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ITER (www.iter.org) will take advantage of tungsten (W) actively cooled plasma facing units (PFUs) in the lower divertor. These PFUs will receive a steady state plasma heat flux of 10 MW m−2 and up to 20 MW m−2 in slow transients, pushing these components to their limit. For machine protection reasons and for the study of the plasma wall interactions, temperature measurements are foreseen with mid wave infra-red (MWIR: 3–5 μm) thermography systems to cover most of the ITER chamber, including the divertor (tungsten material) and first wall (beryllium material) [1]. Absolute temperature measurements from 70 °C and the cooling temperature of the PFUs, up to 3500 °C (W melting temperature at 3422 °C), are considered. Those measurements require knowledge of the emissivity of the tungsten PFU surfaces as a function of the temperature and wavelength used for the IR monochrome thermography system. This paper summarizes the emissivity measurements performed on tungsten surfaces in high heat flux test beds and the WEST tokamak [2] and uses the experimental emissivity values to compute the expected uncertainties in ITER (ΔT/T) using monochrome and bicolor thermography techniques. The results show that the monochrome technique is not able to fulfill the ΔT/T < 10% requirement, while the bicolor technique is able to reduce the temperature uncertainty below 10%. Laboratory bicolor thermography measurements using a filter wheel (including six MWIR interference filters) have been successfully performed up to 830 °C with temperature uncertainty ΔT/T < 3%. In the WEST tokamak, the two dimensions emissivity map is varying by a factor of five within 27 cm along a PFU, from 0.13 to 0.65, showing that the monochrome IR thermography will have difficulties staying within the ITER requirements ΔT/T < 10% from 70 °C up to 3500 °C. [ABSTRACT FROM AUTHOR]

For the long-pulse high-confinement discharges in tokamaks, the equilibrium of plasma requires a contact with the first wall materials. The heat flux resulting from this interaction is of the order of 10 MW/m 2 for steady state conditions and up to 20 MW/m 2 for transient phases. The monitoring on surface temperatures of the plasma facing components (PFCs) is a major concern to ensure safe operation and to optimize performances of experimental operations on large fusion facilities. Furthermore, this measurement is also required to study the physics associated to the plasma material interactions and the heat flux deposition process. In tokamaks, infrared (IR) thermography systems are routinely used to monitor the surface temperature of the PFCs. This measurement requires an accurate knowledge of the surface emissivity. However, and particularly for metallic materials such as tungsten, this emissivity value can vary over a wide range with both the surface condition and the temperature itself, which makes instantaneous measurement challenging. In this context, the multi-spectral infrared method appears as a very promising alternative solution. Indeed, the system has the advantage to carry out a non-intrusive measurement on thermal radiation while evaluating surface temperature without requiring a mandatory surface emissivity measurement. In this paper, a conceptual design for the multi-spectral infrared thermography is proposed. The numerical study of the multi-channel system based on the Levenberg-Marquardt (LM) nonlinear curve fitting is applied. The numerical results presented in this paper demonstrate the design allows for measurements over a large temperature range with a relative error of less than 10%. Furthermore, laboratory experiments have been performed from 200 °C to 740 °C to confirm the feasibility for temperature measurements on stainless steel and tungsten. In these experiments, the unfolding results from the multi-channel detection provide good performance on temperature measurement, which supports our numerical evaluation and demonstrates the potential feasibility for metallic surface high temperature measurement with this method. [ABSTRACT FROM AUTHOR]

• We presented the WEST full tungsten actively cooled divertor, mentioning its relevance with the ITER one. • Main features including key elements related to the large-scale production, the reception tests, and the installation into the WEST tokamak are reported. • Main manufacturing issues as well as the reception strategy, in particular the handling of non-conformities, are highlighted. • Results related to the assessment of heat removal capability by IR-thermography and high heat flux test are discussed. The WEST (W - for tungsten - Environment in Steady-state Tokamak) platform aims to support the ITER tungsten divertor technology, manufacturing and long pulse operation. For this purpose, the Tore Supra tokamak has been deeply modified (mainly the installation of a lower and upper divertor coil structure), enabling a restart in 2016 and a first phase of operation (Phase I) until the end of 2020. Following this first phase, a limited number of actively cooled PFUs (Plasma Facing Units), based on ITER divertor technology, were industrially produced and implemented into the WEST vacuum vessel. The second phase of operation (Phase II) will be with a full actively cooled divertor. The first WEST experimental campaign with this new configuration (Phase II) started in 2022. This paper reports on the key elements related to the large-scale industrial production, the reception tests, and the installation of the ITER-like divertor components (including embedded instrumentation) into the WEST tokamak. Main manufacturing issues as well as the reception strategy, in particular the handling of non-conformities, are highlighted, mentioning its relevance with ITER divertor specifications. Results related to the assessment of heat removal capability by IR thermography examination and high heat flux test, as well as the He-leak tightness control are also discussed. [ABSTRACT FROM AUTHOR]

Abstract The WEST (Tungsten Environment for Steady State Tokamak) platform aims at testing ITER like divertor targets in an integrated tokamak environment, to minimize risks for procurement and operation. After 4 years of construction, WEST is now operational, with the first plasma breakdown achieved in December 2016. To operate long plasma discharge in WEST, infrared thermography is a key device, which enables a safe operation by means of a real time surface temperature monitoring, while providing essential data for various physics studies. For WEST, the IR thermography system has been deeply renewed, to match with the new tokamak configuration, and to fulfil the new measurement requirements. It consists of a set of 5 different diagnostics: 1) 7 endoscopes located in upper ports viewing the whole lower divertor and the 5 heating devices 2) a tangential endoscope located in a median port, providing a wide angle view of the vacuum vessel, and in particular of the upper divertor and first wall protections 3) a submillimetre resolution view on the divertor strike points from an upper port endoscope 4) 2 additional views of the divertor and of the heating devices. The paper describes the new IR diagnostics configuration (spatial covering, IR cameras, optics, data processing hardware and software), the main design options, manufacturing and installation issues, and some measurement performances. [ABSTRACT FROM AUTHOR]

Abstract: In the course of the development of a concept for a spectrally resolving thermography diagnostic for the ITER divertor using optical fibres experimental development work has been carried out in three different areas. Firstly ZrF4 fibres and hollow fibres (silica capillaries with internal AG/AgJ coating) were tested in a Co60 irradiation facility under γ irradiation up to doses of 5kGy and 27kGy, respectively. The ZrF4 fibres suffered more radiation induced degradation (>1db/m) then the hollow fibres (0–0.4db/m). Secondly multi-colour pyroreflectometry is being developed towards tokamak applicability. The emissivity and temperature of tungsten samples were measured in the range of 700–1500°C. The angular working range for off normal observation of the method was 20–30°. The working distance of the method has been be increased from cm to the m range. Finally, encouraging preliminary results have been obtained concerning the application of pulsed and modulated active thermography. [Copyright &y& Elsevier]