in laboratory and his distribution to the surface state pollution and structure.
• References:
• [2] C. Martin et al., First post
• mortem analysis of deposits collected on ITER
• like components in WEST after the C3 and C4 campaigns Phys. Scr [3] N. Fedorczak et al., "Infra
• red thermography estimate of deposited heat load dynamics on the lower tungsten divertor of WEST", Physica Scripta T [4] J. Gaspar et al., "Emissivity measurement of tungsten plasma facing components of the WEST tokamak", Fusion Engineering and Design [5]J. Gaspar et al.

, "In-situ assessment of the emissivity of tungsten plasma facing components of the WEST tokamak", Nuclear Materials and Energy,
Nature du financement:

• Autre financement public

Précisions sur le financement:


Présentation établissement et labo d'accueil:

• IUSTI CNRS UMR 7343

Le laboratoire IUSTI est une unité mixte de recherche CNRS-Aix Marseille Université (UMR 7343).