Validation of the Cross-Calibration Multispectral Infrared Thermography in Surface Temperature Measurements

Abstract

The tokamak is nowadays one of the most promising methods to meet today’s energy needs without CO2 emissions and radioactive wastes. Moreover, the undertaking aiming to connect the tokamak to the electric grids is on its way [the Join European Torus (JET), then the International Thermonuclear Experimental Reactor (ITER) and finally the Demonstration Power Plant (DEMO)]. Surface temperatures in in-vessel are important parameters to know whether the JET ITER-like walls can withstand the high temperatures. To get these surface temperatures, many means exist to measure the surface temperature without any contact, in one of which the pyrometry method uses pre-calibrated multispectral infrared (IR) cameras. In this paper, a new method, called the cross-calibration method, was described to calculate surface temperatures by multispectral infrared cameras without any pre-calibration. By calculating the neutral density (ND) filters transmissivities and normalized digital levels for various configurations, the calibration coefficients in the cross-calibration method were validated and the error on the surface temperatures could be evaluated within 10%. Given that the environment in the vessel is highly contaminated during the operations, many contaminants due to partial oxidation and others deposits can distort the measuring results on the cameras. Thus, it is essential to be able to re-calibrate the infrared cameras; we will be able to remotely cross-calibrate cameras without sending people inside the tokamak.