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An ITER Challenge Absolute Surface Temperature Measurements of Low and Varying Emissivity Tungsten Plasma-Facing Components
IEEE Transactions on Plasma Science ( IF 1.5 ) Pub Date : 2020-07-01 , DOI: 10.1109/tps.2020.2998327
D. Guilhem , J. Gaspar , C. Pocheau , Y. Corre

One of the challenges that International Thermonuclear Experimental Reactor (ITER) will face during plasma operation is to determine the absolute divertor surface temperature of the actively water-cooled (70 °C, 3 MPa) tungsten plasma-facing units (PFUs) to ensure their integrity. The expected steady-state heat flux up to 10 MW/m2 is close to the operational limit and so one of the goals of the thermographic system is to make reliable measurements (wavelength band: 3.5– $4.5~\mu \text{m}$ ) with relatively low error bars to avoid tungsten melting and material damages. The tungsten emissivity is low and dependent on wavelength, temperature, and surface state (roughness, cracks, oxidation, and erosion/deposition processes) which can evolve during the time along with plasma operation. An error on the absolute emissivity can lead to large absolute temperature errors, and consequently to either a reduction of the operational window to fulfill safety limits, or an increased risk regarding the integrity of the components. For the past years, a number of emissivity measurements have been performed with ITER-like PFU mock-ups made of different grades of tungsten, with different techniques, from different material makers, and from different manufacturers. The overall emissivity discrepancy is large, indicating that tungsten emissivity is a major issue for temperature measurement and wall protection. The accuracy of the temperature measurement is investigated for both monocolor and bicolor IR thermography techniques. We present laboratory tests performed with an IR camera equipped with a rotating filter wheel for bicolor temperature measurement. It shows that the bicolor technique can reach high precision $\Delta \text {T}/\text {T} < 10{\%}$ at high temperature assuming the emissivity ratio is constant regarding the two selected wavelengths.

中文翻译:

ITER 挑战 低辐射率和变化率的钨等离子面组件的绝对表面温度测量

国际热核实验反应堆 (ITER) 在等离子运行期间将面临的挑战之一是确定主动水冷 (70 °C, 3 MPa) 钨等离子装置 (PFU) 的绝对偏滤器表面温度,以确保其正直。高达 10 MW/m2 的预期稳态热通量接近操作极限,因此热成像系统的目标之一是进行可靠的测量(波长带:3.5– $4.5~\mu \text{m}$ ) 具有相对较低的误差条,以避免钨熔化和材料损坏。钨的发射率很低,并且取决于波长、温度和表面状态(粗糙度、裂纹、氧化和侵蚀/沉积过程),它们会随着等离子体操作的时间而演变。绝对发射率的误差会导致较大的绝对温度误差,从而导致满足安全限制的操作窗口减小,或者组件完整性的风险增加。在过去的几年里,已经使用不同等级的钨、不同技术、不同材料制造商和不同制造商的类似 ITER 的 PFU 模型进行了许多发射率测量。整体发射率差异较大,表明钨发射率是测温和壁面保护的主要问题。研究了单色和双色红外热成像技术的温度测量精度。我们展示了使用配备旋转滤光轮的红外相机进行的实验室测试,用于双色温度测量。它表明双色技术可以在高温下达到高精度 $\Delta \text {T}/\text {T} < 10{\%}$,假设两个选定波长的发射率比是恒定的。
更新日期:2020-07-01
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