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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. [ABSTRACT FROM AUTHOR]

In this paper, an array wire-to-wire surface dielectric barrier discharge (DBD) structure is used to generate large-scale plasma by bipolar nanosecond pulse power in atmospheric air. The quantity of electrodes can be adjusted from 1 to 10 for varying discharge area. The applied voltage and discharge current are measured, the discharge images are captured, and optical emission spectra (OES) are collected. The discharge power, discharge area, and OES intensity for a single group of/and whole structure are calculated. The vibrational and rotational temperatures are simulated by the OES of N2 (C-B, $\Delta \nu =-2$), and the effects of the quantity of electrodes on discharge current, discharge power, discharge area, OES intensity, and vibrational and rotational temperatures are investigated. The results show that the discharge current has two main peaks during single applied pulse voltage, and decays in a fluctuant type. As the quantity of electrodes increases, the peak value of discharge current increases and the decaying time from peak value to zero around becomes longer. The discharge power, discharge area, and OES intensity have increasing tendencies, and those of the single group of wires decrease. In addition, when the quantity of electrodes increases, the vibrational temperature increases first and then decreases, and the rotational temperature varies in a fluctuant type. [ABSTRACT FROM AUTHOR]