Bidirectional reflectance measurement of tungsten samples to assess reflection model in WEST tokamak.

M Ben Yaala,M.-H Aumeunier,M Schönenberger,R Steiner,M Le Bohec,L Marot,C Martin,E Meyer,C Talatizi

doi:10.1063/5.0046140

Abstract

This paper presents the measurement of the bidirectional reflectance distribution function of tungsten (W) samples and the resulting reflection models in the nuclear fusion device WEST (tokamak). For this, an experimental gonio-spectrophotometer was developed to fully characterize the material's optical and thermal-radiative properties of metallic samples with different roughnesses. Ray-tracing photonic simulation was then carried out to predict the photon behavior in a fully metallic environment as a function of reflectance measurement. Low emissivity (0.1 at 4 μm) and highly specular reflectance (fitting with a Gaussian distribution around the specular direction with a small width lower than 10°) are found for W samples. These measurements have been used as input for the photonic simulation, and the resulting synthetic image reproduced the reflection features well on the upper divertor, detected in WEST infrared experimental images.

Highlights

This paper presents the measurement of the Bidirectional Reflectance Distribution Function (BRDF) of tungsten (W) samples and the resulting reflection models in the nuclear fusion device WEST
Infrared thermography is a reliable and robust method widely used in fusion reactors to monitor and protect the plasma-facing components (PFCs) by measuring in real-time their surface temperature
The study in this paper aims to improve the model of photon-materials interaction from experimental measurements of a particular optical material property known as the bidirectional reflectance distribution function

Summary

Introduction

Infrared thermography is a reliable and robust method widely used in fusion reactors to monitor and protect the plasma-facing components (PFCs) by measuring in real-time their surface temperature. It was reported that the contribution of the reflected flux from the upper port visible/infra red system of ITER can lead to overestimation of the surface temperature of up to 20 % for the hottest targets and up to 90 % for the coldest surfaces. It was reported that the contribution of the reflected flux from the upper port visible/infra red system of ITER can lead to overestimation of the surface temperature of up to 20 % for the hottest targets and up to 90 % for the coldest surfaces1 These false hotspots resulting from the incorrect interpretation of the IR measurements could lead to excessive interruptions of the plasma shots as well as to limitations on scenario development towards high performance

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