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In this work, the reaction between H 2 O 2 and tungsten powder in the presence of Tris(hydroxymethyl) aminomethane was studied experimentally. The production of hydroxyl radicals can be quantified indirectly by quantifying the scavenging product formaldehyde (CH 2 O). XRD, XPS, and SEM analysis shows that no significant structural or compositional changes occur after reaction. We compared H 2 O 2 consumption and CH 2 O formation in both heterogeneous W (s) /H 2 O 2 /Tris system and homogeneous W (aq) /H 2 O 2 /Tris system. Increasing the amount of W powder leads to the increase in dissolution rate of W species, insignificant increase of H 2 O 2 consumption rate and the decrease of final CH 2 O production. By contrast, the consumption rate of H 2 O 2 increases as increasing the concentration of dissolved W species. Based on the experimental results, a mechanism of H 2 O 2 reacting with W powder in the presence of Tris is proposed. The mechanism well explained the relationship between surface reactions and homogeneous Haber−Weiss peroxide chain breakdown.
A new Infrared diagnostic has been developed by CEA-IRFM and installed in the WEST tokamak to measure surface temperature of the actively cooled W-monoblocks components as foreseen for the ITER Divertor, with a very high spatial resolution of 100µm. The goals are to investigate the effects of the shaping of these components on the heat load deposition pattern, the evolution of pre-damaged components specifically introduced in WEST, the behavior of the leading edges regarding the assembling tolerances between adjacent monoblocks, and finally to contribute to the specification assessment of the ITER divertor units. In WEST, each Plasma Facing Unit is composed of 35 W-monoblocks of individual surface of 28x12mm. To analyze heat load pattern and phenomena on such tiny surfaces, the leading edges and in the narrow gaps between monoblocks (400-500µm), a 100µm spatial resolution is required. Then, a Very High spatial Resolution (VHR) infrared diagnostic has been specially developed at CEA-IRFM. The VHR operates at 1.7µm wavelength to take advantage of the dynamic of the signal for the temperature range (400 to 3600°C). The VHR infrared diagnostic is now operational above the divertor sector made of actively cooled W-monoblocks and graphite inertial components with W coating. This paper gives a description of the diagnostic.
Twelve ITER-like plasma-facing units made of tungsten were exposed in the WEST tokamak divertor, with three PFUs significantly overexposed to plasma heat flux: one sharp-edged PFU (vertical misalignment h = 0.8 mm) and two chamfered PFUs (h = 0.6 mm and 0.3 mm, respectively). This paper describes the first temperature analysis obtained with a very high spatial resolution infrared camera (pixel size ~ 0.1 mm) on the misaligned PFU edges and shows the consistency obtained on the parallel heat flux derived from these measurements. The analysis is focused on the hottest areas of the PFU misaligned leading edges, since the temperature detection threshold of the VHR camera is high (Tthreshold,BB ≈ 370°C). The heat flux parallel to the magnetic field lines is assessed by matching the toroidal temperature profile in the vicinity of the leading edge with 3D finite element modelling. The tungsten emissivity assumed in this study is 0.6, consistent with laboratory measurements for damaged PFUs. For the three PFUs studied (with different vertical misalignments, incident angles, geometries), the derived parallel heat flux is similar, and consistent with independent measurements by a Fiber Bragg grating embedded in a graphite PFU at another toroidal location, giving confidence in future experiments using the same settings.
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